Eddy Keming Chen
University of California, San Diego
In a quantum universe with a strong arrow of time, we postulate a low-entropy boundary condition to account for the temporal asymmetry. In this paper, I show that the Past Hypothesis also contains enough information to simplify the quantum ontology and define a unique initial condition in such a world. First, I introduce Density Matrix Realism, the thesis that the quantum universe is described by a fundamental density matrix that represents something objective. This stands in sharp contrast to Wave Function Realism, the thesis that the quantum universe is described by a wave function that represents something objective. Second, I suggest that the Past Hypothesis is sufficient to determine a unique and simple density matrix. This is achieved by what I call the Initial Projection Hypothesis: the initial density matrix of the universe is the normalized projection onto the special low-dimensional Hilbert space. Third, because the initial quantum state is unique and simple, we have a strong case for the \emph{Nomological Thesis}: the initial quantum state of the universe is on a par with laws of nature. This new package of ideas has several interesting implications, including on the harmony between statistical mechanics and quantum mechanics, the dynamic unity of the universe and the subsystems, and the alleged conflict between Humean supervenience and quantum entanglement.
Keywords quantum entanglement  Humean supervenience  Past Hypothesis  density matrix  wave function  fundamentality  objective probability  time's arrow
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Reprint years 2018
DOI 10.1093/bjps/axy068
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The Emperor’s New Mind.Roger Penrose - 1989 - Oxford University Press.
Time and Chance.David Z. Albert - 2000 - Harvard University Press.

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Realism About the Wave Function.Eddy Keming Chen - 2019 - Philosophy Compass 14 (7).

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