My black body story (it's physics)
commandcenter.blogspot.com
commandcenter.blogspot.com
One of the big problems at the time was the problem of the self-force of electric fields and the structure of the electron. In classical mechanics we approximate an electron as a point charge --- an infinitesimally small source of electric charge. This works for a lot of practical problems, but by the 20th century it was known that this couldn't be the real story because if you integrate up the energy in the electric field around a point source you find that it's infinite! And with Einstein's discovery of relativity, that meant that it would be infinitely massive.
To avoid this infinity physicists generally assumed that the electron had to have some finite radius. (Estimates of this size are how we get the notion of the "classical radius of the electron.") But now there was a new problem. If you assume that the electron is a little sphere packed with charge, what keeps it together? The self-repulsion from the electric field will try to make it explode apart. That means there has to be a new force acting like rubber bands to hold the thing together.
To make matters worse, if you accelerate an electron, the electromagnetic waves generated by one part of the electron will act on the other part. This will introduce new forces. Moreover, when the electron radiates an electromagnetic wave, that wave will in turn impart a force to the electron, resulting in a "self-force." Calculating these self-forces and internal stresses occupied many of the brightest physicists of the early 1900s, including Poincaré. But the results they got were paradoxical. They imply that due to its self-force an electron can spontaneously accelerate exponentially --- or, even worse, act with retrocausality and start moving before you even touch it!
In the end these problems were "resolved" because the classical picture doesn't hold on these small length scales --- you need a quantum mechanical description. But interestingly, the fundamental problems that those physicists were grappling with didn't exactly disappear in the quantum picture, they just got transmuted into new problems in quantum electrodynamics. The problem of the diverging energy of an electric field around a point source has a mirror in the issue around renormalization in QFT.
As you say, the existence of photons wasn't immediately jumped to. All that he deduces is that energy transfer must be quantized, and this is the real insight of quantum mechanics, but it gets lost in the woo-ey clickbaity world of modern pop sci.
It was so nice to read the derivation from the point of view of a contemporary 20th century physicist, made me want to start reading a bunch of other 20th century physics papers in their original form.
That said, I'm ashamed to say I've not had a copy of his book Quantum Theory in my hands. You're one of many I've seen mention it in recent times so I'll have to remedy that. :-)
Incidentally, I have read the original Aharonov–Bohm paper. Understanding that physics I reckon is crucial to getting a good handle on EM, potentials, etc.
But the first few chapters are so conversational and grounded in historical context that it's a real joy to read, even if you're not following along on pen and paper through all of the steps. If you know of any other "must reads" of the 20th century like this, please let me know! I love to hear the arguments presented as they were actually discussed at the time, not just what was settled on as the end result a century later.
Thanks!
Edit: I've always considered this historical context most important and we do not stress it enough in teaching physics (same in math and chemistry or in just about every subject that has developed and progressed over the years - 19th C. scholars translating ancient Greek texts for instance).
As far as far as is possible, we need to get inside the heads of these people and try to picture the obstacles and difficulties they were facing at the time. Moreover, it's my experience that if I try to understand where they are coming from then I find that I get a much deeper appreciation (and better understanding) of the subject. Similarly, old scientific and engineering textbooks of the era are very useful in further illuminating this historical thinking; for example, 19th C. postulations about how the sun got its energy before we knew anything about nuclear fusion.
That said, it seems we largely ignore this historical context because it is hard to do well and that most courses are already short of time. Still, if any subject needs it, it's QM and I've said so here on HN and elsewhere on many occasions: https://news.ycombinator.com/item?id=31980008. Big warning, here I'm in long-rave mode!
Re: other good reads on the subject, at short notice I'm at a bit of a loss. Your best bet are textbooks on HPS - History and Philosophy of Science (which was one of my subjects decades ago). The trouble is comments on this topic soon time out, so in future when I think of them I won't he able to update you. (Much of my knowledge comes from snippets in individual texts, unfortunately, it's not all collected into one volume.)
I already have a downloaded version and I like very much what I see. Soon I'll have a hardcopy. Still not sure how I missed this given its prominent position amongst texts on the subject.
Anyway, glancing through the book pretty much at random I've seen many phrases that tickle my fancy and pique my interest. For instance, take the 2nd para on p151 wherein he's discussing Newton's Laws of Motion and force, it's pretty hard to stop reading a paragraph that begins "It is a curiously ironical development of history that,....". Further down the same page when discussing gravity he makes a very straightforward statement but with a twist:
"Thus, the laws of gravitation can be expressed as follows: Two bodies suffer a mutual acceleration, in the direction of the line adjoining them, which is inversely proportional to the square of the distance between them."
Here, 'suffer' conjures up the notion of imposition - of gravity imposing an acceleration on bodies which otherwise wouldn't be the 'natural' order of things. Had he used words like 'experience' or 'influence' it wouldn't have been nearly as effective writing. From the little I've read so far I note the way he writes forces me to think laterally, in effect he's forcing me to perceive things from a different perspective.
