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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."
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
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?
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.
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.
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.
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.)
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.
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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.
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.
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
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.
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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."
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.
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
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.
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)'
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?
File under 'M' for 'Manic ranting'
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.
>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)'
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.
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.