# Colliding galaxies in expanding universe

I recently came across a discussion on the expansion of the universe (click here to read the discussion). Have you tried to reason out how galaxies collide in a universe in which we know that objects are moving further away from each other at a rate that is directly proportional to the distance between them ?

Note by Bruce Wayne
4 years, 7 months ago

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The expansion of the universe is something which you observe at super-cluster scale. You don't observe expansion at the level of galaxies. Galaxies are bound systems. A few ten to hundred galaxies form a cluster. They are bound gravitationally and they have their own motion. So collision can occur between galaxies. What moves with a velocity/rate proportional to distance are the clusters/super-clusters and not galaxies. Galaxies don't move with the hubble flow.

- 4 years, 7 months ago