Why the Universe started from a low entropy state

We show that the inclusion of backreaction of massive long wavelengths imposes dynamical constraints on the allowed phase space of initial conditions for inflation, which results in a superselection rule for the initial conditions. Only high energy inflation is stable against collapse due to the gravitational instability of massive perturbations. We present arguments to the effect that the initial conditions problem cannot be meaningfully addressed by thermostatistics as far as the gravitational degrees of freedom are concerned. Rather, the choice of the initial conditions for the universe in the phase space and the emergence of an arrow of time have to be treated as a dynamic selection.

Figure 1

Density of states as a function of energy for the landscape system as derived from the Douglas and Altland probability distribution. Time-reversal invariance is preserved, i.e. gravity is not switched on yet.

Figure 2

Density of states as a function of energy for the landscape +gravity system, namely, when time invariance is broken. Notice the difference with the previous distribution around zero energy, namely, localized states exist at zero energy.