Grand unification epoch

A hypothesized early-universe era when the strong force and electroweak force were unified under a grand unified theory, before cosmic expansion cooled the universe enough to separate them.

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Grand unified theory: A proposed framework that unifies the strong, weak, and electromagnetic interactions at very high energies. It supplies the symmetry that would unite the strong and electroweak forces during this epoch.
Big Bang: The expansion of the universe from an early hot, dense state into its present form. The grand unification epoch is an early stage in this broader cosmic history.
Georgi–Glashow model: A 1974 SU(5) grand unified theory proposed by Howard Georgi and Sheldon Glashow. It gave a concrete model in which the forces could have unified during this epoch.
Proton lifetime: The mean time a proton would survive before decaying, if proton decay occurs. Its measured lower bound rules out many simple grand unified models.
Electroweak interaction: The unified description of electromagnetic and weak interactions in the Standard Model. This force sector was already unified when the proposed grand-unification era began.
Planck epoch: The earliest proposed era of the universe, when quantum-gravitational effects would have been essential. It precedes grand unification and marks the higher-energy boundary of established cosmological descriptions.
Pati–Salam model: A grand unified theory that groups quarks and leptons within an SU(4) symmetry alongside left-right symmetry. It is an alternative framework for the high-energy unification associated with this era.
Magnetic monopole problem: The tension between predicted abundant primordial monopoles and their apparent absence in the observable universe. It challenges straightforward accounts of relic production during this epoch.
Spontaneous symmetry breaking: A state’s laws possess a symmetry that its lowest-energy state does not preserve. Cooling could break grand-unified symmetry and split the strong interaction from the electroweak force.
Planck energy: An energy scale of about 1.22 × 10^19 gigaelectronvolts, where quantum gravity is expected to matter. It provides an upper reference point for the still lower grand-unification energy scale.