Is something wrong with statistical interpretation of QM?

[universal_101]

The probabilistic nature of QM seems apparent(in theoretical formulation as well as experimentally), then why do most of the physicists give the credit of in-determinism to the nature itself and look for many worlds, abruptly collapsing observer conscious experiment setups, and the likes.

Whereas it seems that in-determinism lies with the fact that there are far too many degrees of freedom involved in QM. That is, why does that cat has to be dead and alive at the same time or one cat dead and other alive in two different worlds, when it is perfectly understandable that we don't know the state of the cat because there are more degrees of freedom involved for which we can solve this particular setup.

Similarly, why do we make the Quantum Entanglement superior than the classical case of a pair of shoes at different places? Is it because, the in-determinism of QM is currently considered fundamental in nature and therefore the states of the two annihilation photons must be entangled somehow so as that when we measure the spin of one photon the spin of the other photon is known simultaneously?

Thanks

 

[Nugatory]

Similarly, why do we make the Quantum Entanglement superior than the classical case of a pair of shoes at different places? Is it because, the in-determinism of QM is currently considered fundamental in nature and therefore the states of the two annihilation photons must be entangled somehow so as that when we measure the spin of one photon the spin of the other photon is known simultaneously?

Google for "Bell's Theorem". Entanglement is indeed fundamentally different from the classical case of a pair of shoes at different places.

 

[bhobba]

The probabilistic nature of QM seems apparent(in theoretical formulation as well as experimentally), then why do most of the physicists give the credit of in-determinism to the nature itself and look for many worlds, abruptly collapsing observer conscious experiment setups, and the likes.

Who told you that? I don't. For me its simply the most reasonable probability model that allows entanglement.
http://arxiv.org/abs/quant-ph/0101012
http://arxiv.org/abs/0911.0695

Actually many physicists don't care that much about the interpretational stuff - they simply use it.

That is, why does that cat has to be dead and alive at the same time or one cat dead and other alive in two different worlds

You have been reading too many popularizations. According to the standard Copenhagen interpretation the cat is alive or dead - period. Schrodingers cat is not about a cat that's supposed to be alive and dead - no one seriously doubted that - its about the real issue with QM - namely how a theory that's a probability model about things that occur here in the common sense classical world explain that world which it assumes from the start.

A lot of work, particularly in the area of decoherence, has been done on that issue with a lot of progress made - but some issues still remain.

Similarly, why do we make the Quantum Entanglement superior than the classical case of a pair of shoes at different places?

Entanglement is totally inexplicable by classical probability theory. In fact as the links I gave above show its what distinguishes it from standard probability theory in modelling physical systems.

If you REALLY want to understand what QM is ACTUALLY about start here:
http://www.scottaaronson.com/democritus/lec9.html

Its not about wave particle dualities, wavefunction collapse, Schrodinger's Cat, consciousness causes collapse, and the usual stuff in popularizations - it's really simply a generalization of probability theory with features more suitable to model continuous changes, or, equivalently, allows entanglement.

Thanks
Bill

 

[jtbell]

Google for "Bell's Theorem". Entanglement is indeed fundamentally different from the classical case of a pair of shoes at different places.

Or a pair of Bertlmann's socks.

 

[stevendaryl]

The probabilistic nature of QM seems apparent(in theoretical formulation as well as experimentally), then why do most of the physicists give the credit of in-determinism to the nature itself and look for many worlds, abruptly collapsing observer conscious experiment setups, and the likes.

Whereas it seems that in-determinism lies with the fact that there are far too many degrees of freedom involved in QM. That is, why does that cat has to be dead and alive at the same time or one cat dead and other alive in two different worlds, when it is perfectly understandable that we don't know the state of the cat because there are more degrees of freedom involved for which we can solve this particular setup.

Similarly, why do we make the Quantum Entanglement superior than the classical case of a pair of shoes at different places? Is it because, the in-determinism of QM is currently considered fundamental in nature and therefore the states of the two annihilation photons must be entangled somehow so as that when we measure the spin of one photon the spin of the other photon is known simultaneously?
Thanks

It's the combination of two features of quantum mechanics that make it difficult to interpret in terms of classical probability. One is entanglement, and the second is incompatible observables--the fact that perfect knowledge about the value of one observable can preclude knowledge about other, noncommuting observables.

