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Is age of universe adjusted for gravity?

  1. Nov 5, 2012 #1
    The estimated age of the universe is often stated to be about 13.7 billion years. But I've never seen any qualifiers on that age.

    We know that time passes slower the greater the gravity field you're in. Even the difference in gravity between the earth's surface and orbit is enough to cause crystal oscillators in satellites to keep the wrong time if they're not adjusted for it.

    And every spot in the early universe would have been much closer to a gravity source than many points are today.

    So when we read the age of the universe (or even of the solar system or earth), is that time adjusted for gravity? Is it hypothetically measured from some point outside any galaxy where gravity is minimal? Or does it take into account the proximity to mass that must have been true in the early universe?
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  3. Nov 5, 2012 #2


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    The uncertainty on all those time measurements is at least of the order of 0.1%, while gravitational time dilation is several orders of magnitude smaller (as we don't live on a neutron star or near a black hole). It can be measured with atomic clocks today, but we did not have them running 13.7 billion years ago.
  4. Nov 5, 2012 #3


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    The age of the universe is usually expressed in terms of clock time on earth. The gravitational correction is insignificant. For further discussion see http://www.physics.fsu.edu/users/ProsperH/AST3033/cosmology/ScaleFactor.htm [Broken]
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  5. Nov 5, 2012 #4


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    The age of the universe is strongly dependent on the value of the Hubble constant, which is not all that accurately known. Latest indications are that Ho may be revised upwards, e.g.


    "Applying the Spitzer calibration to the Key Project sample, we find a value of H0 = 74.3 with a systematic uncertainty of +/-2.1 (systematic) km/s/Mpc, corresponding to a 2.8% systematic uncertainty in the Hubble constant."

    Given the other parameter refinements mentioned in the report, the age may then come down to around 13.0±0.36 billion years.
  6. Nov 5, 2012 #5


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  7. Nov 5, 2012 #6
    This is interesting stuff.
    But I'm a little skeptical that the effect of gravity is fully accounted for in the early universe.

    Doesn't time slow to a crawl at the event horizon of a black hole? And yet all of the mass of all of the black holes plus all of the galaxies was very close together early on.

    This almost segues to my next question, but I'll ask it in a new thread.
  8. Nov 6, 2012 #7


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    You seem to be thinking that time would have run more slowly in the early universe. The problem with that is that you would have to say what it was running slowly relative to.

    When we say that time runs slowly near the event horizon of a black hole, we mean relative to time far away.

    BTW, I think the best evidence is that there were no black holes in the early universe. It's certainly true that the early universe was not perfectly uniform, although the near-perfect uniformity of the CMB shows that it was very nearly so. IIRC the variations are on the order of 1% or smaller. So there were certainly small local differences in the relative rate of time in the early universe. The figures people quote are for the average.
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