Talk:De Broglie–Bohm theory/Archive 3

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Archive 3

Why in the world was this moved to de Broglie-Bohm theory?

It's such a bad name, and it clearly goes against WP:COMMONNAME. Everyone refers to the Bohm interpretation as the Bohm interpretation (and sometimes Bohmian mechanics). I'd skim over the previous debate, but it just way too massive. The article on Feynman diagrams is at Feynman diagram, not at Feynman-Stückelberg diagram even though the last one is the more "historically accurate". Headbomb {^ταλκ_{κοντριβς} – WP Physics} 06:45, 16 November 2009 (UTC)

The main problem (in my mind) is that "Bohm interpretation" confuses "implicate order" with Bohm's 1952 presentation. They need separate articles. The confusion had blurred things repeatedly in the past.--Michael C. Price ^talk 10:40, 16 November 2009 (UTC)

Not sure how to point to another point in the talk page, so here it is repeated:

Just passing through. As I was doing a Web of Knowledge search anyway, I plugged "Bohmian interpretation" and "Bohmian mechanics" into it. The former returns 19 hits, while the latter manages 209. "Pilot wave" only polls 109, and "de Broglie-Bohm" nets 251 (or, suspiciously, 42 if "... theory" is appended). Regarding Zicovich's point about a recent book, I'd have thought that use (or disuse) in the scientific literature should trump this. Anyway, good luck solving this one! --PLUMBAGO 11:31, 27 October 2009 (UTC)

From my reading of WP:COMMONNAME (thanks for the link), this is the exact evidence needed to argue for the name change and that the change was correct. Please explain how the most commonly cited terms in the literature should be ignored according to that policy. Other than the former version of this article, I have never heard anyone refer to it as the Bohm interpretation. I have seen both de Broglie-Bohm and Bohmian mechanics used. While my personal preference is the latter, it was very reasonable to go with the former. Saying "everyone refers" without citations is vague and not in line with Wikipedia standards. Cite some prominent sources that call it this, if you really want to engage in this argument.Jostylr (talk) 12:14, 16 November 2009 (UTC)

At the very least it should be de Broglie-Bohm interpretation. I'll get some textbooks citations for the Bohm interpretation thing. Headbomb {^ταλκ_{κοντριβς} – WP Physics} 19:36, 16 November 2009 (UTC)

Jostlyrn makes a number of points which I would like to respond to anon, but regarding the name change I think there is a degree of consensus that De Broglie-Bohm Theory (or Interpretation) is better than the awkward “Bohm Interpretation” and, for different reasons, “Bohmian Mechanics.” I did some touring around the German version of Wikipedia that they too changed the article and redirected from Bohmsche Mechanik to Die De Broglie-Bohm Theorie with some interesting discussion which to some extent parallels the talk going on here. FYI here is the table of contents of that article (which is also written from the POV of Bohmian Mechanics Formalism, but includes a rather elegant presentation of Bohm’s quantum potential approach ):

1. History 2. Formalism

 2.1 Quantum Equilibrium Hypothesis
 2.2 Characteristics of Bohmian Trajectories
 2.3 Spin in Bohmian Mechanics

3. Important Characteristics

 3.1 Resolution of the Quantum Measurement Problem
 3.2 Status of Observables and Contextuality
 3.3 Non-Locality
 3.4 Determinism
 3.5 The Superfluousness of “Complementarity”

4. Schools of the De Broglie Bohm Theory

 4.1 The Quantum Potential

5 Criticisms of the De-Broglie-Bohm Theory

Sfwild (talk) 23:39, 16 November 2009 (UTC)

More Bell

First off, this page is not about Bell and probably has too long a description of it. There's already a wiki for it. Second, and more importantly, Bell did NOT prove that non-locality is necessary for a theory that's consistent with QM. As I already pointed out in my edit comments, the many-worlds interpretation is completely and fully consistent with the predictions of QM in the Copenhagen interpretation, but is completely local. It's compatible with Bell because Bell assumes two things: locality AND "reality", or contextuality as it's sometimes called. On top of that, relativistic quantum field theory, the best tested and most accurate scientific theory in the history of the human race, is absolutely local and quantum. There are no hidden variables and no pilot wave anywhere in its description, and relativity guarantees that there cannot be without violating causality. Waleswatcher (talk) 03:06, 18 November 2009 (UTC)

Correct. "Contextuality" also known as Counterfactual definiteness if you want the link. --Michael C. Price ^talk 07:25, 18 November 2009 (UTC)

First of all, let me say that I agree that the de Broglie Bohm's page is not the right place for a detailed discussion on Bell's theorem; perhaps, the best is to keep the Bell talk on this page to a minimum. Second, let me warn that this is a messy subject for Wikipedia. The trouble is that 99.9% of the literature on this subject is wrong (to make it worse, different parts of the literature are wrong for different reasons). Luckily, the tiny amount of good literature on this subject includes... Bell's original papers (often cited, but rarely read by those who cite it). The best of Bell's articles on this subject is the last article he wrote on this, it is called "La nouvelle cuisine" (it is the last article of his book, "Speakable and Unspeakable in Quantum Mechanics", but it only appears in the second edition; and, as far as I know, it is not available on the Web. I do have a scanned pdf, in case anyone is interested).

Now, let me make some clarifications (I'm not suggesting anything for the article, I'm just doing this for the benefit of Waleswatcher and Price).

First, there are several statements (some of them are more well-defined than the others) one can make about a theory, which are often confused with one another, but are all mutually non equivalent:

(a) relativistic/Lorentz invariant;

(b) local (in the sense of Bell);

(c) forbids super-luminal signalling;

(d) observables supported by spacelike separated regions of spacetime commute.

property (a) is more delicated than most people realize. One can actually make finer distinctions:

(a1) consistent with the empirical predictions of relativity ("observationally Lorentz invariant");

(a2) absence of any foliation-like structure in the formulation of the theory.

(actually, full Lorentz invariance is a trickier concept than most people realize, since any theory can be made Lorentz invariant simply by adding more structure to spacetime and letting the Lorentz group act also on the additional structure).

Relativistic Bohmian theories satisfy property (a1), but not property (a2) (and, yet, one could regard them as fully Lorentz invariant). They do not satisfy property (b), but they do satisfy properties (c) and (d). The theory rGRWf (the relativistic GRW theory with flash ontology, see http://arxiv.org/abs/quant-ph/0406094) satisfy both (a1) and (a2), do not satisfy (b), but satisfies (c) and (d).

Now, what did Bell prove? Bell has proven that no theory sharing some of the empirical predictions of quantum theory can satisfy (b), i.e., be local (but there are a couple of caveats to this statement, which I will clarify in a moment). This was Bell's position on this subject and he was right. The typical physicist would say that Bell has proven that one has to either abandon locality or "reality" --- but what they mean by "reality" is usually (not very clear and) not the same that Waleswatcher means. Actually, Waleswatcher is more right about what he says than the typical physicist. The typical physicist is wrong (other types of confusions shared by many physicists: that Bell's mistake was to use "classical probability" instead of "Quantum probability"; yet another type of confusion is that Bell assumed "counterfactual definiteness", which is also wrong. By the way, counterfactual definiteness is not the same thing as contextuality).

As I promised, here are the caveats to Bell's statement:

(1) the "no-conspiracy caveat". This is made explicit in Bell's later articles. This is the assumption that the random number generator that chooses the settings of Alice and Bob's apparatuses is stochastically independent of the physical processes that go on at the source, during the preparation of the entangled state.

(2) the "definite outcomes caveat". This is not so explicit in Bell's articles and is related to Waleswatcher complaint. It is the assumption that the region of spacetime supporting the outcome of the experiment contains a well-defined single outcome. This assumption is violated in theories with a Many-Worlds character.

Is MWI local (in the sense of Bell)? For typical formulations of MWI, the question does not even make sense, since such formulations have no local beables at all in their formulation. Recent reformulations of MWI:

http://arxiv.org/abs/0903.2211

do have local beables, but are nevertheless non local.Dvtausk (talk) 14:48, 18 November 2009 (UTC)

A quick comment on that. To ask whether MW is "local" one has to define first define local (which is much trickier than it might seem). One way is this: consider a relativistic quantum field theory on a rigid, fixed spacetime background (i.e. this definition won't apply in quantum gravity). If the lagrangian for that QFT is local, meaning specifically it can be written as an integral of a density where all the fields in the density are inserted at the same spacetime point, there are only a finite number of derivatives, it's quantized in the usual way (operators commute outside the lightcone), and the theory is well-defined (no ghosts etc.), then we can say that its wave function (defined by the Feynman path integral) evolves according to a local (and causal) Schrodinger equation. The only thing that could possibly make it non-local is some additional ingredient beyond the path integral like a Copenhagen-style collapse postulate or a Bohmian quantum potential. Therefore if by MW we simply mean that the theory evolves according to the Schrodinger equation period, standard relativistic QFT (of the type that appears to describe the particle physics of our world with exceptional accuracy) in the MW interpretation is in fact local.

I should add that this is probably the definition of "local" (more precisely, a sufficient but not necessary condition for locality) that's most widely used by physicists.

If you want to see specifically how locality can be consistent with QM and entanglement, solve the SE for an EPR-type experiment, including pointer variable terms to represent the measuring devices. You'll see that even if every interaction is absolutely local so that measurements on one particle have absolutely no effect on the wave function of the other, the results are still completely consistent with QM in the Copenhagen interpretation. Waleswatcher (talk) 16:45, 18 November 2009 (UTC)

Yes, does look like contextuality is not the same as CFD. (I have the 2nd edition of Bell, so I must read the chapter mentioned.)

I would tend to go with Waleswatcher's notion of locality (so MWI would be local, as would non-relativistic de Broglie-Bohm insofar as that means anything). I would drop the caveat about ghosts (assuming these are Faddeev-Popov ghosts), since these QFT theories are still well defined and covariant.--Michael C. Price ^talk 17:39, 18 November 2009 (UTC)

Indeed, the definition of locality is tricky. For me (and for Bell), "locality" means what is defined in "La Nouvelle Cuisine". After thinking about the subject for a couple of years, I got to the conclusion that it is really the "right" definition of locality --- by the way, I came up with a sketch of the same definition by myself, independently of Bell, so Bell's definition seems really natural to me (in the sense that it is an adequate mathematical formalization of the informal idea that the consequences of an event are inside its future cone and its causes in its past cone). I think that any serious definition of locality has to be formulated in terms of local beables (http://en.wikipedia.org/wiki/User:Tnorsen/Sandbox/Beables) and that any serious physical theory must have some local beables in its formulation, even if just those necessary to encode macroscopic configurations of the familiar objects around us (and even if the theory happens to have a Many-Worlds character). But I don't want to engage in a discussion about what is meant by a "theory" or by "locality", since that would take forever.Dvtausk (talk) 17:46, 18 November 2009 (UTC)

You won't find the word "contextuality" in "La Nouvelle Cuisine", in fact I think the word never appears in Bell's book (even though the concept does, in the very first article, where Bell explains what is wrong with several "no go" theorems, such as Von Neumann's, Gleason's, etc). In the jargon of "hidden variables experts", a non contextual hidden variable theory is a theory in which all quantum observables have well-defined values all the time, which are revealed by the so called measurements and are independent of the experimental context used to make the "measurement". The existence of a non contextual hidden variable theory implies the existence of a value map $A\to v(A)$ that assigns to each self-adjoint operator $A$, an element $v(A)$ of its spectrum, in such a way that $v(A+B)=v(A)+v(B)$ and $v(AB)=v(A)v(B)$, for any pair of commuting self-adjoint operators $A$, $B$. The several "no go" theorems concerning hidden variables (Gleason's, Kochen-Specker's, etc) are all proofs of the impossibility of such a value map (and thus of the impossibility of non contextual hidden variables); also Bell's argument can be used to rule out non contextual hidden variables. Counter-factual definiteness, on the other hand, is related to the possibility of discussing "what would have happenned if, instead of performing experiment A, we had performed experiment B". There is a lot about that in the works of H. Stapp.Dvtausk (talk) 17:59, 18 November 2009 (UTC)

Loss of clarity and correctness

I'm concerned that the article is degrading. For instance the current section on MWI is incorrect. It says Bell "responded" to Everett's criticism. Bell did not respond (look at the sources in Bell's article - he doesn't cite the correct Everett source). The point Bell is making is about a completely different problem (as he sees it) with MWI. This issue was spelt out much more clearly in the old version of the article, which I reproduce below:

Q: Hugh Everett says that Bohm's particles are not observable entities, but surely they are - what hits the detectors and causes flashes?

A: Both Everett and Bohm treat the wavefunction as a complex-valued but real field. Everett's Many-worlds interpretation is an attempt to demonstrate that the wavefunction alone is sufficient to account for all our observations. When we see the particle detectors flash or hear the click of a Geiger counter or whatever then Everett interprets this as our wavefunction responding to changes in the detector's wavefunction, which is responding in turn to the passage of another wavefunction (which we think of as a "particle", but is actually just another wave-packet). But no particle in the Bohm sense of having a defined position and velocity is involved. For this reason Everett sometimes referred to his approach as the "wave interpretation". Talking of Bohm's approach, Everett says:

“ Our main criticism of this view is on the grounds of simplicity - if one desires to hold the view that $\psi$ is a real field then the associated particle is superfluous since, as we have endeavored to illustrate, the pure wave theory is itself satisfactory. ”

In this view, then, the Bohm particles are unobservable entities, similar to, and equally as unnecessary as, for example, the luminiferous ether was found to be unnecessary in special relativity. We can remove the particles from Bohm's theory and still account for all our observations. The unobservability of the "hidden particles" stems from an asymmetry in the causal structure of the theory; the wavefunction influences the position and velocity of the hidden variables (i.e. the particles are influenced by a "force" exerted by the wavefunction), but the hidden variables do not influence the time development of the wavefunction (i.e. there is no analogue of Newton's third law -- the particles do not react back onto the wavefunction) Thus the particles do not make their presence known in any way; as the theory says, they are hidden.

The Q & A format was much clearer and was correct. The current format leads to confusion and is probably why it is factually incorrect. I suggest a cut-and-paste restoration of the old Q&A section. --Michael C. Price ^talk 21:58, 18 November 2009 (UTC)

PS the solution to the problem is not to delete the existing section in its entirety; Everett's critique is correctly sourced. I have restored Everett's material to the article, although I think the best solution is to restore the entire original Q&A section.--Michael C. Price ^talk 12:48, 19 November 2009 (UTC)

I think many of us would argue Everett misunderstands Bohm's viewpoint and perhaps Bell and the rest of us do not understand Everett. I tried to give citations from both camps (Wikepedia cares about literature, not correctness), but I think the main resolution is to remove this section (which I tried to do) since this section is not important to dBBt itself. If you feel strongly that this should be somewhere, maybe you can get it on the page on the interpretations of quantum mechanics. If you really want it here, try rewriting the Q&A version as a normal section, put it up, and we shall see what it says. But just giving Everett's interpretation of dBBt with no rebuttal in line with dBBt literature is not NPOV. Again, I say we leave it out as I doubt agreement can be found and this issues is minor. In particular, most literature in dBBt would say that the particles are not only not "hidden" but are in fact the only things actually seen in experiments. Rather the opposite of "hidden".

The Bell quote is accurately sourced too. His article may be citing the wrong paper, but we are not here to adjudicate on the correctness of literature. We simply use it as is. And simply because Everett made these statements, that does not demonstrate relevancy. Please consider removal.

As for the Q&A, Wikipedia discourages such sections Wikipedia:Trivia sections. They want subject matter organized by topics. It is okay to have it if there is no other way to present it, but I think there is and that is what I have done. Also, Q&A can much more easily lead to POV problems as this shows very well.

As for the page degrading, give a list of problems and sections. From what I can tell there is a lot of disagreements about stuff from a MWI perspective going on here. Particularly, the section just removed and Bell's theorem. I would like to get the Bell stuff made neutral and move most of the disagreement to the Bell's theorem page. What other problems are there? I know Sfwild objects to what seems to be a Bohmian slant on dBBT, but I think the recent literature supports the current presentation and that the facts are not in question, according to the literature. Waleswatcher made the blanket claim of factual inaccuracies throughout the page, but so far has only cited the Bell stuff (which is disputable). Please either correct any of the other problems or cite them here.

Jostylr (talk) 12:59, 19 November 2009 (UTC)

I picked the Everett example because it was one I was most familar with and was absolutely sure of my facts. Bell is not responding to Everett's critique. He's citing the wrong source for that, even if it wasn't obvious from the text. I'll grant that it isn't obvious from the text unless you really understand MWI. I thought the Q&A version made a pretty could job of explaining this, so I won't repeat it here since you can read just a few paragraphs above (no doubt it can also be improved). The reason why there is no response from the Bohmites in the current version is simply because there has never been any published response, AFAIK. (See also earlier discussions on this on this talk page: [1] and [2].)

Finally, just to be clear on one thing. Where you say:

The Bell quote is accurately sourced too. His article may be citing the wrong paper, but we are not here to adjudicate on the correctness of literature.

Yes, the Bell quote is accurately sourced, just as the Everett quote is. What was incorrect original research was where these two quotes were linked with the word "responded" in the statement:

Bell responded to this criticism by noting that ....

Since it wasn't a response, it was incorrect.

Perhaps Bell's criticism of MWI should appear in the MWI article, but not here.

--Michael C. Price ^talk 16:31, 19 November 2009 (UTC)

Understood about the response. It was certainly written as if it was Bell responding to the quote and that was wrong. It was not wrong that it is, in fact, a valid response to the criticism so the mistake was not an absolute disaster. But it sounds like there might be a tradition in wiki of citing criticisms, but not responding to them. So the current minimal version is now fine with me, but it is out of place so a criticism section might be in order.

I also disagree that the Q&A is clearer. I am reading it and I am not sure what thesis the A is supporting. It certainly does not represent the Bohmian point of view and would lead a casual reader to get very confused about the importance of the particle positions. It also seems to be expanding and interpreting Everett's quote which might be original research.

I am supportive of a criticism section. I think it should be mainly quotes from critics and very little in the way of interpretations or responses. So it would be different than the Q&A. Again, the content of the theory as presented in the A should be in the article itself, as I understand the Wiki guidelines. The format itself might be good pedagogy, but it is also prone to POV and original research.

