Lecture 40 - The Big and the Small The Inflationary Universe
We do not yet have a convincing, detailed model of how and why inflation transpired because the models of particle physics that we have are not adequate at the huge energies of inflation.
Understanding inflation requires a much better knowledge of particle physics than we have now, and possibly a full knowledge of string theory and quantum gravity." - Edward Witten (2002)
In this lecture, ideas developed in the previous lecture will be invoked to understand why the universe might have initially expanded exponentially – the so-called inflationary phase. First, the idea of spontaneous symmetry breaking and phase transitions are reviewed. Then the concept of “cosmological phase transitions associated with symmetry breaking” are introduced. With this background, Alan Guth’s idea of exponential expansion associated with the Grand Unified Theory phase transition is explained.