Before the Big Bang the universe was contracted?

The big bang theory says the early universe was made up of hot plasma of photons, electrons and baryons. The photons were constantly interacting with the plasma through Thomson scattering. As the universe expanded, adiabatic cooling caused the plasma to cool until it became favorable for electrons to combine with protons and form hydrogen atoms. 

The question is how that hot plasma formed? Like today’s process there was some process which were converting photons, electrons and baryons into the hot plasma. Perhaps it was a contracting process converse to adiabatic cooling.

As in the present universe, expansion causes the cooling. What will happen when universe will become too cold? Its answer is depending upon the current density of universe. The problem with measuring the current density of our Universe is that we cannot see most of the matter in it (The dark Matter). 

If the universe is heavier than the critical point, it will result in a shrinking universe. Though probability of this situation is only one third, but combining with the big bang it becomes more probable.