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Searching for the Quantum Universe

Arsalan Adil, UC Davis
Wednesday, November 20, 2024 - 1:00pm
PAT C-421

All structure in the Universe originates from quantum fluctuations in the earliest epoch. But where does this “quantum-ness” go? Are features of this quantum epoch observable in the sky? Anisotropies in the cosmic microwave background (CMB) provide a pristine record of these quantum fluctuations but suffer from “cosmic variance” – a limitation arising from our restrictions to observe the CMB in only one universe, now, and from our fixed vantage point. Can we beat cosmic variance to unveil the quantum Universe? In this talk, I take a two-pronged approach towards answering these questions. First, I introduce our work on circumventing cosmic variance where we quantify the additional information gained by measuring the polarization induced by the scattering of CMB photons in galaxy clusters. This signal is proportional to the CMB at the location and look-back time of the cluster and, as I will show, provides significant constraints on early Universe physics beyond existing CMB data. I will discuss the prospects of measuring signatures of entanglement from the early Universe using this method. Second, I will discuss the role of decoherence in the quantum-to-classical transition. While in the lab we assume a partition of the Hilbert space into constituent subsystems, who decides how to partition the Universe? I show that this division into subsystems with quasi-classical features can be derived, instead of being assumed, from the spectrum of the Hamiltonian. This result allows us to apply decoherence on cosmological scales (though it is confronted with challenges in recovering locality).

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