Questions on Entanglement and Double-Slit Experiment

[ttn]

They [i.e., orthodoxy and bohm] aren't really comparable, at least not if "orthodox QM" is taken to mean the ordinary shut-up-and-calculate version (which is basically what the purely positivist version of the Copehagen interpretation is, although some people use 'Copehagen interpretation' to mean the view that the collapse of the wavefunction is a real physical event), which is just a recipe for making predictions about probabilities without any assumptions (one way or another) about hidden variables, other worlds, or any other aspect of reality that can't be tested directly. Of course, you could also use the formalism of Bohmian mechanics as a recipe for making predictions, without any assumptions about the "reality" of hidden variables or the pilot wave, but this isn't what people usually mean by Bohmian mechanics.

Yes, I completely agree. If you take "orthodoxy" to just mean the "shut up and calculate" attitude, then it's true that "orthodoxy" and Bohm are no longer on an equal footing: one is a mere calculational algorithm, while the other is an actual *theory* about physical processes in the world. (But of course, people who support "orthodoxy" in fact *don't* take this attitude seriously, or at least consistently. They invariably accept the very non-positivist claims that the wave function alone provides already a complete description of physical states, contra "hidden variables.")

I also agree that, if one takes a hard-core positivist attitude toward Bohm's theory, one is simply left with a calculational algorithm -- the same one, in fact, that we called "orthodoxy" just above. In other words, if you insist that any theory *just is* its calculational algorithms, you would have a difficult time understanding what all the fuss (in regard to Bohm vs Copenhagen vs this vs that) is about.

Of course, that attitude is just dumb. I mean, seriously, what scientist actually thinks it's *wrong* to try to figure out how things work? What the heck are the string theorists doing then? Or all the astrophysicists trying to figure out exactly what happens during a core collapse supernova? Or basically every other physicist and scientist currently in existence? Sure, it's always useful to figure out what happens first -- to be in a kind of purely descriptive mode -- but then the whole point is to try to dig deeper and ask "what's going on that makes it come out this way?" or "why does it come out this way instead of some other way?" etc. Practically every important discovery in the whole history of science is an example of this. Gases obey PV = const... but *why*, what is going on physically that makes the pressure vary this way? (Then, 200 years later or whatever, "Oh, the kinetic/atomic theory explains this...") Or: Kepler noticed that planets move in ellipses, etc., but *why*? Newton provided a big part of the answer to those questions with his theory of gravitation. Or: some materials exhibit superconducting or superfluid behavior at certain temperatures... but why? So then people come up with a theory which explains that in terms of some deeper facts about the nature of the substances. Asking why (or "how", which amounts to the same thing but some people for some reason make a big deal over this distinction) is *essential* to good science. Indeed, it is practically synonymous with good science.

In other words, to take this positivist attitude seriously is to spit in the face of the whole entire history of science. So it's no wonder the people who advocated this in the 1920's cooked up a big philosophical set of pseudo-arguments for why the case of quantum theory was fundamentally different, why we really had to accept this new attitude not just because of philosophy but because of certain problems inherent to microphysics, etc. etc. But de Broglie and Bohm put the lie to it by showing explicitly that it's all bogus, that it's not impossible to give a coherent physical theory which tells a comprehensible physical story to explain physically why the measurements come out the way the calculation algorithm says they should. In short, they proved by explicit example that the *real* basis for the Copenhagen hegemony was *not* physics discoveries, but, rather, philosophical bias. Hence the irony of contemporary Copenhagen supporters dismissing Bohm on the grounds that his theory is just philosophical bias. In the end, it does come down to philosophical questions (such as: is there an external physical world, and is it the task of physics/physicists to figure out what it's like and how it works), but the right question is not "who is less biased?" but rather "which philosophy is reasonable?" That's why I'm happy and proud to admit that it's because I'm a realist and a scientist that I am "philosophically biased" in favor of Bohm, GRW, etc. as against "shut up and calculate".

 

[NateTG]

If there are experiments for which 'plug and grind' QM is ambiguous, and Bohmian Mechanics makes falsifiable predictions, then the two are clearly distinct from a scientific perspective, and, Bohmian Mechanics can, at least in theory, be tested there. Barring any such scenario, choosing one over the other is a matter of taste.

Bohmian Mechanics is primarily interesting from a philosophical perspective because it AFAICT provides a deterministic realist interpretation of QM, and thus, Bell's Theorem notwithstanding, if we assume a 'big bang', Bohmian Mechanics is a local realist interpretation of QM. (Locality follows readily from common history and determinism.)

 

[ttn]

If there are experiments for which 'plug and grind' QM is ambiguous, and Bohmian Mechanics makes falsifiable predictions, then the two are clearly distinct from a scientific perspective, and, Bohmian Mechanics can, at least in theory, be tested there.

The classic example of this is "tunneling times". Imagine a particle initially in a metastable bound state, out of which it will (asymptotically) tunnel, i.e., emerge with positive energy at some large radius. What does OQM say about (say) the average time you have to wait before the particle appears at some particular radius? It's not clear how to calculate such a thing in OQM -- and indeed not clear that there is any way to do it. Bohm's theory on the other hand can answer such questions unambiguously. Or so it seems. I don't have any interest in discussing this, really, but I just wanted to note the existence of a huge literature on this specific point.

