Hi, can someone remind me why should we expect a proton to decay? The last I heard, people put detectors around stored protons and expected some of them to undergo spontaneous decay, but nothing was ever detected, suggesting that the half-life of protons was longer than measurable time scales, perhaps even the age of the Universe. What is not clear to me is why do we expect them to decay? What half-life did we expect in the first place? What should they decay into? And what's the current state of the experiments and theory relating to this?