<P> The earliest phases of the Big Bang are subject to much speculation . In the most common models the universe was filled homogeneously and isotropically with a very high energy density and huge temperatures and pressures and was very rapidly expanding and cooling . Approximately 10 seconds into the expansion , a phase transition caused a cosmic inflation , during which the universe grew exponentially during which time density fluctuations that occurred because of the uncertainty principle were amplified into the seeds that would later form the large - scale structure of the universe . After inflation stopped , reheating occurred until the universe obtained the temperatures required for the production of a quark -- gluon plasma as well as all other elementary particles . Temperatures were so high that the random motions of particles were at relativistic speeds , and particle -- antiparticle pairs of all kinds were being continuously created and destroyed in collisions . At some point , an unknown reaction called baryogenesis violated the conservation of baryon number , leading to a very small excess of quarks and leptons over antiquarks and antileptons -- of the order of one part in 30 million . This resulted in the predominance of matter over antimatter in the present universe . </P>
which term refers to an assumed rapid expansion of the universe immediately after the big bang
cosmic inflation