### Re: Many Worlds invalidated?

Jeff Bone forwards: http://www.boingboing.net/2004/04/26/many_worlds_theory_i.html Many Worlds theory invalidated Kathryn Cramer breaks the story on a to-be-presented Harvard talk on an experiment that appears to invalidate both the Many Worlds and Copenhagen theories of quantum mechanics. Kathryn is the daughter of John Cramer, a physicist whose Transactional Interpretetation hypothesis is the only one left intact by the experiment's findings. This is nonsense. It's nothing but sophistry and playing with language. Neither the Copenhagen nor the Many Worlds interpretations says what she claims. The CI has always been vague about what constitutes a measurement, and it looks to me like this experiment falls through the cracks. The MWI merely says that experimentally unrealized quantum worlds exist just like ours, it makes no absolute claims about distinguishable worlds lacking interference. The MWI is just the quantum formalism minus wave function collapse and is therefore perfectly compatible with this experiment, since the experiment is itself compatible with the quantum formalism. Hal Finney It has been widely accepted that the rival interpretations of quantum mechanics, e.g., the Copenhagen Interpretation, the Many-Worlds Interpretation, and my father John Cramer's Transactional Interpretation, cannot be distinguished or falsified by experiment, because the experimental predictions come from the formalism that all such interpretations describe. However, the Afshar Experiment demonstrates in an interaction-free way that there is a loophole in this logic: if the interpretation is inconsistent with the formalism, then it can be falsified. In particular, the Afshar Experiment falsifies the Copenhagen Interpretation, which requires the absence of interference in a particle-type measurement. It also falsifies the Many-Worlds Interpretation which tells us to expect no interference between worlds that are physically distinguishable, e.g., that correspond to the photon's passage through one pinhole or the other. Link (Thanks, Kathryn!) http://www.kathryncramer.com/wblog/archives/000530.html

### Re: Many Worlds invalidated?

Hal Finney wrote: The MWI is just the quantum formalism minus wave function collapse and is therefore perfectly compatible with this experiment, since the experiment is itself compatible with the quantum formalism. Would this experimental result actually be predicted by the quantum formalism, though? It sounds like they had a setup similar to the double-slit experiment and found a small amount of interference even when they measured which hole the particle traveled through, but I thought the quantum formalism predicts that interference would be completely destroyed by such a measurement. Either way, the claim that this supports the transactional interpretation but not the MWI interpretation can't be right, since both are supposed to be equally compatible with the quantum formalism. Jesse _ Stop worrying about overloading your inbox - get MSN Hotmail Extra Storage! http://join.msn.com/?pgmarket=en-uspage=hotmail/es2ST=1/go/onm00200362ave/direct/01/

### RE: Many Worlds invalidated?

A powerpoint reviewing these ideas is at John Cramer's website: http://faculty.washington.edu/jcramer/PowerPoint/43 I suspect that advocates of the Copenhagen and MW Interpretations will give different applications of their interpretations to the Afshar experiment than Cramer does. His applications of these rival interpretations to the experiment have a straw man flavor to them. -- Ben -Original Message- From: Jeff Bone [mailto:[EMAIL PROTECTED] Sent: Monday, April 26, 2004 2:27 PM To: [EMAIL PROTECTED] Cc: [EMAIL PROTECTED] Subject: Many Worlds invalidated? Hot off the press, via Boingsters: http://www.boingboing.net/2004/04/26/many_worlds_theory_i.html Many Worlds theory invalidated Kathryn Cramer breaks the story on a to-be-presented Harvard talk on an experiment that appears to invalidate both the Many Worlds and Copenhagen theories of quantum mechanics. Kathryn is the daughter of John Cramer, a physicist whose Transactional Interpretetation hypothesis is the only one left intact by the experiment's findings. It has been widely accepted that the rival interpretations of quantum mechanics, e.g., the Copenhagen Interpretation, the Many-Worlds Interpretation, and my father John Cramer's Transactional Interpretation, cannot be distinguished or falsified by experiment, because the experimental predictions come from the formalism that all such interpretations describe. However, the Afshar Experiment demonstrates in an interaction-free way that there is a loophole in this logic: if the interpretation is inconsistent with the formalism, then it can be falsified. In particular, the Afshar Experiment falsifies the Copenhagen Interpretation, which requires the absence of interference in a particle-type measurement. It also falsifies the Many-Worlds Interpretation which tells us to expect no interference between worlds that are physically distinguishable, e.g., that correspond to the photon's passage through one pinhole or the other. Link (Thanks, Kathryn!) http://www.kathryncramer.com/wblog/archives/000530.html