Jostylr (talk) 03:00, 20 November 2009 (UTC)

You say I also disagree that the Q&A is clearer. I am reading it and I am not sure what thesis the A is supporting. as if that is a problem - it isn't, it is a benefit, since it doesn't support any thesis. It is an explanation or a rephrasing, which is perfectly admissiable under WP:OR. Yes, it is expanding and interpreting Everett's quote.which is exactly what it should be doing, not just pushing the Bohmite POV. --Michael C. Price ^talk 03:46, 20 November 2009 (UTC)

From the quote of what Everett said, there is no mention about the unobservability of the particles. His quote is very much saying "Since I just showed all we need is the wavefunction, then extra stuff is superfluous." He is not arguing that the particles in dBBt are unobservable, at least not from that quote and it sounds like to me that A is written as if that quote is supposed to be the basis for what follows. Everett's statement quoted here sounds like "We have two perfectly good theories. One theory has wave. One theory has wave+particle. So it seems the first is simpler." This has nothing to do with whether the positions of particles in dBBt are observable; in fact, they are and they also have no back action.

Unless this source or others discuss the unobservability and no back action in connection with Everett's statement, it certainly seems like OR to me. As I said, I think the quote should stand for itself. I imagine paraphrasing is used largely to avoid lengthy quotes or overly technical ones. Here is a beautifully succinct quote which states Everett's position in an easy to read way. It does not seem to me to need any interpretation from others.Jostylr (talk) 16:33, 20 November 2009 (UTC)

No, quotes do not always stand by themselves; if they did then Wikipedia would just be a mass of quotes, which it isn't. The quote is in the middle of a 100+ page thesis, so I think a bit of explanation is required. The mere fact that you think that He is not arguing that the particles in dBBt are unobservable shows that further explanation is required, since that is what Everett is arguing. --Michael C. Price ^talk 18:43, 20 November 2009 (UTC)

So section VI is entirely devoted to dBBt and why its particles are unobservable? Or is it the whole thesis? I guess I need to go and obtain that book. Is that quote on any particular page?Jostylr (talk) 20:38, 20 November 2009 (UTC)

Page 112. Section VI critiques non-MWI interpretations generally. There is a bit of preamble to the quote about Bohm's hidden variables, but nothing that would be new to you. But from Everett's POV the wavefunction is everything and all experiences flow from it (for this you have to read much of his thesis). If the particles don't act on the wavefunction, then they are unobservable by definition, since all observations can be deduced from the wavefunction alone. Think about it from Everett's POV; observations leave their mark on the wavefunction - the particle's don't, therefore they aren't observed. --Michael C. Price ^talk 21:49, 20 November 2009 (UTC)

I think that a section with some quotes from people criticizing de Broglie-Bohm is needed in this article; and, certainly, Everett's quote should be among those. Until someone finds time to write a decent criticism section, I think we should keep the small section that Price wrote.

Concerning what Everett meant in that sentence: it seems obvious to me that what Everett meant is "there is a viable theory with just a wave function (MWI), and such theory is simpler --- and therefore better --- than the theory with wave function and particles (dBB)". It seems to me highly unlikely that Everett meant that dBB particles are not observable. But, I haven't read the entire article from which the Everett quote was taken, so I cannot be sure.

I think that if Price wants to support the view that Everett meant "dBB particles are not observable", then he should do so by presenting more Everett quotes supporting that conclusion. What Price (still) does not seem to understand, is that the wave function has one role in MWI and a very different role in dBB. In MWI, it describes all of physical reality, including the observers. In dBB, it is merely a particle mover, while the physical reality and the observers are described by the position of their particles. The particles would indeed be unobservable in the chimeric (never proposed by anyone) theory in which the wave function plays the same role it plays in MWI, but there are also particles moving around.

David Bohm wasn't that good a expositor, his 1952 articles contain some misleading passages... but, it is not impossible to understand him, if you read him carefully. In any case, the expositors of the theory that came after Bohm (like Bell, Dürr et al.) did a much better job than Bohm's, making perfectly clear what the theory is.Dvtausk (talk) 22:28, 20 November 2009 (UTC)

It seems to me highly unlikely that Everett meant that dBB particles are not observable. is more evidence that the full explanation is required here. Also, let me add, that I did not write the full Q&A section -- the ether analogy was added by someone else, but I think the analogy is perfect. --Michael C. Price ^talk 03:53, 21 November 2009 (UTC)

The ether analogy is not bad. But to write down a quote from Everett saying X and then "explaining" that he actually meant Y is very bad, if you cannot present some serious back up to the claim that he meant Y by presenting a few more Everett quotes. You might even happen to be right that Everett meant Y, but if you have to read, say, 100 pages of Everett's writings in order to get to that conclusion, then it means that discovering Everett's opinion on the subject requires a highly non trivial interpretation work, and it is not unlikely that different readers of Everett might reach different conclusions about what Everett meant. So, Wikipedia is not the right place for your original research about Everett's opinions (even if it happens to be high quality original research).Dvtausk (talk) 13:59, 21 November 2009 (UTC)

Whether this is original research is debatable. WP:OR says Carefully summarizing or rephrasing source material without changing its meaning is not synthesis—it is good editing. But this is exactly that, a rephrasing. Whether it is a rephrasing of just one paragraph or 100+ pages doesn't matter. I'm trying to explain what Everett meant, not draw some new conclusion applied to a situation the original author hadn't envisaged. And one way to rephrase or explain something is by the use of analogies. The aether is such an analogy; Einstein identified it as superfluous, what that meant was that it was unobservable. Same with the particles; Everett identifies them as superfluous and what that means is that they are unobservable -- in Everett's view. --Michael C. Price ^talk 21:29, 21 November 2009 (UTC)

I'm not arguing against the use of analogies. I'm arguing against presenting a quote in which the author says X and then claiming that the author actually meant Y. Changing the meaning of the sentence is exactly what you are proposing. To make it worse, you are not even trying to support your view of what Everett's intention with that sentence was, by presenting more quotes. Studying the work of an author and then drawing conclusions of the sort "the author meant Y when he wrote X" is the kind of thing that Historians, Sociologists and Philosophers sometimes publish as their original research. It is not appropriate for Wikipedia. If you are an expert on interpreting Everett's intentions, I suggest you write an authored article about that, get it published, then come back here and cite it: "According to Price (see ...), in that quote Everett's meant that dBB particles are not observable".Dvtausk (talk) 22:28, 21 November 2009 (UTC)

You say I'm not arguing against the use of analogies. but it seems to me that that is exactly what you are doing. Analogies are only ever used to show that superficially disparate positions or arguments are actually the same. I'm arguing that Everett is saying Y when he says X and the aether analogy shows this. Where is the flaw in the analogy? --Michael C. Price ^talk 23:18, 21 November 2009 (UTC)

I agree that it is not such a bad idea to use the ether to give the reader an example of something in Physics that was regarded as superfluous (in the same way that, in Everett's view, particles are superfluous). But the ether analogy really doesn't help at all in showing that Everett believed that dBB particles are unobservable. Yeah, it is true that, relatively to the theory "special relativity + ether" the ether is not observable. But no conclusion about observability of dBB particles or about Everett's opinion concerning the observability of dBB particles follows from that. This conversation is just making me more skeptical about your ability to correctly understand Everett. When you talk about showing that "superficially disparate positions or arguments are actually the same", it makes me think that you see logical connections where none exist (i.e., the connection between what Everett actually wrote and the unobservability of particles in dBB). It is possible that Everett sees the same non existent logical connections that you do, but I have no reason to believe in that.Dvtausk (talk) 00:53, 22 November 2009 (UTC)

If, within the framework of MWI, my inference is incorrect then I'll accept that Everett did not see the same inference. But if my inference is correct then you agree that Everett saw the same inference? So it boils down to whether my inference is correct or not, do you agree? --Michael C. Price ^talk 06:14, 22 November 2009 (UTC)

PS I see that Craig Callender in "The Redundancy Argument Against Bohmian Mechanics" [3] seizes upon exactly the same quote from Everett and argues that the only rescue for Bohm is to drop Bohm's 1952 assumption (shared by Bell) that the wavefunction is ontologically real. He also talks about Everett's "wavefunction cats" and Bohm's "particle-cats", in the same way as the Q&A text was doing about Geiger counters. --Michael C. Price ^talk 06:43, 22 November 2009 (UTC)

PPS once you start looking you find this argument everywhere. E.g "Solving the measurement problem: de Broglie-Bohm loses out to Everett" by Harvey R Brown and David Wallace (Foundations of Physics 35 (2005), pp. 517-540) Abstract: "The quantum theory of de Broglie and Bohm solves the measurement problem, but the hypothetical corpuscles play no role in the argument. The solution finds a more natural home in the Everett interpretation." [4] --Michael C. Price ^talk 07:07, 22 November 2009 (UTC)

The validity of the inference "superfluous ==> non observable" does not depend on any "framework"; it is invalid, period (maybe, what you have in mind, is that particles are unobservable in a universe governed by the chimeric theory in which the role of the wave function is the same as it is in MWI, but there are also particles moving around, with no back reaction to the wave function. If that is your point, then you are right, but that is irrelevant to dBB, as dBB is not such chimeric theory). But I'm tired of trying to help you understand that. You simply don't get (or prefers not to understand) what the role of the wave function in dBB is; it is merely a particle mover (in the view of Bohm, for instance, it is a physical field that makes the particles deviate from their classical trajectories; it doesn't follow from that that, for instance, the matter and the observers are "made of" wave functions, or that the state of mind of observers is to be found in the wave function). The sad thing is that the Everett quote doesn't make such a bad point, while the claim that particles in a dBB universe are not observable (which is the claim that you believe Everett believes in) is trivially wrong and incredibly ignorant. Yeah, sure, finding articles making wrong statements about dBB is very easy; takes a few seconds of google search.

But, if you know about published sources claiming that dBB particles are not observable (or claiming that that is Everett's opinion), why have you been wasting my time with this discussion? Simply expand the criticism section of this article by adding new quotes (attributing them to the corresponding sources, and giving the references). I'm against using Wikipedia to put words in Everett's mouth, but if someone else has published an article doing that, then it is ok to cite that article.Dvtausk (talk) 19:36, 22 November 2009 (UTC)

Your repeated assertions about what I "don't get" are incorrect, although no doubt you will repeat them again.

I shall follow your advice and expand the criticism section with the new material, although I give you fair warning that I shall not be sticking to pure quotations (neither does the rest of the article, I note). We shall have to disagree as to whether the material is correct; happily that is irrelevant to Wikipedia.

--Michael C. Price ^talk 19:45, 22 November 2009 (UTC)

Sure, you don't have to stick to pure quotations. But that doesn't mean that you can attribute to a source stuff that the source does not support (like you were trying to do with Everett). If you do that, I'll complain.Dvtausk (talk) 20:00, 22 November 2009 (UTC)

Of course - except that the source does support the explanation given, and the other sources support that interpretation as well.--Michael C. Price ^talk 20:07, 22 November 2009 (UTC)

Well, a Wikipedia article cannot be about your opinion about what a source supports (even if your opinion happens to be right). Imagine, if lots of people believing to be interpretation experts start to write on Wikipedia their opinions about what the hidden intentions of the authors of their sources are.Dvtausk (talk) 21:24, 22 November 2009 (UTC)

It can be about anyone's opinions if they are reflected in the literature. Plenty of sources now. --Michael C. Price ^talk 22:08, 22 November 2009 (UTC)

Let us not make Everett look stupid. If you want to keep the claim of unobservability of dBB particles, attribute it to an author that clearly supports it.Dvtausk (talk) 23:55, 22 November 2009 (UTC)

I am still aiming to tidy up the history section and respond in a more substantive way to some of Jostylr’s comments about what an article on De-Broglie Bohm Theory should be about, but it seems to me that some of the confusion and bickering between Michael and Dvtausk here is due to a basic lack of clarity as to who is saying what. For instance, when Everett says the particles are hidden in Bohm, he is in fact referring to Bohm’s original ’52 presentation. They are “hidden” in the sense that they are unobservable by detection experiments, and “hidden” as well because they stand outside of the wave function. Remember that for Bohm the whole point was to show that alternative interpretation involving extra parameters and forces beyond the formalism of the Copenhagen Interpretation could be possible, thereby rebutting the then-held assumption that the quantum formalism developed by Bohr and Heisenberg was the most “complete” possible interpretation. In this sense, Bohm and Everett both adhere to the standard vocabulary which distinguishes between actual real particles (which may or may not exist, depending on the viewpoint) and the observables which are the result of our experiments.

The basic difference between Bohm and, say, Schrodinger is that in addition to the wave function (which is considered a real field) there are also really such things as particles, which have a definite position and momentum at all times. Nothing amiss so far. Then what happens is Bell comes along and says “look guys, the particles aren’t hidden after all!” and that it’s all about particle positions. That’s fine too, as far as it goes, and Bell’s main point is to express a view that any theory should be about the real particles—the beables—in a non-Romantic way, without any mysterious wave function collapse or twisted references to the observer’s consciousness or anything like that. It’s a fair viewpoint. But then, after that, the Bohmian Mechanics folk come along and they develop a whole new kind of shop talk to talk about the status of operators and observables and measurement along with things the “conditional wave function” and so forth (reproduced in the current form of the article) which further obfuscates the discourse. Dvtausk’s insistence that the particles are observable comes out of that approach too, though for Bohm the particles were both hidden and unobserved (but certainly not superfluous).

As a practical matter I think it’s ok to represent the Everett quote in a criticism section, as Michael has proposed, along with any other quotes backing that up. But keep in mind that most of these criticisms from the perspective of MWI (and there are many) will be referring to Bohm and not the BM formalism reproduced here. For Bohm’s own reply there is a lengthy section in Undivided Universe which Bohm acknowledges some of the basic similarities between his approach and MWI (both theories attribute ontological realism to the wave function, for instance), but where he also spells out his objections (basically having to do with the absurdity of trying to construct a coherent realist ontology in Hilbert space alone).

Sfwild (talk) 00:19, 23 November 2009 (UTC)

Hi Sfwild, your last comment puzzles me. keep in mind that most of these criticisms from the perspective of MWI (and there are many) will be referring to Bohm and not the BM formalism reproduced here. I thought that one of the points of renaming the article deBBt was to concentrate on the 1952 / Bell presentation here, and for the Hiley-"later Bohm"/Implicate order stuff to be discussed in a different article? --Michael C. Price ^talk 00:42, 23 November 2009 (UTC)

Hi Sfwild,

the particles are not non observable in Bohm's original theory either (which is, really, not a different theory than what Bell or Dürr et al. present). The problem is that Bohm's original articles contain some misleading passages that might give the reader that impression. But, really, if the particles were not observable, the theory would be just a bunch of nonsense and no one would propose it.

Look, for instance, at the second of Bohm's articles. The second section of that article is called "Quantum Theory of Measurements". There, Bohm presents an analysis of a "quantum measurement" using his theory (I have a pdf, in case you don't have easy access to the article). In that section, (pg. 182, left side, top), Bohm writes:

"Now, the packet entered by the apparatus variable y determines the actual result of the measurement, which the observer will obtain when he looks at the apparatus."

The variable y is the particle configuration of the apparatus, which, as he says, represents "the actual result of the measurement" and what "the observer will obtain when he looks at the apparatus".

It should be clear from this that y is observable. By the way, right after that, Bohm writes:

"The other packets can (as shown in Paper I, Sec. 7) be ignored, because they affect neither the quantum-mechanical potential acting on the particle coordinates x and y, ...".

This procedure of "ignoring the other packets" is exactly what, in the modern language of Dürr et al., would be described as the conditional wave function of the subsystem. The ad hoc rule presented by Bohm has been replaced with a sharp mathematical definition, but it is really the same thing.

Now, it is true that Bohm calls the particle positions and momenta "hidden variables" (well, it is in the title of the article, by the way). In section 4 of the article, Bohm insists that the particle positions are "hidden" (notice that he always use scare quotes when he writes "hidden"; even in the title). That's surely misleading. What he means is that, after the preparation of the initial quantum state, but before the "measurement" of a quantum observable, the position of the particles (which --- as he says --- determine the outcome of the measurement) are unknown to the experimenter (well, the experimenter could measure those positions if he wanted to, but that would seriously disturb the prepared quantum state). This is why, even though the dynamics of the theory is fully deterministic, experimenters cannot go beyond the probabilistic predictions of ordinary Quantum Theory.

By the way, I don't understand what's your objection to talking about "operators as observables". Dürr et al have indeed presented clean mathematical proofs of the emergence from the Bohmian formalism of the "operators as observables" formalism of ordinary Quantum Theory. Isn't that good?Dvtausk (talk) 02:07, 23 November 2009 (UTC)

No one disputes that Bohm, de Broglie, Bell etc regarded the particles as observable. But Everett, Brown, Wallace, Deutsch etc do not. You don't seem to understand that any "entity" that is Occamically superfluous is unobservable by definition (can we detect the aether? No!)--Michael C. Price ^talk 09:55, 23 November 2009 (UTC)

To Price: I haven't really read Craig Callender's article with care, but it seems to me that he actually is defending the opposite of what you want. Look, for instance, at the begginning: "In this brief note I argue that Redundancy is a nonstarter." and the end: "In sum, I've argued that even with all the major presuppositions of the argument granted, Redundancy doesn't yet pose a problem for Bohmians. Moreover, what is arguably the most natural way of understanding Bohm's theory makes Redundancy simply inapplicable. Either way, Redundancy shouldn't worry the Bohmian."Dvtausk (talk) 02:15, 23 November 2009 (UTC)

Yes, Callender is a Bohmite. So? --Michael C. Price ^talk 09:55, 23 November 2009 (UTC)

Well, Price, what you never understood (which is indeed a subtle point, but after all my explanations should be clear) is that the issue of what entity has or has not been observed in a given experiment, is not absolute, but depends on the theory that you use to analyze the experiment. For instance, according to currently well-accepted theories, stars can be observed; but, someone might have a theory which gives a different explanation for the bright spots in the night sky which does not involve any stars (and, according to that competting theory, what is normally regarded as "observing a star" is observing something else). Probably, what you mean when you say that "particles are not observable", is that one cannot prove that particles exist. Surely, I (and, I think, everybody) would agree with that. Everybody agrees that there are viable theories whose ontology has no particles (even people who thinks that MWI is not viable agree with that; for instance, GRW theories do not have particles in their ontologies). Surely, the fact that "particle detectors" flash is no proof of the existence of particles. What is normally meant when it is said that "dBB particles are observable" is that if dBB is true (or, in a universe governed by dBB) then particle detectors detect the dBB particles (and make us aware of their positions). Someone who agrees with Everett's "Occam's razor" argument might say that MWI is preferable to dBB, but such a person can still agree that dBB particles are indeed observable (in the sense that I just explained).

