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It's not known if quarks are fundamental, nor is it known if they are pointlike. We've never seen a free quark, so we just don't know.
by ars 4y ago
It's not known if quarks are fundamental, nor is it known if they are pointlike.
We've never seen a free quark, so we just don't know.
- davrosthedalek 4y agoDoesn't have to be free to be studied. We can do deep inelastic scattering to measure the quark shape, the same way we can do quasi-elastic scattering to study the neutron shape. SM certainly assumes leptons and quarks to be point-like. (of course, in general, we can not prove any theory, only disprove.)
- ars 4y agoDeep inelastic scattering of the nucleus did not find quarks. It only found nucleons. The same thing here: it's not known if quarks have an internal structure. And unless your energy is higher than the size of the object being measured you certainly can't tell if it's point like.
- davrosthedalek 4y agoNo, that's quasi-elastic scattering. DIS was done, for example, by HERA, an elctron-proton collider. SLAC did it in 1968 and essentially discovered the quarks. Of course there is always a measurement limit. Current limits for the size are "smaller than 1e-19m". That's why I wrote "as far as we know", as we have no evidence that they are not point-like, and we have rather strong limits.