Ballentine's Ensemble Interpretation Of QM

[wuliheron]

Yes, the original post asked for opinions, and I gave mine-- the OP question also poses a false dichotomy. So I give that same answer to your question. The difference is, the original post didn't complain about the answers it got. So why did you?
Excellent, then it appears you have formed your own metaphysical opinions. Just don't fall into the tiresome fallacy that your own views aren't philosophy, and everyone else's are! There's no particular reason you should care what I think, so let's see what Einstein thought:

Assumptions about what I meant and appeals to authority? Is this a discussion about quantum mechanics or politics? If you want to know what I think just ask and if you want my favorite authority it is Lao Tzu.

"By his clear critique Hume did not only advance philosophy in a decisive way but also- though through no fault of his- created a danger for philosophy in that, following his critique, a fateful 'fear of metaphysics' arose which has come to be a malady of contemporary empiricist philosophising; this malady is the counterpart to that earlier philosophising in the clouds, which thought it could neglect and dispense with what was given by the senses. ... It finally turns out that one can, after all, not get along without metaphysics."
I interpret Einstein's "not get along" to mean "not be capable of doing good science", because I'm sure he knew one can be a fine electrician or carpenter without any metaphysics at all. But his quote certainly speaks to the difficulties in imagining that physics and metaphysics are completely separable, any more than mathematics and metamathematics are separable. It seems this forum sees some of what Einstein is arguing for-- the ways that metaphysics can be combined into the basic understanding of physics itself. Done with care, of course-- rampant philosophizing is certainly not the goal of this section of the forum, there needs to be some connection with the meaning of the physics theories themselves. I believe that the OP can be paraphrased, "is there some usefulness to the understanding of quantum mechanics that is achievable with Ballentine's interpretation?", and when paraphrased like that, it is more clear why it can have a connection to the theory of quantum physics.

Einstein was also notorious rejecting quantum mechanics and wasting the last ten years of his life trying to reconcile it with Relativity. That's not exactly what I would call an objective source or even a particularly good authority on the subject.

 

[jfy4]

In what context and is it useful? The theory of phlogiston is clearly defined and has a clear context and is useful in some cases, but I believe many would now call it metaphysical mumbo jumbo even if it is more parsimonious then thermodynamics. Just because a theory can make sense and be occasionally useful does not mean it is not metaphysical mumbo jumbo.

Then it looks like you can answer all your own questions! just apply what you have said above to different QM interpretations and you'll find the sturdy ones satisfy your criteria in many ways. Some of which have been discussed earlier in this thread... Take Ballentine's for example, this thread is about how for a great many situations the ensemble interpretation fits in nicely with experiments preformed and satisfies a number of discrepancies physicists have with the oddities of QM. Not all! but many. Its sturdy, so let's talk about it... if you want to join this discussion support this "Just because a theory can make sense and be occasionally useful does not mean it is not metaphysical mumbo jumbo" claim by defining terms like "occasionally", or giving definitions that define a "good" theory and how Ballentine's fails to meet those definitions.

 

[Ken G]

Is this a discussion about quantum mechanics or politics?

Please don't bring politics into this, I'm sure no one is interested.

Einstein was also notorious rejecting quantum mechanics and wasting the last ten years of his life trying to reconcile it with Relativity. That's not exactly what I would call an objective source or even a particularly good authority on the subject.

Irrelevant point. Your argument hinges on Einstein not knowing anything about the role of metaphysics in physics because he failed to find a theory that no one else has found in 100 years either. Not a particularly logical position.

 

[bhobba]

Einstein was also notorious rejecting quantum mechanics and wasting the last ten years of his life trying to reconcile it with Relativity. That's not exactly what I would call an objective source or even a particularly good authority on the subject.

Where did you get the idea he rejected it? He didn't think it was wrong - merely incomplete. He tried to derive it from a more fundamental theory not reconcile it with relativity - it and QFT were already reconciled with that.

Thanks
Bill

 

[wuliheron]

Then it looks like you can answer all your own questions! just apply what you have said above to different QM interpretations and you'll find the sturdy ones satisfy your criteria in many ways. Some of which have been discussed earlier in this thread... Take Ballentine's for example, this thread is about how for a great many situations the ensemble interpretation fits in nicely with experiments preformed and satisfies a number of discrepancies physicists have with the oddities of QM. Not all! but many. Its sturdy, so let's talk about it... if you want to join this discussion support this "Just because a theory can make sense and be occasionally useful does not mean it is not metaphysical mumbo jumbo" claim by defining terms like "occasionally", or giving definitions that define a "good" theory and how Ballentine's fails to meet those definitions.

