Three neat resources on QM. Deduction-based vs. historically oriented approaches in teaching physics. A new “ambition”, + miscellaneous.

Okaay… So… How are you?

… On my side, I’ve been having quite some fun studying QM. I’ve reached a certain point in my studies, and it seems like this is a right time to take a little break, and write down an update, and thereby keep some momentum going at this blog.

Today I am going to write a little bit about three neat resources on QM, and also share some random thoughts, which occurred to me as a result of my wondering as to why I find these resources useful. In the process, I am going to touch a bit on the various approaches for systematically presenting a difficult topic like QM. The approaches I have in mind are: deduction-oriented, historically sequenced, and some combination of the two. Finally, I will also write a bit about a new ambition that has arisen in my mind. … OK, so let’s get going…

0. Preliminaries:

Lecture notes (and even full text-books) on QM tend to be organized in a highly deductive manner, especially when it comes to the topic of the QM spin. OTOH, many of you probably are very well aware that I tend to dislike any deduction-heavy treatments, even if these come from Nobel laureates and are highly praised, e.g., The Feynman Lectures vol. 2 and 3. … If fully or almost fully deductive, then sometimes, I even hate them—I mean such notes and  books, the prime example here being: Dirac’s book on QM! … So… Where do we begin?

Ummm… First, a word about how the element of deduction can be put to some good use too!…

1. Some textbooks / lecture-notes / course-videos lean towards a deductive approach but still are good:

One good point with a somewhat deductively organized presentation is that it can achieve a greater efficiency in teaching—assuming that a class-room teacher (not to mention TAs for conducting the recitation sessions) are available to the student for clarifying his doubts and difficulties right then and there in an informal, personal, settings. A somewhat deduction-oriented pedagogy has its uses, given the time constraints of the typical university schedules—provided that it’s done right—and provided that resources like systematic recitation (or tutorial) sessions are available.

However, in general, if the organization of topics is more heavily slanted towards deduction, then, even if TAs are available, the main teacher himself has to be very careful. He has to exercise special care, especially on these two counts:

  • he has to keep on giving at least some “intuitive” feel for the logical starting point of each topic separately, again and again, and
  • the scope of the logical “fanning out” to implications, starting from the major premise(s) selected for deduction, also has to be kept judiciously delimited.

Deduction is powerful—too powerful, in fact! Just like a sharp, double-edged sword. If handled right, it can work wonders. In teaching-learning, it means: Deduction is useful to the student provided he already knows the general outline and meaning of a topic and its scope. But if you are completely new to a topic, then a deduction-heavy treatment is more likely to induce in you a large number of small but enduring misconceptions. Reason: Objectively speaking, induction has primacy. Deny it its rightful role by suppressing it, and it’s going to try and figure out some way out of the suppression. Splintering of knowledge, therefore, is a very easy possibility—if not splintering of the mind as well!

However, if due care is exercised on the aforementioned two counts, then a semi-deductive treatment can come in quite handy. Let me give you an example from engineering, just to illustrate what I have in mind here.

Consider the very first course in engineering mechanics, viz., the vector mechanics of Newtonian particles and rigid bodies.

For more than two centuries, physicists actually theorized certain natural phenomena, and solved problems related to these, without ever using the idea of vectors. They explicitly worked with systems of equations: three coupled scalar equations, one each formulated along a principal coordinate axis.

So, a pedagogical approach that sticks to a purely historical order would have to teach all the topics in applied mechanics—not just acceleration in 3D, and angular momentum, and the Coriolis forces, and everything else, but eventually, also the entirety of Maxwell-Lorentz EM—using only systems of coupled scalar equations! The task of teaching would become unwieldy in practice (and require black-boards on all sides of a class-room, with student-chairs that can rotate through 360 degrees). The task of learning would become even harder, and therefore, knowledge would become accessible to relatively very few students.

However, experience shows that a combination of the historical and the deductive approaches does work great for engineering mechanics. It definitely takes less amount of time to generate a good grasp of the subject for most students. (To get to the best possible grasp, you have no choice but to look up the history and fill in the details from such sources, purely on your own.)

So, what you do, for courses in engineering mechanics, using the “combination” approach, is this:

You begin with the separate scalar component equations, and list them once. But you actually use them only in the simplest cases like motion of particles in 1D and 2D (e.g. the parabolic path of a projectile, the uniform circular motion, etc.). Then, soon enough, you take a jump of approximately one–two centuries, and immediately introduce the idea of vectors right at this stage. You don’t get into all the complications of the concept, like the distinction between a true vector and a pseudo-vector, right at this stage. And, you certainly don’t give a formal definition of vector spaces at all. But, you do begin deploying the idea of vectors in calculations. And, you do so using only a simplified (or “curtailed”) sense of the term “vector” (which is: as a directed line segment). Then, as the physical systems to be analyzed become more and more complex, you also go on expanding and clarifying the idea of vectors and operations with them further. You introduce the scalar and cross products of vectors, and explain the necessity of their differences in reference to different aspects of physical phenomena, then you go on to the calculus of vector-valued functions, etc…

So, all in all, you are going back and forth in history a bit, but without necessarily creating too much confusion about the proper hierarchical relations among the physical concepts. Going back and forth in this way is OK, up to an extent, if the jumping around is kept limited to the concepts and techniques of mathematics. However, I would definitely say, such jumping around does not work for the concepts and contents of physics as such.

Now, an interesting fact here is that a lot of ideas from physics also have a heavy methodological, even mathematical, context to them. For example, ideas like: the variational principles (taught initially as the “energy” principles), operators, and of course, the spin in QM.

Teaching such topics too can become more efficient using the “combination” approach, but then, doing so requires a teacher who is comparatively more skillful, and also, much more careful.

The combination approach might be characterized, using a slightly more fundmental terminology, as the following:

Start with the phenomenological knowledge, and use induction to introduce certain important facts that are also generally applicable. Then, translate these preliminary ideas into more formal concepts. These new, formal concepts might themselves be of a far greater methodological scope, but start using them anyway, without pondering over all aspects of the expansion in scope which such a formalization implicitly brings in. Then start working out simple mathematical manipulations, while using the greatly generalized formalism, but only in the simpler contexts, and thereby make students comfortable with the rules of manipulations as well as the hieroglyphics (i.e. symbols). Then progressively go on fleshing up the meaning behind the symbolism as the student understanding deepens (and his facility in using the rules and symbols improves). And, all through this activity, always keep on dropping small bits of physical insights (or at least some hints) which show where the “floor” of the “ocean” lies. Do that frequently.

It works. Provided that, what the teacher is aiming at is only a more systematic treatment, i.e., if, emphatically, he has not sold out his soul to deduction as such. Not all teachers or textbook writers are of the latter kind.

Now, the trouble with today’s teachers (and text-book writers) is that they just don’t know how to stop short of being an outright slave to deduction—and in the process, they also pull their students in the same vortex. Their short-coming is especially evident as the physics gets more and more complicated and therefore more and more abstract, starting right from the fields idea in EM, and up to the modern physics of special relativity and QM.