Entanglement by itself is not particularly quantum-mechanical; as you point out, it has an analogue in joint probability distributions in classical probability theory. Incompatible observables by themselves don't force us to a new type of probability. Early on, the uncertainty principle was given a heuristic interpretation in terms of disturbances caused by measurement: The attempt to measure precisely a property such as position inevitably disturbs the object being measured, so that other incompatible properties are made uncertain. This disturbance interpretation of the uncertainty principle is different from what we would expect from classical physics, where it is assumed that all properties can be measured as precisely as we like without disturbing the object being measured. But it's not that difficult to understand in classical terms.

But the combination of entanglement and the uncertainty principle both together makes quantum mechanics impossible to interpret in terms of classical probability. That's what experiments such as EPR show. In the classical case of entanglement, we can always assume that an entangled probability distribution simply reflects a lack of information: If we knew more precisely what the situation was, the entanglement would disappear. In the quantum case, because of the uncertainty principle, there is no more precise knowledge possible in some cases. And because entanglement can affect objects that are arbitrarily far apart, it's not plausible to think of the uncertainty principle in terms of disturbances due to the measurement process: Measuring the spin of one particle in an EPR twin-pair experiment might be disturbing that particle, but certainly it isn't disturbing the other particle far, far away (unless disturbances travel instantaneously, which is the interpretation given by the Bohm-DeBroglie model of quantum mechanics.)

 

[universal_101]

Google for "Bell's Theorem". Entanglement is indeed fundamentally different from the classical case of a pair of shoes at different places.

Does incapability of current classical science to explain the probabilistic outcome of Entangled particles at different detectors, makes the Quantum Entanglement fundamentally different from classical case ?

If so, then how does Entangled states are aware of each other's measurement, according to Quantum theory? Or am I asking the wrong question, because there is NO intuitive explanation for it, except ofcourse Quantum formulation.

 

[universal_101]

Actually many physicists don't care that much about the interpretational stuff - they simply use it.

Is it because of present understanding that there can be NO reasonable interpretation for Quantum formulation? (Entanglement)

You have been reading too many popularizations. According to the standard Copenhagen interpretation the cat is alive or dead - period.

Well, Does this interpretation falls apart for bell's theorem, is it not ?

namely how a theory that's a probability model about things that occur here in the common sense classical world explain that world which it assumes from the start.

What does the above mean?

Entanglement is totally inexplicable by classical probability theory. In fact as the links I gave above show its what distinguishes it from standard probability theory in modelling physical systems.

If you REALLY want to understand what QM is ACTUALLY about start here:
http://www.scottaaronson.com/democritus/lec9.html

Its not about wave particle dualities, wavefunction collapse, Schrodinger's Cat, consciousness causes collapse, and the usual stuff in popularizations - it's really simply a generalization of probability theory with features more suitable to model continuous changes, or, equivalently, allows entanglement.

Thanks
Bill

Seems like Quantum Entanglement which is very much similar to the classical pair case, cannot be explained by generalized classical probability theory, and therefore there is NO intuitive interpretation for quantum formulation.

 

[universal_101]

And because entanglement can affect objects that are arbitrarily far apart, it's not plausible to think of the uncertainty principle in terms of disturbances due to the measurement process: Measuring the spin of one particle in an EPR twin-pair experiment might be disturbing that particle, but certainly it isn't disturbing the other particle far, far away (unless disturbances travel instantaneously, which is the interpretation given by the Bohm-DeBroglie model of quantum mechanics.)

I think principle of causality is more "sacred/superior" than any interpretation for Quantum Entanglement, therefore on must consider Quantum formulation as incomplete, falling-short. But wait that was exactly the point of EPR, and it was Bell's theorem which showed that classical hidden variable cannot explain the Entangled particles detection probabilities. Well, my point is why should classical physics be able to explain Quantum Entanglement when it was not able to explain even hydrogen atom, black body radiation, photoelectric effect, etc. The bigger question is, Does quantum physics respect the principle of causality or not, and this question lies entirely with the quantum physics and it has nothing to do with classical physics.

 

[DevilsAvocado]

Does incapability of current classical science to explain the probabilistic outcome of Entangled particles at different detectors, makes the Quantum Entanglement fundamentally different from classical case ?

Yes, very much so.

If so, then how does Entangled states are aware of each other's measurement, according to Quantum theory? Or am I asking the wrong question, because there is NO intuitive explanation for it, except ofcourse Quantum formulation.