What is important for a scientific theory is that it prove useful. Santa Claus and the tooth fairy might be occasionally useful, but certainly are not good theories much less scientific. No matter how persuasive an interpretation might be, if it cannot prove itself at least significantly more useful then no interpretation whatsoever then it can certainly be described as metaphysical mumbo jumbo. Being useful for the odd task is simply not enough anymore then it is for Santa and the tooth fairy.

 

[wuliheron]

Please don't bring politics into this, I'm sure no one is interested.
Irrelevant point. Your argument hinges on Einstein not knowing anything about the role of metaphysics in physics because he failed to find a theory that no one else has found in 100 years either. Not a particularly logical position.

That no one else has found any metaphysical solution after a hundred years supports my position. He insisted one must exist despite the evidence to the contrary and history has proven him wrong thus far. That's called "empirical evidence" if you were wondering. My family is from Missouri, the "show me" state, and you'll just have to prove there is any underlying metaphysics to quantum mechanics before I'll assume such a thing exists. As far as I'm concerned metaphysics is nothing more then a useful analytic tool and not to be confused with the territory anymore then a road map.

 

[wuliheron]

Where did you get the idea he rejected it? He didn't think it was wrong - merely incomplete. He tried to derive it from a more fundamental theory not reconcile it with relativity - it and QFT were already reconciled with that.

Split semantic hairs all you want. If you prefer, he rejected it as "incomplete".

 

[bhobba]

Split semantic hairs all you want. If you prefer, he rejected it as "incomplete".

Splitting semantics? Rejecting QM would be like rejecting Thermodynamics. Thinking QM is correct but incomplete, being a limiting case of another theory would be like thinking Thermodynamics is correct but incomplete and a limiting case of another theory - which it is. Einstein accepted the ensemble interpretation of QM - in fact he was a major supporter of it. He just thought, just like the ensembles of statistical physics, they were determined by a deeper theory. I am inclined to agree with him.

Thanks
Bill

 

[wuliheron]

Splitting semantics? Rejecting QM would be like rejecting Thermodynamics. Thinking QM is correct but incomplete, being a limiting case of another theory would be like thinking Thermodynamics is correct but incomplete and a limiting case of another theory - which it is. Einstein accepted the ensemble interpretation of QM - in fact he was a major supporter of it. He just thought, just like the ensembles of statistical physics, they were determined by a deeper theory. I am inclined to agree with him.

hairsplitting [ˈhɛəˌsplɪtɪŋ]
n
the making of petty distinctions
adj
occupied with or based on petty distinctions
hairsplitter

I don't need lessons in the English language and I don't need lessons in Einstein. My advice would be to learn to ask questions, stop trying to read between the lines of everything people write, and stop trying to lecture people. Meaning can be implied as well as explicit and only a computer is incapable of inferring meaning from context.

 

[Fredrik]

I also strongly disagree with the claim that Einstein rejected QM. It's not a matter of semantics, it's just wrong.

 

[bhobba]

I don't need lessons in the English language and I don't need lessons in Einstein. My advice would be to learn to ask questions, stop trying to read between the lines of everything people write, and stop trying to lecture people. Meaning can be implied as well as explicit and only a computer is incapable of inferring meaning from context.

OK I will ask a question. What in your view is the standard QM theory?

Thanks
Bill

 

[Ken G]

That no one else has found any metaphysical solution after a hundred years supports my position.

No it doesn't. First of all, Einstein was not looking for a "metaphysical solution," he was looking for a new theory, using metaphysics as his guide, just as he had done with relativity. I doubt the success of relativity should be viewed as a bad reason to try a similar approach again, yet apparently that is your only argument. Secondly, the fact that he did not succeed is not a logically valid argument that it was some kind of fools errand. Many physicists have failed at attempts to find something that was later found by someone else, sometimes by using the groundwork they laid even if unsuccessful on its own. Your argument is worse than just opinion- it is demonstrably bad logic.

The ultimate irony is how badly you have sidetracked this thread, apparently on the grounds that this thread is some kind of sidetrack. Threads like this work just fine in a section on quantum physics as long as they are only read and posted to by people who understand how that works.

