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Does Antimatter Fall Up Or Down?

KentuckyFC writes "There are enough loopholes in the general theory of relativity to allow antimatter to fall up rather than down in a gravitational field. We've never been able to make enough of the stuff to do the experiment. But at the European particle physics laboratory at CERN, where scientists have been refining the technique for making antihydrogen, researchers are designing an experiment called AEGIS that will finally settle the matter. The idea is simple — fire a beam of antihydrogen atoms and watch which way they fall — but the details are fiendish (abstract). The answer should help solve a number of important conundrums such as why there is so little antimatter in our part of the universe and what the value of the cosmological constant is."

480 comments

  1. Confused by wasted · · Score: 5, Funny

    "There are enough loopholes in the general theory of relativity to allow antimatter to fall up rather than down in a gravitational field. We've never been able to make enough of the stuff to do the experiment. But at the European particle physics laboratory at CERN, where scientists have been refining the technique for making antihydrogen, researchers are designing an experiment called AEGIS that will finally settle the matter.

    Or will it settle (or unsettle) the anti-matter?
    1. Re:Confused by master5o1 · · Score: 1

      bad pun, i know!

      --
      signature is pants
    2. Re:Confused by Anonymous Coward · · Score: 5, Interesting

      how fast things can change:

      Gravity affects matter and antimatter the same way because gravity is not a charged property and a matter particle has the same mass as its antiparticle.

      So the above is no longer believed to be true?

    3. Re:Confused by complete+loony · · Score: 5, Insightful

      There's a big difference between a belief that something is most likely true, and an experiment that removes all doubt.

      --
      09F91102 no, 455FE104 nope, F190A1E8 uh-uh, 7A5F8A09 that's not it, C87294CE no. Ah! 452F6E403CDF10714E41DFAA257D313F.
    4. Re:Confused by that_itch_kid · · Score: 1

      Perhaps, but not if you observe it happening.

    5. Re:Confused by K.+S.+Kyosuke · · Score: 4, Insightful

      Until now I thought that ouside the real of mathematics (where things can be proven and no further revision is possible, save for attacking the logic of the proof), there is no such thing as "an experiment that removes all doubt"?

      --
      Ezekiel 23:20
    6. Re:Confused by dnwq · · Score: 4, Informative

      An experiment that reduces doubt. Does that work for you?

    7. Re:Confused by Anonymous Coward · · Score: 0

      There's a big difference between bad experimental results, when you know you're right. It cuts both ways mon capitan.

    8. Re:Confused by ErikZ · · Score: 1

      Once you shown some anti-particles and anti-hydrogen falling down in gravity, you better have a *really* good theory why the non-tested stuff will behave differently.

      This will remove all doubt, unless it falls up.

      --
      Democrats or Republicans. They are both taking us to the same place and they are not afraid of us anymore.
    9. Re:Confused by Nathrael · · Score: 1

      Does that really matter?

      --
      A good education is a bit like a STD - it makes you unsuitable for a lot of jobs and gives you a desire to spread it.
    10. Re:Confused by K.+S.+Kyosuke · · Score: 2

      Yes, absolutely. Thanks! :-)

      --
      Ezekiel 23:20
    11. Re:Confused by Mr.+Underbridge · · Score: 1

      Until now I thought that ouside the real of mathematics (where things can be proven and no further revision is possible, save for attacking the logic of the proof), there is no such thing as "an experiment that removes all doubt"?

      Within the defined parameters. If you're sufficiently clever, you can fire a beam of antimatter and observe it. That is a purely empirical matter, unless you want to get into metaphysical crap like what it means to observe, etc. One can argue the causality, come up with alternate hypotheses, but if the beam goes up (or down), that's what it does.

    12. Re:Confused by mattcasters · · Score: 1

      The mass of such an anti-hydrogen particle must be pretty low. As such, it could perhaps be influenced by the container it's flying through, some unknown property, the previous of the next particle in the series, etc.
      I think there is always room for doubt in these experiments.

      --
      News about the Kettle Open Source project: on my blog
    13. Re:Confused by glas_gow · · Score: 4, Funny

      Yes, absolutely. Thanks! :-) Can you prove that it works for you mathematically?
    14. Re:Confused by K.+S.+Kyosuke · · Score: 1

      Dammit, you got me! :)

      --
      Ezekiel 23:20
    15. Re:Confused by Anonymous Coward · · Score: 0

      You mean an experiment where antimatter falls down won't remove all doubt that it falls down?

      Sure, it won't prove that antimatter always falls down. But I really don't think anyone (who matters) would continue to doubt whether it falls down or not.

    16. Re:Confused by peragrin · · Score: 1

      container it's flying through? have you never watched startrek? If you had you would know that antimatter explodes on contact with regular matter.

      There should be no container other than the magentic fields that keep it from hitting any matter in the vacuum that it was created.

      --
      i thought once I was found, but it was only a dream.
    17. Re:Confused by complete+loony · · Score: 2, Insightful

      If the 2 possible outcomes are polar opposites, and it goes one way and not the other. I'd say "removes all doubt" is a fair statement. Note I didn't use the word "prove", more like doubt in the legal prosecution sense.

      But now were just arguing semantics. Oh wait, this is /. never mind.

      --
      09F91102 no, 455FE104 nope, F190A1E8 uh-uh, 7A5F8A09 that's not it, C87294CE no. Ah! 452F6E403CDF10714E41DFAA257D313F.
    18. Re:Confused by smilindog2000 · · Score: 5, Interesting

      While this is a reasonable guess, it's about the same as guessing heavier objects fall faster. Consider electron-hole pairs in a silicon lattice. They act very much like electron-positron pairs. However, electrons fall down, and holes fall up. To me, it would seem odd if anti-matter fell down.

      Why is there so much matter around, and no anti-matter? Perhaps because they repel each other? There is some evidence that nearby galaxies are made of matter and not anti-matter, but the universe is very big, and time could be effected differently by anti-matter gravity (speeding up). Why are galaxy clusters accelerating in their separation from each other? Could anti-matter still be present somewhere, causing the acceleration? Why is matter in the universe so clumped together, and not more uniformly spread out? Could there be clumps of antimatter between the clumps of matter?

      Evidence suggests that there simply is no anti-matter left in the universe, but it's fun to speculate upon implications of anti-matter falling up.

      --
      Beer is proof that God loves us, and wants us to be happy.
    19. Re:Confused by Anonymous Coward · · Score: 0

      Doubt is just a state of mind, irrespective of any proof. Removes all doubt in a personal sense just means there's sufficient evidence to not doubt anymore.

      Removes all doubt in a social sense won't ever happen. There'll always be at least one whack job doubting for no other reason than because he can.

    20. Re:Confused by Torvaun · · Score: 1

      Two things. First, what is holding your vacuum in? Some sort of container, I'll bet. Like a tube. Second, it seems to me that if you're holding it in place magnetically, it'll be hard to discern gravity's effect.

      --
      I see your informative link, and raise you a pithy comment.
    21. Re:Confused by Anonymous Coward · · Score: 0

      '...that will finally settle the matter...'

        Someone needs to come up with an anti-pun to make that pun disappear in a flash of light never to be spoken again.

    22. Re:Confused by Anonymous Coward · · Score: 0

      Gravity exerts a much smaller force than the electric and magnetic fields likely to be used in this experiment, so yes, there will still be room for doubt in the outcome. Without actually reading the FA, I will guess that they compare the deflection of uncharged atoms and anti-atoms and try to isolate the effect of gravity.

    23. Re:Confused by Intron · · Score: 1

      My auntie says that it does.

      --
      Intron: the portion of DNA which expresses nothing useful.
    24. Re:Confused by Sygnus · · Score: 3, Funny

      Can you prove that it works for you mathematically?

      |It works|

      --
      First posting isn't trolling. It's...first posting. :) -- Illiad
    25. Re:Confused by MiniMike · · Score: 1

      Simple then. Turn off the magnetic field (after the anti-particle is stabilized), and see if the boom comes from the top or the bottom of the vacuum container. Or determine the vector in the magnetic field, turn off the field, and see where the impact location deviates from the expected path.

    26. Re:Confused by somersault · · Score: 2, Interesting

      Surely more massive objects do accelerate towards the eart slightly faster than less massive ones, since the objects themselves will be exerting a gravitational pull on the earth themselves? So the natural human instinct to believe that heavier objects fall faster is semi-right (I say semi right because it's right, but for the wrong reasons!) in that case, just not observably so over short distances.

      --
      which is totally what she said
    27. Re:Confused by phoenixwade · · Score: 1

      Or will it settle (or unsettle) the anti-matter? I hate people asking questions with no answer so much that I think I'm going to throw up my hand and start practicing Zen.
      --
      A positive attitude may not solve all your problems, but it will annoy enough people to make it worth the effort.
    28. Re:Confused by courtarro · · Score: 5, Informative

      Consider electron-hole pairs in a silicon lattice. They act very much like electron-positron pairs. However, electrons fall down, and holes fall up. To me, it would seem odd if anti-matter fell down.

      Holes are a virtual particle with no mass, whereas anti-matter has mass. Electrons actually exist, but holes are simply a place where an electron can fit. Take the example of a helium balloon in a car: if you slam on the breaks, it flies to the back of the car because all the air is rushing forward, and the balloon's relative vacuum gets pushed backward. A hole behaves similarly. Antimatter, on the other hand, has mass just like its matter counterpart and therefore isn't directly comparable to a hole.

    29. Re:Confused by garglblaster · · Score: 2, Interesting
      If you think about it: Antimatter can be considered as matter which is travelling backwards in time (Please check up on the famous CPT-theorem on this subject for more info).

      In this view it would be quite natural that antimatter is 'falling' upwards.

      In addition it would explain why we don't see antimatter in our universe: The antimatter universe simply evolved into the other (negative) direction of the timeline.

      On the other hand - matter and antimatter as just another manifestation of energy - it should fall down

      So, _YES_ I personally am looking anxiously forward to hear about the results of this experiment!!

      Just my humble few cents on this subject..

      --

      perl -e 'printf("%x!\n",49153)'

    30. Re:Confused by mshannon78660 · · Score: 4, Informative

      Uh, no, actually, they don't. Because F=Gmm'/r (m being the mass of one object, and m' the other, G being the gravitational constant and r being the distance between them), and a=F/m (acceleration equals force divided by mass). When you substitute one for the other, you get a=Gm'/r - which is completely independent of the mass of the object being observed. Now, you could argue that (as you seem to) that the earth is also accelerating towards the other mass, leading to what seems to be a higher rate of falling - but (contrary beliefs about relativity aside), you can't really treat all of the acceleration as relative in that manner - that simplification of relativity only works for uniform motion - it is possible to detect acceleration (although you can also replace it with a gravitational field, but that would then invalidate our original formulas - can't change horses in mid-stream like that).

    31. Re:Confused by FooAtWFU · · Score: 1

      Why is there so much matter around, and no anti-matter? Answer that, my friend, and you can secure a Nobel Prize.
      --
      The World Wide Web is dying. Soon, we shall have only the Internet.
    32. Re:Confused by element-o.p. · · Score: 1

      ...I think I'm going to throw up my hand...
      You swallowed your hand?!?!?!? (Sorry, couldn't resist!)
      --
      MCSE? No, sir...I don't do Windows. Yes, I am an idealist. What's your point?
    33. Re:Confused by courtarro · · Score: 1

      I just reread my comment, and my "breaks" typo is driving me mad. s/breaks/brakes

    34. Re:Confused by Anonymous Coward · · Score: 0

      Or will it settle (or unsettle) the anti-matter? It doesn't matter to the anti-matter.
    35. Re:Confused by Tenebrousedge · · Score: 2, Informative

      Why did you bother posting this? Honestly. "Here's why I, a non-physicist, think is wrong with this plan." What hubris. If you want to know how the experiment is going to be performed, read the abstract! It's quite readable, and even has pretty pictures and diagrams.

      --
      Those who advocate genocide deserve every protection afforded by law, and none afforded by common human decency.
    36. Re:Confused by somersault · · Score: 2, Insightful

      Yes I would be arguing that the earth would also be accelerating however infinitescimally quicker towards the other object. I know that the differences are purely academical and have pretty much no bearing in real terms, but consider you had 3 different orbs of the same volume but different masses, say A=1 large mass unit, B=2 large mass units and C=1 large mass unit.

      If you left any of these orbs near each other in space then they would exert a significant gravitational pull on each other and would both be accelerated towards each other. A and B would accelerate towards each other at the same rate as B and C. A and C would accelerate towards each other slightly slower. I don't see how relativity makes much of a difference in that case, it's basic newtonian stuff. For relatively small masses next to a large mass then the gravitational pull that they exert is negligible compared to the pull of the large mass, but technically it is still happening. You can argue about relativity if you want, but observing from a place standing on earth watching 2 very large moons accelerating towards the earth, I'm pretty sure the more massive moon would appear to impact first to the observer.

      --
      which is totally what she said
    37. Re:Confused by JebusIsLord · · Score: 0

      Nope. in fact one of the first experiments they did on the moon was test this out by dropping a feather and a (rock? can't remember). Both hit the ground at the same time. This isn't relativity, by the way, this is Newtonian stuff.

      --
      Jeremy
    38. Re:Confused by ickpoo · · Score: 1

      No no no.

      The force is greater because of the greater masses, but the acceleration is the same. F = MA or F/M = A.

      Basically you are saying that if we take the heavier moon and cut it in half the halves will accelerate more slowly than the whole.

      --
      I am not a script! .Sig?
    39. Re:Confused by somersault · · Score: 1

      Like I said (or at least implied), when one of the objects is significantly more massive, you're not going to notice much difference in that kind of test. You'd also have to do them one at a time or at least in different locations otherwise they would both be pulling the moon in the same direction ;) I'm not saying that larger masses would be accelerated faster if they themselves did not exert a gravitational pull, and I know that a feather and a rock will fall at a very very similar rate in a strong gravitational field.

      --
      which is totally what she said
    40. Re:Confused by somersault · · Score: 1

      Oh and when I said "one of the objects" I was implying the moon, not the rock ;)

      --
      which is totally what she said
    41. Re:Confused by Beriaru · · Score: 1

      it's about the same as guessing heavier objects fall faster.
      It does fall faster... if you take in consideration the attraction of the object to the earth.
    42. Re:Confused by somersault · · Score: 1

      That is the force exerted by gravity by the earth/moon/whatever on the object on its surface, but you have to take into account the (almost completely insignificant in this case, but still present) gravitational force being exerted by the object that is moving towards the earth too surely? If you think of it another way - what if you substitute the feather for the earth here, and then drop the earth and a rock near the feather - which will hit it first, the rock or the earth?

      --
      which is totally what she said
    43. Re:Confused by Anonymous Coward · · Score: 0

      You are correct. Ignore what others say to the contrary. If you have two low-mass objects (marbles for instance) whose surfaces are separated by 1 meter in an otherwise empty space, they will come together over a fairly long period of time. If you had two planet-massed objects (planets for instance) whose surfaces are separated by one meter, they will come crashing together in an instant.

      The same is true for any objects that are separated and then allowed to come together, as long as they don't have angular velocity with respect to each other. The larger the sum of masses, the quicker the distance between them will decrease.

    44. Re:Confused by sharperguy · · Score: 2, Funny

      You know, I really had to try to resist commenting on your grammar there.

      Wait....

      crap...

      --
      "sudo rm -rf your-face"
    45. Re:Confused by Anonymous Coward · · Score: 1, Funny

      He's not a physicist, but he did stay at a Holiday Inn Express last night.

    46. Re:Confused by digitrev · · Score: 1

      That's actually why they're using anti-hydrogen instead of positrons or anti-protons: to try and eliminate the issue of the much stronger electromagnetic force.

      --
      Cynical Idealist
    47. Re:Confused by digitrev · · Score: 1

      Umm, gravitational force is proportional to 1/r^2, not 1/r. So while your original point about acceleration being independent of the mass of the object being accelerated, your formula is wrong. Compare this vs this. Even if you change the units of the gravitational constant, the earth would be a much different place.

      --
      Cynical Idealist
    48. Re:Confused by Tenebrousedge · · Score: 1

      Oh god.

      I'm going to be haunted by the ghosts of William Strunk and my fifth grade English teacher tonight...

      --
      Those who advocate genocide deserve every protection afforded by law, and none afforded by common human decency.
    49. Re:Confused by Some_Llama · · Score: 1

      "Can you prove that it works for you mathematically?

      no but he can help to reduce your doubt... does that work for you?

    50. Re:Confused by Anonymous Coward · · Score: 0

      I'm confused now, too. We nerds should all know that antimatter particles can be created from ordinary Energy in accordance with E=mc^2 (along with an equal amount of ordinary-matter particles). Well, in General Relativity, because of that simple equation, it doesn't matter in the least what FORM ordinary mass/energy takes, it all attracts gravitationally. Anti-matter would have to have "negative mass energy" to be able to be gravitationally repelled. But since we nerds should all know that antimatter particles can be created from ordinary Energy in accordance with E=mc^2, it logically follows that antimatter must gravitationally attract ordinary matter (and fall in the Earth's gravity field).

    51. Re:Confused by cez · · Score: 1

      ...well, what if Gravity affects anti-matter the same way as it does matter... just in the opposite or anti-direction, away from the source?

      --
      Walk with Music;
    52. Re:Confused by Anonymous Coward · · Score: 0

      Holes only have meaning in a material, such as silicon. You can't say that electrons in silicon fall down with respect to the silicon. Gravity is much too weak to produce anything like a Hall effect, where an electric field deflects charge carriers.

    53. Re:Confused by Anonymous Coward · · Score: 0

      That is utter nonsense. If that were the case, then we would never be able to create antimatter. If it traveled backwards in time, then we would see it before we did the experiments that create it. However, in the lab, we create antimatter and it is still present after we create it. This would not be true if it traveled backwards in time. Just think about what you are saying.

    54. Re:Confused by Jamu · · Score: 1

      Actually matter does fall upwards. The reason matter tends to fall downwards isn't due gravity, it's due to to thermodynamics and friction in particular.

      As an example, consider an apple falling from a tree. The reason it doesn't "fall" upwards is that its kinetic energy is mostly dispersed into the ground when it lands. If the ground wasn't there, the apple would follow at orbit and fall down just as much as it "falls" upwards.

      Gravity is attractive. CPT wouldn't be violated by antimatter falling upwards. The orbital motion for matter is similar in both temporal directions.

      --
      Who ordered that?
    55. Re:Confused by Anonymous Coward · · Score: 0

      If you're going to be pedantic about it, mathematics isn't all that real, either.



      It's perfectly clear what the phrase "removes all doubt" means in this context.

    56. Re:Confused by TubeSteak · · Score: 2, Informative

      If the 2 possible outcomes are polar opposites, and it goes one way and not the other. I'd say "removes all doubt" is a fair statement. Note I didn't use the word "prove", more like doubt in the legal prosecution sense. To get pedantic about it:
      the experiment only shows that, under a certain set of conditions, antimatter behaves a certain way.

      You've only removed all doubt if you expect every single possible type of antimatter to behave the same as antihydrogen.

      You can extrapolate from the observed behavior, but as we've seen time and time again, there are plenty of edge cases & fringe behaviors that are completely unanticipated.
      --
      [Fuck Beta]
      o0t!
    57. Re:Confused by Anonymous Coward · · Score: 0

      Holes may not have mass, but neither do electrons when they are in the band structure of a material such as silicon. Rather, both holes and electrons take on an effective mass that is proportional to the curvature of the band they occupy.
      --Some PhD Candidate

    58. Re:Confused by Crispy+Critters · · Score: 1

      While you have a point, it is a silly one. Wouldn't the difference like 1 part in 10^22? Human intuition is developed from watching objects fall with significant air resistance.

    59. Re:Confused by Anonymous Coward · · Score: 0

      It doesn't work because you're forgetting about inertia. Yes, larger objects exert more gravitational force, but they have more inertia as well. The increase in the amount of force is balanced by the increase in inertia, leading to the same acceleration.

      Remember your basics: F = ma, or a = F/m. In the case of gravity, any increase in F requires a proportional increase in m, leading to constant a.

    60. Re:Confused by SilentBob0727 · · Score: 4, Interesting

      The point of gp is that when you apply maxwell's equations in four dimensions, an antiproton is indistinguishable from a proton moving backwards in time.

      If we maintain that causality only travels in the forward direction (not an unreasonable assumption to make), then you could actually solve this problem by saying the antiproton was, from its own frame of reference, annihilated, at the same time that it was created from your frame of reference, and vice versa.

      Even more interestingly, when you consider that we travel through spacetime at the speed of light, you can think of the creation of a PP- pair as an antiproton "bouncing in time" off a burst of energy, one that is exactly equal in magnitude to the energy required to reverse the direction of a proton traveling at the speed of light.

      Then, when you consider a recently-generated PP- pair that re-self-annihilates, releasing their combined energy, you can think of the same "bounce" in reverse, at which point, you have a single proton bouncing around in a game of nanoscopic temporal ping-pong!

      --
      Life would be easier if I had the source code.
    61. Re:Confused by Anonymous Coward · · Score: 0

      If you're going to be pedantic about it, mathematics isn't all that real, either.


      It's perfectly clear what the phrase "removes all doubt" is supposed to mean in this context.

    62. Re:Confused by quanticle · · Score: 0

      if you slam on the breaks, it flies to the back of the car because all the air is rushing forward, and the balloon's relative vacuum gets pushed backward.

      No. First, of all, if you slam on the brakes, the balloon flies to the front of the car. The balloon only flies to the back if you slam on the gas. Second, the reason for the balloons behavior doesn't have anything to do with its "relative vacuum", but is because of Newton's first law - an object at rest tends to remain at rest, and an object in motion tends to remain in motion. In this case, the balloon tends to remain in motion when you slam on the brakes, leading it to hit the front of the car, at which point the car's windshield exerts a force to stop the balloon. Finally, balloons are not a "relative vacuum". In fact, they are quite the opposite - the interior of the balloon is at a higher pressure than the exterior, not lower. The reason that the balloon rises is because the stuff inside the balloon is lighter than the stuff outside the balloon, not because there's proportionally less stuff in the balloon.

      I don't normally say this, but whoever modded this interesting needs to be taken out back and beaten over the head with an introductory physics textbook until concussed.

      --
      We all know what to do, but we don't know how to get re-elected once we have done it
    63. Re:Confused by Anonymous Coward · · Score: 0

      How about "an experiment which fails to disprove."

    64. Re:Confused by garglblaster · · Score: 3, Interesting
      >That is utter nonsense. If that were the case, then we would never be able to create antimatter. If it
      >traveled backwards in time, then we would see it before we did the experiments that create it. However, in the
      >lab, we create antimatter and it is still present after we create it. This would not be true if it traveled
      >backwards in time. Just think about what you are saying. Not at all dear anonymous coward!

      You may or may not have to check Feynmans precious books here, - he's going to explain it to you very well.

      In short: When we 'create' antimatter - from the perspective of the antimatter this is the point of time of its annihilation (because for the antimatter time is running backwards)

      When antimatter gets annihilated by the contact with ordinary matter (lateron in our timeframe) from the perspective of the antimatter this is the moment of creation of the antimatter.

      I know it's not easy in the first place, but if you give it a few moments of thought it's logical and natural.

      And it's been an accepted theory in physics for many years.

