Talk:De Broglie–Bohm theory

For archived comments, see /Archive 1 Deadly Nut (talk) 13:27, 29 October 2008 (UTC)

Old comments

In my view the comments in this section have already been dealt with. If you feel there is still life in any of these topics, please take it out of this section and place it in the main body of the talk section.

Bell

There's a lot of stuff about Bell appearing that should really be in the Bell's theorem article. --Michael C. Price ^talk 23:32, 22 August 2006 (UTC)

I'm ging to delete it unless its presence is explained. --Michael C. Price ^talk 01:36, 24 August 2006 (UTC)

Hidden variables merge

Anyone object to merging Hidden variable theory into this article? It was what Bohm originally called his theory. --Michael C. Price ^talk 01:36, 24 August 2006 (UTC)

I see someone is of the opinion that this shouldn't be called "hidden variables" and has removed some references to the term. Well that's what Bohm called it originally -- and how it is often called -- so we should mention it, even if John Bell thought otherwise. --Michael C. Price ^talk 20:14, 26 August 2006 (UTC)

I personally think that there is a difference between the Bohm interpretation, which is one HV theory, and Hidden variable theory, which summarises several. Anyway, as there has been no movement on this in 2 years, I'm marking it as 'old'. Deadly Nut (talk) 08:24, 14 December 2008 (UTC)

Completed points from 'Sfwild's comments'

can be thought of as taking its cue from what one sees in the laboratory, say, in a two-slit experiment with electrons.

--- This is false. Bohm's interpretation, written after his textbook on QM, takes as its starting point certain fundamental shortcomings of the standard interpretation, and attempts to resolve the antinomies btw. Schrödinger wave equation and the Bohr-Heisenberg interpretation of such in terms of pure probabilities, e.g. radical and "unaccountable" indeterminism, or what Bohm calls "irreducible lawlessness." ---

I've removed this text. Deadly Nut (talk) 12:32, 26 November 2008 (UTC)

We can see localized flashes whenever an electron is detected at some place on the screen. The overall pattern made by many such flashes is governed by a pattern closely matched by simple wave dynamics. Bohm and de Broglie posited that in the world of quantum phenomena, every kind of particle is accompanied by a wave which guides the motion of the particle, hence the term pilot wave.

Note that Bohm only uses the term "pilot wave" when referring to de Broglie's work.

I'm removing this term as I edit that part of the article. Deadly Nut (talk) 12:32, 26 November 2008 (UTC)

Mathematically, the pilot wave is described by the wavefunction of conventional quantum mechanics, but with an added piloting influence on the motion of the particles. We can formulate the pilot wave's influence using a wavefunction-derived potential called the quantum potential,

The wavefunction of the early Bohm (the 50's) is virtually the same as it is for all interpretations quantum mechanics: basically it’s the S. equation. To that de Broglie first adduced the concept of the "pilot wave" which is somewhat reinterpreted by the early Bohm in terms of the "quantum potential” Mathematically it doesn't make any difference whether you add the quantum potential or not.

Which acts upon the particles in a manner analogous to the interaction of particles and fields in classical physics.

I don't know what the writer is saying here: that the effects of the quantum potential are analogous to classical field theory? Nothing could be farther from the truth; that's why Bohm found himself not only, in the end, dissatisfied with the paradoxes of the Copenhagen Interpretation, but even felt the need for a "new order" of physics, what he calls early on the "subquantum order," and which he would call later the "implicate order." There is no analagon in classical physics for any of this.

I've removed this. Deadly Nut (talk) 12:32, 26 November 2008 (UTC)

The pilot wave governs the motion of the particle and evolves according to the Schrödinger equation. Unlike the Everett many-worlds interpretation, the Bohm interpretation does not assume that the universe splits when a measurement occurs,

Why is the writer talking about Everett here? It is a digression and has no place except perhaps in a footnote...assuming that what the article is trying to do is present Bohm's interpretation in an objective, informed manner. Everett many worlds interpretation can some relation to Bohm's later cosmological thinking, but has no bearing on Bohmian Mechanics per se.

I've removed this, but not the comparison with the Copenhagen Interpretation, because Bohm made the comparison explicitly. Deadly Nut (talk) 12:32, 26 November 2008 (UTC)

Two-slit experiment

Thus, in this theory all fundamental entities, such as electrons, are point-like particles that occupy precisely defined regions of space at all times. When one performs a double-slit experiment (see wave-particle duality), one is concerned with noting the positions on a screen at which electrons arrive individually, one at a time. Over time, the positions at which the electrons are detected build up a pattern characteristic of wave interference. The usual Copenhagen interpretation is puzzling in that a single entity, the electron, is said to exhibit characteristics of both particle and wave. The Bohm interpretation accounts for the same phenomena by saying that both a particle and a wave do exist. The particle aspect is present because each electron traverses one slit or another, but never both. The wave aspect is present because the electron's pilot wave traverses both slits.

-- Ok, as far as this goes, but this paragraph has more to do with double slit experiment itself, and de Broglie's early interpretation as opposed, say, to Bohr's notion of complementarity. --

Thus, the Bohm interpretation resolves the puzzle quite simply and naturally. The electron's motion is guided — both in its choice of slits and its subsequent trajectory towards the screen — by the wave. The characteristic wave-interference pattern seen in the detection of the electrons arises by considering that the guiding wave exhibits interference in the familiar way one learns in the elementary physics of waves.

--- It's not so simple. What you have is S's wave equation+Heisenberg probabilities+what Bohm calls quantum potential. These are not classical waves after all. ---

One might also note that what is measured in such an experiment — the position on the screen at which each electron arrives — is itself none other than the "hidden variable" the Bohm interpretation adds to the description, as we show in the formulation below. --- How does the writer get this? Is he saying that the experimental data=the hidden variables? I think he misses the point---

It might seem that the term "hidden variables" is an inappropriate name for the positions of particles, the quantity that is apparently most conspicuously manifested in the experiment. However, the particle's position has no influence on the guiding wave and hence is unobservable or "hidden" in some sense (see criticisms). --- "Hidden variables" does not designate "positions of particles" as writer believes. And these in turn certainly do not correspond to quantities "conspicuously manifested in the experiment." Writer would make Bohm into a naive and "deterministic" realist.

I've rewritten this section. Deadly Nut (talk) 12:41, 1 December 2008 (UTC)

Nonlocality

Now we must address the question of nonlocality.

-- "One must"... "Now we must address"... Editor please!-- --

Within Bohm's interpretation, it can occur that events happening at one location in space instantaneously influence other events which might be at large distances: thus we say that the theory fails to obey locality, i.e., it is non-local. The response many physicists have to Bohm's theory is often related to how they regard this concept.

--This is a gross generalization of the role of non-locality in Bohm's thinking. Since one has to address the issue, why not start with EPR?--

The question of nonlocality hinges upon the attitude one takes towards the Einstein-Podolsky-Rosen paradox and Bell's theorem (see p.14 in).

--Talk first about non-locality, intent of EPR thought experiment, Bohm's interpetatation, and then talk about Bell--

There are often two camps into which people fall regarding the issue.

--That may be true, but first explain the issues--otherwise it's all hearsay---

According to one camp, it has been shown that quantum mechanics itself is nonlocal and that this cannot be avoided by appealing to any alternative interpretation. The same Bell responsible for Bell's theorem was a member of this group (p. 196 in): "It is known that with Bohm's example of EPR correlations, involving particles with spin, there is an irreducible nonlocality." If this is indeed the case, then the nonlocality of the Bohm interpretation can hardly be regarded as a strike against it.

--Logic? Writer identifies one "camp" with some off the cuff comments from Bell here to the effect that all quantum mechanics is non-local in order to question relevance of Bohm's model?--

Others see the consequences of EPR and Bell's theorem in a different way. They regard the correct conclusion to be related not so much to quantum theory itself, but only to deterministic interpretations of the same (i.e., to hidden-variable theories such as Bohm's interpretation).

--Again, writer makes the mistake of equating the "Bohm Interpretation" with early hidden variable interpretation with a "deterministic interpretation." I doubt he has read much Bohm, because if had, he would realize that this is a gross oversimplification

According to the people who think this way, what has been shown is that all deterministic theories must be nonlocal. For example, Niels Bohr was a member of this group.

