From my understanding, it's a know fact even though they will "collide" the area is so large that they will not literally collide in a sense where it's planets/stars will collide with eachother. But rather just pass by eachother and affect the gravity of one another. But in reality who the fuck knows. "Science! "
Andromeda-Milky Way Collision
The stars involved are sufficiently far apart that it is improbable that any of them will individually collide.
The result of the collision between Andromeda and the Milky Way will be a new, larger galaxy, but rather than being a spiral like its forebears, this new system ends up as a giant elliptical.