      --

      perl -e 'printf("%x!\n",49153)'

    65. Re:Confused by Anonymous Coward · · Score: 0

      Ok, the current experimental proof shows that antimatter is affect by fields generated by posi-matter the same way that posi-matter is affected by those fields.

      1. Positrons and anti-protons are held in a magnetic/electrical field the same as electrons and protons.
      2. So presumably there has been enough experimental proof to show that positrons are affected by currents of anti-matter particles i.e. no extra-easy escapes of multiple charged anti-particles from magnetic fields,
      3. Similarly with electrical fields i.e. the very formation of anti-hydrogen

      This should remove all reasonable doubt that antimatter affects other antimatter in the same ways for electromagnetism (with just the sign switched between charged particles).

      So if gravitational fields generated by posi-matter bends anti-particles "up" then why wouldn't the gravitational fields of all of the anti-particles do the same to each other.

      KICKER:

      If so then we know where all the "missing mass" is: Evenly spread out antimatter between the visible galaxies.

      There can never be stars or planets or even much "dust" of anti-matter because anything that is not chemically bonded will eventually drift-apart.

      More importantly there will never be anything naturally with a higher atomic weight than hydrogen produced past the "big bang".

      My guess is that anti-hydrogen also produces the same spectoral lines as posi-hydrogen. So even heated gas clouds in interstellar-galaxial space will look the same to astronomers regardless of anti vs. posi as long as little or none of the other is present (15 Billion years will let such things settle-out won't they!)

    66. Re:Confused by quanticle · · Score: 1

      No. For the apple to behave as you describe, it'd have to have an initial horizontal velocity large enough to put it in orbit. Even without kinetic energy absorption, the apple would still fall down - it'd just bounce back up to the same height it fell from afterwards. (For the purposes of the discussion, I'm assuming that "down" is towards the center of the Earth)

      --
      We all know what to do, but we don't know how to get re-elected once we have done it
    67. Re:Confused by Torvaun · · Score: 1

      I'm not commenting on the physicist's plans, I'm commenting on the guy who's getting all his information from Star Trek. I'm sure the people doing the experiment know what they're doing.

      --
      I see your informative link, and raise you a pithy comment.
    68. Re:Confused by Kjella · · Score: 1

      In an absolute sense, no. But when you have a theory that's generally well recognized like gravity, experiments that are generally agreed test gravity, and perform the same experiment on the matter in question then it's about as close as you get without going into metaphysics. It's just another experiment confirming the status quo, there's nothing to discuss if you get the expected results, and if not you look for sources or error but barring those... Either you would have to challenge the theory of gravity itself, or you would have to argue that there is a force that works exacrly like gravity, but it isn't gravity". Ultimately, we don't know "what" gravity is - if it's the same thing drawing apples and oranges towards the ground, we just assume that it is. Same thing with anti-matter, we don't know what exactly but if it works the same...

      --
      Live today, because you never know what tomorrow brings
    69. Re:Confused by courtarro · · Score: 2, Insightful

      First, of all, if you slam on the brakes, the balloon flies to the front of the car. The balloon only flies to the back if you slam on the gas.

      Next time you've got a balloon, put it in the car and give this experiment a try. When you have a helium-filled balloon in the car, it reacts opposite to the way most other things in the car react. When you slam on the brakes, a ball on the floorboard will roll forward, but the balloon will float backward.

      Second, the reason for the balloons behavior doesn't have anything to do with its "relative vacuum", but is because of Newton's first law - an object at rest tends to remain at rest, and an object in motion tends to remain in motion. In this case, the balloon tends to remain in motion when you slam on the brakes, leading it to hit the front of the car, at which point the car's windshield exerts a force to stop the balloon.

      Sure, when you slam on the brakes the balloon wants to go forward, but so does the rest of the air in the car's interior. Since the air is more dense than the helium-filled balloon, it wins out and pushes the balloon backward.

      Finally, balloons are not a "relative vacuum". In fact, they are quite the opposite - the interior of the balloon is at a higher pressure than the exterior, not lower. The reason that the balloon rises is because the stuff inside the balloon is lighter than the stuff outside the balloon, not because there's proportionally less stuff in the balloon.

      You got me there to an extent, but with a loosely-inflated mylar balloon, the pressure can be equal between the interior and exterior of the balloon ... in either case you're right that "relative vacuum" was not really valid. My original point was that the helium means there's less mass in the same amount of volume, which was the point of my original "hole" analogy.

    70. Re:Confused by Anonymous Coward · · Score: 0

      1. Pay cousin It to rake the leaves.
      2. Monitor his performance, determine if work is occurring.
      3. If ($work_output > 0) returns true, the proof is in the pudding!

    71. Re:Confused by DarthStrydre · · Score: 1

      No. First, of all, if you slam on the brakes, the balloon flies to the front of the car. The balloon only flies to the back if you slam on the gas. I'm sorry. Your argument on the pressure is correct, but the reaction of a helium balloon to acceleration and deceleration is incorrect.

      The balloons do indeed go rearwards as you stop as per the gp, and forwards as you accelerate. The reason is also "because of Newton's first law". Deceleration changes the direction of the net force exerted on all objects in the car. The net normal force, which is what the balloon cares about, is rearwards and up. In other words, buoyancy pushes the balloon backwards in the car as the air moves forward, creating a slight (depending on the deceleration) pressure differential between the front and rear faces of the balloon.

      You should try it sometime :-) tie the string down so the balloon is not touching anything, and watch it lean into turns, and prove your statement incorrect for accel and decel.

      This is the same thing that causes you to feel colder or warmer in a car, while turning sharply in the wintertime with the heat on low. Cold air "sinks" normally. Apply a centrifugal (I know... imaginary) force in a turn, and the cold air sloshes towards or away from you, similar to gas vs air in the fuel tank.
    72. Re:Confused by Anonymous Coward · · Score: 0

      Well probably not, but his smiley reduces the doubt that it doesn't work for him at all.

    73. Re:Confused by asCii88 · · Score: 0

      Well, I believe that there will be no reaction. And anti-matter will turn out to be atracted by anti-matter due to a property called anti-gravity.

    74. Re:Confused by BitterOak · · Score: 1

      Antimatter, on the other hand, has mass just like its matter counterpart and therefore isn't directly comparable to a hole. Actually, this is what they are trying to test. If anti-matter "falls" up, rather than down, then it would also behave like the helium balloon in a car, i.e., if you slam on the brakes, a lump of anti-matter, according to this negative-mass hypothesis, would fly backward. This follows from the so-called equivalence principle, which asserts that a uniform gravitational field is indistinguishable from a uniformly accelerating frame of reference. It is the principle which underlies Einstein's General Theory of Relativity.
      --
      If I can be modded down for being a troll, can I be modded up for being an orc, or a balrog?
    75. Re:Confused by Anonymous Coward · · Score: 0

      Why don't they just have Eugene Podkletnov increase the "gravity field" around the the experiment to make it easier to detect?

    76. Re:Confused by Anonymous Coward · · Score: 0

      If you think about it: Antimatter can be considered as matter which is traveling backwards in time...

      I prefer not to rely on any argument that hinges on "If you think about it". Pretty much every crank pseudo-scientist I've ever investigated relied on such an appeal sooner or later. Unfortunately, intuition is only good for guessing; not checking.

      (Please check up on the famous CPT-theorem on this subject for more info).

      Good save, but it's still asking the reader to do the homework. To wit:

      In this view it would be quite natural that antimatter is 'falling' upwards.

      I don't see how this is possible without interpreting something in a perverse way, such as any of the following:
      a) Reverse the "arrow of time"; I think this is really the heart of your suggestion. This would break entropy and the 2nd law of thermodynamics, and the uncertainty principle, and thus clobber causality on at least two fronts in one swoop. In addition: *any* mass, be it matter or anti-matter, "falls up" if you run time backward. I don't see how you can have positive mass for matter and antimatter and observe them moving forward in time without changing one of those things by arbitrarily writing a negative sign next to it.
      b) Consider antimatter to somehow exist in the superluminal regime of its own light cone, which might involve giving it a "different kind" of mass but in any case involves writing negative signs on whims. This has the same effects as (a) because it still allows massive objects (of some speculative "kind" of mass) to move backward in time.
      c) Do anything worse than the above, since if we don't require Lorenz covariance and can break any symmetry, the sky's the limit. Things could get so bad so fast that it wouldn't even be worse if we decided not to bother using an orthonormal basis to parametrize our measurements/interpretations.
      d) Play semantics with the relativity of simultaneity. That's the "standard" interpretation, and saying antimatter falls "up" is rather disingenuous, because the antimatter isn't falling "up" when viewed from its own frame. You can close the garage door before the ladder truck smashes into the back wall, but you always drive the ladder truck into the back wall before anyone can shut the door.

      ...matter and antimatter as just another manifestation of energy...

      In a deep sense that may turn out to be true, but I just want to make sure you don't overgeneralize it. Energy isn't a thing in or of itself; it's a property of other things. In the E=m*c^2 relation you're likely thinking of, m is mass and not matter. The Higgs mechanism is not well-understood, but there remains a conceptual difference no matter what.

      I personally am looking anxiously forward to hear about the results of this experiment!!

      I'm glad you're enthusiastic, but I don't think this a particularly contentious experiment. It's about like dropping a ball just to make sure it falls the way you think it will; you're reasonable confident in your understanding and thus prediction, and it's likely to be a mundane result even though it would indeed be big news if the book falls "otherwise". Since they're dealing with very small quantities of mass, there's spontaneous and local symmetry breaking involved, and at best I suppose this experiment might allow refinements of their application.

      ...it would explain why we don't see antimatter in our universe: The antimatter universe simply evolved into the other (negative) direction of the timeline.

      I think it already does, as much as it ever can. It seems an entirely semantic interpretation that there is such a mirrored universe, because such a universe would be inherently isolated from our realm of observation, let alone experimental examination. In a sense, it doesn't matter if there is such a universe because we already have a universe with exactly the opposite info

    77. Re:Confused by whopub · · Score: 1

      "There are enough loopholes in the general theory of relativity to allow antimatter to fall up rather than down in a gravitational field." But then there's places like Soviet Russia where the opposite of up or down will probably be the norm, so there's really no easy way to answer that one...
    78. Re:Confused by LionMage · · Score: 1

      I was with you (more or less) right up to the point where you started talking about how "we" are moving through space-time at the speed of light... which is confusing, since I don't think any human being has ever attained that velocity in any frame of reference. :-) Similarly, talk of protons traveling at the speed of light doesn't make much sense because protons have mass. Yet the context doesn't make it clear that you meant to say photons. So I think you may have confused matters further here.

    79. Re:Confused by Anonymous Coward · · Score: 0

      Dear anonymous coward - You are just what an anonymous coward. So sad.

    80. Re:Confused by mshannon78660 · · Score: 1

      Good catch - it was a typo on my part.

    81. Re:Confused by Anonymous Coward · · Score: 0
      Anonymous Coward!

      You have nothing to say!

      Just Go Away!

      Nobody wants you!

      You're useless.

    82. Re:Confused by JebusIsLord · · Score: 2, Informative

      You've got gravitation wrong I'm afraid. The feather and the moon pull on each other and both accelerate towards the common center of mass (which obviously is almost exactly the center of the moon, since it is far more massive). The force of the moon's pull on the feather is small, but since the feather is also not very massive, it accelerates at 1.62 m/s2 towards the moon. A dropped rock will experience many times more FORCE, since the gravitational attraction between the moon and rock are (comparatively) larger. However, this force has to overcome the rock's equally greater inertia, meaning that the rock also accelerates at 1.62 m/s2 towards the moon. The only real difference is that the rock-moon gravitational center is slightly closer to the rock, than to the feather.

      Make sense?

      --
      Jeremy
    83. Re:Confused by Anonymous Coward · · Score: 0

      Yes, absolutely

    84. Re:Confused by camperslo · · Score: 2, Funny

      Excuse me, but isn't asking is something will fall up or down asking a loaded question?
      Shouldn't we instead be asking how it will fall?

      What if it falls on an imaginary axis and ends up travelling in time or to a parallel universe?

    85. Re:Confused by SilentBob0727 · · Score: 1

      The speed of any inertial frame of reference can be seen as a rotation in spacetime. As such, there always exists a frame of reference that can observe any particle traveling a speed of light, e.g. the frame of reference of a photon. To that end, any object can always be said to be going the speed of light in four dimensions; one's apparent speed to an observer, then, is a measure of the relative angle between the observer's and the traveler's arrows of travel in four dimensions.

      --
      Life would be easier if I had the source code.
    86. Re:Confused by UnknownSoldier · · Score: 1

      Except that you can't prove a negative, only predict what the outcome "should" be.

    87. Re:Confused by Anonymous Coward · · Score: 0

      Read it again. If it doesn't hit anything (the ground) it's always going to orbit.

    88. Re:Confused by Anonymous Coward · · Score: 0

      Not really.

      The experiment is not charged, therefore it has no effect on the doubt, or the anti-doubt. In order to reduce the doubt, you need to apply some amount of anti-doubt.

    89. Re:Confused by TeknoHog · · Score: 2, Funny

      An experiment that reduces doubt. Does that work for you?

      No. I'm a chemist, and it doesn't help much to add more electrons to doubt.

      --
      Escher was the first MC and Giger invented the HR department.
    90. Re:Confused by ClassMyAss · · Score: 1

      While this is a reasonable guess, it's about the same as guessing heavier objects fall faster. Consider electron-hole pairs in a silicon lattice. They act very much like electron-positron pairs. However, electrons fall down, and holes fall up. To me, it would seem odd if anti-matter fell down.
      To a physicist, though, it would not square well with everything we know if anti-matter fell up. In particular it would violate the equivalence principle of general relativity, and would be at odds with the general idea that energy density (roughly speaking) causes gravitational attraction, since anti-matter most definitely has positive energy density.
    91. Re:Confused by Ethan+Allison · · Score: 1

      How can something travel backwards in time? That doesn't even begin to make sense to me.

    92. Re:Confused by snookums · · Score: 1

      if you slam on the brakes, a lump of anti-matter, according to this negative-mass hypothesis, would fly backward

      Wouldn't this only be true if the anti-matter had negative inertial mass? I thought that the idea being tested was that while an anit-particle may have the same inertial mass as its regular counterpart (i.e. same force required to produce a given acceleration), that perhaps the force of gravity between matter and anti-matter was repulsive rather than attractive.
      --
      Be careful. People in masks cannot be trusted.
    93. Re:Confused by mysidia · · Score: 1

      You mean they hit the ground after perceptibly the same amount of time (to within the precision they could measure).

      A more telling experiment would be to drop a 500 trillion teragram boulder and a 1 kilogram pebble from the same height on the planet Jupiter.

      (They cannot be dropped at the same time, because the gravitational forces on one falling object could have a dampening effect on the other object falling, causing them to land at a closer time)

    94. Re:Confused by mysidia · · Score: 1

      Not true. The acceleration due to gravity is known to not be a constant. Every planet has their own approximation for the constant "g" (lowercase g); in fact, g is not a constant.

      F=ma with 'm' and 'a' constant are only a rough approximation; the assumption that 'F' or 'a' is constant is only allowed under highly restricted conditions, and when the assumptions are not true, merely "F=ma" does not suffice.

      The real formula for the gravitational force vector includes more details.

      Acceleration due to gravity is a function of the force exerted by a graviatational field between the two objects which is simultaneously dependent on two quantities the mass of the two objects and the distance of the mass of the objects from one another.

      See Newton's Law of Universal Gravitation.

      F = G (m_1 * m_2) / r^2

      F being the gravitational force between two point masses.

      Calculating the acceleration between two objects according to Newtonian Physics requires using Newton's Calculus.

      And the acceleration will be different at every moment during the fall, as will be the gravitational force between two objects.

      For massively large, irregularly shaped objects, different parts of the object may also be a different distance away at various times during the "fall", and the gravitational force against the planet may vary across the mass of the object.

      But (assuming the object doesn't break during the fall), you can be assured the total acceleration of the object down any particular axis will be the same, despite that (acceleration during the fall may change the orientation of the object).

    95. Re:Confused by Kgosi+Makwati · · Score: 1

      Better yet, we should use our knowledge of the subject to predict the result. Then, use experiment to verify our prediction.

    96. Re:Confused by clarkcox3 · · Score: 1

      One thing, along those lines, that I've often thought of:

      What if there really is only one of each kind of subatomic particle in the Universe (after all, all electrons are identical to each other, all protons are identical, etc.). This one electron starts at the big bang, and weaves its path through existence until the end of time.

      At that point, it hangs a U-turn, and travels back in time to the big bang (if we encounter this electron on its return trip, we observe it as a positron).

      Then, when it gets back to the big bang, it hangs yet another U-turn and repeats the same process, only this "time", there appear to be two, and so on.

      Or, take it a step farther:

      What if all matter is actually made of a single quark making such back-and-forth trips through time, and that all of the different particles are really just that same quark interacting with itself on different loops. This would mean that it is possible that there is only one particle in existence, and that all of the observable universe is essentially a fabric weaved by its repeated trips back and forth through time.

      --
      There are no tiger attacks in my area and it's all because this rock I'm holding keeps the tigers away.
    97. Re:Confused by clarkcox3 · · Score: 1

      >That is utter nonsense. If that were the case, then we would never be able to create antimatter. If it >traveled backwards in time, then we would see it before we did the experiments that create it. However, in the >lab, we create antimatter and it is still present after we create it. This would not be true if it traveled >backwards in time. Just think about what you are saying. Not at all dear anonymous coward!

      You may or may not have to check Feynmans precious books here, - he's going to explain it to you very well.

      In short: When we 'create' antimatter - from the perspective of the antimatter this is the point of time of its annihilation (because for the antimatter time is running backwards)

      When antimatter gets annihilated by the contact with ordinary matter (lateron in our timeframe) from the perspective of the antimatter this is the moment of creation of the antimatter.

      I know it's not easy in the first place, but if you give it a few moments of thought it's logical and natural.

      And it's been an accepted theory in physics for many years.

      Or, there is no creation and annihilation, it is just a single particle caught in a closed loop, going back and forth through time :)
      --
      There are no tiger attacks in my area and it's all because this rock I'm holding keeps the tigers away.
    98. Re:Confused by AxelBoldt · · Score: 1

      If you really came up with that idea on your own, then you are a genius. That idea is usually attributed to Wheeler. He told his student Feynman about it, who immediately shot it down: if it were true, we'd see just as many electrons as positrons, but we don't. See Feynman's Nobel lecture.

    99. Re:Confused by somersault · · Score: 1

      Wow, someone who gets what I've been trying to be saying! I didn't know Newton's Law of Universal Gravitation, but I remember having conversations with my high school physics teacher about this stuff, him talking about an elephant and the feather and how fast they'd fall to earth. I always used to ask him awkward questions (everyone else in the class loved that because it would put him off on a tangent talk meaning we didn't have to do any work :P ), and I'm pretty sure I came up with the idea that the elephant would be exerting its own gravitational pull.. so while the difference may not be noticeable, there is still a slight difference.

      Isn't it great how all these /.ers have been told that a feather and a rock dropped in a vacuum would accelerated towards a source of gravitational pull at the same rate, and so they don't even bother to actually think about the physics involved anymore, just accepting that F=ma and forgetting that gravity isn't just a one way thing? Every mass in the universe exerts a gravitational pull on every other mass, but often effect is so small as to be completely negligible because of the inverse square (at least I'm assuming it follows that kind of relationship, same as radiation) nature of the effect :)

      --
      which is totally what she said
    100. Re:Confused by somersault · · Score: 1

      It may be silly, but it's still true ;) Yep air resistance plays a large part in our atmosphere, so a glider would fall slowly to earth, while a much less massive pebble would 'sink like a stone' so to speak.. human intuition between dropping a canonball and a small rock would be pretty sensible, though there still wouldn't be a measurable difference in the acceleration over short distances this close to the eart, but when dropping a feather the fact that it is meant to aid flight totally throws things off.

      --
      which is totally what she said
    101. Re:Confused by somersault · · Score: 1

      Yeah I get what you're saying, but I think the extra gravitational pull has more of an affect than you think - see here and here.

      While it is true that you need a larger force to accelerate a more massive object at the same rate as a smaller object, I think the extra gravitational pull has more effect than that. For example the first poster's example of two planets. Clearly even though a planet is more massive and requires more force to move it towards another planet than would be required to move a small rock towards that planet, since a planet exerts a larger gravitational pull than a small rock, then the total acceleration is larger. If what you were saying is true then you could keep increasing the mass of the objects that you are dropping towards the moon until you are 'dropping' an object that is more massive than the moon, in which case it would be more like dropping the moon onto another object. Yet the moon would drop at a different speed were it dropped near Jupiter than if it were dropped near earth. If gravitational force were a certain amount weaker then maybe you could get a situation where the acceleration would only depend on the larger mass though, as the extra gravitational pull of the object being 'dropped' exactly counteracts the force needed to overcome its inertia.

      --
      which is totally what she said
    102. Re:Confused by syukton · · Score: 1

      I was actually reading about this recently, so I'll try to explain it as best I can from what I understand.

      Everything in existence is traveling through spacetime (three spatial dimensions and one temporal dimension) at the speed of light. Put another way, the speed at which you travel spatially and the speed at which you travel temporally, when combined, will always equal the speed of light. This is why, for example, when we peer into our telescopes and see distant galaxies, we see them just as they were millions of years ago; because a photon travels through space at the maximal speed limit, it doesn't travel through time and therefore does not age in any way. This is also the reason behind the time dilation effects experienced at very high rates of (spatial) speed. As you increase your speed in the spatial dimensions, you decrease your speed in the temporal dimension, which leads to localized time dilation from your frame of reference. They've seen this on a very small scale with the space shuttle: they synchronize two very expensive and very precise clocks, keep one here on the ground and send the other up in the shuttle. When the shuttle returns, the clock that went with it will be slightly (a small fraction of a second) behind the clock left on earth, because the speeds achieved during its journey were significant enough to cause localized time dilation. The GPS satellite network can also be considered an ongoing experiment into this effect. More information can be found here: http://en.wikipedia.org/wiki/Time_dilation

      Disregarding that it would take a power source and propulsion method far beyond our current level of technology, it is possible to journey across the entire universe at a small fraction less than light speed (say 99.9999... percent), all within a single human lifetime. Also, at a constant acceleration of 1g, it would be possible to reach that speed in about 354 days.

      --
      Reinvent the wheel only at either a lower cost, greater effectiveness, or your own personal enrichment and satisfaction.
    103. Re:Confused by tehcyder · · Score: 1

      While this is a reasonable guess, it's about the same as guessing heavier objects fall faster.
      Uh, hello? That's not a guess, it's true. Everyone knows if you chuck a pound of feathers and a pound of lead shot off a tall building, the feathers hit the ground last and slower.

      Jeez.

      --
      To have a right to do a thing is not at all the same as to be right in doing it
    104. Re:Confused by SilentBob0727 · · Score: 1

      I wonder if maybe there's a second universe containing all that missing antimatter; that universe's big bang could be our big crunch and vice versa. Then time would essentially be one big circle. Of course I have no sound justification to back that up, last time I studied physics was 2003... it's just interesting to take what I think I understand about theoretical physics and extrapolate...

