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Big Bang and Simultaneity question

  1. Oct 5, 2006 #1
    I realise this question includes relativity, but I think it is more appropriate here than in that forum? [Tell me if I should cross-post it elsewhere; I'm new to this forum :)]

    I'm working on a paper based on reading material that doesn't address big bang cosmology directly, but rather focuses on relativity, with a lot of emphasis on special relativity and its influence on time and simultaneity. The question I'm working on is:
    "According to the currently accepted Big Bang Cosmology the universe is expanding uniformly. Hence there is no absolute rest but there is absolute simultaneity." Discuss.

    I don't want a direct answer of course, just a little help with my research... as far as I can make out special relativity alone doesn't allow for absolute rest or absolute simultaneity, but this is not in reference to the big bang. So does the Big Bang have a significant effect on relativity, or vice versa? I think I'm in danger of sidestepping the question, but I'm not sure how the two ideas are actually linked. As far as I can see, lack of absolute rest is confimed by BB theory, since the universe is expanding in every direction, and not away from any central point of reference, while I can address simultaneity by explaining a thought experiment along the lines of the train-and-platform scenario. However, am I missing something vital? Should I be looking at general relativity as well, or something else not in the reading?

    Thanks in advance.
  2. jcsd
  3. Oct 7, 2006 #2
    Take a look at Ned Wright's cosmology tutorial which explains what the expansion looks like when you choose different coordinate systems, and in particular different time coordinates.

    Personally, I think that absolute simultaneity appears in cosmology because people want to believe in absolute simultaneity rather than for any physical reason. See Cosmology, Special Relativity and the Milne Universe for more discussion of this.
  4. Oct 8, 2006 #3


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    The finite speed of light makes simultaneity a moot point in GR.
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