[Aside: IMO, not even that great teacher—Feynman—could manage this challenge right, always. In evidence, see his deductive treatment in the Volume 2 of his Lectures, and compare it not just with Resnick and Halliday, or Sears and Zemansky, but also with Purcell (recently updated by Morin). I don’t know about you, but I would always go in for the latter three as my primary sources for learning. Once you have already learnt the topics, then Feynman does become good—especially for the occasional insights that are hard to find elsewhere (and more occasionally, for your cocktail party points). Personally, I have avoided The Feynman Lectures’ second volume (after a rapid but careful browsing some three decades ago). Aside over.]

So, yes, using some degree of a deductively oriented organization can lead to efficiency in terms of classroom time. Actually, the gain is in terms of generating an averagely good sort of competency, in the least possible time, for more number of students. But such methodology also is a bit more demanding on the main teacher.

And, this problem becomes an order of magnitude worse when it comes to teaching quantum mechanics.

That’s why, when one runs into a mildly-deductive treatment of QM that’s also done competently, one not only appreciates it, one also wants to applaud it. In this post, I will mention two such examples.

2. “Notes on Quantum Mechanics” by Prof. Daniel Schroeder:

This is a set of notes for an introductory UG course on QM at the Weber State University, available here [^].

The organization and presentation style followed in these notes is such that a definite slant towards deduction is very easy to make out. Yet, the writing is such that the notes remain very easy to follow—even in the absence of a class-room teacher, i.e., even for a “pure” self-study mode (without any video recordings and all).

I had noticed these notes some couple of years ago or so, but in the sea of all the material available on the ‘net for QM, I had come to postpone reading through it, back then. Then, some time later, I somehow came to forget about these notes.

Recently, I checked out Prof. Schroeder’s Web pages after a while; found a new version of these notes; and immediately downloaded the freely available PDF [ (PDF) ^]. A quick browsing later, I now decided to keep the MIT course-work on a further hold, and instead to go through these notes first.

Turns out that it was a very good decision to make.

By now, I have gone through the angular momentum- and spin-related parts of this book. (I skipped most of the initial parts of the book, simply because I knew those topics pretty well.) I have found the treatment of the QM spin here to be outstanding.

It in fact is the best introduction to spin among all notes and books I have seen so far.

Yes, the treatment of the spin here is, IMO, better than that in Townsend’s text-book. Reason: Schroeder’s notes are short, more readable, and the problems too are “doable”. In contrast, Townsend’s book is big in size, too big in fact. (I think it’s 800 pages long. I have merely browsed through it once or twice, but have not properly read through even one section completely. (TBD later!))

The treatment of spin in Schroeder’s notes also is better than that in Eisberg and Resnick (and many other text-books). An important reason: Schroeder’s notes have a distinctly modern “flavour”, and so, you can so easily transition from the introductory QM to reading the special-purpose books and literature (say on the QC) without much effort.

Another plus point:

These notes are the only source I know of which shows how to “implement” two-state systems using the spatial wavefunctions (i.e. without at all using the spin).

[Aside: To tell you the truth, I had independently figured out something like this—two-state systems using only \Psi(x,t) some time ago, as also the fact that entanglement can be explained in reference to the spin-less particles too.

… The earliest memory I have about thinking of entanglement with only spatial wavefunctions, i.e., without involving any spin at all, goes back at least to November 2014, when I was teaching engineering courses in Mumbai; and then, a highlight also occurred around Diwali-time in 2017. … But my ideas were rather “conceptual” in nature. Actually, my ideas were relatively vague, though they were not quite “floating” abstractions. And remember, all my studies and research in QM has been purely on a part-time basis, except for the last one year (since the Covid-19 began).

Anyway, when I saw Schroeder’s paper, “Entanglement isn’t just for spin” [^] (which was may be in 2018 or so), I remember, how I had marveled at it. Now, coming back to the present, to these notes, the marvel repeated. I mean, it was pleasant to read a description which was also physics-wise fully correct! Aside over.]

The only “downside” (if it can be called that) which I found with Schroeder’s notes is this:

There is no coverage of topics like the “total” wavefunction (spatial + spinor) for the many-particle systems. … May be it was not practical for them to cover this topic during their regular university coursework. However, an additional chapter dealing with the details of this topic would have been very helpful.

Added attraction: The simulation applets written by the author himself. (His HTML5 code is clean!)

All in all:

Strongly recommended, especially for the topic of the spin.

If you come from a BS in CS sort of a background, but have never studied QM beyond the Modern Physics courses, and still, if you have somehow grown very enthusiastic about the QC, and are championing it around, then, for God’s sake, let me dispense away this completely gratuitous and unsought advice to you:

Don’t even consider opening your mouth to champion the QC until you have have already mastered this book, cover-to-cover, complete with solving the section-end problems too. (As to for my opinion about the pre-requisites required for this book, see the section 4. below.)

And yes, I mean it!

3. “Quirky Quantum Concepts: The Anti-Textbook” by Prof. Eric Michelsen:

I’ve forgotten the track of where I gathered about Prof. Michelsen’s background (even if I did it within the last fortnight!). Anyway, here it is, in brief. Michelsen started out as an engineer. He spent quite some time (“decades”) in engineering industry (IIRC, in electronics / semiconductors). Then, I gather, he also founded start-ups in software. Then, he turned to research, and did a PhD in lasers and astrophysics, from UCSD. He is now a professor at UCSD [^].

… In short, I might say that I am sort of like him (or he is sort of like me), minus his practical success. [See the endnote at the end of this section.]

…Anyway, to come back to the “Anti-Textbook” by Prof. Michelsen….

Looks like I had downloaded an old PDF for the draft of this book too, though I don’t seem to have much of a recollection of my initial impressions about it. May be I had downloaded it around the same time as Schroeder’s notes were (i.e. in 2018 or so). I guess I must have downloaded this book, looked at some equations, and closed the PDF, saying to myself that I would have to return to it for a careful look later on. Then, as usual, I must have come to forget it along with Schroeder’s notes too.

Anyway, so… A couple of weeks ago or so, I once again downloaded the latest copy of Michelsen’s draft. (The book has been published by Springer, but the draft version is still available for free, here [ (PDF) ^] ).

I am still going through it. However, by now, I have read significant parts from: chapter 2 (“Riding the Wave: More on Wave Mechanics”), chapter 4 (“Matrix Mechanics”), and some initial parts from chapter 5 (“Angular Momentum”). In particular, I’ve not yet completed the portion on the spin, and haven’t even begun with the next chapter (which is on the many-particle systems).

My impression?

I am plain astounded at the richness of the insights offered here, full stop. This is one of the best resources for understanding the subtle aspects of QM.

