curiosity1
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- Quantum Entanglement
What is the mechanism behind Quantum Entanglement? Why do only subatomic particles exhibit Quantum Entanglement?
It kinda depends on what level you want the answer, and from which viewpoint.curiosity1 said:What is the mechanism behind Quantum Entanglement?
Same as why a huge rock does not exhibit any quantum phenomenacuriosity1 said:Why do only subatomic particles exhibit Quantum Entanglement?
Please tell me more. Thank you.malawi_glenn said:It kinda depends on what level you want the answer, and from which viewpoint.
Same as why a huge rock does not exhibit any quantum phenomena
What search in the literature have you done to try to answer these questions yourself?curiosity1 said:Please tell me more.
Well, it's a direct conclusion from the formalism of QT. Why Nature is well-described by QT, is a question, one cannot answer within the realm of the natural sciences.curiosity1 said:Summary: Quantum Entanglement
What is the mechanism behind Quantum Entanglement? Why do only subatomic particles exhibit Quantum Entanglement?
That is wicked!vanhees71 said:
curiosity1 said:Summary: Quantum Entanglement
What is the mechanism behind Quantum Entanglement? Why do only subatomic particles exhibit Quantum Entanglement?
I have not done any search in any literature. I am not a university student. I am just curious about how it works. I have no understanding of this.malawi_glenn said:What search in the literature have you done to try to answer these questions yourself?
What is your current understanding?
As noted in #6, because the equations of quantum physics says that it should happen.curiosity1 said:Summary: Quantum Entanglement
What is the mechanism behind Quantum Entanglement?
Quantum mechanics is a mathematical model that predicts the behaviour of microscopic systems. This includes systems where the particles are entangled. There is no underlying "mechanism", although there are "interpretations" of the mathematics.curiosity1 said:Summary: Quantum Entanglement
What is the mechanism behind Quantum Entanglement? Why do only subatomic particles exhibit Quantum Entanglement?
The most comprehensive QT is relativistic QFT, the Standard Model of elementary particle physics is based on, and that's the most successful theory of matter that has been hitherto discovered. It's so successful that it is hard to find "physics beyond the Standard Model", for which HEP physicists strive vigorously, because we know on the other hand that it is incomplete since there's very convincing evidence from astronomy and cosmology that there should be more particles than described by the Standard model (the socalled dark matter) and because there is no satisfactory quantum theory of the gravitational interaction.ohwilleke said:As noted in #6, because the equations of quantum physics says that it should happen.
While it is true that we don't know, it is also true that experiments have essentially ruled out "classical" physics type mechanisms. We don't know because all of the "first guess" answers scientists had for a mechanism have been ruled out.
One shorthand way of describing the issue is that quantum entanglement is not possible unless one or more of the following is not true in quantum entanglement cases:
1. Locality.
2. Causality.
3. Reality.
The only "mechanism" that explains entanglement is simply Q(F)T itself. There is no other mechanism behind it, at least not one that we know about today.ohwilleke said:The exact definitions of those terms are somewhat technical, but all seem like very reasonable axioms to have about how physics works. And, all three of these assumptions hold true for all other aspects of physics. Yet, at least one of them must not be universally true or quantum entanglement would not give rise to the phenomena that we observe.
There are a variety of speculative hypotheses for the mechanism of quantum entanglement, but none of them can be singled out as correct with existing experiments.
But Newton emphasised this, because the gravitational force was nonlocal, before Einstein discovered general relativity. So gravity seems rather unsuitable (from my POV) as an argument to dismiss the search for a deeper theory or better understanding of how nonlocal effects arise.PeroK said:There is no underlying "mechanism", although there are "interpretations" of the mathematics.
Note that there is also no "mechanism" in classical mechanics to describe how the gravitational force is propagated. Newton, himself, was at pains to emphasise this.
I think this is too narrow a view of causality that is at odds with quantum theory. We are habituated to think of the past as influencing the future, just like we are accustomed to read from left to right (at least in English). But quantum theory offers a more time-symmetric picture. It is well known that the decay rate of a particle, for example, depends on the density of available final states. And surely you must be aware that QFT achieves its magic with propagators that extend also into the backward light cone. I think this is the "mechanism" that @curiosity1 is wondering about. Having forward and backward traveling waves (linking what we somewhat arbitrarily distinguish as "cause" and "effect") ensures that the events that we observe follow a consistent pattern. In my view, the consistent histories interpretation, the transactional interpretation, and the closed time-path formalism all favour a time-symmetric picture.vanhees71 said:Causality means that the state of a (quantum) system can be influenced only by the past and not the future.
