There is a really nice article in the most recent Quanta magazine on phase transitions. A phase transition is like when liquid water becomes solid water, ice or when liquid water becomes a water vapor, steam. This got me wondering about all the different phase transitions that occurred in the early universe. So lets look at and count them from most recent to the farthest one in time.
Phase transition 1: When electrons could combine with nuclei and make stable atoms. This occurred about 380,000 years after the big bang in the inflationary model of the big bang. This has given us the cosmic microwave background (CMB) radiation that has been in the news and I blogged about here. This would occur at energy levels of electron volts (eV).
Phase transition 2: When protons and neutrons had cooled down at the million electron volt (MeV) scale to form nuclei, namely the deuteron, He and Lithium nuclei, along with high energy photons.
Phase transition 3: When the quark-gluon plasma had cooled down to give rise to hadrons. This would occur at the billion electron volt (GeV) range. These hadrons would give as all the particle that we observe at large particle accelerators such as pions, kaons, but also the protons and neutrons that make up nuclei. All of these particles except the proton are unstable and decay creating all the known leptons such as the electron muon and the three different neutrino types.
Phase transition 4: This is when possibly the inflaton field undergoes a phase transition to create free quarks and gluons. Maybe leptons were also created at this time, I just don't know Also it is possible at this time that whatever particle(s) that makes up dark matter were also created at this time.
Phase transition 5: When the inflaton field was created.
Phase transition 6: When the universe was created.
Was there a phase transition that created spacetime? Were space and time created at the same time or separately?
The big question is what kind of observable signal might we observe from phase transitions 2-6?
What could we observe that could help us understand transitions 2-6? I have some ideas but I'm not sure of them.