About Callender: what was the point that you were trying to make when you cited Callender's article? It seems to me that, in every issue in which you disagree with me, Callender agrees with me.Dvtausk (talk) 11:23, 23 November 2009 (UTC)

As I predicted, it didn't take very long for Dvtausk to repeat his accusations of stupidity or ignorance. Dvtausk was the one who claimed that Bell's quote was a response to Everett's, so I think Dvtausk should be a bit more careful about assuming that other people understand as little as he does. Pots and black kettles and all that.

Re Callender, I see Dvtausk still doesn't understand how citing sources to support statements work. Dvtausk, examine very carefully, if that is possible for you, and see what statements are supported by the cites. Are you disagreeing that I have correctly represented Callender's views w.r.t to the supported statements or not? Period.

--Michael C. Price ^talk 14:53, 23 November 2009 (UTC)

Your (Price's) discussion about "Bell's response to Everett" was with Jostylr, not with me; I haven't participated on that discussion at all (and, by the way, I wasn't very happy with what Jostylr originally wrote on that section anyway).Dvtausk (talk) 15:20, 23 November 2009 (UTC)

True, it was Jostylr. My mistake. --Michael C. Price ^talk 16:11, 23 November 2009 (UTC)

Callender does not give any support to your view that Everett's argument is an argument trying to establish the unobservability of dBB particles. That's what the subject of the discussion was when you mentioned Callender, so I can't see what point you could possibly be trying to make there. I agree, however, that in the current version of the "Occam's razor criticism" section, you have cited Callender appropriately (it is indeed an article containing a useful discussion of Everett's argument).Dvtausk (talk) 15:20, 23 November 2009 (UTC)

Glad we can agree about that. --Michael C. Price ^talk 16:11, 23 November 2009 (UTC)

PS. According to you (Price), "No one disputes that Bohm, de Broglie, Bell etc regarded the particles as observble.". Well, it seems to me that it is exactly what Sfwild was disputing (that Bohm regarded the particles as observable). I was responding to him. By the way, in our last discussion, a few months ago, it seemed like you were trying to push the "unobservability claim" into the "Interpretation of Quantum Mechanics" article, by citing (out of context) some misleading passages from Bohm's original articles about the particles being "hidden". So, it seems to me, that also you had doubts about Bohm's view of his own theory regarding the observability of particles.Dvtausk (talk) 13:27, 23 November 2009 (UTC)

Sfwild used quotes, as in "hidden". As in "hidden variables". This "hidden" is used in a different sense from "unobservable". Subtle point, I know. :-) Cf Brown and Wallace's mention of Bohm's implicit "result assumption". --Michael C. Price ^talk 14:53, 23 November 2009 (UTC)

Swfild wrote: "They are "hidden" in the sense that they are unobservable by detection experiments...". I rest my case. I notice that you have become very hostile. I can't see any point in continuing the discussion with you.Dvtausk (talk) 15:20, 23 November 2009 (UTC)

I shall make clearer the distinction between "hidden variables" and "unobserved partciles" in the article. Cf the "result assumption" made by Bohm, mentioned by Wallace and Brown. --Michael C. Price ^talk 16:11, 23 November 2009 (UTC)

PPS. Here is why I believe that Everett's intention with his "Occam's razor argument" is not to claim unobservability of particles in dBB: the "Occam's razor argument", as presented in that quote, is merely an argument that might lead the reader to think "Everett's theory is better than Bohm's theory". On the other hand, if you believe in the claim that dBB particles are not observable, then it is not only that you would find MWI preferable over dBB, you would instantly reject dBB as meaningless nonsense. So, if that were Everett's view, I guess he would have made it explicit and would have elaborated on it. But I could be wrong about Everett's intentions.Dvtausk (talk) 13:32, 23 November 2009 (UTC)

If by "meaningless" you use it in the Ayerian sense of "metaphysical", then yes I do reject dBB as "meaningless". Why should Everett belabour the obvious? And I note that Brown and Wallace interpret Everett in exactly the same way, viz that the Bohm particles play no part in measurement. (And they also make the same point about the lack of any back reaction from the particles onto the wavefunction and tie that to Occam cf their footnote 47). And Callender also undertstands Everett's point as being an Occamite reference to the Bohm particle's irrelevance (which he disputes, of course, although it seems you can't understand the distinction). --Michael C. Price ^talk 14:53, 23 November 2009 (UTC)

I've just caught up on reading the discussion in this section, about the Everett quote in particular. The current version of the "occam's razor criticism" section is certainly better than the Q&A version, which was just vague and confusing. Michael Price is surely correct to want to have this objection to the theory presented in the article; obviously there should be a separate "polemics" section where this and other such objections are briefly presented. But Dvtausk is entirely correct in the way he understands the logical structure of the objection and its relation to the Everett quote in question. Quite simply, what that quote actually expresses is an occam's-razor-based preference for the many worlds theory over the bohm theory, on the grounds that one generally "gets along fine" without the bohmian particles. That may be a good argument, but it's just not the same thing as a statement that the bohmian particles are -- according to the dBB theory -- unobservable. It's just a basic postulate of the dBB theory, really, that everything we observe (in the ordinary, literal sense) is made of particles. That's just what the theory is/says. Somebody else might have another theory in which there are no particles, and so clearly from the point of view of that other theory the particles are somehow superfluous or fantastic or pointless or ether-like or whatever. That other theory might even be true. But still, it's ridiculous to think that it is somehow objective or neutral or fair or reasonable for the article about the dBB theory to take the point of view of that other theory for granted. The article should present dBB theory on its own terms, and this should include making very clear that the ordinary world of observational experience is "in the particles" -- i.e., for this theory, it's the wave function which is the weird spooky invisible behind-the-scenes actor. The different perspective (from which the particles appear superfluous) should then be explained in a section on polemical objections to the theory. Tnorsen (talk) 18:17, 23 November 2009 (UTC)

I agree that section should not imply that the bohmian particles are -- according to the dBB theory -- unobservable. If it does imply that then it should be corrected, but I thought it said that they were regarded as unobservable from the Everettian perspective. --Michael C. Price ^talk 18:36, 23 November 2009 (UTC)

Notice the difference between "Everett believes that, according to the dBB theory, the dBB particles are not observable" (which --- I believe --- is the claim we have been disagreeing about the whole time) and "The dBB particles are not observable in Everett's theory" which is sort of meaningless, since there are no dBB particles in Everett's theory.Dvtausk (talk) 19:51, 23 November 2009 (UTC)

The idea of "the particles being unobservable from the Everettian perspective" is dangerously ambiguous. It could mean all kinds of very different thing, some of which (as Dvtausk pointed out) are meaningless. The proper way to say it, actually, is just how Everett himself does say it in the quote in question: from the Everettian point of view, the Bohmian particles are superfluous. There is simply no good reason to try to twist this into an issue of observability. Tnorsen (talk) 20:06, 23 November 2009 (UTC)

It's not twisting anything. All superfluous entities are unobservable, by definition. Can you detect the ether? --Michael C. Price ^talk 01:14, 24 November 2009 (UTC)

According to a certain theory, there are no cats and what people normally describe as the experience of "seeing a cat" is actually a hallucination. Since such theory explains experience without positing the existence of any cats, cats are superfluous. Are cats observable?Dvtausk (talk) 02:39, 24 November 2009 (UTC)

Sounds like the "certain theory" is more complex and it is superfluous, not the cats. Again I ask, can you see the luminiferous ether? --Michael C. Price ^talk 07:09, 24 November 2009 (UTC)

Someone (not me) could disagree and prefer the "no cats" theory; and that someone could still appreciate that cats are observable when "cat detection experiments" are analyzed with respect to the theory that posits the existence of cats (and that was the point I was trying to make, I wasn't defending the "no cats" theory). By the way, no, I can't see the ether. Is there a point to that question? Is that supposed to be an argument of some sort? Do you think that by giving an example of something which is both superfluous and non observable you can establish a logical connection? Apples are both tasty and red. Does tasty implies red?Dvtausk (talk) 13:35, 24 November 2009 (UTC)

A single example can be suggestive; a single counter-example would be definitive. Got one?

In the meantime, let's look at it more generally. If something is superfluous to a theory then it can be removed, by definition, without any effect, which would include any effect on observation. Ergo superfluous => unobservable. What part of that don't you follow?

--Michael C. Price ^talk 14:25, 24 November 2009 (UTC)

(obs: transforming dBB into MWI is not just about removing the particles, it is about removing the particles and changing the role of the wave function; but we don't even have to agree on that for now). Let's add more stuff to dBB --- let's call the new stuff "angels" --- now we have a new theory, let's call it new-dBB. As long as the dynamics of the angels is related to the dynamics of the particles (say, the angel configuration $A(t)$ is given as a function of the particle configuration $Q(t)$, say A(t)=f(Q(t))), the angel configuration would be observable in a universe governed by new-dBB. On the other hand, I guess anyone would agree that the angels of new-dBB are superfluous. That's the counter-example that you asked for. The mistake in your argument is the failure of appreciating that two empirically indistinguishable theories can give different accounts of what has been observed in a given experiment.Dvtausk (talk) 15:49, 24 November 2009 (UTC)

Dvtausk, your counter-example is flawed because you have assumed that the angels would be observable, just as you assumed the particles would be observable. That's called begging the question. Find a real-world counter-example, i.e. find a superfluous entity that is observable. BTW we know that empirically indistinguishable theories can give different accounts of what has been observed - they're called gauge theories, but "unobservable gauge fields that are not superfluous" (which exist) are not the same as "superfluous gauge fields that are observable" (which don't exist). That's why we have to stick to real-world examples - to filter out absurdities. --Michael C. Price ^talk 20:12, 24 November 2009 (UTC)

I haven't assumed that the angels are observable. It is a consequence of the theory that they are observable (with respect to that theory).Dvtausk (talk) 22:30, 24 November 2009 (UTC)

That's still begging the question. As I said, real world example please. --Michael C. Price ^talk 22:54, 24 November 2009 (UTC)

It’s hard to keep up with this chatter—which I’m not sure is leading anywhere—but I will comment briefly on some of the points:

@Michael. You are right that the Bohm in question is the Bohm of the '52 articles, not the Bohm the implicate order stuff. But there are important differences between the presentation of the '52 theory (which was done explicitly in terms of "hidden variables") and the BM formalism (where, following Bell, the particles aren't really "hidden" after all). All of this creates confusion about the basic concepts of the theory which the article in its current iteration does little to clarify. The point of last comment is simply that most of the existing commentary comparing MWI and Bohm refers to Bohm's own approach (that is, his approach to QM as elaborated fairly consistently--with some modifications--from '52 until his death) and not to the BM formalism as presented here.

@Dvtausk. I think we are basically in agreement about the fundamentals of the theory, the issues having more to do with semantics than anything else. What is important to recognize is that when Bohm speaks of “particles” and “observables” he does so in much in the same way as in the standard presentation. Thus particles are not “observables” though of course they are observed when a measurement is taken. The other way that they are “hidden” is in the sense that they lie outside the formalism developed by the Copenhagen school and their contention that there could be nothing (eg. no “hidden” variables) beyond the wave function. The historical-theoretical context is important insofar as what Bohm tried to do in the ‘52 papers was to disprove those assumptions (along with the impossibility “proofs” of Von Neumann etc). What gives rise to confusion are not Bohm’s own formulations—which tend to be very precise—but statements to the effect that “particles are the observables.” I can see how such misunderstandings arise from the current BM formalism and certain off-the-cuff remarks by Bell to the effect the particles are not hidden after all, but to say that “particles are the observables” is misleading and needs clarification.

The essential difference between Bohm and the Copenhagen Interpretation--or MWI for that matter is—is not in the distiction between "particles" and "obsrvables," but in the ontological reality accorded to the particles. In other words, for Bohm, not only does the wave function correspond to a real field, but the particles are real as well. They don’t have that status in CI or MWI.

You ask me why I don’t like the formalism of BM as presented by Duerr et al. I could go on and on, but here are two reasons: 1) Because many of the terms such as “Conditional Wave Function” are newfangled formulations which only the committed partisans of BM employ, and which are awkward baggage in any sort of “foundations of physics” discourse (for instance in trying to compare MVI with Bohm). 2) With regard in particular to the so-called “Quantum Equilibrium Hypothesis” what is questionable is the misleading analogy with Classical near-equilibrium thermodynamics and the supposition that probabilities are the result of our ignorance of the initial positions. This seems to me to be a particularly retrogressive approach, and corresponds to nothing you will find in Bohm or de Broglie, but rather to an ideological commitment on the part of the BM crowd to cast the formalism in a way which is consistent with a worldview of absolute quasi-Laplacian deterministic mechanism. The whole approach could not be more foreign to Bohm’s approach, and takes the theory in a direction that Bohm himself would be appalled at. It is at least a bit odd that even as the field of thermodynamics is moving away from the classical formulations of Boltzmann etc, and towards things like chaos theory, dissipative structures, irreversibility, non-linearity, and non-equilibrium dynamics, the BM school seems intent at casting the measurement problem in such a simplistic fashion.

Sfwild (talk) —Preceding undated comment added 18:41, 23 November 2009 (UTC).

Please note the difference between "particles are the observables" (which is very strange --- and false, if by "observables" we mean what is usually meant in quantum theory) and "particles are observable".Dvtausk (talk) 19:54, 23 November 2009 (UTC)

Sfwild: "With regard in particular to the so-called "Quantum Equilibrium Hypothesis"... and the supposition that probabilities are the result of our ignorance of the initial positions. This seems to me to be a particularly retrogressive approach, and corresponds to nothing you will find in Bohm or de Broglie...". Bohm's formulation of the "Quantum Equilibrium Hypothesis" (he does not use that name), first of Bohm's original articles, pg. 171, right side, bottom of the page, hypothesis (3): "That we do not predict or control the precise location of the particle, but have, in practice, a statistical ensemble with probability density $P(x)=|\psi (x)|^{2}$. The use of statistics is, however, not inherent in the conceptual structure, but merely a consequence of our ignorance of the precise initial conditions of the particle."Dvtausk (talk) 20:03, 23 November 2009 (UTC)

I would like to remove/rewrite some sentences from this Occam's Razor section. In particular, this stuff: The unobservability of the "hidden particles" stems from an asymmetry in the causal structure of the theory; the particles are influenced by a "force" exerted by the wavefunction and by each other, but the particles do not influence the time development of the wavefunction (i.e. there is no analogue of Newton's third law -- the particles do not react back onto the wavefunction[18]) Thus, if we regard the wavefunction as real and the source of all experience, the particles do not make their presence known in any way; as the theory says, they are hidden, but in a far more profound way than de Broglie and Bohm had intended.

It simply isn't true that the (alleged and highly controversial) unobservability of the particles "stems from an asymmetry in the causal structure of the theory." Rather, it stems completely and exclusively from the assumption that "the wavefunction [is] the source of all experience". That alone is (obviously) sufficient to render the particles (not unobservable but) superfluous. Imagine, for contrast, a dBB-like theory in which the particles did somehow react back on the wave function, but (somehow) the wave function still evolved in the usual way (or maybe in some stochastic way as in GRW/CSL type theories). That theory would be just as open to the charge of superfluity as regular dBB. So clearly the causal asymmetry is simply irrelevant to the objection that this section is supposed to be laying out.

Any objections? If not, I'll go ahead and clean this up. Tnorsen (talk) 20:14, 23 November 2009 (UTC)

Hi Tnorsen,

if the particles reacted back on the wavefunction then the particles would not be labelled as superfluous; nothing that has any effect on the wavefunction can be superfluous; and anything superfluous can't have any effect on the wavefunction (it's an identity: superfluous <=> no effect <=> unobservable). Look at it another way; if the particles effected the wavefunction there would be particle terms appearing in the Schrodinger wave equation - and there aren't. Your proposition Imagine, for contrast, a dBB-like theory in which the particles did somehow react back on the wave function, but (somehow) the wave function still evolved in the usual way is internally inconsistent. For the particles to be unobservable we require both the lack any back reaction and for all experiences to flow from the wavefunction.

--Michael C. Price ^talk 01:10, 24 November 2009 (UTC)

To Tnorsen: Certainly that section needs cleaning up. But I'm not sure if I understand what you are saying. For Everett's "Occam's razor" argument, the absence of back reaction in dBB is irrelevant (all that is important for that is the belief that MWI works and is simpler). For the "unobservability" argument, the absence of back reaction matters: if you misunderstand dBB in such a way that the state of mind of the observers is to be found in their wavefunction, then because of the absence of back reaction, it follows that the particles are not observable.Dvtausk (talk) 22:15, 23 November 2009 (UTC)

Dvtausk: as I tried to clarify below, I am only concerned about the Occam's razor argument. There simply doesn't seem to be anything to argue about vis a vis "unobservability". That said, I don't understand the second half of your comment just above. If you misunderstand dBB in such a way that the state of mind of the observers is to be found in their wavefunction -- i.e., if you consider what you elsewhere called the chimeric theory whose ontology is like dBB's but in which it is stipulated that what we observe is the wf -- then the particles are unobservable whether there is a back-reaction or not. Well, now that I think about it, maybe there is some ambiguity about the word "observable" here. It could mean either "amenable to direct, unaided perceptual awareness" (meaning that only stuff you can literally see is "observable") or it could be used in a more general sense to mean "amenable to direct, unaided perceptual awareness or able to be detected by indirect scientific inference". If the latter then, for example, the wave function would be "observable" in dBB despite its being "invisible", and in that same way the particles would be "observable" in the chimeric theory despite being "invisible". One could also say that, in the former sense of "observable", nobody ever thought the ether was observable. But people did think it would be observable in the second sense -- which is why MM and others tried to detect it, and why it was such a surprise when they failed. But anyway, the real point is that all of this is a complete red herring, because it is just an aspect of the definition of dBB theory that the particles are "observable" (in the former, literal sense). The whole world of ordinary perceptual experience is, according to this theory, made out of particles. And any claim to the contrary (be it a bald assertion or the conclusion of some kind of misconceived argument) is just wrong. And so the issue shouldn't even come up here. —Preceding unsigned comment added by Tnorsen (talk • contribs) 15:14, 24 November 2009 (UTC)

Tnorsen: The meaning of "observable" that I have in mind (and that I had in mind during the whole conversation) was your second sense (in which the observation proccess is aided by instruments, and theory, and deduction). So, for instance, bacteria are observable (with the aid of microscopes, the physical theory that justifies the functioning of the microscope, etc). So, in the chimeric theory without back reaction, the particles are not observable, and in the chimeric theory with back reaction, the particles might be observable (but no one cares about the chimeric theory anyway). In normal dBB the wave function is something like "partially observable", as there are no experiments that allow one to fully determine the (conditional) wave function of a subsystem (because of the theorem that says that outcomes of experiments are given by positive-operator-valued-measures in the wave function space), but one can get partial information about the wave function of a subsystem (and, more importantly, control it).Dvtausk (talk) 16:48, 24 November 2009 (UTC)

To Tnorsen and Price: By the way, it is very easy to formulate a version of dBB in which the particles affect the wave function. This is done here: http://arxiv.org/PS_cache/quant-ph/pdf/0603/0603027v4.pdf (section 7.2). But, this observation does not work as a response to Everett's superfluosness argument, as he could still argue that the pure wave theory is viable and simpler.Dvtausk (talk) 01:56, 24 November 2009 (UTC)

There are no particles in GRW theory. And the wavefunction does not obey the Schrodinger wave equation. Therefore it is not an equivalent theory.--Michael C. Price ^talk 07:09, 24 November 2009 (UTC)

Just weighing in: I definitely don't object to fixing up the Occam's Razor section in the way you mentioned, Tnorsen.

