Does the EPR experiment imply QM is incomplete?

[PeterDonis]

I can do one or more of the following
a) let you have datasets as csv text files
b) Let you have the simulation if you have a windows machine so you can make datasets
c) the code is Delphi and the source is available

For me, a) and c) would be fine; I don't have a Windows machine but I can read Delphi source code. If you'd rather send them privately, PM me.

 

[Boing3000]

Like yours nothing it is added except the shared state. I don't know why you think there's anything special about it. It is standard programming.

I don't know why you think there's anything special about it. I have said over and over that is absolutely basic. You've just quoted a post when I said " It is a straightforward implementation. There is no fuss, no weirdness added, no information added."

Could you let me have some simulated data for analysis ?

The code is free to use, there is nothing special about it.

Actually the only thing special, is that is does not have anything special. The sharing of variable is the default behavior in computing. Doing otherwise requires extra work. Everything is classical.

I am sure yours will be fine to, especially if you use QM formula (or complex number) or if some function use input from A & B (which seem to be the case).
Mine do not.

 

[Mentz114]

I don't know why you think there's anything special about it. I have said over and over that is absolutely basic. You've just quoted a post when I said " It is a straightforward implementation. There is no fuss, no weirdness added, no information added."The code is free to use, there is nothing special about it.

Actually the only thing special, is that is does not have anything special. The sharing of variable is the default behavior in computing. Doing otherwise requires extra work. Everything is classical.

I am sure yours will be fine to, especially if you use QM formula (or complex number) or if some function use input from A & B (which seem to be the case).
Mine do not.

OK. The essential thing is that the entangled particles share one wave function. So quantum theory implies a 'shared register' which does not depend on time or distance separation and so is non-local.

 

[DrChinese]

OK. The essential thing is that the entangled particles share one wave function. So quantum theory implies a 'shared register' which does not depend on time or distance separation and so is non-local.

However, as I keep mentioning: the angle of the first measurement (say on A) is an INPUT to the equation that yields a value for the other (B). The measurement context is critical.

 

[DrChinese]

The code is free to use, there is nothing special about it.

What's special is that you have not repaired it yet, and still refer to it as something for discussion. Alice=0, Bob=120 yields around .75 on your model, the correct is -.50 correlation (25% match rate).

 

[Mentz114]

However, as I keep mentioning: the angle of the first measurement (say on A) is an INPUT to the equation that yields a value for the other (B). The measurement context is critical.

That is true and implied by the equations, I think. But knowing which came first seems to break something in my probability model.

 

[Boing3000]

Assuming you are making proper correlation be Matches - Non-matches: the results will vary from 1 to -1 as theta changes. The correlation is 0 at 45 degrees, 1 at 0 degrees, -1 at 90 degrees. At 60 degrees, it should yield -.5 (.25-.75).

OK, that's again different from what you were asking at post #31. Just for you I have added both. Correlation A is what you require now. correlation B is what you required at post #31

BTW, did you ever fix your simulation?

That's so kindly asked for a simulation that don't need any fixing. Peter knows it, he can read java-script, and the program is trivial.

The simulation is NOT build around any "special" input value, your type of correlation is meaningless globally. Globally what is interesting is that QM (3/4) beats Classical probability (2/3), you have made an entire site about it David.

 

[Boing3000]

If those posts made sense we would not still be having this discussion.

A discussion happens only when there are two people that are willing to listen.

Do you mean the EPR setup with local hidden variables, as described in Bell's paper? (Apparently you do--see below.)

There are 3 unambiguous word forming a sentence in post #48 "It does both.". No matter how mny time I have write "non-local", I am countered with a "local", which can mean "you don' read my post" or "you are trolling me"

But I am quite sure it is non-nonsensical to have an algorithm that can reproduce both classical (the "wrong" one) and QM (the "good" one), even though it is a click away.

I thought you were claiming that your algorithm reproduced the correct QM predictions.

I thought it too. But apparently that simple claim is very complicated to understand.

There is no "hidden polarization angle" in the correct QM model.

Bell's proof is not part of the QM formalism. It is a logical proof that can apply to QM statistics. Nobody is arguing the QM model.
There is a "hidden variable" in Bell's proof. In the simulation that variable is an angle.

