Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Communication with no time boundaries?

  1. Oct 11, 2008 #1
    Assuming a perfectly rigid pole stretching from the Moon to the Earth. Wouldn't pushing on one end be felt instantly at the other?
     
  2. jcsd
  3. Oct 11, 2008 #2

    Hootenanny

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    If perfectly rigid poles exists, then yes information could be transmitted instantly. However, perfectly rigid bodies are forbidden by Special Relativity.
     
  4. Oct 11, 2008 #3
    Hmmm. Thanks! How in particular does Special Relativity forbid perfectly rigid bodies?
     
  5. Oct 11, 2008 #4

    Hootenanny

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    SR forbids perfectly rigid bodies precisely because it violates the postulate that information cannot be transmitted faster than the speed of light.
     
  6. Oct 11, 2008 #5
    Information and matter are two different things. In a sense matter isn't moving anywhere. Its the communication between each particle?
     
  7. Oct 11, 2008 #6

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    What do you think holds the molecules in a material together? Electromagnetic forces, which is governed by SR. When you transmit any vibration in a material, that vibration is being transferred via such EM forces. So it cannot be faster than c. In fact, it is quite a bit slower because the molecules/atoms have masses.

    Zz.
     
  8. Oct 11, 2008 #7

    Hootenanny

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Information and matter are indeed two different things, but matter does move in this case. If you apply a force to a rod - it moves.
     
  9. Oct 11, 2008 #8

    f95toli

    User Avatar
    Science Advisor
    Gold Member

    If you push one end of the pole of length L the other end won't start to move until a time t=c/L later,where c is the speed of sound; which is much, much lower than the speed of light . Hence, it is not a very efficient way of transfering information.

    Example: the speed of sound in e.g. steel is about 4500 m/s, meaning if you push one end of a 1 km long steel pole the other end won't start to move until 1000/4500=0.2 seconds later.
     
  10. Oct 11, 2008 #9
    Says who? Oh how naive we are...."we know much, we understand little."

    New views of the universe as a quantum computer say information is the basic constituent of matter and energy...and anyway, information theory can be viewed as a more general theory of entropy...as usual, everything is linked in mysterious ways we so often fail to discern.

    Before Einstein, time and space were thought to be fixed, different, unrelated entities.....having little if anything to do with gravity...people would have laughed at the thought they are so intimately related before Einstein's insights.

    As nature increases entropy over time it also dissipates information....see DECODING THE UNIVERSE, Charles, Seife....also some views in Wikipedia...
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?