How quantum physics can rewrite history | Avshalom Elitzur

Quick Overview

Quantum mechanics suggests that measurement effects propagate both forward and backward in time, challenging classical physics and relativity by allowing the determination of a particle's entire history backward when a measurement is made, which is formalized by the Two-State Vector Formalism (TSBF) developed by Yakir Aharonov.

Key Points: Opening the box in Schrödinger's cat experiment determines not only the cat's state but also its entire history backwards, suggesting measurement affects the past. Quantum mechanics implies that measurement effects travel not only forward but also backward in time in many cases, contradicting the unidirectional time assumed by relativity. Yakir Aharonov's Two-State Vector Formalism (TSBF) states that measurement effects go in both directions of time, meaning a particle at an intermediate time is shaped by effects from both the past and the future. Using TSBF, one can potentially outsmart Heisenberg's uncertainty principle by measuring non-commuting variables in the morning and evening, allowing prediction and retrodiction about the noon state. In rare cases where initial and final conditions are incompatible, nature recruits physical variables like negative mass or negative energy to stitch together the two histories, similar to how the Soviet encyclopedia rewrote history. An experiment based on Aharonov's work, involving a nested interferometer, showed the emergence of a real particle resulting from the overlap of a 'fake future' and a 'fake past', which cancels out with a particle of negative mass. The speaker concludes that the understanding of time derived from relativity theory plus ordinary quantum mechanics is incomplete, and the passage of time may underlie a new physics.

Context: The speaker, Avshalom Elitzur, analyzes the implications of quantum mechanics, particularly concerning time and causality, using Schrödinger's cat paradox and the Wheeler's delayed-choice experiment as starting points. He introduces the work of his mentor, Yakir Aharonov, specifically the Two-State Vector Formalism (TSBF), which posits that quantum measurements influence the past as well as the future, contrasting sharply with classical physics and Einstein's relativity.