Slashdot Mirror
The Speed Of Gravity Revealed
redwolfoz writes "New Scientist is reporting that the speed of gravity has been measured for the first time. 'The landmark experiment shows that it travels at the speed of light, meaning that Einstein's general theory of relativity has passed another test with flying colours.' Researchers made the measurement of the fundamental physical constant with the help of the planet Jupiter. One important consequence of the result is that it will help constrain the number of possible dimensions in the Universe."
Wow, that's pretty cool. Now if we could only figure out why and how gravity works, we'd be in business.
Every year during my review, I just pray the words "slashdot.org" aren't mentioned.
But of course, travelling at the speed of light, all the flying colours just appeared red due to the red-shift.
Does this make my brain look big?
Sure, this experiment will "help constrain the number of possible dimensions in the Universe" ... but will it lead to new weapons?
-kgj
I'm sorry, I don't mean to ask the stupidest question ever, but how does gravity have speed? The last I was taught on the subject (and believe me, it was a while ago) was that gravity was a force, but didn't have mass. Doesn't something need to have mass in order to have speed?
Well, if gravity travels at the speed of light, wouldn't the gravitational pull of black holes be confined by the event horizon as is the case with light?
...a topic like this to be a bit more precise in the summary. There's a signifigant difference between .95 times the speed of light, and the speed of light. Not to mention the large .25 margin of error. Which theoretically shouldn't be able to get to +.25 anyhow.
You're confusion arises because you were taught elementary Newtonian physics. In general relativity, one learns that any "information" cannot travel faster than light. Gravity is considered information because if you feel a gravitational force on you, you know that there is a body out there acting on you. That is, you have information about it (you could even estimate its mass by measuring the tug it exerts on you).
In Newtonian physics, lots of things are assumed to happen instantaneously (like gravity) so they don't have a speed per se. But in general relativity, everything has a speed -- and that speed is no greater than the speed of light.
GMD
watch this
"Kopeikin found another way. He reworked the equations of general relativity to express the gravitational field of a moving body in terms of its mass, velocity and the speed of gravity. If you could measure the gravitational field of Jupiter, while knowing its mass and velocity, you could work out the speed of gravity."
The theory of relativity was appearantly used to detect the speed of gravity. This would be fine if the theory of relativity didn't assume a speed of gravity. Basically, all he did was prove his given. So, if eggs are green, then eggs are green!
Karma Clown
Well, this says that Einstein's theory of relativity passed another test with flying colours.. but... According to THIS previous article on /. (and the NYT), the theory of relativity is generally flawed, so then did they really find the speed of gravity?
I'm confused...
[sig]www.masterslate.org[/sig]
Sure, we could pull Saddam out of Iraq with a gravity generator ... pull out the Tigris and Euphrates, while we're at it -- the whole damned Cradle of Civilization.
-kgj
If this theory of gravitiational propagation is true then gravity would have to exhibit doppler effects. The force of gravity would be stronger and act at a shorter distance towards the velocity vector of an object and conversely it would be weaker and act at a greater distance in the opposite direction in violation of the inverse square rule for gravitational effects. This has not been noted in any observations. All present observations of moving astronomical objects moving at anywhere near to relativistic speeds, or even those moving much slower taken as a statistical whole, show no such effect.
The observed effect is mearly an artifact of the observational process.
What next? The speed of magnetism?
I love it! Take a formula with an assumption in it, rework the formula, then get the formula to prove the assumption.
Example:
Let a = 2b + c (1)
a - 2b = c
-2b = -a + c
2b = a - c
Now substituting for 2b in (1):
a = a - c + c
a = a!! Brilliant!! Gravity travels at the speed of light!!!
So we prove relativity using relativity. Erm... what's wrong with this picture?
I am artificially intelligent.
Photons are not particles in the sense of neutrons, electrons et. al which are massy particles.
Photons are better described as 'packets of energy'. Gravity doesn't just affect mass - it affects energy as well. Light doesnt get 'pulled into' a black hole, it just gets redshifted so much (by the gravity sucking the energy out of it), that its wavelength becomes infinite, and thus immeasureable.
Photons can exert a pressure though because they have MOMENTUM. Thus they have a 'mass equivalent', but they do not have mass, and that is not why they cannot escape black holes.
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On the other hand, what if light does have mass? I know it supposedly doesn't, and I know most anybody who know anything about physics will say it doesn't and even do the math to "prove" it doesn't. But what if that math is wrong?
If light did have mass, no matter how minute, could not also gravity have mass? Could the two together when added account for much of the "Dark Matter" in the universe?
What if a good portion of the "Dark Matter" was in fact light. Wouldn't that be an irony?
Okay, I'll shut up now.
"Everything you know is wrong. (And stupid.)"
Moderation Totals: Wrong=2, Stupid=3, Total=5.
What about his Unified Field Theory? IMO that's where the meat is, e=mc^2 is just the sizzle to help explain it to the dumber scientists.
If all energy comes from a single origin, then it would make sense that they have the same speed (on or off, 1 or 0). Quite an interesting theory, i suspect that the final equation will have a third denominator though.
Hammer of Truth
Well, now we have the speed of light AND the speed of gravity! If we can find out the Speed of Darkness, we'll be all set!
The sun couldn't suddenly disappear, although that scenario works for the purpose of explaining the speed of gravity. Consider this alternative.
Take the sun and instantly accellerate it to almost the speed of light, toward a collision course with Earth. For most of the 8 minutes between acceleration and collision, nobody would notice anything, as light, all other energy, and gravity would all present the sun as occupying its original location.
However, brief moments before the collision, the sun's change of accelleration toward earth will be noticed. Of course, you're noticing the change that happened 93 million miles away, even though the sun is about to impact. However, one second later, the sun will appear to be almost 186000 miles closer, and it will FEEL like it's 186000 miles closer. Suddenly the gravitational accelleration has increased to reflect the new position of the sun. But within that second, you get all the accumulated influences of gravity over a much larger stretch of space than just the 186000 miles it travelled in that time. Since the sun is moving at almost the speed of light, let's say 99% of it, after 99 seconds, the influence of the sun's gravity will only be 1 second ahead of the sun. However, within that one second between the position of the sun and the gravitational influence of the sun is contained the gravitational influence of the sun over the last 99 seconds. You get the combined force in 1 second that you normally would have gotten in 99. So when the Sun's influence is finally felt by Earth, you will not get a force that implies a steady rise in gravitational force of a sun massed object until impact, you'll get a very quick rise in force of an object that is, generally, about 99 times as large as the sun.
And if you remember relativity, when an object is travelling near the speed of light, the mass increases. So the theory at least makes sense. Here's another thing to ponder. If an object the size of the sun suddenly acquired the 99x its mass, would it not either collapse upon itself, or expand rapidly, nova, and the core would collapse upon itself, causing the same result, a singularity, with a small event horizon. And it will be this singularity that will collide with Earth, ripping through it in a fraction of a second, and the sudden, combined gravitational effect on earth will cause it to very suddenly pull out of it's orbit toward the origninal center of gravity of the sun, with a nice city sized hole carved through it.
Ok, this had no purpose at all, but it was interesting to think about. Go on with your business... nothing to see here. Rant over.
-Restil
Play with my webcams and lights here
While this is very interesting, is the speed of the propogation of gravity constant or can it be affected by certain conditions? This brings to mind the experiments at slowing down light in a special supercooled gel (is this an Einstein-Bose condensate?).
I don't think I like the idea of light being the fastest anything can travel, though. Perhaps it is for many things, but what happens if some forces travel at speeds faster (or multiples), or perhaps simple fractions, and we discount those readings instead of seeing if the old model can be adapted or remade? Well, many questions, few answers from me.
Does anyone remember the 'gravity shielding' story a while back, where a spinning superconductor was supposedly responsible for changes in weight? Podkletnov comes up in a google search for 'superconductor gravity shield' but I haven't heard anything further about it.