 

[qsa]

in some earlier thread a reqular PF contributer posted a paper of his , which is sort of a new interpretation but looks very close to ensemble one.

here is what he claims in his paper. What do you think?

http://arxiv.org/PS_cache/quant-ph/p.../0509044v1.pdf

It seems that there may exist a somewhat different
interpretation of real charged fields: the one-particle Ψ-
function may describe a large (infinite?) number of particles moving along the above-mentioned trajectories. The
total charge, calculated as an integral of charge density
over the infinite 3-volume, may still equal the charge
of electron. So the individual particles may be either
electrons or positrons, but all together they may be regarded as one electron

 

[Ken G]

That link is coming up dead. But there are certainly many applications where one might imagine the electron charge is effectively spread out over its wave function when calculating an expectation value-- I'm not sure how that view is advanced by including more particles than just the one, there's not much difference between an expectation value and an ensemble value. It sounds like the particles would have to be virtual ones, so that gets into the usual issues with whether or not it is a good idea to take virtual particles literally in the interpretation.

 

[qsa]

That link is coming up dead. But there are certainly many applications where one might imagine the electron charge is effectively spread out over its wave function when calculating an expectation value-- I'm not sure how that view is advanced by including more particles than just the one, there's not much difference between an expectation value and an ensemble value. It sounds like the particles would have to be virtual ones, so that gets into the usual issues with whether or not it is a good idea to take virtual particles literally in the interpretation.

here is the right link,SEE PAGE 3



http://arxiv.org/PS_cache/quant-ph/pdf/0509/0509044v1.pdf

 

[bhobba]

here is the right link,SEE PAGE 3

Had a quick squiz. My first reaction is in suggesting an interpretation along the lines of Bohm you run into experimental problems. See:

http://arxiv.org/PS_cache/quant-ph/pdf/0206/0206196v1.pdf

Thanks
Bill

 

[juanrga]

Hi Juaringa

Yes it does help thanks.

I still think it is by far the best interpretation though and really helps in developing the theory.

Interesting new paper by Smolin where he thinks the Ensembles could actually be real:
http://arxiv.org/PS_cache/arxiv/pdf/1104/1104.2822v1.pdf

Thanks
Bill

After explaining why the ensemble 'interpretation' is not equivalent to QM {*}, I would add that I wonder how people as Smolin want to substitute, what them perceive as the weirdness in QM, by really weird «alternative formulations» that are, in essence, just another misconception of QM, to be added to the notorious misconceptions by Einstein, Everett, DeWitt, Deutsch, Dirac {**}, Hartle, Tegmark...

{*} QM is what one finds in standard textbooks as Cohen-Tannoudji.

{**} It is fair to say that in latter years (70s), Dirac recognized some of his mistakes and claimed for abandoning his previous work in R-QM and QED, asking for the search of a new relativistic quantum theory based in sound principles and consistent mathematics.

 

[Fredrik]

After explaining why the ensemble 'interpretation' is not equivalent to QM {*},
...
{*} QM is what one finds in standard textbooks as Cohen-Tannoudji.

I haven't read Cohen-Tannouji, but I doubt that it contradicts the ensemble "interpretation", which is arguably not an interpretation at all. If QM tells us how to use a state vector to calculate probabilities of possible results of experiments, then it's undeniable that the state vector can and should be thought of as a representation of the statistical properties of an ensemble of identically prepared systems. Interpretations are about what other meanings can be assigned to it, in addition to the obvious one.

Ballentine likes to point out that the assumption that a state vector represents all the properties of a single system is unjustified. That doesn't mean that what he's doing "is not equivalent to QM". QM is the set of rules that tells us how to associate probabilities with results of experiments. That assumption isn't part of those rules. So it's not a part of QM.

 

[Ken G]

I agree, I see the ensemble interpretation as the minimum interpretation of quantum mechanics, it is the interpretation you pretty much have to have to use QM at all, but you don't attribute any ontological content to the theory, you don't think there are any messages about "how the universe is", there's just how to calculate statistical outcomes for large ensembles of seemingly identically prepared systems (without even making any claims that they are truly identically prepared, just that they are prepared a certain way). Even Copenhagen allows a little ontology to creep in-- in CI you say that the wave function is useful for making a statistical prediction because it holds some statistical information about an individual system, it has something to say about what is happening for that system. The ensemble interpetation is like studying how poker hands behave without ever introducing the concept of "a card" or "shuffling". Cohen-Tannoudji is not going to refute the ensemble interpretation anywhere, but the authors might (or might not) have a little something more than that in their minds when they think about QM.

