joigus Posted October 5, 2022 Posted October 5, 2022 (edited) 2 hours ago, bangstrom said: Also, you said quantum teleportation is a misnomer from what it is "actually" So I will ask again, What is quantum teleportation "actually" or at least explain why you think it is a misnomer? "teleselection," "telefiltering," or even better perhaps "Q-teleselection," "Q-telefiltering," to further insist that these cannot be replicated by dice, gloves, or boots, would be far more honest-to-goodness terms than "teleportation." The reason, of course, being that correlations after measurement involve selecting a basis which wasn't implied in the initial preparation of the state. I know by now that the reasons for this will fly right over your head. It's no insult to your intelligence, which I assume perfectly sufficient in order to understand any of this. It's because of your very limited attention span. Maybe you're busy and have no time to read anything... Who knows. I must honour the possibility that you may be having some impediment I can't see. Here. This may be helpful: https://arxiv.org/abs/quant-ph/0105127 Wojciech Zurek was the one who coined the term einselection. The famous "teleportation" (tele-einselection?) is a particular case. 45 minutes ago, Eise said: So what is left? Correlation. And correlation can be faster than light even classically: that is the example of the left and right hand shoes. Exactly. I like to put it in a (hopefully) intuitive way I've used before: The speed at which 1-1=0 is infinity Edited October 5, 2022 by joigus Addition
bangstrom Posted October 5, 2022 Posted October 5, 2022 11 hours ago, joigus said: Maybe you're busy and have no time to read anything... Who knows. I must honour the possibility that you may be having some impediment I can't see. Here. This may be helpful: https://arxiv.org/abs/quant-ph/0105127 Wojciech Zurek was the one who coined the term einselection. The famous "teleportation" (tele-einselection?) is a particular case. This was helpful because, if you knew anything about quantum teleportation, you would know that Zurek's work was not quantum teleportation. I have been trying to explain how quantum teleportation gives real life experimental support to the speculation behind the Bell Test and its violation of the EPR effect and how it clearly demonstrates non-locality. I even explained how Zeilinger’s quantum teleportation works in case there was anyone not familiar with the experiment itself. Apparently you were one of those who knows nothing about quantum teleportation which is why you were so confused by my explanations. Quantum teleportation and the Quantum Eraser Experiment have been large in the news about advances in QM in both technical journals and the pop-sci press for many years but you apparently have no awareness of either one. Your statement about how nobody believes in non-locality anymore was surprisingly out of touch with the present day reality. Quantum teleportation is one of the most appropriately named experiments because the name itself tells what it is about. When you said quantum teleportation was a misnomer, that made me suspect you didn't know what quantum teleportation was. Now that Zeilinger has won the Nobel we will all be hearing a lot about non-locality and quantum teleportation so this is your chance to become better informed.
joigus Posted October 5, 2022 Posted October 5, 2022 (edited) 1 hour ago, bangstrom said: This was helpful because, if you knew anything about quantum teleportation, you would know that Zurek's work was not quantum teleportation. I have been trying to explain how quantum teleportation gives real life experimental support to the speculation behind the Bell Test and its violation of the EPR effect and how it clearly demonstrates non-locality. I even explained how Zeilinger’s quantum teleportation works in case there was anyone not familiar with the experiment itself. Apparently you were one of those who knows nothing about quantum teleportation which is why you were so confused by my explanations. Quantum teleportation and the Quantum Eraser Experiment have been large in the news about advances in QM in both technical journals and the pop-sci press for many years but you apparently have no awareness of either one. Your statement about how nobody believes in non-locality anymore was surprisingly out of touch with the present day reality. Quantum teleportation is one of the most appropriately named experiments because the name itself tells what it is about. When you said quantum teleportation was a misnomer, that made me suspect you didn't know what quantum teleportation was. Now that Zeilinger has won the Nobel we will all be hearing a lot about non-locality and quantum teleportation so this is your chance to become better informed. Quote Quantum teleportation is a technique for transferring quantum information from a sender at one location to a receiver some distance away. While teleportation is commonly portrayed in science fiction as a means to transfer physical objects from one location to the next, quantum teleportation only transfers quantum information. The sender does not have to know the particular quantum state being transferred. Moreover, the location of the recipient can be unknown, but classical information needs to be sent from sender to receiver to complete the teleportation. Because classical information needs to be sent, teleportation can not occur faster than the speed of light. From: https://en.wikipedia.org/wiki/Quantum_teleportation With my additional emphasis for the parts where you are embarrassing yourself the most. For quantum teleportation you need to select an observable --a measurement always implies a selection of basis--, so you have loss of quantum coherence. Plus you need to supplement the output: "Because classical information needs to be sent, teleportation can not occur faster than the speed of light." Not even Zeilinger's Nobel Prize --very well deserved, as I said-- can change that fact. Zurek's work is about any kind of measurement, your "teleportation" --which is not the superluminal teleportation of anything-- included. If you go back to the previous posts, you will see I already said or implied that. Abundantly. You're a bad, bad, very very bad reader. 29 minutes ago, joigus said: output Or just the observable that you have measured. The particular einselection. In this case, it's the environment (the experimentalist and her experimental equipment) that selects the observable ("one selection")=einselection. Totally Zurek. Understand? Edited October 5, 2022 by joigus Addition
