NASA’s EM drive, and the nature of the quantum theory

NASA’s EM drive has made it to the Forbes. Brian Koberlein, an astrophysicist who teaches at the Rochester Institute of Technology, provides a decent coverage; see, here [^].

First things first. I hardly know anything about the EM drive. Yes, I did go through the news reports about it a week ago or so, but about the only salient thing I noticed was that it was a replication of a result. The original result itself was found by the physicists community to be, to make an understatement, something like absolutely enormously incredible. … Given NASA’s reputation (at least among the physicists community), therefore, the scene would be ripe for quite some energetic speculations—at least discussions. Newsworthy.

But still, I myself don’t know much about the experiment. Not even a schematic sketch of the apparatus was provided in the general news coverage about the experiment so far, and I didn’t look into the paper itself because I knew it would be beyond me.

But since it was the Forbes where Koberlein’s coverage appeared, I decided to go through it. The description would be dumbed down enough that even I could get something out of it, I thought.

Well, even in this Forbes piece, there was no discussion of the actual apparatus, but the author did discuss the issue in terms of the Copenhagen interpretation, and that’s where the story became interesting to me. Koberlein writes:

In the usual Copenhagen interpretation of quantum theory, an object is defined by its wavefunction. The wavefunction describes the probability of finding a particle in a particular location. The object is in an indefinite, probabilistic state described by the wavefunction until it is observed. When it is observed, the wavefunction collapses, and the object becomes a definite particle with a definite location.

I am not an expert on the Copenhagen interpretation. However, I can tell that most popular science books would present the Copenhagen interpretation exactly in this manner. So, you can’t say that the author was presenting the Copenhagen interpretation in a misleading way. (Why, I even remember John Gribbin (Schrodinger’s Cat, and later, … Kitten), and Alastair Rae (Illusion or Reality) presenting these matters more or less precisely this way about a quarter of a century ago, if not earlier.)

Still, I did have an issue here. It is in the very last sentence in the quoted passage.

As you know, I have been writing and re-writing, and arranging and re-arranging the “syllabus” for my planned “book” on QM. In particular, these past few days, I have been doing exactly that. Since the subject matter thus was fresh in my mind, I could see that the way that the QM was developed by the original masters (Heisenberg, Schrodinger, Pauli, …), the spirit of their actual theorization was such that the last sentence in the quoted passage could not actually be justified.

Even though the usual mainstream QM presentation proceeds precisely along those lines, the actual spirit of the theorization by the original founders, has begun looking different to me.

I have a very difficult position to state here, so let me try to put it using some other words:

I am not saying that Koberlein’s last sentence is not a part of the Copenhagen interpretation. I am also not saying that Heisenberg did not have the Copenhagen interpretation in his mind, whenever he spoke about QM (as in contrast to discovering and working on QM). I am also aware that Schrodinger wanted to get rid of the quantum jumps—and could find no way to do so.

Yet, what I am saying is this: Given my self-study of QM using university text-books (like McQuarry, Resnick, Griffiths, Gasiorowicz, …), esp. over the last year, I can now clearly see that the collapse postulate wasn’t—or shouldn’t have been—a part of the spirit of the original theory-building.

Since I am dwelling on the spirit of the original (non-relativistic) QM, it is relevant to point out to you to someone who has putting up a particularly spirited defence of it over a period of time. I mean the Czeck physicist Lubos Motl. See, for example his post: “Stupidity of the pop science consensus about `many worlds’ ”  [^]. Do go through it. Highly recommended. I know that Motl often is found involved in controversies. However, in this particular post (and the related and similar posts he has been making for quite some time), he remains fairly well-focused on the QM itself. He also happens to be extraordinarily lucid and clear in this post; see his discussion of the logical OR vs. the logical AND, for instance.

Even though Motl seems to have been arguing for the original founders, if you think through his writings, it also seems as if he does not place too much of an emphasis on the collapse postulate either—even though they did. He in fact seems to think that QM needs no interpretation at all, and as I suppose, this position would mean that QM does not need the Copenhagen interpretation (complete with the collapse postulate) either.