--all very fuzzy. Bohr himself never advocated non-locality; his objections to the "thought consequences" of EPR had more to do with his appreciation of the "wholeness of the quantum phenomenon"--

This group would claim that retaining orthodox quantum mechanics — with its probabilistic character — permits one to retain locality, or at least to avoid the EPR type of nonlocality, at the expense of having no way to picture particles as objective elements of reality that occupy definite regions of space at all times. Armed with such a viewpoint, these physicists tend to be less receptive to Bohm's interpretation.

This simply doesn't follow. Is he saying that the same folk who believe all deterministic theories are non-local (not so many actually) are the ones who favor the probabilistic character of the standard interpretation? It's true that in the Bohr-Heisenberg approach, what Einstein called "spookiness" of non-locality is avoided, but there are deeper things going on... Whole discussion dividing discussion into two camps, and then misinterpreting the viewpoints of each camp, trivializes a very important chapter in the history of QM. And then what about Vigier, and the Alain Aspect experiments and such? Not a word

Sfwild 04:11, 11 June 2007 (UTC)

I've rewritten the section on Nonlocality, and named it EPR, to fit the logic of the article better. I've also added a mention of Alain Aspect's work. Hopefully this addresses most of Sfwild's comments on the section. Deadly Nut (talk) 10:44, 2 December 2008 (UTC)

A Non-Specialist Writes

I am not clear as to where Bohm's theory stands at the moment from this article. If its not been 'proven experimentally' or rather, as the articles suggests, its been disproven experimentally, then presumably its dead? Or is it the case that no Theory, including the Copenhagen and Multiple Worlds Theories have been proven experimentally either?

Also, the article suggests that Bohm viewed the theory as a starting point for experimentation rather than a finished theory. If he thought it could be adapted/enlarged then presumably it isn't dead?

Also, as a real non-Specialist, for a knuckle-head like me, is the Theory basically saying that everything is exchanging 'information' with everything else through waves and thus interacting in a way which is not dependent upon measurement and 'wave collapse'?

If this theory is 'disproven', where does that leave Bohm's other ideas? ThePeg (talk) 17:49, 16 November 2008 (UTC)

Presumably the article is not being clear enough; Bohm's theory is an interpretation, so it is neither dead (disproven) nor alive (proven over the alternatives) but rather in a state of limbo with many others. --Michael C. Price ^talk 19:18, 16 November 2008 (UTC)

I think ThePeg has an important point - thank you. I've tried to highlight this at the highest level of the article. I've also tried to clarify the basic ideas of the theory, and to remove the Benefits section, which should now be represented in the section labelled Results. Because I've changed the content of Benefits quite drastically, I've removed the POV notice - please reinstate it if it still applies. Deadly Nut (talk) 13:01, 24 November 2008 (UTC)

Criticism section (now called FAQ)

Critcism ? Or ignorance

Although personally I dont think Bohmian interpretation will bear much fruit-when criticised, it must be on fair basis. And, at least half of "criticisms" are, to put it mildly- lame. I've deleted, now, only the 1st point, since "inelegance" is personal preference, and, judging from the majority of opinion- this would be the last objection re Bohmian view. As for redundance-current physical theories are full of variables that are not directly verified and are props that may very well turn out to be just concoction: for instance, Higgs boson and dark matter. Other cristicism will be reviewed in due time, but, weaknesses of Bohm's interpretation cannot be addressed in such a manner, teeming with half-truths, since Copenhagen formulation abounds with even more "unacceptable" or concocted notions (anyone remember problems with classsical-quantum division, "healed" by Bohr's Correspondence pronciple-pure scholasticism, not provable at all). Bohm's "sin", if any, is that he was too timid and not radical enough. Mir Harven 12:57, 29 Oct 2004 (UTC)

Everett's Criticism

The response to Everett's criticism looks like original research, with the claim that Everett's theory requires extra assumptions -- also such issues about other interpretations should really be dealt with on their respective talk pages (e.g. Talk:Many-worlds_interpretation) rather than here, so I propose we delete this claim.

Focusing on Bohm's theory and role of the particles, I don't think the response actually addresses the issue of the unobservability of other universes (empty parts of the universal wavefunction), although of course adherents of the various interpretations are never going to agree about this. Can we say that followers of Everett (who hold the non-collapsing wavefunction is sufficient to account for all observations) see the Bohm particles as superfluous, whilst others regard them as necessary to realise one possibility from amongst many? --Michael C. Price ^talk 21:21, 1 October 2006 (UTC)

The response is not original, just a brief summary of Bohm's own critique of MWI. See e.g. §13.6 of The Undivided Universe:

If we adopt DeWitt's approach, then, as we have seen, it is necessary to supplement this with some further principles involving an as yet unavailable definition of complexity and further equations determining just how this would determine the splitting of universes. On the other hand, if we adopt Everett's approach or indeed that of the many-minds interpretation, we have to do something similar with regard to the splitting of awareness. In this connection a complete and consistent expression of these interpretations would, as we have seen, require new principles and assumptions of a speculative nature going beyond our present knowledge of awareness and its possible relationship to Hilbert space. (p. 315)

Regarding how one possibility is realized from among many, it would be misleading to give the impression that one theory needs to explain this and the other doesn't. Both Everett and Bohm recognized that they have to explain it, they just did so in different ways. Everett used the splitting of universes (or awareness), so he didn't need the particles. Bohm used the particles, so he didn't need the splitting. Any comparison of the two theories ought to bring out this parallelism. —Were-Bunny 17:16, 9 October 2006 (UTC)

Thanks for supplying the Bohm quotation, this demonstrates that this particular claim about the necessity of particles is not original research -- what it doesn't show is that this is universally accepted, especially by adherents of other interpretions (as you would expect). Hence the qualifer "in Bohm's view" is required to WP:NPOV it. --Michael C. Price ^talk 00:01, 10 October 2006 (UTC)

Bohm's interpretation is not universally accepted, so it is highly unlikely that his views on this particular point (or any other point) of his interpretation are universally accepted. But that's irrelevant to the issue at hand, which is the question of how Bohm responded to Everett's criticism of the Bohm interpretation—i.e., a question about what Bohm thought, not aboout whethter others agree with him. If universal acceptance were the requirement for explaining the features of the Bohm interpretation, the whole page would have to be empty. Since The Undivided Universe is Bohm's most authoritative work on his interpretation, no further evidence of his views is needed here. Furthermore, the redundant qualifiers ("in Bohm's view," "Bohm maintained that," "in Bohm's view") also are not needed because the reader already knows that the whole page reflects Bohm's views, except where otherwise noted. A qualifier is needed only once following someone else's views, to alert the reader to the transition. —Were-Bunny 22:12, 10 October 2006 (UTC)

You misunderstand my point (or rather the Wikipedia guidelines). No one is saying that Bohm's views are inappropriate in the article -- but it must be made clear where they are Bohm's views and where they are views endorsed by the wider community. All statements in Wikipedia articles should be explicit about their sourcing if challenged; the qualifiers are not redundant, placing a single qualifier is not sufficient since this article (like others) contains statements which vary with their acceptance from statement to statement. --Michael C. Price ^talk 01:41, 11 October 2006 (UTC)

You are misapplying the Wikipedia guidelines in this case. This paragraph makes no mention of general opinion. It states that Everett made a criticism of the Bohm interpretation (e.g., that particles are not needed) and that Bohm responded to that criticism by explaining why they are needed. These are claims of fact, not opinion--i.e., the fact that Everett and Bohm did or did not make the respective statements. To verify the accuracy of these facts, all that is needed is to cite the appropriate writings of Everett and Bohm. Other people's acceptance doesn't matter because no claim is being made about whether the expressed views are generally accepted. If you think the paragraph makes some additional claim about general opinion, the burden is on you to point out specifically what it is. If there is such a claim, it should be clearly identified as such. At present it is not; all opinions are attributed to either Bohm or Everett. —Were-Bunny 20:01, 11 October 2006 (UTC)

I must have been unclear -- I have no problem with Everett's and Bohm's views being reported: it was those opinions that were not clearly attributed and that could be misinterpreted as general statements of scientific fact that concerned me. Best wishes, --Michael C. Price ^talk 20:10, 11 October 2006 (UTC)

