An Enumeration of Some of the More Important Events in Early Cosmic History

(Times are measured from the birth of our universe.)

(1) 10-12 seconds: Electroweak symmetry breaking takes place and masses for the fundamental elementary particles (the quarks, the electron, the W and the Z) are generated.

(2) 10-9 seconds: All top quarks and anti-top quarks combine and annihilate, producing bottom quarks, gluons, photons, W's and Z's.

(3) 0.5 x 10-8 seconds: W's and Z's self-destruct into photons, quarks and leptons. (A lepton is an electron, muon, tau or neutrino.)

(4) 10-8 seconds: All bottom quarks and anti-bottom quarks combine and annihilate, producing photons, gluons and lighter quarks. The same thing happens to charm and anti-charm quarks and tau and anti-tau leptons.

(5) 10-6 seconds: Quark confinement sets in: Up and down quarks and antiquarks bind to form pions, and some groups of three up and down quarks bind to form protons and neutrons.

(6) 10-5 seconds: All strange quarks and anti-strange quarks combine and annihilate. The same thing happens to muons and anti-muons and to pions.

(7) One second: Neutrinos and anti-neutrinos decouple, meaning that they are released as a non-interacting relic that will survive forever. Also at this time, positrons and electrons combine and annihilate into photons. All the positrons disappear but for every billion positrons, there is one extra electron and these electrons survive.

(8) Three minutes: The nuclei of helium and lithium are forged.

(9) 20,000 years: The expansion of the universe increases somewhat as it becomes driven by the mass in protons and neutrons. Previously, it had been driven by the energy in photons, leptons and other light particles and radiation.

(10) 300,000 years: Atoms form: Electrons join with nuclei to form electrically neutral atoms of hydrogen, helium and lithium. When electrons are captured by nuclei, flashes of light are released that will survive cosmic history eventually becoming stretched due to the expansion of the universe and turning into microwaves. Today, these incredibly ancient microwaves permeate all space and are known as the microwave cosmic background radiation.

(11) About 500,000,000 years: The first quasars, galaxies and stars form.



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