Steinhardt and company imagine a universe that expands for perhaps a trillion years, driven by the energy of an omnipresent (and hypothetical) field, whose behavior we currently attribute to dark energy. When this energy field eventually grows sparse, the cosmos starts to gently deflate. Over billions of years a contracting scale factor brings everything a bit closer, but not all the way down to a point. The dramatic change comes from the Hubble radius, which rushes in and eventually becomes microscopic. The universe’s contraction recharges the energy field, which heats up the cosmos and vaporizes its atoms. A bounce ensues, and the cycle starts anew.
In the bounce model, the microscopic Hubble radius ensures smoothness and flatness. And whereas inflation blows up many initial imperfections into giant plots of multiverse real estate, slow contraction squeezes them essentially out of existence. We are left with a cosmos that has no beginning,