You're being extremely vague and unclear. Please try to be much clearer. I've asked you to identify specifically which opinions you believe are not attributed to either Bohm or Everett. Please do so as clearly as possible. —Were-Bunny 16:46, 12 October 2006 (UTC)

I find your requirement rather odd. I have already corrected the article by adding the appropriate attributions, which you originally objcted to. So to be completely explicit: I am happy with the article as it is since the questionable statements (i.e. opinions) are appropiately attributed. --Michael C. Price ^talk 19:26, 12 October 2006 (UTC)

Criticism section

I am not sure if Bohmian mechanics are just really insecure, but the `criticism' section truly is a fiasco. Surely there is some Wikipedia policy or guideline against having criticisms each followed immediately after with a `response'. In many cases, moreover, the `responses' have a whiff of original research, or at least original syntheses from existing literature, and many of them don't actually address the criticisms in any meaningful way (probably because no such way exists). I don't want to edit the article and disturb the equilibrium that tends to develop around these sorts of topics, but could a regular please try to sort this out? Rosenkreuz 08:50, 11 January 2007 (UTC)

The point of the criticism section is to inform the reader: this is what the critics say, and this is how the adherents defend their position. Whether the responses are adequate is left for the reader to judge. (I wrote one of the responses and I'm not a Bohmian.)--Michael C. Price ^talk 08:58, 11 January 2007 (UTC)

I understand as much. Only most similar articles don't have such `response' opportunities, I don't think...the reader judges the validity of the criticisms based on the content of the theory as discussed in the article itself, not on a list of possible fixes. Having such a list, moreover, invites an endless cycle of criticisms and counters, surely? It seems like a bit of a `POV-trap', to me, which is wide open to abuse. Rosenkreuz 09:07, 11 January 2007 (UTC)

Yes, but interpretations of quantum mechanics are a particularly controversial area, even amongst leading researchers who care to venture an opinion. Controversial topics often (but not always) have a criticism section. That's not POV abuse, provided all viewpoints get to be expressed (whether or not they are valid -- which Wikipedia has no opinion about, of course). Any controversial subject will attract an endless cycle of criticisms and counters -- the criticism section is an attempt to channel this more productively. --Michael C. Price ^talk 09:13, 11 January 2007 (UTC)

I know that. I don't object to a criticism section at all: that much is necessary. It is the responses which are misplaced, I think. For example, the article on the relative state idea contains an `acceptance and criticism' section — which is good — but it doesn't have a list of comebacks by the Everites to every point raised in objection to the theory — and nor should it. Why should the same rules not apply to the Bohm interpretation? Rosenkreuz 09:19, 11 January 2007 (UTC)

Hmmm.. Heh, I helped write the MWI criticism section. I guess that section has a more unified approach than here. I hesitate to remove the "response"s here because I'm sure someone will object. And I admit I'm too lazy to do the complete rewrite you seem to be suggesting. --Michael C. Price ^talk 09:26, 11 January 2007 (UTC)

A nonspecialist reader says: the criticism/response format is VERY helpful; please don't delete it. —The preceding unsigned comment was added by 72.70.250.127 (talk) 02:26, 2 April 2007 (UTC).

I am not a physicist, either (not even an armchair physicist ^^), and while the "criticism" section certainly is interesting, I agree with Rosenkreuz that it's suboptimal at best - the way it's written gives undue weight to the Bohmians' responses by always letting them get "the last word". I think it'd be better to rewrite this section entirely, as an actual text instead of a bulleted list; I feel I'm not qualified to do it myself, but it definitely needs work, since right now, it reads as if it was lifted straight from a pro-Bohmian website. -- Schneelocke 17:31, 13 April 2007 (UTC)

I am a physicist but not an expert in Bohm mechanics. As a reader, I did get the impression that each point in the criticism section was rushed through, in order to get as fast as possible to the subsequent rebuttal of it. It is more sounding as a biased advocacy of Bohmian mechanics, whereby (unfortunately) criticism may be raised and must be rebutted immediatetely, than as a neutral exposition of different viewpoints. As it is, the section would be more appropriately entitled "Rebuttal of Criticisms" than "Criticisms". The rebuttals do sound as the central issue and reason of existence of the section. I agree that it is fair in general to have both the criticism and the rebuttal, but the section cannot stand in the present form (at least equal balance is needed). Overall, the whole article does not look as citing all necessary sources either (incidentally, not one single statement in the criticisms section is sourced, in either verse, thus raising doubts about WP OR policy issues). --209.150.240.231 01:05, 5 July 2007 (UTC)

I am a physicist, too, and I read various articles about different interpretations of quantum mechanics. Most of the critics in the criticism section show a misunderstanding of Bohm mechanics, and the "rebuttals" are more an explanation what Bohm mechanics really says. For example, look at the topic "scientific theory", "collapse", "observables", "non-locality", "spin", "decoherence", "quantum potentials and trajectories". All of these critics are based on misunderstandings of Bohm mechanics. I know it would be provocative, but replacing the header "Criticisms" by "Resolving misunderstandings" would be more accurate.87.163.97.82 10:54, 3 October 2007 (UTC)

More accurate, yes, but definitely more provocative. --Michael C. Price ^talk 11:45, 3 October 2007 (UTC)

I'd love to see a reference for each criticism and response. Some of the responses probably should have counter-responses too.--Per Abrahamsen (talk) 20:12, 19 May 2008 (UTC)

I agree with rosenkreuz above wholeheartedly. This section needs total cleanup. It's not written for readers but rather for people who like to argue. counter-responses would make it even worse. There is no reason to have more than one description per side, and even *that* is pushing it, since the *rest* of teh article should function as the "for" argument. Keep the pro-Bohmian stuff in the rest of the article. Make the critism section succinct and one sided, *unless* there is a very large and valid point that sounds more intelligent than "no, you're wrong", cause that's how a lot of the responses sound right now, simply stating taht the critisism is unfounded, and using lots of words to do so. —Preceding unsigned comment added by 84.12.134.165 (talk) 20:49, 19 May 2008 (UTC)

Criticisms section renamed as FAQ

I've rearranged this as a Frequently Asked Questions section, and tried to simplify (and shorten) the content. I have tried not to lose information in the process; however,

• I really did not understand the last two points, and I have removed them. If either of these has a serious point, please reinstate it and rewrite the question (and preferably the answer) so I can understand it. Thanks.

• The last point says that Bohm's particles are not observable entities, but surely they are - what hits the detectors and causes flashes? After making the edit, I realised that Hugh Everett raised this point, so I need to take it seriously. Does someone have a reference, to help me understand it?

• Some of the points made look speculative.

• Should I remove the style marker, or will someone else do that if the improvement is enough?

Deadly Nut (talk) 09:20, 14 November 2008 (UTC)

• I will happily rewrite the answers of the two points you deleted, if you would be so kind as to reinstert the text. As for a reference for the last point (Everett's criticism), you will find that elsewhere in the article, but I am happy to add that as well to the reinserted text when it reappears. --Michael C. Price ^talk 11:22, 14 November 2008 (UTC)

• Thank you for the offer, Michael. I've reinserted the text. Deadly Nut (talk) 18:28, 14 November 2008 (UTC)

Okay, I see the text. I like the way you phrased the question -- I think I'll use that in the FAQ section. --Michael C. Price ^talk 21:03, 14 November 2008 (UTC)

Article Cleanup Co-Ordination Point

Uhh, this request for cleanup is confusing and unclear. Is there some specific complaint? linas 04:39, 13 December 2006 (UTC)

Pockleanbot has been removed, so unless a real person has something to say, I'd say to ignore it. Fephisto 01:10, 14 December 2006 (UTC)

I restored the cleanup template (I was not the one who put it there the first time). The problem is the overall tone throughout the entire article. It's exceedingly didatical, in a manner that accentuates the "feeling" that the article assumes Bohm interpretation to be correct, and adds greatly to its POV. The problem is most obvious in (but not exclusive to) the Introduction and the Criticism section. It had been pointed out by others, albeit not in these words. Perhaps a complete rewrite or copyedit tag would be more appropriate. AoS1014 17:00, 19 May 2007 (UTC)

Sfwild's comments

Please find below general comments on the opening "Background" secion of article on "Bohm Intepretation"

There are big problems with this article!

