It's not exactly like raisins in a loaf, though that's a good way to explain it to layperson. Unlike a loaf of bread or surface of a balloon, there isn't a firmament in which galaxies are suspended, and only the firmament expands such that they never touch. It's more like an infinite stew that keeps getting infinitely watered down - slowly. Sometimes the bits in the stew will still hit each other as everything cooks and swirls. They'll just do it less and less often as more water gets added.