Cosmology and the Universe: The Big Bang, Dark Matter and Dark Energy 269
anticlusters are optically identical. The only way to differentiate them is
to observe their interaction with matter. A rocket ship fired from Earth
into a cluster would be stable whereas a rocket ship fired into an
anticluster would be annihilated. This is an impossible experiment since
the nearest clusters are millions of light years away.
The Lepton Era
As the universe passes out of the hadron era 10-4 seconds after its
inception it passes into the lepton era in which lepton (electrons, muons
and neutrinos) and antileptons dominate the landscape. This condition
holds until the universe is 10 seconds old, has dropped in temperature to
1010 K, had achieved a radius of approximately a million kilometers and
a density of 10^4 grams per cubic centimeter. At this point, the photons,
which are still in great abundance, can no longer produce electron-
antielectron pairs and hence, the lepton-antilepton pairs annihilate each
other. According to the first variation of the Big Bang theory, the
universe also begins with more electrons than positrons. In fact the
electron excess just equals the proton excess so that the number of
electrons, which survive the lepton era just, equal the number of protons
that survive the hadron era. A very tidy coincidence indeed!
According to the second variation the number of electrons and
positrons are the same. The electron and positrons are naturally attracted
to blobs of protons and antiprotons during the lepton era because of their
mutual electrostatic attraction. The blobs of matter and antimatter are,
therefore, electrically neutral like the cluster and anticluster into which
they evolve.
The Radiation Era
The next era the universe passes through is known as the radiation era in
which photons and neutrinos illuminate the world completely dominating
the protons, neutrons and electrons that have survived the hadron and
lepton eras. Matter is ionized into positive and negative charges during
this era since the photons have enough energy to ionize any electrically
neutral atoms, which might form. While the photons have enough energy
to keep electrons separated from nuclei they do not have enough energy
to break up deuterium or helium nuclei. The temperatures during the
radiation era range from 10^10 K to 3000 K.