Barring any such scenario, choosing one over the other is a matter of taste.

Sure, "taste". For example, whether one prefers a mathematically precise formulation which is 100% crystal clear about what it says exists and happens, or prefers instead something "unprofessionally vague and ambiguous" (like such-and-such happens whenever there's no "measurement" happening, while so-and-so happens instead when a "measurement" is happening, and with no further clarification or definition about what the heck a "measurement" is). So, yeah, it's merely a matter of taste: as in, whether one prefers the taste of a good theory to a bad theory.

Bohmian Mechanics is primarily interesting from a philosophical perspective because it AFAICT provides a deterministic realist interpretation of QM, and thus, Bell's Theorem notwithstanding, if we assume a 'big bang', Bohmian Mechanics is a local realist interpretation of QM. (Locality follows readily from common history and determinism.)

Bohm's theory is not local. But then, neither is any other theory which agrees with the experimental results violating Bell's inequality. That's what Bell's theorem proves. Nonlocality is a fact of the world which all empirically viable theories are going to have to include (and, so, they do). People who dismiss Bohm's theory on the grounds that it is nonlocal aren't paying attention.

 

[ueit]

Bohm's theory is not local. But then, neither is any other theory which agrees with the experimental results violating Bell's inequality. That's what Bell's theorem proves. Nonlocality is a fact of the world which all empirically viable theories are going to have to include (and, so, they do). People who dismiss Bohm's theory on the grounds that it is nonlocal aren't paying attention.

It is not true that "nonlocality is a fact of the world". A fully deterministic theoy cannot be ruled out by Bell because it denies the possibility of statistical independence between the source and detectors. All classical theories are of this type and they are not therefore eliminated by Bell.

 

[metacristi]

I've promised once that I'll never return on this forum as much as Zapper Z remains moderator here [nothing personal but I don't think that a too strong authoritarianism is a good thing for science, I still maintain that] but seeing, for some time now, the quality exchange of ideas here I cannot resist writing again (at least today :-)).

The main argument of those defending the 'shut up and calculate' stance is indeed not too far from that of logical positivists. According to this point of view - given that the 'interpretations' do not really make novel, potentially testable, predictions (only the standard mathematical formalism does, around which almost all interpretations are constructed) - we cannot accept them (the 'interpretations') as scientific (in short the interpretation part does not really account for the empirical success of the theory and there is under-determination at this level now, possible forever). Not surprisingly then that such positivists label all interpretations as being 'philosophy' not science.

I would not consider the positivistic stance without any merit (in the case of QM) but I think we can safely attack the claim (of some) that this is the only rational stance for the moment. Fact is that all valid compounds 'formalism-interpretation' are capable to account for the observed facts (post hoc is enough) and they are empirically evolving at the moment (for example Bohmian mechanics has been able to account basically for all new experiments so far though sometimes some auxiliary hypothesis are needed; the same is valid for the other valid interpretations).

In this respect the theoretical constructs used by these compounds 'mathematical formalism-interpretation' (even Copenhagen Interpretation does have such constructs) can be seen as necessary to account for the empirical success of the ‘compound’ they are part of; thus we can see, at limit, every such compound 'formalism-interpretation' as forming at least as a valid scientific program deserving to be pursued further.

Of course if we take in account now the other traditional (but weak) requirements of actual scientific methodology (ontological and logical simplicity, capacity to unify things thought previously as being not connected, coherence with other accepted parts of science etc) we can even make a weak distinction between the different existing compounds 'formalism-interpretation'.

Here clearly (though no interpretation is without problems) Bohm's interpretation appears [with its auxiliary assumptions - like Vigier's explanation of why electrons do not fall into nucleus - or the actual absence of a Lorentz invariant relativistic version] on a lower level than the evolutions of Copenhagen Interpretation (the same is valid for MWI or the transactional interpretation, for other reasons of course etc) but we cannot say that these alternatives are ‘dead ends’ (as some argue wrongly; L. Motl among the most vociferous (at least in the case of BM and TI, I wonder why he is not against MWI which after all 'want to modify physics' too with its resort to possible, but untestable, worlds).

The above mentioned ‘weak’ distinction is informative but not prescriptive, it is still fully rational at the moment to pursue such alternative programs in spite of the fact that currently they comply less with the accepted scientific methodologies (the decision to pursue a certain program as the first choice, personal, program does not automatically involve ontological commitments or claims of epistemological privilege). Indeed the history of science teach us that even seemingly degenerative programs at a certain moment can become theoretically and empirically progressive later (when the ‘background’ is prepared for their emergence) so it would be a big mistake to bar still legitimate directions of research (crucial breakthroughs could be lost forever).

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"...even the most obvious connections remain unseen if we are constantly brainwashed that such connections are impossible or meaningless" - K. Popper (paraphrased)

 

[RandallB]

A fully deterministic theoy cannot be ruled out by Bell because it denies the possibility of statistical independence between the source and detectors.