I've moved some of sfwild's points, which I believe have been dealt with, to the 'old comments' section. Please bring them back if they are still current. Deadly Nut (talk) 08:24, 14 December 2008 (UTC)

Article name

The Bohm interpretation--

"The Bohm Interpretation" is not an accepted usage. Rather one speaks either "Bohmian Mechanics" (as they do in Europe) or one speaks of Bohm's early "Hidden Variables Interpretation," or a bit later, the "Causal Interpretation" or, finally, the "Ontological Interpretation" of QM. Sometimes one hears, in a more general way, of the "de Broglie-Bohm" interpretation. Not a good start!---

Causality and determinism

And unlike the Copenhagen interpretation it is both objective and deterministic. It says the state of the universe evolves smoothly through time, with no collapsing of wavefunctions. Thus, Bohm called the hidden variable or pilot wave the quantum potential force.

Here again, the author obviously misunderstands (or deliberately misleads?) the reader when he says, broadly, that the Bohmian interpretation is "deterministic." This may be to some extent true in the very early presentations, but after Causality and Chance, and throughout the middle and late period, Bohm is adamant that "causal" is not the same as "deterministic." Any accurate presentation of Bohm's theories needs to address this. Sfwild 04:11, 11 June 2007 (UTC)

I'll bear this in mind. For the time being, I've just substituted the word "causal". Deadly Nut (talk) 08:17, 3 December 2008 (UTC)

When Micheal C Price reverted this, I looked it up - I note that Holland (1993) describes the Causal Interpretation as deterministic, (but points out that there is a non-deterministic variant proposed by Bohm and Vigier in 1954). Deadly Nut (talk) 08:17, 3 December 2008 (UTC)

Vigier and Aspect

Is there anything published about Vigier and Alain Aspect with respect the Bohm interpretation?--Michael C. Price ^talk 16:14, 5 July 2007 (UTC)

There is too much published--Google it! Vigier worked closely with Bohm first in Brazil and then in regular collaboration during the summers in Paris. They published a number of articles together, extending Hidden Variable approach. In the European discourse, one hears all the time of the "de Broglie-Bohm-Vigier interpretation" or what is sometimes called the Causal Stochastic Interpretation of QM. The '82 Aspect experiments come right out of this approach. Note that results were first published as a realization of the ERPB (B=Bohm)Gedankenexperiment defined in terms of violation of Bell Inequalities. The Aspect exeriments are important because they brought the discussion of non-locality out of the realm of the purely theoretical into the realm of the experimentally verifiable. There is no shortage of literature on the subject.

Sfwild 15:52, 6 July 2007 (UTC)

It's an idealogical dispute, not an encyclopedia article

I think all this will be hopeless, this article is bounded to remain non-neutral forever, for reasons that have nothing to do with Science. I've been around in wikipedia lately and I can see perfectly well what's going on here and eslewhere. What is going on is that we have a worldview of philosophers who base all their speculations about what we are on the bet that the current understanding of quantum physics is completely wrong. This page is all too important to them, and it will always have support in a somewhat biased way. I see something weird. Arxiv papers put on a par with peer reviewed papers. That is telling. We have sixty years years of tons of published peer-reviewed work on the one hand, in the development of reliable quantum field theory that has made astonishing predictions and justified the attribution of a dozen Nobel prizes, against two non peer-reviewed Arxiv papers that we have to believe on faith. --Gibbzmann 03:20, 28 October 2007 (UTC)

I think Gibbzmann is right in that the debate here is embedded in deep ideological disputes, though what I find objectionable is the presentation of what is called the "Bohm interpretation" purely in terms of the rather limited approach of what is sometimes called "Bohmian mechanics." To argue, for instance, that Bohm's interpretation of QMis "deterministic" is to seriously misunderstand what Bohm is trying to say. It is, as it were, a naive misreading of the very early '52 papers. That is why I continue to believe the article should be re-written and the positions clarified as being not Bohm's interpretation but the derivative interpretation of some of his latter-day followers. In other words, pure POV. Bohm himself hated the word "mechanics" and almost never used it; he would certainly be shocked if someone informed him beyond the grave that his legacy is being so confused.

Sfwild (talk) 19:35, 25 November 2007 (UTC)

Gleason

The article about Gleason's_theorem seems to use quantum logic to imply that no hidden variables theories can exist. Is this tackled in the criticisms anywhere? —Preceding unsigned comment added by 65.96.162.192 (talk) 04:22, 22 February 2008 (UTC)

Article cleanup

I have cleared out the old comments in this discussion because I'm planning to make some improvements to this article. Here's what I'm planning to do:

Improve the structure. I suggest this contents list:

• Overview
  • Background
  • Principles
  • Benefits
  • History
  • Beyond Bohm
• Examples
  • The Uncertainty Principle
  • The Two Slit Experiment
  • EPR
• Mathematical foundation
  • Bell's simplification
  • Bohm's formalism
  • Computational Bohmian Dynamics
• Criticisms
• See also
• References
• External links

Improve the History and Principles sections, with references.

Try to make sure that any subject discussed in this article has references to back it up.

The Criticisms section seems very long, and it has attracted a lot of criticism. Can we reduce it to those criticisms that are published?

Generally, make sure information is covered by references.

I'd be most interested in your feedback on this proposal, especially on the new contents list. Thanks. Deadly Nut (talk) 13:27, 29 October 2008 (UTC)

The Criticisms section has also attracted praise. Please try to improve rather than delete. Also note that a lot of science material in Wikipedia is unreferenced -- that doesn't make it useless or incorrect, just in need of a citation tag, perhaps. --Michael C. Price ^talk 05:16, 30 October 2008 (UTC)

Response

joliverst (talk 10/31/08) I have recently taken an interest in this page and would also like to change things.

I see you're much better qualified than me to do this. I've come to this theory recently, and was trying to take this article off the bottom rung, as a way to clarify my understanding. Why don't you take the initiative here, and ask me for help if I can provide it. I've started by researching the history, so I may be able to write something on that. I've also written a rather brief piece on de Broglie's pilot wave theory recently (it was a stub before I did that). it's a bit light on mathematics, because I haven't followed up the right references yet to be able to tell which were de Broglie's contributions and which were due to Bohm. Perhaps you'd like to look it over. Deadly Nut (talk) 08:29, 5 November 2008 (UTC)

I would organize it as having the theory first. Start with the simple idea: this is a theory about particles whose motion is governed by the wave function. At all times, these particles have definite positions and velocities though they are generally inaccessible to measurement. Next state the simple formulation for R^1 with scalar-valued wave functions. Then expand to R^3N, then add spin-valued wave functions. Finish with words that this generalizes to very general spaces such as manifolds and sections of a vector bundle, giving a reference. I would not do Bohm's version here, but rather the simple version that generalizes, i.e., the velocity formula and Schrodinger's equation. The quantum potential part is unneeded and can be relegated to the history section.

Sounds like a good plan. Deadly Nut (talk) 08:29, 5 November 2008 (UTC)

One thing to get across is that this is a theory, not an interpretation. One should present as such. Is it possible to get this renamed? Bohm interpretation makes this into philosophy. It is not. It is a physical theory and it should be treated as such. It is distinct from quantum mechanics though they have the same empirical predictions, in as much as quantum mechanics has predictions.

I agree in principle; however, to be a distinct theory, it must be possible to prove that this is right and that the Copenhagen Interpretation is wrong. What tests would allow this? Deadly Nut (talk) 08:29, 5 November 2008 (UTC)

I agree that the name looks wrong; I gather Bohm wouldn't like the current name. However, I don't see a consensus on what's right. My nomination is the De Broglie-Bohm theory, but I'd guess you'd prefer Bohmian mechanics. They both get forwarded to the right place. Deadly Nut (talk) 08:29, 5 November 2008 (UTC)

I would also recommend removing the criticisms. If there are places where this is located, then point there. If not, perhaps one should write a paper, get it published, and point there. I would rather see that the points that need to be made to defend against criticisms be made simply in the article as relevant without it being from a defensive posture.

