How Certain Are We That Protons Don’t Decay?
“There is no arguing, however, that in all our endeavors to measure the stability of the proton, we’ve never observed even one event of a proton spontaneously decaying into lighter particles and violating the conservation of baryon number. If the proton is truly stable and will never decay, it means that a whole lot of proposed extensions to the Standard Model — Grand Unification Theories, supersymmetry, supergravity and string theory among them — cannot describe our Universe.
Regardless of whether the proton is truly stable forever and ever or “only” stable for a septillion times the current age of the Universe, the only way we’ll figure it out is by performing the critical experiments and watching how the Universe behaves. We have a matter-filled Universe almost completely devoid of antimatter, and nobody knows why. If the proton turns out to be truly stable, many of our best ideas for what could cause it will be ruled out.
The secrets of nature may remain a mystery for a little while longer, but as long as we keep looking, there’s always the hope of a new, revolutionary discovery.”
Do protons decay? If they do, we’d have a hint of where our matter-antimatter asymmetry comes from. We’d have an idea that grand unification might be correct, either with or without supersymmetry, extra dimensions, or string theory. And we’d learn that nothing, not even the humble atom, will be stable forever; much like galaxies and black holes, they’ll also eventually decay.