The notion of past as implied by Many-Worlds Theories leads to inconsistencies

The notion of past as implied by Many-Worlds Theories leads to inconsistencies

Seminar author:Kathrin Gerhard

Event date and time:04/20/2023 04:00:pm

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Many-Worlds theories of Quantum Mechanics understand measurements as interactions between subsystems of the universe, which “split” the universal wave function into branching alternative “worlds” in an overall unitary evolution. The emerging global state vector after a measurement is then a superposition of terms that are characterized by macroscopically distinguishable outcome states according to the possible measurement results received by the observing system. Each of these terms is associated to a world that persists over time and thus must have a past.

In this talk, I present a No-Go Theorem, which shows that defining such a “past” according to the mathematical branching structure used in Many-Worlds Theories necessarily leads to inconsistencies. The proof of the theorem is based on an analysis of the extended Wigner’s Friend Gedankenexperiment proposed by Frauchiger and Renner in 2018.

Even though the argument is inspired by and formulated in a Many-Worlds context, we strongly believe in a wider applicability of our result to the general understanding of “past” in Quantum Theory.