So the universe is expanding, and the distance between the earth and very distant galaxies is increasing due to this expansion. Does this mean that these distant galaxies are experiencing relativistic effects with respect to the earth (such as time dilation)?
I am confused about this, because it would seem that two points in space, neither of which have ever experienced acceleration of any kind, would still be moving apart solely due to the expansion of the universe. So one of them could be experiencing time dilation? If so, which one, and how could you tell?
Or does the increase in distance between the two points due to the expansion of the universe not count as velocity?
In: 0
“Time dilation” occurs between reference frames. A single object can’t “experience time dilation” without something to compare it to.
Yes, the expansion of the universe causes relative velocity between objects that causes time dilation, but both observers see the other as “slowing down”. The only way to actually “compare clocks” would be to be in the same place, which would require one of the objects to start accelerating towards the other.
>Or does the increase in distance between the two points due to the expansion of the universe not count as velocity?
It does. You will often hear answers that say meaningless things like “the objects aren’t moving, new space is being created between them”, but that’s the same thing. “Relative velocity” and “things getting further apart” are the same thing.
Latest Answers