As the Universe expands, do things like planets expand also, or just the space in between? Just what the question says. As the universe expands, and space expands, do objects like planets ever expand? Does the space INSIDE of those objects expand?
Things that are bound by other forces will not be seperated by the expansion of the Universe. For instance, planets do not expand due to cosmic expansion. The solar system does not either because it is held together by gravity. However, the space between galaxies or between galaxy clusters does expand.