The Radiation Era

The Radiation Era began two or three minutes to 300,000 years after the Big Bang, with a process known as nucleosynthesis.  This was when helium nuclei (in fact all the helium nuclei in the universe) were formed out of protons.  So this is the initial start of the atomic kingdom.

Protons react with other protons to create Deuterons.  The temperature had  has dropped to about a billion degrees kelvin.  At this temperature deuterium (the heavy hydrogen nucleus, 2H) is stable. This enabled nearly all of the neutrons and one of the seven protons per neutron to turn into deuterium. The deuterium quickly reacted with some of the remaining neutrons and protons to form the helium nucleus (originally called the alpha particle) consisting of two protons and two neutrons, 4He.  This gives a ratio of 3 protons to 1 neutron.   About one in 10,000 deuterium nuclei escaped from being turned into helium nuclei and about one in 10,000 of the helium nuclei remained as the atomic mass 3 isotope, 3He.  This is the same ratio that is found in stars today, (except for the heavier elements produced later ) which argues in favour of the Big Bang theory.

For the rest of the Radiation Era (a period of 300,000 years) the universe remained fully ionized, and continues to expand. The entire universe was a plasma of freely moving protons, neutrons, and electrons, just as one finds in stars today.  Plasma, considered the fourth state of matter (after solid, liquid, and gas) is a state of charged ions (atomic nuclei) and electrons; with photons scattering off them and reionized any atoms that had formed.  There are no atoms as exist normally - i.e. electrons orbitting a nucleus, because the heat is so great that any electrons are automatically stripped away.

During the Radiation Era therefore the entire universe was like one single gigantic star, thousands of light years across.  During this period the universe was in thermal equilibrium, and  opaque to radiation.  Any radiation was absorbed by all the free electrons wizzing around.
  Big Freeze Out

The Plank Era
The Inflationary Era
The Quark-Lepton Era
The Radiation Era
The Matter Era

Big Bang page
Big Bang page

Universe page


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page uploaded 31 March 2000