 

[bhobba]

I haven't read Cohen-Tannouji, but I doubt that it contradicts the ensemble "interpretation", which is arguably not an interpretation at all. If QM tells us how to use a state vector to calculate probabilities of possible results of experiments, then it's undeniable that the state vector can and should be thought of as a representation of the statistical properties of an ensemble of identically prepared systems. Interpretations are about what other meanings can be assigned to it, in addition to the obvious one.

I would say that as well. I have read stuff that suggests the ensemble interpretation has problems, but I have not seen a detailed explanation of any, because, as you say, basically it is not an interpretation at all. All you are really doing is giving pictorial vividness to the probabilities by ensembles. However that 'picture' does suggest possible underlying processes such as Nelson's theory and Primary State Diffusion that QM is a limiting case of. I haven't read Cohen-Tannouji but know it by reputation. Most definitely it would be a reasonable candidate as the 'standard' version of QM. But then again so would Ballentines textbook.

Ballentine likes to point out that the assumption that a state vector represents all the properties of a single system is unjustified. That doesn't mean that what he's doing "is not equivalent to QM". QM is the set of rules that tells us how to associate probabilities with results of experiments. That assumption isn't part of those rules. So it's not a part of QM.

It is only part of QM if you accept an interpretation where you believe a Quantum State has a real existence like say an electric field. Ballentine examines why that view has problems but I do not think he rules them out - nor, to the best of my knowledge, can they be ruled out by our present experimental evidence. IMHO it just seems a rather unnecessary complication.

Thanks
Bill

 

[Ken G]

I'd say the whole issue strikes to the heart of what you think an interpretation is for. Those who favor "minimal" interpretations, like the ensemble interpretation, seem to basically think that an interpretation is just something you need to apply the theory and should not be anything more-- it is almost like a "necessary evil" that comes with the theory so you can use it, but it is loaded with misconceptions and traps and should be avoided unless absolutely necessary. But those who favor more "maximal" interpretations, like MWI or deBB, tend to want the interpretation to be the "way to extract the message" from the theory-- they don't view the interpretation as a necessary evil, they view it as the point of the exercise. They might not really care about the prediction that is being made, as they are not actually using the prediction to do anything but test the theory-- it is the theory they want, and more, it is the meaning of the theory, the lesson of the theory, that they want. That can only be extracted via an interpretation.

I would place CI kind of in the middle-- it wants to find a message from QM, but the message is more like a cautionary tale about our limitations as physicists. CI users interpret QM to tell them what they get to know and what they don't get to know about the world, and the limitations they encounter caused Bohr to say things like "there is no quantum world." That stark denial of a valid ontology underlying the theory seems much closer to the ensemble interpretation-- indeed, I'd say there's not a lot of difference there, CI is just more willing to make claims about the lessons of QM.

 

[juanrga]

Effectively some people don't read basic textbooks or messages. Why bother to answer, then?

 

[Fredrik]

Effectively some people don't read basic textbooks or messages. Why bother to answer, then?

Why bother to suggest that only people who have learned QM from that specific book are allowed to tell you why you're wrong?

 

[Ken G]

Effectively some people don't read basic textbooks or messages. Why bother to answer, then?

I'm quite familiar with the Cohen-Tannoudji textbook, but don't recall it mentioning any interpretations of quantum mechanics. The parts I recall are just the mathematics of quantum mechanics, which is perfectly consistent with the ensemble interpretation. The message behind that mathematics is much harder to say, and is generally not uniquely understood.

 

[kith]

{*} QM is what one finds in standard textbooks as Cohen-Tannoudji.

As far as I remember, Cohen-Tannoudji explicitly mentions in a footnote that he uses the Copenhagen interpretation.

Independent of this: Which interpretations are feasible is decided by experiments, not by textbooks. So please provide an example where the ensemble interpretation leads to different predictions than what you consider to be standard QM and we can check the experimental evidence.

 

[Ken G]

Also, I'd like a clear statement of some fundamental difference between CI and the ensemble interpretation-- something that isn't just "tomayto-tomahto". CI is a bit happier with the concept of a "state" of a single system, but in the end it never asserts any ontology for that single system that comes from that "state"-- the "state" is just a calculational tool for statistical statements, much like the ensemble interpretation.

 

[bohm2]

Einstein accepted the ensemble interpretation of QM - in fact he was a major supporter of it. He just thought, just like the ensembles of statistical physics, they were determined by a deeper theory. I am inclined to agree with him.

