The Quark-Lepton Era

During the Quark-Lepton era that follows the inflationary episode the entire universe is a uniform soup of elementary particles.  Radiation dominates the universe. Photons are sufficiently energetic that they can turn into particle/antiparticle pairs (as long as E is greater than mc2, where E is the energy of the photon and m is the mass of the particle and antiparticle). These particle/antiparticle pairs are in thermal equilibrium with the radiation, and generally annihilate back into photons almost immdiately.

The Quark-Lepton era begins at 10-32 seconds after the Big Bang sintgularity (i.e. 1/100,000,000,000,000,000,000,000,000,000,000th of a second, for thos ewho like a lot of zeros). The temperature has cooled to 1015 degrees Kelvin (1,000,000,000,000,000 degrees).  At this time there are only three fundamental forces, gravity, the strong nuclear force, and the electro-weak force.

 Electroweak era

The Electroweak era is that period that lasts for as long as the Electroweak force does.  Although it is called an era it doesn't last evry long (physicists like to use these fancy names to describe almost instantaneous periods of time representing phases of the unfolding of the universe in the wake of the Big Bang singularity).  After a million millionth of a second, if not before,  there is a spontaneous symmetry break and Electroweak unification breaks down into two distinct components, the weak nuclear force and the electro-magnetic force.

The Proton Era

At this time matter and anti-matter continued to exist in equilibrium.  The universe was still so hot that even when matter and anti-matter particles collided and annihilated each other (as they constantly did) they would automatically reform.  The universe was pervaded by a sort of quark soup.

However the universe was still expanding and hence cooling.  By the time a one millionth of a second had passed since the original singularity, the universe was about the same diameter as the Solar System is now (only it was a 4 dimensional hypersphere rather than a sphere such as we can comprehend).  The temperature had dropped to 1,000,000,000,000 degrees Kelvin.  It was no longer hot enough to maintain the creation and annihilation of quark-anti-quark pairs and so quarks freeze out of the universe.  From this moment on they could only occur as pairs or triplets, never alone.

At this time the universe has a baryon-antibaryon asymmetry which results from post-inflationary violating processes, explained in terms of of decay a hypothetical X-boson resulting from an asymmetry in the electro-weak force. This means that for every 109 (i.e. every billion) antiparticles craeted, one buillion and one particles are formed.

As the energy drops further the heavy particles known as baryons (protons and neutrons) freeze out.  The energy density is no longer sufficient to create and maintain protons.  There is a tremendous annihilation as the matter and anti-matter protons and neutrons destroy each other.   The 109 particle/antiparticle pairs annililate, leaving one billion photons for every proton in the universe.  Due to the fortunate (for us) asymmetry in the ratio of baryons to antibaryons one in one billion baryons survive (not having an anti-matter partner to annihilate with).  If not for this there would be no matter in the universe now, and we wouldn't be here.

The Electron Era

For the next second (notice how things are slowing down...), electrons, which are much smaller than protons, remain in energy equilibrium with the universe.  This period is known as the Electron Era.  The universe is now quite huge (a light year and growing), but the temperature is dropping as heat has to be distributed through a larger and larger volume.

At one second after the Big Bang, the universe has a radius of about 4 light-years (about the distance from here to the nearest star outside our solar system) and a temperature of around 1,200,000,000 degrees.  There is no longer enough heat to maintain the creation pairs of the electrons and positrons (the electron's antiparticle).  So they are frozen out, just as the baryons were,  and like the baryons then proceed annihilate each other, only one out of every billion electrons surviving, and the electron era camme toi an end.

The neutrinos meanwhile had lost enough energy so that they pretty much stopped reacting with the other particles of matter.  They became the ghostly particles tehy are now, wizzing aroudn the universe, passing through planets and stars as if they were not there.

The freezing out of the neutrinos ended the ability of neutrons and protons to turn into each other through reactions with the electrons, positrons and neutrinos.  The result is that there were 6 protons for every neutron. Further radioactive decay oiver teh next three minutes (when the Radiation Era began) meant that further neutrons would turn into protons, electron and antineutrinos.
Quark Soup - The Elementary Particle Era

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