Again, sometimes, I was even stunned to find the same insights as I myself had come to develop, independently. … Not so mysterious! The very approach of engineers is like that. Engineers (I mean: people who have worked as engineers for long enough of time so as to internalize the peculiar approach of engineering) do tend to think in a subtly (but definitely) different way than “pure” physicists do. (And we won’t even mention mathematicians here!) That’s why, it shouldn’t come as a surprise that when two engineers think deeply about the same new subject, there is a considerably similarity in terms of all: how they approach it, what they find interesting in it, and what they choose to highlight or take up for detailed considerations.

Of course, with his further formal training in physics (at the level of a PhD in physics), Michelsen has a much better knowledge of the mainstream QM than I do. He certainly has far more insights to offer on the more advanced aspects of the mainstream QM. These are difficult topics, and my studies of QM itself are relatively much more limited. I am not even aware of some of the topics whose quirkiness he notes. Yet, since his thinking retains the characteristic fold of an engineer’s thought processes, I have not found major difficulty in getting his points—even if these are quite quirky!

So, all in all, I think I can say this about my impression of this book (at this point of time):

I can always understand what Michelsen is saying, and often times, I also find myself having already worked through to precisely the same (or very similar) conclusions. However, I don’t always anticipate all his insights pertaining to the peculiarities of the mainstream QM.

But, yes, one way or the other, I find that his book is packed with insights. Even if you are not an engineer, you should benefit tremendously from this book. … Don’t take my word for it. Just go through the book and see for yourself. … OK. Let me copy-paste just one insight (just to help concretize this point); the following excerpt is from the draft copy page 49 (i.e. p. 51 of the PDF file):

Observable Operators Do Not Produce States Resulting From Measurements:

The mathematical result of an observable operator acting on a state is very different from the state resulting from actually measuring that observable.

Many people confuse the result of an observable operator on a state with the act of measuring that observable. These are very different things!

Note that the act of measurement is a nonlinear operation on the wave function; it can not be represented by a linear operator acting on the wave function. Recall that the whole point of a linear operator is to produce a superposition of results based on the superposition that composes the given function (or ket). In contrast, the consequence of a measurement is to choose one specific state out of a superposition of eigenstates.

A measurement eliminates a superposition, in favor of a more definite state. Therefore, a measurement is not a linear operation on the state; it is inherently nonlinear.

[Emphasis in bold original.]

See, see, why I am so impressed with this book? (And if you can’t figure out the reason, then check out my Outline document, here [(PDF) ^].)

… The entire book is filled with such nuggets.

No, this book is not at all induction-primary; it’s not even a historically sequenced presentation. In fact, this book isn’t even your usual text-book. Read the Preface to see why the author himself calls it an “Anti-Textbook”. …So, yes, this book is quirky! But yes, it’s quite rich in insights too.

So far, all that I’ve done is to rapidly read through the aforementioned chapters. But I don’t think that I’ve had enough opportunity to ponder over every subtle point, every nuance. I will have to read through the remaining parts, and then, I will have to return and re-read some parts again (may be 2–3 times).

The whole book is a kind of a teaser, as it were, to me. (Yes, my hard-copy is full of underlines, margin notes, scribblings, and all.)

Yes, this book is going to keep me engaged for quite some time to come.

However, no, do not bring up some points from this book for discussion with me. Not right away. I still have to learn a lot, and I am definitely quite a distance away from mastering the pre-requisite contents. I am also not likely to attempt mastering it any time soon. Reason: Many of these topics are not relevant to the research on Foundations of QM as such, even though the book deals with many advanced or subtle aspects of the mainstream QM, in a very admirable way.

As to me: First, I have to complete the first version of my document on my new approach to QM. Before that, I’ve to complete the MIT course 08.05 (i.e., watching videos). Before that, I’ve to complete the second half of MIT 08.04 too.

So, the bottomline is this:

Bottomline: One of the best books for really learning the subtleties of QM that I’ve ever come across, at such a level that it should be accessible even to the undergraduate students.

But make sure that you have completed the pre-requisites.

[Endnote to section 4: Why do I say that I am like Dr. Michelsen, minus his practical success? … Well, some of you should know the background behind that statement already, but in case you’ve just begun visiting this blog in the more recent times, there is a story about me and UCSD (which doesn’t come up on my CV)…:

After my failure in the PhD qualifiers at UAB in 1993, I was admitted to the mechanics program at UCSD, for the academic year beginning Fall ’93. … Not bad for a guy with a “mere” 8.25/10.00 CGPA at IITM and a 3.16/04.00 GPA at UAB. … OTOH, in fact, people at UCSD were (very) impressed by me. Reason? A literature review document which I had (on my own) attached to my application. It was on the micro-mechanics of fracture in ceramic composites. … Ummm, yes, the document was pretty good. So, they had decided to have me on board as soon as the funding arrives (which was around the May–June 1993 times).

However, roughly around the same time, even their on-going funding got cut down. So, formally, they said that they will keep the offer open for me for at least a year (which, eventually, they did), and informally, they called me to discuss the situation in all its detail with me. (By they, I mean the professors, not the staff at the graduate school.) Some of their on-going PhD students, supported previously via the funded projects which were now cancelled, began working in Pizza Hut, I gathered. I was willing to follow the suit. But starting completely afresh just on Pizz-Hut, i.e., without any prior savings, was not at all practical, someone (an IITian) doing his PhD there told me. The professors confirmed this assessment too, during the several telephonic discussions I had with them. … Anyway, all in all, I had to let go their offer, and return to India (which was in the last week of August ’93).

… BTW, my admission letter at UCSD was signed by Prof. Nemat-Nasser, the then Chair of the program. He and his colleagues had already brought this mechanics PhD program to a very good reputation; it was already ranked within the top 10 US-based programs or so. For comparison: My earlier program at UAB was ranked 60+ at that time (within about 70 PhD programs, in all, in the USA). … BTW, eventually, Prof. Nemat-Nasser also went on to receive the Timoshenko Medal. As to this medal …Well, yes, you may think of it as the “Nobel” of applied mechanics [^] [^]. … So, that’s the part related to UCSD

… But coming back to the other aspects of practical success: As to my later experience in software, in particular, in the SF Bay Area… Well, ask me some other time, preferably in private (so I can be a bit free-er in my… err… expressions). Footnote over. ]

4. Revised recommended sequence for learning QM through self-studies alone:

If you want to study QM through the self-study mode (i.e. completely on your own, without any personal guidance from any one), then condensing down everything (including whatever I have said about this topic in the past, and now revising it), here is my advice in a nut-shell:

Follow this sequence:

Resnick and Halliday / Sears and Zemansky + if necessary, Purcell (updated by Morin) \Rightarrow Beiser (Modern Physics) \Rightarrow First half of McQuarry (Quantum Chemistry), up to and including the Helium atom + augmented readings for the same topics from Atkins (Molecular Chem.) \Rightarrow Schroeder’s notes \Rightarrow Eisberg and Resnick, Alastair I. M. Rae, and may be an occasional look into others like Griffiths / Gasiorowicz \Rightarrow Michelsen.

For the last two stages, you can start with Michelsen and “dip back” into Griffiths etc. as the need arises. Also, consider watching the video series by ViaScience (mentioned in my earlier post here [^]) any time after you are past the books on quantum chemistry (including the He atom).