      --
      Life would be easier if I had the source code.
    105. Re:Confused by clarkcox3 · · Score: 1

      If you really came up with that idea on your own, then you are a genius.

      I'm certainly not a genius, just someone with occasional insomnia :)

      That idea is usually attributed to Wheeler. He told his student Feynman about it, who immediately shot it down: if it were true, we'd see just as many electrons as positrons, but we don't. See Feynman's Nobel lecture.

      Thanks for the link, that's a fascinating read. I wonder if his professor might not have been correct. What if there are an equal number of particles and anti-particles, but that the anti-particles are somehow hidden?

      What if, for instance, Universes occur in pairs; one made primarily of matter, with time flowing in the direction we're used to, and one made of anti-matter, with time flowing in the opposite direction?

      Perhaps the U-turn at each end is accompanied by the particle jumping from one universe (at its death) to its counterpart (at its big bang). The few instances of anti-matter that we do observe might be cases where the particle made the turn, but didn't actually make the jump to the other universe.

      That way, the vast majority of the return trips would be hidden from us

      Or, alternatively, what if we're wrong about the ratio of matter to anti-matter? How would we know if half of the Galaxies in the Universe aren't made out of anti-matter? Wouldn't an anti-star look exactly like a star?

      --
      There are no tiger attacks in my area and it's all because this rock I'm holding keeps the tigers away.
    106. Re:Confused by clarkcox3 · · Score: 1
      I was thinking the same thing in my other response (with just as little justification) :).

      it's just interesting to take what I think I understand about theoretical physics and extrapolate... Isn't that the whole fun of physics? :)
      --
      There are no tiger attacks in my area and it's all because this rock I'm holding keeps the tigers away.
    107. Re:Confused by slashdotwannabe · · Score: 1

      There's a big difference between being silent and being thought the fool and opening your mouth and removing all doubt.
      (Don't mean to insult you; it just sounded like an old Chinese proverb I know).

      --
      This comment is my opinion and does not represent an official position of Donald Trump or others I do not work for
    108. Re:Confused by SilentBob0727 · · Score: 1

      Marty! You're not thinking fourth-dimensionally!!

      --
      Life would be easier if I had the source code.
    109. Re:Confused by JebusIsLord · · Score: 1

      Dropping said feather and rock on the earth (in a vaccuum of course, otherwise obviously the feather would take longer due to air resistance) does accelerate faster, yes (9.81m/s2 if i recall). That's because the total mass of the system (earth + feather) is greater, so there is more gravitational force.

      Let's say you cut the earth in half and drop the 2 halves towards eachother. they will accelerate towards eachother at the exact same speed (9.81m/s2).

      --
      Jeremy
    110. Re:Confused by Stanistani · · Score: 1

      If a Zen Master asks you what is the sound of one hand clapping, slap the master in the face, then bow.

    111. Re:Confused by aqk · · Score: 1

      "what is holding the vacuum in?"

      I like it! Never heard of a vacuum referenced in this this way before!
      And if that vacuum were to ever escape... well, heaven help us.

      Is that what all this CERN "End of the world - black-hole particle" business is about?

    112. Re:Confused by aqk · · Score: 1

      Re "holes" fall up.

      A "hole" is simply a virtual object. It is not matter, but simply a construct to help us understand/ explain things better.
      Think about a hole in the ground. Can you pick it up and throw it? Which way does it fall?

      I'm reminded of a VERY old Beatles song here, but I digress....


    113. Re:Confused by aqk · · Score: 1

      I THINK it was a hammer. And it was Alan Shepard.
      And it was marvelous basic high-school lecture, that sadly, everyone seems to have forgotten.
      But sadly, the hoi-polloi all seem to remember his idiotic golf-drive on the moon.
      (sorry- I'm not a golfer)


    114. Re:Confused by aqk · · Score: 1

      How can something travel backwards in time? That doesn't even begin to make sense to me.

      I remember this equation about an electron travelling backwards in time from many MANY years ago in Atomic physics. When the prof explained that it was simply a heuristic solution, we all started speculating in class as to what it really meant, and proceeded to waste the rest of the period, while the prof grew increasingly frustrated.

      Simple answer: the square root of minus one. Does this make sense either?
      And geez.. don't get me started on the 4000 holes in Blackburn Lancashire...


    115. Re:Confused by smilindog2000 · · Score: 1

      I think it is likely that anti-matter particles are also holes... holes in space. I went through my old college physics books, including the Feynman series, and there are only a couple changes that need to be made to have it all work out. For example, you need E=abs(m)c^2. I let anti-matter have negative mass when checking equations.

      However, two points: first, I'm currently (as of today, not during my original post) on heavy pain meds for a minor operation I had yesterday. Second, my analysis was quite simple and naive. I never took particle physics, nor general relativity.

      --
      Beer is proof that God loves us, and wants us to be happy.
    116. Re:Confused by sco08y · · Score: 1

      Until now I thought that ouside the real of mathematics (where things can be proven and no further revision is possible, save for attacking the logic of the proof), there is no such thing as "an experiment that removes all doubt"?

      I think there's an experiment you can do that involves removing most of the pre-frontal cortex...

  2. I hate "news" like this. by BiggerIsBetter · · Score: 2, Insightful

    It's a cool experiment, but it's news once you get the result, not "a few years" before.

    Unless they're trying to drum up interest for funding...

    --
    Forget thrust, drag, lift and weight. Airplanes fly because of money.
    1. Re:I hate "news" like this. by Swizec · · Score: 1

      Shocker! Even science is about publicity these days.

    2. Re:I hate "news" like this. by JosKarith · · Score: 3, Insightful

      Maybe from the Millitary - "A beam of Antimatter you say... no known armour would stop it you say..."

      --
      'Don't worry' said the trees when they saw the axe coming, 'The handle is one of us.'
    3. Re:I hate "news" like this. by Travis+Mansbridge · · Score: 5, Funny

      Brought to you by: Molten Boron
      Nobody doesn't like Molten Boron!

    4. Re:I hate "news" like this. by Anonymous Coward · · Score: 5, Insightful

      You mean apart from all of the air in-between you and the target?

    5. Re:I hate "news" like this. by SQLGuru · · Score: 5, Funny

      Publicity is especially important in quantum physics because we don't know if they are working or not working until they are observed.

      Layne

    6. Re:I hate "news" like this. by rthille · · Score: 1

      No armor would be needed, the air between you and the enemy would stop it, and cause a large energy release just outside the 'muzzle' of the weapon.

      --
      Awesome furniture, accessories and cabinetry in Santa Rosa, CA: http://humanity-home.com/
    7. Re:I hate "news" like this. by Kingrames · · Score: 1

      Hate to break it to you but there'd most likely be a reaction before even that - what would the gun be made out of?

      And how far away would you be, if you were the target? Most likely still in the blast radius.

      --
      If you can read this, I forgot to post anonymously.
    8. Re:I hate "news" like this. by ShiNoKaze · · Score: 2, Funny

      Heh, Kinda like most shashdot readers.

    9. Re:I hate "news" like this. by Anonymous Coward · · Score: 0

      What about some sort of container with a vacuum (or some sort of containment field), that would release it deadly anti-payload on contact?

    10. Re:I hate "news" like this. by wattrlz · · Score: 1

      You just need to fire a beam with more mass than the air between you and the target. You could help it along by firing a laser-pulse or even a plain matter projectile to clear a path. Think weaponized laser or air-tazer .

    11. Re:I hate "news" like this. by Rolgar · · Score: 2, Interesting

      Of course you don't shoot the antimatter in open air. You shoot it in a containment shell (vacuum with some sort (Magnetic?) of isolation field). The detonator turns off the containment field and the anti-matter annihilates the matter of the containment shell. The difficult part would be maintaining power for the containment field. One little glitch in the power and you'll have a chain reaction, that could probably hit every other shell nearby creating a nasty super explosion that could make the H-bomb look tame.

    12. Re:I hate "news" like this. by Anonymous+Monkey · · Score: 1

      Ah, photon torpids.

      --
      We are the Borg...
    13. Re:I hate "news" like this. by Tenebrousedge · · Score: 3, Insightful

      This discussion is rather academic, however, as one of the largest problems with antimatter is creating and containing enough of it to be useful for experimentation. Creating and storing enough antimatter to be useful in a weapon is probably reserved for science fiction exclusively. H-bombs are much more efficient to produce, and equally useful as weapons---which is to say, not very.

      --
      Those who advocate genocide deserve every protection afforded by law, and none afforded by common human decency.
    14. Re:I hate "news" like this. by kalirion · · Score: 1

      A single-particle wide beam of anti-protons or something would be unlikely to hit any protons, wouldn't it? Then again, it might also just go straight through the target without hitting those protons either....

    15. Re:I hate "news" like this. by rthille · · Score: 1

      As for the more mass than the mass of the air, I suppose that would work, but you'd still have the (I expect, without doing calculations) _large_ energy release as soon as the antimatter leaves the 'muzzle'. As for laser or plain-matter projectile, I doubt that would remove the matter from the path. The laser might, given enough power turn the air into plasma, but that would likely still 'react' with the anti-matter. The plain matter projectile might be interesting, but not to push the air out of the way, just make it a containment vessel for the antimatter that releases the anti-matter on target.

      --
      Awesome furniture, accessories and cabinetry in Santa Rosa, CA: http://humanity-home.com/
    16. Re:I hate "news" like this. by wattrlz · · Score: 1

      That's an interesting idea you have there with the plain-matter projectile as a sort of, "shell" filled with antimatter. I was thinking if you shoot a bullet and have a slug of antimatter follow it closely behind - "drafting" I believe it's called in racing terms.What little air it does encounter will form a nice, "tracer" effect anyway.

    17. Re:I hate "news" like this. by Anonymous Coward · · Score: 1, Funny

      You tell if a quantum physicist is working or what he/she is working on. But not both at the same time.
      If you detect that a quantum physicist is working, then you won't know what on.
      And if you detect what a quantum physicist is working on, then you can't tell if he/she is working.

    18. Re:I hate "news" like this. by Harmonious+Botch · · Score: 1

      That's an interesting idea you have there with the plain-matter projectile as a sort of, "shell" filled with antimatter. I was thinking if you shoot a bullet and have a slug of antimatter follow it closely behind - "drafting" I believe it's called in racing terms.What little air it does encounter will form a nice, "tracer" effect anyway.

      Nice try, but the first 'tracer' explosion will ram the pellet into the back of the bullet.
    19. Re:I hate "news" like this. by philspear · · Score: 1

      Well see, that should be one of the things the researchers don't mention to the military when making their pitch for funding: clearly why they posted it here.

    20. Re:I hate "news" like this. by fbjon · · Score: 1
      This probably works for other situations... like office workers.


      If it looks like one is working, you won't be able to discern what they're working on - the monitor is somehow turned away from you.
      If you discern what one is working on, you won't know if he's really working on that. In fact, he probably never did, it only looked that way.

      --
      True confidence comes not from realising you are as good as your peers, but that your peers are as bad as you are.
    21. Re:I hate "news" like this. by wattrlz · · Score: 1

      I envision it as more of a slow burn than a series of explosions. The bullet's wake should be almost a vacuum with an influx of air [matter] from the sides which will annihilate on contact producing an effect similar to what would be expected from a highly radioactive substance, such as a polonium slug.

      If anti-matter has anti-mass and thus is anti-effected by gravity, wouldn't it have anti-momentum?

    22. Re:I hate "news" like this. by drinkypoo · · Score: 1

      No armor would be needed, the air between you and the enemy would stop it, and cause a large energy release just outside the 'muzzle' of the weapon.

      Perhaps you could encapsulate the antimatter in a cloud of ionized plasma, sort of like the current theory on ball lightning.

      --
      "You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
  3. Gravitons by Carewolf · · Score: 1

    I guess it depends on the existence of gravitons. Does the universe really bend or is that just a description of the gravitational force, or is gravitons exerting the force, and in that case does anti-gravitons exists, and what happens when gravitons collide with anti-matter?

    1. Re:Gravitons by Anonymous Coward · · Score: 0

      Gravitons would be electrically neutral and therefore be its own anti-partner

    2. Re:Gravitons by jandersen · · Score: 4, Interesting

      Gravitons are like photons: simply distortions in the underlying field. When two masses move relative to each other, the change in position corresponds to a change in the force between the two, but this change isn't communicated instantaneously. Instead the change travels as a distortion in the force-field - ie. a graviton (or several, as the case might be). This is what it means, intuitively at least, when they say that "the graviton mediates the force of gravitation"; and the same goes for the other mediators of force: photon, gluon and W- and Z boson. The perceived conflict is an artifact of limitations in the viewpoint of quantum mechanics.

      The gravitational field as a scalar field surperposed on a flat space-time is just another way of describing gravitation - the curved geometry of general relativity is a better model, although it is more difficult to get a handle on. Perhaps it would be worth trying to tackle the other forces in the same way, as geometry in some sort of space-time. Perhaps we can even derive quantum mechanics as a special case of such a model; mathematics has certainly come a long way since the time of Einstein and Bohr, and it isn't unreasonable to hope that we are now approaching a situation where we can solve those old problems, that neither had the tools for.

    3. Re:Gravitons by bickerdyke · · Score: 1

      gravitation"; and the same goes for the other mediators of force: photon, gluon and W- and Z boson. The perceived conflict is an artifact of limitations in the viewpoint of quantum mechanics. Which brings me to one of my favourite questions: can quantum scientiests actually imagine and understand that stuff, or are they merely calculating and thereby proofing it?
      --
      bickerdyke
    4. Re:Gravitons by jandersen · · Score: 4, Interesting

      It is my distinct impression that what they mostly do is start from a classical physical model, which is then "quantified" by putting it through the magical transformation, where the classical Hamiltonian is turned into a differntial equation. I have no idea why this is done, nor have I ever met anybody who could explain it convincingly; but it seems to work. It is of course by no means a intellectually satifying method, which is what makes me wonder why nobody seems to seriously do anything about it. It is also, in my opinion, one of the reasons why quantum mechanics has always been plagued by quasi-religious mumbo jumbo like the Copenhagen interpretation.

    5. Re:Gravitons by Hankapobe · · Score: 1
      ...by putting it through the magical transformation,...

      Ah, the Tooth Fairy or Santa Claus keeps us on the ground.

    6. Re:Gravitons by Dragonslicer · · Score: 3, Interesting

      Gravitons would be electrically neutral and therefore be its own anti-partner So that means neutrons are their own antiparticle? I always thought otherwise.
    7. Re:Gravitons by Tim+C · · Score: 1

      And angels guide the spheres in their heavenly courses.

      We'll work the truth out sooner or later; I just hope it's soon enough that I get to hear. I may be a programmer now but my degree is in physics and I still find it fascinating.

    8. Re:Gravitons by Anonymous Coward · · Score: 0

      Certainly that can be done, Kaluza and Klein did that for electromagnetism in the 30's (or 20's already). However, this approach has some problems, it needs extra dimensions, which give massless and massive states we do not see in practice.

      But, in principle, string theory is the culmination of this work, and is working somewhat along the way you propose.

    9. Re:Gravitons by rumith · · Score: 4, Informative

      I think that the parent means that neutral bosons have no antiparticles. While neutron is a barion and thus has an antiparticle composed of (~u ~u ~d) quarks, neutral bosons (such as photon and Z0) do not have corresponding antiparticles.

    10. Re:Gravitons by markswims2 · · Score: 1

      Mod parent up (I have no points to share). I know nothing about this subject, but if I could guess, I would think that antimatter would exert an antigravity force which would attract antimatter but repel matter the same way that gravity attracts matter. That leaves the question "is there such a thing as antigravity?"

    11. Re:Gravitons by wattrlz · · Score: 1

      I'm pretty sure we can agree to the existence of at least one anti-photon.

    12. Re:Gravitons by rumith · · Score: 1

      Sorry, a typo! ~u ~d ~d is an antineutron; ~u ~u ~d is an antiproton.

    13. Re:Gravitons by SpacePirate20X6 · · Score: 1

      Sorry, a typo! ~u ~d ~d is an antineutron; ~u ~u ~d is an antiproton. Yeah, because we all caught that mistake. ;)
    14. Re:Gravitons by Anonymous Coward · · Score: 0

      Yes they do. They just look and behave exactly the same, so you can't tell they're there.

    15. Re:Gravitons by Anonymous Coward · · Score: 0

      It's called "quantized" FYI, though your description was accurate. As for the reason why people do that, it *is* simply because it works. What better reason do you want?

      And why would people do anything about a model that gives ridiculous accuracy on fundamental particle-physics experiments? It works. You need to learn to deal with it, not the other way around.

      I do agree that people's inability to just see the model as what it is-- a bunch of math that works-- is the reason for the quasi-religious mumbo jumbo.

    16. Re:Gravitons by jandersen · · Score: 2, Insightful

      And why would people do anything about a model that gives ridiculous accuracy on fundamental particle-physics experiments? It works. You need to learn to deal with it, not the other way around. Why? That's the wrong attitude; the real question is "Why not?"

      Yes, for practical purposes QM is fine - but it is not enough for understanding. It's like the difference between engineering and science; engineers are good and worthy people, but their focus is practical: the construction of things, the application of knowledge to a practical purpose. The focus of the scientist is on the unknown, the unanswered questions; the practicality of things is not foremost in their mind, they speculate and grope in the dark. These are of course wild generalisations, but the principle of what I just said is sound, at least :-)

      And thus I find that the proper scientific attitude to QM is not "Who cares, it works", but "Why does it work?" - there must be something better out there, a theory of which QM is just a special case, an approximation. Scientific method relies, after all, on theories being falsifiable - isn't that, more than anything, the very embodiment of "Why not"?
    17. Re:Gravitons by Anonymous Coward · · Score: 0

      Unless the space-time curvature is less of a curve and more of a density shift. Imagine huge clumps of dense Space gathered around stars making it more sticky and therefore difficult to wade through, regardless of your mass. The large gaps between stars etc would be quite thin on the stickyness. This is a basic gravitational/curvature model.

      This would ruin the Newtonian model in an instant : that a constant velocity is a stable one. So the stickyness would have to be a differential stickyness - that only acts on acceleration (or deceleration) - If this were true then all we'd need to do to detect it is to apply a force to something and measure the resistance.

      Which is also easy, this "sticky-force" is called Inertia. But wouldn't that mean that Inertial mass would have to be different from Gravitational mass. At first glance yes, on the other hand. What if the inertial effect, the "sensation" of weight is the inherent, tangible physical manifestation of inertial-sticky-space?

      So, to step back a second, there are two things we can use "mass" to define:

      1. The volume of an object - it's measurable physical dimensions (if any)
      2. The inertial field.

      The inertial field at Newtonian scales will be very much confined to the object's volume, dropping off sharply at the edges, much of it falling into the gaps between atoms.

      At the quantumn-scale objects can have Planck-like volumes whilst also weighing a lot, take for example the atomic nucleus, hideously dense. But the distance to the next atomic nucleus is so large so there is still plenty of room for the drop-off from each to barely overlap.

      If the density of the inertial field is simply related to "how heavy" something is (how many atomic nuclei are packed in there) then a very high density could be correlated to what we currently know as a highly-curved region of space. Solar lensing would suggest the inertial field is not as tightly confined to the solar volume as at human scales - all those gaps between the atoms filling up a fraction of a percent at a time until it starts to spill out of the object as a whole.

      What this theory also explains is "Where does mass come from?". We treat it as a given aspect of matter that it exhibits gravity, generally we just accept that one begets the other, that all matter "has" a gravitational field.

      What I'm saying here is that perhaps there is no difference, no assumed relationship, that the gravity field IS the inertial-field and the inertial-field IS the mass, it's just that at our scale the edge of the object - where we stub our toe on the corner of the wardrobe - is very very very close to the edge of the field - but not exact enough that a ray of light juuuust skimming that same wardrobe-corner wont get caught up in that tiny region of stickyness that extendes from the surface ...and diffract.

  4. It will fall down by little1973 · · Score: 5, Informative

    According to GR, gravity is the curvature of Space-Time. As the anti-matter moves through space it has to follow this curvature. If it does not, that means GR is wrong (which may be the case, but I doubt this experiment will disprove GR).

    --
    Government cannot make man richer, but it can make him poorer. - Ludwig von Mises
    1. Re:It will fall down by $RANDOMLUSER · · Score: 1, Interesting

      Exactly right. And the value of the Cosmological Fudge Factor errrr Constant is zero.

      --
      No folly is more costly than the folly of intolerant idealism. - Winston Churchill
    2. Re:It will fall down by Anonymous Coward · · Score: 0

      According to GR, gravity is the curvature of Space-Time. As the anti-matter moves through space it has to follow this curvature. If it does not, that means GR is wrong (which may be the case, but I doubt this experiment will disprove GR). On the other hand, antimatter is functionally normal matter which behaves arse-backwards with respect to the time axis. Therefore it does things like repel particles it would normally attract.

      This depends on a few things with large scary names being true that we think are true, but that's the gist of the best theory going to explain the stuff. Finding out which way it falls would be amusing and potentially useful.
    3. Re:It will fall down by Anonymous Coward · · Score: 0

      maybe anti-matter creates anti-gravity, which is also a curvature of Space-Time, but a curvature in a different direction than plain-vanilla-gravity.

    4. Re:It will fall down by thue · · Score: 5, Insightful

      Yes, Silly physicist PhDs doing unneccesary experiments. They could have been told the result of the experiment just by asking a random commenter on Slashdot. :)

      Because our understanding of physics is so consistent that it is a waste of time to test the cornercases of our theories *cough*quantum gravity*cough*dark matter*cough*dark energy*cough*

      :P

    5. Re:It will fall down by Anonymous Coward · · Score: 5, Informative

      bollocks. having a faster-than-escape velocity doesn't make things fall upwards. it merely means they don't come down fast enough to hit the earth

    6. Re:It will fall down by something_wicked_thi · · Score: 4, Informative

      Oh, dear. I think you should write these guys a letter before they waste all this time and money on an experiment with such an obvious flaw!

    7. Re:It will fall down by drsquare · · Score: 1

      If hydrogen tends to move away, why isn't it all in space by now?

    8. Re:It will fall down by that_itch_kid · · Score: 5, Funny

      GR is bunk. I find your lack of faith disturbing.
    9. Re:It will fall down by Anonymous Coward · · Score: 0

      Except that in a particle accelerator, the hydrogen molecules are in a vacuum, and their velocity is tightly controlled (99.9999...% c forward).

    10. Re:It will fall down by Anonymous Coward · · Score: 0

      Hydrogen gas doesn't fall up, it's because everything else is *heavier* that it's pushed up (and quite a bit of hydrogen does escape the Earth's gravitational pull). But because this experiment will most likely be performed in the most extreme vacuum they can fabricate this won't be a problem.

    11. Re:It will fall down by JasterBobaMereel · · Score: 1

      But how does antimatter react to curved spacetime
      (could it 'roll uphill')..

      and how does antimatter (with mass) curve spacetime?
      (could it 'outdent' rather than 'indent' it)

      --
      Puteulanus fenestra mortis
    12. Re:It will fall down by oodaloop · · Score: 0

      Yeah, I don't know why they didn't consult with me first. I could have saved them a lot of time.

