# This Experiment Just Ruled Out The Many Worlds Theory, Physicists Claim Source: https://www.youtube.com/watch?v=f_Hv0APV0S8 Recap page: https://rapidrecap.app/video/f_Hv0APV0S8 Generated: 2025-07-21T22:05:05.07+00:00 --- ## Quick Overview A recent experiment by physicists in Hiroshima claimed to rule out the Many Worlds Interpretation of quantum mechanics by demonstrating a photon's past depends on future measurements, but this interpretation is flawed as the experiment actually confirms known quantum phenomena without disproving Many Worlds. **Key Points:** - Physicists in Hiroshima published a paper claiming their experiment provides evidence against the Many Worlds Interpretation of quantum mechanics. - The Many Worlds Interpretation states that the quantum wave function never collapses, and universes split at each measurement. - The experiment used a Mach-Zehnder interferometer, where a single photon is split into two paths and then recombined, demonstrating it effectively travels both paths simultaneously. - Researchers introduced 'weak measurements' by slightly twisting the photon's polarization in each path, aiming to gain information about its path without destroying interference. - The observation of photons in the 'dark' output port led the authors to infer a 'negative presence' of a photon in one path, which they claim implies the photon's past depends on future measurements. - The speaker argues that the experiment merely confirms that single photons traverse both paths in an interferometer, a known quantum phenomenon. - The speaker concludes that the paper's interpretation of a 'negative photon' and its claim to disprove Many Worlds are misinterpretations of standard quantum mechanics. ![Screenshot at 6:45: A 'Bullshit meter' graphic with the needle pointing to the red zone, representing the speaker's assessment of the paper's interpretation.](https://ss.rapidrecap.app/screens/f_Hv0APV0S8/00-06-45.png) **Context:** The video discusses a recent physics experiment from Hiroshima that claims to challenge the Many Worlds Interpretation (MWI) of quantum mechanics. MWI is a theory suggesting that every quantum measurement causes the universe to split into multiple parallel universes, each representing a different possible outcome. The experiment uses a Mach-Zehnder interferometer, a device known for demonstrating wave-particle duality and interference patterns, even with single photons. ## Detailed Analysis Physicists in Hiroshima conducted an experiment using a Mach-Zehnder interferometer, claiming their results disprove the Many Worlds Interpretation (MWI) of quantum mechanics. The MWI posits that the quantum wave function never collapses, and universes split into multiple branches whenever a measurement has several possible outcomes. The experiment involved splitting a single photon into a superposition of two paths, then recombining them, which typically results in constructive interference at one output port and destructive interference (darkness) at the other. The researchers introduced a 'weak measurement' by inserting plates that slightly twisted the photon's polarization in each path, designed to preserve the interference. They observed photons in the normally 'dark' output port and interpreted this as a 'negative presence' of a photon in one path, leading to the claim that the past of a quantum particle depends on future measurements. However, the video's host argues that the experiment merely confirms that single photons traverse both paths in an interferometer, a known quantum phenomenon. The concept of a 'negative photon' is dismissed as a misinterpretation, and the claim that the measurement affects the past is a misapplication of quantum principles. The Many Worlds Interpretation does not require a photon to choose a single path before measurement; it inherently allows for superposition, meaning the experiment does not provide evidence against it. The paper is characterized as an attempt to sensationalize an experiment that teaches nothing new about quantum mechanics. ### The Controversial Claim - Hiroshima physicists published a paper claiming to disprove the Many Worlds Interpretation (MWI) of quantum mechanics, suggesting a photon caught in two places at once could 'destroy the multiverse' according to New Scientist. - The paper's authors claim their experiment provides evidence against the need for a superposition of different universes, removing the need for MWI. ### Many Worlds Interpretation Overview - MWI posits that the quantum wave function never collapses, and whenever a measurement has multiple possible outcomes, the universe splits into several branches, each containing one outcome and its corresponding observer. ### The Mach-Zehnder Interferometer - This device splits an incoming photon into a superposition of two paths, then recombines them, leading to constructive interference in one output port (signal) and destructive interference in the other (dark), even for single photons. - The fact that one output port remains dark implies the photon must have interfered with itself, meaning it effectively traveled both paths. ### The 'Weak Measurement' Experiment - The experiment involved inserting a plate in each path of the interferometer that slightly twisted the photon's polarization in opposite directions, a technique called 'weak measurement' designed to leave interference intact. - By measuring the polarization in addition to the output port, the researchers claimed to gain information about where the photon 'must have gone.' ### The 'Negative Photon' and Past Dependence - The researchers observed photons in the normally dark output port and interpreted this as a 'negative presence of the photon in one path,' leading to the claim that the past of a quantum particle depends on future measurements. ### Critique of the Interpretation - The speaker argues that the experiment simply confirms that photons go both paths in an interferometer, which is a known phenomenon in quantum mechanics. - The concept of a 'negative photon' is a misinterpretation, and the claim that the measurement affects the past is a misapplication of quantum principles. - The Many Worlds Interpretation does not require a photon to choose a single path before measurement; it inherently allows for superposition, meaning the experiment does not disprove it. ![Screenshot at 0:00: Speaker Sabine Hossenfelder introduces the topic with a New Scientist article headline 'A photon caught in two places at once could destroy the multiverse'.](https://ss.rapidrecap.app/screens/f_Hv0APV0S8/00-00-00.png) ![Screenshot at 1:43: Graphic illustrating the 'Many Worlds Interpretation' with numerous Earths, and text 'Universes Split at Measurement'.](https://ss.rapidrecap.app/screens/f_Hv0APV0S8/00-01-43.png) ![Screenshot at 2:06: Speaker gestures as text 'Many Worlds' is crossed out with a red 'X', indicating the paper's claim to disprove it.](https://ss.rapidrecap.app/screens/f_Hv0APV0S8/00-02-06.png) ![Screenshot at 2:34: Screenshot of the paper's title: 'Experimental evidence for the physical delocalization of individual photons in an interferometer'.](https://ss.rapidrecap.app/screens/f_Hv0APV0S8/00-02-34.png) ![Screenshot at 2:50: Animated diagram of a Mach-Zehnder interferometer showing a photon splitting and recombining, with output detectors D1 and D2.](https://ss.rapidrecap.app/screens/f_Hv0APV0S8/00-02-50.png) ![Screenshot at 3:52: Detailed diagram of the experimental setup, showing the laser, filters, beam splitters, mirrors, and detectors, with labels for Path1 and Path2.](https://ss.rapidrecap.app/screens/f_Hv0APV0S8/00-03-52.png) ![Screenshot at 4:21: Text overlay 'Negative Photon' with a confused emoji, highlighting the controversial interpretation of the results.](https://ss.rapidrecap.app/screens/f_Hv0APV0S8/00-04-21.png) ![Screenshot at 5:14: Meme image of Jim Carrey from 'Dumb and Dumber' with the text 'THAT'S INSANE', reacting to the paper's claims.](https://ss.rapidrecap.app/screens/f_Hv0APV0S8/00-05-14.png) ![Screenshot at 6:45: A 'Bullshit meter' graphic with the needle pointing to the red zone, representing the speaker's assessment of the paper's interpretation.](https://ss.rapidrecap.app/screens/f_Hv0APV0S8/00-06-45.png)