• Wayfarer
    16.3k
    Did the action at a distance take place at a rate faster than the speed of light?T Clark

    'Instantaneous' means 'no time'. That's why Einstein couldn't accept it.

    Does the experiment described contradict that?T Clark

    The 'Bell inequalities' experiments confirm that the correlation between the two particles that occurs at the measurement of one of the pairs is instantanous.

    If not what's the big deal.T Clark

    That's why it's a big deal. Hence Niels Bohr's oft-quoted statement, 'Those who are not shocked when they first come across quantum mechanics cannot possibly have understood it.'

    (For the attribution of that quote, it's in Werner Heisenberg's book Physics and Beyond: Encounters and Conversations, in the chapter on Positivism, Metaphysics and Religion. It relates to a lecture Bohr gave to representatives of the Vienna Circle when they came to Copenhagen. Bohr felt by their polite applause and lack of questions that they didn't understand what he was telling them, 'otherwise they would have been shocked by it'. I think this still holds true.)
  • T Clark
    9.8k
    The 'Bell inequalities' experiments confirm that the correlation between the two particles that occurs at the measurement of one of the pairs is instantanous.Wayfarer

    It is my understanding that is not the same as information being transmitted at a rate greater than the speed of light. I admit I don't understand why not. Wikipedia says:

    Superluminal communication is a hypothetical process in which information is sent at faster-than-light (FTL) speeds. The current scientific consensus is that faster-than-light communication is not possible, and to date it has not been achieved in any experiment.

    Yes, I know Wikipedia is not an unimpeachable source.
  • Wayfarer
    16.3k
    The article is correct - information cannot be transmitted faster than light. Yet in the Bell experiments, the correlation between separated particles is instaneous. So, information is not being transmitted between the two particles, and yet the correlation is happening. By what means does that correlation happen, in the absence of tranmission of information? You see the question? Something done in one place seems to have an instaneous effect on something in another place. Hence, 'spooky action at a distance'.
  • T Clark
    9.8k
    The article is correct - information cannot be transmitted faster than light. Yet in the Bell experiments, the correlation between separated particles is instaneous. So, information is not being transmitted between the two particles, and yet the correlation is happening. By what means does it happen? You see the question?Wayfarer

    I've struggled with the whole idea. I keep holding on to the the no-superluminal-communication floatation device hoping someone will rescue me.
  • Deletedmemberzc
    2.5k


    Not competent to speak on the subject - but it's still fun.

    It seems the particles must be either, in some sense, the same particle or, in some sense, in the same location.


    Madness.
  • Wayfarer
    16.3k
    I've struggled with the whole idea.T Clark

    And you wouldn't be alone in that, but I've long since reconciled myself to it.
  • Agent Smith
    7.6k
    Interesting to say the least.

    I don't know if this is related or not, but I recall reading that electrons/particles are only a fuzzy probability distribution (pure potential) and acquire a fixed locus i.e. pop into existence at the moment of observation (actualization of potential); in a sense, the mind via measurement/observation causes particles to be (mind-dependent reality).
  • jgill
    2.4k
    The Schrödinger equation is linear and so linear combinations of solutions are also solutions. This is the superposition concept in its mathematical garb. The superposition principle leads to quantum entanglement, since a measurement identifies a state and illuminates a solution. Thus entanglement can occur, since otherwise an entangled pair would be nothing more than the common example of a coin split into a head half and a tale half. So the roots of this notion arise in elementary differential equations or linear algebra. Or so it seems to me.

    Not that this solves anything.
  • Wayfarer
    16.3k
    that’s how I understand it too. This idea of there being permanent, unchangeable objects - the original meaning of ‘atom’! - no longer holds. So the answer to the question ‘does the electron exist’ just is the wave-function. The answer it gives is again a distribution of possibilities, not a yes/no. ‘Exists’ doesn’t apply. ‘Does not exist’ doesn’t apply. (Does that ring a Bell?)