I also agree that, while the Occam's Razor objection from superfluousness can (at least on first blush) be leveled against the dBBt, the "unobservable particles" objection could only come from some assumption that the role of the wavefunction in dBBt is the same as its role in MWI, which is false. It should please everyone on this page to separate these points, since leaving the section as it is (1) perpetuates a gross misunderstanding of the dBBt, and (2) muddies a legitimate objection (superfluousness) by mixing it in with a silly one (unobservability). Bohmians and good wikipedians should dislike (1) and critics of dBBt should dislike (2). So it should make everyone who matters happy if we change this section so that neither (1) nor (2) hold.

As a side point, I think Sfwild is kind of right in saying that there is a problem with including certain mathematically heavy apparatuses (like the notion of a conditional wavefunction) on the ground floor. I'm not suggesting we get rid of talk in terms of the conditional wavefunction. I just think there should be a section early on that sketches the idea of "empty channels" and effective collapse in a non-formal and non-jargony way, and then present the conditional wavefunction talk as being a mathematically rigorous way to express these notions and the role they play in the physical theory. (As it stands, the conditional wavefunction sounds like a new mechanism that's being brought in, when really (insofar as I understand it, assuming that I do (which I very well may not)) its just a rigorous way of talking about a phenomenon that falls out of the basic tenets of the theory in a very straightforward way.) ZRPerry (talk) 20:40, 23 November 2009 (UTC)

Hi ZRPerry,

you say the "unobservable particles" objection could only come from some assumption that the role of the wavefunction in dBBt is the same as its role in MWI, which is false. But the role of the wavefunction is the same; dBBt, Bell & Everett all presume an objectively real wavefunction that obeys the same wave equation.

Incidentally, the "conditional wavefunction" sounds like Everett's "relative states" - if so you are correct that it is just a "phenomenon that falls out of the basic tenets of the theory in a very straightforward way" and we can probably avoiding using any interpretation specific jargon about it.

--Michael C. Price ^talk 07:22, 24 November 2009 (UTC)

"both have the same role" is not a logical consequence of "both satisfy the same differential equation and both are objectively real".Dvtausk (talk) 13:39, 24 November 2009 (UTC)

Nevertheless it is assumptions about the particles (i.e. the "result assumption") that makes them observable, not assumptions about the wavefunction. --Michael C. Price ^talk 14:10, 24 November 2009 (UTC)

You are right when you say "its just a rigorous way of talking about a phenomenon that falls out of the basic tenets of the theory in a very straightforward way". I think the "heavy math" (not really that heavy) should be included in some place, as I have seen many Wikipedia articles containing lots of very technical mathematical details. But, I also agree that there should be lots of sections that are as much math free as possible. I wrote that section about the conditional wave function and I didn't really know where to insert it, so I just inserted it more or less at random. But if you have ideas about changing the order that things are presented, please go ahead. There are certainly lots and lots of things that have to be improved in this article. For instance, it is awkward that the guiding equation appears twice.Dvtausk (talk) 22:02, 23 November 2009 (UTC)

I wasn't sufficiently clear before. My general perspective is that the entire issue of the particles in dBB being "unobservable" is a confusion -- as evidenced by the confused and illogical responses that Michael Price keeps giving to everybody's comments here. The fundamental point here is that "observability" is theory-relative. So there is no such thing as some kind of general argument from "superfluity" to "non-observability", the way that Price keeps insisting. The situation is clear: it is a fundamental assumption of dBB that the ordinary 3D material world of perception is made of particles. In that theory, the particles are most definitely observable. No argument of any kind whatsoever is going to change that. The only question is: what does one think of the theory? Of course, people who think that an image of the familiar 3D material world can be found in the wave function, and so regard MWI as empirically adequate, will prefer MWI to dBB on grounds of simplicity. As I think everybody has agreed, that is an interesting and important and valid polemical point to make against dBB and it should certainly appear on the page. But it is simply wrong to think that this is equivalent to or implies an argument for the (general) unobservability of dBB particles. Indeed, there isn't even any such thing as "general unobservability" because what is observable or not is theory-relative. Theories, to some degree, just get to stipulate what is observable. In any case, certainly the way Price has most recently worded this section is completely wrong. It now states that In the Everettian view, then, the Bohm particles are unobservable entities. That simply doesn't make any sense. If in the Everettian view means according to Everett's theory, then the particles aren't unobservable -- they just don't exist. If on the other hand in the Everettian view means from the perspective of someone who likes Everett's theory, then the correct statement would be that the addition of particles to the ontology (and the stipulation that they, and not the wave function, are what we observe) makes for a pointlessly more complicated theory -- which is of course precisely what the Everett quote actually says.

So let me be clearer about my intentions: I would like to edit this section so as to remove completely any discussion of "unobservability" -- except maybe in so far as to clarify "the Everettian view" by noting that, for dBB it is the particles that are observable, while for MWI it is the wf. Does anybody have any sensible objections to this?? Tnorsen (talk) 14:55, 24 November 2009 (UTC)

Tnorsen, you say The situation is clear: it is a fundamental assumption of dBB that the ordinary 3D material world of perception is made of particles. In that theory, the particles are most definitely observable. No argument of any kind whatsoever is going to change that. No, it is not a fundamental assumption of dBB. I have Bohm 1952 in front of me. Where is that assumption made? This is what Wallace and Brown mean by the "result assumption", that Bohm implicitly tied perception to the particles, but he did not explicitly make it an assumption, because he (and Bell) wanted the foundations of their theory to be free of any measurement language (as did Everett of his theory). Yes, dBB explicitly assumed the particles existed, but they did not explicitly assume that perceptions flowed from the particles. The latter is implicit, and there lies the problem. You go on to say Theories, to some degree, just get to stipulate what is observable., yes, that's true, but the point is that Bohm did not stipulate what was observable. Such a stipulation would have run counter to his ethos. Again, note what Wallace and Brown say about the "result assumption". --Michael C. Price ^talk 20:38, 24 November 2009 (UTC)

I think the bottom line is that there are two very distinct objections to dBB: let's call them the "superfluousness objection" and the "unobservability objection". There are many sources that present the "superfluousness objection" (including Everett), so certainly that should be presented --- and Everett and critics of dBB certainly have nothing to gain if this decent objection is mixed up with the silly "unobservability objection". I haven't found, so far, any source presenting the "unobservability objection"; so, for now, my suggestion is that such objection not be presented. However, as a general sociological rule of thumb, given a stupid statement S, there exists a person P that believes in S, so it might well turn out that some author supports the "unobservability objection"; if anyone finds such an author (explicitly supporting that view), then a comment about that could be included. I have read the Brown & Wallace reference given by Price, and they don't support the "unobservablity objection" either. A summary of their view, is more or less something like this: assuming that the state of mind of observers is related to their particle configuration and not to something in the wave function (or any other such assumption that implies that stuff in our world is made out of the particles) is unjustified/unnatural/bizarre, etc. So, in that view, the dBB theory (as proposed by the Bohmians) is unjustified/unnatural/bizarre, etc.Dvtausk (talk) 16:31, 24 November 2009 (UTC)

Dvtausk: I think we're on the same page. I agree, there are two different possible objections, one (the superfluity or occam's razor objection) that actually makes sense (even if at the end of the day I don't agree with it), and one that (a) doesn't make any sense, (b) hasn't been argued for in print that I am aware of, and (c) shouldn't be confused with or attached to the superfluity argument. If Michael Price or someone else who thinks the second argument does make sense wants to try to find something in the literature to cite and summarize, so be it. (And like you, I suspect that, with enough effort, some such thing could be found.) More likely, such an argument should be considered original research and anybody who thinks it makes sense should write a paper about it and try to get it published -- not try to awkwardly squeeze it in here. Anyway, what's clear is that this second objection doesn't belong in the "occam's razor objection" section and shouldn't be associated with it in the way that Michael Price keeps trying to do. Tnorsen (talk) 17:00, 24 November 2009 (UTC)

Tnorsen, I'll say the same to you I've said elsewhere; find me a single example of a superfluous entity we can observe and I'll accept that superfluity doesn't imply unobservability. But until then I see what Wallace and Brown say about the particle playing no role in the measurement process as a direct confirmation that I'm merely rephrasing what they're saying. --Michael C. Price ^talk 20:45, 24 November 2009 (UTC)

I gave you one example (the new-dBB theory, with the angels). You complained that I "assumed that the angels are observable". It seems to me that there are lots of important issues that you don't get here. First, you shouldn't complain, when a theory is presented, that one is making assumptions. That's what it means to present a theory. To present a set of statements (which are the "postulates" or "assumptions" of the theory). Such statements/assumptions/postulates include things like existence of things, how they behave (differential equations), initial conditions, what role in the world each of the things that appear in the formulation of the theory has, etc. You can complain that you don't like the statements/assumptions/postulates of the theory. That simply means that you don't like the theory. But, still, the theory is what it is. Brown & Wallace, for instance, criticize some of the statements/assumptions/postulates of dBB. You can agree or don't agree with them; if you do, you might believe that dBB is a bizarre or unnatural theory. But, still, it is what it is. There shouldn't be any disputes about what are the logical consequences of (the statements/assumptions/postulates made by) the theory. More importantly, you don't seem to understand what "observing" means. "Observing" depends on experiments but also on an analysis of the experiment which has to be made with respect to a given theory. For instance, an experiment that is usually understood as a "measurement of the magnectic field", is only a "measurement of the magnectic field" if one analyzes it using Maxwell's theory. In the new-dBB theory of my example, it is assumed (as in normal dBB) that the particle configuration $Q(t)$ is observable; the fact that the "angel configuration" $A(t)$ is observable, is then simply a consequence of the dynamics of the theory (which postulates a certain relationship between the $Q(t)$ and the $A(t)$). The $A(t)$ is observable because one can make up an experiment that correlates the A(t) with something which is, by assumption, observable (the Q(t)).Dvtausk (talk) 22:57, 24 November 2009 (UTC)

And what you don't seem to get is that Wallace and Brown are not criticising the stated assumptions, but the unstated "result assumption". And angels are not real world examples. Heavens, man, what are you smoking? --Michael C. Price ^talk 23:04, 24 November 2009 (UTC)

The assumption being "unstated" only means that the author who presented the theory wasn't very careful when he presented the theory (that he didn't put all the assumptions on the begginning of the article, for instance, that some of them appeared in the middle of the article). That's more a criticism about the careless style of writing of the author, not really a critic to the theory itself. "Angels" was just the first word that came to my mind. Oh dear. It's like talking to a child.Dvtausk (talk) 23:17, 24 November 2009 (UTC)

It is a criticism if the unstated assumptions run counter to the declared aim of a measurement free foundation.

And it doesn't matter what word you used, it still wouldn't be a real world example. Don't you understand? An example drawn from real, accepted physics, not some imaginary disputed, begging-the-question example.

--Michael C. Price ^talk 23:22, 24 November 2009 (UTC)

In Classical Mechanics, isn't there some tacit "result assumption" that the particle configuration of the apparatus is the actual result of an experiment? Does anyone bother to write it down? Does anyone complain? I guess not (but I agree that, since Quantum Theory is messier, people should be more careful than usual about what they write). Moreover, the formulation of any physical theory must contain some statements explaining the relationship between the math and the ordinary objects of our experience, otherwise it is impossible to make sense of the math. In any case, I think the best way of presenting the necessary assumptions of dBB is like Bell does, in terms of psycho-physical parallelism between the particle configuration of the brain of the observer and the state of his mind; from that, the "result assumption" of Bohm follows, and that assumption doesn't refer to experiments and measurements.Dvtausk (talk) 00:51, 25 November 2009 (UTC)

The result assumption is not a problem in classical mechanics since the particles act on ("generate") the fields and the fields push the particles around. The fields and the particles are both "aware" of each other. In dBB, as has been explained, there is no particle action on the wavefunction; the wavefunction is not "aware" of the particles. --Michael C. Price ^talk 01:23, 25 November 2009 (UTC)

It seems that your complaint about the "result assumption" was that it makes explicit reference to experiment/measurement. The same exact complaint works for Classical Mechanics. The absence of back reaction is completely irrelevant with respect to that complaint. If you have other complaints (like Brown & Wallace do, for instance) about the result assumption (or related similar assumptions) then that's fine. You don't have to agree on whether that is a good assumption. You might think that, under some such assumption, dBB becomes a very unlikeable, unnatural, stupid, bizarre theory. That is simply irrelevant to the discussion. We are not discussing about whether dBB is a good theory; we are discussing about what follows from (the assumptions of) dBB.

I don't understand what you mean by a "real world example". Our discussion has absolutely nothing to do with the one Real World in which we live in. The issue of whether some entity whose existence is posited by a theory T is observable (with respect to the theory T) is an issue that concerns only a hypothetical world which is governed by theory T.Dvtausk (talk) 00:51, 25 November 2009 (UTC)

The luminiferous ether was a real world example. Find a similar counter-example. You can't. Why not? Because none exist. Why? Because all superfluous entities are unobservable. Why? Because it is an illogical concept. As I said, and about which you have never directly answered: If something is superfluous to a theory then it can be removed, by definition, without any effect, which would include any effect on observation. Ergo superfluous => unobservable. What part of that don't you follow? . --Michael C. Price ^talk 01:23, 25 November 2009 (UTC)

Does by "real world example" you mean something which is related to some theory that was actually considered during the History of Physics, involving some entity which was abandonned on grounds of superfluity? I can't think of any example like that. I'm not a Historian and maybe there aren't any examples like that. How is that relevant to the discussion? The historical contingency of whether some theory was or was not proposed or considered by physicists during some period of time cannot possibly be relevant to this discussion.Dvtausk (talk) 01:56, 25 November 2009 (UTC)

Price: Let me make a proposal that might be helpful to this "discussion": present a clear explanation of what "observing" something means to you and then, apply your concept of observation to the sentence "dBB particles are observable". I hope you don't say something like ""observing" for me means "having an effect on the wave function""; that would be truly bizarre, since that definition does not even apply for theories that have no wave function.Dvtausk (talk) 01:56, 25 November 2009 (UTC)

Let's just stick to the question of whether superfluous => unobservable and note that in the following we don't need to know the definition of "observation", details about dBB, MWI etc. It's just a straightforward syllogism:

If something is superfluous to a theory then it can be removed, by definition, without any effect, which would include any effect on observation. Ergo superfluous => unobservable.

Where's the flaw?

--Michael C. Price ^talk 02:13, 25 November 2009 (UTC)

Ok, since you insist, I will make a careful analysis of your argument: "If something is superfluous to a theory then it can be removed, by definition, without any effect, which would include any effect on observation. Ergo superfluous => unobservable", even though I don't think it is going to help you understand anything. The mistake in the argument is a change of meaning of the word "observation" that you made during the course of the argument. Let's analyze it. Start with a theory T, which posits the existence of an entity X. Let's assume that X is superfluous in the theory T ("superfluity" is not really such a sharply defined concept, but it is sharp enough for the sake of the argument). Consider the theory T' obtained from T by removing X. The superfluity assumption implies that T and T' are empirically equivalent, i.e., "removing X has no effect on observation". The meaning of the word "observation", in this part of the argument, is "what the observer will see during the experiment". Now, it is possible that a given experiment E, when analyzed in terms of the theory T, is interpreted as an observation of X; obviously, that won't be the case in theory T', since there is no X in theory T'. So, even though the experimenter sees the same thing when the experiment E is performed in a world governed by T and in a world governed by T', it happens that the interpretation of what was seen changes when the theory is changed. The word "observation" that appears in the second part of the argument doesn't refer simply to what was seen during the realization of the experiment (the meaning of "observation" in the first part of the argument), but also to the meaning/interpretation that was assigned to what was seen (which is different in theories T and T').

I have little hope that this explanation will help you, but that's life.Dvtausk (talk) 02:17, 25 November 2009 (UTC)

The interpretation of the observation may have changed, but that doesn't change the observation itself. The observation is of the flash, the interpretation is "the particle caused the flash". The interpretation has changed by removing the particle from the theory, but the observation itself has not changed. And the fact that the observation hasn't changed, despite the particle being removed from the theory, means that it was never the particle that was being observed in the first place. --Michael C. Price ^talk 02:40, 25 November 2009 (UTC)

Well, the last sentence of your paragraph simply does not follow from what comes before. Both theories predict that the experimenter will see the same thing (say, the "flash"). If the experimenter interprets what he has seen using Everett's theory, he will say "I have observed a wave packet", if he interprets what he has seen using dBB, he will say "I have observed a particle", if he interprets what he has seen using GRWm, he will say "I have observed a piece of the density matter field". What has he really observed? It depends on what theory is true, which we don't know (and is not under discussion). That's it. I'm sorry. I don't know how to make it clearer.Dvtausk (talk) 02:50, 25 November 2009 (UTC)

Yes, the interpretation of their observation is a function of the theory they believe in. Which is why an Everettarian will say that a Bohmite has not observed a a particle, even though the Bohmite is convinced they have. Hence why, in the Everettarian view, the superfluous particles are unobservable. --Michael C. Price ^talk 03:17, 25 November 2009 (UTC)

Great. Maybe we are making some progress here. Sometime ago there was a discussion about the meaning of "In Everett's view, dBB particles are not observable". Now is a good time to get back to it. I don't think the meaning of that sentence is clear (which was also a point Tnorsen was trying to make). I see, basically, two possibilities:

(1) it means: "Everett believes that, in a world governed by dBB, the observers cannot observe the dBB particles";

(2) it means: "In a world governed by Everett's theory, the observers do not observe dBB particles".