This V is a local hidden variable, in Bell's terminology, and it means your algorithm (if it is correct in all other respects) will produce results that satisfy the Bell inequalities, not results that match the correct QM predictions.

And yet, you have seen the code, and it works both as a classical simulator and a QM simulator.

I don't see the point of trying to make sense of the rest of your description since the above shows that you already have the most important point wrong.

It is thus clear that you don't bother to get what I say correctly, nor what can be said generally about the EPR and Bell's proof, nor how it can be very simply explained in term of simple logic object, nor what non-locality mean in a non-philosophical/spooky kind of way.

It is kind of ironic, given that I got the motivation after reading DrChinese site.

 

[kurt101]

No, it doesn't. As I said in my previous post, it give a probability of $\left( b_1 + b_2 + b_3 \right)^2$. But since these are complex numbers, and the probability is a real number, you actually need to take the squared modulus, i.e., the probability is actually $\vert \left( b_1 + b_2 + b_3 \right) \vert^2$. Or, to write it another way: $\left( b_1 + b_2 + b_3 \right) \left( b_1 + b_2 + b_3\right)^*$, where the asterisk denotes the complex conjugate. None of these things are the same as what you wrote; none of them are the same as just multiplying out the two factors of $\left( b_1 + b_2 + b_3 \right)$. The only correct way to describe the process in words is that you add together all of the amplitudes for the different ways a particular outcome can happen, and then take the squared modulus of the result.

I left out the complex conjugate because it did not seem important to the point I was making. So if you include complex numbers and the complex conjugate operation then you have:

For outcome B there are 3 ways that it can happen. This gives a probability of b₁*b₁ + b₁*b₂ + b₁*b₃ + b₂*b₁ + b₂*b₂ + b₂*b₃ + b₃*b₁ + b₃*b₂ + b₃*₃.

You are multiplying all of the ways the path b₁ can interfere with plus all of the ways path b₂ can interfere with plus all of the ways path b₃ can interfere with. The only difference between the complex and the non-complex case seems to be that in the complex case the other path being interfered has an opposite rotation to it.

And with the scenario involving complex numbers you are still left with terms that have 2 paths. So assuming this is the correct math, why wouldn't you take this to mean that for any given instance only 2 paths can interfere at a time to give you a definite state.

Also to be clear, by instance I mean a single measurement.

 

[PeterDonis]

There are 3 unambiguous word forming a sentence in post #48 "It does both.".

Does both wrong, apparently. See below.

Bell's proof is not part of the QM formalism. It is a logical proof that can apply to QM statistics

No, it is a logical proof that shows that no local hidden variable model can produce the same statistics as QM. QM statistics violate Bell's inequalities.

it works both as a classical simulator and a QM simulator.

Apparently you haven't read the posts by myself and @DrChinese telling you that your "working" simulator is giving obviously wrong answers.

You are now thread banned, since you continue to make incorrect assertions and you refuse to listen to people trying to correct you.

 

[PeterDonis]

with the scenario involving complex numbers you are still left with terms that have 2 paths.

Because you are taking the squared modulus of a sum, which means you can never have terms with more than two factors.

why wouldn't you take this to mean that for any given instance only 2 paths can interfere at a time to give you a definite state.

Because that's not what taking the squared modulus of the sum means. "Interference of different ways something can happen" is what the sum of amplitudes itself means. "Interference" means adding amplitudes for all of the different ways an outcome can happen, to get a total amplitude for that outcome.

Taking the squared modulus of an amplitude--whether it's an amplitude obtained by adding a bunch of other ones, or just one amplitude corresponding to only one way that a particular outcome can happen--means "calculating the probability of an outcome". That's all it means.

 

[PeterDonis]

why wouldn't you take this to mean that for any given instance only 2 paths can interfere at a time to give you a definite state.

Another indication of why this must be wrong: the terms in the squared modulus of the sum include, for example, $b_1^* b_1$. By your logic this would mean "path" $b_1$ is interfering with itself. But that's not what "interference" means; a single way an outcome can happen can't "interfere" with itself.

Again, the resolution of all this is that "interference" means taking the sum of the amplitudes, not taking the squared modulus of the sum.

 

[DrChinese]

That's so kindly asked for a simulation that don't need any fixing. Peter knows it, he can read java-script, and the program is trivial.