Welcome to the club buddy!

No one knows how entanglement works, except for the mathematical description. Not even the smartest professors that work with this stuff every day. At current state of affairs, we can't even tell if it's locality or realism (or both) that has to be abandoned – so how could you expect an intuitive explanation in this situation...

Most certainly there's a Nobel Prize awaiting the genius(es) cracking this nut.

 

[DevilsAvocado]

Well, my point is why should classical physics be able to explain Quantum Entanglement when it was not able to explain even hydrogen atom, black body radiation, photoelectric effect, etc.

The key point is that QM entanglement + Bell's theorem hit quite a drastic blow on classical local realism. It's gone forever, period.

The bigger question is, Does quantum physics respect the principle of causality or not,

Macroscopic "cause" and "effect", yes. Mathematically/microscopically, there are some interpretations that use retrocausality, however no one knows which interpretation is the right one (yet).

(However, if you chose to preserve realism in the EPR-Bell case, you will run into trouble with relativity of simultaneity)

 

[bhobba]

Does incapability of current classical science to explain the probabilistic outcome of Entangled particles at different detectors, makes the Quantum Entanglement fundamentally different from classical case ?

Why do you think we don't know why QM is probabilistic?

Check out Gleason's Theorem:
http://en.wikipedia.org/wiki/Gleason's_theorem

The reason its fundamentally different is, as the papers I linked to proved, if you want continuous transformations between pure states, which is impossible in standard probability theory, you inevitably get entanglement which is impossible classically.

But before going any further can you tell me what you think entanglement is?

Thanks
Bill

 

[bhobba]

Is it because of present understanding that there can be NO reasonable interpretation for Quantum formulation? (Entanglement)

No - its because they believe in shut up and calculate.

And why do you believe there is no reasonable interpretation? Whats reasonable and not reasonable is in the eye of the beholder.

Well, Does this interpretation falls apart for bell's theorem, is it not ?

No interpretation falls apart for Bells Theorem or it wouldn't be an interpretation

What does the above mean?

It means the formalism of QM is a theory about observations (or more generally 'marks') here in an assumed classical world. But that classical world is in fact quantum - so how does a theory that assumes a classical world explain it.

therefore there is NO intuitive interpretation for quantum formulation.

What is intuitive depends on the intuition of the person concerned. No one would have come up with QM without experiments forcing you, but when you understand its rock bottom essence you start to get a feel for what's going on.

Again I urge you to read:
http://www.scottaaronson.com/democritus/lec9.html

Thanks
Bill

 

[universal_101]

Why do you think we don't know why QM is probabilistic?

Check out Gleason's Theorem:
http://en.wikipedia.org/wiki/Gleason's_theorem

Why? is it because nature itself is inherently probabilistic since no classical hidden variable can explain Quantum entanglement, or is it because there are far too many degrees of freedom involved in any particular quantum measurement.

The reason its fundamentally different is, as the papers I linked to proved, if you want continuous transformations between pure states, which is impossible in standard probability theory, you inevitably get entanglement which is impossible classically.

Are they the Unitary transformations which can change pure states to other pure states yet keep the probabilistic outcome(or say expectation values) same. Whereas, the argument goes similarly for quantum physics, that since quantum entanglement requires that local-realism must be abandoned, the quantum formulation must be falling-short, for there are no experiments which denies the local-realism. (ofcourse other than the quantum formulation requirement)

But before going any further can you tell me what you think entanglement is?

OK, let's see, Quantum entanglement according to quantum physics says the state of the two particles are said to be entangled, if they produce opposite (or similar depending on the experiment) results every time there is similar measurement done on the two particles state. But since the two states are not co-related according to QM(i.e they are independent of each other) therefore the only solution according to QM is that the two states somehow change the state of each other depending on what is measured on the other, to get the opposite/similar final results.

Classically, there is no need for one particle to change the state of the other particle, because they can be understood to be co-related to each other, just like a pair of shoes, but classically we cannot produce the probabilistic outcome.

 

[universal_101]

Welcome to the club buddy!

No one knows how entanglement works, except for the mathematical description. Not even the smartest professors that work with this stuff every day. At current state of affairs, we can't even tell if it's locality or realism (or both) that has to be abandoned – so how could you expect an intuitive explanation in this situation...

