A Brief Timeline

• < 10-43 sec,  >1032 K or 1019 GeV--- “This is where smoke comes out of the computer, but physics is still going strong.” (John Archibald Wheeler)  Presumably at t = 0 a spacetime boson popped into existence in nothingness.  If the boson has E = 0 it can persist indefinitely.

• < 10-36 sec,  >1016 GeV--- Possibly all four fundamental forces have close to the same strength.

• 10-33 to 10-32 sec, 1028 dropping to 1022 K--- The universe undergoes a phase transition which results in expansion of space by a factor of around 1026. The extremely rapid cooling may  “freeze out” the strong force.  As this “inflation field” collapses into very massive bosons, the bosons in turn decay, through a long chain, ultimately to particle-antiparticle pairs.

• >10-12 sec, near 1012 K--- An excess of quarks, as well as dark matter particles, has been slowly forming as a result of particle-antiparticle annihilations which are nonsymmetric (CP-violating) and leave  behind an excess of particles, about 1 in 109. Photons are therefore dominant. The Higgs field is active in providing mass to both fermions and bosons.

• 10-11 sec, 1012 K--- The end of electroweak unification also marks the end of the era of creation of excess dark matter, leptons and quarks via various possible CP-violating processes.
• 10-6 sec, >1010 K--- The quark-gluon plasma condenses into protons and neutrons. The strengths of the four fundamental forces have their present values. Hadronic antimatter has now vanished completely.

• 1 sec, 1 MeV (1010 K)--- Neutrinos decouple from baryonic matter. Leptons and anti-leptons, along with  dark matter, still dominate the mass of the universe, with most particles still being photons, and still in thermal equilibrium with all other particles.  The part of the universe we can observe has a radius of about 10 light years at 1 second age.

• 1 to 10 sec,  >109 K--- Leptons and anti-leptons are still in thermal equilibrium with photons. Pair creation and annihilation closely balance out.

• 10 to 103 sec--- the First Era of Nucleosynthesis! Protons and neutrons can fuse to form helium, lithium and isotopes of hydrogen without being knocked back apart by photons. Essentially all the helium in the universe (24% of all atoms) was formed during this era, since the amount of matter that has ever been inside a star is negligible.  At 1000 sec the radius of the part of space which is today the observable universe was about 300 light years.

• 3 minutes to 240,000 years, 105 K to 4000 K. Matter and Dark Matter dominate over radiation density and Dark Energy density.  At about 3 minutes, photon kinetic energy drops low enough that leptons can survive without being annihilated by anti-leptons, and a sea of leptons and antileptons no longer dominate the mass of the universe (apart from dark matter).

• 380,000 years, 3000 K--- The universe cools to a gas, as electrons combine with protons and other nuclei. At last photons go out of thermal equilibrium with matter. This is the moment that the so-called Cosmic Microwave Background is created, and also the “last scattering surface,” which has yielded a goldmine of information about the composition of the entire universe at this time.  The part of the universe currently observable to us had a radius of about 42 million light years during this era.

• 380,000 years to 550 million years--- The Dark Ages, when photon absorption was extreme due to the universe consisting of cool hydrogen and helium gas, with few stars to ionize it again.  Reionization was not complete until about 900 million years on.  During the Dark Ages, dark matter played the key role, by providing extreme density variations which through gravity formed structures of ordinary matter... the earliest stars
("Population III)" and galaxies.  Today the diameter of our part of the universe is around 93 billion light years. It was pointed out by Loeb a few years ago that when the universe was in the age range from 10 to 17 million years, the temperature of space itself was between 100 and 0o Centigrade, so that liquid water could have existed on even starless rocky planets! Did life first form in this Dark Age, only to die out as space cooled?

• Today--- The universe has transitioned from matter-dominated to dark-energy-dominated.

Wikipedia Version of Similar Timeline