The theory which (we hope!) will unify the strong, weak, and electromagnetic interactions is called the "Grand Unified Theory." Physicists can write such theories today, but more data is needed to tell which of the many versions, if any, describes nature.
If a Grand Unification of all the interactions is possible, then all the interactions we observe are all different aspect of the same, unified interaction. However, how can this be the case if strong and weak and electromagnetic interactions are so different in strength and effect? Strangely enough, current data and theory suggests that these varied forces merge into one force when the particles being affected are at a high enough energy.
Contemporary work on GUT also suggests new force-carrier particles that could cause the proton to decay. Such decays must be extremely rare; otherwise our world would not exist today. Measurement tells us the lifetime of the proton is greater than 10 to the power of 32 years!