A wish. Looking for a couple of suitable post-docs. Covid-19 in India.

1. A wish…

I wish there were a neat, scholarly, account of the early development regarding the relativity theory. …

… There are tons of material on the topic, but not a single one seems to be to my liking…. I mean, even while rapidly browsing through so many of them, they all seem to fall short—rather, so awfully short. Reason: Most, if not all of them, seem intent on deifying Einstein, and / or, the primacy of maths over physics. [Did I cover all the eigenbases? May be not. So, let me add.] … The worst of them spend themselves out on promoting the idea that coming up with good but radical ideas in physics is all about getting lucky in some day-dreaming involving some mathematical ideas. 

OTOH, The “model” for the book which I have in mind here is something like what Prof. Malcolm Longair has done for QM; see his book: “Quantum concepts in physics: an alternative approach to the understanding of quantum mechanics.” [^].

… High time someone should have undertaken a similar effort. But unfortunately, it’s entirely lacking.

… The wish isn’t without purpose. The more I study the quantum mechanical spin, the more I realize the handicap which I have of not having already studied the relativity theory.

I can always postpone the fully consistent description, following my new approach, for the QM spin. [No one / no organization has ever sponsored my research. [Though, they all are hell bent on “following up” on me.]]

However, now that I have developed (what I believe to be) a good, basic, ontology for the QM phenomena, I have begun to see a promising pathway, at least from the viewpoint of a basic ontology, from a non-relativistic description of QM to a relativistic one—I mean the special relativistic one.

2. Looking for a couple of suitable post-docs…

Another possibility I am toying with, currently, is this:

Over a considerable period of time, say over a year or so, to build a series of Python/C++ scripts/programs that illustrate the classical EM in action, but following my new ontological ideas. These ideas are for the Maxwell-Lorentz EM, but I do anticipate that these would provide the easiest pathway to integrating the Special Relativity with the non-relativistic QM.

The trouble is: I will have to get into the FDTD algorithmics too, and I don’t have the time to do it. (In case you didn’t know, when it comes to EM, the best technique is FDTD.)

Wish I had a competent post-doc—actually two—working simultaneously with me! Right now!!

One could build the above-mentioned FDTD applets, but following the way I want them to be built.

The other one could work on “FEM-ization” of my FDM code (i.e., for the He atom, done with my new approach, and yet to be published). Once he is done, he could explore doing the same with FDTD (yes of course!), and compare and contrast the two. The FEM-ization of my FDM code won’t be very highly demanding, in the sense, people have done the finite elements formulation for the helium atom, and also have implemented it in code—decades ago… But of course, they did so following the mainstream QM. It would be a fun for the post-doc to implement it using the ideas I will be proposing—shortly.

Then, both could work on the ideas for the relativistic QM. … The pace of the work would depend on what they bring to the table, and how they perform.

Fallout? If you are a smart PhD in the concerned areas, I need not provide even a hint about it…

3. Status update on my QM research:

Currently, I am typing a set of notes on the topic of the quantum mechanical angular momentum, including the spin. For the time being, I am mostly following Dan Schroeder’s notes (which I mentioned in the post before the last, here [^]). Once done, I don’t mind uploading these notes—for proofreading by you the potential post-docs. [Who else?]

While typing these notes, it has become once again very clear to me—crystal clear, in fact—as to how my “theory” for the QM spin (following my new approach) falls short. … So short, in fact. … My “theory” doesn’t just look awfully arbitrary; it is so.

All in all, don’t expect the same kind of confidence from me for the spin-related aspects as for the spin-less ones. I mean, in the upcoming document on my new approach.

4. Back to the potential post-docs:

Exciting enough?

If yes, drop me a line. Especially, if you are working with Google / similar company. I gather they officially allow you some fraction of your official time for your own hobby projects too…

5. If you are someone young and enthusiastic, say from the Pune city and all (and in general, from India):

They have relaxed the curbs. However, I have a word of advice for you.

Don’t step out unless absolutely necessary, and if so doing, take all the precautions.

It’s just a matter of a few months now…

…BTW, I am also thinking whether the government shouldn’t relax the enforced gap of three months in between the first and the second dose for the jabs. … There are circumstantial matters which indicate that a gap in between two to three months might be ideal; that three months might be too long a period. (Actually, this matter had struck me right on the day that the Central Government increased the gap from 6 weeks to 12 weeks in one, single, move. …However, at that time, I had thought it prudent to wait and watch. Now, I think I can—nay, should—share my opinon. … I also have some other points about these matters, but these are not so important. I will sure mention these as and when it becomes necessary to do so.)

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

A song I like:

(Hindi) ज़िंदगी आ रहा हूँ मैं… (“zindagi aa rahaa hoon main…”)
Lyrics: Javed Akhtar
Music: Hridaynath Mangeshkar
Singer: Kishore Kumar


Credits happily listed in a random order. A good quality audio is here [^]. … Although I haven’t seen this movie, recently I watched the video for this song, and found that I enjoyed it too. A good quality video is here [^].

