Question

Why isn't everything in space at one point? Is there some force called "anti-gravity" that makes stars drift apart? I can see that they would drift apart at the expansion of the universe, but how would to close stars not merge? How do stars keep apart from each other?

Answer 1

A lot of these answers aren't incorrect, but they miss the point of the question. There IS a kind of antigravity, as others have mentioned, it's been dubbed dark energy but this only works at scales much bigger than the scale of stars within a galaxy. The reason stars within a galaxy don't collapse all together is pretty much the same reason that the planets in our solar system don't collapse into the sun - the stars in a galaxy are orbiting the center of that galaxy. Stars do move a little haphazardly because they are influenced by each others' gravity, but that relatively small influence is swamped by their motion about the center of the galaxy. But yeah, stars are moving relative to one another, and that's called "proper motion." Even if two did come dangerously close, they would almost certainly end up orbiting one another rather than colliding together though. (To complicate matters, there is an exception to all of this... look up Globular Clusters if you're interested - the only places where stars DO collide on a -fairly- regular basis).