[Aside: Once my viewing of the MIT course-work (08.04 and 08.05) is over, it’s possible that I will revise the above sequence. So far, I’m half-way through 08.04 (2013 version), and I’m impressed with it. However, I don’t think that I am going to include the MIT course work in the shortest sequence presented above, and I don’t think I am eventually going to drop anything from the above sequence either. So, there. Aside over.]

Addendum: If your interest is in the Foundations of QM, rather than in QM itself or the QC, then my advice would depend on your background. 

If you come with a background in physical / engineering sciences, then go through the above mentioned sequence at least up to and including Schroeder’s notes. Then, follow this sequence:

Travis Norsen (Foundations of QM) \Rightarrow Tim Maudlin (Philosophy of Physics: Quantum Theory), both augmented with David Harriman (Induction in Physics).

(BTW, I have only browsed through some initial parts of Maudlin’s book, but I can definitely recommend it without any reservations.)

If you come with a background in other sciences or philosophy, then follow this sequence:

David Harriman (Induction in Physics) + Tim Maudlin (Philosophy of Physics: Quantum Theory), in any order \Rightarrow  Travis Norsen (Foundations of QM).

If you cannot understand the physics part of Harriman’s or Maudlin’s book even after a second or a third reading, then I would suggest: Quit pursuing Foundations of QM; this field is not for you. The field of Foundations of QM has a far greater basis in physics rather than philosophy—regardless of what other people might have led you to believe.

But if you still must persist with this field (Foundations of QM) at any cost, then quit pursuing all philosophical and popular science books on this topic (including those by Bell, and Bohmians), and instead, begin with the first sequence (given above), right from Resnick & Halliday etc., and going up to (and including) Schroeder’s notes. Once you are through with it (which should take at least a couple of years, may be 3–4 years), then once again check out Maudlin. If you can follow it right on the first read, then you may follow either of the two sequences given for the Foundations of QM.

Good luck!

5. A new, personal, long-term ambition:

Now that I had accidentally “re-discovered” the two gems mentioned above (the notes by Schroeder and Michelsen), I chastened myself a bit. Then, straining my memory, I remembered about

Malcom Longair’s book: “Quantum Concepts in Physics: An Alternative Approach to the Understanding of Quantum Mechanics”.

I had bought this book way back [^]. However, I have never been able to take it up for a systematic and comprehensive reading. … All that I’ve been able to do is sometimes to “take a dip” into it, may be for some 2–3 pages at a time, only then to toss it aside once again. “No right time for this book!” That’s what I’ve been saying to myself, invariably…

The last time I checked Longair’s book was, may be, 3+ years ago. It certainly was at least months before February 2019, which is when I wrote the Outline document [^].

A few days ago, I picked up this book once again. It was the first time I was touching it after the Outline document was posted. Presently, I came to a conclusion.

But before telling you the conclusion, let me ask: Remember Dr. Jennifer Coopersmith’s book “The Lazy Universe”? I had mentioned it pretty recently, just a few posts ago, here [^]. In the preface to her book, Coopersmith says that her book is like a simplified version of Lanczos’ book on the variational calculus. Now, Lanczos’ book is the Ultimate One, when it comes to the calculus of variations (i.e. the “energy” principles). And Coopersmith seems to have handled the simplification very well…

Now, coming back to Longair’s book and my long-term ambition.

I would like to write a simplified account of QM, based on Longair’s book.

The write up would be in a text-book like manner—complete with some solved problems and some review questions.

I would like to work at it slowly, one section at a time, and also irregularly, as my free time permits. I would like to post each section (or sub-section) in a GitHub repo or so. It will be, by intention, a long-term, and also irregular, hobby project.

But why rewrite a book if the original itself is so great?

Well, there are multiple reasons for that:

Yes, Longair has done a very admirable, scholarly, job in his book. However, he also gives greater detail of the initial analyses of experimental results, events and personalities than what a modern UG student of QM could possibly handle. If the goal is to simplify the presentation, one could omit many such details—precisely because Longair’s book is there!

Another point. Just the way the teacher has to exercise great care when presenting anything with a deduction-oriented approach (e.g. vector mechanics), similarly, the teacher also has to exercise a great care when presenting anything with a historically-oriented approach. Reason: Following the historical sequence helps in achieving a focus on the inductive roots of concepts and ideas. However, the former does not automatically ensure the latter. Isolation of the inductive roots is a separate task by itself.

With my enhanced understanding of induction (as brought about by David Harriman’s book “Induction in Physics”), I think that I can have a good shot at simplification. …

Let me be clear: I wouldn’t be explaining, let alone proving, how this or that development does have inductive roots; that’s not my goal. But I would like to present the physics points in such a way that their inductive roots become easier to grasp (even if they don’t become inescapable). I might not always do a great job for this aim; it’s too lofty for me. But I do think that I stand a good chance in converting the description from a mainly historically oriented account to one that is (i) simplified and (ii) highlights the nature of the respective inductive generalizations performed by the physicists at various stages of the main development. I think I can do that, to an acceptable degree.

One more point: I also think that, in the process of developing my new approach to QM, I’ve achieved a good clarity regarding what the mainstream QM theory is trying to say. This greater clarity, brought about by my new approach, should help in my goal, even if the explicit concern remains only with the development of the mainstream theory.

OK, so… I will begin working on it some time after the upcoming document on my new approach is done. I will work at it purely at leisure, purely as a hobby, and by intention, without any explicit plan… I think one should have some long-term hobby project like that going at any time…

6. But when will I start writing my planned document on the new approach?

Oh well. You tell me. … I’ve already told you the status as of now, and also the plan. Here it is—the plan—once again:

A few days more for going through Schroeder and Michelsen  \Rightarrow II half of MIT 08.04 (videos) \Rightarrow MIT 08.05 \Rightarrow Some rest \Rightarrow Thinking as to how my new approach holds up—if it does! And, if it does hold—and I see no reason why it shouldn’t hold, including for the spin–then (and only then) \Rightarrow Some planning for writing \Rightarrow Start actually writing.

So, whaddaya think? When will I begin writing (that goddman document on that goddamn new approach of mine)? …

Well… Want to consult astrologers / tarot card readers / psychics?  … Fine by me! Just let me know what they think (if they do), and then, also, what you think, if you do, after you have heard from them. … Or may be, want to consult some AI program? may be after you implementing a rough-and-ready one? Fine by me, again! … Or, perhaps, want to put to a practical use some certifiably random RNG (random number generator)? simply on the grounds that QM is supposed to be fundamentally random, and physics is universal? Or simpler still: want to toss a coin a few times? … Once again, fine by me. Whatever floats your boat! … From my sides, I’m all ears…

As to me, from my side, I will come back with a status update some time after watching the videos for the MIT 08.04 course is over, and watching for 08.05 is already in progress… That is, may be after two weeks or so (unless I have some brief update to post or so)…

In the meanwhile, take care, and bye for now…

Two songs I like:

Actually, I’ve two songs this time around. … Let me first give the credits and the links for both:

(Hindi) हम प्यार में जलने वालों को… (“ham pyaar mein jalane waalon ko…”)
Singer: Lata Mangeshkar
Lyrics: Rajinder Krishan
Music: Madan Mohan

A good audio for the original version is here [^]. There are other versions, including a so-called “revival” series version, but I won’t bother to give you the links to them.