bangstrom Posted October 6, 2022 Posted October 6, 2022 6 hours ago, joigus said: If you go back to the previous posts, you will see I already said or implied that. Abundantly. You're a bad, bad, very very bad reader. Did you read your own quote? I underlined the part you failed to understand. 6 hours ago, joigus said: Quote Quantum teleportation is a technique for transferring quantum information from a sender at one location to a receiver some distance away. While teleportation is commonly portrayed in science fiction as a means to transfer physical objects from one location to the next, quantum teleportation only transfers quantum information. The sender does not have to know the particular quantum state being transferred. Moreover, the location of the recipient can be unknown, but classical information needs to be sent from sender to receiver to complete the teleportation. Because classical information needs to be sent, teleportation can not occur faster than the speed of light. Classical information, that is person to person type of communication, can not be faster than light but quantum transactions among particles are the exception. This is the level where non-local interactions take place. Here is a quote from Anton Zeilinger's book. " Nearly all physicists agree that the experiments have shown that local realism is an untenable position. The viewpoint of most physicists is that the violation of Bell's inequality shows us that quantum mechanics is nonlocal. This nonlocality is exactly what Albert Einstein called "spooky"; it seems eerie that the act of measuring one particle could instantly influence the other one." From "Dance of the Photons" p. 286 Quantum teleportation involves measuring one particle and instantly teleporting the quantum identity of one particle to another particle that may be a considerable distance away. This involves a difficult to achieve three way entanglement among at least four entangled particles but it is a real life, repeatedly demonstrated experiment. And the fact that it can not be used for human FTL communication does not detract from the fact that it is a real effect. 6 hours ago, joigus said: Or just the observable that you have measured. The particular einselection. In this case, it's the environment (the experimentalist and her experimental equipment) that selects the observable ("one selection")=einselection. Totally Zurek. Understand? Yes, but this has nothing to do with quantum teleportation.
joigus Posted October 6, 2022 Posted October 6, 2022 2 hours ago, bangstrom said: Nearly all physicists agree that the experiments have shown that local realism is an untenable position. (Zeilinger) This is correct, but because of the "realism" bit of it, not because of the "local." The Schrödinger equation is 100% local. 2 hours ago, bangstrom said: The viewpoint of most physicists is that the violation of Bell's inequality shows us that quantum mechanics is nonlocal. (Zeilinger again, with my boldface.) This is not correct. I think I've proved it. People who don't (or didn't) think quantum mechanics forces you to give up on locality: Feynman, Gell-Mann, Coleman, Susskind, Hossenfelder... It's a long list. It's perhaps interesting to point out that most of them are (or were) field theorists. I could add more. Do you want me to? 2 hours ago, bangstrom said: it seems eerie that the act of measuring one particle could instantly influence the other one. Yeah. It seems eerie, because that's not what happens. You also quote my quote. I will quote your quote of my quote (with your underline) now. Pay attention, please, because this is somewhat subtle: 2 hours ago, bangstrom said: , quantum teleportation only transfers quantum information. The sender does not have to know the particular quantum state being transferred. Moreover, the location of the recipient can be unknown, but classical information needs to be sent from sender to receiver to complete the teleportation. This is from Wikipedia. It seems to assume "a quantum state is being transferred." Now, here's an interesting question that I would like you to answer: A pure quantum state cannot be measured. It's not an observable of the theory. In particular, its global phase cannot be measured, and gauge invariance tells us that infinitely-many local prescriptions of it cannot be measured either. How can anybody tell they have teleported something that cannot be measured, and according to many people, it could represent a human idea? If you happen to know Zeilinger, you can pass that question to him, if you wish. Please, do. This cannot be addressed by scavenging for quotes in pop-sci books, declaring yourself to be the proud owner of a T-shirt, or any of the like. 3 hours ago, bangstrom said: Quantum teleportation involves measuring one particle and instantly teleporting the quantum identity of one particle to another particle that may be a considerable distance away. You keep repeating this and proving that you don't understand the first thing about QM. There is no such thing as "the quantum identity." Identical particles are fundamentally indistinguishable. This doesn't mean they're perfect lookalikes. It's deeper. It means they're rather more like instantiations of one thing. Or they are multi-represented. Find your own language to say it, if you will. But please don't misunderstand and misrepresent QM any longer. 