Some time after inflation, the created particles went through thermalization, where mutual interactions lead to thermal equilibrium. The earliest stage that we are confident about is some time before the electroweak symmetry breaking, at a temperature of around 10 K, approximately 10 seconds after the Big Bang. The electromagnetic and weak interaction have not yet separated, and the gauge bosons and fermions have not yet gained mass through the Higgs mechanism. However exotic massive particle-like entities, sphalerons, are thought to have existed.