### Re: Many Worlds invalidated?

BTW, just a caveat --- and I should've caveated the initial forward. I'm not endorsing this or any interpretation of this experiment at all, rather just offering it up to the list in case others had not seen it. $0.02, jb On Apr 26, 2004, at 2:34 PM, Jesse Mazer wrote: Hal Finney wrote: The MWI is just the quantum formalism minus wave function collapse and is therefore perfectly compatible with this experiment, since the experiment is itself compatible with the quantum formalism. Would this experimental result actually be predicted by the quantum formalism, though? It sounds like they had a setup similar to the double-slit experiment and found a small amount of interference even when they measured which hole the particle traveled through, but I thought the quantum formalism predicts that interference would be completely destroyed by such a measurement. Either way, the claim that this supports the transactional interpretation but not the MWI interpretation can't be right, since both are supposed to be equally compatible with the quantum formalism. Jesse _ Stop worrying about overloading your inbox - get MSN Hotmail Extra Storage! http://join.msn.com/?pgmarket=en-uspage=hotmail/es2ST=1/go/ onm00200362ave/direct/01/

### Re: Many Worlds invalidated?

I wrote: Would this experimental result actually be predicted by the quantum formalism, though? It sounds like they had a setup similar to the double-slit experiment and found a small amount of interference even when they measured which hole the particle traveled through, but I thought the quantum formalism predicts that interference would be completely destroyed by such a measurement. After googling, I found a power point presentation by John Cramer (creator of the transactional interpetation) at http://tinyurl.com/29atj which towards the bottom discusses Afshar's experiment and what it says about the various interpretations...this page claims that while the MWI and CI predict no interference, the transactional interpretation Predicts interference, as does the QM formalism. So, it sounds like he really is claiming that the MWI predicts something different than the quantum formalism, which cannot be correct since the MWI is just the pure formalism (ie the deterministic rules for the evolution of a system's wavefunction over time) without the idea of the wavefunction being collapsed when the system is measured (the projection postulate). Jesse _ Lose those love handles! MSN Fitness shows you two moves to slim your waist. http://fitness.msn.com/articles/feeds/article.aspx?dept=exercisearticle=et_pv_030104_lovehandles

### Re: Many Worlds invalidated?

Even if there is only one World, there would still be a sort of Many Worlds branching after each quantum observation, see here: http://arxiv.org/abs/gr-qc/0102010 Many worlds in one Authors: Jaume Garriga, Alexander Vilenkin Comments: 9 pages, 2 figures, comments and references added Journal-ref: Phys.Rev. D64 (2001) 043511 A generic prediction of inflation is that the thermalized region we inhabit is spatially infinite. Thus, it contains an infinite number of regions of the same size as our observable universe, which we shall denote as $\O$-regions. We argue that the number of possible histories which may take place inside of an $\O$-region, from the time of recombination up to the present time, is finite. Hence, there are an infinite number of $\O$-regions with identical histories up to the present, but which need not be identical in the future. Moreover, all histories which are not forbidden by conservation laws will occur in a finite fraction of all $\O$-regions. The ensemble of $\O$-regions is reminiscent of the ensemble of universes in the many-world picture of quantum mechanics. An important difference, however, is that other $\O$-regions are unquestionably real. - Oorspronkelijk bericht - Van: Jeff Bone [EMAIL PROTECTED] Aan: [EMAIL PROTECTED] CC: [EMAIL PROTECTED] Verzonden: Monday, April 26, 2004 08:26 PM Onderwerp: Many Worlds invalidated? Hot off the press, via Boingsters: http://www.boingboing.net/2004/04/26/many_worlds_theory_i.html Many Worlds theory invalidated Kathryn Cramer breaks the story on a to-be-presented Harvard talk on an experiment that appears to invalidate both the Many Worlds and Copenhagen theories of quantum mechanics. Kathryn is the daughter of John Cramer, a physicist whose Transactional Interpretetation hypothesis is the only one left intact by the experiment's findings. It has been widely accepted that the rival interpretations of quantum mechanics, e.g., the Copenhagen Interpretation, the Many-Worlds Interpretation, and my father John Cramer's Transactional Interpretation, cannot be distinguished or falsified by experiment, because the experimental predictions come from the formalism that all such interpretations describe. However, the Afshar Experiment demonstrates in an interaction-free way that there is a loophole in this logic: if the interpretation is inconsistent with the formalism, then it can be falsified. In particular, the Afshar Experiment falsifies the Copenhagen Interpretation, which requires the absence of interference in a particle-type measurement. It also falsifies the Many-Worlds Interpretation which tells us to expect no interference between worlds that are physically distinguishable, e.g., that correspond to the photon's passage through one pinhole or the other. Link (Thanks, Kathryn!) http://www.kathryncramer.com/wblog/archives/000530.html