The second song I have in mind is this:

(Hindi) फिर तेरी कहानी याद आयी… (“phir teri kahaani yaad aayee…”)
Singer: Lata Mangeshkar
Music: Naushad
Lyrics: Shaqeel Badayuni

A good quality audio is here [^].

Both are Hindi film songs based on Indian classical music. Both are sung by Lata. Both have been composed by highly acclaimed music composers. The two songs also have a certain unmistakable kind of a similarity in terms of certain turns of the tune, certain phrases of melody, so to speak. Both are serious kind of songs, evoking a sombre kind of a mood, one that borders on sadness but in a somewhat abstract sense. Further, people usually describe both these songs in quite superlative terms, and generally speaking, I quite agree with such assessments too.

However, personally, I happen to like one of them a bit more than the other. The question is: Which one? And, why, i.e., for what aspects / reasons? (And we consider only the audio aspects of the two songs here.) …

… I will let you think for a bit about it, and only then tell you my answer, in briefest possible terms, say in one sentence or two at the most, say via an update to this post (which may occur after 2–3 days or so). … In the meanwhile, happy guessing and / or consulting (once again) astrologers / tarot card readers / psychics / whoever, or even using (or implementing) an AI, or using RNGs / tossing coins. … Optionally, thinking too!…

BTW, if the songs are new to you, see if you enjoy any of them, or both…

Bye for now and take care…

— 2021.05.31 20:01 IST: First published
— 2021.06.01 19:39 IST: Added a sub-section in section 4, covering a recommended sequence for Foundations of QM. Also, generally streamlined content, with some minor additions throughout.
— 2021.06.02 13:22 IST: Some more streamlining and fixing of typo’s. Now, I am done with this post.


Still loitering around…

As noted in the last post, I’ve been browsing a lot. However, I find that the signal-to-noise ratio is, in a way, too low. There are too few things worth writing home about. Of course, OTOH, some of these things are so deep that they can keep one occupied for a long time.

Anyway, let me give many (almost all?) of the interesting links I found since my last post. These are being noted in no particular order. In most cases, the sub-title says it all, and so, I need not add comments. However, for a couple of videos related to QM, I do add significant amount of comments. … BTW, too many hats to do the tipping to. So let me skip that part and directly give you the URLs…

“A `digital alchemist’ unravels the mysteries of complexity”:

“Computational physicist Sharon Glotzer is uncovering the rules by which complex collective phenomena emerge from simple building blocks.” [^]

“Up and down the ladder of abstraction. A systematic approach to interactive visualization.” [^]

The tweet that pointed to this URL had this preface: “One particular talent stands out among the world-class programmers I’ve known—namely, an ability to move effortlessly between different levels of abstraction.”—Donald Knuth.

My own thinking processes are such that I use visualization a lot. Nay, I must. That’s the reason I appreciated this link. Incidentally, it also is the reason why I did not play a lot with the interactions here! (I put it in the TBD / Some other day / Etc. category.)

“The 2021 AI index: major growth despite the pandemic.”

“This year’s report shows a maturing industry, significant private investment, and rising competition between China and the U.S.” [^]

“Science relies on constructive criticism. Here’s how to keep it useful and respectful.” [^]

The working researcher, esp. the one who blogs / interacts a lot, probably already knows most all this stuff. But for students, it might be useful to have such tips collected in one place.

“How to criticize with kindness: Philosopher Daniel Dennett on the four steps to arguing intelligently.” [^].

Ummm… Why four, Dan? Why not, say, twelve? … Also, what if one honestly thinks that retards aren’t ever going to get any part of it?… Oh well, let me turn to the next link though…

“Susan Sontag on censorship and the three steps to refuting any argument” [^]

I just asked about four steps, and now comes Sontag. She comes down to just three steps, and also generalizes the applicability of the advice to any argument… But yes, she mentions a good point about censorship. Nice.

“The needless complexity of modern calculus: How 18th century mathematicians complicated calculus to avoid the criticisms of a bishop.” [^]

Well, the article does have a point, but if you ask me, there’s no alternative to plain hard work. No alternative to taking a good text-book or two (like Thomas and Finney, as also Resnick and Halliday (yes, for maths)), paper and pen / pencil, and working your way through. No alternative to that… But if you do that once for some idea, then every idea which depends on it, does become so simple—for your entire life. A hint or a quick reference is all you need, then. [Hints for the specific topic of this piece: the Taylor series, and truncation thereof.] But yes, the article is worth a fast read (if you haven’t read / used calculus in a while). … Also, Twitterati who mentioned this article also recommended the wonderful book from the next link (which I had forgotten)…

“Calculus made easy” [^].

The above link is to the Wiki article, which in turn gives the link to the PDF of the book. Check out the preface of the book, first thing.

“The first paper published in the first overlay journal (JTCAM) in Solid Mechanics” [^]

It’s too late for me (I have left mechanics as a full-time field quite a while ago) but I do welcome this development. … A few years ago, Prof. Timothy Gowers had begun an overlay journal in maths, and then, there also was an overlay journal for QM, and I had welcomed both these developments back then; see my blog post here [^].

“The only two equations that you should know: Part 1” [^].

Dr. Joglekar makes many good points, but I am not sure if my choice for the two equations is going to be the same.

[In fact, I don’t even like the restriction that there should be just two equations. …And, what’s happenning? Four steps. Then, three steps. Now, two equations… How long before we summarily turn negative, any idea?]

But yes, a counter-balance like the one in this article is absolutely necessary. The author touches on E = mc^2 and Newton’s laws, but I will go ahead and add topics like the following too: Big Bang, Standard Model, (and, Quantum Computers, String Theory, Multiverses, …).

“Turing award goes to creators of computer programming building blocks” [^] “Jeffrey Ullman and Alfred Aho developed many of the fundamental concepts that researchers use when they build new software.”

Somehow, there wasn’t as much of excitement this year as the Turing award usually generates.

Personally, though, I could see why the committee might have decided to recognize Aho and Ullman’s work. I had once built a “yacc”-like tool that would generate the tables for a table-driver parser, given the abstract grammar specification in the extended Backus-Noor form (EBNF). I did it as a matter of hobby, working in the evenings. The only resource I used was the “dragon book”, which was written by Profs. Aho, Sethi, and Ullman. It was a challenging but neat book. (I am not sure why they left Sethi out. However, my knowledge of the history of development of this area is minimal. So, take it as an idle wondering…)

Congratulations to Profs. Aho and Ullman.

“Stop calling everything AI, machine-learning pioneer says” [^] “Michael I. Jordan explains why today’s artificial-intelligence systems aren’t actually intelligent”

Well, “every one” knows that, but the fact is, it still needs to be said (and even explained!)