See, there is an important difference here between "Everett's view" in the sense of "Everett's beliefs and opinions about things" and "Everett's view" in the sense of "what is true in a world governed by Everett's theory". Anyone who has studied Everett's theory --- even people that do not agree that it is a good theory --- is supposed to be able to figure out what is true or not in a world governed by Everett's theory (i.e., what follows from the assumptions of that theory). The same happens in the case of dBB. On the other hand, Everett's opinions and beliefs are private to him; the only way to get information about them, is to read what he writes, ask him questions (and hope he doesn't lie).

If (1) is true, then Everett would be trivially wrong --- as he would have simply misunderstood what are the assumptions of dBB. I don't believe that (1) is true. Do you believe that (1) is true? If you do, please try to prove it by supplying us with the relevant Everett quotes.

About (2): is it true? Certainly no one would claim that it is false. Either (2) is an utterly trivial true statement or it is meaningless. No one observes things that do not exist, that's for sure. Or maybe it is better to say that, since the true theory of the world we are talking about (the world in which Everett's theory is true) does not talk about dBB particles at all, there aren't even in principle any experiments that could possibly count as an observation of a dBB particle, so the observability question becomes meaningless. In any case (be the sentence utterly trivial or meaningless), I don't see any point in writing it down in an article. Like, for instance, no one would propose to write in an article that the matter density field of GRWm is not observable in a world governed by dBB.Dvtausk (talk) 03:46, 25 November 2009 (UTC)

(1) is the intended meaning. The statement within (2) is also true, but rather trivial. And no, I am not going back to supply quotes again about (1) - that's what this whole thread has been about. --Michael C. Price ^talk 04:01, 25 November 2009 (UTC)

Ok, so now it is really getting hard to understand what is going on. Because I had the impression that you had understood that in a world governed by dBB (i.e., in a world in which dBB is indeed true) --- so that, in particular, all assumptions made by dBB are true in that world, including Bohm's "result assumption" or something like Bell's "psycho-physical parallelism assumption", which implies Bohm's "result assumption" --- the observers do indeed observe the dBB particles. That is almost a tautology. I can't see how you could possibly disagree with that, or why on earth you would think that Everett would disagree with that. It is understandable to me that you don't believe that our Real World is a world in which dBB is true, and it is even understandable to me that you think that some or all of the assumptions of dBB are stupid and crazy and unnatural. But it is not understandable to me that you disagree with a tautology. About the Everett quotes: you have never really supplied any but the one that appears in the current version of this wiki article.Dvtausk (talk) 04:24, 25 November 2009 (UTC)

Yes, only one supplied, which I find sufficient. Although Deutsch & Zeh are saying the same thing. --Michael C. Price ^talk 10:40, 25 November 2009 (UTC)

I should add: it's just not possible to be convinced, by looking at that Everett quote, in which he makes a perfectly reasonable and rational point (which I happen to disagree with), that (1) is true, i.e., that Everett would disagree with a tautology.Dvtausk (talk) 04:52, 25 November 2009 (UTC)

The way Everettians view it, if dBB were true it wouldn't matter whether the result assumption is made implicit or explicit, it contradicts the rest of the theory. Since, according to MWI (as Everett says), the wavefunction is sufficient to account for all observations. Tacking on extra particles or assumptions about particles doesn't stop MWI being a subset of dBB. i.e. dBB with an explicit result assumption is not a tautology, it is internally inconsistent. --Michael C. Price ^talk 10:40, 25 November 2009 (UTC)

Surely, the distinction between "explicit" and "implicit" assumption is irrelevant, as that only concerns the style of writing of the author of the article, not the theory. Notice that I haven't said that "dBB with an explicit result assumption is a tautology" (which would be really a stupid thing to say), I have said that the implication "dBB ==> dBB particles are observable" is a tautology (where, as usual, in dBB I include the "result assumption" or something that implies that).

Ok, so you believe that dBB (with the "result assumption" or something that implies that) is an inconsistent theory. From which, I hope, you mean that there exists a logical deduction of a contradiction from the assumptions/postulates/statements that constitute dBB. I could ask you to present that logical deduction, but I won't, since I have already wasted too much time with you. Going back to Everett's beliefs: it seems that you want to insist on statement (1) (Everett believes that, in a world governed by dBB, the dBB particles are not observable), not by saying that Everett disagrees with a tautology, but by saying that Everett (like you) believes that dBB is inconsistent. Now, logical inconsistency is the most serious accusation one can make against a theory, so if you want to say that some author (like Everett, or Brown & Wallace) believes that dBB is inconsistent, you really have to supply a quote where they say that very explicitly. I have read Brown & Wallace's article, and I'm sure they never made any such claims in that article.Dvtausk (talk) 12:55, 25 November 2009 (UTC)

I have now read Everett. Brilliant work, so much better than what I have seen said about MWI elsewhere. Having read it, I can say that I found no evidence that Everett meant that the Bohm particles are unobservable. I read it very much as he wrote it, namely that MWI accounts for everything without additional diff eqs. So that theory is simpler, according to him. In saying what someone meant, it is very important to be conservative.

As Everett says, every theory must say what corresponds to our experience. For MWI, that is correlations in the wave function. Those correlations are present in standard dbb since they come from psi, but they are not used in that way in dbb. All the infinitely many realities that could be constructed out of those correlations are superfluous and certainly unobservable according to dbb. Instead, the dbb mapping is that our experience is rooted in where the particles are according to dbb, e.g., if I run into a table, that is because its particles are there. And note that in dbb, the particles influence each other via the wavefunction. If for example we have a table that I run into under one set of initial conditions, it is possible to keep the same wavefunction, change the location of the actual table particles, and then I will not run into it. My experience changes based on what the actual values of Q are, according to dbb. Q is not superfluous in dbb. Q does not exist in MWI.

As for the back action/unobservable stuff, the example that Dvtausk pointed to in the Common Structure of BM and GRW paper is crucial. It shows that, if anything, it is the wave function which is not observable in dbb. In section 7.2, they give a theory which has the wave function collapsing where the particles are. The branches are being discarded. It no longer has superfluous correlations in the wave function. Yet, it is empirically equivalent to dbb and hence to standard qm. So radically altering Psi does not need to affect anything while making slight changes in Q will often radically alter the outcomes.Jostylr (talk) 13:24, 25 November 2009 (UTC)

I would like to suggest that the discussion about "observability", the Everett quote, the occam's razor objection, etc., should stop. It seems to me the issue is clear. First, somebody needs to restructure the page so there is a separate objections/polemics section. Second, words (especially stupid ones) should not be put in Everett's mouth; the "superfluity" objection to dBB is a meaningful and sensible objection (even if, as I think, it is ultimately wrong) which Everett (and others) actually expressed; it should be included in the article. Third, if M Price or anyone else thinks there is some meaningful and sensible other objection regarding the observability of particles in dBB, they are free to try to find a published source making this objection (not making a different objection which they interpret as this one, but actually making this one) and quote it under an appropriate sub-heading in the objections/polemics section.

There is also a "neutral point of view" issue here that needs to be made explicit. Dvtausk and Jostylr and myself and others seem to be complying with this principle in the sense that we welcome meaningful/sensible objections (like the "superfluity" objection) to a theory that we like, even though apparently we all think this particular objection is ultimately wrong/misguided. Note that none of us has even gone into why we think this objection is ultimately wrong/misguided -- why, that is, it is completely groundless handwaving to claim that MWI (which has no local beables at all) can account for our experience. The reason I at least haven't gotten into this is that it shouldn't be relevant to the dBB page: there are people who have a different basic understanding of what it means for and/or what is required for a theory to be empirically adequate; such people see dBB's particles as superfluous; and right or wrong that view should be included on a list of objections to dBB on the dBB wikipedia page. On the other hand, it seems that Michael Price is fundamentally unable or unwilling to adopt a "neutral point of view" on this issue. He personally believes strongly in MWI and so personally believes strongly that the dBB particles are superfluous -- and unobservable. Fine. As far as Wikipedia is concerned (i.e., leaving aside questions of truth) there is nothing wrong with his having those views. But there is something wrong with his unwillingness to do what everybody on the other side is willing to do -- namely, recognize that there is an other side -- i.e., adopt a NPOV and accept that, even if he doesn't agree with it, there is a reasonable and coherent position according to which dBB's particles are anything but superfluous and unobservable.

How to proceed? I think we need to recognize that (i) not only is this issue kind of small potatoes in the sense that there are other more important things that should be worked on in the dBB article, but (ii) there is no need or obligation to convince people like M Price that he is wrong before corrective improvements to the article can be made. Instead, the obligation lies with M Price -- just as it lies with every editor here -- to adopt a NPOV and make the article clearer/better in terms of what published experts actually think about the topic at hand. So let's just get on with the business of doing that, already. Tnorsen (talk) 14:05, 25 November 2009 (UTC)

Tnorsen, I note that you have not even attempted to refute the simple syllogism I posted earlier. No matter, Wallace and Brown say that the particle is not involved in measurement. Do you propose pedantically splitting measurement and observation apart, or are you happy to say that Wallace et al understand Everett as regarding the particle as unobservable?

BTW, since you don't understand Everett, and in particular how he thinks the wavefunction "can account for our experience", I don't think you are in any position to judge whether I am correctly presenting or rephrasing his views, or those of his followers.

--Michael C. Price ^talk 17:50, 25 November 2009 (UTC)

There is a difference between understanding something and agreeing with it. I actually do understand Everett. I even have quite a high respect for MWI. I just happen at the end of the day not to agree with it. But unlike you, I don't let that "end of the day" assessment blind me to what different people are saying and why. That's why I'm comfortable saying: Everettians and Bohmians have different basic attitudes about what it means for a theory to be empirically adequate; from the perspective of most Everettians, the wf alone provides enough ontology for an empirically adequate theory, and so they think of dBB's particles as superfluous complications; whereas Bohmians deny this and think that a theory must have local beables to even stand a chance of being empirically adequate; but the fundamental disagreement (about what empirical adequacy means, exactly, in the context of fundamental physical theories) is subtle and complicated and shouldn't stand in the way of a fair and neutral presentation of dBB or the Everett-type objections to it. You, on the other hand, apparently cannot set aside your views -- i.e., adopt a neutral point of view -- even enough to recognize that, on its own terms, dBB's particles are anything but superfluous and/or unobservable. Instead you keep making these ridiculous arguments -- which have been refuted a hundred times over by Dvtausk -- that are based entirely on your own biased, un-neutral point of view. So, starting now, I'm going to follow my own advice and stop responding to such arguments and instead devote whatever time I have for wikipedia on improving the article(s). Tnorsen (talk) 18:47, 25 November 2009 (UTC)

I understand the difference between understanding and agreeing. Your claim that you understand Everett is contradicted by the statement you made: it is completely groundless handwaving to claim that MWI (which has no local beables at all) can account for our experience. --Michael C. Price ^talk 19:02, 25 November 2009 (UTC)

Certainly I have to stop the discussion with Price. I do have a life and other things to do, and I would like to also have time to work on other aspects of this article that are more substantial and that need improvement. People should have at least a little bit of good judgement and realize that, for a Wikipedia article, if there is a big polemics about what a given author's intentions were in a given quote, then one should be as faithful as possible to that author's words, instead of trying to push into the article their own views of what the author's intentions were.Dvtausk (talk) 17:41, 25 November 2009 (UTC)

Quotes can be taken out of context. Since you don't understand the concept "superfluous", nor that all observations flow from the wavefunction in Everett's theory, this is what is happening. --Michael C. Price ^talk 17:50, 25 November 2009 (UTC)

Price: "Do you propose pedantically splitting measurement and observation apart, or are you happy to say that Wallace et al understand Everett as regarding the particle as unobservable?". I propose to say exactly what those authors (Brown & Wallace) have said: that (according to them), the particles play no role in the solution of the measurement problem (instead of twisting what they said into "the particles play no role in measurement", which can mean all kinds of things). I certainly know that in Everett's theory all observations flow from the wavefunction. It is certainly a bad thing to try (like you did once, with Bohm's quotes) to take quotes out of context in order to make it seems like the author is saying something that he doesn't mean. But no one has claimed that the Everett quote, when taken out of its context, says something that Everett wouldn't agree with. Maybe it says less than what Everett would like to say. But that is just your opinion and we can't risk putting words in Everett's mouth because of your opinion. As Jostylr said, "In saying what someone meant, it is very important to be conservative". I really have to stop wasting time on you. You have stopped being reasonable for a long time, now.Dvtausk (talk) 19:42, 25 November 2009 (UTC)

Since you (and I don't just mean Dvtausk) choose not to understand words and syllogisms when they conflict with your POV, perhaps you will have to be spoonfed quotes. Such as this Wallace and Brown gem:

the corpuscle’s role is minimal indeed: it is in danger of being relegated to the role of a mere epiphenomenal ‘pointer’, irrelevantly picking out one of the many branches defined by decoherence, while the real story — dynamically and ontologically — is being told by the unfolding evolution of those branches. The “empty wave packets” in the configuration space which the corpuscles do not point at are none the worse for its absence: they still contain cells, dust motes, cats, people, wars and the like. The point has been stated clearly by Zeh:

It is usually overlooked that Bohm’s theory contains the same “many worlds” of dynamically separate branches as the Everett interpretation (now regarded as “empty” wave components), since it is based on precisely the same . . . global wave function . . .

Deutsch has expressed the point more acerbically:

[P]ilot-wave theories are parallel-universe theories in a state of chronic denial.

No problems with that appearing in the article, I take it?

And of course footnote 47 should appear as well:

It is noteworthy that the active role of the corpuscles in the de Broglie-Bohm theory is merely to act on each other, not back on the wavefunction. So it is striking that such passive entities are purportedly capable of grounding consciousness experience.

Along with their parting words:

observation—in so far as this is related to the cognitive process of “knowing” the outcome of the measurement process—is not discovering the position of the de Broglie-Bohm corpuscle even if it exists.

--Michael C. Price ^talk 22:58, 25 November 2009 (UTC)

This quotes are good too (from the same article):

"This last sentence is unimpeachable, and it applies as much to the Everett as to the de Broglie-Bohm interpretation. But Maudlin seems to be taking it for granted that our conscious perceptions supervene directly and exclusively on the configuration of (some subset) of the corpuscles associated with our brain. If this is so, it is true we gain information by way of such correlations between corpuscles in and outside of our craniums. But the question is, why believe this theory of psycho-physical parallelism?" (pg. 14)

"To restrict supervenience of consciousness to de Broglie- Bohm corpuscles in the brain does succeed in restricting conscious goings-on to one and only one branch of the Everett multiverse but it seems unwarranted and bizarre." (pg. 15)

which prove exactly my point. This authors agree that, once all the assumptions that constitute dBB are made, the observability of the dBB particles follow. They just don't agree that the assumptions that constitute dBB are reasonable.Dvtausk (talk) 23:36, 25 November 2009 (UTC)

Quotes from the abstract or "conclusions" have greater weight. And, of course, your interpretative comments would not be permitted in the article by the standards that you preach. --Michael C. Price ^talk 23:52, 25 November 2009 (UTC)

Well, if some reader (familiar with the standard assumptions of dBB, as presented in the dBB literature) sees just the quotes that you present (specially the last one, in isolation), he might think that those authors (Brown & Wallace) are ignorant and merely unaware of what the standard assumptions of dBB are. That's unfair to Brown & Wallace. If the reader also sees the quotes that I suggested, he will realize that the authors are not ignorant and unaware of the standard assumptions of dBB, but that they have bothered to present some type of argument explaining why they consider those assumptions unreasonable. But I'm guessing that you couldn't care less about not making some authors look ignorant and stupid, as long as the Wiki article says exactly what you want to say.Dvtausk (talk) 12:28, 26 November 2009 (UTC)

It is more likely that they will see the Everett quote about superfluous particles, and realise that the Wallace and Brown quote about unobservable corpuscles follows directly from it. That's if they're open minded. Not otherwise, as we've seen. But that's your choice and your problem, not mine. --Michael C. Price ^talk 16:24, 26 November 2009 (UTC)

I'm writing this "for the record" and for any reasonable person who might be reading it (not for Price, since too much time was already wasted with him): from my discussion with Price, it became clear that he does not even agree that the dBB particles are observable in a world governed by dBB, and that knowing that dBB assumes that the observers and the ordinary objects of experience are made out of the particles. So, it seems like he disagrees with a tautology of the form $P\Rightarrow P$, so it is beyond unreasonability (Brown & Wallace don't share his "position", they don't disagree with a tautology, they merely believe that the dBB assumption that observers and ordinary objects of experience are made out of the particles is unreasonable). Maybe Price thinks that dBB is logically inconsistent (as he claims to believe), but if that is the case, that's should be his central criticism of dBB, as logical inconsistency of dBB would make the issue of observability of things whose existence is posited by dBB irrelevant. Maybe Price does not even understand the difference between the activity of trying to figure out what theory should we believe is true and the activity of trying to figure out what follows from a given theory (i.e., from its assumptions). When I have more time, I will rewrite the "objections" section, in a way that does not misrepresent the critics positions, don't make them look stupid and ignorant, and I will be as faithful as possible to the wordings of their quotes. In a nutshell, Everett thinks that particles are superfluous, as his pure wave theory is already satisfactory. Brown & Wallace believe that certain assumptions about the relationship between the dBB particles and physical reality are unreasonable and unjustified, and that the particles play no role in solving the measurement problem.Dvtausk (talk) 22:33, 26 November 2009 (UTC)

Supplying the critics' quotes (as I have listed earlier) only makes "them look stupid and ignorant" to people who are too stupid or ignorant to read the linked sources. Since we are unable to resolve the logic of the situation here I am quite content to follow Dvtausk's earlier advice of letting the quotes speak for themselves and post them in their entirety into the article, devoid of interpretive comments by either side. However if he now finds his earlier advice inconvenient I'm quite happy to continue the discussion about how to rephrase things for clarity.--Michael C. Price ^talk 23:22, 26 November 2009 (UTC)

Most people will just read the Wiki article and not all the references. I imagine that Price would be "happy to continue the discussion", since it is me who is really doing all the discussing, i.e., I actually went through the trouble of trying to understand his point of view, trying to find some common ground, presenting full careful explanations of my points, giving examples/counter-examples when he asked for them, and presenting careful analysis of the arguments that he has proposed. That consumes a lot of energy and time and I have other things to do. Price, on the other hand, ignores most of what I write. But, let's be fair, he has finally said something reasonable and took notice of the existence of another side. I have never given advice that one should write nothing but quotes (for instance, I didn't complain about the use of the ether as an example of superfluous). My advice has been that, whenever there is disagreement about what a quote means, interpret it as little as possible and be faithful to the wording of the author (i.e., be conservative). It's hard to imagine how someone could dispute, after reading pgs. 14, 15, that Brown & Wallace agree that, under a certain set of assumptions (considered unreasonable by those authors), the dBB particles become observable in a world governed by dBB. But I don't doubt that Price will dispute that claim (or pretend that he does, for whatever strange reasons he might have). In any case, I'm actually ok with using nothing but quotes (and, obviously, a small introduction to the quote of the sort "According to ...:"). Of course, that doesn't mean that Price gets to veto the quotes that I find relevant (I wouldn't be surprised if he actually proposes something absurd like that). But I should say that writing nothing but quotes is not good editing and the section will look strange, but still much better than it is right now.Dvtausk (talk) 02:30, 27 November 2009 (UTC)

Since most of what you have written has been evasive or repetitive, of course I ignored most of it. I note yet another howler: It's hard to imagine how someone could dispute, after reading pgs. 14, 15, that Brown & Wallace agree that, under a certain set of assumptions (considered unreasonable by those authors), the dBB particles become observable in a world governed by dBB. I am content to let their words speak for themselves on this matter:

The Result Assumption appears to be inconsistent with .. or at least to override it [i.e. dBBt] in some mysterious way.