3 hours ago, bangstrom said: And the fact that it can not be used for human FTL communication [...] Good! We're getting somewhere. At least you admit that now. Unfortunately, your sentence ends badly: 3 hours ago, bangstrom said: [...] does not detract from the fact that it is a real effect. Well. It seems you're implying that there are two channels; one classical, and one quantum. It's the classical one that's under the strictures of sub-luminal propagation. But the quantum is not. Again: How do you know, if a pure quantum state cannot be measured? All those quantum changes can be measured on the mixed quantum state, which implies a considerable fewer degrees of freedom than the pure quantum state, and a lot more measurements. As a matter of fact, infinitely many experiments. How do you know it's FTL if you need infinitely-many measurements to measure it? 3 hours ago, bangstrom said: Yes, but this has nothing to do with quantum teleportation. Oh, I'm sorry. It does. It has everything to do with it. This is the generally accepted protocol for quantum teleportation (with my emphasis in boldface): Quote A Bell state is generated with one qubit sent to location A and the other sent to location B. A Bell measurement of the Bell state qubit and the qubit to be teleported ) is performed at location A. This yields one of four measurement outcomes which can be encoded in two classical bits of information. Both qubits at location A are then discarded. Using the classical channel, the two bits are sent from A to B. (This is the only potentially time-consuming step after step 1 since information transfer is limited by the speed of light.) As a result of the measurement performed at location A, the Bell state qubit at location B is in one of four possible states. Of these four possible states, one is identical to the original quantum state , and the other three are closely related. The identity of the state actually obtained is encoded in two classical bits and sent to location B. The Bell state qubit at location B is then modified in one of three ways, or not at all, which results in a qubit identical to , the state of the qubit that was chosen for teleportation. Mmmm. "both qubits at location A are then discarded." Don't look now, but that's the projection postulate in disguise. Because measurements are involved, there is an extraction of classical data from a quantum state, in order to package this output in the whole signal. This measurement always implies the choice of a basis. In the case of spin, you must decide which polarisation direction you're going to use for the signal. Is it x, is it y, or is it 45º in between? Or is it any other from the infinitely-many possibilities? Once you do that, if you express your density matrix in the corresponding representation you've chosen for the qubit, you will see, very transparently I might add, that it now corresponds to a mixed state. Nothing has travelled anywhere. You've dropped infinitely many components that were initially packaged in the Bell state. You've performed an einselection (one selection.) Zurek's work is about measurement. And so-called quantum teleportation is a particular example. Epilogue: You should be very careful when/if trying to extract hard conclusions by the very iffy method of scavenging for quotes by famous physicists. Some of them prefer to stick to the old-school Copenhagen prescription of the projection postulate which, as I told you, is good for all practical purposes, but incompatible with the Schrödinger equation and formally non-local.* Zeilinger seems to be one of them. People working in field theory, cosmology, etc., of course, know it is hopeless. It works in a quantum-information laboratory at extremely low temperatures, but you cannot make sense of it anywhere else, particularly in cosmology. If you want to go there, you need Zurek's analysis: It works in the laboratory and also for dissipative systems. Even though it's not completely free of problems. Representing the pointer states --in a way that's general enough-- being the real conundrum. Oh, I've just remembered another (Nobel Prize) who disagrees with Zeilinger: https://en.wikipedia.org/wiki/Gerard_'t_Hooft#Fundamental_aspects_of_quantum_mechanics Cheers. *Not only non-local. It's non-unitary, and non-linear. On 10/4/2022 at 5:52 PM, studiot said: I haven't post much in this thread as I view it as a non-argument. Why? I would agree that behind it there's no argument at all, but I find it very interesting to hear your reasons, when you have the time. 1
Eise Posted October 6, 2022 Posted October 6, 2022 (edited) 6 hours ago, bangstrom said: " Nearly all physicists agree that the experiments have shown that local realism is an untenable position. The viewpoint of most physicists is that the violation of Bell's inequality shows us that quantum mechanics is nonlocal. This nonlocality is exactly what Albert Einstein called "spooky"; it seems eerie that the act of measuring one particle could instantly influence the other one." From "Dance of the Photons" p. 286 This is not fair. You should have included the next paragraph, where Zeilinger gives his own viewpoint. It fits pretty well to @joigus post. Pity enough I only have the the original German version, and translating from one foreign language to another one is a bit difficult. But in my summary: he carefully proposes that letting go realism is the better solution, and refers to the Kochen-Specker theorem, which leads to a similar solution, even without entanglement. Maybe you could cite this paragraph here too? Until now I could not find the text somewhere on the internet. So now, I can add Zeilinger to my list, but only half-half, because he does not express himself as strong as the others on the list. But his tendency is clear. Edited October 6, 2022 by Eise 1
joigus Posted October 6, 2022 Posted October 6, 2022 (edited) 41 minutes ago, Eise said: This is not fair. You should have included the next paragraph, where Zeilinger gives his own viewpoint. It fits pretty well to @joigus post. Pity enough I only have the the original German version, and translating from one foreign language to another one is a bit difficult. But in my summary: he carefully proposes that letting go realism is the better solution, and refers to the Kochen-Specker theorem, which leads to a similar solution, even without entanglement. Maybe you could cite this paragraph here too? Until now I could not find the text somewhere on the internet. So now, I can add Zeilinger to my list, but only half-half, because he does not express himself as strong as the others on the list. But his tendency is clear. Very interesting comments. And superb work in documenting. +1 At this point I will commit to clarifying the discussion to the best of my abilities. If, at any point, I have sounded derisive to @bangstrom, I'm sorry. I apologise. That's not what I meant. Discussion with Bangstrom has proved to be frustrating