As a software professional, I assumed you would fix the program immediately. I was surprised when you didn't. But it works nicely now. I think our point of departure is around your statement: "There is a "hidden variable" in Bell's proof. In the simulation that variable is an angle."

a) Bell assumes there is a function that can replicate the QM prediction arbitrarily closely. It does not specifically require a hidden variable, but it could - no particular objection to that in an algorithm either.

b) You call the hidden variable an angle. There is no angle that can serve to give us the QM statistics unless it is one of the measurement angles A or B. Which is exactly what you do. If A is measured first: A's measurement angle is copied to B's setting. That's what you do in your code, and that's how it should be done.

// this is kind of the crux of the matter,
// even for a single photon, to keep 100% probability to still have the same polarization at the same angle later on, we have to change its polarization

if (isPolarized) {
photon.polarization.angle = detectorAngle; // not so incidentally, if polarization is **shared** by some other photon, it will then be 100% correlated too
}
else {
photon.polarization.angle = detectorAngle + (Math.PI/2); // 90 degree will force 100% non-polarized
}

c) So all is good. Your code is essentially transmitting the value of the measurement angle on A so that B is polarized identically to A (that being prior to the measurement of B). A good non-local influence from first measured to second measured. Which as you say in your comments, doesn't matter which comes first.

Overall, I like the way you laid out your code and the straightforward interface.

 

[PeterDonis]

Bell assumes there is a function that can replicate the QM prediction arbitrarily closely.

As a clarification: Bell assumes that there is such a function, but then proceeds to prove that, if there is such a function, it cannot have the "locality" property he defines (because no function that has that property can replicate the QM predictions).

 

[PeterDonis]

You call the hidden variable an angle. There is no angle that can serve to give us the QM statistics unless it is one of the measurement angles A or B. Which is exactly what you do. If A is measured first: A's measurement angle is copied to B's setting. That's what you do in your code, and that's how it should be done.

And, as you note, such an algorithm explicitly encodes a non-local influence from A to B (assuming A is measured first). But Bell's "hidden variable" was explicitly defined as something whose value was already determined at an event that is in the past light cone of both measurement events.

 

[Lish Lash]

Bohmian Mechanics has faster-than-light signals, but for us to never see them or use them requires our ignorance of the particles' positions to mask the signals precisely.

This is a misrepresentation of Bohmian Mechanics. To claim that the Bohmian pilot wave posseses a "faster than light" velocity is to imply that it propagates through the medium of 4D spacetime. If that were the case, it would become a local phenomenon subject to relativity, in contradiction to the non-local nature of Bohmian Mechanics. The pilot wave is instead manifest in complex-valued configuration space, the non-local domain where the quantum wave function is defined. This is consistent with the pilot wave's non-relativistic simultaneous guidance of all particles with which it is entangled.

The issue is whether a non-local influence is occurring. Clearly, that is a viable possibility per Bell. And, for example, Bohmian Mechanics postulates a manner in which that can occur. However, there is mutual influence between A and B in that model.

This is not how Bohmian Mechanics describes correlation of entangled particles. In Bohmian Mechanics, there is no "mutual influence" between entangled particles - ALL guidance propagates unidirectionally (non-locally) from the pilot wave to the entangled particles. The particles exert no "influence" (i.e. transmission of information) back to either the pilot wave or each other. The pilot wave simply evolves in configuration space in accordance with the quantum wave function.

 

[DarMM]

This is a misrepresentation of Bohmian Mechanics. To claim that the Bohmian pilot wave posseses a "faster than light" velocity is to imply that it propagates through the medium of 4D spacetime. If that were the case, it would become a local phenomenon subject to relativity, in contradiction to the non-local nature of Bohmian Mechanics. The pilot wave is instead manifest in complex-valued configuration space, the non-local domain where the quantum wave function is defined. This is consistent with the pilot wave's non-relativistic simultaneous guidance of all particles with which it is entangled.

Out of quantum equilibrium there is superluminal signalling right? Alteration of Bob's statistics by Alice's experiments (usually called signals/signalling) even when Bob is outside Alice's lightcone. I'm not talking about a wave moving in 4D space, just signalling faster than light could achieve.

