Protons decaying

[Kakorot]

Do proton's decay?
and if so, what do they turn into?
and can they decay when they are in a nucleus?
I read a theory on how the universe will end up being a sea of electrons, and what protons become when they decay.

[Chronos]

Proton decay is a prediction of certain grand unification theories [GUT's]. No confirmed events have been detected and evidence to date indicates a lifespan of greater than 10E33 years... a very long time. See here for more details:
http://hep.bu.edu/~superk/pdk.html

[Astronuc]

Article on 'free' proton decay:
http://hyperphysics.phy-astr.gsu.edu/hbase/particles/proton.html#c2

In some radionuclides with a difficiency of neutrons, a proton will decay by positron emission (weak force) according to:

p^+ = n + e^+ +\nu_e, where e^ is the positron and \nu_e is an electron-associated neutrino. Note that it is a neutrino and not an anti-neutrino as in beta-decay. Also, this is in an atomic nucleus where the protons and neutrons are affected by the strong nuclear forces.