Note the word "inconsistent" please, along with their final words:

observation—in so far as this is related to the cognitive process of “knowing” the outcome of the measurement process—is not discovering the position of the de Broglie-Bohm corpuscle even if it exists.

Note: "even if it exists" i.e. irrespective of what dBB result assumptions are made . --Michael C. Price ^talk 03:46, 27 November 2009 (UTC)

You have proven my point by again ignoring what I write (and what others write) when it is incovenient to you. I said "It's hard to imagine how someone could dispute, after reading pgs. 14, 15, that Brown & Wallace agree that, under a certain set of assumptions (considered unreasonable by those authors), the dBB particles become observable in a world governed by dBB.". I said "a certain set of assumptions", not "the result assumption", and if you had bothered to actually read pg. 14 (the discussion after the Maudlin quote), you would know that the "certain set of assumptions" that I was refering to was the so called "psycho-physical parallelism" (implied by the Maudlin quote and explicitly suggested by Bell), not the "result assumption". Moreover, notice that "even if it exists" does not mean "irrespective of what dBB result assumptions are made", it means that it is not enough to assume that it [the particle] exists (and in fact it isn't). Reading the passages you suggested (yes, I have actually bothered to do that, as I have the habit of not ignoring what you write) in the article (bottom of pg. 6, you could have been helpful and have given me the page, as I do when I suggest quotes), I see that you have twisted it a bit (by adding your [i.e., dBBt]) and making it sound like the authors are talking about logical inconsistency of the result assumption with the theory, while the authors are discussing the solution of the measurement problem (comparing the single outcome case with the multiple outcome case). Anyway, formulating dBB using a explicit "result assumption" is indeed a strange way of formulating dBB. Bohm wasn't such a good expositor of the theory and if one wants to make a careful analysis of its assumptions it would be ridiculous to focus only on Bohm (I guess Brown & Wallace would agree, as they don't focus only on Bohm).

But why are we back discussing this? Apparently, there was agreement on the quotes only strategy.Dvtausk (talk) 13:41, 27 November 2009 (UTC)

And if you find a Wallace & Brown quote that says "the dBB particles become observable in a world governed by dBB" you are welcome to insert it into the article. --Michael C. Price ^talk 16:36, 27 November 2009 (UTC)

Great. There is no quote with that exact wording, of course, but I will use the quote where they respond to Maudlin on pg. 14 (along with the Maudlin quote, so that some context is given). I know that you will object to an explicit explanation of the sort "Brown & Wallace agree that, under such and such assumptions, the dBB particles are observable in a world governed by dBB", but since that meaning is clear from the quote itself, I don't really have to add any explanation.Dvtausk (talk) 22:17, 27 November 2009 (UTC)

Quite what you think the relevance of Maudlin's quote is escapes me, but, as along as you don't tack on one of your imaginative fairy stories next to it, I don't care. Be my guest! --Michael C. Price ^talk 22:31, 27 November 2009 (UTC)

This back and forth between Michael and Dvtausk is not going anywhere. For an up to date response to MWI from the viewpoint of pilot wave theory, I would recommend:

http://arxiv.org/PS_cache/arxiv/pdf/0811/0811.0810v2.pdf

To respond briefly to a couple of points that Dvtausk made earlier, note that I am not saying that particles are hidden—don’t misquote me!—merely that for Bohm the hidden variables were in fact hidden (in spite of loose statements by Bell and others that the particles “are” the hidden variables). The point here being that much of the confusion on this talk page and in the article has to do with confusion surrounding the basic concepts with which we talk about particles, observables, hidden variables and so forth. The “hidden variable” section in the current article, for instance, does little to explain what Bohm himself understood by “hidden variables” or why in the world he called his first approach ‘an interpretation in terms of hidden variables.’ Regarding PSI squared and equilibrium thermodynamics, the passage from Bohm is the starting point but already in 1952b (Bohm’s initial response to the “measurement problem”) you have chaotic motions of the subquantum level, and the then there is the article in 1953 where he lays out his own view of how to interpret the Born rule (aka quantum equilibrium hypothesis), and finally you have the Bohm-Vigier hydrodynamic model which explicitly incorporates a stochastic element above and beyond the “deterministic chaos” approach. But again, for Bohm, the important thing about the rule is that it provides a measure of the probability of a particle actually “being “somewhere-(think beables) rather than “finding” a particle somewhere (think observables). Also, what is interesting about the Bohm approach is not so much that through p=Psi squared you come to the same results as CI, but rather that it can account for situations in which p does not equal Psi-squared. Valentini has some interesting comments along these lines which at least brings the theory in line with non-equilibrium thermodynamics and modern cosmology.

Signing off for the weekend.

Someone start a new section!

Sfwild (talk) 19:48, 27 November 2009 (UTC)

Thanks Sfwild, for supplying us with a new source. An interesting presentation, especially about the historical development w.r.t. de Broglie and Schrodinger. The core of their claim lies in the section "'microscopic' many worlds". I was a bit disappointed in the level of their logic in that section, which basically is "since there is only one particle there is only one particle, ergo many worlds is refuted". Their "counter-claim" is amusing: they "accuse" MWI of being motivated by a desire to return to a classical world-view. I thought that common knowledge..... --Michael C. Price ^talk 22:43, 27 November 2009 (UTC)

I had to laugh at the sentence just added:

Most importantly, the "more than minimally necessary" criticism depends on the premise that the Many World interpretation is valid science. Since Everettian theory requires an infinite number of alternative realities, it is clearly meta-physical instead of scientific. The premise fails and Bohmian mechanics remains the leading philosophical foundation of quantum mechanics that is complete, rigorous and self consistent.

so blatantly biased and unsubtle that I think I'll leave it in.--Michael C. Price ^talk 03:39, 30 November 2009 (UTC)

I have undone it. The sentence is not only biased, it is also very strange. It is not clear what is meant by "metaphysical" in that sentence. But you (Price) are not in a position to laugh at anybody.Dvtausk (talk) 22:10, 1 December 2009 (UTC)

Price. You squat on this article like a rabid Islamist who somehow ended up being in control of the article on Christianity: "Well, the filthy heathens might say that, but of course we all know Jesus was at best a minor prophet." It has been established beyond doubt - multiple times - that you are not an expert on de Broglie-Bohm theory, you have admitted to having read very little on the subject, and the only reason you insist on hanging around here seems to be to lash out violently if anyone dares to write anything nice about it. I threatened to give this article the major rewrite it so badly wanted a few months back but you irritated me so much that I gave up in frustration. So now three or four other guys have now come in and done the great job that you so manifestly failed to do in the previous five years, why don't you just give them a bit of encouragement and be grateful instead of acting like a moron? Please, you've been asked before - go and edit the article on ballet dancing or something. Are you even a physicist, or just some unemployed Wikipedia nerd sitting in a basement somewhere getting a rise out of annoying people? Just go somewhere else and do something useful.. please. If you give me your address, I might even send you 50 dollars to lessen the pain. Zicovich (talk) 20:39, 30 November 2009 (UTC)

No, Zicovich, I am not "in control of the article"; my only interest is in seeing that Everett's criticism is not distorted, in one small subsection of the article, by POV-pushers who can't bridge the paradigm-gap between the two world views. I have expressed opinions on the rest of the article, but have applied no edits to it for quite awhile.--Michael C. Price ^talk 01:13, 1 December 2009 (UTC)

Michael, seriously. Give it up. Everyone is so bored of you I can't express it in words. Have you considered alcoholism? Zicovich (talk) 01:24, 1 December 2009 (UTC)

Yes, having your POV pushing blocked is boring, isn't it? What you, and some others, need to do it to re-examine your own prejudices and preconceptions. But, you're right, I'm wasting my time here since no one seems interested in actually trying to understand what Everett, Wallace, Brown et al are saying. Quit trying to understand MWI through a dBBt prism and you might get somewhere. --Michael C. Price ^talk 01:36, 1 December 2009 (UTC)

Vodka perhaps? Cheap bourbon? Zicovich (talk) 01:59, 1 December 2009 (UTC)

Some curious comments about my "discussion" with Price. This is something that Price wrote up there in this section of the talk page, in a reply to Tnorsen: "I agree that section should not imply that the bohmian particles are -- according to the dBB theory -- unobservable. If it does imply that then it should be corrected, but I thought it said that they were regarded as unobservable from the Everettian perspective" Now, a while after that, I asked Price about whether his claim "In Everett's view, dBB particles are not observable" is supposed to mean:

(1) "Everett believes that, in a world governed by dBB, the observers cannot observe the dBB particles";

or

(2) "In a world governed by Everett's theory, the observers do not observe dBB particles".

? Price's reply was that he means (1). That seems to be somewhat inconsistent with his own earlier statement that he does not want to claim that "the bohmian particles are -- according to the dBB theory -- unobservable".

The problem with Price is not just ignorance of dBB, the problem is that he does not understand the criticism of Everett (or of Brown & Wallace) to dBB, and that he has serious trouble following very simple logical reasonings. He does not seem to get that his "position" denies a tautology of the form $P\Rightarrow P$ (i.e., he denies that, according to a theory having P among its assumptions, P holds). More importantly, he does not seem to understand the difference between the following two activities:

(a) given two competting theories T, T', which one is the best? Which one should I believe in?

(b) given a theory T, what follows from it? (i.e., what follows from its assumptions?).

Occam's razor has a role for activity (a), but it has no role for activity (b). Activity (b) rarely generates controversies (it involves only logical deductions from a given set of assumptions), while activity (a) often does. The disagreement between a typical Bohmian and Everett (or between a typical Bohmian and Brown & Wallace) is a disagreement that appears during the practice of activity (a), i.e., during theory selection. Everett believes his theory is simpler and better. Brown & Wallace dispute the reasonability of certain fundamental assumptions of dBB. If (1) were true (i.e., if Everett thought that dBB particles would be unobservable in a world governed by dBB), Everett would disagree with the Bohmian in the practice of activity (b).Dvtausk (talk) 22:05, 1 December 2009 (UTC)

Well, if you going to quote me out of context, we not going to get anywhere. The full paragraph was more explicit (although evidently not explicit enough):

I agree that section should not imply that the bohmian particles are -- according to the dBB theory -- unobservable. If it does imply that then it should be corrected, but I thought it said that they were regarded as unobservable from the Everettian perspective.

So let's be clear. According to the Bohmites, the particles in dBBt are observable. According to the Everettarians the the particles in dBBt are unobservable. i.e. it depends on your perspective.

--Michael C. Price ^talk 23:19, 1 December 2009 (UTC)

The sound of mass snoring begins to echo around the world. Zicovich (talk) 00:00, 2 December 2009 (UTC)

So, Price is complaining that I quoted him out of context, that I should have quoted the full paragraph instead. Should I mention that my quote turns out to be exactly the same as what Price calls "the full paragraph"? (it is indeed the full paragraph! And if someone needs more context than that, just press page up a few times).

Maybe, when Price wrote the paragraph "I agree that section should not imply..." he was a little careless and didn't mean exactly what he wrote. That's ok. The sad thing is that the paragraph that he wrote "by mistake" is actually very sensible, while his later claims about the subject are not. He says: "According to the Bohmites, the particles in dBBt are observable. According to the Everettarians the the particles in dBBt are unobservable. i.e. it depends on your perspective.". Maybe what he means when he writes this is that, when a detector flashes, the experimenter that believes in dBB thinks "I detected a particle", while the experimenter that believes in Everett's theory thinks "I detected a wave packet". If that is what Price means, then Price is trivially right. Maybe that is just what he really meant all the time. Notice that the experimenter that believes in dBB and the experimenter that believes in Everett's theory disagree about theory choice (what I called (a)), not about what follows from a given theory (what I called (b)). The trouble is, Price also insists in disagreeing with the claim "in a world governed by dBB, the dBB particles are observable". Now, this is disagreement about what follows from a given theory (the (b)), not about theory choice (the (a)). Sometimes people do disagree about what follows from a given theory; sometimes, the formulation of a given theory is not completely sharp, so that there can even be some reasonable disagreement about what follows from a given theory. However, in the case at hand, the disagreement is particularly odd, since it is among the assumptions of dBB that the observers and the ordinary objects of our experience (tables, chairs, cats, ...) are made out of the particles. So, while there could be some reasonable disagreement about what follows from a given theory, no sane person would disagree that an assumption follows from itself. When one says "in a world governed by dBB", it is meant "a world in which all of the assumptions of dBB are true" and, in particular, "a world in which the observers and the ordinary objects of our experience are made out of the particles". Obviously, in a world like that, the observers observe the particles. If a sane person disagrees with the claim "in a world governed by dBB, the dBB particles are observable", I can only think of two possible explanations:

(i) the person is unaware that the assumptions of dBB include "the observers and the ordinary objects of our experience are made out of the particles";

(ii) the person believes that dBB (which includes the assumption mentioned above) is an inconsistent theory.

In the case of Price, (i) cannot possibly be true, as he has been informed many times, during this discussion, about the assumptions of dBB. He might complaint (as he has done before, in this discussion) that such assumptions are not all very explicit in Bohm's original articles. But so what? We are not here to criticize the exact writings of Bohm, but to talk about "the theory dBB", a theory which is the object of work of a certain community of people. Just ask any of those people what the assumptions are, or look up the literature.

Maybe, in the case of Price, (ii) is true, i.e., Price believes that dBB is inconsistent. He has said that a few times during this discussion. If that is the case, then he is wrong, but at least his position would be more understandable (it is certainly more sensible than denying $P\Rightarrow P$). But, if Price believes that dBB is inconsistent, our situation here is still quite odd; for, if Price believes that dBB is inconsistent, then he should in fact object to any discussion about what would be observable in a world governed by dBB, as it doesn't really make much sense to talk about a world governed by an inconsistent theory. Any author who believes that dBB is inconsistent would not bother to "criticize" dBB, such author would plain and simply explain how a contradiction can be logically deduced from the assumptions of dBB, and that would be fatal to dBB. That author wouldn't really have to say anything else about the subject.

Price, in one of his (not so uncommon) dirty moves, seizes on a quote from Brown & Wallace in which the word "inconsistent" appears and tries to make it look like they are saying that dBB is inconsistent. But, it is easy to see, by actually reading the entire quote, that they are not saying that. I believe that there are people out there who (wrongly) believe that dBB is inconsistent; normally, these are people who do not understand why something like dBB is not ruled out by the many so called "no hidden variables" theorems that are out there. But this is not the position of Everett, or Brown & Wallace.

It would be quite amusing to let Price write down what he thinks might be a proof that dBB is inconsistent. Is it possible that Price believes that the "Occam's razor" argument can be used to prove that dBB is inconsistent? Is it possible that Price believes that, if one can find a theory which is (empirically equivalent and) simpler than T, then it follows that T is inconsistent? That would be very odd indeed, as it would also show that he does not even understand what "consistency" means.Dvtausk (talk) 02:31, 2 December 2009 (UTC)

You are correct, I was not quoted out of context; however this changes none of the substantive points. As you indicate, option (ii) is my belief and also that of Brown and Wallace and Everettarians generally, namely that the particles are not observable. Obviously Bohmites don't accept this result, which is why it is a matter of perspective. This is the inconsistency that Brown and Wallace refer to (which I don't accept is a misreading of their paper). The inconsistency is between "dBBt as explicitly formulated by Bohm" and the implicit result assumption.

To be explicit: in "dBBt as explicitly formulated by Bohm" the particles are not observable. Adding the result assumption to the theory produces the inconsistency, since the particles can't be both observable abd unobservable.

--Michael C. Price ^talk 07:08, 2 December 2009 (UTC)

So, Price's idea is that "Everettarians" have a proof that dBB is an inconsistent theory, but instead of saying that out loud, i.e., having a section on an article whose title is "Proof of the Inconsistency of dBB", they decide to hide that claim in the middle of some discussion of the measurement problem? That's really interesting.

For those who don't know, here is the Brown & Wallace quote we are talking about (it starts on pg. 6):

"Most discussions of the measurement problem in quantum mechanics take it for granted that no difficulties arise in this case of the predictable outcome -- that the problem only rears its head in the more interesting and more general case of unpredictability, when the initial state of the object system is some linear combination of eigenvectors of the relevant observable. But if analysis of the predictable case is successful without appeal to hidden variables, then Bohm’s Result Assumption in the general case is problematic. In the general case, each of the non-overlapping packets in the final joint-system configuration space wavefunction has the same credentials for representing a definite measurement outcome as the single packet does in the predictable case. The problem, if it is one, is that there is more than one of them. But the fact that only one of them carries the de Broglie-Bohm corpuscles does nothing to remove these credentials from the others. Adding the corpuscles to the picture does not interfere destructively with the empty packets. The Result Assumption appears to be inconsistent with the treatment of the predictable case, or at least to override it in some mysterious way."

Brown & Wallace are saying that "Bohm's result assumption" is (or "appears to be") inconsistent with the idea that there is no measurement problem in the single outcome case. Nowhere in this paragraph are Brown & Wallace claiming to have a proof that dBB is inconsistent.