      --
      Tic-Tac-Toe, Global Thermonuclear War, and relationships all have the same winning move.
    13. Re:It will fall down by JackassJedi · · Score: 1

      In fact the curvature can even be negative, if we have negative mass density. Normal matter is attracted to each other since it creates a positive spacetime curve. If antimatter has negative mass only then we would see the effects discussed here, that is, (anti-)matter creating a negative spacetime curvature, leading to it "roll off" pff the positive spacetime curvature of e.g. the earth).

      Also, it wouldn't exactly disprove GR, it would only violate the positive energy condition of the GR, however it would not break up the consistency of GR mathematically.

      --
      Power corrupts the few, while weakness corrupts the many.
    14. Re:It will fall down by Anonymous Coward · · Score: 1, Informative

      Seems to me that hydrogen isn't ''falling up'' but rather oxygen/nitrogen and so forth are pushing it up.

    15. Re:It will fall down by fireboy1919 · · Score: 4, Informative

      Didn't you have to take high school chemistry? What you're saying has quite a few problems:

      1) That determines the rate of effusion. Molecules don't just go straight up. They bounce around. What actually happens in reality is that the force holding those molecules to the earth isn't actually enough to force it to happen. But the upward movement is going to happen slowly. You can still measure the effect that gravity has while this upward movement happens.

      2) Also because it has to do with effusion, a *beam* of antiparticles in a vaccuum won't be affected by it. They're not going to bounce around and have effusion effects happen; it's going to be more like a batting practice machine - balls come out and curve, and are done the moment they hit something. This is obviously what they're going to do since antimatter is quickly eliminated in the presence of matter.

      3) Even if that was a problem, it's not actually a problem at all temperatures and pressures. If you wanted to do an experiment where *normal* hydrogen didn't rise, just lower the temperature.

      --
      Mod me down and I will become more powerful than you can possibly imagine!
    16. Re:It will fall down by Anonymous Coward · · Score: 1, Interesting

      This is a test of predictions from certain types of quantum gravity not of General Relativity. The equivalence principle of GR says there shouldn't be a difference. This is essentially a test of the equivalence principle. (Likely it will just put a lower bound on the difference in g from normal matter and anti-matter.)

    17. Re:It will fall down by oodaloop · · Score: 0

      So why does hot air rise? Does heating air make it lighter? Hot air rises because the individual particles have more energy (heat), and so move faster. I will grant that this experiment removes some of the variables by forcing the anti-hydrogen to move at a particular velocity, but the vacuum has nothing to do with it. Hydrogen rises because of its velocity, which is mostly due to its light weight. Most, but not all, of hydrogen (think bell curve here, people) moves faster than the escape velocity of earth and so most of the hydrogen the earth started off with is gone. Some has remained, and some of what little we have left will also escape.

      Googling hydrogen escape velocity got this on the first result:

      "So the lighter molecules, such as hydrogen have enough velocity to escape from the earth, where as heavier ones such as nitrogen and oxygen don't. That's one of the reasons that you don't see much hydrogen or helium floating around in the air."

      http://physics.ucsc.edu/~josh/6A/book/gravity/node12.html

      --
      Tic-Tac-Toe, Global Thermonuclear War, and relationships all have the same winning move.
    18. Re:It will fall down by Anonymous Coward · · Score: 5, Informative

      I'm a physics PhD and this is definitely one of the experiments where there is no reason to expect things to behave differently from the theory. Any reasonable theory already allows us to put low limits on the difference in gravitational behaviour between matter and anti matter and there certainly is no theory of gravity that I know of where antimatter "falls up". There are some where it might fall differently.

      There also is some direct evidence that if you have differences they are not due to gravity:

      Reference e.g.:

      http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/antimatter_fall.html

      "The only direct experimental result on antimatter and gravity comes from Supernova 1987A. This supernova in the Large Magellanic Cloud emitted both neutrinos and antineutrinos, some of which were eventually detected on Earth. Those neutrinos and antineutrinos took 160,000 years to reach Earth, and while travelling were bent from a "straight line" path by the gravity from our own galaxy. The bending with gravity changed the time needed to reach Earth by about 5 months, yet both the neutrinos and the antineutrinos reached Earth at roughly the same time (within the same 12 second interval). This shows that the neutrinos and antineutrinos "fell" similarly, to a very high level of precision (about 1 part in a million). [4] and [5] provide some background information on this."

    19. Re:It will fall down by jandersen · · Score: 4, Funny

      An alternative explanation is of course that the anti-particles are distracted and therefore miss the Earth, as demonstrated in the well-known experiments performed by Arthur Dent.

    20. Re:It will fall down by Hankapobe · · Score: 4, Funny

      Yes, Silly physicist PhDs doing unneccesary experiments. They could have been told the result of the experiment just by asking a random commenter on Slashdot. :)

      Why not? This is where I get my IP legal advice!

    21. Re:It will fall down by geekgirlandrea · · Score: 5, Interesting

      But how does antimatter react to curved spacetime (could it 'roll uphill')...

      That's what the experiment in the article is testing. Does antimatter react the same way to an external gravitational field as normal matter, or oppositely?

      It'd be Big News if it turned out to be oppositely, though. General relativity describes gravitation in terms of space-time curvature; particles under the influence of gravity alone move along geodesics which only depend on their initial position and velocity. There isn't any way to accomodate different particles feeling gravitation differently in that framework. There are generalizations like Einstein-Cartan gravity to accomodate spin, but that just allows the connection to have an antisymmetric part, and doesn't change the fact that there's only one curvature for every particle to feel. The key axiom of GR is the equivalence principle, which states that, locally, there is no observable difference between gravity an accelerated reference frame. This requires that gravity accelerate every particle by the same amount, independent of any other particle-specific variables.

      Put briefly, this has never been tested before, but it'd be a very big surprise if antimatter behaved any differently from normal matter, and would throw most current theories of gravitation out the window. It'd be like a modern-day Michelson-Morley experiment.

      and how does antimatter (with mass) curve spacetime? (could it 'outdent' rather than 'indent' it)

      That's a different question, and one that would be far more difficult to test. You'd need to gain a few dozen orders of magnitude of precision in measuring these things, or assemble a macroscopic chunk of antimatter somehow.

      It'd also be a big surprise for a different reason. This is essentially treating antimatter as having negative mass and thus producing a repulsive gravitational effect. There's no deep reason why this would be mathematically inconsistent with GR, although it would have wacky consequences like perhaps the possibility of stable wormholes and FTL. In technical terms, it violates the weak energy condition. It's also unlikely for a different reason: conservation of momentum in GR requires inertial mass and gravitational mass to be equal, so for antimatter to produce a repulsive gravitational field like this would also require it to have negative intertial mass. It would respond oppositely to ordinary, non-gravitational forces, a positronium atom would have *negative* net mass (the electron and positron masses cancel, and the binding energy makes it negative), and a whole host of other consequences that would be readily observable but haven't been seen. Further, in quantum field theory having negative mass particles would create problems with vacuum stability.

      So, both of these are possible in the sense that the experiment hasn't been done yet, so we don't know for sure they aren't true, but either one would invalidate huge swaths of physics and definitely qualify as Big News.

    22. Re:It will fall down by Enrique1218 · · Score: 2, Interesting

      That assertion may not be true. A prominent physicist once suggest that antimatter in not antimatter at all but rather matter traveling in anti-time or backwards in time from are perspective. That explains why we measure opposite charges from normal matter. If placed in curvature of space, it would appear to move up against the gradient. That interpretation would preserve GR. I would also remind you that every law like GR is just an approximation.

      --
      You don't have to be smart to use a Mac, you just have to be smart enough to buy one
    23. Re:It will fall down by geekgirlandrea · · Score: 2, Informative

      I suppose you have an alternative that is also consistent with all the observed instances of gravitation and meets your personal criteria for not being 'bunk'? Would you care to enlighten us? Why the heck is this drivel +1 Insightful anyway?

    24. Re:It will fall down by oodaloop · · Score: 0, Troll

      This got modded informative? Are you all retards? See my comment further downthread, or just google hydrogen escape velocity for yourselves.

      --
      Tic-Tac-Toe, Global Thermonuclear War, and relationships all have the same winning move.
    25. Re:It will fall down by JasterBobaMereel · · Score: 1

      Thanks for the explanation ....

      So if it falls up then General relativity is wrong (or at least has severe problems) and if this is because it has negative mass then something is very wrong with many theories not just GR ...?

      --
      Puteulanus fenestra mortis
    26. Re:It will fall down by sdrawkcab3 · · Score: 1

      GR will not be wrong if anti-matter falls up. The stretched fabric analogy of space-time depends on an outside force (Earth's gravity) to provide direction. GR lacks a dependence on an outside force - especially Gravity - to provide a direction. Anti-matter could still follow the curvature of space-time, just in the opposite direction.

      --
      http://images.slashdot.org/hc/92/f975cee5e74b.mp3
    27. Re:It will fall down by redxxx · · Score: 1

      Except, if it has negative mass, wouldn't that affect other accelerations?

      Anti-protons have a negative charge and are attracted by positive charges. If both charge and mass were negative, shouldn't they accelerate in the other direction? Very weird thing happen to that whole a=f/m thing when m is negative, and we would have noticed it. Energy equations yields even stranger results. E=mCC, means anti-particles would have total negative energy, and annihilating particle pairs releases a net amount of energy? The mass can't be negative.

      There is a total amount of mass between the two particles, that mass gets changed into energy which is released. The net mass can't be 0, and the amount of energy released matches up with our understand of mass of both particles being positive.

      There is no reason to believe that the mass of anti-particles would be treated as negative by gravity alone and no other forces. Unless a massive chunk of what we think we know about how the universe is wrong.

      If they fall up at all, then there are some pretty serious issues that the hard science folk need to start looking into.

    28. Re:It will fall down by Anonymous Coward · · Score: 0

      How about this: antimatter is just normal matter, but moving backwards in time. That is, like watching the movie Memento, we watch the previous locations of the particle. What does an electron in reverse look like? A positive particle with the same mass.

      If that were the case, then of course they would fall up, since we're just looking at it fall down backwards.

      This isn't a new idea, and there's probably some (read: lots of) problems with thinking that way, but so long as we're being all touchy-feely with "curvatures of spacetime", I thought I'd throw out a touchy-feely way for antimatter to fall up.

    29. Re:It will fall down by Goaway · · Score: 1

      Before calling people retards, perhaps you should try to actually understand the topic being discussed, to avoid looking quite so foolish.

    30. Re:It will fall down by Anonymous Coward · · Score: 0

      Oh, right, because GR shares all of those properties.

      Not the OP, but the GR isn't perfect. Nowhere near.

    31. Re:It will fall down by Anonymous Coward · · Score: 0

      I wonder though if antimatter would also generate such a distortion in space-time, or maybe the opposite distortion. In that case, anti-matter would fall down, but it would not attract other anti-matter and so could not form a star or a planet. But that's just random speculation on my part.

    32. Re:It will fall down by gardyloo · · Score: 1

      Das ist Ganz Falsch

          Not only is your post wrong, it's not even internally consistent. To wit: This is a test of predictions from certain types of quantum gravity not of General Relativity. The equivalence principle of GR says there shouldn't be a difference. This is essentially a test of the equivalence principle. You've just said "This won't test A, it will test B. It will test part of A."

    33. Re:It will fall down by Lijemo · · Score: 1

      Oh, right, because GR shares all of those properties.

      The "properties" she mentioned were

      1. consistent with all the observed instances of gravitation
      2. meets your personal criteria for not being 'bunk'

      Would you care to enlighten us either

      1. where General Relativity diverges from observed data OR
      2. another theory that meets ALL observed data
    34. Re:It will fall down by mpeskett · · Score: 1

      I'm still waiting for all the other possible combinations of the words "dark", "matter", "quantum", "energy" and "gravity" to become recognised theories.

      When I hear about the effect of dark gravity on quantum energy, and how the resulting exotic matter is possibly able to annihilate the Earth but probably won't, so we don't need to worry about them making some in the Even Larger Hadron Collider... *then* I'll believe the physicists are getting somewhere.

    35. Re:It will fall down by FromellaSlob · · Score: 1

      So why does hot air rise? Because it floats on top of the denser air beneath.
    36. Re:It will fall down by smaddox · · Score: 1

      There isn't any way to accomodate different particles feeling gravitation differently in that framework.

      Unless, of course, the particle were sitting on the other side of the spacetime "sheet". What that means physically is hard to say, though.
    37. Re:It will fall down by lazlo · · Score: 1

      I recall reading an article long ago, where it discussed the possibility of negative matter (distinct from antimatter, although if it does exist, then there's probably also negative antimatter)

      It's negative because it has a negative inertial mass. Thus, since F=MA, if you apply a force in the Northerly direction to it, it will accelerate more Southerly. Gravitationally, it causes an inverse curvature of space-time, so, IIRC from the article, if you had two objects, a mass and a negative mass, then the mass would be repelled from the negative mass (because the force of the gravitational equation would be negative), but the negative mass, because the force is in the direction away from the normal mass, would accelerate towards the normal mass. Thus, they would just sort of chase each other. Where the energy to do this comes from is a mystery to me, and I don't believe it was mentioned in the article.

      Of course, I think this was in an issue of Analog, so it's not like it was a peer reviewed scientific journal, but I thought it was pretty interesting nonetheless.

      --
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    38. Re:It will fall down by NJ+Hewitt · · Score: 1

      You're still missing the point. At the same pressure, a litre of hot air does have less mass than a litre of cold air. Hot air rises because it is less dense than cold air, because the particles bounce off each other more energetically. So yes, heating unconfined air does make a given volume lighter. The relationship between the particles average speed (be careful here, you said velocity) and the Earth's escape velocity is such a smaller effect as to be negligible.

    39. Re:It will fall down by Anonymous Coward · · Score: 0

      "The only direct experimental result on antimatter and gravity comes from Supernova 1987A. This supernova in the Large Magellanic Cloud emitted both neutrinos and antineutrinos, some of which were eventually detected on Earth. Those neutrinos and antineutrinos took 160,000 years to reach Earth, and while travelling were bent from a "straight line" path by the gravity from our own galaxy. The bending with gravity changed the time needed to reach Earth by about 5 months, yet both the neutrinos and the antineutrinos reached Earth at roughly the same time (within the same 12 second interval). This shows that the neutrinos and antineutrinos "fell" similarly, to a very high level of precision (about 1 part in a million). [4] and [5] provide some background information on this." Really? I don't have my doctorate, but do have a degree in physics. Neutrino's have been proven to oscillate between their different type's, electron, tau, etc. neutrino's. If that's true, and it is, the oscillations could easily interact with the electromagnetic field in between there and here. Not saying it has, but because of the distance traveled, there would be enough "noise" in that experiment to invalidate it. So an earth based experiment would be prudent.
    40. Re:It will fall down by Anonymous Coward · · Score: 0

      negative mass also implies negative energy according to E=mc^2. I guess that will have to change as well. I want to see how that plays out with nuclear reactions.

    41. Re:It will fall down by Free+the+Cowards · · Score: 3, Insightful

      Are you sure you have a degree in physics? Neutrinos have no charge, and thus are not affected by electromagnetic fields. The name sounds like "neutral" because of this. If they were charged they would be called something else.

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    42. Re:It will fall down by Free+the+Cowards · · Score: 1

      Actually, if you run time backwards then things still fall down. Think about throwing a ball up in the air. It goes up, comes down, hits the ground, and its energy dissipates into vibrations in the ground. If you run it backwards, random vibrations in the ground come together to launch the ball into the air. It goes up, then falls back down into your hand.

      Also I think that business with antimatter being normal matter going backwards in time was only for electrons and positrons.

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    43. Re:It will fall down by marcosdumay · · Score: 1

      conservation of momentum in GR requires inertial mass and gravitational mass to be equal

      I think that is the most weard of all. The inertial mass increases with the velocity module (going into infinity when the later goes to c), but if the gravitational mass increses proportionaly, a body could have a speed that is highter than c just by falling into a strong enough gravitational field.

      Or did I just "discover" a black hole?

    44. Re:It will fall down by neo-mkrey · · Score: 1

      You really should go see a doctor about that cough. I sounds bad. ;)

    45. Re:It will fall down by markswims2 · · Score: 1

      Sounds more like a density problem to me. If Hydrogen is on average above the escape velocity of the earth, shouldn't we be seeing a deterioration of our atmosphere, or at least the amount of Hydrogen decreasing at some rate?

    46. Re:It will fall down by Actually,+I+do+RTFA · · Score: 0, Troll

      You are thinking of neutrons.

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    47. Re:It will fall down by oodaloop · · Score: 0

      Even granting that hot air rises for other reasons, I don't think I'm missing the point. The subject is about hydrogen. Hydrogen rises because its particles' average speed is above the escape velocity of earth. This can be found on any number of scientific websites.

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    48. Re:It will fall down by oodaloop · · Score: 1

      I have. I read it in these things called books.

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    49. Re:It will fall down by oodaloop · · Score: 0, Troll

      Hydrogen is both produced in our atmosphere and constantly bleeding away into space. It was also much more plentiful in the earth's past, and the vast majority of it has since escaped.

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    50. Re:It will fall down by Anonymous Coward · · Score: 0

      Please go back to your electric universe, autodynamics and perpetual motion machines.

    51. Re:It will fall down by NotBornYesterday · · Score: 3, Insightful

      I think you are confusing molecular energy with anti-gravity.

      TFA questions whether anti-matter will be attracted (mass-> <-mass), or whether it will be repulsed (mass<- ->mass) by gravity.

      Hydrogen is attracted rather than repulsed by earth's gravitational pull. Whether the earth's gravity well is deep enough to keep hydrogen captive is a separate topic. Having enough energy to escape earth does not mean that it is repulsed by earth's gravity. The Space Shuttle has enough energy in its fuel tanks to reach escape velocity, and there is no doubt that is is attracted, not repulsed, by earth's gravity.

      Hot air is still attracted by earth's gravity. However, its higher energy state forces it to occupy a larger volume at a given ambient pressure, which makes its density lower than the surrounding cooler air. Hot air doesn't defy gravity by rising; cool air pushes the hot air up because it is denser.

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    52. Re:It will fall down by The_Wilschon · · Score: 1

      Neutrinos only interact via the weak interaction (and gravity, which is much weaker), and thus interact only very very very rarely. They most certainly do not couple to the EM field.

      --
      SIGSEGV caught, terminating

      wait... not that kind of sig.
    53. Re:It will fall down by The_Wilschon · · Score: 1

      No, the GP is right. Look it up if you aren't convinced.

      --
      SIGSEGV caught, terminating

      wait... not that kind of sig.
    54. Re:It will fall down by xPsi · · Score: 1

      However, because the neutrino has mass (or at least 2 of the flavors do for sure, but probably all 3), there is the possibility it may actually be its own antiparticle where the object we call "antineutrino" is merely a different chirality state of the neutrino (i.e. is the neutrino a Majorana or Dirac fermion?). There are a number of experiments (past and pending) around the world trying to address this issue. I wonder how this information affects the Baez supernova discussion above in the context of the article? (IAAP too)

      --
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    55. Re:It will fall down by Free+the+Cowards · · Score: 1

      If I were thinking of neutrons, I would have said neutrons.

      The name "neutrino" is in fact a play on the word "neutron". It is so called because "neutrino" is a diminutive form of "neutron" in Italian, the native language of Enrico Fermi, who created the name. The name was chosen because neutrinos, like neutrons, are neutrally charged but they have much smaller (possibly no) mass.

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    56. Re:It will fall down by Goaway · · Score: 1

      That's nice. Now try reading the actual issue at hand instead, and try to comprehend why you are talking about something else entirely.

    57. Re:It will fall down by Rogerborg · · Score: 1

      Bullshit; you just need to reverse the polarity of the Space-Time flow.

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    58. Re:It will fall down by oodaloop · · Score: 1

      Um, yeah, I basically said that in another post that this experiment is different. What I said was REGULAR hydrogen rises because of the escape velocity. Someone else denied this is the case and got modded +5 insightful. I pointed out that a simple google search will return multiple scientific sites showing this is the case, and I got modded flamebait. I don't feel bad about calling those people retards at all.

      --
      Tic-Tac-Toe, Global Thermonuclear War, and relationships all have the same winning move.
    59. Re:It will fall down by Anonymous Coward · · Score: 0


      Actually I was thinking of MSW effect. As quoted by Wikipedia,

      The presence of electrons in matter changes the energy levels of the propagation eigenstates of neutrinos due to charged current coherent forward scattering of the electron neutrinos (i.e., weak interactions). ie. electrons in plasmas and the like.
    60. Re:It will fall down by locofungus · · Score: 1

      I think you're getting confused with CPT invariance. Reverse the charge, reverse the parity and reverse time and everything looks the same.

      IIRC CP symmetry (reverse the charge, reverse the parity) is broken with the decay of the Kzero and anti-Kzero. (There was an article about this some years or decades ago in SciAm but I'm too lazy to go and look it up now). Given that then I don't think, in general, an anti-particle can be a particle moving backwards in time.

      Tim.

      --
      God said, "div D = rho, div B = 0, curl E = -@B/@t, curl H = J + @D/@t," and there was light.
    61. Re:It will fall down by Jasper__unique_dammi · · Score: 1
      At least when the masses are small compared to those causing the gravitation, negative masses will actually fall down in GR. The spacetime paths of particles are actually independent of their mass.

      "That's what the experiment in the article is testing. Does antimatter react the same way to an external gravitational field as normal matter, or oppositely?" Oppositely? The movement of a something is a path in spacetime. Where you see the particle is a matter of how the light travelled from the thing to you. There is no such thing as 'forward' or 'backward' of time in the object, other then the one that is 'provided' by thermodynamics. Time going 'forward' seems to be derived from the fact that the state of things at the time we call 'past' is very atypical.(Physics without thermodynamics does not care which direction time goes.)

      Btw the curvature of spacetime is might need an arbitrary amount of dimensions to embed it in. (Not just four) Your idea of going uphill/downhill is not exactly correct.

      I was thinking of explaining what time travel is, but i dont seem to find a good way to explain. (I dont fully get it either.) The 'thermodynamic time direction' stays the same, but the spacetime path 'goes backward in time' for some other observers.

    62. Re:It will fall down by Goaway · · Score: 1

      No, you did not. You just stumbled into an discussion you didn't understand, started yelling about unrelated things, called people retards when they pointed out that you are completely misunderstanding the topic, and now you're still going on about it.

      Nobody said that hydrogen doesn't rise from the Earth. That is another misunderstanding on your part. Now slow down, take a deep breath, re-read the discussion and try to figure out how you are talking about something completely different than everyone else.

    63. Re:It will fall down by oodaloop · · Score: 1

      OK, I'll slow down. Just for you. Apparently you need it.

      I brought up hydrogen rising as a related issue, understanding that this experiment is different (and yes I actually did acknowledge this in a different post, and yes I understand the topic at hand). And yes no one has denied that hydrogen doesn't rise. But that's not what I am arguing, so that is pretty much irrelevant.

      What several people HAVE denied is HOW it rises, which is most emphatically due to its average speed being above the escape velocity of earth. I realize this is isn't taught in school. I spent years reading science books, and only stumbled on it myself a few years ago. But I pointed out that a simple google search will uncover it in multiple scientific web sites and got modded flamebait, while the AC who posted that esacape velocity has nothing to do with hydrogen rising got modded +5 insightful. I'm sorry if this ludicrous reversal of common sense got me upset, but this still is a geek website, is it not?

