Last night when I was out with the dog I was looking at the stars and remembered that our Galaxy (the Milky Way) will collide with Andromeda in about 4½ billion years.

I wonder if there will really be many collisions or whether the two galaxies will simply amalgamate?

In (enjoyable) times past on here, I once said "Matter is indestructible" and someone (I forget who) argued that you could destroy matter but never said how that would happen. Anyone want to take that up?