Well, if we don't know how does it work, how can we be sure that QM is not wrong or incomplete. Or does producing the statistical probabilistic outcome same as experiments, is more fundamental than let's say, what is the physics behind it?

Since a theory can only be complete when we know/understand how does it work, right?

 

[ZapperZ]

Well, if we don't know how does it work, how can we be sure that QM is not wrong or incomplete. Or does producing the statistical probabilistic outcome same as experiments, is more fundamental than let's say, what is the physics behind it?

Since a theory can only be complete when we know/understand how does it work, right?

Let's go back a bit, because by saying that, you are implying that we DO know something that we can be SURE that "is not wrong or incomplete". Can you point to me one? Do you think classical mechanics is "not wrong and not incomplete"? How about Relativity?

There is a very strange criteria put on physics here by claiming something it never claimed. Science, and certainly physics, NEVER makes any claim on any theory or description to never be wrong and to be complete. That is a COMPLETE fallacy. Only politicians and talking heads on TV make such definitive claims.

What we CAN make is a claim on the validity of something over a certain range that we have encounter. And until we discover the limits on such a range, we will continue to uphold the validity of it! It is why we still use Newtonian physics to build your house! It is why we continue to use classical E&M when we design all those antennas to pick up your cell phone signals. And this why we continue to use the Drude model that give you Ohm's Law. We don't use them because they are "never wrong and complete", but rather they are VALID and correct within the range of parameters that they are applied to!

Please note that in these things are you questioning about, it was NEVER based on either a logical inconsistency (i.e. mathematical error) or experimental evidence. You questioned it based on TASTES or personal preference! You need to be very clear on this, because a lot of people seem to think that their feelings, or uneasiness, are somehow sufficient to offer a valid evidence against something in science! This is another fallacy!

The statistical interpretation of QM can only be shown to be wrong IF there are evidence that can separate out all the different interpretations. That's it! Experimental evidence trumps everything else, even one's "feelings" and personal tastes.

Until that happens, this is nothing more than a discussion on one's favorite color. And unless there is a high physics content in this discussion rather than just a discussion on one's personal preferences, this discussion is about philosophy and is subject to being closed.

Zz.

 

[TheOldDog]

Let's go back a bit, because by saying that, you are implying that we DO know something that we can be SURE that "is not wrong or incomplete". Can you point to me one? Do you think classical mechanics is "not wrong and not incomplete"? How about Relativity?

There is a very strange criteria put on physics here by claiming something it never claimed. Science, and certainly physics, NEVER makes any claim on any theory or description to never be wrong and to be complete. That is a COMPLETE fallacy. Only politicians and talking heads on TV make such definitive claims.

What we CAN make is a claim on the validity of something over a certain range that we have encounter. And until we discover the limits on such a range, we will continue to uphold the validity of it! It is why we still use Newtonian physics to build your house! It is why we continue to use classical E&M when we design all those antennas to pick up your cell phone signals. And this why we continue to use the Drude model that give you Ohm's Law. We don't use them because they are "never wrong and complete", but rather they are VALID and correct within the range of parameters that they are applied to!

[snip]
Zz.

Isn't it amazing how many people in the world don't understand this? :-(

 

[Nugatory]

Well, if we don't know how does it work, how can we be sure that QM is not wrong or incomplete.

We can't.

That's always been true of all scientific theories. And, because the answer to any "why?" question can always be met with another deeper "why?", I expect that it will be true of all scientific theories in the future as well.

It's also worth noting that QM has "improved" a lot since the early days. There's a better understanding of the limits of the formalism and the point where science stops and interpretation begins; a clearer understanding of the limits of hidden variables; the statistical interpretation cleans up the axiomatic structure no end; the discovery of decoherence has helped enormously with the macro/micro split; and more. There's every reason to expect that it will continue to improve over time.

 

[WannabeNewton]

OK, let's see, Quantum entanglement according to quantum physics says the state of the two particles are said to be entangled, if they produce opposite (or similar depending on the experiment) results every time there is similar measurement done on the two particles state. But since the two states are not co-related according to QM(i.e they are independent of each other) therefore the only solution according to QM is that the two states somehow change the state of each other depending on what is measured on the other, to get the opposite/similar final results.