      --
      Tic-Tac-Toe, Global Thermonuclear War, and relationships all have the same winning move.
    64. Re:It will fall down by Goaway · · Score: 2, Informative
      This is what you said:

      According to GR, gravity is the curvature of Space-Time. As the anti-matter moves through space it has to follow this curvature. If it does not, that means GR is wrong (which may be the case, but I doubt this experiment will disprove GR). Except that regular hydrogen falls up. Since the average velocity of its molecules is above the escape velocity of Earth, hydrogen tends to move away from Earth. If anti-hydrogen has similar velocities, it should also rise. That is not "bringing it up as a related issue".

      the AC who posted that esacape velocity has nothing to do with hydrogen rising He did not say anything of the sort. You misunderstood that. He said:

      bollocks. having a faster-than-escape velocity doesn't make things fall upwards. it merely means they don't come down fast enough to hit the earth He was essentially pointing out that you were confusing unrelated issues in your original post.
    65. Re:It will fall down by Steve+Max · · Score: 1

      They could, either via sufficiently complicated Feynman diagrams or if their magnetic moment isn't zero (as it has to be). Anyway, the cross section should be orders of magnitude smaller than the weak ones. About the GP's quote on SN1987A, there is still some controversy. There actually were some events recorded at the Mont Blanc experiment more than four hours before the Kamiokande, Bakun and IMB detections. If you don't disregard any of the data, you have a time spacing between the first and the last SN1987A neutrinos of almost 4.5 hours. This points to either a high mass difference between the three mass eigenstates or a possibility of breaking the equivalence principle (or, more remotely, the possibility of tachyonic movement).

    66. Re:It will fall down by Steve+Max · · Score: 1

      The most interesting part is that the neutrino should be Majorana. In QFT, if a term is not forbidden by any symmetry, it is mandatory. There is no symmetry preventing a Majorana mass term for the neutrinos, so that term must exist within the current standard model. Of course, a Dirac term must exist too, so the real question is which term is dominant, and therefore how does the neutrino behave? Depending on the parameters, this will be energy dependent, so we need to know about them (not the mass-squared differences, but the actual mass terms on the Lagrangian) before making any predictions. (IAANP, a neutrino physicist).

    67. Re:It will fall down by kalirion · · Score: 1

      I bet anti-matter will appear to fall down, but only because it's in reality falling up and moving backwards through time.

    68. Re:It will fall down by Anonymous Coward · · Score: 0

      I suggest you stop calling people retard and assuming that they are stupider or more ignorant than you.

      You're wrong in so many ways it's hard to know how best to explain things to you.

      I mean, you're even wrong about the average speed being higher than the escape velocity of the earth.

      The escape velocity of the earth is 11km/s (or 11000 metres per second)
      The classical formula:
        velocity = sqrt ( 3 * temperature * bolztmann constant/ mass of molecule)

      bolztmann constant = 1.38*10^-23 J/K
      weight of hydrogen molecule = 3.347 &#215; 10^-27 kg

      Go paste the following in google:
      sqrt ( 3 * 300 * 1.38*10^-23 / ( 3.347 &#215; 10^-27))

      And you'll get the average speed in metres per second. Divide by 1000 to get km per second.

      The average velocity of a hydrogen molecule at 300K is 1.9km/s
      The average velocity of a hydrogen molecule at 800K is 3.1km/s
      The average velocity of a hydrogen molecule at 1800K is 4.7km/s
      The 1800K figure is assuming an average hydrogen molecule in the ionosphere _when_ it's really hot (normally it's about 800K).

    69. Re:It will fall down by Anonymous Coward · · Score: 0

      What you said is total BS. It repels particles? I think a particle and it's antiparticle disagree when the come to meet. In fact, I think the proton and antiproton are quite attractive, in the electrical sense. It's a positively and negatively charged particle, respectively; what would make you think they would normally repel? Stop spewing this crap!

    70. Re:It will fall down by Big+Frank · · Score: 1

      If the theory is true that anti-matter is normal matter traveling backwards through time, then anti-Hydrogen can fall upwards without violating GR. From the Hydrogen atom's perspective while traveling backwards through time it is falling downwards. We watch the process while traveling forwards through time and from our perspective we see it happen in reverse, thus it appears to us the "anti" Hydrogen atom is falling upwards. This way GR is not violated.

    71. Re:It will fall down by Actually,+I+do+RTFA · · Score: 1

      Mea culpa. I thought the three types of neutrino were +/0/-, and the name an artifact because the neutral one was found first. Sorry.

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    72. Re:It will fall down by Anonymous Coward · · Score: 0

      You may be quoting books on this, but it is apparent that you are misunderstanding the concepts behind what you are talking about. Temperature affects the density of a gas. Any gas will rise above the other present gases as long as they are of lower density than the surrounding gas. A gas can be of lower density for different reasons. The two most influential are molecular mass and temperature. The molecules in a gas do not have to have an average velocity greater than Earth's escape velocity to rise above all the other gases present in our atmosphere. You are right that in Earth's environment (temperature) that the average molecule of hydrogen has a velocity that is greater than Earth's escape velocity. This is why we don't see much hydrogen in our atmosphere.

      So, you are wrong in that hydrogen rises only because it's average molecule's velocity is greater than Earth's escape velocity. It rises because it is of lighter mass, and therefore lower density at a given temperature, than all surrounding gases in our atmosphere.

      At the risk of letting it go to your head; you are right that there isn't much free hydrogen present in our atmosphere (there is some) since the average molecule of hydrogen has a velocity greater than the escape velocity of Earth. The reason there is some is due to a combination of hydrogen releasing processes that occur on our planet and a concept known as mean free path.

      If you want to really look into this, please take a look at Brownian Motion. This has to do with average velocity. Which gases will rise and fall is independent of the Earth's escape velocity. However, the molecules that will stay in our atmosphere is dependent on the Earth's escape velocity.

    73. Re:It will fall down by Anonymous Coward · · Score: 0

      If a bear drops a rock in the woods does it fall? Now what if it's made of antimatter? Trick question since the action of the bear holding the rock results in said rock exploding blowing up the bear and a good chunk of the woods.......on second thought the question still stands because does an exploding antimatter rock fall up or down or is the answer to the question simply "yes".

    74. Re:It will fall down by qeveren · · Score: 3, Insightful

      Hydrogen in the atmosphere does not 'fall up'. It's pushed up; it's called buoyancy. Hydrogen molecules at sea level are on average moving at less than 1/4 of Earth's surface escape velocity.

      And do you honestly think that these physicists are going to be so stupid as to not do their antimatter experiments in a vacuum? That's about the only conditions where you could measure the rate of fall of individual atoms.

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    75. Re:It will fall down by qeveren · · Score: 1

      Hydrogen at sea-level rises due to buoyancy, because hydrogen molecules don't move at escape velocity at the surface of the Earth. Once it rises high enough into the atmosphere, and as the atmosphere grows warmer in its upper regions, then escape velocity considerations come into play.

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    76. Re:It will fall down by pclminion · · Score: 1

      A prominent physicist once suggest that antimatter in not antimatter at all but rather matter traveling in anti-time or backwards in time from are perspective.

      If that were true, then there should be a precisely equal number of matter particles as antimatter particles. But this is not what we observe.

    77. Re:It will fall down by geekgirlandrea · · Score: 1

      So if it falls up then General relativity is wrong (or at least has severe problems) and if this is because it has negative mass then something is very wrong with many theories not just GR ...?

      Well, if it falls up, the equivalence principle is wrong, so general relativity fails, but would likely turn out to be the limit of some other theory. If it has negative mass (generates a repulsive gravitational field), then general relativity is wrong in that gravitational and inertial mass would not necessarily be the same. We *know* antimatter has positive intertial mass.

    78. Re:It will fall down by DMUTPeregrine · · Score: 1

      "Possibly no" has been shown rather convincingly to be false, given that neutrinos can change type.

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    79. Re:It will fall down by geekgirlandrea · · Score: 2, Interesting

      negative mass also implies negative energy according to E=mc^2. I guess that will have to change as well. I want to see how that plays out with nuclear reactions.

      That would be how we know it isn't true. Antimatter is already well known to have positive inertial mass/energy.

    80. Re:It will fall down by geekgirlandrea · · Score: 1

      No, the geodesic equation is second-order. If you follow a geodesic backwards in time you get the same geodesic.

    81. Re:It will fall down by acheron12 · · Score: 1

      If the mass of antiparticles were negative, wouldn't conservation of momentum also imply that in pair production, the two particles would have to end up going in the same direction?

      --
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    82. Re:It will fall down by kmac06 · · Score: 1

      That interaction with the electrons is still a weak interaction, not electromagnetic as you initially asserted.

    83. Re:It will fall down by JCOTTON · · Score: 1
      I think that after the Big Bang, all the anti-matter went the other way. The other way in time. To see the anti-matter universe, you would have to travel back in time to the Big Bang, and then keep going past the BB even earlier. Then you would be in the anti-matter universe, but of course, going the wrong way. In other words, the anti-matter universe is sorta like driving in England. Everybody is going the wrong way, and on the wrong side.

      My wife has a habit of asking me "what is the matter?" I found that answering her "Energy" is highly satisfying.

    84. Re:It will fall down by novakyu · · Score: 1

      Except, of course, even assuming that no mistake was made in that case at all, that particular observation only tells us about neutrinos. There are enough about neutrinos that we do not know (e.g. are they Majorana particles (in short, antineutrino = neutrino), so they would behave the same way in every testable way), so it's bordering on silliness to say that some observation on neutrinos would allow us to say the same for other, more massive and charged particles with any kind of certainty.

      Everything is subject to experimental verification. Everyone thought parity was a fundamental symmetry until it was found to be maximally violated with weak forces.

    85. Re:It will fall down by brendank310 · · Score: 1

      It never claimed to have a degree in physics. It IS a degree in physics.

    86. Re:It will fall down by ady1 · · Score: 1

      Well since everyone seems to speculate, I would say that it would go against the gravity.

      The reason being that according to a theory I read somewhere, antimatter travels back in time and if that theory is correct, gravity would cause it to fall but since it is moving back in time, the movement will be in reverse.

    87. Re:It will fall down by ady1 · · Score: 1

      Again, if it does get pulled towards the gravity, the theory which says that antimatter travels back in time would be in jeopardy due to the same reason.

    88. Re:It will fall down by Taibhsear · · Score: 1

      TFA questions whether anti-matter will be attracted (mass-> <-mass), or whether it will be repulsed (mass<- ->mass) by gravity. I think this experiment's findings could be even more important than finding antigravity. IANAP but if my rough sketches based on my undergrad physics classes are correct than if antiparticles are repelled by one another, gravitationally speaking, then this could possibly lead to cold fusion. Fusion, in normal matter, has to have energy added (kinetic or pressure) in order to overcome the coulomb barrier so that the strong interaction can take over and bind the nuclei. The nuclei are normally attracted gravitationally until they reach the coulomb barrier. If antimatter responds inversely to gravity then the antinuclei will repel each other, gravitationally, up until the coulomb barrier. Once that barrier is reached, the antinuclei should spontaneously combine releasing the energy it normally would need to overcome the barrier. I do realize that due to the gravity repulsion the antinuclei would need energy added in order to overcome it. However the force of gravity is far weaker than the nuclear repulsion. So in my amateur analysis the net result would be vastly in favor of higher output energy.
    89. Re:It will fall down by The_Wilschon · · Score: 1

      Not my field, but is the possibility of a supernova producing a large neutrino flux twice ruled out? Naturally, maintaining such a huge flux for 4 hours is out of the question due to energy considerations, but two neutrino bursts seems like another possibility. AFAIK, our understanding of the dynamics of supernovae isn't that great yet.

      --
      SIGSEGV caught, terminating

      wait... not that kind of sig.
    90. Re:It will fall down by JasterBobaMereel · · Score: 1

      Yes the "Strong enough" gravitational field would be very large and more importantly very dense i.e. a black hole....

      So theoretically something could be accelerated *to* c by falling into a black hole ... but at that point it would have infinite mass ... ... so the black hole would have to have infinite mass to do it ...

      So no.... sorry ....

      --
      Puteulanus fenestra mortis
    91. Re:It will fall down by JasterBobaMereel · · Score: 1

      This is the point about the difference between negative mass and how it reacts to a gravity field

      What you describe is negative mass - which is not what we observe ....

      This experiment is testing antimatters interaction with a gravity field

      --
      Puteulanus fenestra mortis
    92. Re:It will fall down by Anonymous Coward · · Score: 0

      Is "drops a rock" a euphemism for "shits"? I had a fun time thinking of a bear with anti-shit. Imagining an anti-bear was funnier still.

    93. Re:It will fall down by Steve+Max · · Score: 1

      It's highly unlikely. The huge neutrino flux happens for a simple reason: the SN process generates lots of neutrinos continually, but they are trapped in a very high density medium. It's exactly the same thing that happens to photons in the sun: they basically can't escape due to the high density. However, the supernova keeps expanding until its density reaches a critical point where it's not high enough to trap the neutrinos. At this instant, they escape almost all at once. Of course, the fact that current simulations cannot explode a supernova in 3D (only in 1D and perhaps in 2D) shows that we still don't know a lot about them; but still, since all the numbers seem to agree with this idea, and it's hard to imagine this amount of neutrinos being produced at once by the SN. It has to be the result of an integrated flux.

    94. Re:It will fall down by paulgrant · · Score: 1

      Marry ME!!!!!!!!!!!!!!!!!!!! Lord that was a pleasure to read :)

    95. Re:It will fall down by geekgirlandrea · · Score: 1

      Marry ME!!!!!!!!!!!!!!!!!!!! Lord that was a pleasure to read :)

      Uh, sorry, but I'm about as lesbian as it gets. :)

    96. Re:It will fall down by Goaway · · Score: 1

      Seeing as how you seem to have conceded the point now, can we expect some apologies for being called "retards" and "slow" and so on now? Like an honourable man would give?

    97. Re:It will fall down by oodaloop · · Score: 1

      Mmm, no I haven't conceded anything. I just got tired of explaining the same thing over and over again. I said 3, maybe 4 times now, that I explained in another post how I understood the main point, understood how the experiment was different, and was discussing this as a related topic. None of which you even acknowledged ("no you didn't, you just stumbled in and started yelling" etc). I realize I didn't SPECIFICALLY say that I was referring to something offtopic, but I didn't realize I needed to precede it with WARNING: OFFTOPIC. I realize(d) that anti-hydrogen will not rise in the experiment due to escape velocity, but merely brought it up as another factor, perhaps even as an interesting point of discussion since no one else even mentioned that it is a factor on which way gas particles move.

      The part about falling upwards still leaves me in amazement. I used it as a metaphor (I thought an obvious one), instead of just saying hydrogen rises. The fact that everyone argued why hydrogen doesn't ACTUALLY fall upwards seems pretty, well, retarded.

      I don't feel any apologies are in order. I got modded for my comments as did everyone else and I'm tired of explaining them.

      --
      Tic-Tac-Toe, Global Thermonuclear War, and relationships all have the same winning move.
    98. Re:It will fall down by Anonymous Coward · · Score: 0

      Read it again - the poster said nothing about electromagnetic fields affecting neutrinos. Gravity is what was bending the path of the neutrinos/antineutrinos.

    99. Re:It will fall down by Goaway · · Score: 1

      Even accounting for that, what you said was plain wrong, and yet you still felt you had to call others "retards".

    100. Re:It will fall down by oodaloop · · Score: 1

      Whatever. I got modded troll and flamebait so it appears justice has been done. Now goaway.

      --
      Tic-Tac-Toe, Global Thermonuclear War, and relationships all have the same winning move.
    101. Re:It will fall down by Goaway · · Score: 1

      You don't handle mistakes very gracefully, do you?

    102. Re:It will fall down by aqk · · Score: 1

      Fuck all this "anti-hydrogen" shit! I await the creation of "anti-lead" or at least "anti-iron"!
      Then we shall see which way the atom falls!

      1. Create a big story about how you have created Anti-hydrogen. - then -Claim it works great in the latest GM SUV hybrid, and you figured out a satisfactory containment vessel!
      2. Start issuing your IPO.
      3. Profit!


    103. Re:It will fall down by Anonymous Coward · · Score: 0

      Are you sure you have a degree in physics? Neutrinos have no charge, and thus are not affected by electromagnetic fields. The name sounds like "neutral" because of this. If they were charged they would be called something else. Nothing in the post you're replying too even mentions or implies that neutrinos have charge. Gravitational lensing is responsible for deflecting the neutrinos and antineutrinos. We're interested in any difference between gravity acting on particles and antiparticles. No one even mentioned electromagnetic fields.

  5. neither by Anonymous Coward · · Score: 0

    It bends gravity to its will... which is why it can only exist in a vacuum like state...

  6. Re:Gravitons and Graviolis by andyh3930 · · Score: 3, Funny
    Futurama quote

    Professor: And the microwave radiation, combined with the gravitons and graviolis from the supernova, blasted us through time itself.

  7. Obvious? by neokushan · · Score: 5, Funny

    It doesn't-matter.

    --
    +1 IDisagreeSoHeMustBeATrollOrAnAstroturferOrAShill
    1. Re:Obvious? by goldaryn · · Score: 1

      It doesn't-matter. ..non-news for nerds!
    2. Re:Obvious? by Anonymous Coward · · Score: 0

      It DOES anti-matter.

  8. What if some falls up and some falls down? by X10 · · Score: 0

    What if some antimatter turns out to fall up, and some to fall down? Would that require ordinary matter to come in upfalling and downfalling types too? If upfalling matter is just never created any more, all upfalling matter that exists has been pushed away from us a long time ago.

    --
    no, I don't have a sig
    1. Re:What if some falls up and some falls down? by JosKarith · · Score: 1

      And is too far away to see properly as it repels other matter so dissipates into a fine particulate spray. A fine candidate for being the missing "Dark Matter" An interesting theory - we'll just have to wait and see I guess.

      --
      'Don't worry' said the trees when they saw the axe coming, 'The handle is one of us.'
    2. Re:What if some falls up and some falls down? by something_wicked_thi · · Score: 1

      What makes you think the downfalling case would be any better? If it falls down, then it will annihilate with whatever it falls into. If it falls up, then it won't be around anymore. Either way, it's not going to stick around for long.

    3. Re:What if some falls up and some falls down? by m.ducharme · · Score: 1

      Except that the anti-particles would have negative mass -- we'd be looking for more dark matter, not less.

      --
      Rule of Slashdot #0: You and people like you are not representative of the larger population. - A.C.
    4. Re:What if some falls up and some falls down? by Anonymous Coward · · Score: 0

      Except that the anti-particles would have negative mass... Ah, no. Matter and antimatter are related by having quantum numbers, charges, etc. that are in some sense "opposite". But there is only one flavor of mass. When you talk about negative mass, you talk about a place where mass, and therefore matter, isn't. For example, you can use the concept of negative mass to calculate the center of mass of an object with a hole cut in it, but that "negative" mass is a property of matter that isn't; not matter that is.

      Another way to rather disingenuously speak about "negative" mass is to give "normal" mass the negative sign you get by running the arrow of time backward; that's still just a problem-solving technique that exploits the relativity of simultaneity in a paradoxical way. So negative mass is an artifact of semantics and not a physically real property; the "arrow of time" always points the same "direction", which you might say as "there is no 'arrow of time' at all".
  9. i wonder... by Anonymous Coward · · Score: 0

    If gravity is a field proportional to the mass of matter, and if it so happens that anti-matter "falls" away from a center of gravity, then would a "anti-gravity" perhaps be a property of anti-matter? Would matter in the presence of a sizeable amount of anti-matter "fall" away from its center of "anti-gravity?"

  10. Perhaps sideways? by Anonymous Coward · · Score: 0

    Or maybe in a twirling fashion?

    1. Re:Perhaps sideways? by apathy+maybe · · Score: 2, Funny

      What like http://xkcd.com/417/ ?

      --
      I wank in the shower.
  11. I wish it fell upwards by ShooterNeo · · Score: 2, Interesting

    I wish the results were that antimatter falls upwards. If that were true, while it would have no practical use in the near future, it would be a hole in physics that our far descendants could exploit.

    1. Re:I wish it fell upwards by dapyx · · Score: 0

      I misread that as "it would be a hole in physics that our fat descendants could exploit."

      --
      I'm sorry, the number you have dialed is an imaginary number. Please rotate your phone 90 degrees and dial again.
    2. Re:I wish it fell upwards by pla · · Score: 5, Insightful

      If that were true, while it would have no practical use in the near future

      Not necessarily - Merely opening that particular conceptual door would lead to a massive influx of funding and revisited anomalous past results.

      Interesting thing about experimentation, even the most honest of researchers tends to throw away "bad" results (in the sense of not publishing them, not in the academically-dishonest sense of omitting them from the data). If the scientific community suddenly accepted the possibility of spooky-effect-X, you can bet that dozens or even hundreds of research groups would dredge up their past efforts to see if effect-X explains their results.

      Case in point, l'Acedemie des Sciences and meteorites. Up to the turn of the 19th century, only idiots would dare claim that rocks could fall from space... Until the scientific community decided they could, at which point a huge body of past evidence appeared practically overnight supporting the existance of such falling objects.

    3. Re:I wish it fell upwards by krnpimpsta · · Score: 5, Funny

      I wish the results were that antimatter falls upwards. If that were true, while it would have no practical use in the near future, it would be a hole in physics that our far descendants could exploit. Dude, please don't exploit holes in physics. I don't want my access to the universe revoked just because God banned us all from our reality for hax. All it takes is one noob hax0r particle physicist to ruin it for us all.
      --

      New webcomic updated on Sundays: HERE

    4. Re:I wish it fell upwards by coinreturn · · Score: 1

      It will definitely fall up. Well, according to my Star Trek education, anyway.

    5. Re:I wish it fell upwards by Anonymous Coward · · Score: 0

      Don't listen to the snake.

      That usually goes badly.

    6. Re:I wish it fell upwards by smaddox · · Score: 4, Funny

      Yeah, like that time this Jesus guy found an overflow in the kill process routine, and was able to resurrect himself after 3 days.

      I heard God banned him for 3,000 years.

    7. Re:I wish it fell upwards by Anonymous Coward · · Score: 0

      I don't think a noob hax0r particle physicists would need holes in physics to get us all banned by God, if he had access to antimatter in the first place.

    8. Re:I wish it fell upwards by Anonymous Coward · · Score: 0

      Ironically, this is the exact argument used to keep the LHC from coming online.

    9. Re:I wish it fell upwards by Gamer_2k4 · · Score: 1

      Hmmm...wouldn't that be interesting if it applied to young earth creationism as well...

      "Up until the mid 21st century, only idiots would dare claim that the earth was only 6000 years old...Until the scientific community decided it was, at which point a huge body of past evidence appeared practically overnight supporting the existence of a young earth."

    10. Re:I wish it fell upwards by digitrev · · Score: 1

      And if there is legitimate evidence with a legitimate theory behind it (that is, one that can make predictions and have them be right), and it is the best explanation of the phenomena at hand, then it will probably be accepted.

      --
      Cynical Idealist
    11. Re:I wish it fell upwards by pla · · Score: 1

      Hmmm...wouldn't that be interesting if it applied to young earth creationism as well...

      Yes, actually, it would.

