theory which (we hope!) unifies the
       strong, weak, & electromagnetic interactions

more data is needed to tell which of many theories,
       if any, describes nature

all interactions we observe appear to be
       different aspects of the same,
       unified interaction current data & theory:
       forces merge into one force at a high enough
       energy, at small distances, at early times
       in the universe

this primordial force-carrier particles would cause
        the proton to decay
such decays extremely rare; otherwise our world
       would not exist today