    Of course! All of what we are talking about ‘fell out of the equations’ so to speak. Superposition, for instance, about which it’s difficult to form any kind of real concept.
  • noAxioms
    1.1k
    So making a measurement here creates an outcome there without any apparent means for that information to be transmitted - because it's instantaneous, then it is faster than the speed of light which is the upper limit for any actual transmission.Wayfarer
    The 'Bell inequalities' experiments confirm that the correlation between the two particles that occurs at the measurement of one of the pairs is instantanous.Wayfarer
    This wording suggests that there is a concept of 'instantaneous', or absolute simultaneity, which is an entirely naive wording.
    What they have is two measurement events of these entangled particles and those two events are separated in a space-like manner. That means that there exists some frames where those two events are simultaneous, and many frames where one occurs first, and many where the other occurs first.
    But the wording in the above statements suggests that there is but one measurement that somehow 'instantaneously' changes the state of the other particle, even in the absence of it being measured, which is exactly begging not only absolute simultaneity, but also that there is an objective state of reality independent of measurement. Begging the latter assumption voids any falsification of locality. Local interpretations cannot presume an objective reality (again, with that one loophole exception), per Bell.

    Did the action at a distance take place at a rate faster than the speed of light?T Clark
    Faster than light yes. Into the past even in the case of delayed choice experiments, which have been performed with cause occuring years after the effect.

    The thing that locality denies is not the faster than light relationship between measurements, but the 'action' part. No local interpretation suggests that anything changes at the far particle when the near one is measured. Copenhagen is about as local as it gets, and it being an epistemological interpretation, all it says is that a measurement here causes knowledge here of what the other measurement will be when we learn of it. Other local interpretations word it differently, but none suggest any FTL action.
  • Wayfarer
    16.3k
    This wording suggests that there is a concept of 'instantaneous', or absolute simultaneity, which is an entirely naive wording.noAxioms

    I don't believe so. You haven't read the evidence about it. If it was as trivial a matter as you're suggesting, then there would be nothing to discuss.

    the wording in the above statements suggests that there is but one measurement that somehow 'instantaneously' changes the state of the other particle,noAxioms

    The instantaneous nature of the correlation is precisely the point at issue. Whether the measurement of one changes the state of the other is another point at issue.

    Copenhagen is about as local as it gets, and it being an epistemological interpretation, all it says is that a measurement here causes knowledge here of what the other measurement will be when we learn of it.noAxioms

    I'm not a physicist, but based on the plain English accounts that I've read of this matter, of which there are quite a few, I don't think this is so. If you would like to validate your intepretation with some sources (other than technical physics papers), please do.

    Perhaps for a start you could explain why Einstein objected to the suggestion of entanglement with the word 'spooky'.
  • T Clark
    9.8k
    The thing that locality denies is not the faster than light relationship between measurements, but the 'action' part. No local interpretation suggests that anything changes at the far particle when the near one is measured. Copenhagen is about as local as it gets, and it being an epistemological interpretation, all it says is that a measurement here causes knowledge here of what the other measurement will be when we learn of it. Other local interpretations word it differently, but none suggest any FTL action.noAxioms

    Thanks. It's hard to grasp.
  • Wayfarer
    16.3k
    Don't be mislead, the statement you've quoted is wrong in every particular, to my knowledge. Review Matt O'Dowd's PBS Space Time video above, he gives the correct account of the issue, and also of the Copenhagen interpretation.

    Quantum entanglement is the physical phenomenon that occurs when a group of particles are generated, interact, or share spatial proximity in a way such that the quantum state of each particle of the group cannot be described independently of the state of the others, including when the particles are separated by a large distance. The topic of quantum entanglement is at the heart of the disparity between classical and quantum physics: entanglement is a primary feature of quantum mechanics lacking in classical mechanics.

    Measurements of physical properties such as position, momentum, spin, and polarization performed on entangled particles can, in some cases, be found to be perfectly correlated. For example, if a pair of entangled particles is generated such that their total spin is known to be zero, and one particle is found to have clockwise spin on a first axis, then the spin of the other particle, measured on the same axis, is found to be anticlockwise. However, this behavior gives rise to seemingly paradoxical effects: any measurement of a particle's properties results in an irreversible wave function collapse of that particle and changes the original quantum state. With entangled particles, such measurements affect the entangled system as a whole.

    Such phenomena were the subject of a 1935 paper by Albert Einstein, Boris Podolsky, and Nathan Rosen, and several papers by Erwin Schrödinger shortly thereafter, describing what came to be known as the EPR paradox.Einstein and others considered such behavior impossible, as it violated the local realism view of causality (Einstein referring to it as "spooky action at a distance") and argued that the accepted formulation of quantum mechanics must therefore be incomplete.

