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Faster than light?

  1. Jul 4, 2005 #1
    I know light is the fastest thing in the universe. But what about forces, namely gravity, magnetism, strong and weak forces. Do these forces act instantaneously OR do they act as fast or slower than light, does the medium they are acting in matter or not?
     
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  3. Jul 4, 2005 #2

    dextercioby

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    Nothing is instantaneous, that's for sure. All fundamental forces are described by bosons, gravity, electromagnetism and strong interactions are described by massless bosons, which means that they propagate wih "c". The weak interaction is mediated by massive bosons, whose velocity is obviously less than "c".

    Daniel.
     
  4. Jul 4, 2005 #3

    James R

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    Are gluons massless?
     
  5. Jul 4, 2005 #4
    gluons are "massless", but i don't know what "massless" means. maybe it is more tricky than that.
     
  6. Jul 13, 2005 #5

    DaveC426913

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    They all operate at the speed of light.
     
  7. Jul 14, 2005 #6
    Can someone describe an experiment or simply give me a link where an experiment showed that these forces travel at the speed of light. (Does the medium the forces travel in matter?)
     
  8. Jul 15, 2005 #7
    Sometime back, when I was actively reading material on astrophysics, I came across a paper which shows the speed of gravity much greater than light. The idea is that if the speed of gravity is equal to that of light, by Poynting-Robertson effect, the earth would speed up and run away from the Sun. But no such evidences are perceived by the astronomists. The content of the paper seems plausible. It is worth reading http://www.metaresearch.org/cosmology/speed_of_gravity.asp

    I don't know of any papers, as I am no expert in Physics, which negate the above theory but I hope experts of this forum may suggest something.

    Regards,
     
  9. Jul 15, 2005 #8

    ZapperZ

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    Here's a hint: If this "paper" only exists at this website and no references have been made to it appearing in any peer-reviewed journal, the "plausibility" degree drops WAAAAAY down.

    Also, those people are called "astronomers", not "astronomists".

    Zz.
     
  10. Jul 15, 2005 #9
    OK, thanks for the correction. Can you let me know what is wrong with the paper? Not appearing in a peer reviewed journal may be one reason.
     
  11. Jul 15, 2005 #10

    ZapperZ

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    I will deal with JUST the first few lines in the abstract, which already contain something weird

    Where exactly are these measurements that "all yield propagation speeds too great to measure"? The speed of gravity requires the ability to measure gravity waves, either from a supernova, a binary star, etc.. i.e. something that is producing a fluctuating gravity as observed on earth. Now unless I've missed something, such gravitational waves have NOT been observed YET! LIGO still hasn't made any conclusive detection, and it is being upgraded further to be even more sensitive.

    The only valid attempt so far as showing such measure was done a couple of years ago [http://arxiv.org/abs/gr-qc/0206022]. However, even this is still controversial, and people like Clifford Will has shown that the calculation/model is flawed [http://wugrav.wustl.edu/people/CMW/SpeedofGravity.html]

    So judge for yourself.

    Zz.
     
  12. Jul 17, 2005 #11

    ZA

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    All known forces travel at the speed of light. All known particles travel at or under the speed of light. All massless particles travel at the speed of light. The neutrino, which is now thought to have mass, travels at the speed of light too. The existence of certain particles called "tachyons" have been theorized, which are supposed to have a minimas speed at the speed of light and maximum speed at infinity. They supposedly don't inetract with matter and get more massive as they get closer to the speed of light from the opposite direction of mater. However, they have never been observed and may turn out to be a mistake. There is one way of random information traveling faster than the speed of light called entanglement, which means that we can find out the spin of an electron at any distance from us immediately by observing it's partner electron.
     
  13. Jul 17, 2005 #12

    George Jones

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    A little background for interested readers. In late 2002, the measurement was performed by Fomalont and Kopeikin when a quasar passed behind Jupiter. Fomalont and Kopeikin claimed that this experiment showed that the speed of light and and the speed of gravity are the same. Cliffored Will disagreed, saying that Fomalont and Kopeikin's experiment didn't actually measure the speed of gravity.

    In general relativity, the speed of gravity and the speed of light are the same, so an alternative to general relativity is needed to even talk about a difference. Steve Carlip has written a nice, thoughtful paper on this. According to his analysis, the interpretation of what was measured depends on the which class of alternatives to general relativity is used.