 

[Lish Lash]

Out of quantum equilibrium there is superluminal signalling right? Alteration of Bob's statistics by Alice's experiments (usually called signals/signalling) even when Bob is outside Alice's lightcone. I'm not talking about a wave moving in 4D space, just signalling faster than light could achieve.

Once again, you are postulating the physical 4D spacetime manifestation of a "superluminal signal" that propagates at a faster-than-light velocity to convey information between mutually entangled particles. No such signal exists in Bohmian Mechanics. The Bohmian pilot wave manifests in complex-valued configuration space, a domain where the relativistic concept of "faster-than-light" is meaningless. This is the essence of the pilot wave's non-locality, which impels it to act simultaneously (rather than locally) in guidance of all particles with which it is entangled.

 

[DarMM]

Once again, you are postulating the physical 4D spacetime manifestation of a "superluminal signal" that propagates at a faster-than-light velocity to convey information between mutually entangled particles. No such signal exists in Bohmian Mechanics. The Bohmian pilot wave manifests in complex-valued configuration space, a domain where the relativistic concept of "faster-than-light" is meaningless. This is the essence of the pilot wave's non-locality, which impels it to act simultaneously (rather than locally) in guidance of all particles with which it is entangled.

Yes, I get the basic ontology of Bohmian Mechanics, but this does constitute superluminal signalling as per the standard definition of those terms. I'm not assuming the superluminal signal is physically propagating like a wave or something in 4D spacetime. Signalling in the sense of altering Bob's statistics in a way that can convey information (when out of quantum equilibrium) and doing so before light would be capable of doing so.

 

[Lish Lash]

I'm not assuming the superluminal signal is physically propagating like a wave or something in 4D spacetime. Signalling in the sense of altering Bob's statistics in a way that can convey information...

I have the impression you're envisioning this "superliminal signal" as something akin to the way a shadow projected by a laser situated on Earth can appear to dart across the surface of the moon at a faster-than-light velocity. Here's an entertaining examination of this phenomenon:



As explained in the link, the phenomenon is real, but no information is transmitted at FTL speeds from (4D spacetime) "point A to point B". That is likewise the case with mutually entangled particles in Bohmian Mechanics. Regardless of how it may appear to occur in our 4D spacetime measurements, no information is conveyed between entangled particles (at any 4D spacetime velocity whatsoever). All such correlations are produced by the non-local guidance of the pilot wave, acting simultaneously on all particles with which it is entangled.

 

[PeterDonis]

All such correlations are produced by the non-local guidance of the pilot wave, acting simultaneously on all particles with which it is entangled.

The nonlocality in Bohmian Mechanics is in the pilot wave; it "knows" instantaneously what is happening at spacelike separated locations, and guides the particles appropriately to produce the correlations. The "guiding" of the particles by the pilot wave is indeed local; each particle is guided by the wave at its location.

 

[DarMM]

I have the impression you're envisioning this "superliminal signal" as something akin to the way a shadow projected by a laser situated on Earth can appear to dart across the surface of the moon at a faster-than-light velocity.

I'm not picturing it that way, nor am I talking about how it appears or moves in 4D spacetime. I'm talking about signalling in the standard sense used in quantum foundations.

As explained in the link, the phenomenon is real, but no information is transmitted at FTL speeds from (4D spacetime) "point A to point B". That is likewise the case with mutually entangled particles in Bohmian Mechanics. Regardless of how it may appear to occur in our 4D spacetime measurements, no information is conveyed between entangled particles (at any 4D spacetime velocity whatsoever). All such correlations are produced by the non-local guidance of the pilot wave, acting simultaneously on all particles with which it is entangled.

This is true, when in quantum equilibrium. Out of equilibrium information can be transferred.

 

[Lish Lash]

This is true, when in quantum equilibrium. Out of equilibrium information can be transferred.

The Quantum Equilibrium Hypothesis is a postulate specific to Bohmian Mechanics - it is what ensures that BM maintains consistency with the Born Rule (and consequently, reproduces all predications of Quantum Mechanics). I'm not sure whether you're referring to "out of equilibrium information" or instead claiming that "Out of equilibrium, information can be transferred." In either case, such conditions lie outside the domain of Bohmian Mechanics.