    Later, however, the counterintuitive predictions of quantum mechanics were verified in tests where polarization or spin of entangled particles was measured at separate locations, statistically violating Bell's inequality. In earlier tests, it couldn't be ruled out that the result at one point could have been subtly transmitted to the remote point, affecting the outcome at the second location. However, so-called "loophole-free" Bell tests have been performed where the locations were sufficiently separated that communications at the speed of light would have taken longer—in one case, 10,000 times longer—than the interval between the measurements.

    According to some interpretations of quantum mechanics, the effect of one measurement occurs instantly. Other interpretations which don't recognize wavefunction collapse dispute that there is any "effect" at all. However, all interpretations agree that entanglement produces correlation between the measurements and that the mutual information between the entangled particles can be exploited, but that any transmission of information at faster-than-light speeds is impossible.

    Quantum entanglement has been demonstrated experimentally with photons, neutrinos, electrons, molecules as large as buckyballs, and even small diamonds. The utilization of entanglement in communication, computation and quantum radar is a very active area of research and development. ...

    Paradox
    The paradox is that a measurement made on either of the particles apparently collapses the state of the entire entangled system—and does so instantaneously, before any information about the measurement result could have been communicated to the other particle (assuming that information cannot travel faster than light) and hence assured the "proper" outcome of the measurement of the other part of the entangled pair.
    Wikipedia entry on Quantum Entanglement
  • T Clark
    9.8k
    Don't be mislead, the statement you've quoted is wrong in every particular, to my knowledge. Review Matt O'Dowd's PBS Space Time video above, he gives the correct account of the issue, and also of the Copenhagen interpretation.Wayfarer

    I watched the video and, as I understand it, it confirms the statement from Wikipedia I quoted before:

    The current scientific consensus is that faster-than-light communication is not possible, and to date it has not been achieved in any experiment.

    I'm just as confused as I was, but the guy in the video doesn't seem to be.
  • Wayfarer
    16.3k
    The current scientific consensus is that faster-than-light communication is not possible, and to date it has not been achieved in any experiment.Clarky

    That is true. But as the article then says. 'the paradox is that a measurement made on either of the particles apparently collapses the state of the entire entangled system—and does so instantaneously.'

    I'm by no means suggesting a solution, but I think it's important to at least acknowledge what the paradox is. (Richard Feynman said 'Do not keep saying to yourself, if you can possibly avoid it, 'But how can it be like that?' because you will get 'down the drain,' into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that.') That's why I think quantum physics is kind of like sorcery. ;-)
  • noAxioms
    1.1k
    I don't believe so. You haven't read the evidence about it. If it was as trivial a matter as you're suggesting, then there would be nothing to discuss.Wayfarer
    I'm talking about relativity of simultaneity (RoS). If you don't know what that is, then you don't have the tools to assess the validity of my criticism of the wording used in the article. If you do know what it means, then you know that the article wording implies absolute simultaneity, something often done in pop articles but not science papers. This is why you don't get your science from pop articles, despite the credentials of the author.

    The instantaneous nature of the correlation is precisely the point at issue.
    The correlation of the measurements is simultaneous (very different from instantaneous) in a few frames and not in most. The absence of a frame specification renders the assertion meaningless, and even if they did supply the frame specification, they've still only demonstrated simultaneity of correlated measurements, not action-reaction.

    Whether the measurement of one changes the state of the other is another point at issue.
    That of course has not been demonstrated. If for instance the measurement of one collapsed the state of the other, the abrupt cessation of superposition of the remote particles could be measured and that would constitute FTL communication and it would be news indeed. But no such thing has ever been demonstrated.

    Copenhagen ...
    — noAxioms

    I'm not a physicist, but based on the plain English accounts that I've read of this matter, of which there are quite a few, I don't think this is so. If you would like to validate your interpretation with some sources (other than technical physics papers), please do.
    Copenhagen was originated as an epistemological view: Back in the early days, quantum physics defied classic description, so they came up with a set of rules about what could be known about a system. You could have two people standing next to each other and one would know the result of a measurement and the other not. No metaphysical interpretation would suggest that the superposition of the measured system itself was collapsed for one of the two people and not the other simply pending verbal communication.

