English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

In a quantum universe with a strong arrow of time, it is standard topostulate that the initial wave function started in a particularmacrostate--the special low-entropy macrostate selected by the Past Hypothesis.Moreover, there is an additional postulate about statistical mechanicalprobabilities according to which the initial wave function is a "typical"choice in the macrostate (the Statistical Postulate). Together, they support aprobabilistic version of the Second Law of Thermodynamics: typical initial wavefunctions will increase in entropy. Hence, there are two sources of randomnessin such a universe: the quantum-mechanical probabilities of the Born rule andthe statistical mechanical probabilities of the Statistical Postulate. Ipropose a new way to understand time's arrow in a quantum universe. It is basedon what I call the Thermodynamic Theories of Quantum Mechanics. According tothis perspective, there is a natural choice for the initial quantum state ofthe universe, which is given by not a wave function but by a density matrix.The initial density matrix of the universe is exactly the (normalized)projection operator onto the Past Hypothesis subspace (of the Hilbert space ofthe universe). Thus, given an initial subspace, we obtain a unique choice ofthe initial density matrix. I call this property "the conditional uniqueness"of the initial quantum state. The conditional uniqueness provides a new andgeneral strategy to eliminate statistical mechanical probabilities in thefundamental physical theories, by which we can reduce the two sources ofrandomness to only the quantum mechanical one. I also explore the idea of an"absolutely unique" initial quantum state, in a way that might realizePenrose's idea (1989) of a strongly deterministic universe.

Time's Arrow in a Quantum Universe: On the Status of Statistical Mechanical Probabilities