3.1. Friedmann's Equation Exponential Expansion

One way to describe inflation is that during inflation, a inf term dominates Eq. 11. Thus, during inflation we have,

 (22) (23) (24) (25) (26)

where ti and Ri are the time and scale factor at the beginning of inflation. To get Eq. 26 we have assumed 0 ti << t < te (where te is the end of inflation) and we have used Eq. 22. Equation 26 is the exponential expansion of the Universe during inflation. The e-folding time is 1/H. The doubling time is (ln 2) / H. That is, during every interval t = 1/H, the size of the Universe increases by a factor of e = 2.718281828... and during every interval t = (ln 2) / H the size of the Universe doubles.