Astrophysics

I present a one-function family of solutions to 4D vacuum Einstein equations. While all diffeomorphic to the extremal Kerr black hole, they are labeled by well-defined conserved charges and are hence distinct geometries. Out of the appropriate combination of these charges, we construct a Virasoro algebra and consistency conditions lead us to a proposal for identifying extreme Kerr black hole microstates, dubbed as extreme Kerr fluff. Counting these microstates, we correctly reproduce the extreme Kerr black hole entropy.

The emergence of classical behavior from an out-of-equilibrium quantum wavefunction is determined by its entanglement structure, in the form of redundant information shared between many local subsystems. We show how this structure can be generated via cosmological dynamics from the vacuum state of a massless field, causing the wavefunction to branch into classical field configurations.  An accelerating epoch first excites the vacuum into a superposition of classical fields alongside a highly sensitive bath of super-horizon particles. Gravitational interactions allow these quanta to collect information about the long-wavelength field. During a subsequent decelerating epoch, this information propagates spatially, creating long-range redundant correlations in the wavefunction. The resulting classical observables (field configurations), preferred basis for decoherence, and system/environment decomposition emerge from the translation invariant wavefunction and Hamiltonian, rather than being fixed by hand. We discuss the implications for the classicality of cosmological perturbations.