“How a gene for fair skin spread across India” [^] “A study of skin color in the Indian subcontinent shows the complex movements of populations there.”

No, the interesting thing about this article, IMO, was not that it highlighted Indians’ fascination / obsession for fairness—the article actually doesn’t even passingly mention this part. The real interesting thing, to me, was: the direct visual depiction, as it were, of Indian Indologists’ obsession with just one geographical region of India, viz., the Saraswati / Ghaggar / Mohan Ja Daro / Dwaarkaa / Pakistan / Etc. And, also the European obsession with the same region! … I mean check out how big India actually is, you know…

H/W for those interested: Consult good Sanskrit dictionaries and figure out the difference between निल (“nila”) and नील (“neela”). Hint: One of the translations for one of these two words is “black” in the sense “dark”, but not “blue”, and vice-versa for the other. You only have to determine which one stands for what meaning.

Want some more H/W? OK… Find out the most ancient painting of कृष्ण (“kRSNa”) or even राम (“raama”) that is still extant. What is the colour of the skin as shown in the painting? Why? Has the painting been dated to the times before the Europeans (Portugese, Dutch, French, Brits, …) arrived in India (say in the second millennium AD)?

“Six lessons from the biotech startup world” [^]

Dr. Joglekar again… Here, I think every one (whether connected with a start-up or not) should go through the first point: “It’s about the problem, not about the technology”.

Too many engineers commit this mistake, and I guess this point can be amplified further—the tools vs. the problem. …It’s but one variant of the “looking under the lamp” fallacy, but it’s an important one. (Let me confess: I tend to repeat the same error too, though with experience, one does also learn to catch the drift in time.)

“The principle of least action—why it works.” [^].

Neat article.

I haven’t read the related book [“The lazy universe: an introduction to the principle of least action”] , but looking at the portions available at Google [^], even though I might have objections to raise (or at least comments to make) on the positions taken by the author in the book, I am definitely going to add it to the list of books I recommend [^].

Let me mention the position from which I will be raising my objections (if any), in the briefest (and completely on-the-fly) words:

The principle of the least action (PLA) is a principle that brings out what is common to calculations in a mind-bogglingly large variety of theoretical contexts in physics. These are the contexts which involve either the concept of energy, or some suitable mathematical “generalizations” of the same concept.

As such, PLA can be regarded as a principle for a possible organization of our knowledge from a certain theoretical viewpoint.

However, PLA itself has no definite ontological content; whatever ontological content you might associate with PLA would go on changing as per the theoretical context in which it is used. Consequently, PLA cannot be seen as capturing an actual physical characteristic existing in the world out there; it is not a “thing” or “property” that is shared in common by the objects, facts or phenomena in the physical world.

Let me give you an example. The differential equation for heat conduction has exactly the same form as that for diffusion of chemical species. Both are solved using exactly the same technique, viz., the Fourier theory. Both involve a physical flux which is related to the gradient vector of some physically existing scalar quantity. However, this does not mean that both phenomena are produced by the same physical characteristic or property of the physical objects. The fact that both are parabolic PDEs can be used to organize our knowledge of the physical world, but such organization proceeds by making appeal to what is common to methods of calculations, and not in reference to some ontological or physical facts that are in common to both.

Further, it must also be noted, PLA does not apply to all of physics, but only to the more fundamental theories in it. In particular, try applying it to situations where the governing differential equation is not of the second-order, but is of the first- or the third-order [^]. Also, think about the applicability of PLA for dissipative / path-dependent processes.

… I don’t know whether the author (Dr. Jennifer Coopersmith) covers points like these in the book or not… But even if she doesn’t (and despite any differences I anticipate as of now, and indeed might come to keep also after reading the book), I am sure, the book is going to be extraordinarily enlightening in respect of an array of topics. … Strongly recommended.

Muon g-2.

I will give some the links I found useful. (Not listed in any particular order)

  • Dennis Overbye covers it for the NYT [^],
  • Natalie Wolchoever for the Quanta Mag [^],
  • Dr. Luboš Motl for his blog [^],
  • Dr. Peter Woit for his blog [^],
  • Dr. Adam Falkowski (“Jester”) for his blog [^],
  • Dr. Ethan Siegel for the Forbes [^], and,
  • Dr. Sabine Hossenfelder for Sci-Am [^].

If you don’t want to go through all these blog-posts, and only are looking for the right outlook to adopt, then check out the concluding parts of Hossenfelder’s and Siegel’s pieces (which conveniently happen to be the last two in the above list).

As to the discussions: The Best Comment Prize is hereby being awarded, after splitting it equally into two halves, to “Manuel Gnida” for this comment [^], and to “Unknown” for this comment [^].

The five-man quantum mechanics (aka “super-determinism”):

By which, I refer to this video on YouTube: “Warsaw Spacetime Colloquium #11 – Sabine Hossenfelder (2021/03/26)” [^].

In this video, Dr. Hossenfelder talks about… “super-determinism.”

Incidentally, this idea (of super-determinism) had generated a lot of comments at Prof. Dr. Scott Aaronson’s blog. See the reader comments following this post: [^]. In fact, Aaronson had to say in the end: “I’m closing this thread tonight, honestly because I’m tired of superdeterminism discussion.” [^].

Hossenfelder hasn’t yet posted this video at her own blog.

There are five people in the entire world who do research in super-determinism, Hossenfelder seems to indicate. [I know, I know, not all of them are men. But I still chose to say the five-man QM. It has a nice ring to it—if you know a certain bit from the history of QM.]

Given the topic, I expected to browse through the video really rapidly, like a stone that goes on skipping on the surface of water [^], and thus, being done with it right within 5–10 minutes or so.

Instead, I found myself listening to it attentively, not skipping even a single frame, and finishing the video in the sequence presented. Also, going back over some portions for the second time…. And that’s because Hossenfelder’s presentation is so well thought out. [But where is the PDF of the slides?]

It’s only after going through this video that I got to understand what the idea of “super-determinism” is supposed to be like, and how it differs from the ordinary “determinism”. Spoiler: Think “hidden variables”.

My take on the video:

No, the idea (of super-determinism) isn’t at all necessary to explain QM.

However, it still was neat to get to know what (those five) people mean by it, and also, more important: why these people take it seriously.

In fact, given Hossenfelder’s sober (and intelligent!) presentation of it, I am willing to give them a bit of a rope too. …No, not so long that they can hang themselves with it, but long enough that they can perform some more detailed simulations. … I anticipate that when they conduct their simulations, they themselves are going to understand the query regarding the backward causation (raised by a philosopher during the interactive part of the video) in a much better manner. That’s what I anticipate.

Another point. Actually, “super-determinism” is supposed to be “just” a theory of physics, and hence, it should not have any thing to say about topics like consciousness, free-will, etc. But I gather that at least some of them (out of the five) do seem to think that the free-will would have to be denied, may be as a consequence of super-determinism. Taken in this sense, my mind has classified “super-determinism” as being the perfect foil to (or the other side of) panpsychism. … As to panpsychism, if interested, check out my take on it, here [^].

