You might be surprised, perhaps, that this post does not continue with my series on the hypothesis of homeopathy. The reason is two-fold:
(i) I began writing on the theory of dynamical systems (chaos, catastrophe and all), but soon got confused as how best to present it without using too much of mathematics, this blog being for a more general readership. Also, what models should I pick up. I could not make up my mind very easily on these matters.
(ii) Even as my confusion continued, I got entrapped in a spike of too much work and running around. Here’s a brief: I worked on some time-bound delivery in my day-job; researched a topic for my “other” research work; physically visited IIT Bombay (to gather some literature with the help of a friend there); attended a two-day conference arranged by MSC Software in Pune (nice folks these (I have now almost begun forgetting that they took no action towards employing me just a few years ago at the time that I needed a job so badly), they distributed (to each attendee) a small carry-bag and a wrist watch, and even had invited (each attendee) for cocktails and dinner at the five-star hotel too, though, surprise of the surprise, I didn’t go—I was that busy); wrote some important documentation and physically rushed around to see that it was sent by courier before the deadline of June 30; wrote a couple of lengthy (2,000+ words each, I found out later) emails on certain very fundamentals of physics, that also were thoughtful (and I say thoughtful because these were questions more or less on my research); and wrote a three pages long Extended Abstract for a paper for an upcoming international conference and also sent it; etc.
Naturally, there was no time left for blogging. … Not that anyone noticed, but still, it feels good to talk about talking to the empty universe that includes spammers—thank you, Akismet!
I promise to finish the write up on homeopathy soon and post it, because writing those couple of emails have provided me with some good food for thought too, something to get out the door asap—but after finishing up the series on homeopathy.
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Dr. Eric Dennis on Bohmian Mechanics at OCON 2010
Sometime in the meanwhile, I noticed in a general search related to QM and philosophy that Dr. Eric Dennis [^] would be delivering an optional course on “Modern Physics and Objective Reality” at the Objectivist Summer Conference 2010 [^].
Going through his course description, I found that I would disagree. Therefore, I left a comment on Dr. Dennis’ blog here [^]; see comment # 7. However, I didn’t receive any reply. So, after waiting for a few days, I wrote an email to the OCON organizers, requesting them to forward my email actually written for him. They immediately replied back, saying that my email had been forwarded. Even then, there was no response. In this last email, I had mentioned something to the effect that if no communications occur, then I will write my disagreement on my blog on the same day as his lecture. … Now that I am through with my June-end deadlines, I actually can.
First things first. I attach a great deal of credibility to the lectures/courses given at the OCON conferences. That precisely is the reason why I thought of highlighting my disagreement. Another thing. As a rule, I hate it if people do not reply normal (polite etc.) emails/comments on serious topics/issues being discussed publicly. Naturally, I was disappointed by the absence of Dr. Dennis’ reply, esp. since the OCON organizers did respond. A serious concern here is I think that the weight of Objectivism might be used to support such a basically “wrong” theory as Bohm’s. With that said, I still must note that I was not angry with Dr. Dennis (my usual response in such situations), merely disappointed. Enough. Let’s get to the issue itself.
For ease of referencing, here I in toto copy-paste the description for Dr. Dennis’ OCON 2010 course:
The received story of modern physics features a pioneering group of quantum theorists (Bohr, Heisenberg, Born, Pauli) who showed that critical aspects of the atomic world are observer-created, vindicating subjectivism by reference to what has become a bedrock of experimental science. This story, however, is undermined by a parallel lineage of physicists (Einstein, de Broglie, Schrödinger, Bohm, Bell) whose climax came with David Bohm’s reformulation of quantum mechanics in terms of an objective micro-world.
We contrast these two approaches to quantum theory in layman’s terms, focusing on how they each explain key experiments and on what premises about the nature of explanation itself they each proceed from. Examining the response of Bohm’s opponents will locate the real source of their worldview not in experimental discoveries, but in avant-garde philosophy, which will help to elucidate contemporary disputes about scientific methodology at the frontier of physics.
[Bold emphasis mine].
The first paragraph in the quoted description suggests the idea that Bohm had succeeded in giving an objective description for the mechanics of quanta. This suggestion is, in my honest opinion, completely false.
The second paragraph suggests that none of the arguments against Bohmian mechanics is founded, or is sought to be founded, in “experimental discoveries” i.e. physical/empirical observations. I disagree—I am willing to subject my view of quantum mechanical phenomena to certain new types of observations to be made in actual experiment.
Let me address both these parts. Allow me to be brief; after all, these are subject matters of professional-level papers, not informal blog entries, and my own views, though definite, are nowhere near completion—my research is just beginning. With that note, let’s address the two issues.
I have not studied Bohmian mechanics as a graduate student of physics would; my reading is limited to gleaning what overall kind of ideas he was advocating. Even then, I am against his mechanics. The reason is basically two-fold.
(a) What Bohm Said
To the best of my knowledge of quantum phenomena, I find that one has to concur with Feynman’s observation that the wave-particle duality is the most crucial issue of QM; resolve it, and the fundamental mystery of the QM would basically be gone, even though details and implications would remain.