    So Copenhagen was perhaps a poor example because there is now much writing about it, and many contradictory metaphysical assertions all bearing the same name. Metaphysically, I don't think there is one accepted version and no one accepted author of the interpretation. I don't think there is an accepted scientific paper that IS the Copenhagen interpretation. As for articles written in understandable language, you can find ones that support just about any assertion you like just like the Bible can be used to justify whatever evil you have in mind today. So I'll not link to one that supports my locality assertion since you can equally find one that asserts otherwise.

    Perhaps for a start you could explain why Einstein objected to the suggestion of entanglement with the word 'spooky'.
    Einstein was a realist and very held to the principle that there was an objective state of the universe even in the absence of measurement. But his theory of relativity strongly suggests he held to (heck, he defined) the principle of locality, that cause must precede effect. Bell showed that you must choose between the principles. No valid interpretation of QM can postulate both of them, and many postulate neither.
    All the articles I've seen linked from this topic contain language that assert the objective reality, which of course must contradict locality, but to disprove locality, one must do so without begging the objective reality since none of the local interpretations list it as one of the premises.

    The current scientific consensus is that faster-than-light communication is not possible, and to date it has not been achieved in any experiment.Clarky
    Ah, but the spooky-action folks are not claiming communication, they're claiming FtL action-reaction. But if there was a (remote) empirical test for this having actually happened at the reaction side, a message could be sent via this test, so it would constitute communication. So despite all the assertions, they've not falsified locality.
  • jgill
    2.4k
    The basic observation piece being subject to probability seems crucial. Once the superposition is resolved it would seem that it is like the coin split down the middle to a head half and a tail half. But it's got to be more than that. Wish I had studied QM years ago.

    My best friend, a fellow math prof, departed a physics major after he enrolled in QM.
  • T Clark
    9.8k
    That is true. But as the article then says. 'the paradox is that a measurement made on either of the particles apparently collapses the state of the entire entangled system—and does so instantaneously.'Wayfarer

    Yes. The statements seem to be contradicting each other, but I'm confident they aren't because a lot of really smart people have said so. That doesn't mean I understand it. I am comfortable believing that something is true even though I don't understand how. It gives me something to think about.
  • T Clark
    9.8k
    Ah, but the spooky-action folks are not claiming communication, they're claiming FtL action-reaction. But if there was a (remote) empirical test for this having actually happened at the reaction side, a message could be sent via this test, so it would constitute communication.noAxioms

    It seems to me that what you call faster than light action-reaction is equivalent to communication. It seems I'm wrong about that.
  • Wayfarer
    16.3k
    I'm talking about relativity of simultaneity (RoS). If you don't know what that is, then you don't have the tools to assess the validity of my criticism of the wording used in the article.noAxioms

    To do with reference frames and the relativity of time of measurement, I guess.

    I can only get information from popular science, like Quanta Magazine and PBS Space Time, but the writers in those media are qualified in physics, in fact both have PhD's in the subject. Nowhere have you referred to any sources, so I'm inclined to believe them over you.

    And I can understand what they are saying, whereas I can't understand your objections. For instance:

    (the) theory of relativity strongly suggests... the principle of locality, that cause must precede effect. Bell showed that you must choose between the principlesnoAxioms

    Choose between what principles?

    I don't think there is an accepted scientific paper that IS the Copenhagen interpretation.noAxioms

    Of course not. The 'copenhagen interpretation' is not a scientific theory. Quantum theory is a scientific theory. The Copenhagen interpretation are philosophical speculations about what it means. The expression was coined by Werner Heisenberg, one of its advocates, in one of his popular science and philosophy books written in the 1950's

    Here is one example quoted by Matt O'Dowd in the PBS video:

    It is meaningless to assign reality to the Universe in the absence of observation. — Neils Bohr

    Here, it is explained, "object permanence" is being questioned. It is typical of the 'copenhagen interpretation'.

    All the articles I've seen linked from this topic contain language that assert the objective reality, which of course must contradict locality, but to disprove locality, one must do so without begging the objective reality since none of the local interpretations list it as one of the premises.noAxioms

    :roll:

    But if there was a (remote) empirical test for this having actually happened at the reaction side, a message could be sent via this test, so it would constitute communication. So despite all the assertions, they've not falsified locality.noAxioms

    That is the subject of the first article I quoted in this thread, about the Chinese communications satellite.

