[Seminar] "Q-Screens and Tensor Networks: Two Cosmic No-Hair Theorems" by Aidan Chatwin-Davies


Tuesday, February 20, 2018 - 15:30 to 16:30


C756, Lab 3


Quantum Gravity Unit (Neiman Unit) would like to invite you to a seminar by Aidan Chatwin-Davies from California Institute of Technology.

Title: Q-Screens and Tensor Networks: Two Cosmic No-Hair Theorems

Roughly speaking, “cosmic no-hair” refers to the finding that a positive cosmological constant tends to drive cosmic evolution toward an asymptotically de Sitter phase in a wide range of cosmological models. In semiclassical settings, spacetime itself approaches de Sitter in the asymptotic future and the states of quantum fields evolve to be locally indistinguishable from the de Sitter vacuum state. In this talk, I will discuss two very different approaches that both lead to cosmic no-hair theorems. The first approach exploits a generalized second law of thermodynamics formulated in terms of a co-dimension 1 hypersurface called a Q-screen. This approach connects the monotonic increase of a generalized entropy over time to the spacetime’s asymptotic approach to de Sitter. As such, it results in a precise interpretation of cosmic no-hair as cosmic equilibration. The second approach exploits a conjectured correspondence between de Sitter spacetime and the multiscale entanglement renormalization ansatz (MERA) tensor network to show that the states of fields in a horizon patch asymptote to a unique fixed point, thus realizing a quantum cosmic no-hair theorem.

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