On this count, I believe that Bohm has not at all resolved the wave-particle duality. His scheme physically retains the duality through and through. In his scheme, there is an abstract potential, and then there is the actually propagating particle. The two are related only in his blanket assertion—he provides no physical explanation as to precisely how these two might be physically connected, except for abstractly repeating that they are. This, I believe, is the most important objection against his theory.
Bohm’s explicit aim was to restore determinism in QM. Note, the word is “determinism,” and not causality—i.e. causality in Ayn Rand’s sense of the term [^]. My (early) impression is that he probably would not have known the distinction. I think he could have accepted “infinite precision” as a perfectly legitimate term; he wouldn’t have noticed the epistemological flaw about it. Indeed, “infinite precision” is the one characteristic, even a demand, that he would have made on causality. His description of quantum phenomena is geared to ensure a deterministic propagation of quanta. The only dynamical model he could have thought of, in order to ensure a causal description, would have been the one that had straight-line trajectories as the ideal. That is what determinism would have implied to him. (I speak here in the indefinite sense, using the words “would have” etc. because my study of Bohm is too limited—I can find neither the time nor the physicists who can talk to me about QM and hasten up the process—not even Dr. Dennis (:)).) In ensuring this kind of a variant of causality, I believe he forgot addressing the duality as such, and actually ended up dividing the quantum into two parts: the abstract potential and the particle that travels guided by that potential.
This theory has another flaw. I don’t have the time to spell out (and probably can’t do so on the fly anyway, without referring to Peikoff’s lectures and Objectivist books again) but to those who know it, to elevate Bohm’s ideas, the flaw in his scheme is somewhat similar to Aristotle’s idea of the Unmoved Mover.
The Unmoved Mover does not himself move, said Aristotle, but He sets in motion all the things in the universe (supposedly in one “instant”) and immediately removes himself out of any activity within the universe. Thus, the universe that you and me see around us is orderly; it runs without any form of conscious interjection/interference/even observation on the part of the Unmoved Mover. And yet, the source of its order is: The Unmoved Mover.
Bohm’s quantum is able to travel along any of an infinity of the paths that are in conformance with the abstract potential associated with a particular physical setup such as the double-slit interference chamber. If you let a number of Bohmian quanta successively travel along these possible path, the mathematics is such that the density on the observation screen is exactly as would be observed in the interference experiment. But if you ask a Bohmian, which particular of these infinity of paths would the next quantum take, his answer is: “this can’t be predicted.” The path selection happens before (or concomitant) to the emission of the quantum, as if there is an Unmoved Mover sitting in the source atom which emits a quantum.
In Bohm’s theory, there is no physical mechanism for the construction of that abstract potential. INHO, this is the most crucial issue in any quantum theory having definite trajectories for a particle in its description. I certainly will explain sometime later on why I think that it is the most crucial issue. Two sub-notes are in order (i) The most crucial issue for any quantum theory having a waves-based description (i.e., the mainstream/Copenhagen theory, using, say, the device of the wave-packet—a combination of many waves of differing frequencies, but not a monochromatic radiation) is explaining the definitely local nature of the detector events. On the other hand, the most crucial issue for any quantum theory having a particles-based description (Feynman’s and Bohm’s theories) is explaining the construction of the spatially spread-out field/potential. (ii) Actually, what I plan to do is to present a “poor man’s” version of QM—a pseudo-QM that deals with only an unrealistically abstract view of the actual physical universe. The simpler case allows us to more easily see through the issue. This is what I intend to in a nearer future, say, within a month or so. I guess if you know about QM and if you go through the pseudo-QM, you would agree with my assertion that providing a local-physical mechanism for the construction of the potential indeed is the most crucial issue.
Coming back to Bohm’s theory, the complete absence of even hints towards a physical mechanism for the abstract potential once again suggests as if there was this Unmoved Mover setting that potential up for a particular physical setup (or, to put it in mathematical terms, for the given boundary- & initial-value problem).
In Bohm’s theory, once the path is thus selected—in deference to the potential and the initial probabilistic condition—the quantum “shoots straight,” so to speak. In terms of both the potential and the initial condition, the description is everything except the explicit mention of the Unmoved Mover. No wonder the Brits so readily accepted Bohm!
The thing which I find most troublesome in this account is not, really speaking, that the Unmoved Mover almost got there in that theory. The most disturbing part, to me, is that I don’t know, to precisely what do I ascribe the quantum mechanical motion. If I subtract the potential from the theory, I am at a loss, in the sense I can’t make any prediction about the particle propagation, not even a probabilistic prediction. If I subtract the actually propagating quantum “particle” from the account, once again I am at a loss; the theory then loses the possessor of definite trajectories, and no device is left to explain the detector events. I know that in Bohm’s theory, the propagating particle here is “dumb” enough that it can’t know the territory ahead on its own, but at the same time, I don’t know what physical mechanism does connect the spatially omni-present abstract potential with the spatially definite propagating particle.