    Quantum entanglement—physics at its strangest—has moved out of this world and into space. In a study that shows China's growing mastery of both the quantum world and space science, a team of physicists reports that it sent eerily intertwined quantum particles from a satellite to ground stations separated by 1200 kilometers, smashing the previous world record. The result is a stepping stone to ultrasecure communication networks and, eventually, a space-based quantum internet.

    So, you're disputing that this is evidence of 'spooky action at a distance'? That is what the article is about. There seems to be some major disconnect here. I know it's a tough topic and I'm not wanting to be discourteous. But I am going to say that I think to all intents, (a) simultaneous and instantaneous mean the same in this context, and (b) how this can happen is a mystery, but it can't be disputed that it does happen. Over and out.
  • T Clark
    9.8k
    The Copenhagen interpretation are philosophical speculations about what it means.Wayfarer

    It is my understanding that the Copenhagen Interpretation is not a "philosophical speculation." It represents a refusal to speculate. Metaphysics pared down to a minimum.

    Choose between what principles?Wayfarer

    The video you provided talked about the violation of realism versus the violation of locality. According to the narrator, if realism is violated, but locality isn't, there is no superluminal causality or communication. Or is it the other way around. Please don't ask me to explain,
  • Agent Smith
    7.6k
    that’s how I understand it too. This idea of there being permanent, unchangeable objects - the original meaning of ‘atom’! - no longer holds. So the answer to the question ‘does the electron exist’ just is the wave-function. The answer it gives is again a distribution of possibilities, not a yes/no. ‘Exists’ doesn’t apply. ‘Does not exist’ doesn’t apply. (Does that ring a Bell?)Wayfarer

    :smile: A particle feels more real than a wave function. It's got that tangible quality that (say) an apple/rock has. That should, in my humble opinion, count for something.
  • Wayfarer
    16.3k
    We’ll you can throw a rock, or eat an apple, but you can surf a wave.

    Good pick up. Speculate is the wrong word. But it does concern meanings. You can find Heisenbergs Physics and Beyond on archive.org, it has many conversations with Bohr and Pauli.
  • T Clark
    9.8k
    You can find Heisenbergs Physics and Beyond on archive.org, it has many conversations with Bohr and Pauli.Wayfarer

    I appreciate the reference, but I'm not sure that anything I read is going to clarify things for me. I will take a look.
  • Wayfarer
    16.3k
    I meant to get more of a feel for the Copenhagen interpretation.
  • Bird-Up
    83
    Interesting post. Always want to know more about how the universe works, but I don't subscribe to the religious belief that quantum mechanics is magical beyond all other physics. I think it's just more standard physics that we have yet to learn. Like Einstein said, don't get stumped by a lack of imagination. It makes sense somehow, even if we are struggling to understand it right now.

    Realism and non-locality are compatible. If the wave function is real, it constitutes a causal, non-local fork, causing bothJarjar

    That's how I've always understood the quantum experiments. Like there is a misunderstanding about what exactly is being shown.

    Walking in front of a mirror could constitute "spooky action at a distance". But I've never really had success teleporting myself with a mirror; even thought it appears that I have jumped across the room instantly.
  • Andrew M
    1.5k
    Choose between what principles?
    — Wayfarer

    The video you provided talked about the violation of realism versus the violation of locality. According to the narrator, if realism is violated, but locality isn't, there is no superluminal causality or communication.
    Clarky

    Spot on. As it happens, most physicists choose locality over realism [*]. This rejection of realism (precisely, counterfactual definiteness) is well summed up by physicist Asher Peres, one of the original developers of quantum teleportation, as "unperformed experiments have no results".

    --

    [*] "What can we learn from Bell’s inequality? For physicists, the most important lesson is that their deeply held commonsense intuitions about how the world works are wrong. The world is not locally realistic. Most physicists take the point of view that it is the assumption of realism which needs to be dropped from our worldview in quantum mechanics, although others have argued that the assumption of locality should be dropped instead." - Quantum Computation and Quantum Information - Nielsen and Chuang
  • T Clark
    9.8k
    Spot on. As it happens, most physicists choose locality over realism [*]. This rejection of realism (precisely, counterfactual definiteness) is well summed up by physicist Asher Peres, one of the original developers of quantum teleportation, as "unperformed experiments have no results".Andrew M

    Both of those links are really helpful. Thanks.
  • Frankly
    17
    There are more interpretations than the Copenhagen one.
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