Ask Ethan: Why don’t neutrons bind together?

Here in our Universe, almost every combination of fundamental particles you can imagine will lead to an unstable state. Anything containing a strange, charm, bottom, or top quark will decay in extremely short order, as will anything containing a muon or tau lepton, as well as their antiparticles. In fact, the only quark-containing particles that are stable at all are the proton, and other atomic nuclei (protons and neutrons combined) that contain at least one proton. But if a proton and neutron, when they’re bound together into a deuteron, are more stable together than when they’re free, then why can’t two (or more) neutrons bind together to make a stable, bound state of <a href="https://en.wikipedia.org/wiki/Neutronium" rel="noopener ugc nofollow" target="_blank">neutronium</a>? It’s an idea that dates all the way back to 1926: six full years before the discovery of the neutron. It’s also the question of Scott McGregor, who wants to know: <a href="https://medium.com/starts-with-a-bang/ask-ethan-why-dont-neutrons-bind-together-0ce73065a65a">Learn More</a>