It's not a hypothesis our galaxy and Andromeda are on a collision corse. They are flying towards each other at break neck speed relatively speaking. However that being said our two galaxies are absolutely insignificant in size compared to the universe. The collision of 2 galaxies would be nothing in comparison to the big bang. Think of it like this it would be less noticeable than 2 subatomic particles colliding in a massive galaxy cluster. Or as noticeable as a human burp in our local group of galaxies.