Breathing Comoving Hubble: Initial Condition and Eternity in view of the trans-Planckian Censorship Conjecture

Abstract

In this paper we put forward the idea that the comoving Hubble horizon undergoes multiple stages of contraction (a.k.a. inflationary phase) and expansion. The observable inflation, that produces the CMB anisotropies and generates primordial gravitational waves, follows and is followed by multiple early and late inflations. The trans-Planckian censorship conjecture restricts the duration of each inflationary phases and determines their Hubble rates. Early inflations could start immediately after the universe emerges from the Planck era. It alleviates the initial condition problem for the lower-scale observable inflation. Late inflations collectively assist the observable inflation to accommodate the present horizon. Moreover, it makes eternal inflation possible and consistent with obserbvations.