The NOVA show on the string theory have mention once that the proton and neutron will be disappear in finite amount of time, then reappearing on somewhere else. Is there any experiment have shown that this is true?
closed as not a real question by Ron Maimon, David Z♦ Aug 16 '12 at 20:54
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I will assume you have heard something about proton decay.
There are a number of experiments which test whether such decays occur. For example a current one is here.
There exist limits and in this review they are given depending on the theory that would predict proton decay.
Neutrons decay when free anyway into a proton an electron and an e-antineutrino.
Reappearance would require something like a new Big Bang, i.e. all matter/energy become a plasma and then by expansion the reappearance of nucleons.