Talk:Interpretation of quantum mechanics
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The text below was in the main article. It appears to be notes on topics that should eventually be covered.
- Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth. - Sherlock Holmes (by Sir Arthur Conan Doyle)
- (I'd like to take a hound of the baskerville approach here. Start with the obvious interpretations of quantum mechanics, show why then don't work.)
- Much of the non-intuitive nature of the their deals with its probablistic nature.
- It's not just that it's probabilistic. If that's all, there probably wouldn't be that much fuss. It's that it's not described by classical probability in the measure theoretic sense, but is some sort of noncommutative probability. Phys 20:01, 27 Nov 2003 (UTC)
- (The nature of light)
- (Why light is a wave won't work)
- (Quantum mechanics contains probablistic descriptions of particles.)
- (The double slit experiment and why that doesn't work.)
- (QM is due to local hidden variables)
- (The aspect experiment and why that doesn't work.)
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Why is a Yes or No desirable?
Why is a Yes or No desirable?
It seems to me that it does not make sense to presuppose that all "yes"es in the table is desirable. Nature is the way she is.
I think the last 2 paragraphs should be removed (or significantly changed)
Oz 04:00, 13 Sep 2003 (UTC)
What about this interpretation: Transactional Interpretation of John G. Cramer (http://www.npl.washington.edu/tiqm/home.html) and Online version of old Analog magazine article by Cramer (http://www.npl.washington.edu/AV/altvw16.html)? --Cardiffman 21:55, 29 May 2004 (UTC)
Bell's theorem, hidden variables and loopholes in the tests
The article said that a theory should have no hidden variables. Surely this is the opposite of what EPR and Bell wanted? They wanted hidden variables to convert the theory from a probabilistic to a deterministic one. The variables would be like the exact position and momentum of every molecule in a gas: not knowable in practice but assumed to exist and, under the kinetic theory, to in fact determine its properties.
I've corrected the statement about the experiments that are interpreted as supporting quantum mechanics and ruling out local hidden variable theories. Look carefully at any experimental report and you will find that the interpretation is being made subject to the assumption of "fair sampling" or something to that effect. But it has been known since about 1969 that this assumption is not in fact reasonable for Bell test experiments. If it is false (which is all to likely) then alternative hidden variable explanations can be found for the observations. The fair sampling assumption represents the main loophole in this kind of experiment. There are others. Caroline Thompson 21:08, 19 Jul 2004 (UTC)
- William Connelly seems to think that a fundamental theory should have no "hidden variables", whereas I've always tended to think of them as a "good" thing! I suppose the truth is that when explaining the Bell test results I've got used to referring to intrinsic properties of light pulses (alias "photons") such as polarisation direction as being "hidden variables", but this is only because everyone else does. It is conventional for the basic local realist model (see local hidden variable theory) to term any intrinsic property a hidden variable and proceed to integrate over the hidden variable space. However, if QM had never been invented one would not talk this way. They are just plain "variables", and William is really quite right: a fundamental theory should ideally include all relevant variables. I've compromised on this page by deleting the link to the local hidden variable theory page. The reader should get the picture from following the other links.
- Caroline Thompson 17:15, 21 Aug 2004 (UTC)
Doubt over the Copenhagen interpretation and wave-particle duality
There is currently (August 2004) some doubt over the validity of wave-particle duality and the Copenhagen interpretation due to Shahriar Afshar's 2004 contradictory result using a variation on the double-slit experiment. The results have yet to be peer-reviewed.
Actually...... no....
http://axion.physics.ubc.ca/rebel.html
Roadrunner 06:37, 22 Aug 2004 (UTC)
- I think there was some doubt but the establishment had now reassured everyone that nothing has changed. And indeed nothing has: there have always been doubts. But I'm waiting till I see Afshar's full report before trying to give my own explanation. I get the impression that New Scientist and your link (Unruh, which has nice diagrams but I've not yet read) have oversimplified things.
- So far as the wiki page is concerned, though, I agree. Afshar is probably just a flash in the pan.
- Caroline Thompson 08:46, 22 Aug 2004 (UTC)
POV on quantum mechanics as a weird or unsatisfactory theory
There is a description of quantum mechanics given by this article as expressed in sentences such as
- However it becomes philosophically troublesome once it is mathematically demonstrated that it cannot have all of the properties that one would intuitively expect for it to have.
or even worse
- The possibility that quantum mechanics is simply wrong has still not been completely ruled out by the Bell test experiments.
Of course, nothing rules out any theory being ruled out by experimental evidence, whether it's Bell's inequality or the unexpected discovery of the agency of angels. The phrase "simply wrong" is tendentious. Quite simply, if it's wrong, it's simply wrong.
I have added some comments on interpretation on the Bell's inequalities talk page.CSTAR 20:43, 10 Jan 2005 (UTC)
- Apart from the point you mentioned, I want to express my doubts about:
- that is deterministic: given one set of circumstances, there is only one possible outcome;
- being an undesirable aspect of any theory. I'm fine with it, and there are even voices which feel better this way around, hoping that it also implies a free will.
