"Repulsive Gravity"

The vacuum energy density described in the left panel is equivalent to an effective cosmological constant in the inflationary epoch. The presence of this vacuum energy makes gravity effectively repulsive for a short time. This is what drives the expansion at a rate much higher than the normal Hubble expansion.

We have already met such effects in discussing dark energy and acceleration of the cosmic expansion in the present Universe (see Chapter 26 and earlier in this chapter). In the inflationary epoch the evolution of the Universe was completely determined by the vacuum energy and the expansion was much more rapid than in the present Universe.