In fact, I'm already half way through Chapter 8, An Attempt to Build a Physical Picture of the Quantum Nature of Matter, as it's a breeze to read it's so well written - it's not only informative but also entertaining which is a rare quality for a physics textbook.
Mind you, that's an easy chapter as there's not an integral sign to be seen anywhere. ...But I note they're not forgotten, they reappear in great abundance in Chapter 9! :-)
It's excellent stuff, thanks again for the info.
At a more advanced level, there is Joseph Larmor's 1900 book, "Ether and Matter"[0]. Between the Preface and the first four chapters, you get about 60 pages of discussion of the state of electrodynamics and ether theory, as they were at the end of the 19th century, without any math more than some trig near the end.
Oh no, not luminiferous aether again! I've not seen Larmor's book before but I've just downloaded it from the link and look forward to reading it.
It's somewhat an inspired guess that you thought I'd be interested that topic, the fact is I have been so for quite some years. I've even pontificated on the subject on HN from time to time.
Whilst the original luminiferous aether concept has been debunked, it seems to me that things get interesting at a deeper level. We still don't know why c has the value it has, similarly, why the electric and magnetic constants - vacuum permittivity and permeability - along with the fine structure constant alpha are as they are. If any of those constants were to change so would all the others.
Dare I even mention it, any new conceptual 'Lorentzian'-like framework for a 'new aether' that also incorporates those constants is a far too big a subject to discuss here. What can be said however is that it's logical progression from what Larmor's book is about.
The funniest part of all that is, Bohm's pilot wave theory isn't even wrong. It's one possible interpretation of many, and definitely isn't falsified yet (none of the others are, either), though it does carry some unsettling implications if it happens to be accurate, most notably that it is predicated on determinism, which is probably most of the reason why it's been marginalized. Aside from, of course, the Copenhagen fiasco.
First, everything I've read and learned about Bohm tells me I would have liked the man had I ever met him - even the well-known portrait photo of him hints at his maverick nature. We need more troublemakers in science and physics to stir up the orthodoxy. :-)
Second, I rather like the Pilot Wave theory despite, as you say, its unsettling implications. It sort of makes sense to my simple mind.
I don't consider myself sufficiently expert to say how much leeway there is in the theory but I'll say this, others such as Many Worlds seem somewhat even more incredulous to my mind (despite Carroll's eager proselytizing the cause), but I'm open enough to be convinced come more evidence.
Re Copenhagen, yeah it's a 'fiasco' even though it works. Had I had sufficient brains and been around at Solvay I'm damned sure I would have had arguments with Bohr. Despite Bell, the EPR Paradox mob were onto something, at least they didn't take 'no' for an answer, similarly so with Bohm.
Intelligent-thinking dissenters are good for physics.
Quantum Bayesianism ("QBism") softens the strong claims about reality to merely those about subjectivity, i.e., you cannot know that which cannot be represented by the configuration space of your lightcone. In other words, possible futures are possible only when there is an unbroken causal chain from your present to that future, and you will be ignorant of anything outside of your lightcone. It stresses the uncertainty inherent in a singular perspective of spacetime's unfolding, rather than an uncertainty of some mythical "wavefunction collapse mechanism".
the guy who in 1901 developed the double-slit experiment, actually a single paper card back then, created a mystery that lasted at least a century, if not until today. (it was the same guy who decoded the rosetta stone, weirdly).
In a large way the project of the century was understanding the elements, separating them and measuring their weights. I think constantly about this 1870s essay by an important geochemist asking 'are the elements elementary'[1]. It is nearly poetry (to me at least).
the key observations coevolved with the math, so sometimes experiment led (someone put a wire near a compass and the compass moved), other times the math led. (As in the 20th century, when lasers were a numeric phenomenon before anyone thought to build one). Maxwell's math feels to me like it's at the center of it all. A 20th century physicist, Wigner, has an essay about the 'unreasonable effectiveness of math in science'.
maxwell's equations predict a speed limit for light, and were largely intact in einstein. (the speed of light was known experimentally way before this from eclipse observations, I think). you could say that maxwell + electron research + planck led naturally to einstein, and there's no reason someone's annus mirabilis couldn't have been 50 years earlier other than that it took this long to think of these ideas.
if there's any takeaway from this history it's that big questions, if you sink your teeth into them, lead to big answers
https://press.uchicago.edu/ucp/books/book/chicago/B/bo362239...
Maxwell's daemon comes to mind.
Fermi is noted in Richard Rhodes abomb history having a huge unconscious drive to test a ludicrous substance, against his plans, uncovering how radioactivity behaved.
If you don't know the history of electrodynamics and thermodynamics already I wouldn't skip the first book (which also contains the work of Plank on black body radiation)
I've always felt that science should be taught in schools by a process of discovery or historical discoveries.
Is it wavelength or frequency?