# How quantum physics can rewrite history | Avshalom Elitzur Source: https://www.youtube.com/watch?v=HrzWfg7biQU Recap page: https://rapidrecap.app/video/HrzWfg7biQU Generated: 2026-01-01T16:36:55.561+00:00 --- ## 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. ## Detailed Analysis Elitzur argues that the standard interpretation of Schrödinger's cat paradox, where a student suggests simply waiting two days to see a decomposed or scratched cat as proof against superposition, misses the deeper point: opening the box determines the cat's entire history backward. This concept of backward influence is central to the Two-State Vector Formalism (TSBF) developed by Aharonov, which suggests that measurement effects propagate both forward and backward in time. This bidirectional influence allows for predicting and retrodicting states at intermediate times, potentially bypassing Heisenberg's uncertainty principle if measurements are taken at different times (morning and evening). Elitzur illustrates the historical rewriting aspect using the example of the Soviet encyclopedia removing Lavrentiy Beria's entry and enlarging the entry for the Bering Sea. He details a proposed experiment, related to the Elitzur-Vaidman bomb testing problem, where the overlap of a 'fake future' (an outcome that did not materialize) and a 'fake past' (an origin that was deemed non-physical) results in the creation of a real particle, which is then shown to involve a particle with negative mass. This suggests a new physics emerges where seemingly impossible initial and final conditions are reconciled by recruiting entities like negative mass, indicating that the current understanding of time provided by relativity is insufficient. ### Schrödinger's Cat Reinterpretation - Student's argument about waiting two days to see a decomposed cat misses the point that measurement determines the entire history backwards - The paradox is fundamentally about time, not just superposition. ### Two-State Vector Formalism (TSBF) - Aharonov's contribution states that the effect of measurement goes both forward and backward in time - At an intermediate measurement time, effects from both past and future shape the particle. ### Outsmarting Uncertainty - Measuring non-commuting variables in the morning and evening allows prediction and retrodiction about the noon state, bypassing the standard uncertainty principle. ### Rewriting History Analogy - Nature acts like the Soviet encyclopedia, recruiting unphysical variables (like negative mass) to stitch together rare initial and final conditions that are otherwise incompatible. ### Experimental Verification - The overlap of a 'fake future' and a 'fake past' in a nested interferometer setup results in a real particle - This process involves the cancellation of a particle with negative mass, leading to a profound new physics. ### Implications for Time - The results indicate that what was thought about time through relativity and standard quantum mechanics is incomplete - The passage of time may be the basis for this emerging new physics.