and if you're going to try and look inside one of these things then you're going to have to use very high energy particles, which in quantum physics means something that is very short wavelength that you can actually look inside, and when you look inside these things by, say, scattering electrons from them, very high energy electrons, it appears that inside a proton and inside a neutron is mainly again just free space, and there are other point like objects inside these particles, and these objects are know as quarks.