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If time slows down for an observer as velocity increases, then the earth is moving as fast as the speed of light away from objects at the edge of the observable universe. However when those objects emitted that light, the relative speed was less. So, with regard to the photons that left, would the local time dilation for a galaxy at the edge of the visible universe be faster than here on earth? By the time that light reaches us the earth is moving much faster and therefore slower through time.

How about the local time dilation at every point the photon passes through? Is all of this taken into consideration before saying that dark energy is ripping the universe apart?

Or is it possible that time is slowing down across the entire visible universe? Our visible universe is moving MUCH faster than speed of light away from whatever is 1 trillion light years from us. There is no reason to believe there isn't more stuff an infinite distance away right? So with that said, what is the universal baseline for time? How could there be one? We are completely stuck in time in relation to objects trillions of light years away from us. Or are we? What happens when the distance between points in space is accelerating faster than light? Do they go backwards in time relative to us? For that matter how do we know c (the speed of causality) is fixed? Can it be changing over time/space?

Qmechanic
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Bryan Mason
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    For the record, recessional velocity (due to the expansion of space) is not the same as proper velocity (having some kinetic energy). Only the latter experiences special relativistic effects. Also, while there is no actual universal basis for time, a good standard would be to use the comoving frame, which is the one where the background radiation of space looks the same in all directions. But not having an absolute basis for time means the universe's time can not be slowing everywhere, because there is no basis against which to compare and say "it is slower" – Jim Dec 17 '19 at 20:39
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    Furthermore, experiments show that the speed of light remains constant over time. Making c a constant in our models predicts the universe should look a certain way to us and we find it does indeed look that way. If you would next suggest that time is slowing and c is decreasing so that it looks the same as if c were constant and time wasn't slowing, then I'd point out that Occam's razor says that the most correct solution is usually the one that makes the fewest assumptions. A constant assumes less than having two things change in a way that looks like a constant – Jim Dec 17 '19 at 20:44
  • Possible duplicates https://physics.stackexchange.com/q/315038/2451 and links therein. – Qmechanic Jan 07 '20 at 09:13

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It's not meaningful to talk about changes in the speed of light over time. See Has the speed of light changed over time?

It's not meaningful to talk about gravitational time dilation in the context of a cosmological model. Gravitational time dilation is only a meaningful concept when we have a spacetime that can be described by a scalar potential.