I agree in principle. However, (1) there are criticisms made by Pauli. von Neumann and others that are part of the history. Also, (2) I note Michael C Price's response that people find these critcisms useful. My inclination is to keep them for the time being as "frequently asked questions", and try to condense them. Later when the article is superbly clear and well structured, we won't need them. At the moment, I feel the criticisms are a disproportionate percentage of the article. Deadly Nut (talk) 08:29, 5 November 2008 (UTC)

On the same note, I would think that a Benefits section is also inappropriate. It is a theory, state what it is, where it came from, and what it does. Let others draw the conclusion as to why it is useful. You can mention in the history a few of these things, but minimal is better.

I agree - I was keeping it in only because I wanted to remove it later rather than now.

My ordering:

• The theory
  • Intuitive ideas
  • Single particle on a line
  • Spin-less particles on R^3
  • Spin
  • Generalizations
• Understanding Quantum Mechanics
  • The Uncertainty Principle
  • The Two Slit Experiment
  • EPR (Bell's version)
  • Identical particles
  • Measurement and Quantum Equilibrium
• Computational Bohmian Dynamics
• History
  • Derivations
    • Action
    • Current
    • Invariance
    • Planck's formula
  • No Hidden Variable proofs
• Extensions
  • Nonlocality
  • Curved Space-time
• See also
• References
• External links —Preceding unsigned comment added by Joliverst (talk • contribs) 13:11, 31 October 2008 (UTC)

Looks generally good to me. I'm not sure that nonlocality is an extension - I thought it was a feature of any theory of quantum mechanics... Deadly Nut (talk) 08:29, 5 November 2008 (UTC)

Let others draw the conclusion as to why it is useful. I disagree, since the merits of this interpretation (and it is usually called an interpretation since it is experimentally indistinguishable from other interpretations) are subtle and discussed in the literature we can report on them here.

Perhaps the criticism section could be renamed. It's purpose is to elucidate the interpretation by clearing up common misconceptions. --Michael C. Price ^talk 09:51, 12 November 2008 (UTC)

Contents rearrangement

I've rearranged the article to follow the sequence of Joliverst's suggestion for the contents list. I haven't changed the content, to make later changes more obvious. To follow this principle, I've left in Criticisms and Benefits, but moved them to a less conspicuous part of the article. Deadly Nut (talk) 08:08, 12 November 2008 (UTC)

History section

I've added a History section. Deadly Nut (talk) 08:52, 25 November 2008 (UTC)

The Theory

I've tried to make the 1-particle bit easier to read. I still need to check that it really represents the essence of Bohm's and de Broglie's theory. I've removed the section entitled Mathematical Foundation because it was off-topic. Deadly Nut (talk) 12:41, 26 November 2008 (UTC)

I've rewritten the Principles section, to try to make it really clear. I've also moved a couple of the paragraphs to the Extensions section because they don't seem to be part of the basic theory. I got the $p=\nabla S(x,t)$ bit from Bohm's 1952 paper, but it puzzles me because it looks like if you know the position accurately, you can get an accurate momentum from the wave function - but I thought position and momentum were complementary? Deadly Nut (talk) 13:35, 28 November 2008 (UTC)

That is the whole point of Bohm's approach; that position and momentum of his hidden variables are simultaneously defined. --Michael C. Price ^talk 15:39, 28 November 2008 (UTC)

Good point! Also, thank you for the adjustments to this section. Deadly Nut (talk) 11:11, 30 November 2008 (UTC)

In the section on quantum potential, Cmdulya has put "equating real and imaginary parts". This isn't correct. I've responded by describing what we do as separating R from S (this is the same operation as separating magnitude and phase). I hope this is clearer. To aid clarity to people not familiar with this kind of mathematics, I've written the functions in full instead of abbreviating them (e.g. $R(\mathbf {x} ,t)$ instead of R). I've also added a step (Bohm has this in his original paper) to make it clearer. Deadly Nut (talk) 10:12, 11 December 2008 (UTC)

Determinism

I've made this a separate subject, because there's some really important stuff in here, and it needs to be resolved. Deadly Nut (talk) 09:10, 17 December 2008 (UTC)

I see you have replaced "deterministic" with "causal". Bohm's theory is deterministic since there is no wf collapse; what is your objection to the word? --Michael C. Price ^talk 14:19, 26 November 2008 (UTC)

I was going on SFWild's comment (see above), 'Here again, the author obviously misunderstands (or deliberately misleads?) the reader when he says, broadly, that the Bohmian interpretation is "deterministic." This may be to some extent true in the very early presentations, but after Causality and Chance, and throughout the middle and late period, Bohm is adamant that "causal" is not the same as "deterministic." Any accurate presentation of Bohm's theories needs to address this.' I was taking his words on trust, but I don't know what his credentials are... Deadly Nut (talk) 12:21, 27 November 2008 (UTC)

If is precisely because "causal" is not the same as "deterministic" that the article should describe it as "deterministic". Given the particle's position and momentum at some time it is defined for all other times.--Michael C. Price ^talk 15:39, 28 November 2008 (UTC)

Thank you Deadly Nut for serious improvements to the flow of the article. With regard to Michael Price's comments above, I still take issue with the assertion that the Bohm Interpretation in toto can be described as "deterministic." While it is true that the initial '52 presentation was concieved as a more-or-less deterministic alternative to the a-causal assumptions of the standard model, Bohm is very careful not to use the word "deterministic" to describe his approach. In Chance and Causality he explicitly objects to the notion that his theory is any way a return to Classical deterministic mechanism, and posits a continuum between the two poles of chance and necessity, with neither being absolute. For Bohm, the question of determinism is always dependent on context, so that while the motions of the particles at the quantum level can be seen as being more determined than the standard theory allows (namely by the motions of the sub-quantum hidden variables), those motions are themselves subject to random fluctuations, similar to Brownian motion. Indeed, Bohm himself suggests that there is in fact a deeper kind of Indeterminism than the familiar Heisenberg relations, relating specifically to the chance fluctuations (see Chance and Causality, Chapter 4, Section 2). This is basically the model he persued with Vigier in the sixties. Further, Bohm's notion of causality is considerably richer than the standard definitions of determinism allow (eg Kant), and in Wholeness and the Implicate Order he extends his notion of causality in ways that closely parallel the older Aristotelian notions of formal and final cause, or what he calls "formative causation." It is impossible to reconcile this kind of quasi-teleological thinking with any accepted definition of "determinism." Moreover, insofar as non-locality plays a role, such non-local interactions can be described as causal, but hardly deterministic. In the end, Bohm felt he had to give up even the sobriquet of the "causal interpretation" precisely because it smelled too much of determinism, opting instead for the term "ontological interpretation." While he developed the model in both a causal and stochastic form, it's pretty clear that his own thinking trended away from any sort of deterministic approach. The work with Hiley in the eighties explicitly embraces a stochastic model. See Chapter 9 Section 5 of Undivided Wholeness, and Chapter 14, where he writes "this general approach implies a certain kind of limit to determinism...So ultimately our overall world view is niether absoltuely determinsitic nor aboslutely indeterministic. Rather it implies that these two extremes are abstrations which constitute different views or aspects of the overall set of appearances." While it is true that Bell and others, based on a reading of the early '52 papers, have made the claim that the theory is deterministic, this is not a view held by Bohm himself. Sorry to be long-winded, but I believe this is an important clarification because claiming in an unqualified statement that "the Bohm interpretation is deterministic" is a gross over-simplification and leads to all kinds of confusion, such as is found frequently in the popular literature, where it is sometimes stated that Bohm's theory represents a step backward to the model of Classical determinism and mechanism, which is certainly not the case. Sfwild (talk) 20:01, 12 December 2008 (UTC)

Thanks for this, sfwild. So far, I've read Bohm's 1952 paper, but only parts of the Undivided Universe, so I'd find it tricky to explain all this to a lay reader... I think it needs a statement in the Principles section, and probably some changes to the One-particle formalism section. I'll have a go at the principles if you don't do it first, but I'd appreciate it if you checked the One-particle formalism section to see if it properly reflects the theory. Deadly Nut (talk) 09:25, 14 December 2008 (UTC)

I've written the History section up to about the 1952 paper. Sfwild - would you be able to take it further, describing the development of the theory and some of the more important collaborations? At present, I don't have the knowledge to do this. Deadly Nut (talk) 09:25, 14 December 2008 (UTC)

@Michael C Price - I'm persuaded by the level of detail that sfwild knows what he's talking about here. Also, there are hints in Bohm's 1952 paper that the trajectories might not be exactly what you get by integrating $v=\nabla S/m$. I know you're pressing for determinism here, but sfwild has persuaded me that something more complicated is going on. Deadly Nut (talk) 09:25, 14 December 2008 (UTC)

This subject is too complicated for the introduction, so I've removed this paragraph. Even if the statement is accurate, it doesn't look like a very useful form of determinism! Deadly Nut (talk) 09:25, 14 December 2008 (UTC)

The Bohm interpretation is deterministic in that, if we knew what the current state of a system is, we could predict what its future would be. However, we cannot measure this state beyond the limits imposed by the uncertainty principle, so although the theory is deterministic, we cannot predict an outcome accurately.