Could you clarify exactly what the “it” is in “it denies” in your point here.
(“A fully deterministic theory” or “Bell”)

I often have trouble following the logic of “local” proponents that do not accept the idea of a theory building a version of local in a non-local way (non-local Bell way). Which is why IMO BM is as viable as QM, and they are both non-local.

Taking an “Occum’s” view of which is better between BM & QM; they may be one, but I can not tell. Any more than trying to define if Leibniz Calculus is better than Newton’s or if it’s just a matter historical preference that the Leibniz method has become preferred by the majority but still not all, just like QM is used and preferred over BM by most. They give the same non-local results, and maybe both have a place. Example interference problems seem to be more easily understood using BM; while application work in particle physics seems to have made the best progress using QM.

 

[MaverickMenzies]

I think the real problem with all of these interpretations is that they are all after the fact. In other words, we discovered the mathematical formalism that could predict the various empirical effects that were observed and then we tried to make sense of the meaning of the formalism. I think that quantum mechanics will only make sense if one can discover a physical principle from which the formalism can be derived.

 

[DrChinese]

All classical theories are of this type and they are not therefore eliminated by Bell.

You can say this 100 times and it is still not true. Classical theories give results that are inconsistent with observation. I.e. they do not follow the cos^2 rule. The reason is: the observer must be taken into account in explaining the result, a mechanism for which classical theories - because they are by definition classical - are unable to do. Specifiying a common prior history answers nothing until you can tell us how it ties in.

 

[NateTG]

You can say this 100 times and it is still not true. Classical theories give results that are inconsistent with observation. I.e. they do not follow the cos^2 rule.

Falsification by experimental result is not the same thing as falsification by Bell's Theorem.

Specifiying a common prior history answers nothing until you can tell us how it ties in.

It's really quite simple, and simultanteously rather unsatisfying:

Let's assume, for a moment, that the universe is deterministic, not necessarily local and has a definite beginning. Since the universe is deterministic, we can write a (not necessarily finite) list of all of the uncertain events that occur in the universe, \vec{h}. Notably, this list is not dependant on time - so we can postulate that it's the local hidden state of the big bang, and has propagated forward locally from there.

Unless the HUP is somehow falsified (not likely) it's impossible to make any determination about mechanisms, so you could readily think of maxwell's demon runnning around and pulling strings if you like.

 

[ueit]

Could you clarify exactly what the “it” is in “it denies” in your point here.
(“A fully deterministic theory” or “Bell”)

I don't use "it" for persons, so the answer is "A fully deterministic theory”.

I often have trouble following the logic of “local” proponents that do not accept the idea of a theory building a version of local in a non-local way (non-local Bell way). Which is why IMO BM is as viable as QM, and they are both non-local.

AFAIK there is no relativistic BM, but we have QED.

1. The only theory we have that deals with the nature of space and time itself (general relativity) says our universe is local.

2. As I said many times on this forum, Bell's theory isn't a problem for local deterministic theories because these theories do not allow for statistical independence between the detectors and source. A local deterministic universe is like a clock. Bell's theorem requires that you turn independently two "wheels" (detector switches) but you just cannot do that without breaking the mechanism. Therefore the assumptions used for the derivation of Bell's theorem are logically incompatible with the assumption that we live in a local deterministic universe. Bell's theorem only proves that the law of non-contradiction is still valid, which is hardly a remarcable fact.

From 1. and 2. we can see that a local theory is to be preferred (Occam’s razor).

I agree however that a non-local explanation is much better than no explanation at all or a non-realistic one.

 

[RandallB]

First off, in the context you used "it" for was not for the person Bell

I don't use "it" for persons, so the answer is "A fully deterministic theory”.

you were referring to the "Bell Theorem" or its application.

And just declaring the "assumption that we live in a local deterministic universe" does show anything beyond establishing a point of faith maybe.
And GR has not be shown to be "local" - plenty to read by Smolin on the requirement for indeterminate background for GR (Non-local IMO) that has not been disproved to any reasonable satisfaction .

And the idea that when setting of two space like separated wheels (detector switches) we a powerless to use free will or judgment to set them differently that what the Big Bang preset deterministic universe has already decided what we will do, is just pointless. Talk about an un-testable theory - it demands that we can only know a proof for it IF it has been predetermined for us to learn it.
If you understand what LOCAL means, you would recognize this as a Non-Local Local theory. It is only local within itself as it reaches out to its preset deterministic values to explain correlations. Just like non-local BM and MWI are local within those theories, using invisible guide-waves and multi-dimensional extended realities to explain correlations within their theory.

A deterministic universe (classical or non) is not a Local (Bell Local) theory, and if you want to apply Occum's to the Non-locals this one IMO falls to the bottom of that list.

Personally I think realty is local and real does not need some kind of strange extended reality; but that is just an opinion, I don't go around declaring it as a fact. But unlike yours I know exactly the tool that is required to turn my opinion to fact, and that is the Bell Theorem itself. And it only need do so once, and all the non-locals will fall including yours. But no individual Non-local theory even has a tool that has an expectation of excluding other theories.
So if you cannot even produce a tool that might provide a proof of your theory at least state it as an opinion or personal preference and do not demand it be accepted as a simple fact.