      Of course, you appear to want to conflate "ignorance in the absence of data" with "ignorance despite contradictory data". Not quite the same.

      Honestly, it surprises me that creationists don't recognize the biggest problem with their stance - Not that evolution fits the known facts; Not that "god did it" poses an untestable hypothesis; Not even that it shows a complete lack of understanding of "scientific method". No, the biggest problem with a young Earth? If true, it makes god a mean-spirited bastard who put us here intending us to fail, and continues to plant false evidence to lead us away from "the truth". I can accept a creator as the universal primum mobile; If, however, your god behaves like you would have us believe, well, would you really want to spend eternity hanging out with that?

    12. Re:I wish it fell upwards by Anonymous Coward · · Score: 0

      Err, in the 19th century they didn't have a theory that worked really really really well that said rocks don't fall from space. They were just guessing and had exactly 0 verified theories about it.

      This is more akin to saying we should prove that I fart pixie dust. There is no reason to believe it at all and even the definition of anti-matter/pixie dust says it wouldn't be so. So, by doing this experiment, some experiment that has an open ended answer isn't being done. This only seems interesting if you think of the word 'anti-matter' as some sort of scifi magic futuristic thing. A positron doesn't sound so fun.

    13. Re:I wish it fell upwards by Anonymous Coward · · Score: 0

      ***krnpimpsta has been kicked by GOD (Damn noob hax0r particle physicists!!)

      Is it still blasphemous to say goddamn if god is saying it?

    14. Re:I wish it fell upwards by Mhtsos · · Score: 1

      Just submitted a patent for an antimatter bra, as well as the title "Containment breach" in the context of an exotic dancer bar.

  12. Electromagvitational ? by Joebert · · Score: 1

    I'm probably wrong & welcome being corrected, but I can't shake this thought.
    I'm under the impression Electromagnetic fields & Gravitational fields function similarly or the same.

    I'm thinking of a field situated like the simultanious implosion of a uranium or plutonium bomb, with these antimatter things trapped in the center.
    What if on one point of the field the magnetic strength was weakened, perhaps by touching it with another magnetic field, while on the oppisite end the strength was increased. Shouldn't the antimatter head toward the stronger field point if it were going to rise due to gravity instead of fall ?

    --
    Wanna fight ? Bend over, stick your head up your ass, and fight for air.
    1. Re:Electromagvitational ? by JasterBobaMereel · · Score: 1

      The answer is maybe....

      The Electromagnetic force is mediated by the photon, the Gravitational force is either the warping of spacetime ... or mediated by gravitons ... or maybe both, or neither ... depending on which theory is right ....

      General Relativity says warped spacetime
      Quantum theory says graviton

      Almost certainly they are both wrong (to a degree)
      It could be like the old problem of, is light waves or particles, the answer appears to be yes *and* no. They act like waves and they act like particles but are neither ...

      --
      Puteulanus fenestra mortis
    2. Re:Electromagvitational ? by Anonymous Coward · · Score: 0

      It's a well-supported theory that at least the electromagnetic and weak forces were at one point in history the same (the electroweak force) and even earlier than that (talking, like, minutes from the big bang) the electroweak and strong forces were the same. While there's probably some fundamental difference between electro-weak-strong and gravity, it's also very likely to be the same in other fundamental ways.

    3. Re:Electromagvitational ? by evilbessie · · Score: 1

      That would be the GUT being as we have unified the weak, strong and electromagnetic forces already...

  13. And I didn't even know ... by Ihlosi · · Score: 1
    ... that there was any question about how antimatter behaves in a gravitational field. I thought that
    it had mass just like anything else, and is therefore affected by gravity just like any other particle with mass.



    Wouldn't "falling up" mean that antimatter has negative mass ? And if so, how does this comply with energy/mass conservation laws ?

    1. Re:And I didn't even know ... by jandersen · · Score: 1

      Yes, that is how I read it. Mass is only known to us through its gravitational effect; if anti-matter falls away from matter, it must mean that it has negative mass. There is no conflict with energy conservation - it only means that the total energy (or mass) of a closed system doesn't change.

    2. Re:And I didn't even know ... by Rocketship+Underpant · · Score: 3, Insightful

      Shouldn't that mean that matter-antimatter annihilation would result in no energy being emitted? If antimatter had negative mass, the net mass converted to energy would be zero.

      --
      He who lights his taper at mine, receives light without darkening me.
    3. Re:And I didn't even know ... by Mr2001 · · Score: 1

      Mass is only known to us through its gravitational effect; if anti-matter falls away from matter, it must mean that it has negative mass. Mass is also known to us through its inertial effect, i.e. the relation between a force on an object and the resulting acceleration. If something had negative mass, then pushing on it would make it come toward you.
      --
      Visual IRC: Fast. Powerful. Free.
    4. Re:And I didn't even know ... by jandersen · · Score: 1

      That's a good point; perhaps this is an argument against anti-matter having negative mass and thus their falling up.

    5. Re:And I didn't even know ... by JasterBobaMereel · · Score: 1

      Matter - Antimatter annihilation should result in energy .... but the energy is still conserved, both the matter and the antimatter were created in the first place

      Energy -> matter + antimatter -> Energy

      Antimatter might not have negative mass just negative interaction with gravity, or negative mass still requires the same amount of energy to make ...

      --
      Puteulanus fenestra mortis
    6. Re:And I didn't even know ... by mortonda · · Score: 1

      Mass is also known to us through its inertial effect, i.e. the relation between a force on an object and the resulting acceleration. If something had negative mass, then pushing on it would make it come toward you. That sounds really dangerous when antimatter is involved!

      I suppose it depends on what you push with. Pushing with antimatter would behave as expected. Pushing with matter, well, it blows up so who knows?
    7. Re:And I didn't even know ... by blackdew · · Score: 0

      Err what? Mass is used in mych more than gravity, and any kind of negative mass would majorly fuck up many other, totaly unrelated things. A negative-mass object would cool down when heated, and deccelerate (or accelerate in the whrong direction) when force is applied to it.

    8. Re:And I didn't even know ... by Anonymous Coward · · Score: 0

      E = sqrt((mc^2)^2)

  14. Feynman-Stueckelberg interpretation... by Anonymous Coward · · Score: 0

    ...says something along lines of antiparticles being "ordinary" particles traveling back in time. Perhaps then it could be expected that they would "seem" to fall backwards, i.e. up? If so, then apparent lack of antimatter would be explained by all of them "deflating" while all of "ordinary" universe expanded immediately after the Big Bang. When we see the signs of antimatter "inflation" tide, that will be the sign of imminent Gnab Gib, but we probably shouldn't care... gamma ray photons will fry us prior to that.

  15. Isn't The Cosmological Constant... by this+great+guy · · Score: 0, Offtopic

    42 ?

    1. Re:Isn't The Cosmological Constant... by laejoh · · Score: 0

      For small values of 6 x 9 or large values?

    2. Re:Isn't The Cosmological Constant... by K.+S.+Kyosuke · · Score: 1

      Only in British imperial units. And in four hundred years, it will inflate to 47 due to spacetime expansion.

      --
      Ezekiel 23:20
  16. If light is affected normally by gravity... by Viol8 · · Score: 1, Informative

    ... why should antimatter be any different? In fact every particle with mass yet measured behaves the same way in gravity. I can't see any reason why antimatter should be any different.

    1. Re:If light is affected normally by gravity... by Tom · · Score: 4, Insightful

      And science is all about the difference between "I think..." and "I've tested..."

      If it behaves exactly as predicted, you can make another mark and continue. If not, you've found something potentially very important.

      --
      Assorted stuff I do sometimes: Lemuria.org
    2. Re:If light is affected normally by gravity... by Urkki · · Score: 4, Insightful

      Antimatter *could* be different because the mathematics of GR allow it, and we haven't actually done the experiment before. I wouldn't put much faith in human intuition in these matters, considering how counter-intuitive entire GR is...

      I mean, we see water falling off edges of waterfalls etc. Why should the edge of the world be any different? ;-)

    3. Re:If light is affected normally by gravity... by Vulch · · Score: 2, Informative

      One model for anti-matter is that it is a normal particle travelling backwards in time. The energy from a particle/anti-particle annihilation is the energy released by it changing direction under this model. As far as the particle is concerned, it is behaving normally in a gravitational field by falling downwards, but when we look at it from our usual time axis it appears to be falling up.

    4. Re:If light is affected normally by gravity... by aug24 · · Score: 1

      In fact every particle with mass yet measured behaves the same way in gravity.

      Ahem. I think all of those were matter. That observation therefore tells you nothing about antimatter.

      I wait with bated breath for the discovery of anti-light, by the way ;-)

      Justin.

      --
      You're only jealous cos the little penguins are talking to me.
    5. Re:If light is affected normally by gravity... by JasterBobaMereel · · Score: 2, Insightful

      Because all the other properties of antimatter that have been tested so far are different unlike every type of normal matter ...

      This is a Black Swan problem

      Theory : All Swans are White
      Proof : every swan I see is white, every swan ...
      Problem : Australia was then discovered along with the black swan.....

      --
      Puteulanus fenestra mortis
    6. Re:If light is affected normally by gravity... by Anonymous Coward · · Score: 0

      Show me. Where does the maths of GR allow for antimatter to "fall up"? Keep in mind that anti matter has positive mass, positive energy density, etc.

      There is absolutely NO difference between the energy momentum tensor of matter and a symmetric antimatter configuration, so they definitely create the same gravitational field, now you're telling me that despite this the geodesic principle can fail for antimatter? Do you have ANY reference for this at all?

      The experiment is interessting because if they find a non-null result it would drastically violate and thus modify and go beyond our current understanding, so even though it's really quite unlikely it's worth doing.

    7. Re:If light is affected normally by gravity... by Urkki · · Score: 2, Insightful

      Show me. Sorry, way over my head. It's just that I do trust even the article summary, not to mention the real research proposal the article is about, more than an AC post saying it ain't so.
    8. Re:If light is affected normally by gravity... by zsau · · Score: 1

      If antimatter behaves backwardsly, and this is the reason there's not that much antimatter around earth (as they suggest), then shouldn't there be antimatter galaxys which exert antigravity on matter? If so, why can't we see any?

      Not that I know anything about antimatter. Well, I've heard that the reason there's no antimatter around is because there's more than enough matter to anihilate the antimatter that randomly comes up. But I'm completely not a physicist; I don't think it solves any of life's important questions so I'm content to leave it to other people who find it more interesting.

      --
      Look out!
    9. Re:If light is affected normally by gravity... by Anonymous Coward · · Score: 0

      Well if it behaves !exactly! as predicted, i would say that this is suspicious, so don't trust it :D

    10. Re:If light is affected normally by gravity... by hummassa · · Score: 1

      If antimatter behaves backwardsly, and this is the reason there's not that much antimatter around earth (as they suggest), then shouldn't there be antimatter galaxys which exert antigravity on matter? If so, why can't we see any? (a) we can see a lot of galaxies; how can we tell the difference?
      (b) maybe they are so far away (pushed by the antigravity effects of the inflation, or somesuch) that they are beyond our "visible bubble" ("c" times the age of the universe)
      --
      It's better to be the foot on the boot than the face on the pavement. ~~ tkx Kadin2048
    11. Re:If light is affected normally by gravity... by Anonymous Coward · · Score: 0

      Exactly. Which has always, IMO, placed Cosmic, Chemical, Stellar, Organic, and Macro evolution into the 'faith' bin.

      We have never observed them occurring before our eyes, we, arguably, cannot reproduce any of them, and its supporters commonly argue the point that 'Well, sure, with todays technology we cannot test observe or reproduce this, BUT, the day is coming when we WILL have the technology to prove it, therefore, it's science already.'

      What a leap of faith.

      Just because you use the scientific method (or claim to) to test something, it does not make what you are testing scientific. The word science is becoming so abused all you have to do is say something is scientific and suddenly everyone assumes it's true, because, well, they layman can't understand the complexities of science, these people are experts, remember? So.. Don't second guess them. And don't bother to look over the evidence yourself, you are incapable of understanding it.

    12. Re:If light is affected normally by gravity... by Scott+Carnahan · · Score: 1

      Show me.
      Sorry, way over my head. It's just that I do trust even the article summary, not to mention the real research proposal the article is about, more than an AC post saying it ain't so.

      That's too bad, because the article summary is completely wrong. GR predicts that anything in free fall follows a geodesic in spacetime, including matter, antimatter, and other stuff like photons that are their own antiparticles. Consequently, you should expect the gravity of a massive object to deflect the trajectory of matter and antimatter in exactly the same way. Naturally this sort of hypothesis is something one should test, but that has been done years ago. Other comments before this one have pointed out experimental data from supernovas and particle accelerators that show that any difference in behavior is bounded above by about one part in a billion. In particular, antimatter has been known not to fall up for quite some time.

      --
      "Your notation sucks!" -- Serge Lang (1927-2005)
    13. Re:If light is affected normally by gravity... by DriedClexler · · Score: 1

      And that in turn, leads to the Black Raven problem (or "Raven Paradox").

      Theory: All ravens are black.
      Contrapositive: Everything that's not black, is not a raven.
      Implication: Every time I see something not black, and also not a raven, I support the Contrapositive.
      Problem: The Contrapositive is logically equivalent to the Theory. But why the hell should seeing a red apple make me think all ravens are black?

      --
      Information theory is life. The rest is just the KL divergence.
    14. Re:If light is affected normally by gravity... by Urkki · · Score: 1

      Ok, thanks for clarification. So if this experiment shows that anti-hydrogen behaves differently, then the concept of "mass" needs to be expanded somehow, so that even if matter and antimatter have same mass (in kilograms), their mass is somehow different.

    15. Re:If light is affected normally by gravity... by Anonymous Coward · · Score: 0

      Well, when I read the OP, I was going to ask:

      Which way _is_ up, anyway?

      I suppose it's all "relative", but still, it's
      kind of a challenging concept in a way. How is
      "up" and "down" defined for this stuff since at
      near-speed-of-light velocities, I wouldn't think
      gravity (at least our own 9.8m/sec^2 stuff) would
      have much effect?

    16. Re:If light is affected normally by gravity... by Scott+Carnahan · · Score: 1

      I'm not an expert in this field, but my impression is that with our current technology, this experiment is in fact less precise than ones that have been done previously. I would consider it worthwhile in the sense that it is always worthwhile to check that we haven't collectively gone bonkers, but any statistically significant deviation from the expected behavior is more likely than not to be a failure of methodology, e.g., some uncontrolled source of noise.

      --
      "Your notation sucks!" -- Serge Lang (1927-2005)
  17. The answer is already known by Ed+Avis · · Score: 0, Troll
    From the article:

    The problem is that it's easy enough to trap antiprotons and positrons in electromagnetic fields. It's even fairly straightforwad to put them together so that they form antihydrogen. The problem is that antihydrogen is neutral and simply falls out of the trap.
    This surely contains a clue about whether antihydrogen falls up or down...
    --
    -- Ed Avis ed@membled.com
    1. Re:The answer is already known by MichaelSmith · · Score: 1

      Well you could centrifuge it to enhance the effect, but I wonder if that would answer the wrong question?

    2. Re:The answer is already known by something_wicked_thi · · Score: 1

      I think the problem is likely that you can only build up a large amount of antiprotons and positrons. As soon as you start making hydrogen, you can't trap it anymore and it falls out.

      I think the reason you can't measure the hydrogen is because there's not enough. It falls out before you can get enough to tell what its velocity is. Keep in mind that hydrogen is very light and won't fall downwards because of gravity. Instead, you have to measure the curvature of its path to try to see which way it's accelerating. I'm guessing we hit another problem here, which is the Heisenberg uncertainty principle. If you just have one or two particles, you can't really tell which way they are headed. I think the idea behind this experiment is to create a stream of particles so that you have enough of them to really measure where they are going.

      Of course, I could be completely wrong about all that, too.

    3. Re:The answer is already known by Anonymous Coward · · Score: 0

      Out of which you can conclude that the anti hidrogen is affected by some force, most likely gravity since it's electrically neutral. But it still doesn't tell you which direction it went until you put a detector at the bottom and top of the vat.

  18. The cosmological constant, by Bromskloss · · Score: 3, Funny

    my relativity teacher told his class, is a function of time: At first, it was non-zero, then people said it was zero, then it might be non-zero after all.

    --
    Swedish plasma phys. PhD student; MSc EE; knows maths, programming, electronics; finance interest; seeks opportunities
    1. Re:The cosmological constant, by JasterBobaMereel · · Score: 2, Informative

      The original theory did not need it, but it predicted the universe was expanding, and conventional wisdom at the time said this was not the case... so Einstein add the constant to get a steady state universe ...

      Then Hubble found the universe was expanding so Einstein took it out again ....

      Then the inflational big bang model and observations that the current expansion of the universe was accelerating seemed to require it again ... so it was put back ...

      This is why experiments need to be done ...

      --
      Puteulanus fenestra mortis
    2. Re:The cosmological constant, by Lijemo · · Score: 5, Funny

      my relativity teacher told his class, is a function of time: At first, it was non-zero, then people said it was zero, then it might be non-zero after all.

      I saw a paper in the Journal of Irreproducible Results advancing the theory that the age of the universe is a nonlinear function of time.

      They plotted on a graph the age people (or rather, western civilization) thought that the age of the universe was at various points in history--when the 19th century geologists said it had to be at least hundreds of thousands of years old, when the 20th century astronomers said that it had to be even older than that-- and plotted the points on a graph. They formed a smooth curve demonstrating (I think) a geometric increase.

      So their theory was that, assuming all the age-of-the-universe estimates were correct, that means the beginning of the universe is moving backwards in time, away from us. In 1000ad, the universe really was 6000 years old, and now it really is 14.5 billion years old, and in another century, it will probably be in the trillions of years old

      (I love the Journal of Irreproducible Results!)

    3. Re:The cosmological constant, by BossTree · · Score: 1

      Already computed as 42. The Cosmological Question, however, remains a mystery.

  19. So Guinness is the anti-anti-matter? by will_die · · Score: 1

    So anti-matter falls up in gravity field and Guiness bubbles sink in a gravity field what happens when you mix the two?
    But how does this help explain why our area of space has so little anti-matter? If this was true then it would mean we are at the bottom of the universe, as opposed to what; or is the current thinking that anti-matter is not effected by gravity and this experiment would provide that it is?

    1. Re:So Guinness is the anti-anti-matter? by cnettel · · Score: 1
      If anti-matter "falls" up, then masses of ordinary matter repel antimatter. This would mean that there will be no gravitationally stabilized chunks of matter and anti-matter (which would sooner or later annihilate), but rather that over scales where the gravitational force dominates, we would get separated regions.

      Like many other posters, my "physical intuition" (indoctrination in GR) tells me that this is most unlikely, but it would have tremendous consequences for cosmology.

    2. Re:So Guinness is the anti-anti-matter? by Anonymous Coward · · Score: 0

      If anti-matter falls up, then matter and anti-matter repel eachother, and this explains why there's so little anti-matter in our part of the universe: it is simply pushed out of it, to somewhere else, far far away.

    3. Re:So Guinness is the anti-anti-matter? by Taibhsear · · Score: 1

      So anti-matter falls up in gravity field and Guiness bubbles sink in a gravity field what happens when you mix the two? Annihilation, X-rays, and gamma rays?

      Either that or really drunk irradiated physicists.
  20. Is there a physicist in the house? by Anonymous Coward · · Score: 0

    "The problem is that antihydrogen is neutral and simply falls out of the trap."



    Can someone explain to me why they can't just see which way it fell? Or are they not using that to mean "fall to earth"?

  21. Down by skirmish666 · · Score: 1

    Particle and antiparticle must have
    * the same mass
    * the same spin state * opposite electric charges
    http://en.wikipedia.org/wiki/Antiparticle

    --
    Sigger than your average
    1. Re:Down by MrMr · · Score: 1

      You just spoilt the most uninformed thread of the day.

  22. Oooh... I can answer this one! by njcoder · · Score: 5, Funny

    Does Antimatter Fall Up Or Down? Yes!
    1. Re:Oooh... I can answer this one! by Idaho · · Score: 4, Funny

      Does Antimatter Fall Up Or Down?

      Yes!


      But what if it turns out it falls sideways?
      --
      Every expression is true, for a given value of 'true'
    2. Re:Oooh... I can answer this one! by Dr.+Cody · · Score: 1

      What a strange answer.

    3. Re:Oooh... I can answer this one! by teslar · · Score: 5, Funny

      You may onto something. Perhaps the well-docmumented cases of people falling sideways are due to antimatter build-up within them. We should investigate.

    4. Re:Oooh... I can answer this one! by Anonymous Coward · · Score: 0

      No!

    5. Re:Oooh... I can answer this one! by 192939495969798999 · · Score: 1

      you forget, it's *anti* matter, so the answer is NO, it does not fall up or down.

      --
      stuff |
    6. Re:Oooh... I can answer this one! by Anonymous Coward · · Score: 0

      Yes! I really hate it when you do that.
  23. down? by pcmaniac · · Score: 1

    since it has a mass, and it's mass is not negative (source: wikipedia), it should fall down, right?

    --
    www.soinfo.org
    1. Re:down? by RHSC · · Score: 1

      there is more to science than quoting wikipedia, grand bastion of all accurate human knowledge that it is, which is why the physicists want to test this one

  24. Maybe... by Anonymous Coward · · Score: 0

    It falls sideways http://xkcd.com/417

  25. Imagine this ! by Mr+Europe · · Score: 1, Interesting

    If antimatter "falls up" imagine this:
    In a reasonable empty space exist two particles, one of matter, the other from antimatter. They are of equal mass. They are causing gravity on each other. The antimatter runs away and the matter follows. And with INCREASING SPEED !? OOPS.. There must something wrong here...
    Maybe the matter does not pull antimatter and antimatter does not push matter ?
    Maybe they both pull each other after all.

    1. Re:Imagine this ! by Anonymous Coward · · Score: 0

      Or antimater makes a negative gravitational field and the two particles act like protons and electrons.

    2. Re:Imagine this ! by Anonymous Coward · · Score: 0

      Well that must be the reason why we see so little antimatter around here ...

    3. Re:Imagine this ! by too2late · · Score: 1

      If they pulled each other the universe would have been destroyed a long time ago

      --
      My rights don't end where your feelings begin.
    4. Re:Imagine this ! by Anonymous Coward · · Score: 0

      If small antimatter particles fall up in an environment of matter, then it would stand to reason that small matter particles would fall upwards in an environment of antimatter. So in your example, the particles would repel one another.

    5. Re:Imagine this ! by Anonymous Coward · · Score: 0

      In your example, the repulsion force emitted by the antiparticle would tend to separate both particles (push the anti particle forward and the particle backward). The attraction force of the the particle would pull the two together.

      If the forces are equal (equal mass?) then the two particles don't move. If the antiparticle is stronger, they move away from each other. If the antiparticle is weaker, they come together.

      ---

      In actuality none of this happens because what they're trying to prove is that antimatter and matter push away from each other, not that antimatter pushes away and that matter tries to catch up.

      Either old-school thought is right and they attract each other or this experiment will show they repel each other. No one is attempting to show anything like you described.

    6. Re:Imagine this ! by Anonymous Coward · · Score: 0

      At least this will solve whether pushing or pulling will save us from the terrible secret of space.