I've just been trying to see what the references say. I notice that some people take The Quantum Theory of Motion as the definition (this book calls it the "de Broglie-Bohm theory"). My impression from skimming the book is that it describes the theory as deterministic. Others (including sfwild) take The Undivided Universe (this book calls it the "Causal Interpretation" or "Ontological Interpretation"). Sfwild is clear that Bohm describes a non-deterministic model even when he's not discussing the stochastic model. Both books were published in 1993. Here's an example: the paper arXiv:quant-ph/0206196 describes an experiment that disproves the de Broglie-Bohm theory, and takes as its reference The Quantum Theory of Motion - indeterminism would invalidate the result of this experiment.

What I'd like to do is this:

• Nominate The Undivided Universe as the definition of the theory and point out its indeterminism.
• Describe an "extension" (defined by The Quantum Theory Of Motion) that is deterministic.

Any comments on this plan? Am I right, or have I misunderstood completely? Deadly Nut (talk) 09:09, 17 December 2008 (UTC)

It did occur to me that one of the difficulties in talking about the "Bohm Interpretation" is that there is really no definitive statement as to what that interpretation is. Bohm's interpretation evolves over time and presents a number of different forms or “extensions.” Bohm was always clear that he saw the model as continuous work-in-progress, rather than merely a counter-example to the usual model. Part of the confusion here is that many workers who identify themselves as "Bohmians" or "Bohmites" adhere to a strict "Bell interpretation" of Bohm's work. And if you read Bell and Holland, they are quite clear that their interest is only in the early papers. So I think Deadly Nut hits the question dead-on: Is the "Bohm Interpretation" the interpretation mediated by Bell and which is sometimes expressed as “Bohmian Mechanics” (Durr, Goldstein et al.)? Or is the Bohm Interpretation the interpretation Bohm himself worked on, from ‘52 onwards, sometimes alone and sometimes with collaborators such as Vigier and Hiley, right up until his death in 1992? My vote is obviously for the latter, taking Undivided Wholeness as the most developed or “evolved” form. Either way, clarification is in order, and referencing the workgroups associated with “Bohmian Mechanics” in the extensions seems a reasonable approach. Sfwild (talk) 19:08, 17 December 2008 (UTC)

I don't think it appropriate to make a judgement on what is the definitive version of the theory. Why not just report all the variants? For me the papers Bohm wrote in the 1950s are the clearest. If there are later developments then we can report those as well, but there is no need to lose the earlier stuff. --Michael C. Price ^talk 21:35, 17 December 2008 (UTC)

Thank you, sfwild and Michael C Price, for clarifying this for me. I think Michael is right, that we shouldn't sideline widely used versions of the theory, but I was a bit spooked by the article I took as an example, because it claims to invalidate the theory but (and it doesn't state this explicitly) only if it's deterministic. Anyway, I've added the section Name and Evolution to try to clarify this and to bring it to the reader's attention. I'd have liked to put more detail in the Bohm paragraph, but I'd need to do a bit more research to get it right. Deadly Nut (talk) 09:20, 18 December 2008 (UTC)

I think this is the biggest issue with this article. There definitely needs to be a decision and agreement on whether this article is about Bohmian Mechanics, the theory that happens to share a name with David Bohm, or about the various inter-related interpretations of quantum mechanics presented by David Bohm throughout his career. If this article ends up being about the latter, then I motion to delete it for lack of notability or add it as part of the article about Bohm, then I would suggest we start on an article about Bohmian Mechanics, since that's is a theory that's actually still getting talked about in the literature. Honestly, this article appears (to me) to be extremely deceptive, since "the Bohmian interpretation" is often used as another way of referring to Bohmian mechanics, but this article seems to be about the evolution of David Bohm's personal view. Imagine Einstein had eventually withdrawn his support from the theory of relativity and said that, instead, he thought that spacetime was completely classical and there were just certain optical phenomena caused by some as-yet-unnamed force exerted by certain celestial bodies. We certainly wouldn't want to add, to the Relativity article, the claims that spacetime is classical and that there exists some strange optic force which makes it look like our experiments confirm relativity. We would obviously reject arguments of the form "This article is about Einstein's theory, and I have a quote here from him saying that his theory says this" if the arguer was referring to sources containing Einstein's later position. It looks like the only relevant difference in this case is that the Bohmian Interpretation happens to include the author's name. 67.85.191.28 (talk) 22:32, 22 December 2008 (UTC)

As I understand it, this article is about Bohmian Mechanics - the science in it should apply to any of the theories that carry Bohm's name. However, it was a great surprise to me that Bohm was a heretic in his own religion, and I feel that the reader who is new to the subject should be warned about this. The one major feature that is different between different versions is determinism - I was alerted to the problem by a debate about determinism, and it is apparent to me that there are 'supporters' of both Bohmian Mechanics and the Ontological Interpretation among the contributors to this article; for that reason I feel it is important to reflect the different views in the presentation. Deadly Nut (talk) 07:29, 24 December 2008 (UTC)

I am a little confused by your first sentence. Bohmian Mechanics is the name of a theory. If Bohmian Mechanics is the subject of this article, then the science in it should apply to, and explain, Bohmian Mechanics. The fact that there may have been other theories that bore Bohm's name, or were the product of his research, or garnered his explicit endorsement does not mean they are the subject of this article. I understand that we have advocates of one view and advocates of the other each trying to tailor the article to their respective pet theories. The solution to this problem is not to present two different theories as if they were one either very vague or totally self-contradictory theory (we already have more than enough of this kind of theory in Quantum Mechanics, *coughCopenhagencoughMany-WorldscoughConsistentHistoriescough*). The solution would be to make two articles, one for Bohmian Mechanics and one for Bohm's Ontological Interpretation. (I will withhold my biased and rather snobbish opinions about whether the Ontological Interpretation is notable enough, or dealt with enough in the literature, to justify having its own article). It's a shame that a search for "Bohmian Mechanics" redirects to this *pejorative* of an article, especially since Bohmian Mechanics is such a simple and intuitive theory, explaining it in a wikipedia article should be a walk in the park, not the nightmare it seems to have become. 71.225.239.182 (talk) 04:24, 25 December 2008 (UTC)

I agree too that we don’t want to loose any of the earlier material. In its current form, I think the presentation beginning with the reformulation of S. equation and One Body and Many Body systems works rather well. It gets trickier as the theory develops. For instance, there is undoubtedly a tension between the earlier deterministic-local (100% “causal”) interpretation and the early stochastic model, where the random fluctuations play a greater role. In response to some of the debates around this issue, Bohm would probably say: “well if the formalism of the strictly causal formulation is unappealing, you can always try the stochastic model” (See Undivided Universe, Chapter 3, Section 5, with reference to Stationary States). Then there is the whole question of non-locality, and how to present that aspect of the theory. All commentators agree that non-locality is an important feature of the “Bohm Interpretation” (or whatever you want to call it). But Bohm actually does not talk about non-locality in any of the early papers except perhaps as implied by the non-Classical features of the quantum potential, or in terms of EPR entanglement. The basic model for this period was still presented as Hidden Variables existing within a sub-quantum domain. It’s only when Bell starts promoting the theory in the sixties and seventies that the issue receives attention. Based on the Bell work, the Bohmian research project takes on a whole new life, leading to the Aspect experiments, Bohmian Mechanics, and other things. Based on that work, Bohm comes back to the theory in the eighties and, for the first time, comes to terms with non-locality, so that the overall theory is modified/enriched in ways that were not self-evident in the original papers (See Undivided Universe, Chapter 7). There are other important developments as well. For instance, in the later presentation of the ontological (“post-causal”) formulation, he effectively replaces the earlier notion of the “quantum potential” with the concept of “active information,” so that the guiding wave or force becomes an informational “in-forming” wave which communicates information about the whole system. This is an important feature which is generally overlooked in the literature. And then of course there are concepts or “extensions” such as the Implicate Order, or later, at the level of the second quantization, the “Super-Implicate Order”—all of which have to be addressed somehow.

