joigus

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!

🤣🤣🤣 (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.

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.

(Zeilinger) This is correct, but because of the "realism" bit of it, not because of the "local." The Schrödinger equation is 100% local. (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? 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: 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. 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. Good! We're getting somewhere. At least you admit that now. Unfortunately, your sentence ends badly: 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? 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): 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. 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.

Thanks for the detailed explanation. I've sometimes thought that (even) religious issues should be discussed under the light of scientific evidence (archaeology, literary criticism, history, etc.) But I understand the difficulty of reaching a compromise here.

I just learnt. Rest in peace, Loretta Lynn: And patron of motocross too.

This should go in the Speculations section, @universeteory. Welcome to the forums. Also, religion has never helped science, it's always stood in its way, as far as I know.

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. 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?

How do you propose to reduce the effect of gravity? Why change a theory that already works? Why we never see anything going faster than light?

"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. Exactly. I like to put it in a (hopefully) intuitive way I've used before: The speed at which 1-1=0 is infinity

I made no mistake or omission, therefore no excuse is needed on my part. Read back. @Eise gave a quite economic, quite satisfactory one I agreed to. I gave at least two more mathematical ones and referred to them later when asked. But because mine are perhaps too technical --although perfectly mainstream--, I'm OK with Eise's. All are equivalent and it can be shown mathematically in terms of a so-called Cauchy problem. I can do my best to help people understand or clarify possibly obscure points, but I do not condone laziness.

Of course, you don't. How could you? Sabine Hossenfelder http://backreaction.blogspot.com/2020/05/understanding-quantum-mechanics-3-non.html You're welcome. I disagree with Hossenfelder that it's difficult or "complicated." I think it's obvious if you pay attention to some arguments people have presented here. Are you familiar with Ctrl+F? There are 153 comments. I hope you're not looking for it by skimming through the text! It's not. Believe me.

http://backreaction.blogspot.com/2020/05/understanding-quantum-mechanics-3-non.html There. It took me a couple of seconds. That's what it takes when you actually read what people are telling you.

Very good post, Eise. +1 You certainly bring clarity into the question, and perfectly understand the logical points. You say you're not totally familiar with the formalism, but still. And thanks for the reference to Hossenfelder's blog. And that Nobel Prize is well deserved for Clauser, Aspect, and Zeilinger. Oh, be in no doubt!

(Quoting Hossenfelder.) Of course not: Quantum mechanics forces you to give up on determinism. Period. If you accepted quantum mechanical experimental success, but --in order to save determinism-- accepted some kind --any kind-- of internal determinism to account for it, you would have to give up on locality. Is that clear at long last? Let me guess: No. The problem with the starting sentence is that it opens the gates to a gross misunderstanding, if you remove the essential words "it seems." It's so common a misunderstanding that I don't care how much time I have to spend talking about it as long as the possibility exists that, finally, people who still think this to be the case, are gathered at the gates of quantum heaven at the end of days. This final day you will meet Feynman, Gell-Mann, Sidney Coleman, a repentant Einstein, Bohm, and a repentant Bell --"repentant" for having introduced confusing words in the first place, but redeemed both Einstein and Bell by their accurate and commonly misunderstood respective analyses--, and agree with all of them that quantum mechanics is local. Classical logic, if pressed to account for quantum correlations, would have to be implemented non-locally. But wait a minute, classical logic is not what quantum mechanics is about. End of story. Or is it? There would be a second loophole for the prophets of non-locality. What if the projection postulate is correct? The projection postulate is strongly non-local. It would be a kind of non-locality with zero consequences, by design, because the components of the quantum state that don't carry the actual output of an experiment, must be killed off by decree. Actually, if you think about it, it's no wonder that it entails a non-local prescription: It was designed to implement the fact that real electrons and photons hit the screen at some point. So you introduce definiteness at some point by design. If you remember Bell's theorem, and really understand it, there is no mystery. And that's all. If bangstrom finally has understood this point, we could perhaps proceed from there. The explanation of that monumental fiction: Why does the projection postulate introduce a non-local prescription that produces no non-local consequences? But something tells me we're not getting there any time soon. This would make for an interesting topic of debate on (bare evidence) + (bare assertions of a theory) vs (epistemological prejudices) of people: Illusion of design --evolution--, illusion of non-locality --QM--, and probably more. The theme is more general than it looks.

You are so confused. Let's take Sabine Hossenfelder's video and read carefully her statements. I'm reproducing here the most important ones with my emphasis: Is and is not local? Mmm. What could she mean? Appears to be? So what then? Is it, or is it not? More: In other words, some people choose to say it is non-local. It seems... mmm. Is that a strong statement to you? Here's the killer: If you quote authorities, the least you could do is listen carefully to what they're saying. I get it. Quantum mechanics seems to be non-local. But actually, it is and it is not. That's why some people choose to say it is non-local. Sweet. You could at least listen to the videos you post, @bangstrom

Exactly. Counting particles is beside the point. It's so easy to find examples of many particles in a maximally entangled state. Take any high-atomic number atom. Eg, californium's 4f energy level has 14 entangled electrons. The point is something else. Now, what is that something else? I'll be back. Running out of time now. See my point? Nature has done 4 better than scientists that prepared a 10-silicon-atoms entangled state.

