Quarks

Quarks are elementary particles: as far as we know, they are not made of anything smaller. They are the building blocks of protons and neutrons, which together form the nucleus of an atom. A proton consists of three quarks, two 'up' quarks and one 'down' quark. A neutron consists of two down quarks and one up quark.

How does it work?

There are six kinds of quarks, which physicists call up, down, charm, strange, top and bottom. In ordinary matter you mostly see up and down. The other four are heavier and only appear briefly, for example in collisions in particle accelerators.

Quarks have a property called colour charge. It has nothing to do with real colours; it is just a name for a kind of charge. Gluons, the particles of the strong nuclear force, hold quarks together. That force is so strong that you can never get a quark loose: if you try to pull one away, new quarks appear. The theory that describes this, quantum chromodynamics, is known as QCD for short.

Why it matters

Quarks are the smallest building blocks of nearly all ordinary matter. Their behaviour determines how atomic nuclei are put together and why they are stable.

OpenAI says that its internal AI models have solved three long-standing open problems, in mathematics, computer science and physics. In physics, it concerns a mathematical proof about the theories of the smallest particles, including QCD, which describes how quarks and gluons hold each other together. This is a claim by OpenAI itself: part of the proofs has already been checked by a verification program, and independent physicists led by Nobel laureate David Gross are going to check the proof (link).