how come galaxies collide when everything is moving away from each other

Question

I am puzzled of the “Andromeda–Milky Way collision”, when everything is moving away from the center of the Big Bang?

In: 3

Answer 1

The force that drives the expansion of the universe is *very* easily overcome by gravity. The fabric of space is expanding all around us right now, but gravity keeps us together. This is true for scales all the way up to local galaxies, so despite being two million light-years apart, Milky Way and Andromeda are still gravitationally bound to one another, as are all the smaller satellite galaxies in their local group. You don’t see the expansion force take over until you get well beyond that distance.