A new picture of the cosmos: a two-sheeted, CPT-symmetric universe

After reviewing some key hints and puzzles from the early universe, I will introduce recent work with Neil Turok suggesting a rigid and predictive new approach to addressing them.

Our universe seems to be dominated by radiation at early times, and positive vacuum energy at late times. Taking the symmetry and analyticity properties of such a universe seriously suggests a picture in which spacetime has two sheets, exchanged by a symmetry that, in turn, selects a preferred (CPT-symmetric) vacuum state for the quantum fields that live on the spacetime. In this picture, the Big Bang may be regarded as a kind of mirror.

I will explain how this line of thought suggests new explanations for a number of observed properties of the universe, including: its homogeneity, isotropy and flatness; the arrow of time; several properties of the primordial perturbations; the nature of dark matter (which, in this picture, is a right-handed neutrino, radiated from the Big Bang like Hawking radiation from a black hole); and even the existence of three generations of standard model fermions. I will also mention some observational predictions that will be tested in the coming decade, and some key open questions.