A little bit off topic, but how is the expansion of the universe affecting gravity?,
Ahmed Selim

It was covered just some days ago in Ask Ethan: Will the ‘Great Attractor’ defeat dark energy.

“The gravitational pull of these imperfections matters a great deal. When we look out at a galaxy like Andromeda, our closest neighbor, we see it some 2.5 million light years away. Based on the expansion of the Universe, it ought to be moving away from us. But the gravitational pull of the Milky Way on Andromeda — and of Andromeda back on us in the Milky Way — can defeat the expansion if these two galaxies are massive enough. If the attractive force between them is large enough, and was large enough early enough on, we’ll become gravitationally bound together. although dark energy might push the distant galaxies away from us, we’ll eventually fall into one another, and merge into a single giant structure over time.”

“ Laniakea is real and massive, but it’s also temporary, and it’s not massive enough to hold itself together or to eventually pull us in. The fate of our local group is a lonely one after all.”

That is, the gravitational pull is strong enough to keep our local group of galaxies “together forever,” but everything beyond, according to what we now know, will be always farther and farther away from our part of the Universe. Also discussed in Ask Ethan #69: Is our Universe escaping us?.

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