Moreover, it is a little silly to waste that much time discussing the so called "Bohm's result assumption", as that assumption does not really explicitly appears in Bohm; that's just Brown & Wallace reading of Bohm and in fact Brown & Wallace are not that sure about whether Bohm would agree with that reading:

"How literally Bohm meant this is perhaps open to debate..." (see also footnote number 24 on pg. 6 of Brown & Wallace).

As for Price's last statement: "in "dBBt as explicitly formulated by Bohm" the particles are not observable. Adding the result assumption to the theory produces the inconsistency, since the particles can't be both observable and unobservable." It seems that Price is trying to argue that, if a certain theory T, proves not(P), then adding P to the assumptions of the theory, we get an inconsistent theory. That is indeed true. What is not true is that the theory T="dBB without any assumptions connecting the particles or the wave function to the ordinary objects of experience" proves not(P), where P="the particles are observable". Theory T does not prove P and it does not prove not(P) either. Therefore, adding P does not produce an inconsistency.

Now I would like Price to explain what he thinks Brown & Wallace are saying in the paragraph on pg. 14, after the Maudlin quote.Dvtausk (talk) 15:49, 2 December 2009 (UTC)

Syllogism time. We have two sentences:

1. The Result Assumption appears to be inconsistent with the treatment of the predictable case, or at least to override it in some mysterious way.
2. But if analysis of the predictable case is successful without appeal to hidden variables, then Bohm’s Result Assumption in the general case is problematic.

Given that W&B consider 1) to be true, ergo 2) is true, ergo Bohm’s Result Assumption in the general case is problematic.

--Michael C. Price ^talk 17:21, 2 December 2009 (UTC)

Dvtausk: In the old Usenet days they used to call what you're doing 'feeding the troll'. Do you really have that much free time? Zicovich (talk) 16:59, 2 December 2009 (UTC)

Price, something you surely don't -- and probably won't -- understand is that many if not most if not all people who understand and like dBB theory would actually dispute that "analysis of the predictable case is successful without appeal to [something beyond the wave function]". Certainly it is my belief that if, at the end of some experiment, the wave function for all the degrees of freedom constituting a chair is an eigenstate of the "having a chair shape" operator and also the "being pretty much in some definite place" operator, that isn't the same as the wave function actually containing or implying the existence of a chair in some definite place. Rather, it implies that the wave function has support that is localized in some particular region of the high-dimensional space in which wave functions live. That simply doesn't look like a chair to me, and anybody who says that you can find a chair in that lump of wf if you analyze its structure in just the right way, inherits a rather large burden of explaining exactly how you need to analyze it and why that's the right way. This is why, for example, Ghirardi thinks that some kind of ontology of stuff in 3-space (like mass fields or flashes or who knows what) has to supplement the wave function in the context of GRW theory. And it's why people (like me) who like dBB say things like what I said much earlier (and which you took as somehow proving that I don't understand everett) -- namely, that (from this perspective) one can't even really take seriously the idea of a theory being empirically adequate when it doesn't even have any local beables. Hopefully that should clarify why you are simply off the track from the beginning if you start an argument with: "well, clearly there's no problem or ambiguity in the case where the wave function for the pointer ends up in an eigenstate of the 'pointing in a definite direction' operator."

That said, I invite you to have the last word on it. I agree completely with those who have said (and it includes myself last week) that talking with you further about any of this stuff here is a complete waste of time. My comments here, really, are just for the purpose of acknowledging (for others who might read it) another of the ways in which you (and to some extent Brown and Wallace) simply don't understand the point of view you claim/want to refute. Tnorsen (talk) 22:24, 2 December 2009 (UTC)

Tnorsen, I have no problem understanding that point. What I think you don't realise is for an Everettarian the wavefunction is the local beable. --Michael C. Price ^talk 00:07, 3 December 2009 (UTC)

Tnorsen, I agree with you that, even in the predictable case, a pure "wave function outcome" is not satisfactory, i.e., some local beable (in three-dimensional space) is needed to count as an actual outcome. However, there is room for reasonable disagreement here and there are reasonable people out there who would disagree with the inadequacy of a pure wave function ontology (I think, for instance, David Albert would be an example of a reasonable person with that view). I'm concerned that what you wrote might be misunderstood and lead someone to believe that, because of Brown & Wallace's argument, the consistency of dBB hangs on the settling of that issue. I should mention that the "result assumption", in the precise way formulated by Brown & Wallace, is really just a straw man; it has nothing to do with dBB. The "result assumption", as formulated by Brown & Wallace, most certainly is problematic and shouldn't be in the formulation of a theory (even though, I don't think it leads to any inconsistencies).Dvtausk (talk) 23:57, 2 December 2009 (UTC)

Dvtausk: I didn't mean to claim that what I wrote is the only reasonable point of view, just that it is a point of view held by many eminently reasonable dBB-fans, and one that (his response to the contrary notwithstanding) is simply not on the radar of people like Price. (Note that his response proves about as unambiguously as one could have hoped for that he doesn't know what "local beable" even means!) You might be right about David Albert (whom I certainly agree is quite reasonable); I'm not sure what he would say; but I have a vague recollection that I first heard the point that even in the "predictable case" there is a "measurement problem" from a talk of his. But I don't really remember for sure, and it doesn't matter anyway. Also, I certainly agree with you that the "consistency of dBB" isn't in any way in question here. I was just trying to provide a sense of why/how some Bohmians will reject Price's whole approach at the very beginning: namely, according to a certain reasonable point of view, empirical adequacy requires local beables, and so the idea of jettisoning dBB's local beables (as allegedly "superfluous") but keeping the empirical predictive content the same, is (absent the successful completion of a huge project of showing how appropriate local beables can be unambiguously extracted from nonlocal beables without massive additional assumptions) nonsensical. Tnorsen (talk) 02:03, 3 December 2009 (UTC)

Tnorsen, you can claim that stuff "is simply not on the radar of people like Price" if that makes you feel good, I don't care. Do you understand that this is all irrelevant to the section of the article where we are trying to portray the views of Everettarians? BTW, Bell says The beables of the theory are those elements which might correspond to elements of reality, to things which exist. Their existence does not depend on 'observation'. (p174, Speakable and Unspeakable...) Everettarians regard the wavefunction as real and independent of observation. Think about it. --Michael C. Price ^talk 02:41, 3 December 2009 (UTC)

Price, I'm having a nice day so I'm going to be nice and help you understand what Tnorsen is talking about: be aware of the difference between "beable" and "local beable" (local beables are required to live in three-dimensional physical space --- or in four-dimensional spacetime --- so a wave function, in configuration space, by definition, cannot be a local beable).Dvtausk (talk) 02:51, 3 December 2009 (UTC)

The wavefunction is no different from the particle, which also lives in configuration space, but projects onto our 3-D space. (Hint: the co-ordinates of the wavefunction and particle are the same.) So if the particles are local beables, then so is the wavefunction. --Michael C. Price ^talk 03:13, 3 December 2009 (UTC)

The trajectory of each particle is a curve in 3-dimensional space (alternatively, you could describe the particle configuration as a map defined in 3-dimensional space, taking values in {0,1}, assigning the value 1 to the points in which there is a particle). The wave function, however, is a field in 3n-dimensional configuration space (not in 3-dimensional space), and any type of "projection" of the wave function onto 3-dimensional space would give rise to an object which contains much less information than the wave function. So, now you decided to make a fool of yourself also in the technical subjects?Dvtausk (talk) 03:33, 3 December 2009 (UTC)

The N particles can also be regarded as one trajectory in 3N configuration space, with each particle projecting onto 3-space and containing less information than the total trajectory, just as is the case with the wavefunction. As I said, the co-ordinates of the wavefunction and particle are the same. --Michael C. Price ^talk 03:52, 3 December 2009 (UTC)

Man, you gotta be "playing dumb" here, cause I just can't believe that you are that dumb. The particles can be regarded as a curve in 3n-space, but the important thing is that they also can be regarded as n curves in 3-space or as a {0,1}-valued field in 3-space, while the wave function cannot be understood as something that lives in 3-space (and I don't think the sentence "the co-ordinates of the wavefunction and particle are the same" really means anything; perhaps you're comparing the coordinates of the particles positions with the coordinates of a point in the domain of the wave function, but that's not really relevant). You don't have to agree that local beables are important, but a wave function most definetely is not a local beable, it is like the standard example of something that is not a local beable. Now, go ahead, pretend that you don't understand me and write something stupid below this paragraph. I won't respond.Dvtausk (talk) 11:43, 3 December 2009 (UTC)

I was trying to keep things simple for you. Locality is a slippery concept that is interpretation-dependent. MWI is local, dBBt is not. Once again you are viewing the world through your interpretative prism. Broaden your mind with Locality in the Everett Interpretation of Heisenberg-Picture Quantum Mechanics, which concludes Everett’s model for measurement in the Heisenberg picture provides a quantum formalism which is explicitly local and in which the problem of Bell’s theorem does not arise.. --Michael C. Price ^talk 12:18, 3 December 2009 (UTC)

Tnorsen, my evidence about David Albert's opinion is indirect: I read on the "Common structure" paper http://arxiv.org/PS_cache/quant-ph/pdf/0603/0603027v4.pdf in section 4.3 that David Albert takes GRW0 (GRW without primitive ontology) as a serious theory. I'm not completely sure about what that implies concerning his position on the measurement problem in the predictable case.Dvtausk (talk) 02:58, 3 December 2009 (UTC)

I don't have that much free time. The thing is, once in a while, Price says something sensible and that brings me back to the discussion. But, then, he starts to behave like a troll again (like he just did, playing dumb and pretending that he didn't understand my point), and I regret that I got back into the discussion.Dvtausk (talk) 18:30, 2 December 2009 (UTC)

I don't know what point you think I played dumb over (and no doubt this will be interpreted as playing dumb). I'll grant that I often only respond to one point for the simple reason that where I have made multiple points usually only one has been been responded to. For that reason I always try to respond to what seems the most important point. --Michael C. Price ^talk 18:47, 2 December 2009 (UTC)

Okay this conversation has gone on far, far too long and the exchange is getting less and less civil. So here's what we can take from this when we close this section and move on to things that are actually important: Dvtausk et al are clearly correct that the superfluity objection is distinct from the unobservable objection, and that only the first one is (1) a not-entirely-wrongheaded criticism and (2) based on application of Occam's Razor (and, thus, appropriate given the title of the section in question). Dvtausk et al are also correct that either (1) The superfluity objection was clearly what Everett's criticism of dBBt was, or at least (2) this is the only objection which we can plausibly interpret as being Everett's given the quote that appears in the section.

Michael Price is right that someone could make this sort of objection, and if he finds someone who clearly and uncontroversially makes it (which shouldn't be hard, but which hasn't been done yet in this section), it may be inserted into the article with proper citations and an explanation of why it is so hopelessly wrongheaded.

Michael Price is also right that there is a sense of the term 'superfluous' on which x being superfluous implies x being unobservable. The sense I'm talking about is the one at work in a sentence like this "Given the roles that entities x and y play in the physical theory, P, y does all of the work to procure the consequences of P and x's influence is either nonexistent or over-determined. Thus, given the roles which x and y play in P, we can eliminate x without altering (in any substantive way) P's consequences. That is, x is superfluous on theory P" If a statement of this form were true of dBBt where particles took the x slot, then I think there would be an argument that it followed that x (the particles) was/were unobservable.

However, it is clear that Dvtausk et al are correct that this is NOT Everett's meaning and not the form of his objection. Everett's objection is more of the form: "Given the fact that theory P requires that we admit entities x and y as objectively real, theory P is inferior to theory P* because theory P* requires only that we admit entity y and that the role that entity y plays according to P* is such that it can do all the work that, according to the roles played by x and y as specified by theory P, both are required to do in theory P." In other words, the criticism isn't about the ROLE which the entities play, but about what entities you admit as really existing. Take a look at the quote:

“ Our main criticism of this view is on the grounds of simplicity - if one desires to hold the view that $\psi$ is a real field then the associated particle is superfluous since, as we have endeavored to illustrate, the pure wave theory is itself satisfactory. ”

What Everett is saying (this is not speculation or interpretation but simply (mostly) an analysis of the sentence above) is: "if one desires to hold the view that $\psi$ is a real field" i.e. If one wants to admit the existence of the wavefunction "then the associated particle is superfluous" then there is no need to admit the existence of dBBt particles. Why? because "the pure wave theory is itself satisfactory" that is: Everett's theory (the pure wave theory) is completely satisfactory, and it just relies the wavefunction.

The argument that can be read off the sentence is almost certainly of this second form. Everett objects because dBBt admits of two kinds of entities and assigns them roles such that together they produce a satisfactory theory, while Everett's theory admits of only one of those two and assigns it a different role such that it produces a satisfactory theory (he claims). So, by Occam's Razor (which can only be applied when faced with competing theories), Everett's theory is equal in every way except it admits less onto the ground floor of its ontology, hence it is better.

Regardless of whether you think I'm right about this, it should at least be clear that a statement like "In the Everettian view, then, the Bohm particles are unobservable entities" (my emphasis) which currently appears right after the quote, is unacceptable. First, it is nowhere near obvious that the quote says anything close to this, since the second sense of superfluous seems to be the most plausible given the actual content of the quote, and second, even if this was what Everett meant, it doesn't follow from the quote in any clear way at all! A decent amount of argument and other citations would be required to establish that this was Everett's view, the quote alone comes nowhere near establishing that.

...

That being said, I think we should just give the section a quick fix (or don't, whatever) and move on to something worth arguing about and which we have some chance at reaching a resolution. Seriously, somebody find something else that needs attention and start a new section so we can get started on dealing with it in a civil manner. Remember, the purpose of this talk page is not to prove that Michael Price doesn't know what he's talking about, it's to constructively discuss and argue about dBBt in order to improve the article. (If you read nothing else, pay attention to the sentence right before this one. That sentence applies to you too, Michael, stop saying things that make it sound like you're just trying to prove you don't know what you're talking about, it's only causing frustration and wasting everybody's time, including your own.) ZRPerry (talk) 17:56, 2 December 2009 (UTC)

ZRPerry, quoting Everett is fine, but Everettarians covers people like Deustch and W&B, who have interpreted Everett's statement / position in a less narrow way. Hence the Everettarian view is somewhat clearer and broader than you are portraying. As for whether I am distorting material, I have said for awhiile that I am happy to just post the quotes without interpretation. Are you? --Michael C. Price ^talk 18:14, 2 December 2009 (UTC)

ZRPerry, I think that even in your first sense of "superfluous" the "non observable" does not follow (but that discussion could require some additional fine tuning on what we mean by "observable"). If you are interested, I could tell you what I have in mind, but probably this is not the right place for it. About the "Occam's razor section" and Price: I agree that we should just fix the section; I think I can do a good job there, giving a short summary of Everett's view and of the view of people like Brown & Wallace (supported by some quotes), and I don't think the section should present any judgement about whether the view of Everett, or of Brown & Wallace, is reasonable or not (maybe there should be references, like Craig Callender, and Valentini, in case the reader wants to know about some replies to Everett, and Brown & Wallace). The trouble is: what does one do in Wikipedia when there is some crazy troll that don't want to get convinced?Dvtausk (talk) 19:00, 2 December 2009 (UTC)

I think you're right that non-observable doesn't obviously follow from the first sense of "superfluous", but there is at least an argument there someone could make without having obviously misunderstood the term (I am interested as to what you have in mind. Is this what a User:Talk page is for?).

As for dealing with the trolling, the first step is Attempted Reconciliation: produce a rewrite of the section mostly along the lines you suggested with as little speculative paraphrasing as possible and also throw in a subsection (complete with a dubious factuality and/or no citations tag) about the alleged "unobservable" objection, without attributing it to anyone.

If this step results in more angry ranting on the Talk page, then the next step should be ignoring the troll.

If either of these steps result in unconstructive reverting and/or edit warring on the part of the troll in question, I think we're supposed to submit a complaint to some internet bureaucrat. ZRPerry (talk) 21:10, 2 December 2009 (UTC)

I'm sorry, ZRPerry, that you've joined this hysterical troll-hunt. I think you all need to step back and reflect on what the issue is here. Do you imagine that Deutsch, an Everettarian, thinks the pilot-wave particles are observable? Remember Deutsch says that "pilot-wave theories are parallel-universe theories in a state of chronic denial." Note that I am not asking you whether you believe his claim. --Michael C. Price ^talk 00:03, 3 December 2009 (UTC)

To ZRPerry: Thanks for the advice. See you in your user's talk page.Dvtausk (talk) 23:59, 2 December 2009 (UTC)

To Price: after all the time I spent on this discussion you think I haven't reflected on everything that has been said? I haven't read anything that Deutsch wrote except for the quote that you mentioned up there. However, I carefully read Brown & Wallace, and I think that it is likely that Deutsch, like Brown & Wallace, would regard some of the standard assumptions of dBB (such as "ordinary objects of our experience and the observers are made out of the particles", or "psycho-physical parallelism between the state of mind of the observers and the particle configuration of their brains") to be extremely implausible, or bizarre, or unjustified, or whatever. However, I don't think he would be stupid enough to think that such assumptions would make dBB logically inconsistent (and I think that any "Everettarian" author who believes to have a proof of the logical inconsistency of dBB would quite simply write an article in which such claim appears in the title or something like that; I'm not aware of any article of that kind). You don't understand Brown & Wallace's position quite simply because you don't want to: you carefully avoid taking notice of the part of the article in which they express their opinions on some of the standard assumptions of dBB (for example, the paragraph after the Maudlin quote, that you "played dumb", and decided to ignore), and, instead, you focus your attention on the part of the article in which Brown & Wallace "beat up" a straw man that has never been proposed by Bohmians, i.e., Brown & Wallace's formulation of the "result assumption", in which the particles play the role of a "pointer" (and, even in the analysis of that part of the article, you distort the author's views, by confusing "problematic" with "inconsistent", and by confusing "inconsistent with some standard view of what counts as a result in the predictable outcome case" with "inconsistent with the other assumptions of dBB").

