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Information transfer that is faster than c?

  1. Sep 17, 2010 #1
    If I were to have some material, that was rigid, and was also say, 300,000,000 metres long. If I were to poke it at one end, would another observer see an instantaneous response at the other end? Ie, would the information I put into one end of the material travel faster than the speed of light to the other end?

    I guess it woudln't be so easy. I assume that poking it counts as a sort of pressure wave that would have to be transferred through all the electrostatic processes along the way, which would be limited by c? Then I guess, can you argue that there is such thing as an incompressible material? (at least in regards to the force of my jabbing finger)
  2. jcsd
  3. Sep 17, 2010 #2


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    Correct, the electromagnetic processes have to carry the information the whole way, and no, by your previous thought process, you can't have an incompressible material.
  4. Sep 17, 2010 #3
    Alright then. So if we had the power to observe the material, would we see the side I poke move slightly, and then a sort of compression wave propogate through the material (like you could imagine a sound wave compressing air), warping the dimensions as it goes? Do you know if the speed of this wave has a speed that is constant, or is a consequence of the materials properties, like density I guess?
  5. Sep 17, 2010 #4


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    I believe it literally is a sound wave.
  6. Sep 17, 2010 #5


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    Yes. And the speed at which the wave propogates is the speed of sound in that material.
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