Not surprised. I agreed to that one. Here's what I said: Water bear = tardigrade Essentially no different from experiment with a number of silicon atoms (the fullerene experiment.) There are other: https://phys.org/news/2017-11-physicists-qubit-entanglement.html You can take one qubit, coherently entangle it with another identical qubit, further entangle it with another qubit, and so on. It's an incremental process. I see no problem with that, except technical. Entangle a qubit with a whole bunch of atoms already involved in dissipative --irreversible-- interactions? Impossible. In fact, it doesn't even make sense: What does it even mean to entangle non-identical things? I understand I'm the party pooper here. Some people want to see extraordinary, magical things. Their will to do so takes them on a journey into foolishness and unsupported claims, as well as to drawing conclusions that are not there, and never were. It's all ordinary things. It's the world you see, none other. It's a cat looking at you and being there, alive through and through. Your life passes by before your eyes, and your cat is no longer there, keeping you company, as @MigL knows very well. What I would like some people to see is how magical, how extraordinary, ordinary things are. That's physics' "magic." It takes a while. It doesn't come easy.

Oh, an Iggy. LOL. Sure, as a joke it's really good. The claims of what it implies is what I find more "ignoble."

This is not peer-reviewed work. Cornell's repository is for preprints, not papers. I don't see the peer-reviewed paper anywhere. What I have found is a bunch of people saying this is nonsense: https://phys.org/news/2021-12-peers-dispute-tardigrades-entangled-qubits.html And I agree. I'll keep an eye on it just in case. Don't hold your breath. I see you have no idea how long it takes for a "groundbreaking" paper to get approved for publication, and once there, how long it takes for a Nobel prize to be awarded. You've watched too much Big Bang Theory. Give it a rest. And study some quantum mechanics in the meantime.

This is by far the most ridiculous thing you've said so far on this thread. You're being the mouthpiece of some fat-ass crackpottery, my friend. Through no fault of your own perhaps, just by constantly ignoring the physics involved. Really?, quantum coherent superpositions of order 1024 -plus individual electrons, protons, neutrons and photons making up a tardigrade, --I guess that's what you mean-- which is an animal that has dissipative processes constantly going on in its body? Now for buckyballs --I guess that's what you mean-- those are fullerene particles very common in interstellar soot, so I'm guessing it's possible in principle, like in the case of silicon atoms, although extremely difficult. I already gave you a reference to macroscopic superpositions of bunches of silicon atoms, but again you missed it. Give us the reference to your Schrödinger water bears, please. I wanna have a good laugh. Not only the square of the amplitude ψ∗ψ , but the probability current, which is conserved locally, as an exact theorem of quantum mechanics.

This is a very interesting point. People often change their views during their lifetime. Einstein is no exception. Even when the thinking of one particular person significantly contributed to change everyone else's interpretation, it's interesting to consider the challenges they had to face, the historical climate they stood up against, as well as their own thinking as an ongoing process, and get --be it ever-- the roughest feel for how their thinking must have evolved. I once read that it took Einstein one whole year to realise that Minkowski's 4-dimensional description of his own research was actually relevant. Even if that's an apocryphal story --which I don't think it is--, there's a potential lesson in it. We tend to think of scientific breakthroughs as kind of a static or frozen process, which they are surely not.

Just one: No classical object will serve as an analogue of a quantum system. (Anti-emphasis.) Don't tell anyone, apparently it's a secret, even if you repeat it 6 times. Here they are: Another one: Another one: Another one: Another one --with icecream; maybe it's the concept of coin that's standing in the way, who knows: Another one: It really looks like I've said something about that before. Maybe I didn't and this is all a non-local, superluminal dream. A coin (cat, gloves, icecream, etc.) has no states that are determined (elements of reality in Einstein's parlance) as to the Heads/Tails character, but a superposition of ·Euro/Dollar as to the "coinage" character, so it will never reproduce all quantum peculiarities. You couldn't, so it won't. When will a classical analogue spell out the properties of quantum systems?: No can do, very problemo, when Hell freezes over, never happens, when the cows get home and cook me dinner and sing me a lullaby... So I'm sorry, no classical analogy. You really must think quantum!!!!!!!! Please, tell me it is clear now. Yours truly, Sisyphus Edit: x-posted with @NTuft

I'm not looking for agreement. I'd rather you disagreed with me, or bangstrom, or any other, as long as you provided an argument for the particular point in QM where you see this possibility of superluminal communication, or instantaneous interaction, or what have you. On what grounds do you agree that "communication via entanglement is impossible now"? Are you saying that communication via entanglement will be possible without superseding QM with some other theory that is non-local? Notice, please, what I'm not saying: I'm not saying that communication via a quantum channel --whether it involves entanglement or otherwise-- is impossible. It's only that whatever communication channel will be subject to the strictures of local, sub-luminal propagation. Unless we come up with a theory that substantially changes quantum mechanics, and ushers in a new era with the possibility of superluminal propagation. Such a new theory would also have to explain why we've never observed it so far. Then, it would have to explain: How come relativistic causality is not violated?