Re: Plaga
As an exercise I've been trying to pinpoint exactly what is wrong with Plaga's paper. For anyone who doubts that it *is* wrong, note that it proposed 10 years ago an experiment which he said was feasible with what was then state-of-the-art equipment. This technology has now massively advanced. The experiment would guarantee a Nobel prize for anyone who performed it successfully. In that time the paper has been cited in the published literature only 3 times, and never by an experimental physicist. And this is not because the paper was unnoticed by the community at the time, e.g. it was publicised by John Baez, whose writings are widely read. On careful reading, the paper is just littered with confusions and errors. I guess this explains why no-one bothered to publish a rebuttal; this falls in the class of not even wrong. Probably the root problem is a confusion about the true nature of decoherence. Decoherence is often presented using the maths of density matrices, so I better explain this briefly: Density matrices allow you to handle the case when you don't know the exact quantum state. The procedure is to divide your description into a measurable system and a complex, not-measurable-in-detail environment. One can then define the density matrix of the combined system, and trace out the uncertain state of the environment, giving a density matrix for the system alone in the absence of information about the environment. A test to see if the system has been decohered by its interaction with the environment is that the off-diagonal terms in the system-only density matrix go to zero. Plaga clearly accepts the usual position that irreversible branching in MWI occurs when decoherence is (FAPP) total. If you follow this through in Plaga's example, you do indeed find that the density matrix for the states of his trapped ion, |A1 and |A2, is diagonal, confirming the obvious that once a macroscopic measurement has taken place, we have total decoherence. But what Plaga does in his Eq 8 is to reverse the roles of system and environment (he actually does the algebra wrong but the numerical answer is unaffected). Because at this stage the ion knows nothing about the rest of the lab, he gets a density matrix *for the lab* with large off-diagonal terms, corresponding to a pure state: (|W1 + |W2) / sqrt(2). So far, so correct (after all, in MWI the state is *always* pure). But he now concludes that decoherence has not yet occurred. *WRONG*. The condition off-diagonal terms go to zero is just a sufficient condition for decoherence. It is only necessary if the system itself is so simple that it could not decohere without the help of the environment. But Plaga is treating the complex, macroscopic lab as the system and that certainly can decohere without the help one more ion. The more basic definition is that decoherence has occured once the states are permanently orthogonal, so you cannot demonstrate quantum interference. Plaga correctly states that |W1 and |W2 *are* permanently orthogonal, but does not realise that this means that decoherence *is* complete, contrary to what he says. Another way to put this is that the observer Silvia doesn't need the density matrix in Eq. (8) because she knows for sure already whether she detected the original photon or not, hence whether she is in branch |W1 or |W2. Given this, the rest of Plaga's argument is just irrelevant. But he should have noticed that his process blatantly violates the linearity of time evolution, which is one of the fundamental assumptions of MWI QM. This is manifest in his Eq. 6 which associates an excited ion with the |P2 term in which no excitation took place (if you start with a photon in state |P2, when the photon is guaranteed not to be detected, the ion is never excited). Hence Eq 6 is not a linear superposition of the two possible histories. Hence, if we saw what he predicted, we would actually *disprove* MWI QM, not confirm it as he thinks. Paddy Leahy == Dr J. P. Leahy, University of Manchester, Jodrell Bank Observatory, School of Physics Astronomy, Macclesfield, Cheshire SK11 9DL, UK Tel - +44 1477 572636, Fax - +44 1477 571618
Re: Plaga
Paddy Leahy writes: As an exercise I've been trying to pinpoint exactly what is wrong with Plaga's paper On careful reading, the paper is just littered with confusions and errors Hence, if we saw what he predicted, we would actually *disprove* MWI QM, not confirm it as he thinks. Thanks for looking at this. It seemed clear to me that it could not work but it is good to see a detailed analysis of where Plaga goes wrong. Seems that his result would do more than disprove the MWI, it would actually disprove QM in general. As you have shown, he effectively has to assume nonlinear state evolution (although he does not do so explicitly, he claims to be working in orthodox QM). Bruno noted that Steven Weinberg has done work with possible nonlinear version of QM. Some researchers have found that his model would allow for faster-than-light signalling. Probably communicating with the Everett branches would be possible as well. Hal Finney