in what I perceive as an "argument from gullibility" or, perhaps better, "argument from hurried interpretations of what actually is more subtle." The question at stake is certainly obscure at some points. I'll recognise that. But I do intend for this discussion to be leading to some kind of common ground that we can all agree upon, and faithfully represents what most working physicists see as standard wisdom. From there, a landscape of possible interpretations opens up, which is unfortunate. I'm even willing to admit that a brilliant experimentalist such as Zeilinger differs in posture from what others --important ones-- have expressed. I'm not 100% sure about that. Another very respectful physicist, arguably one of the most brilliant theoretical minds of his generation, Gerard 't Hooft, has been looking for a model based on the idea of cellular automata, in order to save what I would call "a minimally assuming version of determinism that's still compatible with quantum mechanics." I think his attempt falls under the category of superdeterminism. Maybe you can help me with that, @Eise. Why would anyone like 't Hooft pursue such a thing? Why did Weinberg too look for alternatives to the projection postulate? Does not Bell's theorem and the experimental proof of its violation exclude that?* * Exclude determinism, that is. Edited October 6, 2022 by joigus Addition/footnote
studiot Posted October 6, 2022 Posted October 6, 2022 7 hours ago, joigus said: Why? I would agree that behind it there's no argument at all, but I find it very interesting to hear your reasons, when you have the time. Sorry, here's why 1
Eise Posted October 6, 2022 Posted October 6, 2022 Hi Studiot! Does that mean the left and right side of the brain are entangled? Ok, back to business: I found a pdf of Zeilinger's book. This is the paragraph immediately after the paragraph @bangstromcited: Quote The other possibility would be for us to give up the picture of a world that exists in all its properties independent of us. That would mean that we have a very essential influence on reality just by deciding which measurement to perform.There are indeed hints that this might be the message we have to accept. The most significant result in that connection is the so-called Kochen-Specker paradox.It would go too far to explain it in detail here. A brief mention of the result must suffice. The Kochen-Specker paradox can be stated rather easily. It says that even for individual quantum systems, if they are sufficiently complex, it is not possible to assign to them elements of reality that explain all possible experimental results independent of the full experimental context, i.e. which measurement is performed at the same time on the same system. Now, since Kochen and Specker only considered measurements on single quantum particles, the locality hypothesis does not come into play.
joigus Posted October 6, 2022 Posted October 6, 2022 2 hours ago, studiot said: Sorry, here's why [...] 🤣🤣🤣 1 hour ago, Eise said: That would mean that we have a very essential influence on reality just by deciding which measurement to perform. (quoting Zeilinger) Here's where I think Zeilinger is talking about superdeterminism. Again, a bad name. Psychodeterminism? Volition-driven determinism? Anyway. I have to admit I don't know a great deal about models based on that option. I find it unpalatable. That's all I can say. But to me it does sound like Zeilinger does believe in some kind of non-locality, or at the very least in ambivalent about it. @bangstrom may be right on that one. If that's the case, I have no doubt that he is old-school and thinks the projection postulate is physical, not a convention. In any case, that's very old-school. I remember the days in the mid-90's when, if you even dared to suggest the projection postulate was just an artifact, not likely to represent the actual dynamics of the fields, you were considered a heretic. Most people today are convinced that the projection postulate is bollocks, and we have either misunderstood something or not accounted for everything that's relevant.
bangstrom Posted October 6, 2022 Posted October 6, 2022 (edited) On 10/5/2022 at 4:56 AM, joigus said: We can both agree that quantum entanglement can not be used for FTL communication. I think we have both agreed on that from the start and I have never stated otherwise. I see several minor points of disagreement with your previous post but there is one major misunderstanding that I was slow to pick up on because I thought it was too apparent to need clarification. It is in the quotes below. 11 hours ago, joigus said: 16 hours ago, bangstrom said: The viewpoint of most physicists is that the violation of Bell's inequality shows us that quantum mechanics is nonlocal. (Zeilinger again, with my boldface.) This is not correct. I think I've proved it. People who don't (or didn't) think quantum mechanics forces you to give up on locality: To say that QM is non-local means that it includes the possibility of non-locality as an explanation for observations at the particle level. It does mot mean that anyone is "forced" to give up on locality. That doesn't even make sense. This is not an either-or situation where to recognize non-locality at the particle level means that there is no locality anywhere. QM works perfectly well at the local level for most circumstances 3 hours ago, Eise said: Quote Now, since Kochen and Specker only considered measurements on single quantum particles, the locality hypothesis does not come into play. I understand that to mean that that we can abandon locality at the single particle level. Obviously that does not mean that we are forced to abandon locality altogether. 1 hour ago, joigus said: But to me it does sound like Zeilinger does believe in some kind of non-locality, or at the very least in ambivalent about it. @bangstrom may be right on that one. Zeilinger to recognizes non-locality at the particle level and he is not ambivalent about it. Edited October 6, 2022 by bangstrom Spelling correction. lever to level