 

[DarMM]

The Quantum Equilibrium Hypothesis is a postulate specific to Bohmian Mechanics - it is what ensures that BM maintains consistency with the Borne Rule (and consequently, reproduces all predications of Quantum Mechanics). I'm not sure whether you're referring to "out of equilibrium information" or instead claiming that "Out of equilibrium, information can be transferred." In either case, such conditions lie outside the domain of Bohmian Mechanics.

The latter, "Out of equilibrium, information can be transferred"

From my readings I didn't think Bohmian Mechanics had to assume quantum equilibrium, as a few people have worked on showing it arises dynamically and many still call the theory without it Bohmian Mechanics in their papers.

If this is wrong, what is the more general theory without the assumption called? (Genuine question)

 

[Lish Lash]

I didn't think Bohmian Mechanics had to assume quantum equilibrium, as a few people have worked on showing it arises dynamically and many still call the theory without it Bohmian Mechanics in their papers.

If this is wrong, what is the more general theory without the assumption called? (Genuine question)

Good question, my impression is that relaxing the Born Rule takes Bohmian Mechanics into Multiple Worlds terrritory. However, I can't claim to speak authoritatively on the relation of MWI to the Born Rule.

 

[DarMM]

Good question, my impression is that relaxing the Born Rule takes Bohmian Mechanics into Multiple Worlds terrritory. However, I can't claim to speak authoritatively on the relation of MWI to the Born Rule.

I naively don't think it would. Choosing a different initial epistemic restriction asides from the Quantum Equilibrium can't change the underlying ontology. Or so I would think.

 

[DrChinese]

Regardless of how it may appear to occur in our 4D spacetime measurements, no information is conveyed between entangled particles (at any 4D spacetime velocity whatsoever). All such correlations are produced by the non-local guidance of the pilot wave, acting simultaneously on all particles with which it is entangled.

Presumably, that number of particles is 2. After all, there is monogamy of entanglement in these cases.

Which is interesting, because I don't think the pilot wave itself can be "separated" into a component which applies to the 2 entangled particles, and another component that applies to everything else in the universe. And yet, experimentally it acts that way. When Alice-1 is measured, entangled partner Bob-1 - and only Bob-1 - is affected.

Else the rest of the universe is affected in a way that (I guess) must cancel to a net zero. Which doesn't make sense if there are other entangled pairs hanging around (Alice-2 and Bob-2) since we can't let them be affected by Alice-1 and Bob-1.

 

[bhobba]

Good question, my impression is that relaxing the Born Rule takes Bohmian Mechanics into Multiple Worlds terrritory. However, I can't claim to speak authoritatively on the relation of MWI to the Born Rule.

All interpretations of QM have the so called Born Rule (although it has be pointed out to me historically Born meant something slightly different) which I write as the expectation of the outcome of observing a system with an operator O, E(O) is Trace(OS), where S is a positive operator of unit trace by definition called the state of a system. Since this is a B level threads do not worry about exactly what this means - just know its something every interpretation has and is what on this forum (and in all textbooks I am aware of) we call the Born Rule. For pure states it becomes (again do not worry if you have not seen it before) the way its usually written, and found in more elementary texts, E(O) = <S|O|S>. But these are just technicalities.

Now believe it or not we can actually derive the Born Rule from the other main rule of QM - namely given any observation we can find a Hermiton Operator in some complex vector space (called a Hilbert Space) such that its Eigenvalues are the possible outcomes of those observation. The Born Rule follows from this. In fact as QM - A Modern Approach by Ballentine shows all of QM can basically be derived from just these two main 'axioms' - this is done by what's called Gleason's Theorem:
https://en.wikipedia.org/wiki/Gleason's_theorem

Just as an aside Gelason is an unsung hero of modern math - see attached file.

The only out is what is called contextuality:
https://en.wikipedia.org/wiki/Quantum_contextuality

But since the Born Rule has very strong experimental support, in any interpretation with contextuality it must be true as well - but not provably true like in non-contextual interpretations.

There is some debate on if MW is non-contextual or not, and we have discussed it on this forum a few times, some like me think it is non-contextual, and others are not so sure. The experts even do not agree - Wallace for example in his book the Emergent Multiverse thinks in non-contextual (as do I):
https://www.amazon.com/dp/0198707541/?tag=pfamazon01-20

But its not universally accepted.

Thanks
Bill

 

[DarMM]

Just a small comment on Gleason's theorem and Many Worlds(and thanks bhobba for the reminder that this is B level).