 

[exeric]

Hi, I've done some study on this problem of non-locality and have reached my own conclusions. I've written a paper with my own plausible explanation for it. But rather than muck things up with my own ideas right off the bat I'd like to pose some questions for people who are not afraid to think outside of the box.

1.The Bell theorem, as I understand it, simply "assumes" that the EPR paper proposed a condition that required local variables. It may be more logically said that John Bell simply couldn't think of any other way of looking at quantum entanglement than in this way. My understanding is that Einstein never explicitly called for local variables but just for local "realism". In 1930 or thereabouts he produced his own theory of "teleparallelism". This theory could be said to have anticipated the results of quantum entanglement but through a different mechanism - namely "torsion".

2. If Einstein himself proposed a theory 5 years earlier in which non-locality of cause and effect could possibly happen then it could be said that what Einstein was more properly saying in the EPR paper is that quantum entanglement can exist, but that we just need to fill in our picture of physics in a way that it makes sense. It's interesting to me that so many physicists seem to ignore the title of the EPR paper: "Can The Quantum Mechanical Description of Physical Reality Be Considered Complete?"

It almost seems that the physics community has just built this straw man of "local variables" that Bell produced to show Einstein didn't know what he was talking about. Clearly he did and the title of the paper neatly summed it up what he was "really" saying.

Eric

 

[lalbatros]

Dear all,

I have asked this several times here and there. Sorry to repeat myself, for those concerned.

My question: how much can we say that entanglement is an absolute concept?

I explain more:

Let's go back to our particle A and particle B.
Particles are "just" states of a quantum field, the electromagnetic field for example when photons are involved.

This leads me to the idea that entanglement depends on the point of view, since it depends on the states that one takes as reference. In other words, a state can be a mixed state in a basis B and it could be a pure state in another basis B'.

Nevertheles, I have the intuitive feeling that entanglement should be something measurable and with a kind of absolute meaning, like the entropy in statistical physics.

What do you know about that, what are your ideas?
Some references welcome.

Thanks,

Michel

 

[ZapperZ]

Dear all,

I have asked this several times here and there. Sorry to repeat myself, for those concerned.

My question: how much can we say that entanglement is an absolute concept?

I explain more:

Let's go back to our particle A and particle B.
Particles are "just" states of a quantum field, the electromagnetic field for example when photons are involved.

This leads me to the idea that entanglement depends on the point of view, since it depends on the states that one takes as reference. In other words, a state can be a mixed state in a basis B and it could be a pure state in another basis B'.

Nevertheles, I have the intuitive feeling that entanglement should be something measurable and with a kind of absolute meaning, like the entropy in statistical physics.

What do you know about that, what are your ideas?
Some references welcome.

Thanks,

Michel

Even with your explanation, I'm not sure what you mean by an "abolute concept".

Take note that the EPR-type experiments are just ONE consequence of the property of entanglement (and Einstein's non-locality). The fact that "entanglement" means, mathematically, that the state function of the entangled property is not separable, indicates that it can have other measurable consequences.

One such consequence is that the entangled objects' property can be thought of to be one "macro" particle. If that is the case, then 2 entangled photons behave as if it is just one "macro" photon with twice the energy, and thus, half the wavelength. What this means is that if you do optical measurement with such photons, you CAN beat the diffraction limit of the original light source!

This has been done[1]! The higher order interference pattern has been seen, and this is completely consistent with the QM prediction. So I don't know if you consider this as an "absolute concept", but it certainly is very real if you base it on emprical evidence so far.

Zz.

[1] P. Walther et al. Nature v.429, p.158 (2004).

 

[lalbatros]

ZapperZ,

The way you formulate it is clearer indeed:

The fact that "entanglement" means, mathematically, that the state function of the entangled property is not separable, indicates that it can have other measurable consequences.

Indeed, what I mean is that the separability depends on the choice of the basis.
This choice actually depends on the experiment to be analysed in tems of entanglement.

Am I right to say that:

a pair of spins analysed as up or down may be in a separable state
while the same state analysed as a pair of spins left or right would not be separable​

However, I belong to the set of people who believe that the measurement postulate is not more than a pedagogical convenience (or maybe a king of closure of the theory). But still it represents -in some way- an interaction process. I skip here more discussions about the entangled state system + observer after the measurement. However this indicates that entanglement will play a role not only in a (possibly EPR) measurement process, but in any interaction.

Therefore, I believe entanglement is a very important thing. Not only because of some EPR paradox, but even more because I think it plays a big role in the quantum evolution. Maybe this is trivial, but I don't know how to highlight that from -say- the Schrödinger equation.

Considering all that, it could make sense that indeed entanglement is a "relative" property of a composite system. It is relative to the basis states considered (like a reference frame!), and in the end these basis states are related to an (EPR) measurement to be performed.

I was asking myself if entanglement could be given an absolute meaning, and therefore an absolute measure of entanglement could be defined. If there was a "preferred basis", then it would be the case.

Any ideas, suggestions, readings ... ?