All along, I had always thought that super-determinism is going to turn out to be a wrong idea. Now, after watching this video, I know that it is a wrong idea.

However, precisely for the same reason (i.e., coming to know what they actually have in mind, and also, how they are going about it), I am not going to attack them, their research program. … Not necessary… I am sure that they would want to give up their program on their own, once (actually, some time after) I publish my ideas. I think so. … So, there…

“Video: Quantum mechanics isn’t weird, we’re just too big” YouTube video at: [^]

The speaker is Dr. Phillip Ball; the host is Dr. Zlatko Minev. Let me give some highlights of their bio’s: Ball has a bachelor’s in chemistry from Oxford and a PhD in physics from Bristol. He was an editor at Nature for two decades. Minev has a BS in physics from Berkeley and a PhD in applied physics from Yale. He works in the field of QC at IBM (which used to be the greatest company in the computers industry (including software)).

The abstract given at the YouTube page is somewhat misleading. Ignore it, and head towards the video itself.

The video can be divided into two parts: (i) the first part, ~47 minutes long, is a presentation by Ball; (ii) the second part is a chat between the host (Minev) and the guest (Ball). IMO, if you are in a hurry, you may ignore the second part (the chat).

The first two-third portion of the first part (the presentation) is absolutely excellent. I mean the first 37 minutes. This good portion (actually excellent) gets over once Ball goes to the slide which says “Reconstructing quantum mechanics from informational rules”, which occurs at around 37 minutes. From this point onward, Ball’s rigour dilutes a bit, though he does recover by the 40:00 minutes mark or so. But from ~45:00 to the end (~47:00), it’s all down-hill (IMO). May be Ball was making a small little concession to his compatriots.

However, the first 37 minutes are excellent (or super-excellent).

But even if you are absolutely super-pressed for time, then I would still say: Check out at least the first 10 odd minutes. … Yes, I agree 101 percent with Ball, when it comes to the portion from ~5:00 through 06:44 through 07:40.

Now, a word about the mistakes / mis-takes:

Ball says, in a sentence that begins at 08:10 that Schrodinger devised the equation 1924. This is a mistake / slip of the tongue. Schrodinger developed his equation in late 1925, and published it in 1926, certainly not in 1924. I wonder how come it slipped past Ball.

Also, the title of the video is somewhat misleading. “Bigness” isn’t really the distinguishing criterion in all situations. Large-distance QM entanglements have been demonstrated; in particular, photons are (relativistic) QM phenomena. So, size isn’t necessarily always the issue (even if the ideas of multi-scaling must be used for bridging between “classical” mechanics and QM).

And, oh yes, one last point… People five-and-a-half feet tall also are big enough, Phil! Even the new-borns, for that matter…

A personal aside: Listening to Ball, somehow, I got reminded of some old English English movies I had seen long back, may be while in college. Somehow, my registration of the British accent seems to have improved a lot. (Or may be the Brits these days speak with a more easily understandable accent.)

Status of my research on QM:

If I have something to note about my research, especially that related to the QM spin and all, then I will come back a while later and note something—may be after a week or two. …

As of today, I still haven’t finished taking notes and thinking about it. In fact, the status actually is that I am kindaa “lost”, in the sense: (i) I cannot stop browsing so as to return to the study / research, and (ii) even when I do return to the study, I find that I am unable to “zoom in” and “zoom out” of the topic (by which, I mean, switching the contexts at will, in between all: the classical ideas, the mainstream QM ideas, and the ideas from my own approach). Indeed (ii) is the reason for (i). …

If the same thing continues for a while, I will have to rethink whether I want to address the QM spin right at this stage or not…

You know, there is a very good reason for omitting the QM spin. The fact of the matter is, in the non-relativistic QM, the spin can only be introduced on an ad-hoc basis. … It’s only in the relativistic QM that the spin comes out as a necessary consequence of certain more basic considerations (just the way in the non-relativistic QM, the ground-state energy comes out as a consequence of the eigenvalue nature of the problem; you don’t have to postulate a stable orbit for it as in the Bohr theory). …

So, it’s entirely possible that my current efforts to figure out a way to relate the ideas from my own approach to the mainstream QM treatment of the spin are, after all, a basically pointless exercise. Even if I do think hard and figure out some good and original ideas / path-ways, they aren’t going to be enough, because they aren’t going to be general enough anyway.

At the same time, I know that I am not going to get into the relativistic QM, because it has to be a completely distinct development—and it’s going require a further huge effort, perhaps a humongous effort. And, it’s not necessary for solving the measurement problem anyway—which was my goal!

That’s why, I have to really give it a good thought—whether I should be spending so much time on the QM spin or not. May giving some sketchy ideas (rather, making some conceptual-level statements) is really enough… No one throws so much material in just one paper, anyway! Even the founders of QM didn’t! … So, that’s another line of thought that often pops up in my mind. …

My current plan, however, is to finish taking the notes on the mainstream QM treatment of the spin anyway—at least to the level of Eisberg and Resnick, though I can’t finish it, because this desire to connect my approach to the mainstream idea also keeps on interfering…

All in all, it’s a weird state to be in! … And, that’s what the status looks like, as of now…

… Anyway, take care and bye for now…

A song I, ahem, like:

It was while browsing that I gathered, a little while ago, that there is some “research” which “explains why” some people “like” certain songs (like the one listed below) “so much”.

The research in question was this paper [^]; it was mentioned on Twitter (where else?). Someone else, soon thereafter, also pointed out a c. 2014 pop-sci level coverage [^] of a book published even earlier [c. 2007].

From the way this entire matter was now being discussed, it was plain and obvious that the song had been soul-informing for some, not just soul-satisfying. The song in question is the following:

(Hindi) सुन रुबिया तुम से प्यार हो गया (“sun rubiyaa tum se pyaar ho gayaa”)
Music: Anu Malik
Lyrics: Prayag Raj
Singers: S. Jaanaki, Shabbir Kumar

Given the nature of this song, it would be OK to list the credits in any order, I guess. … But if you ask me why I too, ahem, like this song, then recourse must be made not just to the audio of this song [^] but also to its video. Not any random video but the one that covers the initial sequence of the song to an adequate extent; e.g., as in here [^].

2021.04.09 19:22 IST: Originally published.
2021.04.10 20:47 IST: Revised considerably, especially in the section related to the principle of the least action (PLA), and the section on the current status of my research on QM. Also minor corrections and streamlining. Guess now I am done with this post.

Absolutely Random Notings on QM—Part 1: Bohr. And, a bad philosophy making its way into physics with his work, and his academic influence

TL;DR: Go—and keep—away.

I am still firming up my opinions. However, there is never a harm in launching yet another series of posts on a personal blog, is there? So here we go…

Quantum Mechanics began with Planck. But there was no theory of quanta in what Planck had offered.

What Planck had done was to postulate only the existence of the quanta of the energy, in the cavity radiation.

