density of a subatomic particle

[texasratt]

Can this be measured? ie - "What's the density of a proton?" If so, what exactly are we measuring?

If not, at what point does density as a concept break down?

Apologies if this needed to be under the "Classical" forum.

[Bob_for_short]

No, OK for proton. Proton has a certain size, volume and mass, so the notion of its density is correct. Neutron stars are larger but have similar density.