RE: Plaga
You're welcome, Lee. - Original Message - From: Lee Corbin To: everything-list@eskimo.com Subject: RE: Plaga Date: Wed, 25 May 2005 22:04:19 -0700 I could not find who suggested Plaga's paper recently, but thanks to whoever it was. Whether Plaga is right or wrong, his introductory remarks and general presentation are simply superb. There is even the very noteworthy (or humorous, I can't decide) sentence which reads Independent of what one thinks about the MWI a priori, this is also a very systematic way to make experimental progress in the question of the interpretation of QM, because in the MWI the predictions for any conceivable experiment are free from philosophical subtleties...(!) Lee P.S. Thanks also to Saibal: Plaga's paper has been published: Proposal for an experimental test of the many-worlds interpretation of quantum mechanics http://xxx.lanl.gov/PS_cache/quant-ph/pdf/9510/9510007.pdf Found.Phys. 27 (1997) 559 arXiv: quant-ph/9510007 -Original Message- From: Hal Finney [mailto:[EMAIL PROTECTED] Sent: Tuesday, May 24, 2005 5:51 PM To: everything-list@eskimo.com Subject: Re: Plaga We discussed Plaga's paper back in June, 2002. I reported some skeptical analysis of the paper by John Baez of sci.physics fame, at http://www.escribe.com/science/theory/m3686.html . I also gave some reasons of my own why arbitrary inter-universe quantum communication should be impossible. Hal Finney -- ___ Sign-up for Ads Free at Mail.com http://promo.mail.com/adsfreejump.htm
Re: Plaga
If you expect to be quoted correctly, stop posting HTML-only. On Thu, May 26, 2005 at 08:45:34AM -0500, aet.radal ssg wrote: HEY! BRUNO - I, (aet) didn't say that.nbsp;Someone elsenbsp;did. I was quoting them. If you're going to quote somebody, I suggest you get it right.BRBR- Original Message - BRFrom: Bruno Marchal [EMAIL PROTECTED]BRTo: aet.radal ssg [EMAIL PROTECTED]BRSubject: Re: Plaga BRDate: Wed, 25 May 2005 20:40:21 +0200 BRBRgt; BRgt; BRgt; Le 25-mai-05, à 17:59, aet.radal ssg a écrit : BRgt; BRgt; gt; From the initial page from the included link to the archive: I'm BRgt; gt; no physicist so I don't know for sure that these implications BRgt; gt; would BRgt; gt; follow, but I am very doubtful that interworld communication is consistent BRgt; gt; with the basics of quantum mechanics.nbsp; The fact that this paper has not BRgt; gt; been published in peer reviewed journals in 7 years indicates that it BRgt; gt; probably doesn't work. BRgt; BRgt; Ooh... you should not make inferences like that. I could give BRgt; you 10,000 reasons for not publishing. But I have not the time BRgt; because I have a deadline today! BRgt; BRgt; I red Plaga's paper. It is extremely interesting. It belongs to the BRgt; family of Weinberg's result. Some hoped that a slight BRgt; delinearisation of QM would explain the collapse. Reasoning a-la BRgt; Weinberg Plaga shows that it is the contrary which happens. Not BRgt; only we keep the MW but they became more real in some sense. It BRgt; shows the MWI is stable for slight variation of the SWE. this BRgt; confirms MWI in a deeper way. It shows quantum non linearity BRgt; contradicts thermodynamics! This is a powerful argument in favor of BRgt; both pure linear QM and MWI. BRgt; BRgt; (Good for me, it shows nature confirms the lobian machine's BRgt; inability to observe kestrels and starlings when they look enough BRgt; closely to themselves) BRgt; BRgt; Bruno BRgt; BRgt; http://iridia.ulb.ac.be/~marchal/ BRBR -- p___brSign-up for Ads Free at Mail.combr a href=http://mail01.mail.com/scripts/payment/adtracking.cgi?bannercode=adsfreejump01; target=_blankhttp://www.mail.com/?sr=signup/a/p BR -- Eugen* Leitl a href=http://leitl.org;leitl/a __ ICBM: 48.07100, 11.36820http://www.leitl.org 8B29F6BE: 099D 78BA 2FD3 B014 B08A 7779 75B0 2443 8B29 F6BE signature.asc Description: Digital signature
Re: Plaga
Ha, ha. - Original Message - From: Saibal Mitra To: everything-list@eskimo.com Subject: Re: Plaga Date: Thu, 26 May 2005 18:50:01 +0200 Bruno was quoting another Aet from a parallel world :) Quoting Eugen Leitl : If you expect to be quoted correctly, stop posting HTML-only. On Thu, May 26, 2005 at 08:45:34AM -0500, aet.radal ssg wrote: HEY! BRUNO - I, (aet) didn't say that. Someone else did. I was quoting them. If you're going to quote somebody, I suggest you get it right. - Original Message - From: Bruno Marchal To: aet.radal ssg Subject: Re: Plaga Date: Wed, 25 May 2005 20:40:21 +0200 Le 25-mai-05, à 17:59, aet.radal ssg a écrit : From the initial page from the included link to the archive: I'm no physicist so I don't know for sure that these implications would follow, but I am very doubtful that interworld communication is consistent with