Quantum entanglement in the sky: A finite beginning for inflation

Cosmic inflation is widely accepted as the standard paradigm of the early universe since it not only solves the usual cosmological puzzles but also explains observed large scale inhomogeneities as originating from quantum vacuum fluctuations. However, much of its quantum properties remain obscure, and indeed, there have been recent arguments against (some models of) inflation having a consistent quantum embedding into a UV theory. In this talk, I shall explore an often-ignored aspect of this -- the crucial role that quantum entanglement (between the quantum modes of the fluctuating field) plays in the dynamics, and observable predictions, of inflation. The same dissipative effects which are at the heart of decoherence (and how quantum fluctuations turn "classical") will be shown to be responsible for this primordial entanglement, resulting from treating inflation as an open quantum system. I will demonstrate why our conclusions are inescapable, and provide universal upper bounds on the duration of inflation, similar to those coming from quantum gravity considerations.

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