of the universe
universe expands it cools. Thus at early times, the
temperature of the universe was much hotter. At
sufficiently early times, the temperatures were
sufficiently hot that particles moved fast enough to
create particle-antiparticle pairs. As one goes back
further in time, more massive particles could exist and
at a higher density.
to time after the big bang. The instant
of the big bang refers to the instantaneous creation of
all matter and energy from a single point in space-time.
Reaonable observational evidence of the big bang only
extends back to item number 2 in the list below.
sec: The universe was so hot, that the energy of
the particles easily exceeded known masses. Most
of the particles then represent pure energy, and
few are from the restraints of baryon and lepton
number conservation. At high temperatures,
fundamental symmetries are restored, and the
unification of the weak, electromagnetic, and
possibly QCD and gravity are realized.
sec: This is the era of cosmic nucleosynthesis.
Cooling has allowed nuclei to become bound. Light
nuclei are formed such as helium and lithium.
sec: Atoms form as electrons fall into their
lowest orbitals. At this same time, most of the
photons stop colliding and cool without
collision. The remnants of this decoupling is the
three degree background radiation.
sec: Galaxies, stars and planets begin to form.
sec: The present. The universe keeps expanding
and Michigan State University flourishes.
sec: Protons decay (perhaps) atomic matter ceases