the basics of quantum mechanics. The fact that this paper has not been published in peer reviewed journals in 7 years indicates that it probably doesn't work. Ooh... you should not make inferences like that. I could give you 10,000 reasons for not publishing. But I have not the time because I have a deadline today! I red Plaga's paper. It is extremely interesting. It belongs to the family of Weinberg's result. Some hoped that a slight delinearisation of QM would explain the collapse. Reasoning a-la Weinberg Plaga shows that it is the contrary which happens. Not only we keep the MW but they became more real in some sense. It shows the MWI is stable for slight variation of the SWE. this confirms MWI in a deeper way. It shows quantum non linearity contradicts thermodynamics! This is a powerful argument in favor of both pure linear QM and MWI. (Good for me, it shows nature confirms the lobian machine's inability to observe kestrels and starlings when they look enough closely to themselves) Bruno http://iridia.ulb.ac.be/~marchal/ -- ___ Sign-up for Ads Free at Mail.com href=http://mail01.mail.com/scripts/payment/adtracking.cgi?bannercode=adsfreejump01; target=_blankhttp://www.mail.com/?sr=signup -- Eugen* Leitl leitl __ ICBM: 48.07100, 11.36820 http://www.leitl.org 8B29F6BE: 099D 78BA 2FD3 B014 B08A 7779 75B0 2443 8B29 F6BE -- _ Nu 12 maanden gratis Live Eredivisievoetbal bij 20 Mb ADSL voor maar EUR 39,95 per maand. Bestel op www.versatel.nl/voetbal -- ___ Sign-up for Ads Free at Mail.com http://promo.mail.com/adsfreejump.htm
Re: Plaga
At 06:58 PM 5/24/2005, rmiller wrote: In a recent post (5/24) I wrote. . . I would suggest re Plaga or anyone else discussed here, it's not the time spent in a particular academic trench that makes the idea great, it's the quality of the insight. As luck, coincidence or a wide specious present would have it, we have this story in Wired re Peter Lynds: http://www.wired.com/wired/archive/13.06/physics.html R.Miller *(and Elvis Costello was a computer programmer---the list goes on.)
Re: Plaga
Plaga's paper has been published: ''Proposal for an experimental test of the many-worlds interpretation of quantum mechanics'' Found.Phys. 27 (1997) 559 arXiv: quant-ph/9510007 -Defeat Spammers by launching DDoS attacks on Spam-Websites: http://www.hillscapital.com/antispam/ - Oorspronkelijk bericht - Van: aet.radal ssg Aan: everything-list@eskimo.com Verzonden: Wednesday, May 25, 2005 05:59 PM Onderwerp: Re: Plaga From the initial page from the included link to the archive: "I'm no physicist so I don't know for sure that these implications wouldfollow, but I am very doubtful that interworld communication is consistentwith the basics of quantum mechanics. The fact that this paper has notbeen published in peer reviewed journals in 7 years indicates that itprobably doesn't work." Back when I wasn't long in the field of video production I was well aware of the insistance and belief of TV engineers that a single tube industrial color video camera was not broadcast quality. Working in cable, where they were used for cablecast, I had plenty of opportunity to look at picture quality, etc. and came to the conclusion that it shouldn't be a problem. 2 years later I got the chance to prove it when a local news station sent a crew out to cover something that I was shooting. In the end I gave them theeditied sequence I had shot (now downtwo generations), and they took it and edited it into their story, which would have taken it down a third. Then they broadcasted it over the air. I taped it off-air and the results were conclusive - I wasright, all the nay-sayer engineers were wrong.A $40,000 Ikegami vs a $1,500 Panasonic and it was a tie except for one slight red bleed from a costume due to the Saticon tube bias toward red in the camera I used, which could have been color corrected with a time base corrector, but whoever dubbed the tape left the red level a little too hot. My point being that that was the first in a long line of "you can'ts" that I've faced which I eventually proved, "you can". Thus I have a dim view of such positions when they aren't backed up with experiments that prove so *conclusively*. As long as the possibility exists, I keep an open mind. Besides, if unbriddled skepticism was right all the time, we wouldn't be using computers, flying, or even have phones of any kind, just to name a few things.- Original Message - From: [EMAIL PROTECTED] To: everything-list@eskimo.com Subject: Re: Plaga Date: Tue, 24 May 2005 17:51:13 -0700 (PDT) We discussed Plaga's paper back in June, 2002. I reported some skeptical analysis of the paper by John Baez of sci.physics fame, at http://www.escribe.com/science/theory/m3686.html . I also gave some reasons of my own why arbitrary inter-universe quantum communication should be impossible. Hal Finney -- ___Sign-up for Ads Free at Mail.comhttp://www.mail.com/?sr=signup
Re: Plaga
aet.radal ssg wrote: From the initial page from the included link to the archive: I'm no physicist so I don't know for sure that these implications would follow, but I am very doubtful that interworld communication is consistent with the basics of quantum mechanics. The fact that this paper has not been published in peer reviewed journals in 7 years indicates that it probably doesn't work. Back when I wasn't long in the field of video production I was well aware of the insistance and belief of TV engineers that a single tube industrial color video camera was not broadcast quality. Working in cable, where they were used for cablecast, I had plenty of opportunity to look at picture quality, etc. and came to the conclusion that it shouldn't be a problem. 2 years later I got the chance to prove it when a local news station sent a crew out to cover something that I was shooting. In the end I gave them the editied sequence I had shot (now down two generations), and they took it and edited it into their story, which would have taken it down a third. Then they broadcasted it over the air. I taped it off-air and the results were conclusive - I was right, all the nay-sayer engineers were wrong. A $40,000 Ikegami vs a $1,500 Panasonic and it was a tie except for one slight red bleed from a costume due to the Saticon tube bias toward red in the camera I used, which could have been color corrected with a time base corrector, but whoever dubbed the tape left the red level a little too hot. My point being that that was the first in a long line of you can'ts that I've faced which I eventually proved, you can. Thus I have a dim view of such positions when they aren't backed up with experiments that prove so *conclusively*. As long as the possibility exists, I keep an open mind. Besides, if unbriddled skepticism was right all the time, we wouldn't be using computers, flying, or even have phones of any kind, just to name a few things. There is a fundamental difference between claims that we can never do something because the engineering problems are too great, and claims that we can never do something because the laws of physics themselves say it's impossible. For example, I've heard people say things like I'm sure we'll eventually break the light-speed barrier, after all, once people thought it was impossible that we'd ever break the sound barrier but they've been proved wrong. But the two are not really comparable, because no one ever thought the laws of physics said breaking the sound barrier was impossible, they just thought the technical challenges to doing so would be too difficult, whereas the light-speed barrier is built into the basic structure of relativity (although there are possible loopholes in general relativity like wormholes, where you get to distant destinations quickly without ever *locally* exceeding the speed of light). Similarly, when Hal Finney suggests he thinks interworld communication is impossible, I think he's suggesting that it would violate basic principles of QM, not that it's too big of a technical challenge. I also saw this suggested in the book Schrodinger's Rabbits by Colin Bruce, a pop science book about the MWI (p. 137): If only we could do a clear and unambiguous communication-between-worlds experiment. Then there would be no room for argument about the reality of many-worlds. Unfortunately, the laws of physics do not seem to allow such a thing. This is frustrating because two potentially useful methods of harnessing the power of many-worlds, which we will look at in detail shortly, can be described in terms of sharing resources between worlds, or even sharing information between worlds. For example, a loose way of describing the operation of a quantum computer is as follows: As worlds start to diverge, hundreds of billions of different copies of the computer come into existence. Each of these computer copies can work on a different calculation. The shared results of their labors, however, can be made available to all the diverging worlds created when the bubble of Hilbert space describing the computer is systematically collapsed by measurement at the end of the calculation. This makes it sound as if Hilbert space might possibly be used as a kind of mailbox for communicating between worlds. Unfortunately, the mathematics that describes Hilbert space rules this out because it implies that everything that goes on in Hilbert space is reversible. As soon as you try to take information out of Hilbert space, that reversibility is destroyed. Such acts of measurement, by definition, cause decoherence. You can preserve multiworld access to a bubble of Hilbert space only by allowing it to evolve undisturbed. It reminds me of C.S. Lewis's Wood Between the Worlds described in the Magician's Nephew. Any Hilbert space accessible from more than one world line must be a timeless place, in which we can leave no permanent mark.
Re: Plaga
Le 25-mai-05, à 17:59, aet.radal ssg a écrit : From the initial page from the included link to the archive: I'm no physicist so I don't know for sure that these implications would follow, but I am very doubtful that interworld communication is consistent with the basics of quantum mechanics. The fact that this paper has not been published in peer reviewed journals in 7 years indicates that it probably doesn't work. Ooh... you should not make inferences like that. I could give you 10,000 reasons for not publishing. But I have not the time because I have a deadline today! I red Plaga's paper. It is extremely interesting. It belongs to the family of Weinberg's result. Some hoped that a slight delinearisation of QM would explain the collapse. Reasoning a-la Weinberg Plaga shows that it is the contrary which happens. Not only we keep the MW but they became more real in some sense. It shows the MWI is stable for slight variation of the SWE. this confirms MWI in a deeper way. It shows quantum non linearity contradicts thermodynamics! This is a powerful argument in favor of both pure linear QM and MWI. (Good for me, it shows nature confirms the lobian machine's inability to observe kestrels and starlings when they look enough closely to themselves) Bruno http://iridia.ulb.ac.be/~marchal/
RE: Plaga
I could not find who suggested Plaga's paper recently, but thanks to whoever it was. Whether Plaga is right or wrong, his introductory remarks and general presentation are simply superb. There is even the very noteworthy (or humorous, I can't decide) sentence which reads Independent of what one thinks about the MWI a priori, this is also a very systematic way to make experimental progress in the question of the interpretation of QM, because in the MWI the predictions for any conceivable experiment are free from philosophical subtleties...(!) Lee P.S. Thanks also to Saibal: Plaga's paper has been published: Proposal for an experimental test of the many-worlds interpretation of quantum mechanics http://xxx.lanl.gov/PS_cache/quant-ph/pdf/9510/9510007.pdf Found.Phys. 27 (1997) 559 arXiv: quant-ph/9510007 -Original Message- From: Hal Finney [mailto:[EMAIL PROTECTED] Sent: Tuesday, May 24, 2005 5:51 PM To: everything-list@eskimo.com Subject: Re: Plaga We discussed Plaga's paper back in June, 2002. I reported some skeptical analysis of the paper by John Baez of sci.physics fame, at http://www.escribe.com/science/theory/m3686.html . I also gave some reasons of my own why arbitrary inter-universe quantum communication should be impossible. Hal Finney
Re: Plaga
All, In my recent post I noted that Plaga's article has been on the xxx site since their server was a 386. I want to be clear that my comment was not meant as a dig at Plaga, nor his paper--just that it has been around since '95 and I can't recall anyone commenting (constructively) on it. As for astute knowledge in the QM Codex being a requirement, I seem to recall that, before Ed Whitten took an interest in physics, his undergrad degree was in History. Einstein was a---well, we all know what Einstein was during his miracle year.* I would suggest re Plaga or anyone else discussed here, it's not the time spent in a particular academic trench that makes the idea great, it's the quality of the insight. R.Miller *(and Elvis Costello was a computer programmer---the list goes on.)
Re: Plaga
We discussed Plaga's paper back in June, 2002. I reported some skeptical analysis of the paper by John Baez of sci.physics fame, at http://www.escribe.com/science/theory/m3686.html . I also gave some reasons of my own why arbitrary inter-universe quantum communication should be impossible. Hal Finney
Re: Plaga
At 07:51 PM 5/24/2005, Hal Finney wrote: We discussed Plaga's paper back in June, 2002. I reported some skeptical analysis of the paper by John Baez of sci.physics fame, at http://www.escribe.com/science/theory/m3686.html . I also gave some reasons of my own why arbitrary inter-universe quantum communication should be impossible. Hal Finney I don't recall that discussion; may not have been a list subscriber at that time. At any rate, thanks for the info. RMiller