I would say that's not an accurate description of entanglement. There is no necessity for "opposite" or "similar" results and there are correlations. Entanglement occurs when you cannot factorize the state of a two-component system into a product of states of the subsystems. A quantum mechanically described measuring apparatus can get entangled with the system it is attempting a measurement of if the system was in a superposition of eigenstates of the observable(s) being measured which your description does not encompass.

 

[atyy]

There are interpretations in which QM is incomplete (eg. de Broglie-Bohm theory for non-relativistic QM), as well as approaches in which QM is complete (many-worlds).

 

[stevendaryl]

I would say that's not an accurate description of entanglement. There is no necessity for "opposite" or "similar" results and there are correlations. Entanglement occurs when you cannot factorize the state of a two-component system into a product of states of the subsystems. A quantum mechanically described measuring apparatus can get entangled with the system it is attempting a measurement of if the system was in a superposition of eigenstates of the observable(s) being measured which your description does not encompass.

That's the way I always thought of entanglement, in terms of the impossibility of factoring the state describing distant objects. To me, this is a sense in which quantum mechanics is nonlocal in a way that classical physics is not. In classical physics, it's always possible to do the following:

1. Partition the universe up into neighborhoods.
2. Describe the state of each neighborhood.
3. Then the state of the universe is completely described by those "local" states, together with geographic information about which neighborhoods border which other ones.

You can't do that in quantum mechanics, precisely because of entanglement. The state of the universe is not completely described by giving the states of all the neighborhoods that make up the universe.

The exact same thing happens in classical probability theory, though. If you put a pair of shoes into identical boxes, and send one box to Alice and another box to Bob, then before opening the box, both Alice and Bob would describe the state of each box as "probability 1/2 of being a left shoe, probability 1/2 of being a right shoe". But the state of the universe is not completely captured by those local descriptions, because we know that if Alice has a left shoe, then Bob has a right shoe.

But in the classical case, you can interpret the "entanglement" as being due to lack of information about the true state of the universe, which is not entangled. The entanglement of quantum mechanics cannot (or at least not easily) be interpreted as due to lack information.

 

[universal_101]

Let's go back a bit, because by saying that, you are implying that we DO know something that we can be SURE that "is not wrong or incomplete". Can you point to me one? Do you think classical mechanics is "not wrong and not incomplete"? How about Relativity?

I get your point that NO theory can/should/supposed(to) be correct and complete, but I think everybody agrees with it, including myself.

There is a very strange criteria put on physics here by claiming something it never claimed. Science, and certainly physics, NEVER makes any claim on any theory or description to never be wrong and to be complete. That is a COMPLETE fallacy. Only politicians and talking heads on TV make such definitive claims.

I didn't make any such claims, therefore I'm neither a politician nor a TV talking head. Instead what I'm referring to is, that there are certain experiments which decisively put theories(assuming experiment comes under the domain of the theory) under the tags "wrong and/or incomplete".
And Quantum entanglement seems to be such an experiment for QM.

What we CAN make is a claim on the validity of something over a certain range that we have encounter. And until we discover the limits on such a range, we will continue to uphold the validity of it! It is why we still use Newtonian physics to build your house! It is why we continue to use classical E&M when we design all those antennas to pick up your cell phone signals. And this why we continue to use the Drude model that give you Ohm's Law. We don't use them because they are "never wrong and complete", but rather they are VALID and correct within the range of parameters that they are applied to!

I agree completely.

Please note that in these things are you questioning about, it was NEVER based on either a logical inconsistency (i.e. mathematical error) or experimental evidence. You questioned it based on TASTES or personal preference! You need to be very clear on this, because a lot of people seem to think that their feelings, or uneasiness, are somehow sufficient to offer a valid evidence against something in science! This is another fallacy!

I see how easily you equated logical inconsistency to mathematical error in a theory, which is undeniably questionable. For example, a mathematical model which makes superluminal speeds possible is perfect mathematically but logically inconsistent with everything else(i.e no experiment support superluminal information transfer). Same is the case with the quantum entanglement mathematical model, it abandons local-realism which is logically inconsistent with everything else(i.e there is no experiment that does not support local-realism). And all this is not a matter of taste, one must tell how a theory got the results it gets, otherwise it would just be a model to calculate the results while same time not respecting the fundamental tenets of any physical theory(i.e. abandoning local-realism without any experimental evidence).

The statistical interpretation of QM can only be shown to be wrong IF there are evidence that can separate out all the different interpretations. That's it! Experimental evidence trumps everything else, even one's "feelings" and personal tastes.