### RE: Many Worlds invalidated?

Brent Meeker wrote: I don't find any reference to Afshar or his experiment on the Harvard web site or on arXiv.org? Maybe it hasn't been written up yet, or it just wasn't submitted to arXiv.org. But the Kathryn Cramer blog entry on this had a link to a schedule of talks at a Texas AM physics seminar, with Afshar's talk near the bottom: http://faculty.physics.tamu.edu/belyanin/amoseminars.html I didn't find any other references to him being at Harvard, maybe he's just working with physicists at Harvard on this experiment...there's a Shahriar Afshar listed as being an assistant professor in quantum field theory at Urmia University in Iran at http://www.urmia.ac.ir/Fac_Sci/phys/staff_list.htm Jesse _ Test your Travel Quotient and get the chance to win your dream trip! http://travel.msn.com

### Re: Many Worlds invalidated?

From: Jesse Mazer Would this experimental result actually be predicted by the quantum formalism, though? It sounds like they had a setup similar to the double-slit experiment and found a small amount of interference even when they measured which hole the particle traveled through, but I thought the quantum formalism predicts that interference would be completely destroyed by such a measurement. There is a lot of confusion about all that. I hope I do not make more damages here! There are also many different versions of Bohr's complementarity principle. Complementarity of what? Waves (there are no waves in matrix mechanics!) and particles? Interference pattern and which way? Continuous and discontinuous? Localization and superposition? Separability and unitarity? Reversibility and irreversibility? The modern view says that ... The superposition of amplitudes is only valid if there is no way to know, even in principle, which path the particle took. It is important to realize that this does not imply that an observer actually takes note of what happens. It is sufficient to destroy the interference pattern, if the path information is accessible in principle from the experiment or even if it is dispersed in the environment and beyond any technical possibility to be recovered, but in principle 'still out there'. Anton Zeilinger, Rev. Mod. Phys., 1999, page S-288 In an experiment the state reflects not what is actually known about the system, but rather what is knowable, in principle, with the help of auxiliary measurements that do not disturb the original experiment. By focusing on what is knowable in principle, and treating what is known as largely irrelevant, one completely avoids the anthropomorphism and any reference to consciousness that some physicists have tried to inject into quantum mechanics Leonard Mandel, Rev. Mod. Phys., 1999, p. S-274. So, the key word now is indistinguishability. Must this indistinguishability be absolute? What does it happen in case of partial indistinguishability? (Anticipated answer: there is a smooth transition between particle-like and wave-like behaviour). In 1979, Wootters and Zurek (Complementarity in the double-slit experiment: Quantum nonseparability and a quantitative statement of Bohr's principle, PR, D-19, 1979, p. 473-484) presented a famous gedanken experiment, showing that photons still have a wave-like behaviour even if their paths are predicted almost (say: 99%) certainly. The set-up, in the gedanken, was essentially a single-slit plus a double-slit; and also a double-slit plus a specific 'textured' screen capable of detect and record both the interference pattern and the 'which way'. Yes this is possible. Coupling Wheeler's 'delayed choice' and the above gedanken experiment, Wim Rietdijk wrote (circa 1982) an interesting paper. Very shortly, QM explains the two-slit interference via Heisenberg principle. Hence the slits measure the position of the 'object'; because of this measurement there is a scattering; |p(y)|psi|^2 gives the probability function for the 'object' emerging from the slits with momentum p(y); this probability function causes the interference pattern. Thus - that is important - after the 'object' has passed through the two-slit, the probability function |p(y)|psi|^2 is fixed. And - second important point - there is a principle of conservation of momentum. Thus, nothing can change that fixed momentum (rectius: that fixed probability function). Now comes the weirdness. After the 'object' has passed the two-slit, we have *still* some time to choose if we wish to detect the 'welcher weg' (wich way, which path) the 'object' took, or if we wish to record just the 'impact' of the 'object' on the screen or, in general, if we wish to get both, the 'welcher weg' and the 'interference pattern' at the same time (this is technically possible, provided we use a screen with a special 'texture'). Here is the weirdness: does QM say that any knowledge of the 'welcher weg' causes the loss of the interference pattern? Yes? Does Feynman say this in his Lectures? Ok. Thus QM says that the the probability function |p(y)|psi|^2, already fixed at the two-slit level, is a function of our later, delayed, free choice of a specific detector (of the interference pattern only; of the interference pattern and the 'wich path' at the same time). Coming back to the point of that absolute indistinuishability. Greenberger and Yasin wrote down the relation, P^2 + V^2 = 1, where P is the probability for the electron (or photon) taking one of the two possible paths, and V the visibility of the fringes (interference pattern). http://arxiv.org/abs/quant-ph/9908072 http://arxiv.org/abs/quant-ph/0311179 http://arxiv.org/abs/quant-ph/0201026 In other words, the Greenberger and Yasin relation states that the entity (electron, photon, etc.) has a double nature (wave-like, particle-like) and there is a smooth transition between one and the other nature. So, the