So, the only conclusion I can reach is that both are necessary even if the two are physically unconnected, i.e. separate in principle. And if the two are separate, I know that Bohm didn’t resolve the wave-particle duality. If so, he didn’t provide an objective description of the micro-world. And if he didn’t do that, then what, prey, did he do? … And, why is Dr. Dennis lecturing as if Bohm did?
Overall, to my mind, this absence of a resolution of the duality is the most important charge against Bohmian mechanics.
As I said, I would have been perfectly happy even if Bohm were to tell us that there was an Unmoved Mover in his theory—if the theory were otherwise satisfactory, taking care to resolve the duality in a physical sense. I would have been happy with that… I was not at all disturbed when Leonard Peikoff nominated St Thomas Acquinas as the most influential man of the millenium… The reason is simple. If someone gives an actually valid theory with some inessential thread of a minor error (may be even an error that involves mysticism) here and there, even then the theory would be valuable: the mistake would be relatively easy (perhaps even damn easy) to correct—provided there was a (largely) valid theory behind that veil of mysticism. But if there is no basic resolution, then where does that leave one? Back to the square one!
(b) What Dr. Dennis Says
The above section concerned more with what Bohm himself said; this section concerns more with what Dr. Dennis says. Namely, about locating ideas in empirical observations.
(Let me note, judging by his blog-posts, I don’t think there is a very serious difference between Dr. Dennis and me concerning an overall “world-view” i.e. certain broad general philosophic premises. BTW, frankly, I never have understood what precisely people mean by phrases like “experimental discovery;” there is a little philosophic point about it—it’s a very minor point, but if the issue is to be exaggerated, I would say that I smell mysticism of muscle in such an usage—which, BTW, is typical only of 2oth century American physics, not at all typical of the 19th century physics anywhere. … But then, again, it’s a very minor point; forget about it.)
Since this post has already grown to 2,000+ words, let me leave a lot of material out of this one, and cut straight to the point.
As I said, I haven’t studied Bohmian mechanics the way a graduate student of physics would. Therefore, what I am going to say in this point too, have rather indirect bases to them. This does not mean that the point is vague, indefinite, or unworthy of serious professional attention. All that it means is that the following description isn’t IMHO fit for publication in a scholarly journal, that’s all.
If you google for computer simulation following Bohmian mechanics, you come across certain pictures, all of which, invariably show a certain special kind of transient dynamics. For example, see the Web site of Prof. de Raedt [^],[^], or better still, since it more explicitly talks about Bohm, the site at the University of Innsbruck (UoI) [^]. On the UoI site, look for 2D visualization to get to this simulation picture [^].
I am going to cut a lot short here, but enough to say that if I were to simulate this situation using my approach, the implied transient dynamics would be different. Note two points here.
(i) First, it is my general understanding that all of the following approaches would give identical results for the long-time-large-flux situations (i.e. vaguely speaking, the same asymptotic values/limits): (i) Copenhagen (or the standard interpretation), (ii) Feynman’s approach, (iii) Bohm’s approach, and (iv) mine (barely beginning; no way complete; officially, we still talk of only photons as of today). And, all of these have to match with experiments such as the one by Young, of course! [There was a “tongue of slip” here, confusing Young with Hooke, in the first version of this post—I blame my recent preoccupation with elasticity for the confusion!]
But the second point is even more important. I assert that there ought to be differences among these approaches when we look at the early transients at low flux levels predicted by each. The time-series of detector events would be essentially different.
And, precisely because Bohm did put forth a quantum traveling along definite paths, therefore, it is all the more easy to make comparisons between his theory and my approach. (BTW, making such comparisons between all such approaches was a background consideration when I recently wrote a post of the title: “Wanted: Photon Counters” [^]).
In other words, I not only have objections against the Bohmian mechanics not only on conceptual grounds (no resolution of the duality) but I also have a prediction against it (and against all prior approaches, right from the Copenhagen or mainstream view from the mid-20s, onwards through all its modifications/additions, through Bohm) to be settled via experimental verification.
In case you have read (as I did) notable physicists/professors such as Nobel laureates (or people serving on the Nobel selection committees) tell you that all new quantum theories are just “interpretations” for the same mathematical “framework” and that in principle no theory could be built that could make new kind of predictions than what was already known (till, say, the close of the 20th century), well, they all have been plain wrong! My approach does indicate a new class of predictions.
BTW, in case you have noticed that I don’t mention Everette and wonder if I do so deliberately. The answer is that yes, I don’t mention him; this is not always deliberate, but the point is I don’t think he ever had a theory to begin with. But for the present-day American idiots, no one would have read his nonsense. And none will, a century from today (perhaps even just a half-century from today). So, let the nonsense be where it might reside—in the heads of (perhaps reputed) American physics professors and their students (and their colleagues etc. elsewhere). For my purposes, I would like to end this post with a reminder that I have both conceptual issues and specifically predictions-related differences with not only Bohm’s theory but also with the mainstream/Feynman’s theories.
[Updated on July 6, 2010, 10:30 PM IST. Even if there are flaws, I will now let this write-up be as it is.]
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