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Hi,After having studied special relativity, I sometimes see things

  1. Jan 28, 2012 #1

    After having studied special relativity, I sometimes see things mention that physicists now interpret relativity to be the claim that information cannot travel faster than light. I am confused by this - I thought that no information faster than light was a consequence of special relativity, but often these articles sound as though physicists see this as one of the tenets (if not THE tenet) of special relativity.

    My efforts to find discussions about this in my textbooks, and online, have been to no avail. If this is how physicists *now* understand special relativity, I can't seem to find a discussion on that change of understanding. Take for example:
    http://curious.astro.cornell.edu/question.php?number=387 [Broken]
    She says, "You ask a good question, one whose answer lies in the subtle difference between expansion that is faster than the speed of light and the propagation of information that is faster than the speed of light. The latter is forbidden by fundamental physical laws, but the former is allowed; that is, as long as you are not transmitting any information (like a light pulse), you can make something happen at a speed that is faster than that of light"

    I find this odd, since I thought the inability to transmit information was a consequence of special relativity, but this almost sounds like it's a principle of it. You might say, "special relativity prohibits the transmission of information faster than light", and I'd agree. But these statements sound like one step further.

    If any of you have any thoughts on this, or even better a discussion on this change of understanding (if indeed there is one) somewhere in "the literature", I would much appreciate it.
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Jan 28, 2012 #2
    Re: Information

    If something is predicted by a theory and this prediction turns out to be incorrect, then the theory is also incorrect. SR predicts information cannot be transmitted faster than light. Putting more or less emphasis on the idea is of no consequence to the fact that it is predicted by the theory.
  4. Jan 28, 2012 #3


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    Re: Information

    The two principles are:
    1) The laws of physics are the same in all inertial reference frames
    2) The speed of light is the same in all inertial refernce frames

    The second refers to the speed of light, but doesn't explicitly say that no information can travel faster than it. So that can be considered derived from the two principles and considerations of causality.
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