joigus Posted October 6, 2022 Posted October 6, 2022 1 hour ago, bangstrom said: Zeilinger to recognizes non-locality at the particle level and he is not ambivalent about it. Not so fast. He says "abandon local realism." Abandoning faithful Stalinism does not imply abandoning faithfulness, does it? NOT (A AND B) = NOT(A) OR NOT(B) As quantum mechanics abandons realism from the start, abandoning locality is not necessary. In fact, it would be quite silly to do so. The Kochen-Specker theorem is more ontological. It does not say anything about locality. It goes to the heart of the matter, which is indeterminism, of course. The background of it is V. Neumann's theorem. Gleason's theorem is, so to speak, a basic version of it. But these theorems were proven insufficient by John Bell, who also contributed to the theorem, providing a proof. When the dimension of the Hilbert space is at least 3, you can build observables that cannot even be represented consistently by hidden variables, so to speak. Here's a sketch of the argument: https://plato.stanford.edu/entries/kochen-specker/ There's a much more complete account of it in, Incompleteness, Non-locality, and Realism, by Michael Redhead. But it's dealt with by means of the heavy machinery of spectral analysis. It's been a long time since I spent any time reading or thinking about the "ontological" versions of the impossibility theorems for hidden variables. I don't think there's any interesting physics behind them, TBH. Producing noiseless quantum signals, that's another matter. That opens up wonderful technological possibilites. But Star Trek? Forget about it! 1
bangstrom Posted October 7, 2022 Posted October 7, 2022 (edited) 5 hours ago, joigus said: 7 hours ago, bangstrom said: Zeilinger to recognizes non-locality at the particle level and he is not ambivalent about it. Not so fast. He says "abandon local realism." Abandoning faithful Stalinism does not imply abandoning faithfulness, does it? I have never taken “abandon local realism” to be a statement about anything beyond quantum entanglement. Entangled particles interact non-locally while observed particles behave locally. There is a possibility that the quantum world is far more chaotic and non-local for us to make any sense of it but three billion years of bio-evolution have trained us to be selective in our observations and to see only the parts of this chaos that pertain to our survival. To find food, avoid danger and reproduce. I am not bothered that Hilbert space does not allow for non-locality as long as it stays away from my space. 5 hours ago, joigus said: But Star Trek? Forget about it! Quantum teleportation is not like Star Track in that only quantum identities are transported and not the particles themselves. ‘Quantum identities’ is the term I find commonly used, possibly, because only single identities are being observed and ‘quantum properties’ refers to the whole shebang. Also, quantum teleportation is not the same as qubit teleportation. Quantum teleportation involves a difficult to obtain three way entanglement involving four entangled particles. Like A-(BC)-D. Edited October 7, 2022 by bangstrom formatting and removed non from nonentangled
swansont Posted October 7, 2022 Posted October 7, 2022 7 hours ago, bangstrom said: I have never taken “abandon local realism” to be a statement about anything beyond quantum entanglement. Entangled particles interact non-locally while observed particles behave locally. You persist in saying they interact, and yet have not explained what the nature of the interaction is.
joigus Posted October 7, 2022 Posted October 7, 2022 (edited) 8 hours ago, bangstrom said: I have never taken “abandon local realism” to be a statement about anything beyond quantum entanglement. Entangled particles interact non-locally while observed particles behave locally. There is a possibility that the quantum world is far more chaotic and non-local for us to make any sense of it but three billion years of bio-evolution have trained us to be selective in our observations and to see only the parts of this chaos that pertain to our survival. To find food, avoid danger and reproduce. I am not bothered that Hilbert space does not allow for non-locality as long as it stays away from my space. Quantum teleportation is not like Star Track in that only quantum identities are transported and not the particles themselves. ‘Quantum identities’ is the term I find commonly used, possibly, because only single identities are being observed and ‘quantum properties’ refers to the whole shebang. Also, quantum teleportation is not the same as qubit teleportation. Quantum teleportation involves a difficult to obtain three way entanglement involving four entangled particles. Like A-(BC)-D. Quote Bob Woodward: The story is dry. All we've got are pieces. We can't seem to figure out what the puzzle is supposed to look like. John Mitchell resigns as the head of CREEP, and says that he wants to spend more time with his family. I mean, it sounds like bullshit, we don't exactly believe that... Deep Throat: No, heh, but it's touching. Forget the myths the media's created about the White House. The truth is, these are not very bright guys, and things got out of hand. Bob Woodward: Hunt's come in from the cold. Supposedly he's got a laywer with $25,000 in a brown paper bag. Deep Throat: Follow the money. Bob Woodward: What do you mean? Where? Deep Throat: Oh, I can't tell you that. Bob Woodward: But you could tell me that. Deep Throat: No, I have to do this my way. You tell me what you know, and I'll confirm. I'll keep you in the right direction if I can, but that's all. Just... follow the money. Let me do this à la Deep Throat: Woodward (you): But all these guys have proven that quantum mechanics is non-local! Deep Throat (me): Oh, all those guys in the pop-sci media. They're not very bright. Things got out of hand. Follow the concept of realism. Woodward: But these guys, Clauser, Zeilinger, they've come in from the cold. Supposedly they've got a superluminal interaction signal with an n-times FTL tag in it. Deep Throat: Follow the concept of realism. Woodward: But you could tell me what your criterion of locality is... Deep Throat: No, I have to do this my way. You tell me what you know, and I'll confirm. I'll keep you in the right direction if I can, but that's all. Just... follow the concept of realism. Edited October 7, 2022 by joigus diacritics changed