Also, what about magnetic forces? How do those work, and at what speed do they 'travel' ?
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..a landmark conclusion!. People have been deteting the gravitational fields of planets for a long time now, but is is just a new way of looking at it. Shows the power of the Theoreticians over Experimentalists.
:)
I think the single biggest news here is that the rane world has been constrained. I wonder if this has any implications on String theory.. with a max of 26 dimensions (currently 10 I think).
I DID read somewhere that the present Standard Model assumes this... speed of gravity is c, which means funds to the LHC arent going to waste, and places this 'experiment' in importance near to the '82 Aspects experiment.
So all this means we're doing good in Physics, and possibly should expect great advances this century. Now if only someone solves the EPR paradox for good, or produce an invention that utilizes it for higher speed signalling. I can see ISP bandwidths going higher and global pings lower already
"Give orange me give eat orange me eat orange give me eat orange give me you." -Nim Chimpsky
I prefer to think of it as having no loose ends...
___
If you think big enough, you'll never have to do it.
From that they worked out that gravity does move at the same speed as light. Their actual figure was 0.95 times light speed, but with a large error margin of plus or minus 0.25.
So, really, they're triumphantly announcing that the speed of the light is somewhere between 0.7 c and 1.2 c, and just supposing it has to be c for everything to make sense.
Physicists have been accused of being loose with rigour, but this is really stretching it.
I found the results of this experiment particularly reassuring, in an era when all sorts of scientific and technical myths seem to crumble. I admit, after just reading the title, I thought to myself "well, it _ought_ to be the speed of light, but wtf, it's on Slashdot, it could be _anything_!!" but I calmed down quite soon after I read the rest.
:o)
Call me conservative, but I like it if at least some of the laws of physics I learned at school, still apply
Sigged!
+18 Charisma, that's how.
Imagine that the sun exploded, and formed two equally large fragments each traveling perpendicular to the plane of the solar system. (Similar to what Bruce Willis did to a Texas-sized asteroid in Armageddon.) The earth's orbit would not be affected for another 8 minutes. We would see the explosion at the same time that the gravitational perturbation arrived.
This is also why our perceived direction of the pull of the sun lines up with where it is now instead of where it was 8 minutes ago.
"mass equivalence" hmm that means photons are almost the same as that stuff that was laying on the plate on thursdays back at my old junior high. It was a meat-like equivalent.
Here's how we can do space travel.
There are a few laws of physics which are very fundamental and reliable. One of those is the law of conservation of momentum. The classical formula for momentum is as follows:
P = v * m (velocity times momentum)
The relativistic version is:
P = gamma * m * v, where gamma is the Lorentz transform. (gamma = sqrt of 1/(1-v2/c2)), and c is the speed of light.
OK, so the idea is this. As objects approach the speed of light relativity says that they become more massive. Therefore it takes asymptotically more energy to approach c. *But* if there were a way to reduce the mass of that object(by some magical means) then it wouldn't require nearly as much energy to accelerate.
Said another way, this magical technology could reduce an object's mass at the same rate it increased from relativistic effects. Thus allowing the object to approach the speed of light in a way that's energetically economical. An even better option would be to take a spacecraft wieghing say...100tons and accelerate it until it reached a speed of maybe 1000km/s. (This is possible with existing technologies, by averaging a constact acceration over 6 months or so). Then in the 2nd stage of space travel, you would invoke the *magic* technology to dramtically reduce the wieght of the spacecraft.
Since the law of conservation of momentum is true at relativistic speeds, the more the mass of the ship is reduced, the faster it would go! Said simply, if this new technology could somehow reduce the mass of the craft by 1000 times, it would then be traveling at 99% the speed of light.
Traveling at these speeds the people inside of the space craft would effectively "stop aging" with respect to thier destination. Here on earth thousands of years may pass in a single one of thier lifetimes. So we would never hear about thier journey. But the people in that craft would be able to travel all over the galaxy within thier lifetimes.
Basically it's just like star-trek, except more like voyager because there's noone to call home to anymore.
Everything here is completely feasible, and not wacko crack-pot physics stuff.
All someone has to do is invent a single technology that can reduce mass. Or if you prefer, a technology that converts mass to energy, and then converts that energy back to mass again at the flip of a switch. It needs to be 100% efficiect of course.
Any ideas on how?
*sheepish grin*
The government has a defect: it's potentially democratic. Corporations have no defect: they're pure tyrannies. -Chomsky
"In general relativity, one learns that any "information" cannot travel faster than light"
What about quantum pairs? Move them apart, and a change in one is reflected intantly in the other.
That's why I specifically said "In general relativity...". Quantum pairs are from the theory of quantum mechanics, not general relativity. Physicists have been working hard to try to combine relativity and quantum into a single unified theory. However, problems arise when the two theories predict different things -- such as the quantum pairs example you listed. According to relativity, there would be a finite time lag for the change to be reflected in the second entity of the pair whereas quantum would say that the change is instantaneous.
Incidently, I heard that a few years ago an experiment was performed on quantum pairs and, sure enough, the change was indeed instantaneous. Can anyone else corroborate this?
GMD
watch this
YESSS! In your FACE, Infinite-dimension Universe theorists! You SUCK!
Yeaaaaah! Gimme one up top, bro!
pr0n - keeping monitor glass spotless since 1981.
"Light-speed gravity means that if the Sun suddenly disappeared from the centre of the Solar System, the Earth would remain in orbit for about 8.3 minutes"
Since gravity travels, dosn't that mean there is a possiblity that one can block gravity?
So you are speculating that maybe all the "dark matter" in the universe is, in fact, all the light in the universe?
Or that all the missing mass in our models of the universe is the mass of all the gravity that attracts together all the mass in the universe?
My head might soon explode and create a small bang.
"It's overkill, of course. But you can never have too much overkill." - Anonymous Slashdot Coward
I sort of agree... because we observe everything via electromagnetic radiation whose speed is limited to c, can we really measure any speeds that exceed c?
Escher was the first MC and Giger invented the HR department.
Gravity waves have been used in many stories as a FTL communication system, now that's all out of date.
Venus is a big swampy planet, eh guys ?
If we're going to generate a "gravity boom", I think we should start with a very small mass.
Ripping a nation out of the ground is one thing, splitting the whole planetary pumpkin is a more serious matter.
-kgj
So... if the Sun's gravity is pulling on Earth from where the Sun was (i.e. where we see it in the sky, not its actual position, which is about 8 minutes behind where the Sun actually is...), doesn't that kinda mess up the elliptical orbit somewhat? Shouldn't the Earth spiral into the Sun if gravity is pulling on the Earth at some eight minutes behind where the Sun really is?
As far as the Earth's concerned, the Sun is stationary, and as such was always in the same place 8 minutes ago.
At least, so far as it matters to the Earth it is, anyway.
Simon
Coming soon - pyrogyra
Sonny Bono's failure to grasp rudimentary physics can be seen as yet another case of evolution in action.
But can Sonny Bono's failure to grasp rudimentary constitutional law be seen as yet another case of evolution in action?
Will I retire or break 10K?
In Newtonian physics, lots of things are assumed to happen instantaneously (like gravity) so they don't have a speed per se. But in general relativity, everything has a speed -- and that speed is no greater than the speed of light.
The only problem is that GR implicitly assumes that information is available instantaneously over great distances while denying its existence.
The reason is simple. In order for gravity to propagate at c and still result in stable planetary orbits, general relativists have to get on their heads and do a neutron dance, so to speak. They claim that information about the source velocity of body A is transmitted at c to body B. They call it "velocity-dependent interactions." This way body B can react to the actual (extrapolated, of course, from the transmitted velocity info) instantaneous position of body A. This way GR can reproduce the stable-orbit results of Newtonian gravity in weak field approximations without assuming instantaneous information at a distance.
The theory can be found in this paper by GR expert Steve Carlip.
