What is in the space in between the subatomic particles of an atom consist of?

Question

quantum mechanics

Answer 1

If by "subatomic particles" you mean quarks (quarks, also differentiated as "up"-quarks and "down"-quarks, are the subatomic particles that form both the protons and neutrons that comprise the nucleus of atoms), then the spaces between them are populated by still smaller particels named, aptly enough, "gluons".

Answer 2

Well, the subatomic particles themselves do not have a precisely-defined position. Their locations are sort of 'spread out' over a region. They're more likely to be found in some places, and less likely to be found in others.

If you could say for certain that you know where all the particles in the atom were, then there would be nothing but empty space where there wasn't a particle. Of course, the reality is that the particle locations are all spread out, making an atom appear as a 'fuzzy blob'.