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Can Milky Way and Andromeda collision reconcile with an Expanding Universe with galaxies spreading away from each other like "raisins in a loaf"? (lemmy.dbzer0.com)

submitted 5 months ago* (last edited 5 months ago) by [email protected] to c/[email protected]

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I understand that our local galaxy group is considered "gravitationally bound" and therefore exempt from the expansion from each other ((, but we don't seem to have other galaxies collected into their own "local groups" of gravitationally bound clusters, so are we saying we're somehow unique? Is there a trick of perception taking place?)) <---edit:this is wrong

I found this quote in the Wikipedia article on the Expansion of the universe.

While objects cannot move faster than light, this limitation applies only with respect to local reference frames and does not limit the recession rates of cosmologically distant objects.

It seems to me that if we can perceive at cosmological distance something that cannot exist, perhaps we are falsely observing an expanding universe. Maybe everything IS gravitationally bound and we're just seeing expansion because... Relativity?

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[–] [email protected] 10 points 5 months ago* (last edited 5 months ago) (7 children)

Dont we see other galaxy groups though? Im no astronomer, but I do recall the universe having some degree of structure above the scale of individual galaxies, with groups and clusters of them forming larger groups or filaments surrounding voids of space with fewer galaxies in them.

Edit: quick search in wikipedia brings up a list of a few groups and clusters known, of which the local group is merely one: https://en.wikipedia.org/wiki/List_of_galaxy_groups_and_clusters

[–] [email protected] 3 points 5 months ago* (last edited 5 months ago) (6 children)

You are so correct, I'm sorry for not checking myself. I'm not surprised I had errors, just that it was so quick and large.

So I guess the expanding universe is galaxy CLUSTERS moving away from each other? I don't feel like it's explained that way.

[–] [email protected] 5 points 5 months ago* (last edited 5 months ago) (1 children)

(Do note I'm not an astrophysicist, so this may be a bit wrong, but I think the main part of it is right.) Not exactly. Everything in the universe is constantly drifting away from everything else. The reason it is pretty much only visible at the scale of galactic clusters is that literally every force in the universe overpowers this expansion, unless the distances between the objects are truly absurd, in the range of millions or billions of light years.

[–] [email protected] 3 points 5 months ago

This! A nice additional detail is that the expansion is accellerated, so there will be some interesting things happening when the relative strength of the fundamental forces start competing with the expansion.

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