The problem with this is that instantaneous information at a distance is implied from the start. How can body A know about its instantaneous velocity relative to body B (they could be light years apart within a galaxy)?Furthermore, if the instantaneous relative velocity is already available to both bodies, why transmit it at all?
This is the sort of nonsense that make the foundations of general relativity very suspect at best. I, for one, do not trust relativists to conduct impartial tests of GR. It's a political game and way too many people have way too much invested in GR being correct for comfort. It's like trusting Big Tobaco to tell the truth about the dangers of smoking. One man's opinion.
- Strong
- Electromagnetic
- Weak
- Gravitational
I even fetched a URL on a whim, just in case you disagree for some reason.At least I didn't assume the article was correct then use it to argue that the article was correct :)
If I assumed the world is flat, I could probably show that it has an edge. That doesn't mean that that the world is flat or round, because the premise of the experiment was flawed. If I assume the world is flat, and I have no proof, then I can only prove that my assumption is false. There is no evidence presented in his experiment that shows that the theory of relativity is true. In fact, his experiment doesn't grant one shred of knowledge. If you substitute a false equation into itself, you will still end up with a true statement. That sheds no light on the viability of the original statement one way or the other.
Karma Clown
...you see, it's all component forces. If you look at the free body diagram of my car travelling on the road, you'll see the normal force, force of gravity, and my velocity in the x direction. As I mentioned, one of these component forces is gravity, labelled FsubG. It was recently discovered, and posted on slashdot, that the speed of said force is 3x10^7m/s.
And THAT'S why, officer, your radar reported that I was going 60 in a 40 zone!
One important consequence of the result is that it will help constrain the number of possible dimensions in the Universe.
You're damn right. I was worried.
Dimensions running rampant without limit... what's next, violent television and people masturbating???
It's a sad, sad world. Good thing we have that dimensional problem under control!
His big SF series about "Honor Harrington" relied on a FTL communications system based on creating gravity waves.
"Electricity" that is, kicking electrons out of place in a sequence to move them, runs at the speed of light.
*An electron* moves very slowly.
I asked my physics teacher the very same exact question- "if the sun disappeared, would the earth fly off from its orbit instantly, or would it take about 8 minutes?" He goes "it would be like snipping a cord- instantaneous". Discouraged, I went into the slashdot-posting, linux compiling netadmin that I am today, never knowing the true path of lab coats, leather gauntlets, and welding glasses that is physics- How dare you Stockwell! You stole my life with an assumption and I want my five years back!!!
slashdot: where everyone yells sarcastic metaphors to themselves to understand the issue
I remember, back when I was even more ignorant about physics than I am now, envisioning a communications device that worked instantaneously over long distances. I assumed that gravity traveled instantaneously throughout the universe, so all you needed was a significantly large mass that you could perturb in a predictable (to the receiver) way, and a vastly more sensitive perturbation detector than we have now.
Oh well. It was a cool idea, anyway. I wonder if gravity travels at a uniform speed under different space-time conditions, that is, if I perturb a mass on Earth, does the effect travel at the same speed as when 1km from a black hole? Thoughts? Random speculations like this?
If your bitterest enemies are people who hack the heads off civilians, then I would say you're doing something right.
well what they've done here is basically the same thing done to prove that the speed of light isnt infinite- they measure the apparent change in position of an object as the light being emitted from it passed through a gravitational field. The difference here is they did it in many different places at once, so they could determine not where the quasar appeared (as in the measuring of c) but when this change took place.
The article doesnnt go into enough detail, so I have no idea how this experiment actually managed to prove anything other than that distance exists- whether gravity is instantaneous or not doesnt change the fact that these places all accross the world were measuring entirely seperate light rays, each of which should have been effected at a different moment if only because they were being pulled by the field at different times. I think the only way this could have proven anything is if gravity was slower than light (which is what they actually measured). Maybe someone else has more details?
-- 'The' Lord and Master Bitman On High, Master Of All
Why do you think gravity ONLY affects mass? It does not. It also effects energy, mainly, it causes redshifts (from the outside observer's POV) Most of the time gravity is too weak to change it much, but in the case of blackholes, its enough to infinitely redshift, which is why no light escapes them.
Do a google search on 'do photons have mass' and learn something.
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While we think of mass and momentum being related by speed, energy and momentum are related by FREQUENCY.
Here's some equations if you want to wrap your head around them: equations
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Actually, the Earth's orbit wouldn't be affected at all. If it split into two pieces of equal mass traveling at an equal but opposite velocity perpendicular to the plane, there would be no change in the gravitational pull. We could still treat it as a point object.
the slightly longer answer is "because in the sun's inertial reference frame (i am going to leave gen.rel out of this) the sun still has the same mass."
if you don't understand what I just said, read more about special relativity, kay?
My life in the land of the rising sun.
Now, I'm not physics whiz, but I was always taught that acceleration of an object due to gravity was -9.81m/s/s^2. Is this incorrect now?
Also, if gravity's speed is the same as the speed of light, wouldn't an object have to travel at the speed of light to break the earth's gravitational pull?
I think maybe I'm confusing the speed of gravity with the force gravity exerts on an object, but I don't understand how gravity itself could have speed. Is this a measure of the latentcy before gravity takes effect or something?
Like I said, IANAPW (I am not a physics whiz)
So, who's right?
You are not alone. This is not normal. None of this is normal.
Watching South Park can screw with your brain...
Ok, so science has proven that the effect of gravity travels at the speed of light. Again, the speed is relative to the frame of reference of the observer... if gravity is wave-like, then it can be compressed by accellerating the object. So, take a Jupiter-sized object, and fling it. The mass of the object generates gravity waves in the forward direction of movement, but wouldn't they be compressed (blue-shifted of sorts) outside of the the time-compressed reference? Does that mean that the effect of gravity can be time-adjusted, or does the compression increase the amplitude of the gravity wave...
Einstein has also hypothesized the existance of wormholes, shortcuts in space but not time. Suppose that you have a star, and you put one end of the wormhole close to the gravity source... do gravity waves propogate through the hole? If yes, then is mass at the other end of the wormhole attracted towards the mouth of the hole (gravity waves spewing like water out of a hose), or towards the original location of the star in 3-space? Since the ends of a wormhole are linked, does the wave "resonate" the other end of the hole? If gravity does not pass through the hole, is gravity attracting the near end of the hole and moving it in 3-space? And what about an object that is accellerated into a wormhole by the gravity of the star?
Been in the inventory for *years*...
To quote Djikstra (more or less) "testing software can only confirm the presence of bugs, never the absence of them"
:)
Thanks. I'd forgotten that important principle for a moment. Just normally I expect better than 25% error before people start to get all congratulatory.
The enemies of Democracy are
Actually there would have to be a change in the orbit. The masses are both moving away from you, so the force exerted by both of them is decreasing. Imagine the situation when the two halves of the sun are many light years away.
What won't change is the direction of that slowly diminishing force. It'll always point at the same spot that the sun was before it broke into two.
Now, the effect on our orbit would be the following: since the force is always pointing "inwards," and decreasing, the earth is going to spiral outwards from its current orbit. The degree of the spiral depends on the speed of the halves of the sun. I put "inwards" in quotes because inwards doesn't really have a precise meaning for a spiral. But you get my point.
The best way to predict the future is to invent it.
http://www.what-is-the-speed-of-light.com/roemer-s peed-of-light.html
burris
Star trek doesn't need this to be loaded with bad science. Here's a nice gravity related one, in "generations" they alter the course of the nexus by blowing up a star that would have influenced it gravitationally. Unfortunatly they miss the fact that even if the star blows up, the mass is all still there, just spread out, and its center of mass is still in the same place, the path of the nexus wouldn't have changed.
This is hillarious. I am not a Star Trek fan, but the fact that they don't even operate on high school level of physical understanding leaves me in stitches!
You can't use the formulas of a hypothesis to gauge their accuracy against themselves. Einstein made those theories with the idea that gravity move at c. Therefore, any measurement you make, with his math, will make it look like c. It may be 2c, but if his math says that gravity is .5 it's actual speed, then after you take the .5, it will be c again.