Until that happens, this is nothing more than a discussion on one's favorite color. And unless there is a high physics content in this discussion rather than just a discussion on one's personal preferences, this discussion is about philosophy and is subject to being closed.

Zz.

Why are you so inclined to call/label it a personal taste/feeling or philosophy, when it is clearly not. There is obvious high physics involved, when a model requires abandoning of local-realism, all I'm asking is that there should be a proof of it experimentally. Or are you implying that there is no need to ask that question because QM mathematically produces a variety of experimental results where classical physics failed, therefore the classical idea of local-realism is no longer valid in quantum world, and can be safely abandoned/ignored.

I hope you see what I'm concerned about.

 

[universal_101]

I would say that's not an accurate description of entanglement. There is no necessity for "opposite" or "similar" results and there are correlations. Entanglement occurs when you cannot factorize the state of a two-component system into a product of states of the subsystems. A quantum mechanically described measuring apparatus can get entangled with the system it is attempting a measurement of if the system was in a superposition of eigenstates of the observable(s) being measured which your description does not encompass.

Yes, you are more correct than me mathematically, that is the wavefunction of the system must not be separable in the wavefunctions of individual particles, and this implies the measurement of an eigenvalue of an operator acting on the wavefunction of the system inevitably disturbs any other post measurement(for example measuring the spin of one particle and the spin of other). And it is this disturbance which is the source of concern.

Thanks for correcting me.

 

[Doc Al]

Same is the case with the quantum entanglement mathematical model, it abandons local-realism which is logically inconsistent with everything else(i.e there is no experiment that does not support local-realism).

All tests of Bell's inequalities support the results of quantum mechanics and are evidence against local hidden variables (at least local in the Bell sense).

 

[ZapperZ]

I see how easily you equated logical inconsistency to mathematical error in a theory, which is undeniably questionable. For example, a mathematical model which makes superluminal speeds possible is perfect mathematically but logically inconsistent with everything else(i.e no experiment support superluminal information transfer). Same is the case with the quantum entanglement mathematical model, it abandons local-realism which is logically inconsistent with everything else(i.e there is no experiment that does not support local-realism). And all this is not a matter of taste, one must tell how a theory got the results it gets, otherwise it would just be a model to calculate the results while same time not respecting the fundamental tenets of any physical theory(i.e. abandoning local-realism without any experimental evidence).

But there is nothing in the law of nature in which "local realism", adopting or abandoning it, that requires it! And no, telling how a theory got its results is also not a "requirement" for it to be valid. A phenomenological model can be equally valid, all the while without offering any explanation.

And what exactly is a "fundamental tenets of any physical theory"? Who agreed on such a thing? Again, you are imposing these set of rules onto a physical theory without you justifying why it is so necessary. For someone who is insisting that a physical theory must explain where it came from, you seem to be in a habit of not explaining yourself where you got all these ideas from that you are imposing onto science.

Why are you so inclined to call/label it a personal taste/feeling or philosophy, when it is clearly not. There is obvious high physics involved, when a model requires abandoning of local-realism, all I'm asking is that there should be a proof of it experimentally. Or are you implying that there is no need to ask that question because QM mathematically produces a variety of experimental results where classical physics failed, therefore the classical idea of local-realism is no longer valid in quantum world, and can be safely abandoned/ignored.

I hope you see what I'm concerned about.

If all you want are experimental evidence that are in support of QM, why didn't you say so in the very beginning?

F. Buscemi, "All Entangled Quantum States Are Nonlocal", Phys. Rev. Lett. v.108, p. 200401 (2012).

E. Kot et al., "Breakdown of the Classical Description of a Local System", Phys. Rev. Lett., v.08, p.233601 (2012).

J. Yin et al., "Quantum teleportation and entanglement distribution over 100-kilometre free-space channels" Nature v.488, p.185 (2012).

C. Zu et al.,“State-Independent Experimental Test of Quantum Contextuality in an Indivisible System” Phys. Rev. Lett. 109, 150401 (2012).

J. S. Lundeen and A. M. Steinberg, "Experimental Joint Weak Measurement on a Photon Pair as a Probe of Hardy's Paradox", Phys. Rev. Lett. 102, 020404 (2009).