These terms are always the focus of the discussions. In previous discussions I have tend to separate "causality" as in the the causal ordering you refer to, and the paradigm for causal mechanisms. This may have caused miscommunication.vanhees71 said:Causality means that the state of a (quantum) system can be influenced only by the past and not the future.
...
causal effects can only be due to signals that propagate with a speed less than or equal to the speed of light
...
So it can only be "realism" that's violated by QT.
There is not the slightest hint at any causality violation at all. Where do you get the idea from that were the case?WernerQH said:I think this is too narrow a view of causality that is at odds with quantum theory. We are habituated to think of the past as influencing the future, just like we are accustomed to read from left to right (at least in English). But quantum theory offers a more time-symmetric picture. It is well known that the decay rate of a particle, for example, depends on the density of available final states. And surely you must be aware that QFT achieves its magic with propagators that extend also into the backward light cone. I think this is the "mechanism" that @curiosity1 is wondering about. Having forward and backward traveling waves (linking what we somewhat arbitrarily distinguish as "cause" and "effect") ensures that the events that we observe follow a consistent pattern. In my view, the consistent histories interpretation, the transactional interpretation, and the closed time-path formalism all favour a time-symmetric picture.
There is no mechanism. Causality is just an assumption you make in all physical theories, and you build the physical theories in such a way that it is fulfilled. This is not different in QT in any way.Fra said:I agree with most, i just wanted to add that we should not forget the causal mechanism. Reality itself is I think coupled to the presume causal mechanisms it takes part with, otherwise it would be an empty concept.
These terms are always the focus of the discussions. In previous discussions I have tend to separate "causality" as in the the causal ordering you refer to, and the paradigm for causal mechanisms. This may have caused miscommunication.
The standard causal mechanism is somehow that in the view of of system dynamics, the future state depends only on the past states, as per a fixed eternal law(that we do not ask why questions about, we just "discover" them). This is the natural way we think of things in classical mechanics (ie. where obserers play no central role).
But in QM, it becomes important to think about what ontology we assign to the state spaces themselves, to understand in which space to apply the causal mechanisms? In which space does the real causal mechanism happen in QM?
What seems rational is that a single observers "expecation" of the infinitesimal future states, at least in the depends only on it's present knowledge, seems rational as otherwise one would have to add new information and the observer would have to make a measurement and the state revised. Statements about finite future times (as per fixed laws) does not follow from pure rationality arguments - it is empirical only.
The issue in Bells theorem is, just because you assume there are "hidden variables"(existing and beeing encoded by at least one observer), does this necessarily mean that expected future state as per onother observer, are causally depending on these variables? (like ignorance) I think, this does not follow from any logic I know of!
I think Bell assues it from the habit from the tradtional causal mechanisms, which IMO is intermixed with a notion of "realism" that assumes that "mechanisms" must have an objective description. This is a naive "realist type" of causal mechanism. I think it's instructional to see that insight shouldbe possible to get even before you find that QM violates the inequality I think. I think this mixes the notions of "realism" and "causal mechanisms" as we talk about this! This is what makes QM hard to grasp think.
But suppose hidden variables of a system are real, in the senes that they are de facto existing in the system(inside observer) itself, but the nature of this is so that it is can not be communicated due to constraints to other external observers, then this hidden variable will still influence the expexcation of this one inside observer, and potentially explain causal mechanisms, but NOT the expectation of other observers. So a theory built in those principles, could as I see still employ hidden variables that can be thought of as real, and still violate bells theorem. But such theoy would not be deterministic or allow any observer to get rid of the randomness. This is why I would like to say that causal mechanism is just as suspsect as reality.
But I agree, I see no reason to destroty the causal order anywhere.
/Fredrik
I wasn't talking of causality "violation" at all, just the standard QFT formalism. (What would that even mean?)vanhees71 said:There is not the slightest hint at any causality violation at all. Where do you get the idea from that were the case?
Delta2 said:And btw in my opinion the moderators occasionally should show some tolerance in speculative posts because that's how new science is born, by speculations.
If Bell thought so, why did he make the ansatz that the total probability is a written as a sum over a hidden variable, where for each value there was a presumed outcome? This is not a explicit mechanism itself, but imposes a "structure/constraint" on the causal mechanisms.vanhees71 said:There is no mechanism.