The point is, his hypothesis was more like "the speed of gravity is c", and he used the theory of relativity to show that it is so. He makes it out like now that he has shown the speed of gravity to be c, it somehow strengthens the arguement for relativity. His original experiment assumed the theory of relativity, therefore, his findings are only as accurate as the theory of relativity. So, the speed of gravity being c is only as reliably as the theory of relativity. Therefore, when you use this to argue as a strength for the theory of relativity you end up with: The theory of relativity is only as reliable as the theory of relativity.
Karma Clown
To perform the experiment, numerous (probably several thousand) measurements are taken, but due to imprecision in the process of taking the measurements (imperfect measuring equipment, human error, etc) you get a variety of results. These answers could vary from well below c to well above it. If Einstein was right and nothing propogates faster than c, the higher results could only be attributed to imprecise measuremements, but you can't throw those measurements out if you are trying to be objective.
At the end of the process, you have something vaguely resembling a normal bell curve, where the height of the curve at a point along the x axis (velocity) is a measurement of the relative frequency with which that speed of gravity was obtained as a measurement. The total area under the curve will be exactly 1. In many cases, the curve may not be symmetric, but for an experiment such as this, you are unlikely to obtain an assymetric curve (Central limit theorem of statistics, or some such thing). A line right down the middle of the curve shows the measured average result (.95c).
A confidence interval is then picked (it is a shame that this interval is not mentioned in the article, but it is almost assuredly at least 95%, probably even 99%, or 99.9%). This percentage is converted to decimal (95%=.95, 99%=.99, etc), and a symmetric region around the average score with that area is blocked off. This blocked off area has a minimum X component of .7125c, and a maximum X component of 1.1875c, the difference between each of these and the average measured velocity being .2375c, which is 25% of .95c.
And that's where the 25% margin of error comes from -- for their desired level of confidence, the variance in measured results was off by no more than 25% of the value that was actually obtained as the mean.
Since the value of 'c' lies WELL within the bounds of the margin of error of the experiment, and pre-existing theories support the speed of gravity being c, this experiment supports those theories. It is important to note that this experiment did not prove anything, it only failed to disprove that the speed of gravity is anything other than something very close to c.
File under 'M' for 'Manic ranting'
If the gravity is limited to propagating at the speed of light, then consider a pair of neutron stars closely orbiting each other at, say, 1/3 C. Each would be pulled by gravity in the direction that the other used to be, and the differential between the direction of the pull of gravity and the current position of the object would be around 2/3 of a radian. How can this work with the conservation of mass-energy? Wouldn't that just make them spin faster and faster? Wouldn't limiting gravity to the speed of light destroy the reciprocity of forces, especially with respect to torque?
Repeal the DMCA!
Ahh right, anvils from Acme Anvil Company ... like in the Roadrunner cartoons.
-kgj
Well, except that in the initial design, at least, they used an intermediate stage to transfer the momentum from the radiation pressure (generated by a conventional fission bomb)...they use the radiation to ablate the outer surface of a cylinder of U-238 (natural uranium) surrounding the deuturium/tritium to use the uranium to compress it, which also trips an initiator placed with some U-235 centered in the center of the deuturium, causing it to fission, which creates two massive pressure waves, an incoming and outgoing, that compresses the deuturium mightily. This ignites fusion in it, which, in turn, releases enough fast neutrons to ignite fission in the normally unfissionable U-238 that surrounds it. The fissioning of U-238 actually produces most of the yield of this device, "Mike", which was about a megaton. Quite an intricate piece of work, really.
Now, what did this have to do with this discussion again? Oh, yeah, the momentum of photons. I guess it's marginally ontopic. (Please forgive me, I just finished reading about the development of the H-bomb and couldn't keep from showing off the neato stuff I just learned.)
Anywways, that's more or less how my high school science teacher explained it.
File under 'M' for 'Manic ranting'
What, though, if you use one as a qubit in a quantum computer? Something akin to how a quantum fast Forier (sp?) transform is used in Shor's algorithm to boost the probability that the final, classical read operation will produce a factor of the input.
If you can shift the wavefunction's state vector at all then it would seem that you can send information with some nonzero probability faster than light. As long as your ECC has greater corrective abilities than the probability of corruption, why isn't this an FTL information conduit?
Oh, though there still remains the problem of getting the entangled qubits to the ends of the communication channel... well, presumably you could do that at 2c by putting the transmitter in the middle.
--Knots;
Anarchy$ dd if=/dev/random of=~/.signature bs=120 count=1
Then you'll really like the part where the rocket launches up, visually less than FTL, and the sun explodes in about 15 seconds... instead of the 6-12 minutes one might expect, even *at* lightspeed.
Strange, 20 years ago I was taught other people had experimental evidence agreeing with a prediction that the effects of gravity move at light speed:
In 1882 Simon Newcomb observed an excessive perturbation in precession of the orbit of mercury, to the tune of 43 seconds of arc per century. In 1915, Albert Einstein showed this could be explained by the propogation of gravitic wave effects at the speed of light...
But thanks for playing.....
Energy, as far as we know, does not generate gravity (perhaps it generates the elusive dark energy? well thats just idle speculation...don't take my word on it). Without gravity, it would not collapse in on itself. Even if it did have gravity, it most certainly would not be a 'black hole' as we think of them now.
Black holes as we know of them now are stages in atomic collapse - right on past neutron degeneracy into the realm of the currently unknown. Since photons have nothing in common with atomic particles, it definately wouldn't be a black hole.
-
"Remember the Unified Field Theory? Well, forget it. Physicists have pretty much thrown in the towel on unifying gravity with the other elemental forces, so now we have the Standard Model, which says that everything works together in intricate harmony except gravity, which is on holiday in Tasmania and need not concern us further."
- Jon Carroll on the Higgs Boson
Nerd: Derogatory term typically directed at anybody with a lower Slashdot ID than you.
Imagine that you wanted to shine a laser on the Sun from the Earth's surface. Where would you point it considering that it takes 8 1/2 minutes for the light to travel from the Earth to the Sun? Why, you'd point it right at the Sun, of course. The Sun isn't moving.
So basically you're missing [2. ???] in order to reach [3. Profit]. Welcome to the club.
RMN
~~~
The Taylor and Hulse binary pulsar experiments (1993 Nobel Prize) which found indirect evidence for gravitational waves, also found indirect evidence for the speed of those waves -- the speed of light, to within 1%. The results being discussed here on Slashdot are merely a more recent, and less accurate, indirect measurement. Direct measurement will have to wait until the direct detection of gravitational waves (by LIGO or other experiments), when we can actually measure how long it takes a change in the gravitational field to propagate from one observatory to another.
That is not what he's saying. There's no such thing as free energy. It has to come from somewhere (maybe you can get enery out of nowhere but then you also get some anti-energy, and would have a lot of trouble keeping them apart).
It is possible to convert matter into energy with great eficiency. Fireflies do it all the time. With a bit of work, it would probably even be possible to convert all matter into pure energy. The main problem would be converting that energy back to exactly the same matter that it originally was. Probably, the only way to do it would be to send extra energy with information about the original matter's properties.
But the whole process is a bit silly.
If you have the technology to create the matter you want (from "raw" energy), there's no need to convert the original matter to energy in the first place. This would be a bit like converting your hard disk into energy so that it could be sent over the network wires and rebuilt at the other end. It's simpler to transfer just the information necessary to reconstruct the disk, and when the (perfect) copy has been created, you destroy the original one (or keep it, if you prefer). The two problems here are a) how do you determine the exact structure of the original disk and b) how to you build a new disc that matches that structure perfectly. It's easy when you're dealing with abstract entities such as bits and sectors, but not when you need every single particle to match the original one.
I suspect we (humans) will get there, eventually. But I doubt it'll be before Duke Nukem Forever and Team Fortress 2 are actually released.