Eise Posted October 7, 2022 Posted October 7, 2022 16 hours ago, bangstrom said: I understand that to mean that that we can abandon locality at the single particle level. Obviously that does not mean that we are forced to abandon locality altogether. With a single particle, entanglement of course plays no role at all. Which is what Zeilinger says: Quote Now, since Kochen and Specker only considered measurements on single quantum particles, the locality hypothesis does not come into play. But Zeilinger uses it in his argumentation for his view. Look how he is doing it: Zeilinger discusses 5 ways out after the confirmation that QM violates the Bell inequalities. Deny realism Deny locality Deny counterfactual definiteness Accept superdeterminism Accept actions to the past He more or less discards 3 4, and 5 rather briskly. Of locality, as already cited early, he remarks that most physicists think that we should give up on locality. However he tends to give up on realism, because this seems to be the conclusion of the Kochen-Specker theorem, and its first empirical tests. So the KS theorem has directly nothing to do with Bell states. But for Zeilinger it is a hint that of 'local realism' (which, as Joigus explained means 'locality' and 'realism' taken together), we have to loosen our concept of a reality behind our quantum measurements. Please reread the chapter 'What could that mean?'. (Warning: he does not discuss these in the exact order as I did here. I streamlined his argument here. First he mentions the first three assumptions, then he argues against (3), then he discusses locality and realism, and only then he mentions superdeterminism, retro-temporal causation, just to discard them immediately.) @joigus: as you see, Zeilinger argues against superdeterminism. He treats it as a kind of 'last straw'. This is his argument: Quote Just for completeness, let us mention that some other positions are also possible, at least in principle. One is the assumption of total determinism. In that case, everything is predetermined, including the decision of the observer about what he wants to measure. Thus, the question of what property the particle would carry if he were to measure something else would not come up at all, and therefore, the logical line of reasoning that led to Bell’s inequality could not be carried out. It is obvious that such a position would completely pull the rug out from underneath science. What would it mean to do an experiment if that were the case? After all, an experiment is asking nature a question. If nature itself determines the question, then we might as well not ask that question at all. For completeness the 5th: Quote Another logically possible position would be to assume that the individual measurements of the individual particles act back into the past. From that point of view, they would influence the source and tell the source, back in the past, with which properties to emit each particle. It is again obvious that such a position would mean a very radical rewriting of our views of space and time. 2
joigus Posted October 7, 2022 Posted October 7, 2022 (edited) 53 minutes ago, Eise said: With a single particle, entanglement of course plays no role at all. Which is what Zeilinger says: [...] Oh, boy. This is SOOOO exciting. For some reason I'm not allowed to react to your post. I'm not cajoling you, honest. I'm just thankful that you're here. I think @bangstrom is half-way there. Swansont has been there all the time, because he takes no bullshit. Let me just repeat your points (echoing Zeilinger): 53 minutes ago, Eise said: 1: Deny realism 2: Deny locality 3: Deny counterfactual definiteness 4: Accept superdeterminism 5: Accept actions to the past Just one observation: What about a combination of some of them? Eg, it could be: 1yes, 2no, 3no, 4no, 5no. (yes-denying/accepting, no-denying/accepting; that's my take.) Careful everybody, because some are "deny" and others are "accept." The logical tree becomes more complicated when you consider more and more possibilities. 3 is important, but obscure. That's what I think is the case. I think it's a "no." And I also think there's experimental case for it. I'd be very interesting to learn about Zeilinger's take on it. 5no because 5no <= 2yes We're getting there, we're getting there... It's such a pleasure to have you here, @Eise. We may have to agree on terms of what 3 actually means. Edited October 7, 2022 by joigus essential correction in implication map 2
studiot Posted October 7, 2022 Posted October 7, 2022 2 hours ago, joigus said: Just one observation: What about a combination of some of them? Like the cat, dead and alive ? +1 It's a funny old world.
joigus Posted October 7, 2022 Posted October 7, 2022 2 hours ago, joigus said: 5no because 5no <= 2yes Did I get this wrong? Denying locality implies that actions to the past are possible. Would that be 2yes => 5yes instead? I think that's right. I think I did get that one wrong. Somebody help me here. I got confused with the mix of "denying" and "accepting." The possibility of combining "sufficiency" and "necessity," (directional arrows) or even neither one nor the other would turn this into a logical maze.
bangstrom Posted October 8, 2022 Posted October 8, 2022 14 hours ago, swansont said: You persist in saying they interact, and yet have not explained what the nature of the interaction is. The interaction is instant and non-local. I explained before how they interact, and if you found my explanation unsatisfactory, I agree that it was. I can also explain how I really think it works but that would just be just another speculation about the un-observable. This is the mainstream explanation again and you can take it or leave it, or better yet, look it up for yourself. It is easy to find. Entangled particles are in a state of superposition prior to the first observation. That means that they both share the same quantum properties and they can’t be considered as separate. With the first observation the quantum state of the observed particle randomly becomes determinate and the quantum of the state of the other particle instantly becomes both determinate and anti-correlated with its formerly entangled partner. There is no need for a communication or signal to pass between the particles. When entanglement is instantly lost the quantum properties of the particles on both ends instantly appear and the action is non-local.
