system
Given the following post, respond as if you're commenting on Reddit:
human
is there a maximum density?

is there a point where even atoms cannot be compressed any more?
gpt
The Schwarzschild radius of a body of mass is the radius of the sphere into which you would have to compress the mass in order to create a black hole. However, the limiting density as such a mass is compressed depends on how much matter you start with. The more mass you have, the less dense you have to be to turn into a black hole.

On the other hand, suppose you have a uniform distribution of matter in the universe. Then, because gravity cancels out everywhere, you don't turn into a black hole. The universe gets denser and more uniform the further back in time you look and the density is unbounded as you get really close to the big bang. We don't know about the physics that close to the big bang, so it is not possible to say whether there is a maximum density.

To answer your question about atoms: If you squeeze atoms very hard, they turn into aggregates of neutrons. This is what a neutron star is. If you squeeze even harder, there may exist hypothetical forms of exotic matter where the constituents of neutrons, quarks, are compressed into even further degenerate forms. Each time you compress to a new phase of matter, a new force keeps things from collapsing in on itself, until you get a black hole and it doesn't even matter anymore.