Michel

 

[MaverickMenzies]

Hi lalbatros,

There has been some work done to attempt to describe the entanglement of quantum states without requiring a recourse to the tensor product decomposition i.e. the decomposition into subsystems. Here are a couple of e-prints that I have found:

quant-ph/0308043, quant-ph/0305023.

I also think that Prof. Vlatko Vedral (at the university of leeds) has some ideas to relate multipartite entanglement in solid state systems to some order parameter of the system.

I hope that this is of some use.

 

[Doc Al]

Am I right to say that:

a pair of spins analysed as up or down may be in a separable state
while the same state analysed as a pair of spins left or right would not be separable​

No. Whether a two-particle state is entangled or not does not depend on the choice of basis states used to describe it. Perhaps you are thinking of the fact that a "spin-up" state can be expressed as a superposition of "spin-left" and "spin-right" states?

 

[ttn]

No. Whether a two-particle state is entangled or not does not depend on the choice of basis states used to describe it. Perhaps you are thinking of the fact that a "spin-up" state can be expressed as a superposition of "spin-left" and "spin-right" states?

...although the number of terms in the quantum state function (which one might loosely think of as a measure of the "amount" of entanglement) can differ from basis to basis. This, by the way, is the source of the so-called "preferred basis problem" which advocates of the Many Worlds Interpretation are forced to worry about since they are sometimes in the business of "counting worlds" to try to derive Born's rule.

Also, repeating what a previous poster said, there are tons of papers on the question of trying to quantify the "amount" of entanglement. (For the reason I just pointed out, the number of terms in the quantum state function is not a good measure of this since it's basis-dependent!) Search, e.g., on arxiv for "entanglement measure" and lots of things will come up.

Finally, I might be wrong about this, but I got a vague sense that lalbatros was raising these questions about entanglement because of a confusion over Bell's argument for non-locality. Just for the record, the argument is *not* of the form: there's a kind of non-locality associated with entanglement, which is a pretty important/ineliminable feature of quantum theory, hence non-locality is a real physical thing. That's not the argument at all. My sense was that lalbatros was worried that maybe people accepted non-locality too easily (based on some argument like this), when, in fact, there is every reason to wonder if "entanglement" is even an absolute ineliminable concept. It is, after all, a feature of a *theory* -- a theory that there is tons of controversy about whether or to what extent it should be taken as providing a literal true description of physical reality.

I'm not sure I'm saying this very clearly. The point is, anyone who believes that nonlocality is a real feature of the physical world *based on the mere fact that orthodox quantum theory says that spatially separated systems can sometimes be in entangled states* is a crazy fool. Bell was no crazy fool. So anyone interested in understanding why Bell (and those who understand and hence follow him) believed nonlocality was a real physical phenomena, should go read Bell's papers where he explains this all very very clearly!

And now, just in case Zapper Z is still reading... I'm still anxiously waiting to hear what part of the argument in Einstein's Boxes you found unconvincing and/or why you thought the criticisms by Shimony and [that other guy whose name I can't remember] made sense...

 

[exeric]

Hi, I've done some study on this problem of non-locality and have reached my own conclusions. I've written a paper with my own plausible explanation for it. But rather than muck things up with my own ideas right off the bat I'd like to pose some questions for people who are not afraid to think outside of the box.

1.The Bell theorem, as I understand it, simply "assumes" that the EPR paper proposed a condition that required local variables. It may be more logically said that John Bell simply couldn't think of any other way of looking at quantum entanglement than in this way. My understanding is that Einstein never explicitly called for local variables but just for local "realism". In 1930 or thereabouts he produced his own theory of "teleparallelism". This theory could be said to have anticipated the results of quantum entanglement but through a different mechanism - namely "torsion".

2. If Einstein himself proposed a theory 5 years earlier in which non-locality of cause and effect could possibly happen then it could be said that what Einstein was more properly saying in the EPR paper is that quantum entanglement can exist, but that we just need to fill in our picture of physics in a way that it makes sense. It's interesting to me that so many physicists seem to ignore the title of the EPR paper: "Can The Quantum Mechanical Description of Physical Reality Be Considered Complete?"

It almost seems that the physics community has just built this straw man of "local variables" that Bell produced to show Einstein didn't know what he was talking about. Clearly he did and the title of the paper neatly summed it up what he was "really" saying.

Eric

I'd still be interested in any responses to what I said above. I realize what I'm saying maybe a little off in right field to some of you but I really think Bell's inequality is just a starting point for understanding quantum entanglement. It just shows that the non-locality of correlative effects exist but in no way addresses Einstein's real question. I think it misses the forest for the trees. Conversely, I think the EPR paper was concentrating on the forest - something which is done rarely in physics, even today. I promise I won't talk about my own ideas about QE if I can just get you guys to engage on this point.

Eric

 

[ZapperZ]

Indeed, what I mean is that the separability depends on the choice of the basis.
This choice actually depends on the experiment to be analysed in tems of entanglement.

Am I right to say that:

a pair of spins analysed as up or down may be in a separable state
while the same state analysed as a pair of spins left or right would not be separable​

I don't understand this part. How do you separate out, for example

|\Psi> = |up>_1|down>_2 + |down>_1|up>_2 ?

