The ultimate unification of weak and electromagnetic interactions has probably not yet been achieved, but a solid beach-head appears to have been est… - Abraham Pais

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The ultimate unification of weak and electromagnetic interactions has probably not yet been achieved, but a solid beach-head appears to have been established in terms of local non-Abelian gauge theories with spontaneous symmetry breakdown. As a result, it is now widely believed that weak interactions are mediated by massive vector mesons. Current expectations are that such mesons will be observed within the decade. It is widely believed that strong interactions are also mediated by local non-Abelian gauge fields. Their symmetry is supposed to be unbroken so that the corresponding vector mesons are massless. The dynamics of these 'non-Abelian photons' are supposed to prohibit their creation as single free particles. The technical exploration of this theory is in its early stages.