RMN
~~~
Looks like it's back to the good ol' entangled particles, then.
RMN
~~~
Yes, relative speed between the objects also effects time, I'm not saying gravity is the only effect going on, but know that Lorentz Space-Time is a /simplification/, The lack of gravity isnt saying "Gravity has no effect here" it's saying "Gravity would needlessly complicate this equation".
What is important to note is that just as a complete lack of motion would negate the need to define time, a complete lack of gravity would negate the need- as far as the universe is concerned, to define space. Gravity's distortion of space is what defines it. What does this have to do with anything? Without a definition of space, there is no way to define motion- motion isnt occuring. This means that suddenly Lorentz Space-Time doesnt work either.
Maybe the reason there's so many posts about this that need your "correction" is that, well, they are right?
-- 'The' Lord and Master Bitman On High, Master Of All
"You can't go faster than the speed of light."
"Of course not. That's why scientists changed the speed of light in 2208."
If Gravity's speed is equal to that of the speed of Light, then how do you explain the pull descrepencies between blackholes and low graivty environments? Go to the moon, you'll notice that the gravitational pull there is much lower than that of Earth's. And Earth's is far far less then a blackhole's gravitational pull.
:)
So how can one say that Gravity's pull is as fast as the speed of Light when Gravity itself doesn't stay constant in different environments? I never heard light not traveling the "speed of light" so it's a bit confusing.
Ao, from what I gather, blackholes have so much gravitational pull that even light can't escape. Which suggests to me that Gravtiy is stronger than light. It would also suggest to me that gravity is is faster than light because of this. I don't have any sources to back this up, all of this is just my train of thought in words here.
I'd appreciate a simple-as-possible answer as to why my train of thinking is wrong, as i said, i'm no scientist, but this topic is interesting none the less
A Penny for my thoughts? Here's my two cents. I got ripped off!
Actually, you got the order wrong.
:).
Strong, Electromagnetic, Weak, Gravitational
This depends strongly on the distance you choose to measure the force at. At a distance of 1m, as opposed to 1e-15m, the original ordering may be correct.
And as long as we're being nit-picky, I'll point out that human-observable phenomena tend to be larger than 1e-15m
He didn't measure the speed of gravity from what I can tell. He measured other variables then used equations from the theory of relativity to determine the speed of gravity. If that's not what he did, then he wouldn't have needed the theory of relativity to calculate the speed of gravity (the article said he did).
"He reworked the equations of general relativity to express the gravitational field of a moving body in terms of its mass, velocity and the speed of gravity. If you could measure the gravitational field of Jupiter, while knowing its mass and velocity, you could work out the speed of gravity."
Read it carefully. He used mass, velocity, and the gravitational field to measure the speed of gravity. So he measured mass, velocity, and the gravitational pull of Jupiter. He used the theory of relativity then to calculate the speed of gravity. If he didn't, I would like to see the formula that he did use and know where he found it.
Karma Clown
If this experiment had come out differently, it would have been earth-shattering, and because it was cheap to do, it was therefore worth doing. But the way it did come out wasn't a "win" for Einstein, nor was it a "loss" for Einstein, it was simply almost completely uninformative.
It's like buying a lottery ticket when the jackpot is really large: the expected win from the lottery ticket is more than you paid for it, so it may be rational for you to participate, but if you don't win the jackpot, your modest investment is still lost.
Here is how you can use relativity and electricity to "explain" magnetism:
Say we have two wires separated by a certain distance, each carrying a parallel current. There will then be a magnetic force between the wires pulling them together. Where does it come from?
The actual current in the wire is traveling at a very low speed- about a few cm/sec. (Wires transmit electrical impulses very quickly, so usually people are surprised to learn that the actual electric current itself moves very slowly, slower than water through a pipe.)
Look at the situation from the perspective of a test charge, a conduction electron in one of the wires. Although individually it is bouncing around in random directions at thermal velocities, its drift velocity is that of the current in the wire- a few cm/sec, or 10^-13 of the speed of light. And of course, we all learn in school that relativity only becomes important at velocities approaching the speed of light!
From the perspective of this test charge, the negative conduction electrons in the other wire are standing still. But the positive charge in the wire is moving, and shrinking in the direction of its motion. What is its Lorentz length contraction? It's absurdly low, 1 part in 10^26. But this means the linear charge density of the positive charges becomes that much larger than that of the negative charges in the wire, and the test charge feels an attraction to it. How much? It must be tiny. But remember, the positive and negative charge densities in the wire are huge even though they are closely balanced. A gram of copper contains 1500 coulombs of conduction electrons. If you do the math you will find that the predicted electrical force expected from the Lorentz contraction is equal to the ordinary magnetic force we would normally expect between the wires! If the currents in the two wires are antiparallel instead of parallel, it turns into a repulsive force. So that is what magnetism "really is". Except not really, because you can also use magnetism to explain away electricity if no charges are present.
You could (recklessly) extend the analogy to gravity, and consider water in two parallel pipes. Running water "shrinks" in the direction of its motion, so the gravitational field surrounding a pipe increases when the water is running. Except here the pipes have to carry water in opposite directions for this force between them to increase. So you would expect gravimagentism to work in a way that's opposite to how magnetism behaves.
French physicist Alain Aspect performed this experiment in 1982, confirming Bell's Theorem ( which in 1964 proved mathmatically that the EPR thought experiment refuting predictions of quantum theory was, in fact, what DOES happen).
The experiment has not only been repeatedly confirmed, but has been done so at greater and greater distances. I believe they're now up to a seperation of 15 km.
Anyone who wants to understand this stuff should read Nick Herbert's book "Quantum Reality." It is the *ONLY* "popular" book that explains quantum theory properly. Let me repeat that, it is the *ONLY* popular book that explains quantum theory properly, so put that copy of "Alice in Quantumland" back on the shelf where it belongs.
For anyone who wants to understand the differences between, and attempts to integrate quantum theory and general relativity Steven Weinberg's "Dreams of a Final Theory" is the clear choice.
Yes, I am a physicist, and no, I will not fix your Mr. Fusion.
KFG
Here's what bugs me about "extra dimensions rolled up really small".
If you turn and go in that Nth direction, any distance you go just carries you all the way around the universe in that direction and deposits you back where you are.
So how can they be said to have "dimension" when nothing that traverses them gets anywhere?
--Blair
The mass of photons is very real. Try this experiment, which a professor did at one of my Engineering Physics classes:
Take a relatively large gong. Make sure it is reasonably well polished.
Next, take a professional-class camera flash and set the intensity to "fry".
Third, fire the flash at the gong. As the photons bounce off the (polished) gong, it will resound as if having been struck with a solid object.
This was a very awakening demonstration to me...
The information you gain from an experiment is related to the change in the probabilities you assign to different hypotheses. In particular, what that means is that, unless you have a plausible alternative hypothesis, experiments that agree with your hypothesis tell you essentially nothing.
Physicists regularly disregard this simple principle; they pick one hypothesis, elevate it to dogma, and then carry out lots of experiments. And when everything is said and done, they say "hey, see, the hypothesis survived thousands of experimental tests". But none of those tests may have tested against a logically plausible (or possible) hypothesis, or the tests may not have been independent of each other.
More specifically, unless you can come up with a logically consistent alternative to GR, something that makes experimentally testable predictions, there isn't really much point in spending a lot of time and money on experiments. Shots in the dark like this one are only worth it if they are cheap (as this one was), but when the result is as expected, you didn't learn anything from it.
It is actually possible for, say, an electron to move in water faster than light moves in water. In addition, speed of light in water depends on the wavelength. It's hard to tell what happens with the speed of gravity.