Enough said! I think the article is coming along so I’ll desist from further commentary for a while. Meanwhile, here’s a link to a very richly documented paper by Olival Freie, a Brazilian scholar, who relates the evolution of Bohm’s thinking during the Brazil period and his collaboration with Vigier:

http://www.fis.ufba.br/dfg/pice/controversia/index_arquivos/Freire-Bohm-HSPS.pdf.

My understanding is that there is also a collection of Vigier’s early papers and presentation of the “Causal Stochastic” interpretation in a collection edited by Stanley Jeffers, where the thing is called the “de Broglie-Bohm-Vigier Interpretation” (just to confuse things a bit further). Sfwild (talk) 18:29, 18 December 2008 (UTC)

Computational Bohmian Dynamics

When I looked at this, the contents looked like extensions to the theory, so I moved it to the Extensions section. Deadly Nut (talk) 13:35, 28 November 2008 (UTC)

Understanding quantum mechanics

I've worked on the Uncertainty Principle, hoping to clarify it a bit. Deadly Nut (talk) 11:11, 30 November 2008 (UTC)

It seems to me that section on the 2-slit experiment requires only a statement of what the experiment is and how the Bohm interpretation describes it. I agree with sfwild's comments about hidden variables, but this is also not the place a reader would expect to find the topic; I have added a comment on hidden variables to the Principles section. Deadly Nut (talk) 12:41, 1 December 2008 (UTC)

The section on Nonlocality seemed a bit awkward here. I've covered these topics by discussing EPR and how Bohm interpretation deals with it. I've also added a section on measurement of spin because it seemed relevant, especially for people new to the subject. Deadly Nut (talk) 10:44, 2 December 2008 (UTC)

Thank you, 70.137.138.141 for the paragraph on indeterminacy. I've tried to simplify the prose without losing the meaning. Deadly Nut (talk) 09:45, 14 December 2008 (UTC)

Introduction

Thank you sfwild for an excellent opening paragraph. I've added links to other Wikipedia articles. Deadly Nut (talk) 08:35, 7 December 2008 (UTC)

Remove advocacy FAQs, replace FAQ with "criticism" section

The FAQ sections basically reads as advocacy for the Bohm interpretation. Since this is a physical theory which is not supported by experimental evidence and on which there is no consensus in the physical community (or rather, the consensus is that the theory is unnecessary and has serious conceptual problems), I believe this is unacceptable in Wikipedia. This is supposed to be an encyclopedia, not an advocacy site for definite stands in scientific disputes. I therefore introduced a "disputed" sign on this section. Please do not remove until such time as the section reflects the general consensus in the physical community. 84.238.81.116 (talk) 18:15, 15 November 2008 (UTC)

More on the FAQ section: I find these two utterly unconvincing and not up to any encyclopaeding or scientific standards:

Q: While orthodox quantum mechanics admits many observables on the Hilbert space that are treated almost equivalently (much like the bases composed of their eigenvectors), Bohm's interpretation requires one to pick a set of "privileged" observables that are treated classically — namely the position. How can this be justified, when there is no experimental reason to think that some observables are fundamentally different from others?

A: Positions may be considered as a natural choice for the selection because positions are most directly measurable. For example, one does not actually measure the "spin" of a particle in the Stern–Gerlach experiment, but instead measures the position of the light flashes on a detector. Often the observed quantities are positions, e.g. of a measuring needle or of the particles making up a computer display. And so there is justification for making position privileged.

"Often" the observed quantities are positions? Yes, and often they are not. And how is the question of whether the result of a measurement is decided by the reading of a position (e.g., of a measuring needle) related to whether position should be considered a "privileged" observable for particles described by quantum mechanics? But this is immaterial - my point is that this argument is easy to reverse: Often the observed quantities are NOT positions, so there is justification for NOT making position privileged. Just as logical, and just as imbecile.

Q: Why should we consider this to be a separate theory when it looks contrived, and gives the same measurable predictions as conventional quantum mechanics?

A: Bohm's original aim was to demonstrate that hidden-variables theories are possible, contrary to the belief (due to von Neumann) that they are not. To accomplish this aim it was necessary that the predictions of the two theories be the same. However, Bohm's hope was that this demonstration could lead to new insights and experiments. Bohm's theory can be extended in ways that cannot even be contemplated in the conventional theory[citation needed], and these extensions may lead to new measurable predictions.

I inserted the "citation needed". One question: can't conventional quantum theory be extended, and hasn't it actually been extended in various ways over the course of the last decades? Another question: Are we to accept Bohm's theory on the grounds that in the future it "may" be extended to lead to measurable predictions? In other news, the Moon "may" turn out to be a green cheese after all. Who, after all, is to say it may not?

A third question: Is this article really up to encyclopaedic standards? I'm going to place an "expert-subject" tag on the whole article - I have half a mind to delete all "advocating" FAQs, but that'd more or less wipe out the whole section. I think this article should contain a clear exposition of the theory (which it also does) together with a clear exposition of the various criticisms raised, in such a way that it neither comes away as advocacy for Bohm's theory nor for the criticism raised against it by Einstein, Bohr, Heisenberg, etc. 84.238.81.116 (talk) 18:57, 15 November 2008 (UTC)

Regarding your objections to the first question, I believe you are correct that position is not privileged. Nevertheless it is a POV I have heard prominent Bohmites (such as Hilley) espouse, and hence is reportable here. Regarding your second question, the contrived nature of the theory is frequently commented on and needs addressing. I believe Bohm made the response much as it appears here in the book, Ghost in the Atom, in an interview with Paul Davies. --Michael C. Price ^talk 02:24, 16 November 2008 (UTC)

There do seem to be duplicated questions; 2 that address the issue of wavefunction collapse and 2 that address the issue of non-locality.--Michael C. Price ^talk 02:53, 16 November 2008 (UTC)

The reformulation of the answer to the second question above is much better, thank you. Regarding the first question, in that case it should rather be formulated in terms of referring the Bohmites' position, accompanied by a reference, rather than just apparently asserted. I mean, instead of " Positions may be considered ..." we should have "Proponents of the Bohm theory contend, that positions may be considered .... <ref>see, e.g., Hilley (somewhere)</ref>". (I'm sorry just to appear with criticism on the talk section, but unfortunately I can't offer to revise this section myself - I simply don't have the time to locate the references). 84.238.81.116 (talk) 13:15, 16 November 2008 (UTC)

The first FAQ - Q: Quantum field theory has been verified experimentally remarkably well. Since locality is essential to quantum field theory, how can it be reconciled with Bohm's interpretation? - is covered by the fifth - Q: The Bohmian models are nonlocal; how can this be reconciled with the principles of special relativity? However, the first question is unfair (Surely QFT is non-local, and you're asking a non-relativistic interpretation to reproduce a relativistic theory) and its response is weak and defensive. I've therefore removed it, moving the references to the fifth question, where the answer is better. Deadly Nut (talk) 09:06, 7 December 2008 (UTC)

I haven't looked at the article yet, but QFT is definitely local due to relativity. Locality is enshrined on the Canonical commutation relations in QFT. Non-relativistic Bohmian QM can get away with being non-local because it is non-relativistic. --Michael C. Price ^talk 17:20, 7 December 2008 (UTC)

My understanding is that although the wave equations of QFT are Lorentz-invariant, there are still non-local effects that disobey the letter but not the spirit of relativity.

