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What can be the speed of transmitting information?

  1. Nov 1, 2008 #1
    I wanted to clear my doubt that:-
    can speed of transmitting information be greater than speed of light?

    The thing which confuses me is:-
    If i want to transmit a signal to a place 1 light year away than for it
    let say i hv a 1 light yr long rigid rod and i push it for sending information..
    than my question is:-
    For a electromagnetic wave based signal transmitting system time must be 1 year to receive information?
    But if rod is pushed than at what speed the other end will be receiving transmitted signal?

    Is speed of transmitting information limited or infinite?
     
  2. jcsd
  3. Nov 1, 2008 #2

    Doc Al

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    Staff: Mentor

    The push would be transmitted at the speed of sound, much slower than the speed of light.

    The speed of information transmission (signaling) cannot be greater than the speed of light.
     
  4. Nov 1, 2008 #3
    Just to confirm, the tranmsmission of information (intelligence) IS limited by the speed of light, say electromagnetic waves in a vacuum, for example. While examples of superluminal, faster than light transmission, examples can be cited, such examples to not admit transmission of information. So far entanglement ,which appears to be instantaneous, does not permit transmission of information.
     
  5. Nov 1, 2008 #4
    Can we compare propagation of sound in a rod with a push?
    as both have different molecular motion one is to and fro at equilibrium and other is unidirectional.
    Is there any experiment done to differentiate?
     
    Last edited: Nov 1, 2008
  6. Nov 1, 2008 #5

    HallsofIvy

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    yes. we can. Your "pushing" the rod and expecting the other end of the rod to immediately move assumes a perfectly rigid rod. What that proves is that, in relativity, there is no such thing as a "perfectly rigid" rod.
     
  7. Nov 1, 2008 #6
    So this means that by no means in any 'real' material we cannot transmit signal greater than the speed of sound it supports..
     
  8. Nov 1, 2008 #7

    Doc Al

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    Right. Any mechanical disturbance will propagate along the rod at the speed of sound.

    More generally, no material object can move at light speed, so it cannot be used to transmit a signal faster than light speed.
     
  9. Nov 1, 2008 #8
    Thanx..:smile:
     
  10. Nov 1, 2008 #9

    rbj

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    even more generally, all of the fundamental actions; gravitation, electromagnetism, weak and strong nuclear forces, are believed to propagate at the same speed c (i think this is not so much a property of the specific "instantaneous" actions, but is more a property of space and time). because the electromagnetic action moves at c, the disturbance of the atoms of your "rigid" rod could not move any faster (and in fact moves more slowly since the speed of sound, which is faster for more rigid material, is slower than c.

    so, even if you were wagging a planet around to try to signal someone else that would detect the change in gravitational pull, that jerking of gravity would not reach the other guy any sooner than the light of you doing the same would reach him.
     
  11. Nov 2, 2008 #10
    Are you suggesting that W and Z bosons travel at the speed of light?
     
  12. Nov 2, 2008 #11
    Since the strong,weak and electromagnetic forces have been unified via Weinberg-Salaam, the answer should be buried in those equations....
     
  13. Nov 2, 2008 #12
    W and Z bosons have mass.
     
  14. Nov 2, 2008 #13
    well then I guess they DON'T propagate at "c"...

    how about strong force...do quarks have mass?? I guess so since they make up protons and neutrons??

    So are photons the only quanta that don't have mass...that don't interact with the Higgs field??
     
  15. Nov 2, 2008 #14
    The strong force carrier is called a gluon. A gluon, like a photon, is not supposed to have any mass.
     
  16. Nov 2, 2008 #15

    rbj

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    yah, well. it's relativity, not the Standard Model. i'm not sure what the force is in the weak interaction, anyway. the W and Z bosons appear to be the biproducts of a nuclear change (a down quark turning into an up quark with a W- boson getting spit out and that turning into an electron and anti-neutrino). so i thought these sorta unifying concepts of relativity weren't supposed to be compatible with the Standard Model anyway.
     
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