G. Kirchmair et al., "State-independent experimental test of quantum contextuality", Nature v.460, p.494 (2009).

Do you want more?

Zz.

 

[WannabeNewton]

But in the classical case, you can interpret the "entanglement" as being due to lack of information about the true state of the universe, which is not entangled. The entanglement of quantum mechanics cannot (or at least not easily) be interpreted as due to lack information.

Very well put!

 

[universal_101]

All tests of Bell's inequalities support the results of quantum mechanics and are evidence against local hidden variables (at least local in the Bell sense).

Correct, but we don't have non-local(spooky action at a distance) forces/effects/technology/experiments that proves non-locality is a fact, similarly we don't have many-world technology where particles can be put in different worlds. Except, ofcourse in the Bell sense, where one of them must be correct if local hidden variables cannot produce the results.

Now, it seems we have only three options,

a.) non-locality
b.) no definite reality
c.) formulation of bell's inequality using local hidden variables is not done correctly.

Noting the fact that ability of QM to produce statistical probabilities is mutually exclusive with bell's inequality, (i.e. correctness of QM does not guarantee correctness of bell's inequality). Which option would you choose?

 

[vanhees71]

There is a third very unspectacular possibility: Local relativistic quantum field theory is correct! That's it. No problems left.

 

[atyy]

Correct, but we don't have non-local(spooky action at a distance) forces/effects/technology/experiments that proves non-locality is a fact, similarly we don't have many-world technology where particles can be put in different worlds. Except, ofcourse in the Bell sense, where one of them must be correct if local hidden variables cannot produce the results.

Now, it seems we have only three options,

a.) non-locality
b.) no definite reality
c.) formulation of bell's inequality using local hidden variables is not done correctly.

Noting the fact that ability of QM to produce statistical probabilities is mutually exclusive with bell's inequality, (i.e. correctness of QM does not guarantee correctness of bell's inequality). Which option would you choose?

The technical possibility remains that local realism is possible, because there is currently no loophole free experimental demonstration of a Bell inequality.

Even if there were, another technical possibility is superdeterminism.

Incidentally, Bell's inequality does not assume determinism.

If quantum mechanics is complete as in the many-worlds approach, no experimental violation of it will be found. If quantum mechanics arises from a nonlocal realistic hidden variables theory like de Broglie-Bohm, then in principle sufficiently advanced experiments could detect a violation of quantum mechanics.

 

[Nugatory]

Now, it seems we have only three options,

a.) non-locality
b.) no definite reality
c.) formulation of bell's inequality using local hidden variables is not done correctly.

Noting the fact that ability of QM to produce statistical probabilities is mutually exclusive with bell's inequality, (i.e. correctness of QM does not guarantee correctness of bell's inequality). Which option would you choose?

(Did you mean that correctness of QM guarantees the incorrectness of Bell's inequality? The whole point of the exercise is that QM predicts violations of the inequality).

You're rehashing old and tired ground here.

We have enough analysis of Bell's work to relegate #c to the cranks and crackpots. So let's take that off the list.

Then let's add to the list #d - "none of the above". For example, superdeterminism keeps everything in the same light cone and assumes a definite reality, but does not suggest any incorrectness in the formulation of Bell's inequality and is not falsified by Aspect-type experiments.

However, all known #d candidates are either inconsistent with experiment or every bit as weird as #a or #b. So no matter which we choose, we're stuck with the weirdness. As long as there is no way of distinguishing #a, #b, and #d by experiment, the discussion is sterile.

(and eventually the moderators become impatient and close the thread on the reasonable grounds that no one is saying anything new.)

 

[universal_101]

There is a third very unspectacular possibility: Local relativistic quantum field theory is correct! That's it. No problems left.

Does it mean, it is non-realist theory? In a sense that we don't know the state of the particle prior to the measurement and therefore it is the measurement which produces the state right at the moment of measuring the property of the particle. And if after measurement we find some correlations, it is because they were introduced when the entangled particles were created.

All this does not seem very non-realist(except in the Bells sense), it seems very much classical, where we don't know which pair we have until we open the box, and since the pair is entangled when let's say, the pair of socks were packed in different boxes.

Where am I wrong?

 

[universal_101]

(Did you mean that correctness of QM guarantees the incorrectness of Bell's inequality? The whole point of the exercise is that QM predicts violations of the inequality).

