# How does space time differ between galaxies? [duplicate]

Does the gravity wells differ enough between galaxies to have different speeds in space time? How much slower in space time would the biggest galaxy have compared to the Milky Way?

• Here's a similar question from the physics board where John Rennie does the math. physics.stackexchange.com/questions/161453/… Even with the largest galaxy the time dilation would be relatively (hehe) small, unless you're near a black hole, but that would be a localized effect not a property of the galaxy. – userLTK Feb 23 '18 at 4:32
• I mark this as a duplicate because the answers are basically the same for both questions. – Muze Feb 23 '18 at 22:04

Does the gravity wells differ enough between galaxies to have different speeds in space time ?

You are using these terms in a very confused way.

The gravitational field of an object depends on it's mass distribution. It is normally described as a potential field.

A gravitational field does not a have a speed that characterizes it, not do they have a speed through space-time (the field always propagates at the speed of light, regardless of source).

How much slower in space time would the biggest galaxy have compared to the Milky Way?

Keeping in mind that size has nothing to do with speed, note that are normally two aspects to the speed of an object relative to something else (important to remember that speeds are always relative to some other object that "defines" what is at rest and that this choice is arbitrary - that's the theory of relativity for you).

Galaxies can have a local speed due to e.g. motion within the local group like our own local group of galaxies. This aspect of motion is really just governed to "normal" gravitational effects.

On a much larger scale they can have an apparent motion due to the expansion of the universe. This part of motion is due to a large scale effect only explained by using general relativity and which only has an observable effect over cosmological distances.

The gravitational field of an object has no effect on it's relative motion due to the expansion of space-time, whereas it's gravitational field does affect the relative motion of objects local to it and hence their relative motion to that object.

• Really StephenG, it's just non-native English. OP is just asking "What's the time dilation in a galaxy" (Much as you might ask "What's the time dilation X meters from a black hole?!" or "What's the tiny time dilation on Venus' surface?", etc.) – Fattie Feb 23 '18 at 19:33
• Or ... what's the time dilation when it's Friday afternoon and we're all ready for work to end! :) :) – Fattie Feb 23 '18 at 19:34
• If you want to move you answer to the duplicate I will upvote it – Muze Feb 23 '18 at 22:04