Do protons decay?

No proton has ever been seen to decay, and the route grand unified theories predicted has no place here. Those theories fold the strong, weak and electromagnetic forces into one larger symmetry, whose smallest version needs twelve force carriers beyond the known twelve. Each extra one carries color and weak charge at once, so it can turn a quark into a lepton and split a proton into a positron and a neutral pion. Each observer's patch has exactly twelve response directions, split one, three and eight, none linking color to weak charge. Fifty thousand tons of water under a Japanese mountain have watched since 1996, putting the lifetime above 2.4 × 10³⁴ years. One proton decaying that way would break the account. A full lifetime prediction, covering every other route, is work in progress.

Also in Chapter 33: Why Was Every Open Problem the Same Problem?, Appendix A: Eighteen Questions.