bangstrom Posted October 8, 2022 Posted October 8, 2022 15 hours ago, Eise said: On 10/6/2022 at 3:54 PM, bangstrom said: I understand that to mean that that we can abandon locality at the single particle level. Obviously that does not mean that we are forced to abandon locality altogether. With a single particle, entanglement of course plays no role at all. I think of locality as a single particle responding to its local environment. Another particle remote from the first can also respond to its local environment. But, if an event in one location instantly changes an event in a distant location with no apparent connection, the action is non-local. For a little history, as I recall Feynman mentioned in QED that a single photon can not interfere with itself but when a single photon passes through a double slit it unexpectedly produces an interference pattern. Feynman’s explanation was that it was able to interfere with photons that passed through the slit in the past and photons that that will pass through the slit in the future. Feynman’s explanation was too strange for popular consumption but a better version survives in other present day theories such as John Cramer’s TIQM (not my favorite) with advanced and retarded waves that must make a non-local connection between one charged particle in the present, usually an electron, and a similar particle in the past before a quantum of energy called a ‘photon’ can be transacted into the future This means we can send a light signal to the future but not to the past, however a connection extending back to the past is a necessary prerequisite for sending a message into the future. A bit of speculation about this from the 1920’s was that a universe containing nothing but a tea kettle of hot water could never cool because there would be nothing to receive its energy. Zeilinger appears to be open to the idea of present influencing the past and Wheeler and Feynman agreed that the usual quantum theory can be interpreted in terms of direct interaction between an emitter and absorber. These views require a non-local connection ‘instant’ between the past and present. From p. 234 of Zeilinger's book "Dancing of the Photons" REALITY VS INFORMATION First Alice made an observation on her end of an entangled state and later Bob made an observation on his end. From Bob's view, his observation was the first and Alice's came later. ”The interesting point is that in the end we will, for Bob’s results, present a different interpretation depending on what Alice at a later time decides to do. She may decide to do a Bell-state measurement, or she might decide to do a measurement on each photon on its own, there is even an infinite zoo of possibilities in between. Depending on what Alice decides to do, the results registered earlier by Bob, the events that already happened, acquire a very different meaning." Or from p. 287 “Another logically possible position would be to presume that the individual particles act back into the past, From that point of view, they would influence the the source, back in the past, with which properties to emit each particle. It is again obvious that such a position would mean a very radical rewriting of our views of space and time." I find this radical view of space and time to be what is known as ‘Block Universal' time. For one thing, Block time conforms what Minkowsky said about about the inseparability of space and time. I like to think of the little squares in a Minkowsky diagram as little ‘time zones’ where moving through space is simultaneously moving through time. Anything distant from our perspective is also distant from us in time. This view is also consistent with SR where simultaneous events separated by space are always observed as separated by time at the constant rate of one second for every 300,000 km of distance. This is why, non-local events of quantum entanglement can never be used for FTL signaling. We only see events separated by distance as also separated by time. 16 hours ago, Eise said:
bangstrom Posted October 8, 2022 Posted October 8, 2022 18 hours ago, Eise said: Zeilinger discusses 5 ways out after the confirmation that QM violates the Bell inequalities. Deny realism Deny locality Deny counterfactual definiteness Accept superdeterminism Accept actions to the past He more or less discards 3 4, and 5 rather briskly. Where does Zeilinger dismiss #5? From my reading he appears to be leaning in favor of actions to the past. That is, excluding actual EM signals to the past. We can send signals to the future but not the past. "Another logically possible position would be to presume that the individual particles act back into the past, From that point of view, they would influence the the source, back in the past, with which properties to emit each particle. It is again obvious that such a position would mean a very radical rewriting of our views of space and time." Also, quantum entanglement extends both forward and backward in time. The instant loss of entanglement can appear as being either forward or backward in time depending upon from which end you are acting as an observer. On 10/6/2022 at 4:20 AM, joigus said: A pure quantum state cannot be measured. How do we know quantum states are correlated if they can't be measured? Also, can you define what you mean by non-locality?
