Inflation

Professor Susskind introduces the theory of cosmological inflation under which the early universe underwent an exponential expansion during which it doubled in size every 10^-32 seconds and expanded by at least a factor of e⁹⁰.  This all occurred prior to the Big Bang and during this period the universe cooled very rapidly and was essentially empty.  In the early phase of this rapid expansion, the universe was hot enough that magnetic monopoles were formed.  However these were the only particles formed.  The rest of the energy of the universe was contained in the potential energy of the inflaton field, and it wasn't until the Big Bang that this potential energy was converted into the particles that form the matter that makes up the galaxies in the universe today.

This theory of rapid explnsion explains the lack of observed magnetic monopoles and the uniformity of the cosmic microwave background radiation.  The rapid expansion dispersed the monopoles, smoothed out the distribution of photons, and also flattened space itself.