There's no mechanism specified within mainstream QM.Fra said:If you mean we do not know the mechanism, then I agree,
I'm not sure about. I suspect most physicists believe that only an abstract mathematical description of nature is possible at the fundamental level.Fra said:but isn't the search for it is what keeps the fire here?
Bell was demonstrating that that particular ansatz implied his inequality and suggesting that the contrapositive (a violation of the inequality implies that the ansatz is wrong) could be used to invalidate any theory consistent with the ansatz.Fra said:If Bell thought so, why did he make the ansatz that the total probability is a written as a sum over a hidden variable, where for each value there was a presumed outcome?
Yes, so do I but i think it could be done with very different levels of understanding and i am not happy with the models we have.PeroK said:I suspect most physicists believe that only an abstract mathematical description of nature is possible at the fundamental level.
But even abstract principles like Einstein's relativity principle or Stuckey's NoPreferredReferenceFrame principle which he explained in various insights articles might provide hints how to answer questions like "What is the mechanism behind Quantum Entanglement?"PeroK said:I suspect most physicists believe that only an abstract mathematical description of nature is possible at the fundamental level.
As always you forget gravity or leave it for last. Given that the spacetime background is required for formulating QFT it is a major conceptual issue. Although admittedly not a point with the most engineering applications.vanhees71 said:There's not even a little smoke indicating anything that's not described by QT.
For me it's not the correlations that need explanation. A hidden variable explains this.vanhees71 said:The point of Bell's work is that there is a difference in the predictions about probabilities for the outcome of measurements between local realistic hidden-variable theories and QT, no more no less.
Maybe I misunderstand what you mean by "mechanism", but when I say that there is no mechanism behind entanglement I mean there is QT and no other thing (like hidden variables) that may in some sense "explain" the correlations described by entanglement beyond what QT describes.
I appreciate your careful definitions of these terms which I didn't attempt for fear that I'd miss an important nuance. I also agree with you the "realism" is an unfortunate choice of names for this property as it fails, unlikely causality and locality, to clearly and intuitively describe what it means (although perhaps the problem is that the concept itself isn't in the inventory of common sense ideas).vanhees71 said:The most comprehensive QT is relativistic QFT, the Standard Model of elementary particle physics is based on, and that's the most successful theory of matter that has been hitherto discovered. It's so successful that it is hard to find "physics beyond the Standard Model", for which HEP physicists strive vigorously, because we know on the other hand that it is incomplete since there's very convincing evidence from astronomy and cosmology that there should be more particles than described by the Standard model (the socalled dark matter) and because there is no satisfactory quantum theory of the gravitational interaction.
However, this so far most successful theory about the known types of matter and the interaction between its constituents is clearly based on locality and causality, and this is so by construction, i.e., it is built in in its very foundations.
Causality means that the state of a (quantum) system can be influenced only by the past and not the future. In relativistic models of spacetime this implies that there cannot be causal influences from space-like separated events.
So it can only be "realism" that's violated by QT. In my opinion it's a very unfortunate choice of naming, because QT in fact is the most "realistic" theory we have, i.e., it describes the phenomena best in accordance with the observations.
I read this again, and if by "there is no other thing" mean there is no accepted theory that does this, I agree fully, if that was your point.vanhees71 said:The point of Bell's work is that there is a difference in the predictions about probabilities for the outcome of measurements between local realistic hidden-variable theories and QT, no more no less.
Maybe I misunderstand what you mean by "mechanism", but when I say that there is no mechanism behind entanglement I mean there is QT and no other thing (like hidden variables) that may in some sense "explain" the correlations described by entanglement beyond what QT describes.
The mechanism is “average-only” conservation and that happens because everyone must measure the same value for Planck’s constant h, regardless of their orientation relative to the source, i.e., rotational invariance of h. It’s totally analogous to why we have time dilation and length contraction. Those happen because everyone must measure the same value for the speed of light c, regardless of their motion relative to the source, i.e., boost invariance of c. See https://www.physicsforums.com/insig...ciple-at-the-foundation-of-quantum-mechanics/curiosity1 said:Summary: Quantum Entanglement
What is the mechanism behind Quantum Entanglement? Why do only subatomic particles exhibit Quantum Entanglement?