No, considering all his relevant posts about QM over time, I don’t think that I can agree with Motl; my position is that QM is incomplete, whereas he has strongly argued that it is complete. (I will come to show you how QM is incomplete, but first, I have to complete writing the necessary pre-requisites in the form of my book). Yet, I have found his writings (esp. those from 2015-end) quite helpful.

The detour to Motl’s blog was not so much of a detour at all. Here is another post by Motl, “Droplets and pilot waves vs. quantum mechanics” [^], done in 2014. This post apparently was in response to Prof. Bush (MIT) et al’s droplets experiment, and Koberlein, in his Forbes story today, does touch upon the droplets experiment and the Bohm interpretation, even if only in the passing. As to me, well, I have written about both the droplets experiment as well as Bohm’s theory in the past, so let me not go there once again. [I will add links to my past posts here, in the revision tomorrow.] As a matter of fact, I sometimes wonder whether it wouldn’t be a good idea to stop commenting on QM until my book is in at least version 0.5.

Anyway, coming back to Koberlein’s piece, I really liked the way he contrasts Bohm’s theory from Copenhagen interpretation:

The pilot wave model handles quantum indeterminacy a different way. Rather than a single wavefunction, quanta consist of a particle that is guided by a corresponding wave (the pilot wave). Since the position of the particle is determined by the pilot wave, it can exhibit the wavelike behavior we see experimentally. In pilot wave theory, objects are definite, but nonlocal. Since the pilot wave model gives the same predictions as the Copenhagen approach, you might think it’s just a matter of personal preference. Either maintain locality at the cost of definiteness, or keep things definite by allowing nonlocality. But there’s a catch.

Although the two approaches seem the same, they have very different assumptions about the nature of reality.

No, Brian, they are the same—inasmuch as they both are essentially non-local, and give rise to exactly the same quantitative predictions. If so, it’s just us who don’t understand how their seemingly different assumptions mean the same underlying physics, that’s all.

That’s why, I will go out on a limb and say that if the new paper about NASA’s EM drive has successfully used the Bohmian mechanics, and if it does predict the experimental outcome correctly, then it’s nothing but some Bohmian faithfuls looking for a “killer app” for their interpretation, that’s all. If what I understand about QM is right, and if the Bohmian mechanics predicts something, it’s just a matter of time before the mainstream formalism of QM (roughly, the Copenhagen interpretation) would also begin to predict exactly the same thing. (In the past, I had made a statement in the reverse way: whether Bohmian mechanics is developed enough to give the same predictions as the mainstream QM, you can always expect that it would get developed soon enough.)

Anyway, interesting reading.


As to my own writings on QM (I mean presenting QM the way I would like to do), as I told you, I have been working on it in recent times, even if only in an off-and-on manner. Yet, by now, I am done through more than half of the phase of finalizing the “syllabus” topics and sequence. (Believe me, this was a major challenge. For a book on QM, deciding what thesis you have for your book, and finalizing the order in which the presentation should be made, is more difficult—far more difficult—than writing down the specific contents of the individual sections and the equations in them.)

Writing the book itself can start any time now, though by now I clearly know that it’s going to be a marathon project. Months, in the least, it will take for me to finish.

Also, don’t wait for me to put up parts of it on the Web, any time soon. … It is a fact that I don’t have any problem sharing my drafts before the publication of the book as such. Yet, it also is a fact that if every page is going to be changing every day, I am not going to share such premature “editions” publicly either. After all, sharing also means inviting comments, and if you yourself haven’t firmed up your writing, comments and all are likely to make it even more difficult to finish the task of writing.

But yes, after thinking off-and-on about it for years (may be 5+ years), and after undergoing at least two false starts (which are all gone in the HDD crashes I had), I am now happy about the shape that the contents are going to take.


More, may be later. As to the Song I Like section, I don’t have anything playing at the back of my mind right away, so let me see if something strikes me by the time I come back tomorrow to give a final editing touch to this post. In that case, I will add this section; else, not!


[E&OE]

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