But I guess I'm just feeding the troll again. The more constructive thing to do here is to take ZRPerry's advice. I will stop discussing things in abstract in the talk page and I will rewrite the criticism section. I don't like the "just quotes" option; I think the section will look ridiculous like that. But my plan is to be as faithful as possible to the wordings of the authors. I think it will be more productive to discuss over some concrete proposal of text, than to discuss in the abstract.Dvtausk (talk) 02:39, 3 December 2009 (UTC)

I'm not playing dumb over that paragraph; we talked about it before and I've given my opinion on it. BTW I find it amusing that you think you can divine Deutsch's opinion when you admit to having never read a word of his, beyond the quote I've supplied. --Michael C. Price ^talk 03:13, 3 December 2009 (UTC)

Nope, I don't think you ever presented an explanation of what you think that paragraph means (and that, again, is the kind of behaviour that makes me think that you are a troll). So, Deutsch wrote an article entitled "A proof that dBB is inconsistent"? Really?Dvtausk (talk) 03:39, 3 December 2009 (UTC)

You asked about Maudlin's quote and the next paragraph, and I've responded here about why I thought it irrelevant. Why you obsess about the psycho-physical parallelism applied to particles I don't know, since, as W&B ask, "why believe it?". Which is the same reason why I'm not interested. --Michael C. Price ^talk 04:10, 3 December 2009 (UTC)

Oh my God, what the heck is wrong with you? Your response to "what do you think that paragraph means?" is that "it is not in the abstract or in the conclusions, and therefore we should just ignore it"? And who cares about "why believe it"? The discussion is not about what is reasonable to believe, the discussion is about what follows from that assumption, and what follows, according to Brown & Wallace, is that the observer becomes aware of the position of the particles, i.e., he observes the position of the particles ("If this is so, it is true we gain information by way of such correlations between corpuscles in and outside of our craniums."). You are a troll. Period. QED. Write something stupid below this and I will be happy to ignore it.Dvtausk (talk) 11:54, 3 December 2009 (UTC)

What part of "not interested" don't you understand? Unreasonable assumptions have uninteresting consequences by definition. Of course Bohmites think it reasonable and interesting. Everettarians don't. OK? It's just a mid-article strawman that W&B introduce to knock down. --Michael C. Price ^talk 12:25, 3 December 2009 (UTC)

Removal of sourced material

I have restored some of the lost material, which included all mention of occam's razor, Callender's work, context for Zeh's use of "empty", redundancy argument and the result assumption etc etc --Michael C. Price ^talk 15:02, 3 December 2009 (UTC)

Minor objection concerning the "result assumption": it is very important to distinguish between what Brown & Wallace call the "result assumption" (which is indeed a very problematic assumption, that was not formulated or proposed by Bohmians) from the actual assumptions formulated by Bohmians (psycho-physical parallelism-like assumptions, assumptions about ordinary objects of experience being made out of particles, etc). Brown & Wallace dispute both the "result assumption" (invented by them) and the actual assumptions proposed by Bohmians, but the two sets of assumptions should not be confused.Dvtausk (talk) 15:34, 3 December 2009 (UTC)

I don't see where the confusion arises since it was clearly sourced to Wallace and Brown. And why have you also removed the final two citations to Callender? --Michael C. Price ^talk 16:40, 3 December 2009 (UTC)

The current version of the article says: "the other branches are designated "empty" and implicitly assumed by Bohm, in what is called the "result assumption", to be devoid of conscious observers." The "result assumption" isn't really the same thing as the assumption that the empty packets are devoid of conscious observers. Maybe you don't care about the distinction, but I do, so I will remove the reference to the "result assumption" in that passage. The current version of the article also says: "These authors claim that some of the usual tacit assumptions of the de Broglie-Bohm theory (concerning the role of the particles in observation, known as the "result assumption", and the conciousness of observers) are unreasonable." Again, the relevant set of assumptions is not the "result assumption". So, again, I will remove "result assumption" from that passage.Dvtausk (talk) 18:29, 3 December 2009 (UTC)

The final passage of the section says: "This conclusion has been challenged by pilot wave advocates, with a number of suggested resolutions; either make the "result assumption" explicit...". This is a very strange statement. I'm not aware of any pilot wave advocates proposing that "the result assumption should be explicit", as, in fact, there doesn't seem to be pilot wave advocates proposing the adoption of "the result assumption" as formulated by Brown & Wallace.Dvtausk (talk) 18:34, 3 December 2009 (UTC)

To people out there that understand dBB: the "result assumption", as formulated by Brown & Wallace, is the assumption that the particles work as a pointer to the wave packet which is the result of the experiment. I don't think any proponent of dBB would agree that such assumption, formulated like that, is part of dBB. Rather, a proponent of dBB would say that the experimental apparatus is made of particles, so that the result of the experiment is to be found in the particle configuration of the apparatus.Dvtausk (talk) 18:43, 3 December 2009 (UTC)

I see Lewis mentions the "result assumption" extensively, so the subject is going to have to be covered eventually. Just deleting it from the article is not the Wikiway. --Michael C. Price ^talk 19:02, 4 December 2009 (UTC)

Give us the full reference of the Lewis article. One has to check whether Lewis formulation of such "result assumpion" is really the same as the one of Brown & Wallace, or if he just uses the same name. Also, the Wiki article doesn't have to cover every single thing that is in the literature. That section is a just a quick summary of some Everattarian objections, possibly with some quick summary of Bohmian replies. Obviously, there is a huge amount of material that is not going to be covered. By the way, I have to say that your obsession with the "result assumption" is very odd. I don't know if you are able to understand anything that is going on, but, at least in the form formulated by Brown & Wallace, that assumption is simply not a part of dBB (and I would risk saying that no Bohmian would propose an assumption in that form). An inteliggent Everettarian who wants to criticize Bohmians, has to worry about criticizing things that have actually been proposed by the Bohmians (otherwise, they would be using a straw man strategy, i.e., attacking some thesis/assumption invented by themselves, not the actual thesis/assumption of their oponents). Curiously, the parts of the Brown & Wallace article that you claim "not to be interested in" (because they prove some of the points I have been insisting for a long time, but you chose to pretend that you didn't see that), are the parts where they are actually attacking positions that actual real life Bohmians have taken.Dvtausk (talk) 20:24, 4 December 2009 (UTC)

I assumed that you had already read Peter J. Lewis (2007). “How Bohm’s Theory Solves the Measurement Problem”, Philosophy of Science 74 (5): 749–760.

BTW your statement I don't know if you are able to understand anything that is going on, but, at least in the form formulated by Brown & Wallace, that assumption is simply not a part of dBB is just hilarously funny. Of course it isn't explicitly part of dBB -- that's the whole point of Wallace and Brown's contention, it is implicit precisely because it isn't consciously assumed by dBB and followers. Clearly you have absolutely no idea what you're talking about. Dunning-Kruger effect, at work, methinks. --Michael C. Price ^talk 21:29, 4 December 2009 (UTC)

Oh my God, you really can't understand anything, can you? The result assumption (as formulated by Brown & Wallace, where the particles "point to" the wave packet, which is supposed to be the actual outome) isn't explicitly or implicitly assumed by Bohmians. The "result assumption", as formulated by Brown & Wallace, arose from a too literal reading that Brown & Wallace did of a passage of Bohm's article (even Brown & Wallace agree that Bohm might not really mean that, see pg. 6). The "psycho-physical parallelism assumption" (between the state of mind of the observer and the particle configuration of his brain), on the other hand, is explicitly assumed by Bohmians (it is in Bell, for instance). That assumption alone suffices to make the dBB particles observable (Brown & Wallace agree with that; of course, they don't like that assumption --- they say "Why believe in it?" --- but that passage of Brown & Wallace that you are "not interested" in paying attention to, proves that they understand the consequences of the assumption). Once such "psycho-physical parallelism assumption" is made, no "result assumption" (as formulated by Brown & Wallace) is necessary.Dvtausk (talk) 21:51, 4 December 2009 (UTC)

Thank you for immediately confirming my diagnosis. Can you grasp that your assessment of Brown and Wallace's "too literal reading" is just your opinion? It has no bearing on statements that can be attributed to them in the Wiki-article, even if you were correct. BTW you're not correct, but obviously we're not going to agree on that. --Michael C. Price ^talk 22:00, 4 December 2009 (UTC)

Brown & Wallace, pg. 6: "Our concern rather is with the fact that for Bohm it is the entered wave packet that determines the outcome; the role of the hidden variable, or apparatus corpuscle, is merely to pick or select that packet... How literally Bohm meant this is perhaps open to debate,..." (emphasis mine). To this last word, Brown & Wallace attach a footnote: "Taken literally, Bohm’s position in 1952 is not strictly the same as that expressed in Bohm and Hiley [4], as we shall see below.". Clearly, Brown & Wallace are not willing to commit to the statement that Bohm would agree with their formulation of the "result assumption".Dvtausk (talk) 22:53, 4 December 2009 (UTC)

Well, of course an implicit assumption's literallness is open to debate. It could hardly be otherwise. You're taking a long time catching up with me, but at least you're slowly making progress.

And of course Bohm's opinion shifted over the years. Bohm-Hiley's implicate order is not the same as dBBt. Jez, are you completely ignorant of the theory's history? Can't you even remember the reason why we changed the article's name?? --Michael C. Price ^talk 00:05, 5 December 2009 (UTC)

The point was that Brown & Wallace are unwilling to make categorical statements about Bohm's views on that subject. But, most importantly, Bohm's views about the subject matter only to historians. It is sort of pathetic that Brown & Wallace waste that much time (in a 2004 article!) criticizing an assumption that appears in Bohm's original 1952 article (even if happens to be something that Bohm would actually agree with). dBB (aka Bohmian Mechanics) is an active field of research and there is tons of literature about it. You are obsessed with Bohm's original articles because probably that's the only thing you know about the theory (and maybe not even that much). But this Wiki article is not an article about History of Physics, it is about Physics. If some assumption appears only in Bohm, either the article should not even bother to mention it, or it should make clear that it appears only in Bohm.Dvtausk (talk) 05:01, 5 December 2009 (UTC)

I refer you back to the change of name debate. We decided to change the article's name so that it could focus on dBBt (+Bell). Active field? Of course. W&B, Callender, Lewis etc are all recent. --Michael C. Price ^talk 08:51, 5 December 2009 (UTC)

My apologies to the intelligent people who wasted their times reading this, I accidentally started to feed the troll again.Dvtausk (talk) 21:57, 4 December 2009 (UTC)

Sigh. Your views on whether Wallace and Brown's views should be reported are coloured by your (negative) assessment of whether they are correct. That is not how Wikipedia works. If you want to report Lewis's views of Wallace and Brown's views of dBB's implicit assumptions, go ahead, but you can't just delete material because you don't like the views expressed. --Michael C. Price ^talk 22:17, 4 December 2009 (UTC)

Quite the contrary. I very much agree with Brown & Wallace about the fact that the "result assumption" formulated by them is problematic (though I agree with that conclusion for my own reasons, not theirs). I have no intention of "hiding" Brown & Wallace discussion about the result assumption. I have deleted the expression "result assumption" from some sentences of the article, simply because that expression was not being used correctly. If the "result assumption" is to be mentioned, it should be mentioned in the right way. One could add some paragraphs explaining how Brown & Wallace formulate it, how they criticize it, etc; one then could talk about Lewis and explain (as he does) that Bohmians do not assume that assumption and that they don't have to (by the way, I just read Lewis and I'm amazed at how he makes exactly the same point as I did right up there: Bohmians don't need the "result assumption" at all, they should use the "psycho-physical parallelism assumption" instead). But, quite simply, I don't think that one section of a Wiki article on dBB should talk about everything that has been said in the debates between Everettarians and Bohmians. It is just a Wiki article, not a full literature review. I think the present version of the section gives a good idea of the flavor of the Everettarian-Bohmian debate to non expert readers. People can go through the references, if they want more details.Dvtausk (talk) 23:10, 4 December 2009 (UTC)

It is not surprising that you and Lewis share the same conclusions, since you make the same assumptions and share the same prejudices. However that has no bearing on how W&B's views (and Everettarian views generally) should be expressed. And of course we should express Lewis's views (which are probably representative of dBBters generally); no surprise that he doesn't get W&B, just like you don't.--Michael C. Price ^talk 00:14, 5 December 2009 (UTC)

Price, just because you are a fan of Everett's theory, it doesn't mean that every supporter of Everett's theory agrees with you and it doesn't mean that you understand W&B. It seems that you confuse W&B's views with your own. You are in no position to judge whether someone gets or doesn't get W&B.Dvtausk (talk) 05:06, 5 December 2009 (UTC)

Nor you of mine. You were the one who started making assertions about what people "got". If you don't like the heat, get out of the kitchen. --Michael C. Price ^talk 08:51, 5 December 2009 (UTC)

I again removed the expression "result assumption" from sentences where it doesn't belong. Since Price is obsessed with this, I decided to add a small explanation of what the "result assumption" is.Dvtausk (talk) 23:25, 4 December 2009 (UTC)

I corrected the sentence which claimed that the "result assumption" is a standard tacit assumption of dBB. This is simply false. Just look up the Bohmian literature or ask anyone working with dBB. It is not even true that B&W claim that the "result assumption" is a standard assumption of dBB. They just say that such assumption appears in Bohm's original 1952 articles (and they are not even willing to make categorical statements about Bohm's intentions). Price, you will probably tell me that the "result assumption" is really in the subconcious of all the Bohmians, but that's just means that you are crazy. It is the proponents of the theory who get to say what the assumptions of the theory are.Dvtausk (talk) 05:28, 5 December 2009 (UTC)

I shall explain again: It is irrelevant whether dBB made the tacit result assumption or not. When reporting the views of W&B and other Everettarians we, not surprisingly, report the views of W&B. You are trying to judge the sources, which is not permitted. Don't believe me? Go and read policy. Your final statement is just completely wrong and is the root cause of your relentless POV pushing. At least you've "come out" and have admitted it all.

Now please try and report the views of Lewis, without distorting the views of Wallace, Brown etc. --Michael C. Price ^talk 08:51, 5 December 2009 (UTC)

There is no claim in Brown & Wallace that "the result assumption" is a standard tacit assumption of dBB. They claim that such assumption appears in Bohm's article, and that is very different from saying that it is a "standard assumption of dBB". So I will correct what you wrote in the Wiki article and say it right (I know the Wiki police, but the one who is distorting the source is you). Moreover, by the comment that you made when you changed the article ("No need to define the result assumption twice") it seems to me that you didn't get that the assumption that I was talking about is not the "result assumption". The "result assumption" is not the only thing that Brown & Wallace find unreasonable. The assumption that I wrote: "that an observer becomes aware of configurations of particles of ordinary objects by means of correlations between such configurations and the configuration of the particles in the observer's brain" is completely different from the "result assumption" (it doesn't matter if you can't see the difference) and it is explicitly criticized by Brown & Wallace in pg. 14, after the Maudlin quote. The fact that you claim "not to be interested" in that, doesn't mean that it is not in the source. So that's going to stay.Dvtausk (talk) 20:51, 5 December 2009 (UTC)

Yes, W&B find a number of things unreasonable. And I never said the Maudlin quote couldn't go in, I just said I wasn't interested in it, and I didn't think it demonstrated what you thought.--Michael C. Price ^talk 16:14, 6 December 2009 (UTC)

I changed the article. Now there is even a short explanation of B&W's reasons for finding the result assumption problematic (and I even used the word "inconsistent" that Price loves so much). But I kept the explanation that B&W find unreasonable the "psycho-physical parallelism" assumption, which is what they say after the Maudlin quote in pg. 14 (I insist on mentioning that because I think that it is one of the most important points of disagreement between B&W and Bohmians; even if I happen to be wrong about that, there is nothing wrong with mentioning that in the article). Price, you can't simply forbid people to mention the parts of the source that you don't like (or "is not interested in"). If you think that I'm distorting something said by the source, you have to at least try to give a careful explanation of what you think I'm distorting and why. I spent a lot of time explaining to you why you were distorting the Everett quote (from "superfluous" into "non observable"), before I decided to change it. So, stop being a dishonest troll and play fair.Dvtausk (talk) 21:08, 5 December 2009 (UTC)

I gave you a careful explanation about why superfluous implies unobservable, for any theory, in the form of a simple sylllogism, which you never refuted. Nor has anyone else. --Michael C. Price ^talk 22:17, 5 December 2009 (UTC)

Anyone can read our discussion and see that I refuted your "syllogism" both by counter-example and by pointing out very precisely where the flaw was. But let's not get back to that. It seems that we are now getting very close to a "Occam's razor section" which is acceptable for both of us.Dvtausk (talk) 23:08, 5 December 2009 (UTC)

Anyone can read it, that's true. As for the rest, that's matter of opinion - obviously.

I agree that we may be converging on an acceptable wording, although I would like to reintroduce the back reaction material since I notice that W&B give some interesting sources on that matter. --Michael C. Price ^talk 16:14, 6 December 2009 (UTC)

I have no problem with talking about the absence of back reaction, as long as only conclusions supported by the sources are drawn from that. In B&W I see that they mention absence of back reaction in footnote number 41, when they are arguing against the attitude of denying the reality of the wave function; they also mention it in footnote number 47, when they are defending that it is unreasonable to restrict concious going-ons to the particles.Dvtausk (talk) 19:33, 6 December 2009 (UTC)

Occam's razor section

I think that now the "Occam's razor" section is pretty good, but there are small (not so urgent) things there that bother me, specially concerning the last paragraph, about the "suggested resolutions". I don't have in mind a very good strategy for fixing, so I will just get my "complaint" registered here, and maybe someone will have a good idea of how to fix it (obviously, I'm here only talking to people who can actually understand the differences between the several Everettarian objections against dBB). There are two (related, but distinct) types of objections being presented in that section:

(1) Everett's theory works and it is simpler than dBB, therefore it is better than dBB;

(2) it is unreasonable to assume that "particle cats" are cats, but "wave function cats" are not cats, so dBB contains the same many worlds of Everett's theory.

(I say the objections are related, as it seems to me that if you agree with (2) you are forced to agree with (1); but I think that you can agree with (1) and disagree with (2)).

Objection (1) is presented in the first part of the section and is supported by Everett's quote. Objection (2) is presented in the second part of the section and is supported by Zeh's quote, Deutsch's quote and Brown & Wallace.

What bothers me about the last paragraph is that it kinda mixes up the two types of objections. A response to objection (1) would have to argue that, either Everett's theory doesn't work (say, because of the problem with the probabilities, or because of the absence of local beables), or that it works but isn't in fact simpler (say, because its many-worlds ontology is too complicated and extravagant). A response to objection (2) would argue that, either it is more natural to regard the dBB wave function as not physically real, or that it should be regarded as physically real, but that for some reason the "wave function cats" shouldn't count as cats (say, because cats should be made of local beables living in 3-space, because it is not clear that one can really find something cat-like in the wave function, because the dBB wave function is merely a particle mover, while cats are not mere particle movers, etc). Also, maybe there should also be some mention of a Valentini-like response to objection (2).Dvtausk (talk) 17:16, 4 December 2009 (UTC)