There are no unitary transformation to a different basis that you can do that separate them out, are there?

Zz.

 

[exeric]

ZapperZ,



However, I belong to the set of people who believe that the measurement postulate is not more than a pedagogical convenience (or maybe a king of closure of the theory). But still it represents -in some way- an interaction process. I skip here more discussions about the entangled state system + observer after the measurement. However this indicates that entanglement will play a role not only in a (possibly EPR) measurement process, but in any interaction.

Therefore, I believe entanglement is a very important thing. Not only because of some EPR paradox, but even more because I think it plays a big role in the quantum evolution. Maybe this is trivial, but I don't know how to highlight that from -say- the Schrödinger equation.

Considering all that, it could make sense that indeed entanglement is a "relative" property of a composite system. It is relative to the basis states considered (like a reference frame!), and in the end these basis states are related to an (EPR) measurement to be performed.

I was asking myself if entanglement could be given an absolute meaning, and therefore an absolute measure of entanglement could be defined. If there was a "preferred basis", then it would be the case.

Any ideas, suggestions, readings ... ?

Michel

I, myself don't think that quantum entanglement can be considered as something relative to the way that it is measured. It might have been an open question before the vast experimental evidence has built up, but I don't think it can be said anymore. Entanglement is not an "interpretative" event in that respect. And measurement only nails the quantum state of each of entangled composite particles at the instant it is measured.

I think you brought up a very interesting point about composite particles. This is the heart of the phenomena. It has only very recently been broadly realized that entanglement is not a rare event but probably plays a part in all particles that are made from composite particles. In this sense the assymptotic freedom of quarks in a proton could be considered just another aspect of quantum entanglement. In this special case it might be speculated that the binding energy between quarks is just a case where the energy of quantum entanglement equals the energy of the angular velocity of the quarks. So no matter how much energy one puts into a proton that energy divides equally between quantum entanglement energy and the energy of each quarks spin velocity. It would explain a lot about the origin of E=mc^2. Half of the energy in the formation of protons in the first microseconds of the universe occurred exactly at c, i.e.1/2 mv^2 = 1/2mc^2. This is the kinetic energy of the spin angular momentum of quarks. The other half of the energy, also equaling 1/2mc^2, equals the energy involved in quantum entanglement. So no matter how much energy you put into a proton that energy will divide equally between the magnitude of the spin angular velocity and the quantum entanglement energy and quantum entanglement will continue to rigidly confine the quarks.

I think people are starting to wake up to the fact that quantum entanglement plays a part in forming mass in all composite particles. And single photons are the only particles that are not composite particles and thus have no mass. However they do have energy so the 'm' in the kinetic energy of quarks but still be their energy but not in the "mass" sense. But even they can acquire mass through entanglement with other photons.

Eric

 

[ZapperZ]

I, myself don't think that quantum entanglement can be considered as something relative to the way that it is measured. It might have been an open question before the vast experimental evidence has built up, but I don't think it can be said anymore. Entanglement is not an "interpretative" event in that respect. And measurement only nails the quantum state of each of entangled composite particles at the instant it is measured.

I think you brought up a very interesting point about composite particles. This is the heart of the phenomena. It has only very recently been broadly realized that entanglement is not a rare event but probably plays a part in all particles that are made from composite particles. In this sense the assymptotic freedom of quarks in a proton could be considered just another aspect of quantum entanglement. In this special case it might be speculated that the binding energy between quarks is just a case where the energy of quantum entanglement equals the energy of the angular velocity of the quarks. So no matter how much energy one puts into a proton that energy divides equally between quantum entanglement energy and the energy of each quarks spin velocity. It would explain a lot about the origin of E=mc^2. Half of the energy in the formation of protons in the first microseconds of the universe occurred exactly at c, i.e.1/2 mv^2 = 1/2mc^2. This is the kinetic energy of the spin angular momentum of quarks. The other half of the energy, also equaling 1/2mc^2, equals the energy involved in quantum entanglement. So no matter how much energy you put into a proton that energy will divide equally between the magnitude of the spin angular velocity and the quantum entanglement energy and quantum entanglement will continue to rigidly confine the quarks.

I think people are starting to wake up to the fact that quantum entanglement plays a part in forming mass in all composite particles. And single photons are the only particles that are not composite particles and thus have no mass. However they do have energy so the 'm' in the kinetic energy of quarks but still be their energy but not in the "mass" sense. But even they can acquire mass through entanglement with other photons.

Eric

Please re-read the PF Guidelines that you have explicitly agreed to. Pay particular attention to speculative personal theories. Your posts might be deleted and you will be ask to submit your "theories" to the Independent Research forum.

Zz.

 

[DrChinese]

...If Einstein himself proposed a theory 5 years earlier in which non-locality of cause and effect could possibly happen then it could be said that what Einstein was more properly saying in the EPR paper is that quantum entanglement can exist, but that we just need to fill in our picture of physics in a way that it makes sense. It's interesting to me that so many physicists seem to ignore the title of the EPR paper: "Can The Quantum Mechanical Description of Physical Reality Be Considered Complete?"

