2022/08/18 by T. Banks, Banks, T. · 1 voice
Physics and Astronomy · #Black Holes and Theoretical Physics #Cosmology and Gravitation Theories #FOS: Physical sciences #General Relativity and Quantum Cosmology (gr-qc) #High Energy Physics - Theory (hep-th) #Relativity and Gravitational Theory #gr-qc #hep-th
paper · pdf · doi:10.48550/arxiv.2208.08959
openalex publication_date 2022/08/18 · arxiv published 2022/08/18 · arxiv updated 2022/08/18 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We review and clarify ideas proposed many years ago for understanding cosmology in a holographic framework. The basic strategy is to use Jacobson's\citeted95 identification of Einstein's equations with the hydrodynamic equations of the "Area = 4 Entropy" law for causal diamonds, to identify a quantum system whose hydrodynamics match those of a given space-time. This can be done exactly for a system with any positive cosmological constant, which saturates the entropy bound for all times. The quantum system is a sequence of (cut-off) 1+1 dimensional CFTs, with central charge proportional to the entropy in causal diamonds along an FRW geodesic. This matches with a recent\citeBZ proposal that the modular Hamiltonian of any causal diamond for non-negative c.c. is the L0 generator of such a CFT. When an early de Sitter era is followed by slow roll expansion of the horizon, disjoint horizon volumes (which are gauge copies in an eternal dS space, but become physical due to slow roll expansion of the horizon area) manifest as a dilute gas of black holes in a post-inflationary era. Entropy fluctuations of individual black holes manifest as CMB fluctuations, and the tensor/scalar ratio is suppressed by an extra factor of the slow roll parameter ε. Black hole evaporation provides the Hot Big Bang and baryogenesis. Black hole mergers can easily provide a source of primordial BH dark matter that dominates radiation at a temperature of 1 eV, but numerical simulations are required to determine whether the model can explain the actual dark matter in our universe.