Timeline of the Big Bang: Encyclopedia II - Timeline of the Big Bang - The early universe

Timeline of the Big Bang - The early universe

At this time, the universe is filled with a quark-gluon plasma.

Timeline of the Big Bang - The electroweak epoch – 10^-12 s

In electroweak symmetry breaking, all the fundamental particles are believed to acquire a mass via the Higgs mechanism in which the Higgs boson acquires a vacuum expectation value. At this time, neutrinos decouple and begin travelling freely through space. This cosmic neutrino background, while unlikely to ever be observed in detail, is analogous to the cosmic microwave background that was emitted much later.

If supersymmetry is a property of our universe, then it must be broken at an energy as low as 1 TeV, the electroweak symmetry scale. The masses of particles and their superpartners would then no longer be equal, which could explain why no superpartners of known particles have ever been observed.

Timeline of the Big Bang - The hadron epoch – 10^-6 s–10^-2 s

The quark-gluon plasma which composes the universe cools until hadrons, including baryons such as protons and neutrons, can form.

Timeline of the Big Bang - Nucleosynthesis – 1 s

At this time, the universe is cool enough that atomic nuclei can begin to form. Protons (hydrogen ions) and neutrons begin to combine into atomic nuclei. At the end of nucleosynthesis, the universe has cooled to the point where nuclear fusion stops. At this time, there are about three times more hydrogen ions as helium-4 nuclei and only trace quantities of other nuclei.

Timeline of the Big Bang - Matter domination – 70000 years

At this time, the densities of non-relativistic matter (atomic nuclei) and relativistic radiation (photons) are equal. The Jeans length, which determines the smallest structures that can form (due to competition between gravitational attraction and pressure effects) begins to fall and perturbations, instead of being wiped out by radiation free-streaming, can begin to grow in amplitude.

Timeline of the Big Bang - Recombination – 500000 years

Hydrogen and helium atoms begin to form and the density of the universe falls. These cause the photons to decouple from matter, and matter and radiation begins to evolve independently. Most importantly, this means that the photons that compose the cosmic microwave background are all emitted during this epoch.

Timeline of the Big Bang - Dark ages

In this epoch, very few atoms are ionized, so the only radiation emitted is the 21 cm spin line of neutral hydrogen. There is currently an observational effort underway to detect this faint radiation, as it is in principle an even more powerful tool than the cosmic microwave background for studying the early universe.

Adapted from the Wikipedia article "The early universe", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki