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

Information speed limit

  1. Dec 1, 2004 #1
    "Information cannot travel faster than c"
    "If information could travel faster than c, we would loose causality"
    Just wandering - who came up with these and why? In other words:
    1. Why can't information travel at some higher finite speed?
    2. Why would we loose causality in that case?

    Note that I'm posting here in the relativity forum, since I suspect this has much to do with relativity... Was this Einstein's idea?
  2. jcsd
  3. Dec 1, 2004 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    It's based on Special Relativity -- information travelling faster than c breaks cause an effect.

    The basic geometric cause of the paradox is this: If, in one reference frame, information travels from point A to point B, then there are other reference frames in which the same piece of information travels from point B to point A.

    That is, when information is transmitted faster than c, it is impossible to tell the difference between the source and the destination!

    With a little care, you can arrange fun paradoxes, such as FTL transmission of information that's "supposed" to from A to B then back to A, but it arrives back at A before it was ever sent! Thus it is said to violate causality -- it violates the "law" cause and effect.
  4. Dec 1, 2004 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    This may or may not answer your question, but this paper is barely 2 weeks old....


  5. Dec 1, 2004 #4
    information cannot travel faster then c because we would loose causality...This is a consequence of the special theory of relativity where c is postulated to be constant for all observers. This was an idea from Einstein.

    Loosing causlity is not allowed because this is not physical. It means that the consequence of some action can occur before the actual action... Something like you die before you are born...this is crazy talk, wouldn't you say???

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook