tag:blogger.com,1999:blog-8666091.post2993060965960211059..comments2021-04-22T22:09:55.753+02:00Comments on The Reference Frame: Simple proof QM implies many worlds don't existLuboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.comBlogger106125tag:blogger.com,1999:blog-8666091.post-88843084189164114572014-08-04T04:59:11.850+02:002014-08-04T04:59:11.850+02:00Interesting & I'm sympathetic but think th...Interesting & I'm sympathetic but think the quick response would be to say that probabilities only come into play when superposition collapses. So the probabilities are only relevant when it comes to 'discovering which world you are in'. There isn't a specific world where someone would meet both outcomes at once.Jonnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-81760225519097362582014-05-08T19:14:45.983+02:002014-05-08T19:14:45.983+02:00jesus christ you are pretentious. the most amusing...jesus christ you are pretentious. the most amusing bit of this whole "proof" is your tendancy to cobble together a mish-mash of different forms of math. you prepare an algebraic proof, and then try to convince us that your "proof" invalidated MWI by using binary operations (AND, OR, etc). clearly, as stated below in a more polite manner, you do not understand the fundamentals of what you are trying to discuss.pretentiousmuchnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-57904335580214978702014-01-02T20:25:34.162+01:002014-01-02T20:25:34.162+01:00In the same arguement how can you dismiss many-wor...In the same arguement how can you dismiss many-worlds theory without testing it ? Shot down by your own logic....Shaunnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-15207965509171446342013-10-21T15:19:55.790+02:002013-10-21T15:19:55.790+02:00You are really misinformed here, and you're st...You are really misinformed here, and you're stubbornness by calling other people monkeys shows that you are not open to the real ideas MWI proponents have.<br />Since you are considering an isolated electron, first consider a state vector describing an observer measuring the electron. Then we see that<br />observer neutral x measuring system -> observer measures up x electron spin up + observer measures down x electron spin down.<br />Now what MWI adherents do is realistically interpret the resultant wave function and thus there must be two different equally real worlds. Now why exactly some worlds are more probable than others is a difficult question, but it is no more difficult then the question why probabilities arise in the Copenhagen interpretation. Probabilities can be interpreted as the probability of being in a certain branch.<br />You're example is wrong because 1. you consider an isolated system without the observer. Decoherence shows us that a superposition of the electron will quickly get entangled with the observer. 2. you seem to be using the projection postulate in the sence of the Copenhagen interpretation that it gives the probability of the electron being in a state up or down. But in the MWI sence the probabilities can be seen as giving the probability of the observer being in a world in which up or a world in which down is measured. Surely being in both worlds (P_A * P_B) has probability zero, but that doesn't imply the MWI is false.<br />Furthermore, charge and energy conservation are always derived in a single universe framework. And the MWI is pretty much consistent with this, as it can be shown that these quantities are in fact conserved within a single universe. So an observer will do measurements that are in correspondence with the conservation of these quantities.<br />I think many people here have pointed out your fallacies but you keep on calling them monkeys. Though I myself am not yet convinced that MWI is the key to all our questions about QM, I am convinced that you do not understand the MWI debate correctly.Anonnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-65599277783470007672013-08-18T06:56:03.279+02:002013-08-18T06:56:03.279+02:00Dear James, science is about learning objective la...Dear James, science is about learning objective laws while being disappointed also depends on your subjective feelings and preferences.<br /><br /><br />So your being diisappointed, howevever I might prefer another outcome, doesn't imply that there is an iota of inaccuracy in what I wrote.<br /><br /><br />You may use the phrase "many worlds" in any way you want, for example for "one world", you may twist the terminology in any way you invent, but you won't change anything about the fact that there's no viable modification of quantum mechanics, a theory that was first fully defined by the physicists who were meeting in Copenhagen and no one else.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-60389360451017651052013-08-18T05:52:12.667+02:002013-08-18T05:52:12.667+02:00Unfortunately we do not get to decide what people ...Unfortunately we do not get to decide what people call things. I agree many worlds is misleading name.<br /><br /><br />You are right to claim that anyone who believes in what you call "many worlds" is a stupid monkey. <br /><br /><br /><br />Unfortunately the people who profess in many worlds would not agree that what you call "many worlds" is what they believe. As such when in discussions with those people your post is of little use to me which is disappointing.Jamesnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-3603372928118851712013-08-17T06:40:15.440+02:002013-08-17T06:40:15.440+02:00Sorry, the application of quantum mechanics to arb...Sorry, the application of quantum mechanics to arbitrary systems is what conventional orthodox quantum mechanics is all about. It was the Copenhagen school that began to study molecules, metals etc. etc. using quantum mechanics. It is a complete lie that proper quantum mechanics has ever been claimed not to apply to arbitrarily big systems.<br /><br /><br />If you don't have any two electrons (in total) representing one, you can't call it many worlds because it clearly has nothing to do with many worlds. There aren't many worlds if there is only one.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-9404500341392588132013-08-16T20:05:56.478+02:002013-08-16T20:05:56.478+02:00Interesting post but it appears you don't unde...Interesting post but it appears you don't understand many worlds. <br /><br />Take your example of an electron in 0.6|up> + 0.8|down>.<br /><br />You wouldn't argue that there are "two" electrons there, that there is an electron with spin "up" as well as an electron with spin "down"? Of course not.<br /><br />Now lets say that electron interacts with an electron that is 1.0|up>.<br /><br />The joint state would be 0.6|up>|up> + 0.8|up>|down>.<br /><br />Similarly, here you wouldn't argue that there are some how four electrons? Of course not.<br /><br />Now lets say go back to the stern-gerlach experiment.<br /><br />All many worlds says is that if we don't introduce something new to quantum mechanics, scientists and measuring devices are also particles, so if they interact with a spin 1/2 particle:<br /><br />0.60|up> + 0.80|down>.<br /><br />The end state is:<br /><br />0.60|scientist sees up>|up> + 0.80|scientist sees down>|down>.<br /><br />And like before, there aren't two electrons, and there aren't two scientists. And no scientist is every going to see an electron up and an electron down. And this doesn't violate conservation of charge any more than 0.60|up> + 0.80|down> does.<br /><br />That is many worlds.Jamesnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-29567967076486093562013-02-02T12:26:00.188+01:002013-02-02T12:26:00.188+01:00"But there are people who say that electrons ..."But there are people who say that electrons are like classical waves..."<br /><br /><br /><br />There are many people who say many dumb things and indeed, it's the main purpose of all these blog entries of mine to correct the widespread misconceptions. It's disappointing if you don't appreciate it and it's surprising that you seem to read this blog anyway even though the correction of stupidities said by people, especially if it is many people, is self-evidently the defining driver behind this blog.<br /><br /><br />The wave functions evolve according to analogous "deterministic" equations as classical fields and waves but their physical interpretation is completely different so the "determinism" of Schrödinger's equation – or the Dirac equation promoted to a quantum equation for an actual system – does *not* translate to classical determinism of the real world which simply doesn't hold.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-73816529700779729342013-02-01T21:57:59.839+01:002013-02-01T21:57:59.839+01:00Dear Lubos
I really didnt want to make any ad hom...Dear Lubos<br /><br />I really didnt want to make any ad hominem arguments. It certainly wasn't my purspose.<br /><br />I'm not a physicist but a person who would like to become one in the future, so my knowledge in this area is basic, especially when compared to yours.<br /><br />But you must know that it inst an unusual way for the people who teach QM to look on this problem from a differend side than you do.<br /><br />You say that electrons aren't classical waves because they cannot be measured in a classical way.<br /><br />But there are people who say that electrons are like classical waves because the Dirac equation, and more basic Schroedinger one describe a classical i.e. deterministic and unique time evolution so the real difference is in the act od measurement.<br /><br />In the quantum world the measurement is more "drastic" than in classical one. To observe waves on water we only need some light with energy too small to change the pattern in statistically significant way. But in quantum world energy of a wave we need to measure position of the electron is enough big to interfere with it. <br /><br />I've read recently some words by Wojciech Zurek, and I had an impression that he understads QM in in similar way stating that macroscopic objects are all quantum and the reason for which they dont behave like waves and for which they have unique lociaction, is that they're not enough separated from the environment, which is responsible for all this huge amount of interactions that forbid the macroscopic objects to behave like waves.<br /><br />Isnt this view just dual to yours? And how can one interprete interfference patternw in double slit experiment with electrons? If electron is point-like poarticle then what forbids it to behave like classical point-like particle and forces it to change its momentum?<br /><br />Is there any book particular where I could find all the answers to theese questions?<br /><br /><br /><br />Thank you in advancekmutnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-64675470264875273222013-02-01T05:36:28.363+01:002013-02-01T05:36:28.363+01:00Dear Kmut,
one could say that it was the very ma...Dear Kmut,<br /><br /><br />one could say that it was the very main purpose of this statement of mine to emphasize that the electron is *not* a classical wave. Prince de Broglie misunderstood those things much like you do, even after 1924 when he proposed his wave, which is why throwing his name around can't turn your invalid statements into valid ones.<br /><br /><br />A classical water wave goes through both slits - one may detect "something" by an appropriate detector in both of them. But when an electron goes through the pair of slits, there is *nothing* that could ever be detected in both slits simultaneously. If you use a detector of any kind, call it a detector of waves, particles, disturbances, spirits, whatever, and if these detectors only operate in the regions around the two respective slits, they will never beep simultaneously.<br /><br /><br />Also, the electron, unlike a classical wave, will always create a single point at the photographic plate.<br /><br /><br />It's just not true that "there is nothing wrong with electron's being a classical wave". There's a lot of wrong things. A whopping 50% of statements one can make about waves are plain untrue about the electron. Just to be sure, many laymen don't get it: one wrong thing would invalidate your claim. But there are lots of waves to invalidate it, it's just wrong.<br /><br /><br />A classical wave may be a method to think about the behavior of an electron or a quantum particle in some respects but it's surely not a valid model for all of its behavior. An electron is not a classical wave and the wave function isn't a classical wave, either.<br /><br /><br />LMLuboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-75065718372876782622013-02-01T05:04:08.584+01:002013-02-01T05:04:08.584+01:00You write:
"But the statement "an elec...You write:<br /> <br />"But the statement "an electron exists in the region of slit A *and* an electron exists in the region of slit B" is just wrong (...) It's a point-like particle, there is only one electron (by charge conservation etc.), and it can't be in both slits at the same moment."<br /><br />But what about deBroigle's waves of matter? An electron can be described as a wave, and waves are certainly not just single points of space. All kinds of waves occuppy a region of space, so a wave can be in both slit A and B at the same time (just like Russia lays in both Europe and Asia, because it's not a point but an area) and there's nothing wrong with it.<br /><br /><br />It's obvious in the case of double slit experiments performed with waves of water, for many people it's obvoius in the case of light, and I think there is no reason to think different in the case of electrons.kmutnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-23440940029640832142012-09-22T08:00:05.149+02:002012-09-22T08:00:05.149+02:00MWI proponents may "feel" ;-) various th...MWI proponents may "feel" ;-) various things but science is not about feelings and the contradiction is there.<br /><br /><br />It's not true at all that this multi-world fantasy is a "literal interpretation" of the wave function. It's a wrong interpretation designed as crutches for the stupid people but it has nothing to do with the right probabilistic interpretation and indeed, it contradicts it.<br /><br /><br />As always, the key point of MWI that makes it incompatible with the real world - and with quantum mechanics - is the idea that there objectively exists some classical information that is independent of the observers and observations. This ain't the case.<br /><br /><br />Sensible people call about virtual particles but they understand that they are not real physical particles. They're mathematical constructs contributing to probability amplitudes for processes involving real particles. But the point of the many worlds is different. It's the very point of MWI that those worlds are "real" in the classical sense, and this assumption may be shown and has been shown to contradict observations. If you're not getting it, you *are* a stupid ape.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-8104028199372728232012-09-21T23:46:34.106+02:002012-09-21T23:46:34.106+02:00You're basically just saying that it is imposs...You're basically just saying that it is impossible to observe an electron that is simultaneously spin up and spin down, and that every observation will confirm that charge is conserved. I doubt any MWI proponent would disagree with either statement or feel that it contradicts their interpretation.<br /><br /><br />I think there's a valid philosophical objection to an interpretation that talks about the reality of alternate possibilities that can never be observed (if you can't possibly observe them, in what sense do they deserve to be called real?). But I don't see how you'd derive a mathematical contradiction to it, since at its heart it's just a very literal interpretation of the mathematics of the wave function.<br /><br /><br /><br />Personally, I don't see MWI as being much different than people talking about virtual particles in QFT. You'll never observe them, so are they real, or is it just a convenient way to visualize the math behind your theory? Probably the latter, but I'm not going to go to war over it and call people stupid monkeys if they talk about virtual particles.gbushnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-60348884081252783722012-09-19T07:22:34.057+02:002012-09-19T07:22:34.057+02:00Dear notallama, I would endorse a big part of what...Dear notallama, I would endorse a big part of what you write. Just a few comments. The "relative state interpretation" isn't Zurek's renamed stuff. It's the title, perhaps with formulation instead of interpretation, of Everett's 1957 thesis. So Zurek seems to be analyzing the *same* thing. Still, his 2007 paper starts by assuming the probabilistic interpretation, as far as I can read it.<br /><br /><br />I also agree that Sidney Coleman himself used some MWI-like-sounding language. But as far as I can say, it's always just the language. He may have used the word "branch", perhaps because he was inspired to use it, but I don't see any indication that he would actually interpret the squared amplitudes as anything else than the probabilities or that he would try to look for a model where the wave function is "more real".<br /><br /><br />Many of us have adopted certain phrases, especially because the strongest "proselytizers" when it comes to quantum mechanics are those who don't understand QM properly. (I remember a Czech physicist at my Alma Mater in Prague, Bedrich Velicky who knew very many famous world physicists, who always complained how universities don't teach the "real deal", but when it came to his "real deal", it was some naive "realist model", not remember which one.) So each of us picks a tolerable one among them, Coleman probably picked the Everett language as the most tolerable one but I don't think that it has influenced his thinking.<br /><br /><br />I agree that those people are smart and brain-powerful when it comes to some technically more demanding questions but they just become complete idiots when the topic switches to interpretation. And I exactly agree with your observation that their technological capabilities suddenly evaporate and the most difficult maths is on the level of "squared amplitudes", and in most cases, they don't even square it right or they don't care whether it should be squared, and so on. It's completely weird. They probably see other "otherwise very smart" people who are doing the same thing so they feel justified to be equally breathtaking idiots. It's an infection of a sort.<br /><br /><br />The 2007 Zurek paper is full of lots of redundant gibberish but of course I think that it's among the saner papers on the interpretational issues. It explains that MWI can't do almost anything right, as I read it, but one may supplement it with his insights - which are described by 50 different names or metaphors, decoherence, quantum Darwinism, einselection, envariance, and so on, and so on, but the essence is always the same mechanism - to get a sensible "interpretation". Also, if I guess right, the |c|^2 probabilities are extracted by looking at many states of an entangled complicated system including the environment chosen so large that each micro-outcome corresponds to a large number of microstates of the whole big system with the same absolute value of the amplitudes, by symmetries, the probabilities of each are probably claimed to be the same, which allows to "derive" |c|^2 in general by summing over many terms with the same absolute value. <br /><br /><br />I think it's silly to think that this is more fundamental than the general rule for the situation in which the amplitudes have different absolute values - because they almost certainly have different absolute values, so it's contrived to assume that they should have the same absolute value. But it's a part of the hatred against everything that is quantum, including the simple Born rule. Some people just don't want it to be fundamental - well, one of the postulates or derived statements that are so closed to postulates by derivations that it makes no sense not to call them fundamental - and Zurek "partially" joins this idiotic movement in the paper.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-14129299135545536742012-09-18T21:29:06.096+02:002012-09-18T21:29:06.096+02:00As far as the proponents of many worlds go, it'...As far as the proponents of many worlds go, it's not the<br />laymen and self-proclaimed experts and prophets who just can't get their minds<br />around the wave function being a subjective probability distribution because it<br />mathematically looks like a classical wave for one particle, preferably<br />spinless, that bother me. Most of those people are on the level of the Flat<br />Earth Society. It's the slightly bigger names that subscribe to this<br />ill-conditioned interpretation that freak me out, e.g. DeWitt, Zurek, perhaps<br />partly Wheeler (he did talk about the wavefunction of the Universe) and I have<br />a hunch that Sidney Coleman is something more of a fan of many worlds than you<br />would like to think. The language that he uses in his In Your Face talk is<br />kinda MWI-ish, e.g. at about 12:15 he says something like "we were in the<br />branch that got spin up". Also he never says that he takes the<br />wavefunction to be non-physical and his position seems to be<br />"associated" with Everett, obviously, Yakir "Weak<br />Measurement" Aharonov, David Albert, and Zurek. Now Zurek did a lot of<br />great stuff on decoherence, but he subscribes to a modified many worlds<br />interpretation of QM. Anyway, Sidney says a lot of smart things, but I'm really<br />worried about these MWI-style statements. This might not be as serious as I<br />take it to be, though it's hard to know, and even if it is of course none of<br />Sidney's opinions reduce the amount of inconsistency of MWI. But it points the<br />way to a curious psychological phenomenon, or problem, if you will.<br /><br />And that is that otherwise smart people, very smart even, who can extract<br />wonders from the mathematics underlying our physical theories, reduce to<br />complete morons when it comes to interpretational issues, the debating of which<br />usually consists of very simple and irrelevant mathematics obscured to an<br />arbitrary degree by metaphysical/science-philosophical vocabulary that they<br />probably aren't really qualified to use. Take the recent work of 't Hooft and<br />Weinberg for instance. I find that very mystifying.<br /><br />I find Zurek to be the most curious of these figures. In his paper at http://arxiv.org/abs/0707.2832 he<br />advocates a variant of the MWI, of course called “relative-state” to make it<br />more bland. Amongst other things he claims to derive the Born rule<br />non-circularly (funny how after Deutsch et al’s failures it sounds like this is<br />a specific type of its derivation :)) with the aid of envariance, a theoretical<br />aid much in the spirit of the decoherence program. Unfortunately he truly doesn’t<br />sound like he’s talking complete crap. He might be reaching for the deepest interpretational<br />layers of quantum mechanics that can be reached without denying the objective<br />existence of the wavefunction. Of course that might be worse than not reaching<br />for them at all, since the consistency of the Copenhagen interpretation makes<br />it completely unnecessary and it’s probably a ton of bullcrap anyway, only neatly<br />worded and convoluted to the point when it looks convincing. But it does look<br />convincing. Do you have an opinion on Zurek’s derivation? Especially, do you<br />think you can identify a point at which possible inconsistencies arise? I tried<br />debunking it myself but haven’t spotted the obvious problem yet. The only paper<br />negatively addressing Zurek’s interpretation that I could find was by Ulrich<br />Mohrhoff, a curious guy who I think is doing a good job in patiently explaining<br />to the anti-quantum zealots why the probabilistic interpretation is the thing.<br />But while ok, he seems to be doing stuff a bit differently from, say,<br />consistent historians, so I am very much interested in your opinion.<br /><br />Cheers,<br /><br />notallamanotallamanoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-64744432012061837792012-09-11T12:03:19.414+02:002012-09-11T12:03:19.414+02:00Very nice find, Victor.
Also nice (in my opinion)...Very nice find, Victor.<br /><br />Also nice (in my opinion):<br /><br /><a href="http://soundcloud.com/the_number_sixes/rocket-cars" rel="nofollow">Newton's First Law</a>, by the Number Sixes and<br /><br />the <a href="http://soundcloud.com/futuremanagementagency/bad-circuit-millimeters-away-1" rel="nofollow">Double Slit Experiment</a> by Future Management Agency.<br /><br />Both of them Creative Commons licenses so you can't beat the price :DEugene Snoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-76077166882223908442012-09-11T10:39:48.264+02:002012-09-11T10:39:48.264+02:00By a timeline, you probably meant a world line, ri...By a timeline, you probably meant a world line, right? ;-)<br /><br /><br />Show me your "correct MWI" calculation of the same trivial thing but before you do so, please accept the fact that your comment is just a laymen's rubbish.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-44227734144194213062012-09-11T10:35:07.916+02:002012-09-11T10:35:07.916+02:00Your calculations and logic are both wrong.
You&#...Your calculations and logic are both wrong.<br /><br />You're simply calculating the probability that electrons within the same time-line would exist in multiple states at once to be 0, which would obviously be true. Within the same time-line the probability of existing in different states would be 0, but that doesn't have anything to do with the MWI.<br /><br />All interpretations of the double-slit experiment use the same mathematics and quantum theory, the results of double-slit experiment are just interpreted differently.<br /><br />In MWI there is no collapse, you see the electron that exists in your time-line. <br /><br />So your disproof is all wrong.<br /><br />I'm certain that in the future multiple time-lines will be experimentally proven, though I'm not sure about the MWI in particular.anonnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-65038016643286413332012-09-09T15:04:12.008+02:002012-09-09T15:04:12.008+02:00Dear Lubos,
the comment you just replied to was m...Dear Lubos,<br /><br />the comment you just replied to was my oldest comment in the thread. But it was broken, and I only removed "smaller than" and "greater than" symbols from it to make it work.<br /><br /><br /><br />------------------------------------<br /><br /><br /><br />"In such comments, I usually see that any discussion is totally hopeless after the first sentence."<br /><br />Actually, you already convinced me that you are right and the MWI is an incorrect interpretation. :)<br /><br /><br /><br />"Also, if you used the MWI philosophy to arbitrarily insert existential <br />quantifiers ("there exists a universe in which") in front of all <br />propositions, you would totally screw all rules of logic about the <br />propositions. You can't just add quantifiers without totally changing <br />the logic."<br /><br />Yes, you are right. I haven't thought about this, when I wrote my old post.<br /><br /><br /><br />-------------------------------<br /><br />But the old Copenhagen interpretation is incorrect too because it uses an ad hoc wavefunction collapse rule and the preferred basis is chosen by hand.<br /><br />Decoherence theory is the correct interpretation of quantum measurements, <br />where classical probabilities naturally emerge from the density operator after decoherence is complete. But the wavefunction never really collapses.<br /><br /><br /><br />Previously, I thought that the decoherence interpretation can be naturally merged with the MWI, but you convinced me that I was wrong.<br /><br /><br /><br />Cheers,<br />RezsoRezsonoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-91785731023976188382012-09-09T06:47:18.505+02:002012-09-09T06:47:18.505+02:00"What I think is that your position is just a..."What I think is that your position is just a linguistically powered rubbish that can't be given any interpretation that makes sense and you are just wasting my time.<br /><br /><br />In an experiment with one electron, "electron exists with spin up" is exactly the same proposition as "electron has spin up". Trying to create any doubts about this is totally irrational.<br /><br />Also, if you used the MWI philosophy to arbitrarily insert existential quantifiers ("there exists a universe in which") in front of all propositions, you would totally screw all rules of logic about the propositions. You can't just add quantifiers without totally changing the logic.<br /><br /><br />In particular, "electron has spin up" is the exact negation of "electron has spin down" but "there exists a universe with electron up" isn't complementary to "there exists a universe with electron down", especially because both propositions would almost certainly be "true" in an MWI. So this is experimentally excluded because we know that they're negations of each other.<br /><br /><br />In such comments, I see that any discussion is totally hopeless after the first sentence. You say that we have different interpretations of projection operators. Holy fuck. How can you have a different interpretation of a projection operator? It is a very elementary object in principle, both mathematically and physically, and there is only one interpretation that is consistent with observations as well as logic and it's the interpretation of QM.<br /><br /><br />The interpretation is that a projection operator is P obeying P^2 = P, we also want P^dagger=P, that is identified with the observable having No/Yes i.e. 0/1 eigenvalues answering to a question - namely the question Is the physical system in a state inside the lambda=1 eigenvalue (of P) subspace of the Hilbert space? The expectation value of this P in a pure state or Tr(P.rho) is the probability that the proposition holds. That's it. <br /><br /><br />What the fuck is your interpretation? You're always promising some other interpretation but there isn't any. Crackpots like you are talking too much. In reality, the MWI babblers haven't even decided whether projection operators play any role in MWI at all. The reason they haven't decided is that none of the two answers makes any sense and they know it.