In physical cosmology, the electroweak epoch was the period in the evolution of the early universe when the temperature of the universe had fallen enough that the strong force separated from the electroweak interaction, but was high enough for electromagnetism and the weak interaction to remain merged into a single electroweak interaction above temperatures of 159.5±1.5 GeV  (assuming the Standard Model of particle physics). Some cosmologists place this event at the start of the inflationary epoch, approximately 10-36 seconds after the Big Bang. Others place it at approximately 10-32 seconds after the Big Bang when the potential energy of the inflaton field that had driven the inflation of the universe during the inflationary epoch was released, filling the universe with a dense, hot quark-gluon plasma. Particle interactions in this phase were energetic enough to create large numbers of exotic particles, including stable W and Z bosons and Higgs bosons. As the universe expanded and cooled, interactions became less energetic and when the universe was about 10-12 seconds old, W and Z bosons ceased to be created at observable rates. The remaining W and Z bosons decayed quickly, and the weak interaction became a short-range force in the following quark epoch.
The physics of the electroweak epoch is less speculative and much better understood than the physics of previous periods of the early universe. The existence of W, Z, and Higgs bosons has been demonstrated, and other[which?] predictions of electroweak theory have been experimentally verified. In the unextended Standard Model, the transition during the electroweak epoch was not a first or a second order phase transition but a continuous crossover, preventing any baryogenesis. However many extensions to the standard model including supersymmetry and the inert double model have a first order electroweak phase transition (but still lack additional CP violation).