    7. Re:Imagine this ! by loafula · · Score: 1

      I would think the effect would cancel out if the particles were equal masses. The matter would pull, the anti-matter would push, and both particles would remain stationary.

      --
      FOXTROT UNIFORM CHARLIE KILO
    8. Re:Imagine this ! by byron036 · · Score: 1

      You should check out Robert Forward's book Timemaster.

      Forward was a physicist that also wrote science fiction. This book uses the concept of mirror matter which is repelled from normal matter as it attracts it. (Mirror matter is repelled by normal matter, but normal matter is attracted to mirror matter) Thus producing an infinite propulsion with no fuel expenditure via the simple process of wrapping a ball of mirror matter in a sphere of normal matter. When the mirror matter is moved closer to one side of the sphere it pushes the sphere away from itself. As a physicist he worked out the actual math and implications of this process. It has some weird properties (free electricity generation, sustained 1G propulsion, worm holes in time & space, causality when you have a worm hole to the past, etc).

      The best part is that the book's mirror matter is mirror matter alien dung. If mirror matter really does exist (in dung form or not) then hello space travel. But given the something for nothing nature of the process, I'm not holding up high hopes.

    9. Re:Imagine this ! by Ihlosi · · Score: 1
      If mirror matter really does exist (in dung form or not) then hello space travel.

      ... and goodbye to several laws of physics (impulse conservation, energy conservation, 2nd law of thermodynamics, etc).

    10. Re:Imagine this ! by mortonda · · Score: 2, Insightful

      What? no. The matter would not follow, it would be repelled. Think of two magnets with north pointing at each other.

    11. Re:Imagine this ! by giorgist · · Score: 1

      OMG I always knew a Slashdotter will come up with the perpetual motion machine. You've done one better. Infinite energy.

      PS: Cool comment (got no mod points)

    12. Re:Imagine this ! by Anonymous Coward · · Score: 0

      Like men running after women!?!

    13. Re:Imagine this ! by Anonymous Coward · · Score: 0

      No, imagine this instead: matter attracts matter, antimatter attracts antimatter, matter and antimatter repel each other.

      Now work out your thought experiment again.

    14. Re:Imagine this ! by jibjibjib · · Score: 1

      If antimatter falls up, would that mean it has negative mass? That would mean antimatter and matter repel each other, but antimatter attracts antimatter and matter attracts matter. In this case, in the scenario you describe, the matter and antimatter would repel each other, momentum and energy would still be conserved, and there would be no obvious problems.

    15. Re:Imagine this ! by gr8_phk · · Score: 1

      If antimatter falls up, would that mean it has negative mass?
      I've been asking this for a long time. Dirac predicted the existence of the anti-electron as a result of an equation that had both positive and negative roots when solved for MASS. The observation of the positron "confirmed" this. If you put a negative mass into some of the equations for the right-hand rule, it's indistinguishable from using a positive mass and a opposite charge.

      Depending which equation you tweak, and how you do it, all these possibilites are there. This measurement is very important IMHO. Also, if antimatter "falls up" and also repels antimatter, this offers an immediate solution to the question of "where is all the anti-matter?". It's inbetween all the galaxies, and it also exerts an outward pressure on everything causing expansion. It would also explain the anhialation radiation observed at the perimeter of galaxies (matter interacting with the antimatter cloud).

      IMHO this is among the most important physics experiments that needs to be done.

    16. Re:Imagine this ! by largesnike · · Score: 1

      Yeah, I'm pretty sure that's right. The antimatter particle has a weak antigravitational field around it, within which the matter particle would fall upward in. In the same fashion the matter particle has a gravitational field around it, within which the antimatter partle would fall away. The two would repel each other.

      This, of course does not mean that the two particles cannot interact. The gravitational field is weak enough to be overcome by physical momentum, in all but the largest cases.

      --
      "Laugh while you can a-monkey boy!" - Dr Emilio Lizardo
    17. Re:Imagine this ! by byron036 · · Score: 1

      Ah but therein lies the fun. Mirror matter, being on the other side oh the axis from normal matter might just do things that normal matter cannot. Like fall up.

      I don't believe in it myself, I think its just a feature of the math, not of reality. But if you have negative energy (can you have less than nothing?) you can do all sorts of energy conservation, 2nd law of thermodynamics breaking things.

      Its too sweet a deal to be true, granted, but the math all works. Dr. Forward was not a quack.

  26. Ah, so little imagination... by meringuoid · · Score: 4, Funny
    There are more options in particle physics than merely up and down.

    Antimatter falls strange.

    --
    Real Daleks don't climb stairs - they level the building.
    1. Re:Ah, so little imagination... by Yetihehe · · Score: 2, Funny

      Or charming :D

      --
      Extreme Programming - Redundant Array of Inexpensive Developers
    2. Re:Ah, so little imagination... by JasterBobaMereel · · Score: 1

      No No it falls charmingly ....

      --
      Puteulanus fenestra mortis
    3. Re:Ah, so little imagination... by Anonymous Coward · · Score: 0

      How charming....

    4. Re:Ah, so little imagination... by dpilot · · Score: 1

      Or to finish out the matrix,

      It falls Beautifully...

      It falls Truly...

      (Some of use might prefer Truth and Beauty to Top and Bottom.)

      --
      The living have better things to do than to continue hating the dead.
    5. Re:Ah, so little imagination... by Anonymous Coward · · Score: 0

      Charming.

    6. Re:Ah, so little imagination... by Anonymous Coward · · Score: 0

      That was a charming attempt at a joke, but it wasn't funny.

  27. Um by goldaryn · · Score: 1

    solve a number of important conundrums such as why there is so little antimatter in our part of the universe

    Eek, no, leave it where the hell it is!
    Ok, maybe one George Bush sized piece...

  28. antimatter by Stooshie · · Score: 1

    ... why there is so little antimatter in our part of the universe ...

    Surely antimatter can only exist for as long as it doesn't hit matter and since matter exists everywhere (even in the (near) vacuum of space) then that's an extremely short time period (milliseconds? if that).

    This would mean they wouldn't exist much anywhere in the universe, never mind just "our" part.

    Just occoured to me: Are they claiming that the laws of physics could be different in "our" part of the universe?

    Perhaps someone with a little more knowledge on this topic could explain.

    --
    America, Home of the Brave. ... .and the Squaw.
    1. Re:antimatter by Anonymous Coward · · Score: 0

      Surely antimatter can only exist for as long as it doesn't hit matter and since matter exists everywhere (even in the (near) vacuum of space) then that's an extremely short time period (milliseconds? if that). I think the pertinent question is *why* matter exists everywhere[1] and antimatter doesn't. AIUI the accepted theories suggest that matter and antimatter should have been created in equal quantities in the big bang, so there is an unanswered question of "where did all the antimatter go?".

      [1] Everywhere that we can see. This is why the point about "our part of the universe".
    2. Re:antimatter by Cro+Magnon · · Score: 1

      Well, I'm no x-purt on antimatter, but I do read bad Sci-Fi. :-P

      It's possible that there might be other galaxies where antimatter is common. If so, "normal" matter would be as rare there as antimatter is here.

      --
      Slow down, cowboy! It has been 4 hours since you last posted. You must wait another few hours.
    3. Re:antimatter by Stooshie · · Score: 1

      Wouldn't the antimatter galaxy just negate the same amount of matter around it?

      --
      America, Home of the Brave. ... .and the Squaw.
    4. Re:antimatter by Stooshie · · Score: 1

      So, actually, the question is, why was there more matter than anti-matter to start with? Is that right?

      Another thought, if there is another part of the universe with mostly anti-matter, wouldn't they call our part anti-matter?

      --
      America, Home of the Brave. ... .and the Squaw.
    5. Re:antimatter by aadvancedGIR · · Score: 1

      We are pretty sure of the first part, as we can create antiparticules and see them obliterate with their counterparts.

      What actually seems contradictory is that:
      -The universe looks homogenous.
      -Big bang theory implies that there would have been an equal amount of matter and anti-matter created since the creation of the universe (everything was initialy photons).
      -Anti-matter indeed seems to be extremely rare.

      Standard explanation is that the second point was not exactly right, but it is not airtight proved and leaves a lot of room for alternative explanations in which the first and third points could be wrong, and a lot of possible experiments.

    6. Re:antimatter by Anonymous Coward · · Score: 0

      Another thought, if there is another part of the universe with mostly anti-matter, wouldn't they call our part anti-matter?

      It woudn't matter.
  29. Fall up? by Anonymous Coward · · Score: 0

    Would it not be more apt to describe the anti-matter as "rising" rather than "falling up". Falling up... The very notion is absurd to its core.

  30. Pointless by cashdot · · Score: 1
    The whole experiment is pointless in my opinion. First of all, why do they have to synthesize anti hydrogen for doing the test? Why don't they just use positrons, which are much easier to produce

    Secondly, anti-matter is already used outside of particle physics, e.g. see http://en.wikipedia.org/wiki/Positron_emission_tomography. From these experiments it is abolutely clear, that the positrons have the same mass as electrons. After all, two photons are emmitted in the annihilation process, each have an energy equivalent to the mass of an electron. This can only be explained through the fact, that the positron has the same (positive) mass as an electron. Otherwise energy/mass conservation would be violated.

    Furthermore, negative mass would also imply, that anti-matter would be accelerated in the opposite direction with respect to the acceleration force. This would imply many strange phenomena, and in the end, also violate the energy conservation law.

    Oh, wait a minute. This means, that even negative mass would fall down, as it is repelled by the earth, but it reacts to the repulsion by an acceleration towards earth....

    1. Re:Pointless by Andy_R · · Score: 1

      From TFA "I know what you're thinking: why not do the experiment with antiprotons or positrons instead.

      People have tried but it's been impossible to completely remove any residual electromagnetic fields from such experiments. These are many orders of magnitude stronger than gravity and so even the smallest trace of them deflects charged particles by an amount that overwhelms the effect of gravity. That's why neutral antihydrogen is so important."

      --
      A pizza of radius z and thickness a has a volume of pi z z a
    2. Re:Pointless by Gromius · · Score: 2, Informative

      Um I think you are confused.

      First of all they are using anti-hydrogen for two reasons. First of, gravity is proprotional to mass and positrons have a mass of 0.5MeV while protons have a mass of a GeV or so. Thats a difference in mass of a factor of 2000. The second reason is that the electromagnetism is many many many orders of magnitude stronger than gravity, the EM coupling constant is around 1/137 while gravities coupling constant is around 1/ (1.2x10^{19}). So unless the object is electrically neutral, the EM force will vastly dwarf the gravitation force making any measurement extremely difficult (ie impossible practically speaking). Positrons and anti-protons are of course charged, hence you need to combine them into anti-hydrogen.

      Secondly it is only clear that the electrons and positrons have the same absolute mass. The formula you are refering is actually E^2 = (pc)^2 + (mc^2)^2 not E=mc^2. Hence you lose sign information.

      I fail to follow the rest of your post.

      Dr Grom, DPhil (Oxon), Particle Physicist working at CERN (although not on this experiment)

    3. Re:Pointless by cashdot · · Score: 1

      First of, gravity is proprotional to mass and positrons have a mass of 0.5MeV while protons have a mass of a GeV or so. Thats a difference in mass of a factor of 2000 I don't understand how this helps. Do you refer to the mass ratio in the anti hydrogen atom or the ratio of charge to mass of the electron/positron vs charge/mass ratio of the proton?

      I do however understand the second reason. It is quite obvious now. I'm sorry I did not RTFA.

      The formula you are refering is actually E^2 = (pc)^2 + (mc^2)^2 not E=mc^2. Hence you lose sign information. The question is, where does the sign matter (what law)? What kind of mass is affected anyway, inertial and gravitational? If anti matter has negative gravitational and inertial mass, such matter would fall down, right?
  31. Antimatter powered airships, hurrah! by itsdapead · · Score: 4, Funny

    Just a few technical details to sort out, first :-)

    ...and, of course, if your antimatter-powered airship crashes, the phrase "Oh, the Humanity!" is going to be even more applicable. Maybe without the "the".

    --
    In a survey of 100 programmers, 111111 thought that duck-typing was a good idea.
    1. Re:Antimatter powered airships, hurrah! by Ihlosi · · Score: 1
      ...and, of course, if your antimatter-powered airship crashes, the phrase "Oh, the Humanity!" is going to be even more applicable. Maybe without the "the".

      Quite possibly also without the "Humanity".

  32. Hydrogen lighter then air? by pw1972 · · Score: 1

    So with Hydrogen being lighter then air, does this mean anti-hydrogen will fall to the ground?

    1. Re:Hydrogen lighter then air? by tomandlu · · Score: 1

      The thought had occurred.

      I'd make anti-lead if I was them - much less ambiguous.

    2. Re:Hydrogen lighter then air? by trongey · · Score: 2, Funny

      ...does this mean anti-hydrogen will fall to the ground Yes, because, as everyone knows, the Earth repels normal hydrogen. It all gets pushed out into space where it coalesces to form gas giants.
      This also explains why cats and babies act so weird. Down where they live they're practically swimming in a sea of anti-hydrogen.
      --
      You never really know how close to the edge you can go until you fall off.
    3. Re:Hydrogen lighter then air? by aadvancedGIR · · Score: 1

      No.

      Normal hydrogen is attracted to the groung by the gravitation, but pushed upward by the Archiede force (that basically is the mass of air that cannot be in the volume occupied by the hydrogen).

      IF anti-hydrogen has a negative mass, it will simply go upward slightly faster in the presence of normal athmosphere, or to be more precise, during the small fraction of second before it anihilates with normal matter.

      Now, (IF anti-matter has a negative mass), anti-hydrogen in a volume filled with anti-air will be pushed to the ground as the anti-air falls up.

  33. Tested at SLAC with positrons years ago by franknagy · · Score: 5, Interesting

    As I rememeber, this has already been tested by drifting positrons down the length of the SLAC accelerator tube and measuring the beam deflection due to gravity (at least 20+ years ago).

    Yes, anti-matter does fall down just like matter.

    --
    Dr. Frank J. Nagy Fermilab Computing Division Authentication and Directory Services Group
    1. Re:Tested at SLAC with positrons years ago by Anonymous Coward · · Score: 0

      As I rememeber, this has already been tested by drifting positrons down the length of the SLAC accelerator tube and measuring the beam deflection due to gravity (at least 20+ years ago).

      Yes, anti-matter does fall down just like matter. This is definitely not true, by a factor of several billions. Look at the discussion about this false belief in :
      M.M. Nieto and T. Goldman, Physics Report, Vol. 205, p. 221 for a very nice analysis about this question.
      Particle beams in ring have a property of self-focusing, and this means that even if electrons and positrons had different inertial mass, you would not notice it.
      Not to say anything about the gravitational mass.
      Remember that the Earth gravitational field represents less than a tenth of a billionth of volt/meter, while the voltage between you head and toes is usually of a few kilovolts...
      So this is definitely not tested, and therefore the AEGIS (and the ATRAP) experiment(s) at CERN.
  34. Negative curvature ... by Ihlosi · · Score: 1
    In fact the curvature can even be negative, if we have negative mass density.



    Isn't a negative mass density also necessary to create stable wormholes ? As far as I remember, wormholes are possible ... if you can find something that creates a negative curvature of spacetime.



    So, if antimatter falls up, we're one step (of, um, billions, probably) closer to creating artificial wormholes.

  35. PhD Fail by coreyjkelly · · Score: 2, Insightful

    Did it really take 65 physicists to decide that the best way to test gravitational effects was a particle beam deflection? I suppose simplicity is nice, but I honestly expected something more complicated with that many collaborators...

    1. Re:PhD Fail by Lijemo · · Score: 1

      Did it really take 65 physicists to decide that the best way to test gravitational effects was a particle beam deflection? I suppose simplicity is nice, but I honestly expected something more complicated with that many collaborators...

      Or maybe the Slashdot summary of the article isn't giving all the details of the experiment?

      Nah, that's crazy talk. ;')

    2. Re:PhD Fail by coreyjkelly · · Score: 1

      I just read through the paper.. and surprisingly, it's not much more complicated than that... I'm not saying I'd know how to conduct the experiment... I'm just surprised at the simplicity of the concept...

    3. Re:PhD Fail by MadMidnightBomber · · Score: 1

      Dude, it takes like 60 people to switch that damn thing on, let alone do anything with it. That's why you see hundreds of names on a typical particle physics paper.

      --
      "It doesn't cost enough, and it makes too much sense."
    4. Re:PhD Fail by Anonymous Coward · · Score: 0

      One to come up with a complex and elaborate experiment to test if antimatter falls upward.
      Sixty-four to say "no, a particle beam deflection would be better".

    5. Re:PhD Fail by Lijemo · · Score: 1

      Interesting-- that is surprising.

  36. I Bet by Symbolis · · Score: 3, Funny

    It falls sideways, just to screw with those smarmy scientists.

  37. It's news to me by Chuck+Chunder · · Score: 1

    It's a cool experiment, but it's news once you get the result, not "a few years" before.

    The possibility that antimatter might fall "up" is news to me.

    Do you really think that scientists should work away in their own little worlds and only pop their heads up and bother us regular folk when they have an answer?

    Personally I think the questions are often interesting in themselves.
    --
    Boffoonery - downloadable Comedy Benefit for Bletchley Park
  38. No Loopholes in General Relativity by mbone · · Score: 5, Informative

    There are enough loopholes in the general theory of relativity to allow antimatter to fall up rather than down in a gravitational field.

    Uh, no there are not. Gravity (or geometry, same thing in the theory) depends on mass energy in General Relativity. Stuff (with mass energy) follows the metric (the local geodesic). Even photons (which are their own anti-particles) follow the geodesic - and that has certainly been tested. Equivalence principle tests also show that different sorts of nuclear matter (including neutrons) individually follow the geodesic. Anti-matter certainly has mass energy, and (with matter) can be converted to photons and is no different in the theory. In other words "there is only one type of geodesics and there are no antigeodesics for antimatter."

    The original article talks about "flavors" of General Relativity. Ain't so such beasties. Period. If you go to the real original article, you find a proposal for a 1% test of the equivalence principle for antimatter, and no such claims of flavors. Now, the equivalence principle has been tested to better than parts per trillion, and part of the mass energy in ordinary matter is made up of antimatter (in virtual particle pairs), so (based on the experimental evidence) I would claim that this test will be negative and is not actually that interesting as new physics. (The articles say that these older tests are "model dependent," but they are not model dependent enough to matter for this.)

    That doesn't mean that this shouldn't be done (everything should be tested in physics, and different tests are always useful), but the prediction of General Relativity is clear : if anti-matter has anti-gravity, then General Relativity is wrong. The experimental evidence is also clear : this isn't going to be accurate enough to matter. Will make for some good public relations, though.

    1. Re:No Loopholes in General Relativity by mbone · · Score: 2, Informative

      A brief search on the subject reveals this

      we conclude that the Principle of Equivalence between particles and antiparticles holds to a level of 6.5, 4.3 and 1.8 x 10-9,

      Just a little bit better than 1%.

  39. Isn't this already observed? by loafula · · Score: 1

    I always assumed this was the reason for the accelerating expansion of the universe. If anti-matter fell down, then we'd be seeing a deceleration in the expansion.

    --
    FOXTROT UNIFORM CHARLIE KILO
  40. IANAP by Clomer · · Score: 1

    I am not a physicist, but my instinct is that if it proves true that antimatter falls up, then it means that there would be such a thing as antigravity. A large mass of anti-matter (say, a planet, or at least anything big enough to have an appreciable gravity field), will he held together by it's own antigravity, and antimatter objects will fall towards it; while normal matter would be pushed away.

    My guess is that this experiment will prove false, meaning that antimatter will fall just like normal matter, but it is an interesting hypothesis. I'll be interested in seeing the results.

    --
    Intelligent responses welcome, flames will be met with marshmallows.
    1. Re:IANAP by theTrueMikeBrown · · Score: 1

      IANAL, but if antigravity were to exist there would probably be some serious legal ramifications.

      Take the Spindizzy for instance.

      I am sure that Blish would want in on that action.

      We might even set up a interesting legal precedent:

      1) invent Spindizzy
      2) people invent antogravity
      3) ...
      4) profit!

  41. Slightly unrelated questions by Hektor_Troy · · Score: 1

    Somewhat silly questions regarding anti-matter - just in case someone knows the answers:

    What happens if anti-hydrogen hits anti-helium? Do you end up eith energy + hydrogen (ie, does it anihilate 1 proton and one electron from the helium, leaving the rest), or does it fail to react?

    Does anti-matter only react to its opposite particle? I.e. does an anti-proton react to an electron? Somewhat related, does anti-matter anihilate on contact with other stuff, like neutrinos or photons?

    And is the only anti-matter anti-protons and positrons? I.e. is there an anti-photon, anti-quark etc.?

    --
    We do not live in the 21st century. We live in the 20 second century.
    1. Re:Slightly unrelated questions by Ihlosi · · Score: 2, Informative
      I.e. is there an anti-photon, anti-quark etc.?

      There's an anti-photon ... it's the photon. There's anti-versions of several other particles (antineutrino, antiquarks, antineutron, etc).

    2. Re:Slightly unrelated questions by SBacks · · Score: 2, Informative

      Don't think of it as anti-hydrogen hitting helium. Think of it as an anti-proton hitting a proton that just happens to have another proton nearby.

      So, you end up with a bunch of energy and a left over proton (Hydrogen).

      And, no, anti-particles only annihilate their partner particles, not just any particle.

  42. Why a beam? by ACE209 · · Score: 2, Interesting

    Quote:
    The idea is to fire a beam of antihydogen atoms at a target and see how much they are deflected by gravity.

    That's easier said than done. Creating a beam of this stuff turns out to be remarkably tricky. The problem is that it's easy enough to trap antiprotons and positrons in electromagnetic fields. It's even fairly straightforwad to put them together so that they form antihydrogen. The problem is that antihydrogen is neutral and simply falls out of the trap. So some way has to be found to collect and trap these antiatoms.
    ---
    Uh - can somebody explain to me why they need a beam and don`t just take a look if the antihydrogen falls out on the bottom or the top of the trap?

    --
    "we are all atheists about most of the gods that societies have ever believed in. Some of us just go one god further."
    1. Re:Why a beam? by evanbd · · Score: 1

      Getting it cold is the hard part. Hot gases don't fall on a small scale; the particle velocity is too high, so they diffuse. I don't know the details of the expirement, but the beam may be part of how they plan to cool the anti-atoms down (at least in the directions orthogonal to the beam; there might well be a significant velocity distribution within the beam).

  43. Mod parent up by Frangible · · Score: 1

    If I had mod points, I'd mod you up. I could've sworn I'd read something similar.

    And bonus points to whoever finds the actual study paper on it.

  44. I knew it by Anonymous Coward · · Score: 1, Funny

    Women must be made of antimatter. Why else would they levitate away from me?

  45. And regardless of how good human intuition is by Sycraft-fu · · Score: 3, Insightful

    It's not science. Even doing a nice bunch of calculations and saying "Well this shows that anti-matter should do this," is not science, or at least not the important part. Science is testing beliefs by experiment. So regardless of what we think anti-matter will do, and regardless of how sure we think we are, we still need to test it. That's how science works. You come up with an idea, you test it. If the test falsifies it, you come up with a different idea and test it. If the test supports it, you come up with more tests to try and falsify it.

