# Is time absolute?

If I take a spaceship and park it near the event horizon of a black hole and then measure the age of the universe by observing SNe Ia, then travel back out to normal space (no gravitational forces, at rest with respect to CMB), will the dates agree? That is, if the measured age of the universe is 13.8 billion years near the event horizon, and it takes me 100 million years (proper time) to travel back out to normal space, will my new measurement of SNe Ia agree with a date of 13.8 + 0.1 = 13.9 billion years? If that is true, can we say that time is absolute (i.e. all observers will agree on the age of the universe when using SNe Ia when coordinate systems are normalized)?

• The age of the Universe that you measure this way is just an averaged over some class of intrinsic observers quantity with dimensions of time. No, time is not absolute, as is well-known from relativity theories. – Prof. Legolasov Nov 2 '16 at 13:51
• You are suggesting that the age of the universe depends on your reference frame. – Quarkly Nov 2 '16 at 13:56
• I am suggesting that it depends on my history, i.e. on the worldline along which I measure this age. There is no such thing as The age of the Universe, since the Universe is extended. Instead, each observer measures the passage of time as he ages with the Universe from the Big Bang. The age of the Universe is just an expected average over a particular class of observers. Note that I am not claiming to have answered your question completely, that's why this is just a comment. – Prof. Legolasov Nov 2 '16 at 14:00
• Just to clarify: when you measure the age, you approximate General Relativity by a particular solution (FLRW?). In terms of a particular solution it is indeed sensible to define how much time has passed since the beginning of time. However, this can only be considered an approximate quantity and it can not tell us something fundamental like whether time is absolute or not. You have to consider the whole theory for that, and GR is pretty unambiguous on this: no, time is not absolute. – Prof. Legolasov Nov 2 '16 at 14:08
• @AGML's answer is spot on. But I think, perhaps you are conflating some of the language surrounding the issue. When people say, 'age of the universe' they are generally referring to a specific frame of reference: comoving with the Hubble-flow. So you're basically asking, "Will everyone agree on the time Alice measures?" --- sure, because we can all convert to her reference frame. Each reference frame can still measure something different. – DilithiumMatrix Nov 2 '16 at 18:36