Am i the only one that sees an possible selection effect error in this so called discovery? The researchers apparently were able to express General Relativity in terms of gravitation field, mass, velocity and the speed of gravity. They then used this formula to calculate the speed of gravity and unsuprisingly it came out as they expected. Why unsuprisingly? Well they are using as the basis of their proof the very thing they're trying to prove! If General Relativity is wrong in terms of the speed of gravity, then the formula that was used to calculate the speed of gravity was flawed and the result is invalid. Or to put it another way, if General Relativity is wrong, General Relativity is wrong. This statement is clearly useless and means that the experiment proves nothing.
You can't win Darth. If you mod me down, I shall become more powerful than you could possibly imagine
Gravtiy is stronger than light. It would also suggest to me that gravity is is faster than light
Well, it doesn't suggest that to me.
My Karma: ran over your Dogma
StrawberryFrog
Kopeikin's results:
0 links/press/ SOG-Kopeikin.asp
http://xxx.lanl.gov/abs/gr-qc/0212121
And already one harsh criticism by one of his opponents:
http://metaresearch.org/media%20and%2
Unfortunately I could not find Asada's comments on this. As one of the creators of the theory of brane worlds, it would be very interesting to see what he thinks about this.
"How many fucking GR books have you read."
uh, 4, I think [Ones which talk about concepts, not which write out equations]. Does that make me good or something? Does how many books I've read have some meaning?
"False. Gravity's distortion of space does not define space, it defines the distortion of space. There is plenty of motion that has nothing to do with gravity. You could have photons traveling through empty space - motion without gravity.
Yes, motion which does not involve gravity, but what points are they travelling between? What immitted them? Just because something is so trivial that you dont need to bother factoring it in to get an understanding of most situations, doesnt mean that it has absolutely no effect. If the points they were imitted from are of very high mass, space is distorted so that they are farther apart [space has been stetched, 4 dimensionally. Most writings on the subject only mention the bending of space, ignoring that all points in the universe still line up], reduce that mass and the distortion lessens, making them closer together. Eliminate it completely and, no more distance between them[This is of course talking as if they're the only two masses in the universe, and so is hard to explain the same way as distortion is normally explained- showing the bending of a grid which is already there.]
Like it or not, You're stuck in a bigass cluster of galaxies, surrounded eternally by gravity. You say I could have photons travelling through empty space, I say you dont get to have completely empty space. Entirely self-contained space with no mass not only doesnt exist, but of course has no reason to, either.
False. Without gravity you have Lorentz space time. Quantum Mechanics works without any gravity at all!
quantum mechanics has that wonderful advantage of only working on scales to which normal physics don't apply. Small as photons are, I dont think they had to factor in too much quantum-scale reasoning to figure out the effects of Jupiter on them.
False, Lorentz space time is the _solution_ to Einstein's field equation when there is zero stress-energy and therefore no gravity. When there is no gravity, you end up with Special Relativity. If you didn't, then GR would be suspect of being incorrect.
GR Suspect of being incorrect? Unheard of! But seriously, A lack of detailed understanding of Lorentz space time prevents me from giving a meaningful responce to that. I just thought that "..then GR would be suspect of being incorrect." was a pretty funny retort to anything. As I understand it though, [Net fields == 0] != [no fields].
I'm never posting on this website again.
Well that's nice, but want to finish this conversation first? I think that's the point of discussion- the free exchange of ignorance, some of which gets lost in the transfer.
-- 'The' Lord and Master Bitman On High, Master Of All
Gravity is itself the warping of space. The best way to explain is by imagining a 2 dimensional world instead of a 3 dimensional world (spacial dimensions). Imagine a 2-D surface like the top of a soft bed. Objects on the bed that are 3D are simply 2D objects with mass (gravity field). Place a bowling ball in the middle of the bed, and it will warp the surface of the bed into another 3rd dimension (down = force of gravity in this universe). Anything nearby that bowling ball on the bed will be drawn towards the bowling ball (gravity in 2D) if it is nearby. Assume you were to roll a ball in a straight line across the bed, and it came across the pit in the bed made by the bowling ball... the ball's path would curve due to being near the bowling ball... this is what happens to light usually near gravity. Light bends, but it THINKS it's going in a straight line b/c it is space itself that is curved (bed's surface). Imagine a ball travelling in a circle around the bowling ball within the pit formed by the bowling ball on the bed. If it's located at a very specific point, travelling with enough speed, the ball will remain spinning in a circle around the bowling ball forever (assuming no friction). This is how planets stay in orbit and how light can become trapped at the event horizon of a black hole. Many things that are closer or not traveling at the correct speed and direction will be sucked in.
Take this analogy and think about it in our 3D world, and you'll see that gravity is another dimension in which space itself is warped. The "speed" of the warping of space is simply how quickly a change in gravity would affect objects and light nearby. Theoretically, the only known way to shift gravity is to shift the mass of an object, and since matter and energy are restricted to the speed of light, gravity should also be limited to the speed of light. Also, the warping of light from an outside source by jupiter's mass (gravity), should not instantaneously warp the light, but warp it at the speed of light as well.
In case anyone is interested, you can find an abstract link to the original paper that predicts the quasar deflection caused the Sept 8th close approach, here. The paper was published in the Astrophysical Journal in 2001 by S. M. Kopeikin. Interestingly, this theory paper has listed only two citations but the citation rate is sure to climb now that the observations have been made.
Flintstones (Hanna Barbera): Sep 30 1960 (ABC)
Road-runner (Warner Bros.): 1949
I wonder how your CRT works, then. Electrons hitting phosphors at 2 meters per hour? This is bright.
Your name doesn't happen to be Dan Bowen, does it?
What's this Submit thingy do?
Anyway, it's true that just igniting some nuclear fuel into fusion isn't that hugely hard, assuming that you have some tritium, not just deuturium, around. But you don't get that much from it compared to the fission bomb you've exploded to burn that small amount of fuel. In regards to power plants, of course using the heat of the core of a fission explosion is not an option for initiating fusion. And all our current technologies currently use about as much energy to initiate and contain fusion in a fuel than they are to usefully extract from it. The vast gulf seperating fission from fusion power is that once you understand the neutron-capturing cross-sections of various isotopes, cobble together a sufficient mass of an approriate fuel, and find a moderator (and moderator arrangement) to go with it, the actual physical, engineering complexity of the reactor is minimal. You could build one by hand, which is essentially what Fermi did. You can control one by winching a control rod into and out of a pile. In contrast, the fusion reaction is very different in this context and an implementation and control mechaninism is fiendishly complex. I suppose that in a way your teacher was right, in the sense that a fission reactor is very, very different from a bomb; while a fusion reactor must by necessity in some qualitative sense be pretty similar to a fusion bomb.
that tree will have 95 more rings before Sonny's copyrights expire.
:)
I doubt it. Chuckle
-
- - You can't take something off the Internet! That's like trying to take pee out of a swimming pool.
I wouldn't take their word for it.
This paper gives a good case for gravity traveling faster than light and I'm pretty sure all the working Newtonian gravity calculations assume instantaneous gravity:
"Standard experimental techniques exist to determine the propagation speed of forces. When we apply these techniques to gravity, they all yield propagation speeds too great to measure, substantially faster than lightspeed. This is because gravity, in contrast to light, has no detectable aberration or propagation delay for its action, even for cases (such as binary pulsars) where sources of gravity accelerate significantly during the light time from source to target"
OddManIn: A Game of guns and game theory.
Maybe light is traveling at the speed of gravity instead.
When I first heard about this I went and dug up some articles on google. One argued from indirect evidence that the speed of gravity >= 2 * 10^10 * c. (man, I wish I everyone had MathML...). This meant that a gravity drive could theoretically go faster than c. Soooo... I'm wondering if the whole gravity drive thing is bunk now.
-l
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It's much more likely the ringing comes from the air right next to the polished gong surface suddenly heating up.
There's a similar confusion about what drives those "solar radiometer" things - you know, a little black-and-white paddlewheel inside an evacuated glass ball that spins when you shine a light on it? People often say the reason they run is photon momentum, when the actual explanation is that the black sides of the paddles are hotter than the white sides, so when the few gas molecules left inside the ball hit the paddles, they leave the black sides going faster than the white sides.
