Protons are durable little subatomic particles. Our collective best guess that they should take at least years to decay... if they do so at all.
Why do scientists want to figure this out? Symmetry Magazine explains the situation:
Much [the theoritical work on Grand Unified Theories of the universe] rests on the existence of proton decay, and yet we’ve never seen a proton die. The reason may simply be that protons rarely decay, a hypothesis borne out by both experiment and theory... Because of quantum physics, the time any given proton decays is random, so a tiny fraction will decay long before that -year lifetime. So, “what you need to do is to get a whole bunch of protons together,” says [University of California's Jonathan Feng]. Increasing the number of protons increases the chance that one of them will decay while you’re watching.
Several experiments around the world have attempted (and will be attempting) to quantify the whys and wherefores of proton decay.
Two of the most important include:
Super-Kamiokande in Japan:
If we can collect many protons and some of them decay, we can estimate proton lifetime unless waiting for so long time. Super-Kamiokande uses 50,000 tons of pure water and it contains protons. We are measuring proton lifetime with huge number of protons... however, we have not observed any evidence of proton decay yet.
Hyper-Kamiokande is about 10 times larger than SK [Super-Kamiokande] and it can overtake the current reach by SK within two years... Hyper-Kamiokande has sensitivity up to more than one order longer than the current lower lifetime of proton.
What do you think? Will we discover proton decay before 2040?
Question resolves positive if experimental evidence for proton decay is published in a top peer-reviewed journal prior to 2040.