![]() ![]() ![]() But neutrons inside many atomic nuclei can live far longer than the age of the universe such nuclei provide them with a stable home. The other rather long-lived particle is the neutron, which when on its own, outside an atomic nucleus, lives just 15 minutes or so. Protons, for instance, are so long-lived that at most a minuscule fraction of them have decayed since the Big Bang, so for all practical purposes they are probably stable. The other neutrinos, the proton, and many atomic nuclei ( and their anti-particles … I’m going to stop mentioning the anti-stuff, it goes without saying) are probably not stable but are very, very, very long-lived. The only known stable particles in nature are the electron ( and anti-electron), the lightest of the three types of neutrinos ( and its anti-particle), and the photon and (presumed) graviton ( which are their own anti-particles). But why is it that a few types of particles do not decay at all, or at least live much longer than the 13.7 billion-year age of the (current) universe? ![]() I’ve explained in a previous article why most particles decay it’s actually a form of dissipation, something we have some intuition for, from our experience of waves and vibrations. The world exhibits many types of particles - you can read about a lot of the (apparently-)elementary particles here, and there are lots of other particles which you can build out of more elementary ones, like protons and neutrons and atomic nuclei - but most of them decay in a tiny fraction of a second. Although most particles disintegrate into other particles, a few types of particles do not. ![]()
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