Sure, gravity is the big issue, but that has nothing to do with these apparent philosophical issues of QT. In the entire history of science, philosophical ideas helped only to understand the wider implications of the results of the natural sciences in a larger cultural context. Kuhn's paradigm shifts always happened due to discrepancies between scientific observations and the then valid theories. Purely philosophical speculations never helped to find new theories, and paradigm shifts are really rare (on the timescale of centuries!).Fra said:As always you forget gravity or leave it for last. Given that the spacetime background is required for formulating QFT it is a major conceptual issue. Although admittedly not a point with the most engineering applications.
/Fredrik
The conservation laws are not only valid "average-only" but event by event. That's a result known since the 1920ies with Bothe's coincidence measurement of the Compton effect. The Bohr-Kramers theory claiming this "average-only-validity of the conservations laws" was very short-lived ;-)).RUTA said:The mechanism is “average-only” conservation and that happens because everyone must measure the same value for Planck’s constant h, regardless of their orientation relative to the source, i.e., rotational invariance of h. It’s totally analogous to why we have time dilation and length contraction. Those happen because everyone must measure the same value for the speed of light c, regardless of their motion relative to the source, i.e., boost invariance of c. See https://www.physicsforums.com/insig...ciple-at-the-foundation-of-quantum-mechanics/
What I said is exactly true and very easy to understand. I even present this to my gen ed students. Read the Insight linked, you can reference any of the published papers therein if necessary.vanhees71 said:The conservation laws are not only valid "average-only" but event by event. That's a result known since the 1920ies with Bothe's coincidence measurement of the Compton effect. The Bohr-Kramers theory claiming this "average-only-validity of the conservations laws" was very short-lived ;-)).
I figured by now that you think so, but I disagree even though the the link is indeed far fetched seen in the light of the current models.vanhees71 said:Sure, gravity is the big issue, but that has nothing to do with these apparent philosophical issues of QT.
I suspect many creative people keep these speculations private or inside their own heads, and only present the polished results, as it makes the process look cleaner than it really is. Noone wants to read the ugly process of creating a theory that may be wrong. Only once proven right, maybe you can read a little bit about it in biographies or so, but even there I think the ugly turns are omitted, to make it look more sexy.vanhees71 said:Purely philosophical speculations never helped to find new theories, and paradigm shifts are really rare (on the timescale of centuries!).
vanhees71 said:The conservation laws are not only valid "average-only" but event by event. That's a result known since the 1920ies ...
Well, just because you present it to your gen ed students doesn't mean that they understand it any more than the OP of this B-level thread will understand QFT and the "microcausality principle" brought-up by vanhees71:RUTA said:What I said is exactly true and very easy to understand. I even present this to my gen ed students. Read the Insight linked, you can reference any of the published papers therein if necessary.
Even worse, just because you believe that it is "very easy to understand" doesn't even mean that it is strictly true in all contexts.curiosity1 said:I have not done any search in any literature. I am not a university student. I am just curious about how it works. I have no understanding of this.
This introduction not only postpones the proof (which is fine), but also doesn't specify what exactly is meant by "average-only". From the POV of the minimal statistical interpretation (vanhees71's preferred interpretation), the natural interpretation of "average-only" would be that there would exists experiments where actual violations of conservation of momentum, or angular momentum, or energy, or ... would actually be observable. Or to put it differently, his "event by event" conservation claim mean that no statistical significant violation of conservation should ever be observable in any properly performed series of experiments. Even so this is quite a strong claim, I am not aware of any experimental evidence against it.And, just as the light postulate of SR leads to time dilation and length contraction in a perfectly symmetrical fashion between different reference frames (aka the relativity of simultaneity), the “Planck postulate” of QM leads to “average-only” projection and conservation of spin angular momentum in a perfectly symmetrical fashion between different reference frames (explained below).
The assumption that "the radiation is actually composed of indivisible photons" doesn't hold from the perspective of QFT (vanhees71's preferred perspective), but that is less important than that you cannot nail down individual indivisible photons in experiments. So this argument is (most probably) unable to make verifiable preditions about observable violation of conservation in experiments.However, given that the radiation is actually composed of indivisible photons, there is a non-zero lower limit to the energy passed by a polarizing filter, i.e., each quantum of energy either passes or it doesn’t. Thus, we understand that the classical “expectation” of fractional amounts of quanta can only obtain on average per the quantum reality, so we expect the corresponding quantum theory will be probabilistic.
