Originally Posted By: Bill S.
In an expanding Universe, why are Andromeda and the Milky Way moving closer together?

I think I've already indicated that I do not believe in the big bang/expanding universe theory.

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Considering the relativity of motion; is it possible to say if either galaxy is moving towards the other?

I don't see any difference between saying that it is moving toward us or we are moving toward it or we are moving toward each other.

I don't presently see any way of determining if Andromeda is moving relatively to a fundamental reference frame.

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Is there any other, larger, thing in the Universe that could be taken as a static F of R?

I agree that the CMBR provides a fundamental reference frame however detractors argue that the 'singularity' from which it is claimed the universe developed was moving when it exploded but for this to take place it would have to have been moving relatively to something yet their argument is that nothing existed prior to the 'explosion'.

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Do we know why Andromeda and the Milky Way are moving closer?

Gravitational attraction within the LG has to be the reason.

Agreed.

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Where does astronomy end and cosmology begin? Or is it the other way round?

Isn't the latter an extension of the former?