Question: What would happen if all the mass in the universe was in one ball?

James Lees answered on 15 Mar 2020:

That depends on how big the ball is. It might not be unreasonable to say that it is currently all in a ‘ball’ just a very big one.

However the question you’re probably asking is what if it was a small ball, say football size. In which case all of the matter would become so hot and dense that it melts down into a gluon plasma and everything we understand about the universe pretty much breaks down. No atoms or even protons and neutrons.