SIZE ~ 10 billion light years x 6 trillion miles = 6 x 10**22 miles
The Planck era when all four forces of the Universe -- the gravitational, electro-magnetic, strong (nuclear), and weak forces -- may have been unified. This is the era of quantum gravity -- the time when a theory which encompasses both quantum mechanics and gravity needs to be used (more on this shortly). The size of the current Universe is less than 10**(-50) centimeters during this stage.
Era of the Grand Unified Theories (GUTs) when gravity separates from the other three forces (i.e., gravity becomes an interaction distinct from the other forces). Inflation begins in this stage -- the inflation is driven by a repulsive force which can be parametrized by the Cosmological constant.
The strong (nuclear) force becomes a distinct interaction at the beginning of this stage and the inflation of the Universe stops. During inflation, the Universe increases in size by a large factor -- perhaps by as much as a factor of 10**(10**12)!!! Some models say that the size of the current Universe increased from 10**(-50) centimeters to roughly the size of a grapefruit during inflation. The point is that even something as small as the Planck length (~ 10**[-33] cm -- to be defined later) could expand to encompass many observable Universes. The Universe consists of an electron-quark soup during this time.
The electro-magnetic force becomes distinct from the weak force; the quarks combine to form protons; the protons and electrons combine to form neutrons; and nucleosynthesis occurs (hydrogen and helium are produced) during the first few minutes of the lifetime of the Universe. After this, the Universe continues to expand and cool.
The Universe is cool and rarefied enough for the electrons and protons to form neutral hydrogen atoms. As we recall, neutral hydrogen atoms are not efficient at absorbing radiation. Before 500,000 years, there were free electrons which interact fairly efficiently with radiation. The strong electron-photon interaction means that before 500,000 years, the Universe was opaque to radiation, that is, the Universe was "foggy" in that light would not travel very far before it interacted with matter. This means that your view of the Universe was limited to only what was nearby.
After the neutral hydrogen forms (Epoch of Recombination), the Universe is transparent to photons and you now get an unimpeded view of your neighbors. This is the phase of the Universe which we observe when we look at the CMBR. Note that we cannot see any earlier in the history of the Universe in visible light than the Epoch of Recombination.
Protogalaxies begin to form. This may be annoying since the clumps of matter and the clumps of the clumps of overdense matter should distort the CMBR. The reason is that if these clumps are formed by the attraction of gravity, then such large overdensities take a fairly long time to form (recall the discussion of the free-fall time). This means that at the time of recombination, the ovedensities need to be large. Currently, it seems as though we are on the verge of having severe trouble. The largest structures in the Universe are just consistent with the imperfections seen in the CMBR. If we start to see larger structures then we are in severe trouble.
Quasars and some radio galaxies become detectable
Galaxy formation (?)
Solar System, planets, life, ...