- Pjacobi 21:42, 2005 Jan 10 (UTC)
- In fact, this whole business of coming up with desiderata of this kind seems ludicrous. The only desideratum of any merit is whether the theory conforms to the facts or not. If it doesn't, we chuck it and find something else.
- And I fully agree that determinism is not (and arguably hardly ever was) a desirable ingredient in theories. Although I would not say anything about the relation of determinism to free will; that's a red herring. CSTAR 22:59, 10 Jan 2005 (UTC)
Proposed POV tag
This article expresses as a predominant view, what in fact is a fringe view of the nature of quantum mechanics. Fringe views may be presented on WP, and sometimes there is benefit in doing so, but provided such views are labelled as having little or no support in the scientific community. The determination of the level of support is determined by articles in the peer-reviewed literature. In this case there is no doubt that the view of QM as weird or unsatisfactory has is a fringe view.
I therefore propose putting a POV tag on the article and will do so unless there is some compelling reason not to. CSTAR 03:55, 14 Jan 2005 (UTC)
- What are you trying to say? That a page devoted to the interpretation of quantum mechanics has to imply that there are no conceptual difficulties? Surely the whole world agrees that it would be desirable to have a local realist theory instead? It should be deterministic at the lowest level, though it is bound to have effectively random interactions with the environment, giving it an effective measure of indeterminism. This is what Einstein wanted and, indeed, surely what everyone would like to see, if only they had not been persuaded by the Bell test experiments that it was impossible. As you know, the tests were not by any means conclusive and my personal view is that if they were to be repeated with a range of parameter settings it could be shown that the "obvious" local hidden variable theory was perfectly viable.
- When gou say that wikipedia should present the majority point of view, what subset of the world's population are you considering? Just quantum theorists?Caroline Thompson 09:23, 14 Jan 2005 (UTC)
- It's somewhat religious to judge, what everyone would like to see. And yes, the Wikipedia, as every encyclopedia, should present the majority scholarly POV as such. In contrast to other encyclopedias, the Wikipedia will present also other POVs, to some extent, if relevant enough.
- An encyclopedia is rather dull, conservative project. There no original research here and it is not the place to decide any POV clashes, only to report them.
- Pjacobi 11:54, 2005 Jan 14 (UTC)
- I don't think this article needs a {{NPOV}} tag; there is no throughly peer-reviewed experiement with currently favors any particular QM interpretation right now. Samboy 11:58, 14 Jan 2005 (UTC)
- Huh? I'm not talking about favoring one interpretation over another! The article needs to explain what an interpretation is and why some physicists regarded it as necessary for QM and why it wasn't deemed necessary say for statistical mechanics (although in retrospect probability requires intepretation as well). As to the failure of {{NPOV}}, I'm referring to:
- The list of desiderata.
- The view that the reason QM needs interpretation is because it's troubling or bizarre in some way
- The view of causality as expressed in a very limited idea of local realism.
- CSTAR 14:32, 14 Jan 2005 (UTC)
(William M. Connolley 13:38, 14 Jan 2005 (UTC)) CT said: Surely the whole world agrees that it would be desirable to have a local realist theory instead? - this is near meaningless. The world would like truth, justice and harmony but that doesn't mean we're going to get it. The article should spend most of its time on the dominant POV and mention speculative stuff as such. Don't put on a POV tag - edit the article to remove it and hopefully people will support you. I will. CT is welcome to express her personal POV on the talk page but not in the article.
- The reason is that this is an ambitious task that will very likely take several months of edit, counteredit and discussion. CSTAR 14:32, 14 Jan 2005 (UTC)
- (William M. Connolley 15:17, 14 Jan 2005 (UTC)) Maybe. But it would be better to have a good start at getting rid of the worst bits and seeing if that works. If you try that and it fails, then try the tag. In fact, looking at the page, it says One might intuitively like a physical theory... *not* it is desirable for a theory... and the phrase on the page seems fairly reasonable. I've done a bit of an edit which may help.
- One might intuitively like a physical theory... does seem like desideratat to me
- You did remove some of the more egregious offending phrases (such as simply wrong). However the article never says what an interpretation is; a good WP should say this in the first few sentences and why it is necessary. Interpretation in general may have two parts:
- A formal reduction of a set of linguistic structures (such as a language or the terms of a theory) to another formal structure. This can be accomplished by many worlds, consistent histories etc.
- A statement of what there actually is: the elements of these other formal structures are actually elements of the real world (principle of reality)
- Issues of completeness, locality and so on are irrelevant for sayinh what an interpretation is, I think. CSTAR 18:18, 14 Jan 2005 (UTC)
Proposed first paragraph
In a nontechnical sense, an interpretation of quantum of mechanics is an attempt to answer the question what exactly is quantum mechanics talking about. That such a question is even asked is a reflection of a number of facts:
- The mathematical structure of the theory based on fairly abstract mathematics such as Hilbert spaces and operators on Hilbert spaces.