I realize that this is an older thread but is it accurate to say that Einstein accepted the ensemble interpretation? I have come across this post on the Physics Stack Exchange criticizing the wiki article on the ensemble interpretation:

The Wikipedia page erroneously claims that Einstein supported the Ensemble idea. This is false, but there is a quote that makes it seem true. Einstein was referring to hidden variables here, and the reason he states it in terms of ensembles is because he believed that the wavefunction described a statistical pattern for hidden variables which is analogous to statistical mechanical distributions. These statistical distributions do not describe a single particle (at least not in a straightforward interpretation), because the particle has a hidden position deep down underneath. The averages of many position measurements require an ensemble, and these measure the wavefunction. Einstein used the term "ensemble" in the context of quantum mechanics to emphasize the probabilistic nature of the wavefunction, not the inability to describe an individual system.

Einstein also believed that the quantum mechanical description of an individual system, inasmuch as it was deterministic, was correct. It was only the probabilistic aspects of the description that required hidden variables, of course, just like classical thermodynamics. You don't need an ensemble to describe the motion of piston pushing a gas, only for the statistically random motion of individual molecules.

A true ensemble interpretation renounces the description of a physical system entirely, leaving only the description of the statistics of identical measurement. It is not what Einstein had in mind, and it is not reasonable in the majority of cases where quantum systems are in their ground state, and changing adiabatically, so that they essentially reproduce deterministic classical behavior.

What are specific arguments against the ensemble interpretation (as promoted by L. Ballentine)?
http://physics.stackexchange.com/qu...st-the-ensemble-interpretation-as-promoted-by

Moreover, I was under the impression that if one accepts the assumptions of PBR, PBR rules out Einstein's interpretation:

Can the quantum state be interpreted statistically?
http://mattleifer.info/2011/11/20/can-the-quantum-state-be-interpreted-statistically/

On the reality of the quantum state
http://arxiv.org/pdf/1111.3328v3.pdf

 

[kith]

I realize that this is an older thread but is it accurate to say that Einstein accepted the ensemble interpretation?

There are two ways to arrive at the ensemble interpretation. Einstein thought that QM was missing something and is only an effective theory. He thought QM makes statistical statements about ensembles while the true states and dynamics are elements of a more fundamental theory from which QM can be derived.

The other way is to realize that all conclusions from experiments are based on ensembles, so we shouldn't expect our theories to be about single systems in the first place.

I don't think that this makes a difference in the interpretation. It's just a different motivation why you stick to it.

Moreover, I was under the impression that if one accepts the assumptions of PBR that PBR rules out Einstein's interpretation.

Einstein's main point was that QM is not complete, not that the wavefunction is not ontic at all. I think he would have been satisfied by an interpretation which is realistic about the wavefuntion as well as about some local realistic hidden variables.

 

[Ken G]

That question relates back to what I was asking above as well. What exactly is meant by an ensemble interpretation? Should we say it is the rejection of the idea that the behavior of a single particle is a scientifically determinable question, meaning that science relates to ensembles? If so, then it is a lot like CI, because both would be inherently empiricist, i.e., both would stipulate that "what is science" means "what can we measure and then make sense of." Identical measurements on similarly prepared systems is all we'll ever be able to do in science, so if we stick to an empiricist underpinning of science, we will always end up with something that looks a lot like either the CI or the ensemble approach. Or, should we say that the ensemble interpretation goes beyond empiricism, and asserts some hidden variables that we as yet have no empirical access to? Then it ends up sounding a lot like deBroglie-Bohm. So perhaps we should say that the ensemble interpretation lives at a kind of intersection of the CI and dB-B, whereby it maintains its empiricist underpinning, but also retains an agnostic attitude about whether or not the hidden deterministic variables that apply to individual particles will ever enter the empirical realm or not. If so, Einstein might not have enjoyed that agnostic attitude about his most closely held belief-- basic realism.

 

[kith]

That question relates back to what I was asking above as well. What exactly is meant by an ensemble interpretation? Should we say it is the rejection of the idea that the behavior of a single particle is a scientifically determinable question, meaning that science relates to ensembles?

I refer to "interpretation" as the relation between the formalism and the physical world. So the ensemble interpretation is simply the assertion that QM is about ensembles of physical systems and not about individual systems. Of course it is interesting to think about possible philosophical implications but I don't consider this to be part of the interpretation.