"Quantum Macrostates and Microstates of the Cosmic Horizon"
The accelerated expansion of the universe leads to a horizon beyond which we cannot see, with far-reaching implications for cosmology. Structure arises from the quantum variance of early universe fields stretched across the horizon, according to the simplest theory fitting observations. In concrete models in string- (or `M-’) theory, the accelerating universe itself relies on the variance of extra dimensional fields, analogously to the quantum stability of atoms, stars and materials. Theoretical calculations also suggest an enormous unobserved entropy associated with the de Sitter horizon and a corresponding `holographic' formulation from in which familiar four-dimensional gravitational physics emerges from a strongly interacting lower-dimensional theory. Recent and ongoing work of multiple research groups has refined and sharpened the meaning of this entropy along with other thermodynamic quantities such as energy and temperature. Timelike features – such as a fixed-metric boundary or an observer within the system – play a key role, as do novel deformations of three-dimensional field theories defining a family of finite quantum systems. These structures combine naturally into a new proposal for holography of a bounded patch of the accelerating de Sitter universe, realizing the cosmic horizon entropy as a microstate count in a non-gravitational boundary theory.
Research Overview: https://sitp.stanford.edu/people/eva-silverstein