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The nature of causality in special relativity (not faster than light travel)

  1. Dec 7, 2011 #1
    I am having trouble understanding how special relativity reconciles the concept of causality. In one frame of reference event A may be followed by event B, but in another frame of reference event B may occur before event A. In the first frame of reference an observer may claim that event A causes event B, but of course the second frame of reference will disagree. I am sure i am making a simple mistake here...

    Furthermore, how does special relativity deal with the concept of a big bang singularity? I am aware that general relativity is the domain of acceleration (thus inflation), but is it not possible for there to be a preferred frame of reference with respect to some big bang singularity qualifier? (I am aware that this is vague, but the fact that the universe was once a singularity troubles me with respect to the "no frame of reference preferred" result of special relativity).
  2. jcsd
  3. Dec 7, 2011 #2


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    When the order of two events is frame dependent, that implies they cannot be be causally connected. The fallacy of you statement is saying A caused B, or the reverse.

    A little more: such frame dependent order of events only occurs for events with spacelike separation, which means that neither can cause the other - they are said to be causally independent.

    As for the big bang, I am guessing you are picturing the big bang as occurring in some 'place' in a pre-existing space. This is not correct. Space itself expanded from the big bang. However, there is a sense that the big bang provides a preferred frame. Not in the sense of 'you must use it', nor in the sense that the laws of physics are simpler; but in the sense that you can locally detect your motion relative to the cosmic background radiation. If you see it as isotropic, you are a 'comoving' observer, moving with the expanding space without any extra motion.
  4. Dec 7, 2011 #3
    Thanks, i realise my mistake now! That was quite silly.
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