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And when it decays they just fly apart?īut no, the tau isn’t made up of anything, at least not according to all the observations that we currently have. So is the tau maybe just made up of those three particles. It then decays, for example into an electron, a tau-neutrino and an electron anti-neutrino. It’s unstable and has a lifetime of only three times ten to the minus thirteen seconds. The tau is very similar to the electron, except it’s heavier by about a factor 4000. What’s with the other particles? Let’s take for example the tau. And those particles are held together by photons and the 8 gluons of the strong nuclear force. Then there are the constituents of atomic nuclei, the neutrons and protons, which are made of different combination of up and down quarks. But the matter around us is almost entirely made up of only half of them. The standard model of particle physics contains 25 particles. If it decays doesn’t this mean it was made up of something else? And why do particles decay in the first place? At the end of this video, you’ll know the answers. But how can it possibly be that a particle which decays is elementary. Most of those particles are unstable, and they’ll decay to lighter particles within fractions of a second. Physicists have so far discovered twenty-five elementary particles that, for all we currently know, aren’t made up of anything else.