In Quantum Mechanics, unlike Classical Mechanics, the observables like position and momentum don't commute, i.e. if $p$ is momentum and $q$ is position, then $pq \ne qp$. What Gleason showed is that if you want to assign probabilities (in order to estimate the chances of getting various results) to observables that behave like this then you basically have to use the mathematics of Quantum Mechanics, e.g. Hilbert Spaces. Now there are a few ways of assigning probabilities to observables like this, but Quantum Mechanics is the only way that is "non-contextual". Non-contextual means that if I measure $A$ then the chance that $A = 1$, let's say, doesn't depend on what else my device measures along with $A$, e.g. if I measure $A, B$ or $A, C$ in both cases I have the same chance of $A = 1$.

Quantum Mechanic's specific way of assigning probabilities is called the Born Rule. So Gleason's theorem shows that the Born Rule is the only way to assign probabilities to the type of non-commuting observables one sees in microscopic experiments. The Born Rule collects all my chances of seeing observables having various values into one object called "the quantum state".

Now in Many Worlds on the other hand, the quantum state is seen as the main thing. It's not a collection of probabilities, but a physically real "substance". Hence in this case we can't just use Gleason's theorem to explain the success of the Born rule as we're not starting from the observables and finding the state as probabilities on them. Instead we're starting with the state as a physically real thing and in fact the only real thing.

There are many ways to try to derive the Born Rule in Many-Worlds. Wallace's above is the most famous, but I personally found it very confusing and was left with little understanding of why the rule held. Wallace basically says the Born rule arises because, provided the worlds separate in a particular way, it's the only way for a rational agent to predict which world they will find themselves in. There are currently three issues people have with this line of arguing:

1. Do the worlds separate in the way he requires?
2. Is his definition of rational valid? Especially given the way the world works in Many Worlds. Some people have said that if there are multiple worlds there are ways of being rational that Wallace doesn't take into account
3. Even if all this worked, does something being "the best way for agents to bet" really imply it's what you'll see in experiments.

My problem was I couldn't see the physical reason for the Born Rule (so basically 3.)

However a closely related proof by Mateus Araújo (https://arxiv.org/abs/1805.01753) is helpful if you think like myself. Here he shows the Born Rule comes about due to conservation of "world-volume". So there is, from the beginning of time, a continuum of worlds and then a fraction of them get imprinted with one result or another. So my chance to see a particular result (which is what the Born Rule is about) is basically related to how large a fraction of the worlds gets imprinted with that result. "Conserving world volume" just means no new worlds are made.

Araújo has a nice dicussion of how a Many-Worlds theory where the world actually splits and two new worlds are made has a different probability rule than the Born rule. So the Quantum Mechanical Many-Worlds is better thought of as all the worlds already being there.

The real problem with Many-Worlds at the moment is to mathematically prove that 3D semi-classical worlds like the one we experience actually arise. This has not yet been done, so the interpretation cannot be as of yet said to match experiment.

There is some debate on if MW is non-contextual or not, and we have discussed it on this forum a few times, some like me think it is non-contextual, and others are not so sure. The experts even do not agree - Wallace for example in his book the Emergent Multiverse thinks in non-contextual (as do I):
https://www.amazon.com/dp/0198707541/?tag=pfamazon01-20

I would be like yourself and would have thought in noncontextual. I must read the discussions. More so I'm not sure if it really is local. See Travis Norsen's book "Foundations of Quantum Mechanics: An Exploration of the Physical Meaning of Quantum Theory" for a discussion of this. In essence in something like the Bell state:
$$\frac{1}{2}\left(|00\rangle + |11\rangle\right)$$
Since Alice will split into a 0 and 1 world, as will Bob, Alice's "0 result" has to know nonlocally it belongs to the same world as Bob's "0 result". Naively you'd think there would be four worlds.

Many Worlds theories supplemented by extra variables beyond the wavefunction don't have this problem as they attach a "charge" to each outcome and only copies of Alice and Bob with the same "charge" can interact. The Parallel lives interpretation is an example. (https://arxiv.org/abs/1709.10016)

 

[DarMM]

Of course the real derivation is that if Many Worlds is true then there is a reality where Max Born rose to power and established an autocratic state over the whole Earth known as "The Born Rule".