It almost seems that the physics community has just built this straw man of "local variables" that Bell produced to show Einstein didn't know what he was talking about. Clearly he did and the title of the paper neatly summed it up what he was "really" saying.

I'd still be interested in any responses to what I said above. I realize what I'm saying maybe a little off in right field to some of you but I really think Bell's inequality is just a starting point for understanding quantum entanglement. It just shows that the non-locality of correlative effects exist but in no way addresses Einstein's real question. I think it misses the forest for the trees. Conversely, I think the EPR paper was concentrating on the forest - something which is done rarely in physics, even today. I promise I won't talk about my own ideas about QE if I can just get you guys to engage on this point.

Eric

Einstein did not believe in non-locality. As the inventor of relativity, he essentially took locality as a given.

As to the title of the great EPR paper: perhaps you should refresh yourself with EPR's primary conclusion, which was proven and is generally accepted: If Quantum Mechanics is complete (i.e. there is no better description of the state of the system - my words), then there cannot be simultaneous reality to non-commuting operators. The contranegative is also true: if there is simultaneous reality to non-commuting operators, then Quantum Mechanics is incomplete.

EPR then speculates as follows: a) that there is simultaneous reality to non-commuting operators MUST be true; therefore QM is incomplete; or b) there exists non-local forces (spooky action at a distance). Since Einstein did not believe b) was true, this shows that he believed in a) and ultimately that the predictions of QM could not hold in this case.

This speculation is what ultimately led to Bell's paper, which showed that: if QM is incomplete but otherwise correct in its predictions, then there must exist non-local forces. I would not call Bell's assumptions "straw men". Although some have referred to them as "naive realism" and/or "naive locality", they are taken plenty seriously today. And certainly so by Einstein, although he of course never saw Bell's work. I am quite sure he would have appreciated what Bell did.

 

[exeric]

Please re-read the PF Guidelines that you have explicitly agreed to. Pay particular attention to speculative personal theories. Your posts might be deleted and you will be ask to submit your "theories" to the Independent Research forum.

Zz.

Why don't you let people pick apart what I've said before you delete it. And if people wish to pick apart what I've said it is always a good idea to first debate the concepts presented by the messenger than to debate the quality of the messenger himself. That is one of the first principles of open debate. I've done substantial work on quantum entanglement and do not wish to overpromote myself on this. I can email you privately what my background on this is if you are interested.

 

[ZapperZ]

Why don't you let people pick apart what I've said before you delete it. And if people wish to pick apart what I've said it is always a good idea to first debate the concepts presented by the messenger than to debate the quality of the messenger himself. That is one of the first principles of open debate. I've done substantial work on quantum entanglement and do not wish to overpromote myself on this. I can email you privately what my background on this is if you are interested.

You could be a Nobel Prize winner, and we will still enforce the Guidelines. You know what you are getting yourself into from the very beginning.

If you wish to have people pick apart your ideas, that is exactly that the Independent Research forum is for. We apply this rule to everyone, you included.

This forum is not the place for you to work out your personal theory.

Zz.

 

[exeric]

You could be a Nobel Prize winner, and we will still enforce the Guidelines. You know what you are getting yourself into from the very beginning.

If you wish to have people pick apart your ideas, that is exactly that the Independent Research forum is for. We apply this rule to everyone, you included.

This forum is not the place for you to work out your personal theory.

Zz.

Ok, delete those posts. But don't delete my first two posts to this thread. There is nothing wrong with them being placed here. I think its a very fine line between trying to advance knowledge by challenging accepted theory and quarantining new ideas to a "safe" place, where they can be ignored. I think it is something to be concerned about, don't you? Science cannot be entirely extricated from human impulses for overt social control but it should be at least recognized that it also happens in science just as in non-scientific areas.

Eric

 

[exeric]

What on Earth are you talking about? You first say you have a couple questions – but give none, only opinions. Just what is “this point” ??
And then what do you think Einstein's real question was, if not to claim QM cannot be complete as QM claims itself to be, as it calls for reality to be non-local.

It's hard to know where to begin. The most blatant problem with quantum entanglement is in asking where the energy for quantum entanglement comes from. Do you actually think conservation of energy is not involved in the quantum entanglement process? If you accept that "free lunch" premise then I'm sorry, but you've already drunk the quantum mechanical kool-aid. This is the real essence Einstein was getting at in the question: "Can the quantum mechanical description of physical reality be considered complete?" There are no free lunches and Einstein was just stating the worst example of non-conservation of energy in the EPR paper, which is the energy involved in quantum entanglement. What's so difficult in understanding this is a problem?

Eric

 

[ZapperZ]

Ok, delete those posts. But don't delete my first two posts to this thread. There is nothing wrong with them being placed here. I think its a very fine line between trying to advance knowledge by challenging accepted theory and quarantining new ideas to a "safe" place, where they can be ignored. I think it is something to be concerned about, don't you? Science cannot be entirely extricated from human impulses for overt social control but it should be at least recognized that it also happens in science just as in non-scientific areas.

Eric

Since when is the advancement of science done on an open internet physics forum?

