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I Has time always ticked the same?

  1. Feb 9, 2016 #1
    Hi all,
    I have a layman question, if I may.

    As you know better than I do, all sort of conclusions have been drawn from observations of the Doppler shift in light from distant objects: from the universe expansion, to the Big Bang, to the hypothesis of dark energy.

    My question is, has time always ticked at the same rate since the Big Bang? And, if not, what effect would that have on the conclusions drawn from Doppler measurements. (I.e., how would a wave's frequency be affected if it came from a distant region where time was ticking differently then.)

    Thanks!
     
  2. jcsd
  3. Feb 9, 2016 #2
    Wow... just the easy questions eh??!

    Time's a tricky one as it's hard to define it any other way than "what you measure with a clock" - and you'll be aware that two clocks will differ depending on gravity, acceleration, etc.

    However, there is a hypothesis that the speed of light has not always been constant throughout time - see wiki entry (and it wiki say's it's true, how could we possibly doubt it :-)
    https://en.wikipedia.org/wiki/Variable_speed_of_light
    http://www.dailygalaxy.com/my_weblo...n-the-early-universe-todays-most-popular.html
    https://www.newscientist.com/article/dn6092-speed-of-light-may-have-changed-recently/


    Regards
    Matt
     
  4. Feb 9, 2016 #3

    PeterDonis

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    This question isn't well-defined as you state it. There is no absolute meaning to "the rate at which time ticks".

    Yes, and none of those conclusions depend on any assumptions about "the rate at which time ticks". Cosmologists do quote times since the Big Bang, but those times are for a particular well-defined class of observers which are convenient for setting up cosmological coordinates; they are not absolute "time" values and they don't imply any assumptions about the "rate of ticking" of time.
     
  5. Feb 9, 2016 #4

    Chalnoth

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    Time is measured by clocks. You can only measure the rate at which one clock ticks by comparing that clock against a different clock. You can't directly compare two clocks at different times.

    So in the end, we just define the rate at which time passes to be the rate at which a clock measures time to pass.
     
  6. Feb 9, 2016 #5
    Perhaps there is no need for actual clocks. I wonder if you'd be able to make educated guesses about time slowing down, if all matter were closer to each other, as in the early universe.

    P.S.: By the way, thanks mgkii for the links, I'm barely starting to skim over them, but there's a lot of interesting material there.
     
  7. Feb 9, 2016 #6

    PeterDonis

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    Once again, "time slowing down" has no absolute meaning. So there's nothing to make guesses about, educated or otherwise.
     
  8. Feb 9, 2016 #7

    PeterDonis

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    None of these are reliable sources, although the Wikipedia article does link to some. In any case, the hypothesis of a varying fine structure constant (which is how the hypothesis should be phrased, since the fine structure constant is the dimensionless quantity involved), even if it turned out to be true (which it isn't to the best of our current knowledge), would not change the fact that "time slowing down" has no absolute meaning.
     
  9. Feb 9, 2016 #8

    PeterDonis

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    Once again, "time slowing down" has no absolute meaning.
     
  10. Feb 9, 2016 #9

    PeterDonis

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    The OP's question has been responded to sufficiently. Thread closed.
     
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