Appears to be an unsolved physics problem. TODO why? Don't they all fit into the Standard Model already? So why is strong force less unified with electroweak, than electromagnetic + weak is unified in electroweak?
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A theory embedding the Standard Model gauge factors in a larger gauge group. Particular embeddings can relate couplings and matter multiplets or predict proton decay. The unification hypothesis alone does not specify a unique mass spectrum or an experimentally established extension.
The Grand Unified Theory (GUT) is a theoretical framework in particle physics that attempts to unify the three fundamental forces of the Standard Model—electromagnetism, the weak nuclear force, and the strong nuclear force—into a single force. The idea behind GUT is that at high energy levels, these three forces are manifestations of a single underlying force, much as different types of magnetism can be seen as different aspects of the same magnetic force.