<br /><br /><br />At any rate, I am waiting for your prescription how to use projection operators to make the calculations in your non-Copenhagen framework, the MWI counterpart of my paragraph two paragraphs above. Before you actually have something of the sort, could you please kindly shut up and stop these meaningless tirades that only show one thing, namely that you're never willing to learn anything and you prefer to spit tons of this vague nonsensical mud over the Internet?<br /><br /><br />Cheers<br />LMLuboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-51216810902346782122012-09-09T01:58:46.651+02:002012-09-09T01:58:46.651+02:00http://ca.news.yahoo.com/former-us-president-bill-...http://ca.news.yahoo.com/former-us-president-bill-clinton-backs-interstellar-voyage-164714882.html<br />I want to know what you think of this. Do you think interstellar travel is possible, or science fiction? Hearing from a physicist would be great.Shooternoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-26515283196794685782012-09-08T01:47:37.113+02:002012-09-08T01:47:37.113+02:00Dear Lubos,
okay, you convinced me that you are r...Dear Lubos,<br /><br />okay, you convinced me that you are right. The probabilistic interpretation of the density operator follows naturally from it's mathematics, so nothing more (like MWI or something else) is needed, decoherence alone solves the measurement problem.<br /><br />But I still maintain that the fundamental definition of the density operator should use the partial trace and not the classical probabilities. And this is a difference between decoherence theory and ordinary QM (=Copenhagen Interpretation).<br /> <br />In ordinary QM, the construction of the theory goes in the following order:<br />1) Wavefunction, unitary time evolution<br />2a) Measurement axiom, wavefunction collapse, classical probabilities<br />3a) Density operator is defined from the probabilities and from the corresponding collapsed wavefunctions<br /><br />But the decoherence motivated construction of QM goes as:<br />1) Wavefunction, unitary time evolution<br />2b) System+Environment, density operator is defined by a partial trace<br />3b) Classical probabilities emerge from the density operator after decoherence is complete<br /><br />So, I want to say that 2b) is a better definition for the density operator than 3a), because 3a) relies on the ad hoc wavefunction collapse rule, while 2b) doesn't.<br /><br />Do you agree with me in this?Rezsonoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-10886369996604015512012-09-07T18:40:26.737+02:002012-09-07T18:40:26.737+02:00Hi Lubos,
I highly admire your never-ending defe...Hi Lubos,<br /><br /><br />I highly admire your never-ending defence, against all-comers, of the probabilistic interpretation and encourage you to never stop, it's clearly how nature is<br /><br /><br />Problem is, it's a a mix of psychological non-acceptance and miniscule logical loopholes (eg MWI, super-determinism, crazy godlike pilot waves) that allow the fretting deniers of nature's randomness a corner to fight from, and while you deal superbly well with the logical arguments, you'll never solve the psychiatry problems.<br /><br /><br />FWIW, I agree with YOU.James Gallagherhttp://jbg.f2s.com/quantum2.txtnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-26056027606287647892012-09-07T17:22:18.088+02:002012-09-07T17:22:18.088+02:00You say "So, there are no probabilities in th...You say "So, there are no probabilities in the definition!". That's a highly bizarre assertion. Whenever you want to interpret the calculations physically, you *need* to use the word probability because it's the only valid interpretation of the matrix elements of the density matrix, of the expectation values of projection operators, and so on.<br /><br />What I wanted to say above is that this is a new assumption which is needed to connect the theory with experiments.<br /><br /><br />No, there is absolutely no "new assumption" in decoherence. Decoherence is just ordinary quantum mechanics applied to a particular kind of questions about the co-existence of a system with its environment. The interpretations of all objects such as density matrix are exactly the same as they always are in quantum mechanics. The probabilistic interpretation is not only natural but it's also one that may directly derived from observations and the only one that allows the theory to reduce to the previously known classical limits.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.com