 

[bhobba]

The real problem with Many-Worlds at the moment is to mathematically prove that 3D semi-classical worlds like the one we experience actually arise. This has not yet been done, so the interpretation cannot be as of yet said to match experiment.

Some progress has been made in decoherent histories which some like Gell-Mann think is simply MW without the MW:
http://web.physics.ucsb.edu/~quniverse/papers/cop-ext2.pdf

But issues still remain. Some, including a number of very knowledgeable mentors on this forum, think until they are resolved QM is incomplete (ie Einstein was correct - he was anyway because we still have no complete quantum theory of gravity - but most take it to be something a bit different). Others like me think it's basically crossing your t's and dotting your i's. Really it's semantics - either way we are not there yet. Its interesting actually - everyone thought Einstein lost to his good friend Bohr in the Einstein Bohr debates - but here we are today and would say Einstein's intuition did not lead him astray - even here. What the future brings will indeed be interesting - however I may not be around to see what finally emerges. Another interesting thing is just before Einsteins death Bohr came to visit and Einstein would not see him - why - maybe he was too weary of the QM debates - or being so close to death didn't want Bohr to remember hijm like that - who knows - however there is little doubt during their prime they were very good friends - each admiring the other greatly. Bohr never ceased to believe GR was the greatest achievement of the human intellect ever.

Thanks
Bill

 

[vanhees71]

Well, I think nowadays it's pretty obvious that Einstein understood QT way better than Bohr, who was more a philosopher than a physicist after his young years, where he discovered "old quantum mechanics", i.e., did physics in the sense that it described something observable. He also qualitatively got the physical explanation for the chemistry of the periodic table right (to be a bit generous). As we understand QT today, his role in "interpretation" was more towards confusing the subject with quite imprecisely defined philosophical notions like "wave-particle duality" and, even worse, "complementarity". He is topped in obscurity only by Heisenberg ;-))). Of course, Einstein was wrong in thinking that the issue can be "repaired" by the hidden-variable argument, at least when you insist on locality of interactions (as realized in relativistic QFT) and separability, which has been clearly shown by Bell's work on his famous inequality, which brought the philosophical gibberish of EPR and Bohr's response to a clear physical statement which was testable in the lab (as was done by Aspect et al in the 1980ies and later on up to today at ever higher accuracy and with ever more fancy setups to exclude any, if not all!, "loopholes").

Nevertheless, I think that the minimal interpretation is the only thing we need to use the formalism to describe what's seen in Nature. In this sense QT is "complete" as a physical theory, but this completeness is only "for all practical purposes" (FAPP), and as Bell stated, that's not very satisfactory. Indeed, it is very well known that QT as we know it today is for sure incomplete, since there's no quantum description of gravity, and maybe one day some genius finds a solution to this puzzle, which overcomes maybe also the problems with ontology of QT.

For non-relativistic QM, I recently got convinced, that the Bohmian Mechanics, as interpreted and presented by Dürr et al, is an example for such a solution. Unfortunately it seems to be even "less complete" than QT, which also includes a very well working relativistic version in terms of local microcausal relativistic QFT, upon which the all too successful Standard Model of elementary-particle physics is based. So for QT as a whole we still don't have anything better than the FAPP interpretation called "minimal statistical interpretation".

 

[bhobba]

Well, I think nowadays it's pretty obvious that Einstein understood QT way better than Bohr, who was more a philosopher than a physicist after his young years, where he discovered "old quantum mechanics", i.e., did physics in the sense that it described something observable. He also qualitatively got the physical explanation for the chemistry of the periodic table right (to be a bit generous). As we understand QT today, his role in "interpretation" was more towards confusing the subject with quite imprecisely defined philosophical notions like "wave-particle duality" and, even worse, "complementarity". He is topped in obscurity only by Heisenberg ;-))).