The provable (weak) relationship between classical and quantum mechanics given by the Ehrenfest theorem doesn't mean that there cannot be stronger relationships between classical and quantum mechanics when it comes to conservation laws.Thus, as argued by Brukner & Zeilinger, a theory of qubits must be probabilistic. Of course, the relationship between classical and quantum mechanics per its expectation values (averages) is another textbook result, e.g., the Ehrenfest theorem.
No, what you said is a proposal you have made. It is not something that has been experimentally tested and verified. It's not even clear how it could be experimentally tested and verified.RUTA said:What I said is exactly true
Thanks for doing the hard work, digging out the claim from a long text!gentzen said:So let us look at your Insights article how it introduces this "average-only" claim, and how it proves and explains it:
This has nothing to do with interpretation whatsoever, it's simply an experimentally verified fact without any counterexamples observed yet, and it's known even before or just at the time when modern quantum theory has been discovered.gentzen said:This introduction not only postpones the proof (which is fine), but also doesn't specify what exactly is meant by "average-only". From the POV of the minimal statistical interpretation (vanhees71's preferred interpretation), the natural interpretation of "average-only" would be that there would exists experiments where actual violations of conservation of momentum, or angular momentum, or energy, or ... would actually be observable. Or to put it differently, his "event by event" conservation claim mean that no statistical significant violation of conservation should ever be observable in any properly performed series of experiments. Even so this is quite a strong claim, I am not aware of any experimental evidence against it.
That's not true either. The "indivisibility of photons" is one of the stringent proves for the existence of photons, i.e., the validity of relativistic QFT. The claim by many textbooks that this were the case for leading-order treatments of the photoelectric effect or Compton scattering is not conclusive, because both follows from the quantization for charged particles (electrons in this case) alone keeping the em. field classical.gentzen said:So, how can this be reconsiled with your proof(s)?
The assumption that "the radiation is actually composed of indivisible photons" doesn't hold from the perspective of QFT (vanhees71's preferred perspective), but that is less important than that you cannot nail down individual indivisible photons in experiments. So this argument is (most probably) unable to make verifiable preditions about observable violation of conservation in experiments.
gentzen said:The provable (weak) relationship between classical and quantum mechanics given by the Ehrenfest theorem doesn't mean that there cannot be stronger relationships between classical and quantum mechanics when it comes to conservation laws.
Right after Eq. 4. A longer explanation with pictures is at the ScienceX Dialogue link. That’s the level I show my gen ed students. As long as they can understand projection, they can understand that explanation.vanhees71 said:Where in this long Insight can I find the claim that the conservation laws hold on average only? As I said, this contradicts very early empirical evidence from the early history of modern quantum theory. Prominent other ideas, like the famous Bohr-Kramers theory, have been refuted by these observations and finally modern QT in its usual form has been found.
What I shared are mathematical facts about the formalism of QM. It is not a mere proposal.PeterDonis said:No, what you said is a proposal you have made. It is not something that has been experimentally tested and verified. It's not even clear how it could be experimentally tested and verified.
It's really hard to discuss, if you don't give precise quotations. In your Insight Eq. 4 is something about spin. In the paragraph following it there's nothing about energy and momentum conservation.RUTA said:Right after Eq. 4. A longer explanation with pictures is at the ScienceX Dialogue link. That’s the level I show my gen ed students. As long as they can understand projection, they can understand that explanation.
I can only say that many of my gen ed students’ reactions are consistent with them understanding the explanation.gentzen said:Well, just because you present it to your gen ed students doesn't mean that they understand it any more than the OP of this B-level thread will understand QFT and the "microcausality principle" brought-up by vanhees71:
As I pointed out to Peter Donis, what I have presented are mathematical facts about the formalism of QM. So, they are true in the context of QM.gentzen said:Even worse, just because you believe that it is "very easy to understand" doesn't even mean that it is strictly true in all contexts.
Nothing I presented violates established physics. Quite the opposite, it follows exactly according to established textbook QM. Read the papers and it should be readily obvious to someone with your background. “Gen ed students” means “general education students”, i.e., the business, comm, ed, etc. students taking physics. Sorry, that’s a typical term here in U.S. academe, but maybe not where you’re located.vanhees71 said:It's really hard to discuss, if you don't give precise quotations. In your Insight Eq. 4 is something about spin. In the paragraph following it there's nothing about energy and momentum conservation.
So precisely where is this bold claim explained? I'm really puzzled that you teach students (whatever "gen ed" means) such speculative ideas which clearly contradict established empirical facts and the currently established physical theories.