system
Given the following post, respond as if you're commenting on Reddit:
human
When space expands, do objects get bigger?

It seems to me that in an expanding universe, objects would enlarge in tandem with space and so the apparent distance between 2 objects should stay the same over time barring any other movement. Obviously, this can't be the case, otherwise we wouldn't be able to notice the expansion in the first place, but do objects change in size at all? How does the expansion of space affect the size and internal structure of objects?
gpt
No. The expansion of space is only a "global" phenomenon - it's something which makes sense to talk about on the largest scales, but it's not present when you're talking about atoms and the solar system and the galaxy and such.

By the way, you'll often read that this is because gravity "overcomes" the expansion or something like that. That's a very common misconception. The expansion isn't some kind of universal force - it's something that's very specific to the description of the Universe on large scales, where all the matter looks like it's spread out uniformly. When you're not talking about those scales, when you're looking at smaller distances where matter is clearly not spread out uniformly, there isn't really a notion of expansion anymore.