First interesting thing about Heisenberg. Bohr's brother, Harald, who was actually a bit more famous in Denmark because he was a bit better soccer player, was a very good mathematician and friend of Hardy. Heisenberg was visiting and Hardy thought he would play a trick on Heisenberg. He said now you are becoming more involved with advanced physics we should develop your math a bit more. He gave him a problem that was then reasonably famous, and just recently solved. To Hardy's astonishment Heisenberg solved it - Hardy thought he had picked the wrong area - he should do math and come to work with him and Littlewood (too young to work with Ramanujan which would have been interesting). Of course he didn't take him up on the offer, but if he did he would have probably ended up working also with Dirac. So yes Heisenberg sometime spoke philosophical 'gibberish', but extremely talented in math and physics he certainly was. Personally I think pretty much everyone in the early days of QM got it wrong except Dirac, and we now know Einstein actually got it right as well - although it took him a while to reach his final view that QM was correct - but incomplete. To give Bohr his due I believe his debates with Einstein helped him in forming his final view even though Bohr was, to be kind, 'subtle' and with his mumble not a good communicator - but neither was Dirac for a different reason.

And yes Bell understood it as well, even though he was at least at the start into BM. To independently basically come up with a cut down version of what was known as a very difficult theorem to prove (Gleason's Theorem - from which Kochen-Speker followed as a simple corollary. Bell independently proved Kochen-Speker), taking one of the best mathematicians at the time, Gleason, to do it. I simply do not know how to categorize someone like that. Same with Feynman and Wilson - they were Putman Fellows - Feynman put on the team at the last minute, and Wilson twice even though he was accepted into Harvard early - 16 I think and was a Putman Fellow at 18 and 19 - but don't hold me to it. Interesting story - when Wilson got his first one he was given a celebration by the math department. He noticed one thing immediately - his father was a professor of Chemistry at Harvard so knew a number other professors. The math professors, while all very good mathematicians, were quite mad

Thanks
Bill

 

[vanhees71]

Sure, there's no question that Heisenberg was an ingenious theoretical physicist. After all he was the first to discover "modern QM" in 1925 in terms of matrix mechanics. The only thing I criticize is part of his "soft skills". In the beginning he fought Schrödinger's wave mechanics to defend his matrix mechanis as the only true quantum mechanics. Of course, this is nonsense given the fact that Schrödinger himself proved very early that both formalisms are equivalent representations.

Indeed of all "founding fathers" of QT, Dirac is the most clear of all, giving the bare formalism without too much interpretational gibberish, but also Schrödinger's paper are marvels in science-writing style, although he didn't have the correct probabilistic interpretation yet, and he was always critical against it until the end of his life. Dirac's textbook is still among the best ever written, but also his papers are not less clear and can be read easily by undergraduate students beginning to learn QT. That I can't say about Heisenberg's most famous Helgoland paper. I never got to understand it completely from scratch, i.e., not using the knowledge about QT I got from other sources. One also shouldn't underestimate the importance of Born, Jordan, and also Pauli, for the success of Heisenberg's matrix mechanics. The two papers by Born and Jordan as well as Born, Jordan, and Heisenberg ("Dreimännerarbeit") are quite well readable (containing even a part on field quantization by Jordan already then, but this one got forgotten, because people found this "too much", i.e., they though one should treat electromagnetism still via classical Maxwell theory, and it had to be reinvented by Dirac some time later to unerstand spontaneous emission). Pauli's contribution was not only the official one, namely the solution of the hydrogen energy-eigenvalue problem within matrix mechanics, using the O(4) symmetry and the associated Runge-Lenz vector from classical mechanics, but also as a "regulator" of Heisenberg's ingenious but not always very clearly stated ideas.

 

[DarMM]

Having read all their papers recently my personal impression was that Bohr and Heisenberg didn't spell out what they meant by phrases like "the electron doesn't exist between measurements". When you know what they mean a good portion of their writings make more sense, but I think they should have just written a summary account of their similar Copenhagen interpretations where they spell everything out.

By "the electron doesn't exist between measurements" they meant "electron" is a conceptual object we use to describe the type of marking "something" else leaves on our equipment. With that something being impossible to describe. It's a bit like how my signature isn't the same thing as me, but if you only have cheque books and your language only speaks of ink and paper, it's the only impression of me you'll have, but the signature doesn't exist between "cheque signing" events/measurements.
The electron is just this ineffable thing's signature on systems we can describe.

You can draw this out from their later papers, but unadorned and often unexplained it sounds like they don't think an independent reality exists.

Also Bohr assumes you've read Kant, many terms are being given their Kantian meaning rather than the everyday reading. Which just makes him even more difficult to understand.