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.

This would only have a chance of happening if the galaxies were colliding. This is something that can happen in that situation however stars do collid with each other even in their own galaxy. This does happen but it's rare but because of gravitational forces and momentum it's not just 2 stars passing that smack into each other. Here is an article to answer most any questions you might have. That being said passing galaxies won't have stars collide with each other because of generally they have dark matter halos.

https://astronomy.com/magazine/ask-astro/2020/05/what-would-happen-if-two-stars-collided