2017/12/31 by Eddy Keming Chen · 2 citations
Physics and Astronomy · #Advanced Thermodynamics and Statistical Mechanics #Classical mechanics #Density matrix #Interpretations of quantum mechanics #Physics #Quantum #Quantum Mechanics and Applications #Quantum cosmology #Quantum discord #Quantum dynamics #Quantum entanglement #Quantum gravity #Quantum mechanics #Quantum process #Quantum state #Statistical Mechanics and Entropy #Theoretical physics #cond-mat.stat-mech #hep-th #physics.hist-ph #quant-ph
paper · pdf · doi:10.1093/bjps/axy068
published as The British Journal for the Philosophy of Science, Volume 72, Number 4, December 2021 · Minor changes to conform to the published version
openalex created_date 2018/06/13 · openalex publication_date 2018/10/10 · arxiv created 2022/03/05 · arxiv updated 2022/03/08 · openalex updated_date 2026/08/05
In a quantum universe with a strong arrow of time, we postulate a low-entropy boundary condition (the Past Hypothesis) 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 natural initial condition. First, I introduce Density Matrix Realism, the thesis that the quantum state of the universe is objective and impure. This stands in sharp contrast to Wave Function Realism, the thesis that the quantum state of the universe is objective and pure. Second, I suggest that the Past Hypothesis is sufficient to determine a natural density matrix, which is simple and unique. This is achieved by what I call the Initial Projection Hypothesis: the initial density matrix of the universe is the (normalized) projection onto the Past Hypothesis subspace (in the Hilbert space). Third, because the initial quantum state is unique and simple, we have a strong case for the 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, theoretical unity of the universe and the subsystems, and the alleged conflict between Humean supervenience and quantum entanglement.