    This is subtle stuff, and one of Carlip's conclusions is that for a certain class of models that have different speeds for gravity and light, measurements have yet to reach the sensitivity required to measure the difference.

    Regards,
    George
     
    Last edited: Aug 26, 2009
  14. Jul 17, 2005 #13

    Janus

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    Meta Research is run by Tom Van Flandern, who is not a reputable source when it comes to such matters.
     
  15. Jul 17, 2005 #14

    Chronos

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    In Newtonian gravity, the speed of gravity is infinite. Otherwise, planetary orbits would not be stable. Since we are here to have this discussion, we can safely conclude either the speed of gravity is infinite or the Newtonian theory of gravity is incorrect. We have not yet actually measured the speed of gravity [as noted by other posters], but we do know the Newtonian theory of gravity is incorrect. It has been replaced by the much better theory of gravity called general relativity.

    In Newtonian theory gravity is treated as a 'force'. In general relativity, gravity is treated as a field [technically speaking it is more precise to say gravity is the geometry of spacetime, but that needlessly complicates the explanation]. In a field, the attractive force exerted on a body is not directed squarely at the source of that field. It is instead offset by an amount that depends on both the velocity and position of the source and body being acted upon. This almost exactly cancels the effect of the apparent propogation delay predicted by Newtonian gravity. This nearly complete cancellation effect is directly predicted by the field equations.

    Now for the rest of the story: the field equations allow us to predict the slight propogation delay that is not cancelled out. When a body accelerates in a field, GR predicts it will radiate away a small amount of energy [i.e., gravity waves]. This would change the orbit of the body by a predictable amount. And the effect has been verified in the orbital decay of binary pulsars [which earned a Nobel prize]. The decaying orbit effect would not be observed if the speed of gravity was infinite. It was another stunning triumph for the much better [than Newtonian] theory of general relativity, and another resounding defeat for the meta-nonsense of Van Flandern.
     
  16. Jul 18, 2005 #15
    Thanks guys. Point well understood and I will look into the papers you suggested.
     
  17. Jul 18, 2005 #16
    Something more basic.

    I'm a novice at all this, and I have a (perhaps) basic question.

    If time slows as speed approaches the speed of light, shouldn't light (since it travels at the speed of light) get everywhere instantly (i.e. be infinitely fast)?

    One plausible bit of reasoning is as follows:

    1) To have infinite speed, a particle would have to have zero mass.
    2) A particle with zero mass would not exist.
    3) In order to exist, a photon has > zero mass, therefore travels at < infinite speed.

    If so, doesn't the "speed of light" actually measure something just less than a perfect trade-off between speed and time?

    Also, if 1), 2) and 3) are true, wouldn't this provide an easy way to measure the mass of a photon? Just calculate how much mass something would have to have to slow it down to the measured speed of light?

    Anyway, thanks for any thoughts or answers.

    SeaTea
     
  18. Aug 7, 2005 #17
    Would we be able to directly detect something moving faster than light or would it be invisible or "dark"? Might something moving faster than light be only detectable indirectly through an affect that cannot be explained?
     
  19. Aug 8, 2005 #18

    Danger

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    No... just very close to it.

    1) Incorrect. To have a speed equal to that of light in vacuum, a particle has to have zero mass.
    2) Incorrect. Mass is not a requirement for existence.
    3) Incorrect. A photon has zero mass and thus travels at the speed of light (and light, of course, is photons).

    We detect things moving faster than light every day. The trick is that it has to be through a refractive medium rather than vacuum. 'Cherenkov radiation', for example, is the blue glow that is seen in uranium storage pools and is caused by massive particles exceeding the speed of light in water.
     
    Last edited: Aug 8, 2005
  20. Oct 1, 2005 #19

    ZA

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    neutrino

    Are you sure the neutrino travels at under the speed of light? Everywhere I erad, it said it travels at the speed of light. So could you please give me your source for that? thanks.
     
  21. Oct 2, 2005 #20

    Danger

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    Sorry, ZA... I can't cite a specific source. It's just something that's been around for decades. The reason that neutrinos were originally thought to travel at c was because they were believed to be massless. Once the Russians hypothosized that they had something like a 3eV rest mass, and it was experimentally verified, then their speed is of necessity known to be less than c.
     
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