Eise Posted October 8, 2022 Posted October 8, 2022 (edited) 3 hours ago, bangstrom said: But, if an event in one location instantly changes an event in a distant location with no apparent connection, the action is non-local. You should better take care of your words, which is very important in such fundamental questions. I made them italic: action: we had this again and again. There is no action, no interaction, no causal relationship, no information transfer, no affect, no influence between the measurements. These are all excluded by the no-communication theorem. change: there is no change, in the first place because a change needs a cause, and that is already done away with with the previous point. In the second place, we cannot detect this change, because we cannot observe the wave function itself. We cannot look deeper then individual quantum measurements, and therefore we can only detect correlations. 9 hours ago, bangstrom said: This is the mainstream explanation again and you can take it or leave it, or better yet, look it up for yourself. It is easy to find. This is hubris. Swansont knows more about QM than you, me, and Joigus together. You are referring to the mainstream again. And still, you are not able to mention any QM expert precisely arguing why it is that we have to give up locality in QM. 3 hours ago, bangstrom said: ”The interesting point is that in the end we will, for Bob’s results, present a different interpretation depending on what Alice at a later time decides to do. She may decide to do a Bell-state measurement, or she might decide to do a measurement on each photon on its own, there is even an infinite zoo of possibilities in between. Depending on what Alice decides to do, the results registered earlier by Bob, the events that already happened, acquire a very different meaning." Again you do not understand quite what Zeilinger is saying here, and his viewpoint later in the chapter. I italicized the words. Zeilinger does not talk about events 'influencing' events in the past. He is saying that our interpretation of the experiment is different. Alice's measurement occurring before Bob's measurements, or after his measurements are different experiments, i.e. we need different interpretations of the experimental situation. Quote At this point,we might state one point with emphasis. Each of the interpretations we come up with for Bob’s earlier results is completely correct and objective. The fact that an interpretation depends on Alice’s future decision does not at all make it incorrect or subjective. Quantum physics describes all of these situations well. It is just that the mathematical description, the quantum state we assign to the situation, is very different depending on what Alice decides to do. It depends on the specifics of the experimental settings, and therefore, it depends on Alice’s decisions, or in general it depends on the decisions of us as experimenters. And this may include specifics of the experiment that will be decided in the future. Emphasis by me. And then: Quote These kinds of considerations support the point of view that has most succinctly been expressed in the Copenhagen Interpretation of quantum physics as it was created specifically by Niels Bohr. According to that interpretation, the quantum state of a system is not a field, or some entity that spreads “out there” in space and time. On the contrary, the quantum state is just a representation of the knowledge we have of the specific physical situation we are investigating. This representation of our knowledge naturally depends on which situation we have in front of us, which kinds of measurement results we obtain. And then, more specific: Quote In our specific case, our knowledge of the specific situation depends on the kind of measurement Alice performs at a later time and the result she obtains then. We conclude that Alice’s later measurement, and her result, do not influence the physical reality already in existence—namely, the specific results Bob obtained at an earlier time. But they change what we may say about the situation. They change our interpretation of what is going on. This very much calls to mind a famous statement by Bohr: “There is no quantum world. There is only an abstract quantum physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature.” Italics by me. The obvious problem for you is that Zeilinger is a nice and reasonable fellow. So he presents different viewpoints and mentions a few arguments pro and contra these viewpoints. And then you pick out the arguments that fit to your viewpoint. But giving his own viewpoint Zeilinger is very clear: on QM level, we have to depart from realism; not locality. 2 hours ago, bangstrom said: From my reading he appears to be leaning in favor of actions to the past I showed you above that this is not his opinion. And you are using 'action' again! 2 hours ago, bangstrom said: Where does Zeilinger dismiss #5? (...) "Another logically possible position would be to presume that the individual particles act back into the past, From that point of view, they would influence the the source, back in the past, with which properties to emit each particle. It is again obvious that such a position would mean a very radical rewriting of our views of space and time." Underlined it for you. Sure, he does not say this is excluded, but that giving our present insights it is not the best solution, because it would mean a total rewriting our present understanding. It is also, clear from the context in which he discusses this, taking the options 4 and 5 behind the sentence: Quote Just for completeness, let us mention that some other positions are also possible, at least in principle. Meaning 'to be honest, there are two other interpretations, but I do not take them seriously'. You really have a problem understanding texts. Edited October 8, 2022 by Eise
joigus Posted October 8, 2022 Posted October 8, 2022 4 hours ago, bangstrom said: How do we know quantum states are correlated if they can't be measured? 4 hours ago, bangstrom said: Also, can you define what you mean by non-locality? I already have, plus I have accepted @Eise's definition as good enough, as a sacrifice in order to reach a minimal common entendre here. For better or worse --for worse is more like it-- I will have to avoid resorting to mathematics. I will use pictures, plus reference to mathematical symbols. Are you OK with that? Careful here, because an equation can be perfectly local, while violate relativistic causality. Non-local => Relativistic causality is violated But, Relativistic causality is violated =/=> Non-local In words: "relativistic causality being violated does not imply non-locality. Non-locality would be much, much, much, incommensurably much worse. And I'm telling you this knowing full well that relativistic causality is considered sacred by most physicists post-Einstein. It would imply that --in certain simple contexts-- you could make "something" instantly disappear "here," and at the same time appear "there." If you accept this standard, we can go on. If not... Well, the best I can do is recommend you to go back to intermediate physics books and learn about it: Local conservation of charge density, angular-momentum density, probability density (QM), energy, etc. You may well ask: Is it the probability amplitude that's disappearing "here" and appearing "there" instantly? We can tackle that question if you want.
MigL Posted October 8, 2022 Posted October 8, 2022 Clauser, Aspect and Zeilinger were this year's recipients of the Nobel. ( see 'Science News' thread ) For their work in estabilishing that there is no local reality.
Recommended Posts