The proof of this is the direction the paddlewheel turns - it turns white-side-first, and a photon-mass explanation would have the paddle turning black-side-first. If you put a paddlewheel inside a REAL hard vacuum, with a REAL low friction bearing, and REALLY isplate it from outside vibration, it turns the right way. See here for a more coherent and complete explanation.
To a Lisp hacker, XML is S-expressions in drag.
So then does "anti-mass" (ie anti-matter) experience anti-gravity? Would anti-matter repel other anti-matter or repel matter? Is this why we don't get much anti-matter casually passing by?
End of Line.
After all, the Newtonian model assumes infinite speed of propagation for gravity. So, limiting it to something finite, and within spitting distance of c, does accomplish something significant.
Now, if they had found a speed between 1.1 c and 1.4 c, physicists around the world would be racing to replicate the result. If it held up, that 30 Hz thumping you hear in the background would be Albert Einstein, spinning in his grave...
To a Lisp hacker, XML is S-expressions in drag.
I mean, there are so many astronometric techniques that involve measuring things by inference using gravitational influence.
But now, according to this nothing is orbiting the center of mass of a system, it's orbitting where that center of mass WAS (time) ago. And the center of mass of a system isn't between to gravitational points, it's between where they were (time).
What impact does this have on the age of the universe calculations or the rate of cosmic expansion, since the distant quasars etc that we're detecting at the far limit of our instruments are trailing their gravitational effects like a wake?
So what happens if two gravitational sources are travelling at significant fractions of the speed of light, in parallel? Does D=.5AT^2 then become a sliding scale, dependent on the (absolute/relative) velocities of their gravitational centers?
I guess it makes logical sense to say that gravity has speed, but I see that it would complicate a lot of things not to simply assume it was instantaneous.
-Styopa
You must mean The Coyote & Roadrunner!
</OFFTOPIC>
Can I get an eye poke?
Dog House Forum
186,000 Miles Per Second or 300,000 Kilometers Per Second, take your pick.
Can I get an eye poke?
Dog House Forum
I thought that the speed of light was recently found to not be a constant, and that this would imply that maybe the speed of gravity isn't either. Could they be speaking loosely here, or maybe I misunderstood the "speed-of-light-not-constant" discovery also?
The "cue the foo posts in 3, 2, 1..." posts will commence with no subsequent foo posts in 3, 2, 1...
There was another poster that also claimed this would have been due to the air heating up near the gong.
However, this professor continued his demonstration with sooting the gong heavily (taking it from polished to near-black), and then firing the flash again. The sound was significantly softer, noticable by all attendees (around 120), and he explained this by the photon package having been absorbed instead of bouncing (the gong only got half the impulse from before).
In a scenario where heat was the cause of the sound, sooting the gong would have caused a significantly louder sound as the light was absorbed, instead of (as happened) as softer one.
Ok, does this mean that the classic sci-fi "warp drive", where a black hole is projected in front of the ship, which accelerates toward it, which moves the projected hole forward etc, etc, is not possible?
(Makeing the assumption, of course, that it is possible to generate gravity other than the old-fashioned way.)
grnbrg
What if gravity has different properties from a long way away, such as intergalactic distances?
I've often wondered lately if perhaps gravity is both a repulsive and an attractive force. For local (i.e. interstellar) distances, the attractive force prevails. But for really vast (intergalactic) distances, it might act as a repulsive force. This could partly explain why the galaxies are accelerating away from each other.
Physicists don't have much of an idea what dark energy is... maybe it's just gravity, and Newton's law needs an amendment.
I've never heard this idea proposed, but it would make a certain kind of sense to me if it turned out to be the case.
WWJD? JWRTFA!
If I remember correctly, Bell's theorem showed conclusively that information can be transmitted instantaneously (independent of the frame of reference) via interactions with particle pairs.
Bell's theorem evolved from experiments by Einstien, Podolsky, and Rosen IIRC.
If the gong is reflective, the air near it gets heated both by the incoming light and by the reflected light. If the gong is sooted, only the incoming light heats the air.
At least, this seems logical to me. A way to test it would be to put a vibration sensor on the gong, and try it both in air, and in a vacuum. If you're right, the sensor should read the same, if I'm right the impact in vacuum should be much less.
To a Lisp hacker, XML is S-expressions in drag.
Electromagnetic
Weak
Gravitational
There is no strong force. It's a myth. Just like Neutrons are a myth. No, I'm not joking. Anytime you extract a neutron from an atom, it breaks into a proton and an electron (hydrogen). A Neutron is not a true particle, it's simply a compressed proton and electron. Although scientists say it has the same mass as a proton, it actually is a proton with an electron paired with it (electrons have a very small mass... so small, in fact, that quantum physicists usually say it has no mass) The "strong" force is the force atomic physicists had to invent in order to explain how protons and neutrons would sit together so tightly packed while the protons repelled each other (and the neutrons simply needed a reason to be stuck next to anything at all). The truth is, electrons exist at the center of an atom holding protons together. They form shells which link protons and bind them tightly. This cancels out the positive charge of many (thus the many so-called neutrons), and leaves many protons unpaired within the nucleus which gives the nucleus a net positive charge allowing electrons to orbit the nucleus.
Ever noticed that you won't find any nuclei other than hydrogen without a neutron??? Noticed that the larger the atom, the higher the neutron to proton ratio?? The strong force is supposed to be exactly 100 times stronger than the electromagnetic force, which would allow for nuclei of atoms to reach about 100 protons, thus those beyond that are highly radioactive. (means that once there are 100 positively charged protons, their repelling forces would overcome the strong force and shoot them out of the atom). BUT, the best model of atomic nuclei structure shows rings of electrons supporting ever-larger numbers of protons, thus there is no strong force needed. The positive protons are cancelled out by negative electrons, and thus a spherical crystal-lattice type structure is created within the Atom's nucleus. The unusual shape of this crystal only allows about 300 or so protons within the nucleus before the crystal becomes too densely packed and unorganized that it's insanely radio-active. There is a theory that if the structure were re-organized, there could be an island of stability beyond that point, however, I seriously doubt it. Wow... wouldn't it be awesome to have a noble solid??? *grins*
Energy released in matter/antimatter anhilation:
E=m(matter)c^2 + m(antimatter)c^2
Thus, with equal mass pairs - positron/electron or proton/anti-proton:
E=2mc^2
If antimatter had antimass then the equation would be:
E=mc^2-mc^2=0 and NO energy would be released.
Again, antimatter has mass, not anti-mass.
-T
I do think there are a few too many conservation laws being broken there.
You actually agree with the premise that antimatter repulses matter?
Antimatter has _mass_. Not anti-mass, not negative-mass.
Additionally, even if there were some magical uber-repulsor like grandparent claims, that still wouldn't accelerate you past c - force required to accelerate increases to infinity as you approach c. Thus, no passing light speed unless you have a force able to provide infinite acceleration. In which case, you're smoking crack.
-T
There is no strong force. It's a myth. Just like Neutrons are a myth. No, I'm not joking. Anytime you extract a neutron from an atom, it breaks into a proton and an electron (hydrogen). A Neutron is not a true particle, it's simply a compressed proton and electron.
First of all, you're still going to have an interesting time explaining how all of those nice, positively-charged protons are bound into an incredibly tiny space without the strong force holding them together.
Secondly, the production and decay of neutrons is mediated by the weak force, not the strong force.
Thirdly, your model fails to explain mesons and the zoo of other particles that can be produced even in relatively low-energy accelerators, while the quark model explains it nicely.
Protons become neutrons when an electron and an "up" quark interact to produce a "down" quark and an electron neutrino. The inverse process - decay of neutrons into protons and electrons - happens when a "down" quark decays into an "up" quark, emitting an electron antineutrino and an electron.