All I meant was that correctness of Bell's inequality and correctness of quantum mechanics are mutually exclusive, in a sense one does not follow from other.

That is correctness of Bell's inequality is in Bells sense of local hidden variable, which is completely absent in QM.

 

[stevendaryl]

All this does not seem very non-realist(except in the Bells sense), it seems very much classical, where we don't know which pair we have until we open the box, and since the pair is entangled when let's say, the pair of socks were packed in different boxes.

Where am I wrong?

As I said, the difference is exactly Bell's sense. The kind of "entanglement" that exists classically can be explained as due to ignorance about the true state of the system. Quantum entanglement can't be viewed that way, according to Bel's theorem.

 

[stevendaryl]

There is a third very unspectacular possibility: Local relativistic quantum field theory is correct! That's it. No problems left.

Quantum field theory is very nice, in that it puts all the dynamics into the field operators, which evolve perfectly locally. This is the field-theoretic analog of the use of the Heisenberg picture in nonrelativistic quantum mechanics, where instead of having a wave function that evolves in time, the operators/observables evolve in time. The "equations of motion" for these operators look very much like the corresponding equations of motion for Newtonian physics, except that position and momentum are interpreted as operators, rather than real numbers.

In quantum field theory, the field operators are local operators and evolve according to field equations that are perfectly local. So everything is hunky dory.

But that doesn't really solve any of the interpretational problems of quantum mechanics. The problem is that the field operators don't describe any actual events (such as: a particle was detected at this place at this time). They, like the wavefunctions of nonrelativistic quantum mechanics, only give amplitudes for such events. So there is a gap between what the theory describes and what we actually observe in the world. It's the same gap as in nonrelativistic quantum mechanics. It either bothers you or it doesn't, but I think that there is no sense in which the questions of realism and locality and so forth that come up in nonrelativistic quantum mechanics are resolved by relativistic quantum field theory.

 

[EskWIRED]

Until that happens, this is nothing more than a discussion on one's favorite color. And unless there is a high physics content in this discussion rather than just a discussion on one's personal preferences, this discussion is about philosophy and is subject to being closed.

Zz.

I hope that you don't actually believe that philosophy is "nothing more than a discussion on one's favorite color".

Physics is rooted in logic, and logic is a major branch of philosophy. Indeed, discussions of one's personal preferences have little or nothing to do with philosophy.

 

[DevilsAvocado]

Well, if we don't know how does it work, how can we be sure that QM is not wrong or incomplete.

Gosh... you asked for an intuitive explanation, in my world that's something different than a mathematical formulation, which to most "Average Joe" means pretty much nothing.

Furthermore, Bell's theorem is a no-go theorem, i.e. it states that L and R can't both be true – if Q is also true, and thus far no one has ever proven Q to be false.

So, we do have the mathematics describing entanglement and the shared wavefunction, and we can make prefect outcome predictions for all possible measurement settings, and it has worked perfectly for thousands of empirical experiments performed to this date, and there is absolutely nothing indicating that this will ever change in the future.

But we don't have all the answers; this doesn't mean QM is wrong or incomplete in any way.

Or does producing the statistical probabilistic outcome same as experiments, is more fundamental than let's say, what is the physics behind it?

Don't know what crystal ball you are tweaking to get to "the physics behind it", but out in the real world the most widespread method is experiments, experiments, experiments, and even more experiments. AFAIK, this is the only way to confirm the validity of a scientific theory.

Since a theory can only be complete when we know/understand how does it work, right?

Complete is a somewhat 'flexible' word that could change with history, and new knowledge. As for example in the 1935 EPR paper by Einstein, Podolsky and Rosen, they assumed that the principle of locality was "powerful to physical intuition", and defined a complete physical theory as one in which every element of physical reality is accounted for by the theory.

The 1935 EPR paper ends by:

While we have thus shown that the wave function does not provide a complete description of the physical reality, we left open the question of whether or not such a description exists. We believe, however, that such a theory is possible.​

I.e. they drew the conclusion that quantum mechanics is not a complete theory.

I love Einstein, he was an absolute brilliant genius, but every rose has its thorns, and this time he was just simply wrong. In a historical perspective, the EPR paper backfired on him, and today we can be absolutely confident that classical local realism is not a complete 'theory' – it doesn't work in experiment!

I.e. even if QM some day is superseded by a new theory – local realism is already a dead parrot.

Period.