    Through this process, we come to understand the natural world, and come to be fairly certain that our understanding is correct. Math and theoretical work is great, but actually testing those theories is what makes science what it is.

    So even if we are 99.999999% certain that our calculations are solid and anti-matter does something, we still need to test it. There are plenty of things that we've been certain about that, when we tested it, turned out not to be the case.

    1. Re:And regardless of how good human intuition is by pbhj · · Score: 1

      It's not science [...] or at least not the important part. You're not a theoretical physicist then? Most of the recent big names in physics I can think of were theoreticians (http://en.wikipedia.org/wiki/Theoretical_Physics#Prominent_theoretical_physicists gives one list).

      I find your assertion to be like saying the important part of a building is the manufacture of the materials. Sure you can't make a building without making the materials but the architecture and engineering is quite important, no?

      Basically the theoretical framework and the experiment design are equally important elements, the actual experiment is the hook on which you attempt to hang it - the hook can hold or fail.

      ---
      What we need here is a car analogy ...
  46. For that matter.... by mmullings · · Score: 0

    Which way is "up" anyhow?

    --
    I remember when MOD was an audio format, and DOS wasn't a network attack....
  47. Oblig. Simpsons by m.ducharme · · Score: 1

    "What is mind? It doesn't matter.
    What is matter? Never mind."

    Homer

    --
    Rule of Slashdot #0: You and people like you are not representative of the larger population. - A.C.
  48. heh by Anonymous Coward · · Score: 0

    I bet 10 bucks it's not gonna fall at all.

  49. "Ad Hoc" my but hoc! by Zawash · · Score: 1

    When wood burns, oxygen is not added - it is actually the Phlogiston that disappears!

    Phlogiston is antimatter!
    (gasp!) ..Just like Soylent Green is made of people!

    (More info at Wikipaedia, for the historically challenged..)

    --
    File not found. Fake it(Y/N)? _
  50. up or down by Anonymous Coward · · Score: 0

    nope, sideways!

  51. Well? Which is it? by Chelloveck · · Score: 1

    Back {mumble} years ago, I asked my high-school physics teacher this same question. "Do matter and antimatter attract or repel each other by gravitation?" After he firmly put down the ranks of kids who thought antimatter was something made-up for Star Trek, he said he didn't know... And then he spent the rest of the period researching it in the texts that he had. And concluded that he still didn't know.

    Then he assigned the question to me as a research problem. D'oh! In that pre-Internet era I went through the subject in the school and local libraries and found that... I didn't know. I'm glad we were right!

    --
    Chelloveck
    I give up on debugging. From now on, SIGSEGV is a feature.
  52. Monney Whoring by DrYak · · Score: 1

    Unless they're trying to drum up interest for funding... Yup. Because it's hard to persuade some lobby that the direction of the effect of gravity on anti matter will have a significant result on
    "The War Against Evil Pirate That Rob Our Imaginary Property (tm)(c) !!!"
    or on
    "The War Against Evil Pedophiles That Pray On Our Kids, THINK OF THE CHILDREN !!11!oneone"
    I won't either
    "Cure Definitely AIDS And Cancer Within Next 5 Years, This Time We Really Promise It !"
    So the probability of obtaining funds drops dramatically.

    (Although they may try to sell it to military as an exotic weapon, as another /.er pointed out)
    --
    "Sufficiently advanced satire is indistinguishable from reality." - [Tips: 1DrYakQDKCQ6y52z6QbnkxHXAocMZJE61o ]
  53. Opposites attract by Lord+Lode · · Score: 1

    It's really really dumb, but when I was much smaller than now I had this theory that matter and antimatter worked like magnetism where opposites attract. Matter would move away from matter, antimatter would move away from antimatter, and matter would attract antimatter. So why would the earth then have gravity? Because there would be antimatter in the core! But why would the moon circle around the earth then? It would need to contain no antimatter. But then why can people walk on the moon? For that it would have to have an antimatter core too. And why would the sun attract the earth? So the conclusion then was that my theory was stupid. So I shouldn't have posted it here, but hey, this article made me remember that weird theory I had back then I wanted to share it.

  54. Physics would truly be weird if this was true by jtankers · · Score: 1

    Physics would truly be weird if this was true that anti-matter might fall up. First of all, there is no evidense that anti-matter is anywhere near that weird. It is just a form of energy, just as matter is a form of energy. Though some people do not understand that basic notion. When you combine matter with anti-matter you get energy. In terms of energy, adding matter and anti-matter is similar to adding 1 + 1 and getting 2. Not adding 1 and minus 1 and getting 0. That is a very important difference, and that is part of the reason that the notion that anti-matter might 'fall up' is just not credible. But that is not the reason for my post... The following comments were posted this week on a related blog that helps put some of the conversation surrounding the Large Hadron Collider Safety controversy in perspective I think. From a June 2008 blog by Martin Meenagh Quote: âoeBy what means can an Hawaii Court, even if it is a federal one, assert any authority over a facility outside the USA?â I am not a lawyer, but the case has world wide implications, some court must take jurisdiction. Quote: âoegoing to do anything but make Europeans and Canadians determined to go ahead anywayâ A few very credible scientists believe that CERN is basing their theory of safety on at least one flawed assumption. If the following reasonable and plausible assumptions prove to be correct, then the uncomfortable truth is that the probability of destruction of Earth is actually closer to 100%, though only mother nature currently knows for certain due to our limited understanding of the physics involved. A. LHC Creates black holes as CERN Predicted (1 per second) [1] B. Micro Black holes do not evaporate as LSAG accepts is plausible. [2] C. One or more micro black holes are captured by Earthâ(TM)s gravity as LSAG accepts as plausible. [3] D. Micro Black holes grow exponentially as Dr. Otto E. Rosslerâ(TM)s paper predicts and calculates. [4] If the reasonable and plausible assumptions above prove correct, and Europeans and Canadians are determined to go ahead anyway, then that would be an unfortunate situation. The entire world is in this together after all! Quote: âoeThere is a world issue here. In libel, in risk assessment, and in extradition casesâ Yes, there are also potentially issues with respect to freedom of speech, corporate deception, and mis-representation of facts designed to confuse or mislead the public as to risks involved. The lawsuit also alleges on page 15 of AFFIDAVIT OF LUIS SANCHO IN SUPPORT OF TRO AND PRELIMINARY INJUNCTION: [5] Quote: âoeCERN has neither asked mankind to validate these experiments, nor has it been open and clear about those risks to the public. On the contrary it has systematically hidden evidence, and hence it is, in my opinion and hopefully that of this Court, liable of criminal negligence and occultation of proofs, as it carries about what amounts to a potential global genocide.â Quote: âoeWould you have any links that you could send any readers and myself to as a short cut?â I would suggest LHCDefense.org for the legal focus. Sincerely, JTankers Administrator, LHCFacts.org References: [1] http://doc.cern.ch/yellowrep/2003/2003-001/p1.pdf [2] http://xxx.lanl.gov/abs/gr-qc/0304042 [3] http://lhc2008.web.cern.ch/LHC2008/documents/LSAG.pdf [4] http://www.wissensnavigator.com/documents/OTTOROESSLERMINIBLACKHOLE.pdf [5] http://www.lhcfacts.org/?cat=9

    1. Re:Physics would truly be weird if this was true by Slashcrap · · Score: 1

      Thanks for those few relevant sentences followed by your insane copypasta. You certainly know how to draw people in! I especially enjoyed the way you were so desperate to spread your message to us sheeple that you didn't have time to format it or remove the unicode characters.

      I wish you well in your effort to get Ron Paul elected, stop HAARP from controlling your mind and forcing you to kill prostitutes, or whatever the fuck your current obsession is.

      Please take the time to make a detailed reply to my post, as I will definitely make the effort to come back and read it.

  55. from TFA it does fall by nategoose · · Score: 1

    The problem is that antihydrogen is neutral and simply falls out of the trap. Which way?
  56. According to GR by jefu · · Score: 1

    Gravity's Rainbow?

  57. Anti-piano by Christmas · · Score: 1

    So like, they can*t make enough antimatter to make like an anti-piano and throw it out the window and see where it goes ?? :) Ohhhh they should make some Anti-Carries!!! That would be really fun to float in the air!! But would I go into space???? omgosh!

    --
    Carrie -The Christmas Angel
    1. Re:Anti-piano by Christmas · · Score: 1

      Ok so my friends r telling me that i*m already IN space??? I really don*t get it?

      --
      Carrie -The Christmas Angel
  58. If it is repelled by gravity by yellowalienbaby · · Score: 1

    which is what this 'flying up' seems to imply - instead of attraction there is repulsion,

    Then wouldnt all the antimatter be out at the edges of the universe?

    --
    Darwin Hawking Blackmore
    1. Re:If it is repelled by gravity by ubergeek65536 · · Score: 1

      About your quote.... Not if the universe has no edges. I get tired of apparently smart scientists thinking that the universe has a size. It has not size, no beginning and no end. Get over it.

  59. Maybe its just me... by alexborges · · Score: 1

    But doesnt it get you a tad nervous that we are making this "anti-*" stuff here on earth and shooting it up to see which way it falls?

    How does anti-hydrogen work on life thingies? Does it have the potential for a destructive chain reaction? Are the cientists not part of the global-universal conspiracy against america?

    --
    NO SIG
    1. Re:Maybe its just me... by aadvancedGIR · · Score: 2, Informative

      "How does anti-hydrogen work on life thingies?"
      On contact with organic tissues (or pretty much anything else), it will disapear in a burst of highly energetic photons (think gamma rays). So, depending on the dose (approx. ng to kg), it can range from totally harmess to skin burn to radiation poisonning to strategic-grade nuclear explosion.

      "Does it have the potential for a destructive chain reaction?"
      No, the reaction does not create new antimatter, and the potential energy of the created antimatter is only a very small proportion of the lab electricity bill, at worst, it will probably only blow up their building.

  60. Or does it fall at all? by ubergeek65536 · · Score: 2, Insightful

    They missed one option. What if antimatter is not affected by gravity? I'll put my money on falling down.

  61. Stupid experiment by WilburCobb · · Score: 1

    Anti-protons and positrons are anti-matter and are produced very easily in particle accelerators. Why not test gravity on them before testing it on an anti-hidrogen, which is simply a bound state of an anti-electron and an anti-proton? This isn't experimental physics, this is demagogy.

  62. Galactic Black Hole Jets by jameskojiro · · Score: 1

    Do they have a asston of antimatter in them? Could they be filled with antimatter that is being "pushed" away by the gravity of the black hole???

    --
    Tsukasa: All I really want, is to be left alone...
    1. Re:Galactic Black Hole Jets by Anonymous Coward · · Score: 0

      Could they be filled with antimatter that is being "pushed" away by the gravity of the black hole???

      Or, could they be loads of anti-matter?

  63. Yeah, anti-light would be SWEET! by blueZ3 · · Score: 1

    You could walk around the office shining ("darking"?) your ant-flash-light into people's eyes and freaking them out as the world does dark.

    --
    Interested in a Flash-based MAME front end? Visit mame.danzbb.com
  64. Antineutron by amazeofdeath · · Score: 1

    Antineutron consists of 2 anti-down and 1 anti-up quarks.

    --
    U+F8FF
  65. Time? by Anonymous Coward · · Score: 0

    I read some speculation somewhere that antimatter behaved just like normal matter moving backward in time. If so, then I suppose antimatter could (to us) appear to fall up.

  66. Come on People! by RavenChild · · Score: 1, Funny

    "... what the value of the cosmological constant is."

    Duh... 42. Now we just have to figure out the cosmological question.

  67. Anti-Gravity? by Vaibhav_Locke · · Score: 1

    So lets say it does fall up ... Does this mean that anti-matter is actually repelled by gravity? On a larger scale, wouldn't this cause anti-matter to be repelled by large clusters of matter (galaxies)?

    This leads to another question, would anti-matter exert some sort of anti-gravity, in turn repelling normal matter? The mind boggles, especially since I left the boundaries of college physics when I started writing.

  68. What about the third option? by mark-t · · Score: 2, Interesting

    That it doesn't fall at all? Up, or down? That antimatter doesn't interact gravitationally with normal matter in any way. but only with other antimatter?

  69. Re:Gravitons and Graviolis by Anonymous Coward · · Score: 0

    PROTIP: No need to tell us it's a Futurama quote. Most of us get it already.

  70. what about gravitons? by Anonymous Coward · · Score: 0

    If there is such a thing as a graviton as posed by some species of string theory, is there such a thing as an antigraviton? And how would such a thing impact matter vs. antimatter?

  71. whoops goodbye sun by Anonymous Coward · · Score: 0

    this is done in a controlled environment right? not by tinkering college students?

  72. Of course it falls up... by Anonymous Coward · · Score: 0

    ... but it also moves backwards through time!

  73. What about the fourth option? by Kr4u53 · · Score: 1

    Up, Down or not at all? What about a direction orthogonal to the direction of gravity for normal matter?

  74. It would be ugly, ... by Anonymous Coward · · Score: 0

    so it has to be wrong

    Some particles don't have their anti- counterpart, or more precisely they are their own anti-particles. Photons for example, there are no anti-photons, or anti-photons are really just photons.

    If this theory that antiparticles fall up instead of down turned out to be true, it would be mathematically quite ugly, because it would introduce an asymmetry : why photons then fall down rather than up , since they are both anti and normal particles ?

    When it's ugly, it's often wrong too.

    For those who ask, but photons do not fall because they have no mass : they actually do have a mass. Only stopped photons would have no mass, but as we know, photons always run at the speed of light ;)

  75. And does antimatter go backwards in time? by He+Who+Waits · · Score: 1
    So if antimatter falls up, what does that tell us about gravity?

    If we continue to accept that gravity is a distortion of space-time, up-falling antimatter must also move through time in the opposite direction to matter.

    And maybe that explains why there is a relative scarcity of antimatter here-and-now. Antimatter would tend to collect in the past, in the spaces between gravity wells, while matter would tend to collect in the future, inside gravity wells.

    I'm looking forward to some experimental answers.

    1. Re:And does antimatter go backwards in time? by pandrijeczko · · Score: 1
      So if antimatter falls up, what does that tell us about gravity?

      That the Earth sucks.

      --
      Gentoo Linux - another day, another USE flag.
  76. No. by blair1q · · Score: 3, Informative

    Sorry, this is all silly.

    "Anti-matter" is not the opposite of matter. It is matter with opposite charge or other opposite properties. Mass has no opposite. It is there, or it isn't. (Or it is and then it isn't and then it is and then it isn't, on the level of quantum fluctuations of the gravitational field.)

    And no, a hole isn't "anti-matter". It's merely a void in the surrounding matter. It rises because of a principle known as "buoyancy" which is really the gross action of the matter surrounding it causing pressure differentials as a function of distance from the CM. As long as the surrounding matter can flow, it can fill any displacement of the void, and the mass will tend to move down rather than up, and the void will therefore appear to tend to move up rather than down.

    And no, hot-air balloons don't rise because of the heat, they rise because they make the air in the balloon less dense than the air outside the balloon. How they do it is not relevant. A rigid balloon and a vacuum pump would work, too.

    1. Re:No. by Anonymous Coward · · Score: 0

      granted the total average density of the rigid balloon and vacuum inside is less than the density of the air around it...

  77. What is up and what is down? by Orig_Club_Soda · · Score: 1

    Anything with mass will follow the pull of gravitiy, but does anti-matter have mass in the same measue that matter does?

    Also, what is "fall?" Hot air rises and cool air falls - but cool air is really the absence of hot air.

  78. not for physicists by nguy · · Score: 1


    There's a big difference between a belief that something is most likely true, and an experiment that removes all doubt.


    Tell that to the physicists.

    There are many beliefs that physicists stick to about the real world without experiment because the consequences for long-cherieshed of those beliefs not being true would be too awful.

  79. an odd experiment by Goldsmith · · Score: 1

    As a number of other physicists have pointed out here, anti-matter has mass and falls like everything else that has mass.

    If it does not, then far more is wrong in physics than some minor law, or backwater part of relativity. We have been able to very successfully predict the existence and many properties of anti-matter. If gravity does not act on anti-matter normally, it would mean some fundamental understanding quantum mechanics is wrong, and we may not have an explanation for why anti-matter even exists.

    A very high payoff if they get an unexpected result, but very, very unlikely. If I were doing this experiment, I would doubt my own abilities first if I didn't get the result everyone else expected. A hard thing to put yourself up against.

  80. What gravitons? by Roger+W+Moore · · Score: 3, Interesting

    Gravitons are like photons: simply distortions in the underlying field...
    Are they? Ever seen evidence of one? Gravitons are a purely theoretical construction and, worse of all, one that does not work. While you can construct a quantum field theory of gravity it does not work to arbitrary energies. You have to impose a cut-off threshold and since there is no valid reason for doing so the theory is broken...hence all the theoretical activity trying to reconcile GR and Quantum mechanics.

    The gravitational field as a scalar field surperposed on a flat space-time is just another way of describing gravitation
    You mean a vector field since gravity has direction, rather than the Tensor field of GR.
    1. Re:What gravitons? by jandersen · · Score: 1

      Are they? Ever seen evidence of one? Gravitons are a purely theoretical construction and, worse of all, one that does not work. Come to think of it, I haven't seen a photon either. I have seen experiments that are most easily explained by 'light particles', but then it might just be a sort of solitons that are interacting. The fact of the matter is that what we see is simply that light waves can occur in a localised form; of course, that may be what all particles are, at the end of the day: localised packets of waves in some sort of theorectical 'medium'. We don't know - I don't think any theory has gone in that direction; there are simply too many other things to research, that are more immediately important.

      You mean a vector field since gravity has direction, rather than the Tensor field of GR. I meant a scalar field, since it is usual practise to think of the size of gravitation rather than the direction; although of course you are right. Still, it is the same difference, more or less, when the purpose was just to illustrate the different nature of the two theories.
    2. Re:What gravitons? by wattrlz · · Score: 1

      Couldn't we just make gravitons really really small, then?

    3. Re:What gravitons? by Roger+W+Moore · · Score: 1

      Come to think of it, I haven't seen a photon either.
      That's not what I asked - I asked if you had seen evidence. Clearly we have seen evidence for photons.

      that may be what all particles are, at the end of the day: localised packets of waves in some sort of theorectical 'medium'.
      Actually we know that is not the case for light. Michelson-Morley showed in 1896 (IIRC) that light is not a vibration of a medium because otherwise the interference fringes would shift as the motion of the Earth changed which they did not. You can try to explain it as dragging the medium with the Earth but then you would have to see some effect between the stationary medium away from the Earth and the dragged medium near the Earth. So actually the one this we can show is that light is not the vibration of a medium.

      I meant a scalar field, since it is usual practise to think of the size of gravitation rather than the direction
      Not in any physics course I've ever taught, taken or even heard of it isn't. I've never heard anyone EVER refer to gravity as a scalar field or even treat it that way. You can't - even if you confine yourself to 1D you still have to have it act up or down. I think you may be getting confused between constant and scalar. The two are definitely not the same.
    4. Re:What gravitons? by jandersen · · Score: 1

      I think you are deliberately interpreting my words in the least favourable way. Splitting a hair may be a remarkable feat in itself, but it does little to endear you to others.

      The Michelson-Morley experiment: You don't seriously assume that I am unaware of this, do you? Seeing that I know fancy words like 'scalar field', it wouldn't be unreasonable to assume that I know about the experiemnt and its consequences. It is also worth noting my use of the word "theoretical" and the single quotes around the word medium, both of which suggest that I wasn't talking about an aether in any but the metaphorical sense.

      Enough of this - we are not talking stringent, mathematical proofs here, and being contrary about everything that is said will only lead to silly bickering, which I refuse to be pulled further into.

    5. Re:What gravitons? by Roger+W+Moore · · Score: 1

      Seeing that I know fancy words like 'scalar field', it wouldn't be unreasonable to assume that I know about the experiemnt and its consequences.
      I do not think that it is at all unreasonable to assume that someone who thinks Newtonian gravity is a scalar field has not heard of the Michelson-Morley experiment. While you may know the words 'scalar field', your comments show that you do not understand what they actually mean. Likewise you may have heard of the Michelson-Morley experiment but I have my doubts that you fully understand its implications. The results showed that there was no medium through which light propagated.
      My apologies if you think I am being particularly difficult or splitting hairs. However you are throwing around scientific words that have very precise and clear meanings in a manner that is not consistent with those meanings. If you are going to try to talk like a scientist don't complain when you get treated like one.
    6. Re:What gravitons? by Anonymous Coward · · Score: 0

      If you are going to try to talk like a scientist don't complain when you get treated like one.


      This is a great line!

      I heart you so much Roger W Moore!

      -- your /. stalker fan
  81. after the Big Bang, anti-matter went the other way by JCOTTON · · Score: 1

    I think that after the Big Bang, all the anti-matter went the other way. The other way in time. To see the anti-matter universe, you would have to travel back in time to the Big Bang, and then keep going past the BB even earlier. Then you would be in the anti-matter universe, but of course, going the wrong way. In other words, the anti-matter universe is sorta like driving in England. Everybody is going the wrong way, and on the wrong side. My wife has a habit of asking me "what is the matter?" I found that answering her "Energy" is highly satisfying.

  82. duh by Anonymous Coward · · Score: 0

    The answer should help solve a number of important conundrums such as why there is so little antimatter in our part of the universe and what the value of the cosmological constant is.

    Everybody knows it's 42.

  83. ethtrhrh by Anonymous Coward · · Score: 0

    yukyukuyyuky

  84. Who cares? by bradjs · · Score: 1

    The really neat thing about science is that if you do the experiment the answer is only partly relevant because you'll probably learn something else that is equally cool along the way...

  85. Re:Serious discussion? by lpq · · Score: 1

    (Someone actually speaking real physics...wow...)

    Actually, hasn't the anti-matter "falling up" been considered before? I.e. if it fell "up" -- that would
    mean it's repelled by matter? I.e. could explain universe expansion? But I thought that'd been ruled out as a possibility....If it were true, would anti-matter attract other particles of anti-matter?

    Isn't matter and antimatter (as we define them), simply a different mix of quarks? And don't each of
    the quarks have theoretical weights -- none of them are negative -- isn't it just the charge that's different
    on antimatter (though a guess an anti-neutron would still sum to zero on charge?)...b

  86. Neono by Neono · · Score: 1

    Theres some talk about anti matter in the military but from research i have done on anti matter its just another ATOMIC BOMB (but way stronger something like 4 magnitudes stronger in energy nuclear energy, ill check my sources for that) I still might except this idea of "Falling up."

  87. Re:Confused? Well in today's green world- by aqk · · Score: 1

    Besides the MAGENTIC fields, we most also consider the red shift
    But absolutely, not relatively, as had earlier been pointed out.


  88. What about... by Anonymous Coward · · Score: 0

    What about the idea that gravity is just a linear extrapolation of the Casimir force? Shouldn't the anti-matter just annihilate when it touches the vacuum particles?

  89. Anti matter and entropy by shthd · · Score: 1

    I've always wonder about this but I'm not a PHD. Antimatter on a Feynman diagram looks like matter moving backwards through time. In support of this, I think, entropy in a closed system of antimatter would work backwards. Tend towards order. Anyone know if this is BS or not? Is this a worthy experiment?

    --
    brrrrrrrrrppp 'Ey Homer...Why don't girls like me?