the Radio Star

The Andromeda Galaxy is set to collide with the Milky Way between two and three billion years from now. I don't think galaxies would collide with one another if the universe were shaped like a sphere. If everything were radiating from the "point" where the Big Bang occured at the same speed, this simply would not be possible. It shouldn't be possible in a flat universe, either.

I think galactic collisions would only be possible in a saddle-shaped universe.

cavediver

This is another fault of cosmologists simplifying matters. It's not actually the individual galaxies that are moving apart by cosmological expansion - it's occuring on the much larger scale of groups and clusters of galaxies. Within the clusters, the galaxies are gravitationally bound to each other and have their own peculiar motions with respect to each other, just like the Sun and our neighbouring stars. So yes, Andromeda is indeed on a collision course with us, and this has nothing to do with whether the Universe is open, flat or closed.

Draconis

Yes according to the theories of expansion in billions of years the entire visible universe will consist of only our local group of galaxies, or maybe only one big galaxy consisting of all them.

Coragyps

That sounds somewhat more likely just lately to this amateur - Science just had a report on the imaging of two supermassive black holes in one recently merged galaxy - and another paper on how such pairs can end up merging. Just like down here, with the big fish eating the little ones.