A Theory of the Universe

I will describe recent work with Latham Boyle which provides a framework for a new, minimal and predictive cosmology requiring no new particles beyond those already present in the standard model (including right handed neutrinos). We start from the observation that a realistic cosmological background, dominated by radiation at early times and Lambda at late times, has remarkable physical and mathematical properties. Instead of being an "initial condition," the big bang singularity can be regarded as a perfect mirror: in the method of images, the universes on either side are related by CPT symmetry. The ensuing boundary condition eliminates troublesome cosmological perturbations, such as "decaying" modes and vorticity. Choosing the quantum state of the matter to respect CPT symmetry, the abundance of a sterile, right handed neutrino is predicted although it was never in thermal equilibrium, as a kind of Hawking radiation. This provides the most economical and predictive explanation yet of the cosmic dark matter.

I will explain how conformally-invariant, dimension zero scalars may be used to cancel the vacuum energy and trace anomaly in the gauge/fermion part of the standard model, allowing quantum field theory to be consistently coupled to gravity without divergences occurring at leading order. Remarkably, this introduces no new particles. Instead, it requires (and predicts) precisely three generations of standard model elementary particles, including right handed neutrinos of which one forms the dark matter. In this picture, the Higgs boson and the spacetime metric must be interpreted as emergent, large-scale phenomena. The dimension zero scalars connect the UV to the IR, providing a new mechanism for generating large scale cosmological perturbations.

Finally, I will describe new gravitational instantons, namely, saddle points to the path integral for this cosmology. Selecting the saddle for which the tensor modes are well-defined (and strongly suppressed), the gravitational entropy is maximized by a flat, homogeneous and isotropic, radiation-filled background. The Boltzmann brain problem is resolved. Neither inflation nor the multiverse are required. I will outline the observational predictions of the theory, many of which will be checked in the decade ahead.