Again, you AGREED to abide by OUR rules when you signed on. You are more than welcome to 'advance science' elsewhere if you don't care for the guidelines.

Zz.

 

[ttn]

As to the title of the great EPR paper: perhaps you should refresh yourself with EPR's primary conclusion, which was proven and is generally accepted: If Quantum Mechanics is complete (i.e. there is no better description of the state of the system - my words), then there cannot be simultaneous reality to non-commuting operators. The contranegative is also true: if there is simultaneous reality to non-commuting operators, then Quantum Mechanics is incomplete.

I've been over this with you a million times before, but... for the benefit of any intelligent lurkers... the above represents a failure to grasp what is at issue in the EPR argument, and what they were trying to argue for. Dr C suggests that the thrust of the EPR paper was to argue for the following statement: if QM is complete, then there cannot be simultaneous reality to non-commuting operators/observables.

But that's not even the kind of thing one needs to argue for. It's simply a *definition* of completeness -- or more specifically, it's a clear litmus test for completeness in the context of a theory which simply doesn't *allow* the assignment of simultaneous definite values to non-commuting operators. It's just a given that, in orthodox QM, you can't do this. And so, to whatever extent, out there in physical reality, such observables *do* possesses simultaneous definite values, then orthodox QM is not complete.

So not only is that not the main thing EPR are arguing for, it's not the kind of thing one needs to argue for at all. To understand what the statement means is to see it as obviously true. The hard part is to construct some kind of argument that, in fact, out there in physical reality, such observables (i.e., those corresponding respectively to non-commuting operators) do possesses simultaneous definite values. And Dr C seems to completely miss that there is something like this argument in EPR, though, admittedly, it is hard to understand because of the way Podolsky wrote the manuscript. (Einstein didn't see the final draft and got mad that Podolsky had "buried" the main argument.) But now we know what Einstein had in mind. The argument was fundamentally based on *locality*. See "Einstein's Boxes" for further details.

EPR then speculates as follows: a) that there is simultaneous reality to non-commuting operators MUST be true; therefore QM is incomplete;

This is a ridiculous piece of trash. As a fan of Einstein I'm personally insulted that someone would publicly suggest that this was the EPR argument. I mean, come on. Einstein "speculates" (i.e., just makes up arbitrarily because he feels like it, not based on any argument) that observables corresponding to non-commuting operators "MUST" have simultaneous definite values? He just makes it up? I mean, please. It's a disgusting insult to the greatest physicist ever. Anyone who has a shred of respect for the great man should realize, if they think this was the argument, that maybe they just haven't *understood* the argument yet... and so they should go back and do some homework to find out what Einstein actually thought, rather than spread vicious lies and confusions that make Einstein sound like a moron.

or b) there exists non-local forces (spooky action at a distance).

Look, the argument is that *unless* one accepts spooky nonlocal forces, one must posit certain elements of reality. There's an actual *argument* there. If you haven't understood the argument, go back and study the issue some more. But don't keep spouting this nonsense that Einstein just arbitrarily "speculated" that it was a or b... Sheesh.

Since Einstein did not believe b) was true, this shows that he believed in a) and ultimately that the predictions of QM could not hold in this case.

Where did Einstein ever say that "the predictions of QM could not hold"? Actually the whole EPR argument (or his Boxes version) is premised on the predictions of QM being true. The whole argument is that the only way to explain certain correlations (namely, those *predicted by QM*) LOCALLY is to posit certain "hidden variables".

This speculation is what ultimately led to Bell's paper, which showed that: if QM is incomplete but otherwise correct in its predictions, then there must exist non-local forces.

You misunderstand this as well. One needn't assume that "QM is incomplete" in order to derive a Bell type inequality. The inequality follows from locality (a certain mathematically precise definition thereof which Bell first articulated) alone. That's it. Of course, it is possible to get a Bell inequality by first assuming certain hidden variables (and locality). But this doesn't change what I just said, since the existence of those hidden variables is itself a logical consequence of the locality assumption. That, as Bell points out repeatedly in his papers, is the EPR argument. Locality *requires* those hidden variables. So if Bell assumes them (and sometimes he does, but not always and it isn't logically necessary) it doesn't matter one way or the other. Either way, the inequality follows from Locality alone. The only question is whether one gets there in one step or two.

I don't expect to change your mind on any of this since I've tried so many times before and failed completely. But I can't in good conscience sit here and watch you disgustingly pervert these beautiful arguments. Not in front of what might (for all I know) be innocent children.

 

[RandallB]

EPR then speculates as follows: a) that there is simultaneous reality to non-commuting operators MUST be true; therefore QM is incomplete; or b) there exists non-local forces (spooky action at a distance). Since Einstein did not believe b) was true, this shows that he believed in a) and ultimately that the predictions of QM could not hold in this case.

I’m sorry tnn I just don’t see where this is an insult to Einstein any more than calling HV theories a belief in "naive locality / realism". It true and there is nothing wrong with that – it’s just not likely a correct view of actual reality based on testing so far.

Maybe using the word asserts instead speculates would help. I’ll sleep on it and reread your point in the AM.