The neutrino emitted during the decay has significant momentum. Its existence can be shown - and was originally inferred - by tracking the charged particles emitted when a neutron decays into a proton and an electron. In many cases, both of the charged particles are going in the same direction. To conserve momentum, something else had to be fired off in the opposite direction during the decay. That "something" is the neutrino. If a neutron was a bound proton/electron pair, there would be no third particle to explain the momentum discrepancy.
You're also overlooking the fact that a bound system has less energy than an unbound one. Which would mean that in your proposed scenario, _neutrons_ should be the stable nucleon, which is at odds with observations.
Or, you may have written that post as sarcasm. Either way, moderators have been falling for it.
The rest of your post is even sillier, so I'm not going to bother with it.
In summary, your proposed model is demonstrably incorrect.
No it was easy. It was done years ago in the H-bomb that you mention. Of course that doesn't work for a powerplant, but that wasn't the point being made. The point being made was the nuclear fusion was something that people had done before, just not in a controlled fashion.
The fact that coming up with a way to make a fusion bomb wasn't easy and obvious doesn't mean that making one now isn't.
The teacher in question was of course trying to be humourous. He wasn't claiming anything about fusion power being trivial. He was merely saying that nuclear fusion is something people have actually used in the past - as a bomb.
Of course he was a nuclear power nut too, but that's beside the point...
I think I understand why your teacher thinks he was saying something meaningful, and why you think he was saying something meaningful; but it was based upon a false evaluation of how "easy" it is to make a fusion bomb, and a wrong-headed sense that the supposed "ease" of inducing fusion with a fission bomb has anything to do with fusion power generation.
Another way to say what I'm trying to say is that there an implicit analogy being made between fission and fusion regarding bombs and power generation. That is, people seem to think that since the reactor came first and the bomb second in fission, that since we've already achieved the bomb in fusion that in some sense we "should" be most of the way to a reactor. But you can't compare fission and fusion in this way in this context, they're qualitatively different things.
Maybe I'm just picking nits. I'd probably like it much better if he was saying what he was trying to say in a different way. I feel like the way he said it gives a whole bunch of wrong impressions.
It wasn't meant to be meaningful, it was meant to be a joke. Do you have those where you come from?
You know things which intentionally misrepresent something, in order to make people smile.
The whole point is that the ease of fussion power is not the same as the ease inducing fusion with a fission bomb. That's what makes it a joke.
And that goes for the rest of the points you raise. It's meant to be wrong headed, it was a joke. I managed to understand that when the christian fundamentalist "learn evolution from the text books you swines" teacher said it, and I was only a teenager at the time...
Honestly, do people not make jokes where you come from?
I'm not claiming it's actually funny, but it is quite clearly a joke...
I quite liked it I must admit, since it played on a few levels. Making fun of the people who equate fission power with fission bombs, for example.
all reports indicate they are decades away from producing Nukes
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Huh? All reports indicate that they are a few months to a couple of years away from producing nukes.
Sigh. I think it's a good war. But that's based on knowing a hell of a lot more stuff than I can put into a posting.
But just because I'll fail is no excuse not to try:
1. Saddam IS so oppressive that we should go in and liberate the country. I know we're all too damn cynical these days to use words like "liberate" but that's the damn reality. Our grandparents weren't too sophisticated to believe that you can liberate a country, but were too damn "smart".
2. The middle east is a fucking hell hole. Saudi Arabia has 1/4 of all of the world's oil and for them it's fucking free, on tap. But the Saudi princes claim to be descendants of Sheikh Muhammad Ibn Abd Al-Wahhab the founder of an Islamist cult that teaches it is the duty of his followers to invade the entire earth, subjugate all infidels and convert by the sword. Guess what the Saudis spend their oil money on? Spreading the good word. That's why oil matters. The Saudis are our enemies, but whenever they raise the price of oil a little our economy completely tanks. We need enough independent sources of oil that we are no longer reliant on our enemies and can put them in their place.
3. In other ways I'll say it again, "the middle east is a fucking hell hole." It's very hard to describe what you'll read if you read Arab newspapers.
It's a constant stream of what, to western eyes, looks like nonsensical hatred and lies about the west, about Americans and about Isralies. Their sense of history is SO screwed, and they really don't consider non-mulsims to be human beings worthy of survival. I hate to bring up the big old German Fuerer again, but he is a hero over there - every now and then you can find an article moaning that it's too bad he didn't get to finish the holocaust.
Anyway the problem is this. Remember Soviet newpapers? They printed nothing but propaganda too, but there's a difference. No one believed Soviet propaganda, not even the folks back in Russia. They were too well educated and Soviet propaganda was dry, it didn't stir up passion.
Arab's are different. They are very poorly educated when they are educated at all (50% illiteracy) and their propaganda is pure passion. The mob wants blood and lots of it.
Despite all the oil, the regular people in the Arab world are very poor, mostly because they're governments are archaic and becase they've rejected everything the rest of the world has learned over the past couple of hundred years - it's absolutely beneath their dignity to learn anything from us non-muslim trash.
But their newspapers have a ready excuse for every failure. It's a conspiracy. They believe that the Jews (and to a lesser but significant extent, the Americans and other westerners) have stolen them blind. It can be funny. When a poorly constructed radio tower in Afganistan blows over in the wind, the authorities say Massad (Israeli intelligence) must have destroyed it. When the date crop in Saudi Arabia doesn't bring good money on the world market, it must be because the Israelis (who's crop is 1/100th the size) must have spitefully undercut their price.
The place is drowning in ignorance, foolishness, oppression, misery and unimaginable violence.
Oh the violence... I'll get to that in a second, but I want to finish my point.
* The people there are living in a closed society. It's not changing from within. They're stuck.
* They're under terrible oppression.
* Because of Militant Islam, the Suadis, Al Qa'eda etc. they're a danger to us. We need to mess with their society so that, in the eyes of 100 million Militant Mulsims and 400 million Militant Muslim sympathizers around the world, modernity, with 3 squares a day, freedom, tolerance, prosparity and peace look better than destroying all infidels for Allah. I know it sounds crazy, but they don't all believe that right now.
We need to shoehorn a good example into the middle east as soon as possible.
I don't know as much about Korea. On thing I keep hearing is that we can't fight on two fronts at once, so Korea gets a temporary pass.
I should write more but I've got to go...
Rocky J. Squirrel
Here's a very old article on why we are attacking Iraq.
The original is no longer available for free on Strategic Forcasting's web site (it costs $120/year to join these days and it's worth it if your rich). So here's a link to a usenet posting of it post
After eight months of searching I've only turned up four sane Arabs. Since I've included all of their web sites this will give you an unrealistic view that of the sanity of Arab society, but these have to go on any list of the best web sites on the Middle east.
Other good sites:
http://www.memri.org/index.html
(best selection of translations from the Arab press)
http://www.mideastweb.org/LessonofIraq.htm
(other articles by Mahamad Mosaad)
http://www.mideastweb.org/arabpeacenow.htm
http://www.mideastweb.org/Arabpeace.htm
http://www.mideastweb.org/nothinghappened.htm
http://www.mideastweb.org/onlythem.htm
http://www.danielpipes.org
http://www.amarji.org/index.htm
http://www.israelnationalnews.com/articles.php3?t
(this should be their translations of the arab press)
Tarek Heggy (Egyptian writer)
http://www.heggy.org
turn down your sound card before
going there
Ali Salem (an Egyptian writer and playwrite).
My favorite articles so far are at
http://www.meforum.org/pf.php?id=130
http://sol.spaceports.com/~melinks/site2/ali_sale
http://www.pbs.org/newshour/bb/terrorism/july-dec
You can also look up Arab newspapers with english translations on Google Web Directory under newspapers. There's one fake Saudi newspaper to look out for. The editor lives and writes in California if that tells you anything.
Nope, there's no jokes where I come from. I live in creationist country. No humor here.
And that's funny, because the teacher in question was a creationist of no small proportions...
Mmmm... irony as well...