Bell's theory shows that with entangled particles, the statistics of the experimental results depend on the orientation of the detectors for both particles. In Bell-test experiments, you can alter the orientation of one detector outside the light cone of the other; you therefore get non-local effects even if the wave equation is Lorentz-invariant. Check out Bell's Theory of local beables (in Speakable and Unspeakable in Quantum Mechanics), where he says (at the start of section 5) "Quantum mechanics, however, gives certain conditions which do not satisfy the locality inequality."

I've combined the two collapse-related questions and collapsed the answers. The last para of the second (about quantum chaos) looked to me more like an extension, so I've moved it to extensions - quantum chaos. HOWEVER, it looks to me like something that BM can't handle and it has no references.

• Please would someone tidy up the section #quantum chaos and give references to work on the subject. Specifically, we need to know how the Bohm interpretation fits in with it. If no one does this in the next couple of weeks, I'll delete it. Deadly Nut (talk) 15:01, 7 December 2008 (UTC)

I've taken this out because it has serious problems:

Q: The Bohmian interpretation has subtle problems with incorporating spin and other concepts of quantum physics: the eigenvalues of the spin are discrete, and therefore contradict rotational invariance unless the probabilistic interpretation is accepted.

A: This criticism is based on the false assumption that the particle position variables in Bohm's equations must carry spin. There are natural variants of the Bohm interpretation in which such problems do not appear. In these, spin is a property of the wave only; the particle variables have no spin in the mathematical formulation.

The question is quite technical, and I don't understand it - classical spin is a vector, and I can't see how it can be rotationally invariant. I know that quantum spin is more complicated than classical spin, but it's still got an axis and I still wouldn't expect it to be rotationally invariant. So if the question is a reasonable one, could we please have a reference to help us understand it? The answer is a disaster, and is the reason I'm taking this out. Anyone can see that position variables don't carry spin - they're position variables... The second sentance says that the Bohm interpretation can be extended to answer the question. If we're talking about a properly thought-out theory it out to answer the question itself without needing to be extended.

If anyone would like to reinstate this question, please:

• give a reference in the question so that people who don't understand it when reading it can follow up the reference and see what it means. If you can, say who asked it.
• explain in the answer either why the question is invalid or how the Bohm interpretation we've got addresses it.

Thanks. Deadly Nut (talk) 09:09, 15 December 2008 (UTC)

Disproven?

The Comparison with experimental data sections says:

The Bohm pilot wave theory has been disproven experimentally. An important prediction of the Bohm theory is that the electron in the ground state of a hydrogen atom is in rest, as the quantum force introduced by Bohm balances the classical electromagnetic potential.

But this seems incorrect. If the forces balances then particle(s) will be merely non-accelerating, not at rest. Surely??? On a general note, it is easy to prove that Bohm's interpretation reproduces all conventional results. Therefore such a simple disproof must be incorrect. --Michael C. Price ^talk 19:58, 18 November 2008 (UTC)

I've tagged it "disputed" for the moment. I'd like to see better links and/or references so that the claim can be analysed. --Michael C. Price ^talk 20:05, 18 November 2008 (UTC)

How could the bound lepton be non-accelerating and moving with relativistiv velocity and still confined to the atom at the same time? As a matter of fact, the prediction of that s-electrons are at rest is a well-known feature of the Bohm-de Broglie theory and is stated already in Bohm's original article from 1952. Direct measurements will yield the same momentum distribution as predicted by quantum mechanics, though, but according to Bohm's theory, direct measurements of momentum will disturb the bound lepton, causing it to move and yield the quantum mechanical result.

Why does the Bohm theory predict that ground state electrons are at rest? Because "the momentum of Bohm's "hidden variable" particle is defined by" the gradient of S, the phase function. But s states are spherically symmetrical, so the phase is constant (QED).

I suggest we remove the "disputed" tag. Agger (talk) 12:17, 19 November 2008 (UTC)

Okay, I think I see the resolution. The muon "disproof" involves relativity and time dilation, yet Bohm's theory only reproduces the non-relativistic Schrodinger equation. Therefore there is no discrepancy, since all we have shown is that relativistic leptons do not obey the Schrodinger wave-equation -- which is hardly surprising. So no problem for Bohm's non-relativistic theory. I have removed the disputed tags and explained this in the article. --Michael C. Price ^talk 13:21, 19 November 2008 (UTC)

Except that relativity is not involved in the claim that s state electrons are at rest and relatvistic wave functions as used in the relativistic Bohm theory also have spherical symmetry. So there is still a big problem for the Bohm theory: Relativistic or non-relativistic, it predicts that ground state electrons are at rest, and the time dilation in muon decay experiments show they are not. —Preceding unsigned comment added by 80.163.95.210 (talk) 14:52, 19 November 2008 (UTC)

No, your logic is wrong. There is no problem because Bohm did not construct a relativistic theory. Therefore there is no theory to refute. If stationary electrons in the s state are a prediction of the as yet non-existent theory then there would be a problem; but since such a theory does not exist yet it is not a problem.

So the question is: would a relativistic Bohm theory predict stationary electrons in the ground state orbital? Not whether the ground state orbitals are spherically symmetric (of which there is no dispute).

I note you claim that there is a relativistic Bohm theory. Where is the calculation showing that ground state electrons are stationary in it? (Such a demonstration exists in the 1952 papers -- but they are non-relativistic.)--Michael C. Price ^talk 19:20, 19 November 2008 (UTC)

I posted some general criticisms on this discussion page last year, but if anything the article has become muddier. What is needed, before getting into a lot of the minutia or later experimental proofs or disproofs (this last section is especially problematic), is a clear exposition of Bohm’s Hidden-Variable-Causal-Ontological Interpretation(s), including the evolution/elaboration of that interpretation in its historical context. A more direct approach would be helpful to the casual reader who simply wants to know what the Bohmian interpretation is all about, and how it differs from other interpretations. Sfwild (talk) 19:26, 27 November 2008 (UTC)

New Year’s Clean-up?

Deadly Nut, M. Price, et. al:

In the spirit of Bohmian Dialogue and new year's resolve, I would like to propose that we remove some of the more disputed/problematic sections of article to talk page, and either rework them from there or delete altogether.

Below are some suggestions for what I believe should be at least temporarily removed from body of the article:

“Name and Evolution.” Reasons: section needs to be tightened and recast as “history and development of the theory” or something like that. Material here can perhaps be combined with material from “History” and “FAQ” sections for a short narrative providing the historical context of the interpretation, perhaps at the end of article.

“Results.” Most of this material seems frankly superfluous. Besides, how can an interpretation have “results”? Inclination here is to delete altogether.

“Comparison with Experimental Data.” This section reads like a chat page with no references to or meaningful elucidation of the theory. No-one will be any less wise if it is deleted altogether.

“Two Slit Experiment.” Everything which is said here follows from the Principles section. Should be moved to that section or deleted.

“Measuring Spin and Polarization.” None of this is very pertinent to Bohm’s interpretation. Strong inclination to delete.

“History” Some good stuff here, but seems out of place. Probably belongs at beginning of article as “Background” or combined with “Name and Evolution section” in a larger explanatory narrative.

“Extensions.“ I would be in favor of eliminating all of these so-called extensions until there is consensus on the main body of the article. Stuff on Valenteni is very derivative. Comparison with Many Worlds is not the point of the article. Quantum Trajectory stuff is either its own article or a sub-heading of a possible “Bohmian Mechanics” article. Ditto for Quantum Chaos stuff. Regarding relativistic extensions, if we started to go in that direction there would be no end in sight!

“Frequently Asked Questions.” There are some real insights here, esp. as relating to non-locality and Bell’s influence (thank you M. Price), though the presentation needs serious work. Consider removing from body of text to talk section or perhaps incorporate in a more straightforward form into other parts of the article, or even reworking into a section on Bell/Non-locality?

Assuming the above deletions/rearrangements, that would leave the article with the following flow:

Introduction (Background?) Principles Reformulating the Schroedinger Equation One Body Formalism Many Body Formalism Indeterminism/Relation to H. Indeterminacy Relations EPR (Non-Locality) Note on Historical Development

Sfwild (talk) 08:04, 8 January 2009 (UTC)