… I always loved this song, esp. the tune and the arrangement / orchestration. … And of course, Javed Akhtar’s awesome lyrics. … Well, yes, Kishore does sound, at places in this song, just a slight bit… and how shall I put it?… He doesn’t sound as if he were in his best frame of singing, here. His voice sounds a bit too “broad”, and perhaps heavy, and even a bit “tired” perhaps? as if he were straining a bit?…  Even then, of course, being Kishore, he does manage to pull a great job. [It’s just that, knowing Kishore, one wants to note this aside… I know, hair-splitting, it is. … Can’t help. … Sometimes.]

… [BTW, if you are young and dynamic and result-oriented etc.: The guy in this video is Sonam Kapoor’s dad. He used to be young. Once upon time. Me too. [Though I never ever had the hair-style he displays here. A lot of my class-mates did, mostly following The “Bachchan”. Not me. […Yeah, I know.]]

… All the same, all that you’ve to do now is to wait for just a few more months, that’s all… 2021 isn’t a meme on Twitter the way 2020 was. Nevertheless, in India, we have to wait. So, just listen to songs like this for just a wee bit more. … I can tell you, from experience: The scenery, esp. the Sahyaadri’s, does stay great also well until January / February next year. (And if you really love Sahyaadri’s, well, they are there, forever…)

…So there.]

…And if you are new to this song, see if you too like it…

Take care and bye for now…



The monsoon is here! Also, a fun aspect of QM.

1. Status update:

The monsoon is officially here, in the Pune city, and somehow, my spring-break [^] too gets over—finally!

(…There were no rains on the day that the Met. department officially announced the arrival of monsoon in the Pune city. The skies were, in fact, fairly clear on that day! … However, this year, everything is different. It was raining on almost every day in the month of May!)

Anyway, to come back to the reason for the permanent break in the spring-break which I had taken…

Looks like I have found a minimum working clarity regarding the phenomenon of the quantum mechanical spin. … I guess the level of clarity which I have now got is, perhaps, as good as what might be possible within the confines of a strictly non-relativistic analysis.

So… I can now with some placid satisfaction proceed to watching the remaining lectures of the MIT courses.

I will begin writing the document on my new approach a little later. I now expect to be able to put it out by 15th July 2021, perhaps earlier. [Err… Any suggestions for the (Hindi) “muhurat”s for either / both?]

…But yes, the quantum spin turned out to be a tricky topic to get right. Very tricky.

…But then, that way, all of QM is tricky. … Here, let me highlight just one aspect that’s especially fun to think through…

2. One fun aspect of QM:

The Schrodinger equation for a one-particle system is given as:

i\hbar \dfrac{\partial}{\partial t} \Psi(x,t) = \hat{H} \Psi(x,t),

where the notation is standard; in particular, i is the imaginary unit, and \hat{H} is the system Hamiltonian operator.

The observation I have in mind is the following:

Express the complex-valued function \Psi(x,t) explicitly as the sum of its real and imaginary parts:

\Psi(x,t) = \Psi_R(x,t) + i \Psi_I(x,t),

where \Psi_R \in \mathcal{R}, and do note, also \Psi_I \in \mathcal{R}, that is, both are real-valued functions. (In contrast, the original \Psi(x,t) \in \mathcal{C}; it’s a complex-valued function.)

Substitute the preceding expression into the Schrodinger equation, collect the real- and imaginary- terms, and obtain a system of two coupled equations:

\hbar \dfrac{\partial}{\partial t} \Psi_R(x,t) = \hat{H} \Psi_I(x,t)
- \hbar \dfrac{\partial}{\partial t} \Psi_I(x,t) = \hat{H} \Psi_R(x,t).

The preceding system of two equations, when taken together, is fully equivalent to the single complex-valued Schrodinger’s equation noted in the beginning. The emphasis is on the phrase: “fully equivalent”. Yes. The equivalence is mathematically valid—fully!

Now, notice that this latter system of equations has no imaginary unit i appearing in it. In other words, we are dealing with pure real numbers here.


… Ummm, not really. Did you notice the negative sign stuck on the left hand-side of the second equation? That negative sign, together with the fact that the in the first equation, you have the real-part \Psi_R on the left hand-side but the imaginary part \Psi_I on the right hand-side, and vice versa for the second equation, pulls the necessary trick.

This way of looking at the Schrodinger equation is sometimes helpful in the computational modeling work, in particular, while simulating the time evolution, i.e., the transients. (However, it’s not so directly useful when it comes to modeling the stationary states.) For a good explanation of this viewpoint, see, e.g., James Nagel’s SciPy Cookbook write-up and Python code here [^]. The link to his accompanying PDF document (containing the explanation) is given right in the write-up. He also has an easy-to-follow peer-reviewed paper on the topic; see here [^]. I had run into this work many years ago. BTW, there is another paper dealing with the same idea, here [^]. I have known it for a long time too. …Some time recently, I recalled them both.

Now, what is so tricky about it, you ask? Well, here is a homework for you:

Homework: Compare and contrast the aforementioned, purely real-valued, formulation of quantum mechanics with the viewpoint expressed in a recent Quanta Mag article, here [^]. Also include this StackExchange thread [^] in your analysis.

Happy thinking!

OK, take care, and bye for now…

A song I like:


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.