>>12776818I think the best evidence against it right now is from deep inelastic experiments. The harder we probe into the proton, the denser a sea of gluons we see. It suggests if we tried probing infinitely deep into the proton, that it'd just be an infinitely dense plasma of gluons.
But on the other hand, the harder we probe the more likely we are to destroy the proton. Then we observe hadrons, which we also know are constituted of quarks based on our model. So even if we destroy the proton, new particles arise which are also composed of quarks.
If quarks have a substructure, it'd be a truly interesting theory. On the other other hand, perhaps it's possible that leptons such as electrons have a substructure, and the reason we haven't found such substructure is because such leptons are much lighter than the proton, so a DIS experiment on it wouldn't work.
