I had an idea that the theories of the earliest stages of the universe were speculative.  I just never really knew how speculative until I really looked at them.  The CMB is as far back as we have actual data. From that we have to divine everything. 

Consider the two competing theories for a solution to the horizon, flatness, and isotropy problems of the big bang.  Cosmic inflation and VSL.  These two theories are often considered to be at odds.  However they are really the same in one key respect.  Both of them speculate about something which we cannot observe with current techniques and technology.  They speculate about what happened before the emission of the Cosmic Microwave Background radiation was first emitted. 

In pop cultural explanations of the CMB, it has been described as the echo of the big bang.  It has been described as the Doppler shifted protons from the big bang.  Not at all!  In fact the CMB is separated from the big bang by about 380,000 years.  The CMB is the first light to escape into a transparent universe after the cosmic dark age.  During the Cosmic Dark age photons could not propagate very far without recombining into hydrogen atoms, or knocking electrons out of hydrogen atoms.  When the universe cooled enough for the photons to no longer be able to ionize hydrogen the CMB was emitted.  At that time it was in the infrared part of the spectrum.  What that all really means is that the photons of the CMB we see now have almost no relation to the big bang, or any physics which transpired just after the big bang. 

Determining just what happened before this phase is the reason that two very important lines of cosmological research are being undertaken.  

  1. Searches for the B-mode polarization of the CMB.  This would be a gravitational wave signature in the CMB, which could only be from the Big Bang, as no other sources of gravitational waves are expected in the early universe.  No stars had formed.  (Though I suppose we could detect evidence of primordial black holes.)
  2. The proposed future NASA project the Big Bang Observer.  This would be a multi satellite space based interferometer.  With this instrument the actual big bang could be observed, or at least farther back than the CMB will allow with EM based technology.  Though like so many fantastical NASA projects I just have a feeling this will be cancelled for some reason or the other. ($$$$$$$)
I am doing a MS Thesis on the Cosmology of the universe from the Big Bang to the CMB.  My work is mostly theoretical.  So far I have only studied the classical theories, inflation, and VSL.  Why both when inflation is the standard?  Because as I pointed out above at this point there is not direct observational proof either is true or false.