Holographic Inflation and the Low Entropy of the Early Universe

Abstract

This is a completely rewritten version of the talk I gave at the Philosophy of Cosmology conference in Tenerife, September 2014, which incorporates elements of my IFT Madrid Anthropics Conference talk. The original was too technical. The current version uses intuitive notions from black hole physics to explain the model of inflationary cosmology based on the Holographic Space Time formalism. The reason that the initial state of the universe had low entropy is that more generic states have no localized excitations, since in HST, localized excitations are defined by constraints on the fundamental variables. The only way to obtain a radiation dominated era, is for each time-like geodesic to see an almost uniform gas of small black holes as its horizon expands, such that the holes evaporate into radiation before they collide and coalesce. Comparing the time slicing that follows causal diamonds along a trajectory, with the global FRW slicing, one sees that systems outside the horizon had to undergo inflation, with a number of e-folds fixed by the present and inflationary cosmological constants, and the black hole number density on FRW slices just after inflation ends. These parameters also determine the size of scalar and tensor metric perturbations and the reheat temperature of the universe. I sketch a class of explicit finite quantum mechanical models of cosmology, which have these properties. Physicists interested in the details of those models should consult a recent paper\cite{holoinflation3}.