I am very new to the world of relativity, so the answer may be trivial, but to me measuring the age of the universe seems an impossibility due to there being no fixed frame of reference from which to measure it. I feel as though I understand the basic concept of how time dilates with velocity, and also with gravity, although I have no concept of how, or if the two are linked. Any help would be much appreciated, as I haven't found a well-explained answer anywhere.
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1What answers have you found? It would be easier to explain something you don't understand about them, than to post a whole new explanation. eg https://study.com/academy/lesson/how-to-calculate-the-age-of-the-universe.html – sammy gerbil Jan 07 '20 at 23:21
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1The answer by John Rennie to this question is probably what you are looking for. https://physics.stackexchange.com/questions/495821/does-the-age-of-the-universe-depend-on-the-way-it-is-defined – D. Halsey Jan 07 '20 at 23:29
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The age of the universe is defined, by convention, in a comoving reference frame. That is, a reference frame where the universe at large scales is isotropic. For example, where the cosmic microwave background radiation is the same temperature in all directions.
Dale
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The rest frame of the CMB is not just an example. Or do you know any other suitable frames? – my2cts Jan 08 '20 at 00:24
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1It was an example of isotropy. You could also measure isotropy in other ways. All measures of large scale isotropy should give you the same frame – Dale Jan 08 '20 at 01:57
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I believe you yourself have answered your question.
but to me measuring the age of the universe seems an impossibility due to there being no fixed frame of reference from which to measure it.
We measure the age of the universe w.r.t us. Even if our local time is dilated, even if our local time is affected by gravitational fields, whatever we measure is the age of the universe..
And I insist my point that the age of universe (a physically measurable quantity) may vary from place to place.
Do correct me if I am wrong.
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Your point is valid. However, in most parts of the universe, the time dilation due to speed or gravity are relatively small, compared to the error in our measurement of the age of the universe. Still, it's useful to avoid those variations, so we normally use the comoving time mentioned in Dale's answer. – PM 2Ring Jan 08 '20 at 08:40