Einstein used this idea to predict the heat capacities of solids—a remarkable work, one that remains underappreciated in both text-books as well as popular science books on QM.

The first pretense at a quantum theory proper came from Bohr.

Bohr was thinking not about the cavity radiations, but about the spectra of the radiations emitted or absorbed by gases.

Matter, esp. gases, following Dalton, …, Einstein, and Perin, were made of distinct atoms. The properties of gases—especially the reason why they emitted or absorbed radiation only at certain distinct frequencies, but not at any other frequencies (including those continuous patches of frequencies in between the experimentally evident sharp peaks)—had to be explained in reference to what the atoms themselves were like. There was no other way out—not yet, not given the sound epistemology in physics of those days.

Thinking up a new universe still was not allowed back then in science let alone in physics. One still had to clearly think about explaining what was given in observations, what was in evidence. Effects still had be related back to causes; outward actions still had to be related back to the character/nature of the entities that thus acted.

The actor, unquestionably by now, was the atom. The effects were the discrete spectra. Not much else was known.

Those were the days were when the best hotels and restaurants in Berlin, London, and New York would have horse-driven buggies ushering in the socially important guests. Buggies still was the latest technology back then. Not many people thus ushered in are remembered today. But Bohr is.

If the atom was the actor, and the effects under study were the discrete spectra, then what was needed to be said, in theory, was something regarding the structure of the atom.

If an imagined entity sheer by its material/chemical type doesn’t do it, then it’s the structure—its shape and size—which must do it.

Back then, this still was regarded as one of the cardinal principles of science, unlike the mindless opposition to the science of Homeopathy today, esp. in the UK. But back then, it was known that one important reason that Calvin gets harassed by the school bully was that not just the sheer size of the latter’s matter but also that the structure of the latter was different. In other words: If you consumed alcohol, you simply didn’t take in so many atoms of carbon as in proportion to so many atoms of hydrogen, etc. You took in a structure, a configuration with which these atoms came in.

However, the trouble back then was, none had have the means to see the atoms.

If by structure you mean the geometrical shape and size, or some patterns of density, then clearly, there was no experimental observations pertaining to the same. The only relevant observation available to people back then was what had already been encapsulated in Rutherford’s model, viz., the incontestable idea that the atomic nucleus had to be massive and dense, occupying a very small space as compared to an atom taken as a whole; the electrons had to carry very little mass in comparison. (The contrast of Rutherford’s model of c. 1911 was to the earlier plum cake model by Thomson.)

Bohr would, therefore, have to start with Rutherford’s model of atoms, and invent some new ideas concerning it, and see if his model was consistent with the known results given by spectroscopic observations.

What Bohr offered was a model for the electrons contained in a nuclear atom.

However, even while differing from the Rutherford’s plum-cake model, Bohr’s model emphatically lacked a theory for the nature of the electrons themselves. This part has been kept underappreciated by the textbook authors and science teachers.

In particular, Bohr’s theory had absolutely no clue as to the process according to which the electrons could, and must, jump in between their stable orbits.

The meat of the matter was worse, far worse: Bohr had explicitly prohibited from pursuing any mechanism or explanation concerning the quantum jumps—an idea which he was the first to propose. [I don’t know of any one else originally but independently proposing the same idea.]

Bohr achieved this objective not through any deployment of the best possible levels of scientific reason but out of his philosophic convictions—the convictions of the more irrational kind. The quantum jumps were obviously not observable, according to him, only their effects were. So, strictly speaking, the quantum jumps couldn’t possibly be a part of his theory—plain and simple!

But then, Bohr in his philosophic enthusiasm didn’t stop just there. He went even further—much further. He fully deployed the powers of his explicit reasoning as well as the weight of his seniority in prohibiting the young physicists from even thinking of—let alone ideating or offering—any mechanism for such quantum jumps.

In other words, Bohr took special efforts to keep the young quantum enthusiasts absolutely and in principle clueless, as far as his quantum jumps were concerned.

Bohr’s theory, in a sense, was in line with the strictest demands of the philosophy of empiricism. Here is how Bohr’s application of this philosophy went:

  1. This electron—it can be measured!—at this energy level, now!
  2. [May be] The same electron, but this energy level, now!
  3. This energy difference, this frequency. Measured! [Thank you experimental spectroscopists; hats off to you, for, you leave Bohr alone!!]
  4. OK. Now, put the above three into a cohesive “theory.” And, BTW, don’t you ever even try to think about anything else!!

Continuing just a bit on the same lines, Bohr sure would have said (quoting Peikoff’s explanation of the philosophy of empiricism):

  1. [Looking at a tomato] We can only say this much in theory: “This, now, tomato!”
  2. Making a leeway for the most ambitious ones of the ilk: “This *red* tomato!!”

Going by his explicit philosophic convictions, it must have been a height of “speculation” for Bohr to mumble something—anything—about a thing like “orbit.” After all, even by just mentioning a word like “orbit,” Bohr was being absolutely philosophically inconsistent here. Dear reader, observe that the orbit itself never at all was an observable!

Bohr must have in his conscience convulsed at this fact; his own philosophy couldn’t possibly have, strictly speaking, permitted him to accommodate into his theory a non-measurable feature of a non-measurable entity—such as his orbits of his electrons. Only the allure of outwardly producing predictions that matched with the experiment might have quietened his conscience—and that too, temporarily. At least until he got a new stone-building housing an Institute for himself and/or a Physics Nobel, that is.

Possible. With Herr Herr Herr Doktor Doktor Doktor Professor Professors, anything is possible.

It is often remarked that the one curious feature of the Bohr theory was the fact that the stability of the electronic orbits was postulated in it, not explained.

That is, not explained in reference to any known physical principle. The analogy to the solar system indeed was just that: an analogy. It was not a reference to an established physical principle.

However, the basically marvelous feature of the Bohr theory was not that the orbits were stable (in violation of the known laws of electrodynamics). It was: there at all were any orbits in it, even if no experiment had ever given any evidence for the continuously or discontinuously subsequent positions electrons within an atom or of their motions.

So much for originator of the cult of sticking only to the “observables.”

What Sommerfeld did was to add footnotes to Bohr’s work.

Sommerfeld did this work admirably well.

However, what this instance in the history of physics clearly demonstrates is yet another principle from the epistemology of physics: how a man of otherwise enormous mathematical abilities and training (and an academically influential position, I might add), but having evidently no remarkable capacity for a very novel, breakthrough kind of conceptual thinking, just cannot but fall short of making any lasting contributions to physics.

“Math” by itself simply isn’t enough for physics.

What came to be known as the old quantum theory, thus, faced an impasse.

Under Bohr’s (and philosophers’) loving tutorship, the situation continued for a long time—for more than a decade!

A Song I Like:

(Marathi) “sakhi ga murali mohan mohi manaa…”
Music: Hridaynath Mangeshkar
Singer: Asha Bhosale
Lyrics: P. Savalaram

PS: Only typos and animals of the similar ilk remain to be corrected.