- The historical development of the theory which went through through various stages of understanding of what particular formalisms meant. This includes various attempts by leading scientists such as Einstein to come to terms with the theory.
- Why single out Einstein here? He was a local realist who never really came to terms quantum mechanics in anything approaching its modern form. As far as important contributions to interpreting QM, probably the single most important was Bohr's interpretation (or was it Born's?) of Schrödinger's wavefunction as a probability density. Right? I dunno. Just a thought. Lethe | Talk
- You're right about Einstein. I don't think he ever came to terms with it which has been the source of endless hassles. Yeah Bohr, Born one of those two should be mentioned.CSTAR 22:06, 14 Jan 2005 (UTC)
- The apparently peculiar nature of the measurement process in quantum mechanics which is tied in with the statistics of certain ensembles.
CSTAR 21:18, 14 Jan 2005 (UTC)
- (William M. Connolley 21:28, 14 Jan 2005 (UTC)) Could be.
Now that's non-commital. CSTAR 22:06, 14 Jan 2005 (UTC)
- I'm in danger of getting out of my depth here, but... I dislike the first point, or at least your formulation of it. Perhaps something like "In classical mechanics "commonsense" proterties of an object - location, or velocity - are described by a single number and there does not seem to be any need to "interpret" the theory to see the association of number with physical structure. In QM, the objects of the theory are more abstract and the connection to observed reality - via measurement - is <insert your favourite phrase here>.
- Is this really true? If so why did Mach, Bridgeman and others go to such great lengths to provide operational meanings to the physical concepts of classical mechanics? CSTAR 00:15, 15 Jan 2005 (UTC)
- More significantly, however, is that interpretation is now a common theme in any explanatory system: so quantum mechanics is less of an outlier in that respect as it once was.CSTAR 22:06, 14 Jan 2005 (UTC)
- (William M. Connolley 10:44, 15 Jan 2005 (UTC)) Yes, I'd agree with that last. You've added "measurement destroys the state". I don't think thats defensible in that form.
- What Im trying to say in an introductory way is that measurement (generically) carries a pure state to a density state. One should also say something about the double slit experiment. But anyway, if you find a better formulation, please put it in.CSTAR 14:08, 15 Jan 2005 (UTC)
- (William M. Connolley 19:10, 15 Jan 2005 (UTC)) I'm not going to try to correct it, because you've lost me already (I thought measurement took a possibly-mixed state to a pure state; I don't know what a density state is).
- Have a look at quantum operation.CSTAR 22:32, 15 Jan 2005 (UTC)
- (William M. Connolley 19:10, 15 Jan 2005 (UTC)) I'm not going to try to correct it, because you've lost me already (I thought measurement took a possibly-mixed state to a pure state; I don't know what a density state is).
Philosophical problems
One has to define for any interpretation (whether it is understood as a formal equivalence or an ontological one) what it means for that interpretation to have the properties of "reality", "completeness" etc. I am treading on dangerous waters here.
I also agree that the Feynman dictum should be put back in. I only meant to remove the phrase "neutral interpretation". CSTAR 16:47, 16 Jan 2005 (UTC)
Interpretation in classical physics
I suggest changing the sentence
- are described by real numbers nd there does not seem to be any need to provide a special interpretation for these values. A similar comment can made in regard to the understanding of electromagnetism.
- are described by real numbers and functions defined on sets which have direct spatial meaning. In this case, there does not seem to be any need to provide a special interpretation for these objects . A similar comment can made in regard to the understanding of electromagnetism.
CSTAR 20:26, 9 Feb 2005 (UTC)
In a nontechnical sense
Could we remove that adverbial phrase at the beginning? Yes I put it in, but at the time it seemed a like a plausible step to set up a transition from the previous content of the page. CSTAR 23:13, 10 Feb 2005 (UTC)
very high status as a scientific theory
Could we delete this sentence or somehow integrate it into another one? CSTAR 17:44, 19 Feb 2005 (UTC)
Comparison table
I'm not sure the comparison table is accurate. Comments? CSTAR 16:47, 20 Feb 2005 (UTC)
- In particular I'm a little puzzled by the use of "locality" in that table; locality can mean
- local realism (very narowly defined in this article, which suffices for its purposes)
- local of transfer of information (e.g. no communication theorem)
- some other kind of locality (but in reference to some specific property)
- In what sense is MWI local? It is not local realist, but it is local information theoretic. To the maker of this table, what exactly did you mean?CSTAR 06:14, 23 Feb 2005 (UTC)
- Puzzled me too. ---- Charles Stewart 01:38, 24 Feb 2005 (UTC)
Shut up and calculate
"later expressed in Richard Feynman's famous dictum: "Shut up and calculate"." Attribution to Feynman, althought widespread, may be bogus. see http://www.physicstoday.org/vol-57/iss-5/p10.html Mermin is not able to find a reference with a source to Feynman ever saying this, although Mermin said it in 1989 64.165.202.199 22:10, 2 May 2005 (UTC)
- Thanks for the tip. I included your reference into the article.--CSTAR 05:15, 3 May 2005 (UTC)