If people are interested in the historical developments of EM theory and the various physical analogies maxwell used, I'd highly recommend "Faraday, Maxwell, and the Electromagnetic Field" by Forbes and Mahon. It has a interesting description of these, and also emphasizes the insights Faraday had - he wrote about the potential of EM waves ~30 years before maxwell came up with the mathematics.
And if you want to know what kind of thinking Einstein used to move from Maxwell equations to light being quanta I recommend: Einstein lecture by Douglas Hofstadter (Feb 4, 2018) https://www.youtube.com/watch?v=NXdQfPrU64g
I have a quick question: is the modern understanding that "the electromagnetic field itself quantized" OR is it just shorthand for "light emitted specifically by atomic electron orbitals changing is produced in discrete energy levels because the energy levels between orbitals are discrete"?
To me, it always felt like the latter, but I've never seen that written down explicitly, and everyone seems to talk like it's the former. I mean sure, 99.99% of the time experiments that emit or absorb photons are performed using atoms (and hence discrete electron orbitals) but that's certainly not the only way to create or or absorb photons. There's Cherenkov radiation, Bremsstrahlung, etc...
The EM field itself is quantized. You start with the classical electromagnetic field and you try to quantize it. The rules for this are not precise nor formal.
That means something a little different to "photons can only have specific energies" (that applies only to very specific atoms or atoms with certain structure; in many materials, electrons can exist in bands of continuous energy).
No. Absolutely not. This is where physicists get their history wrong and what the lecture explains.
When Planck described black-body radiation, he wrote that it was "as if" there were resonators in the walls that can oscillate at certain discrete frequencies. He did believe that light was a wave.
Even after Einstein published his paper much later, Planck and everyone else thought he was silly for almost twenty years. They accepted the photoelectric effect explanation but not how Einstein came to the result (photons).
OK, but it is worth mentioning, then, that the quantum theory as it has developed in the later years has, in fact, rejected the idea of the light quanta as Einstein thought of them, being "particles of light," i.e. something that is localized in space, whereas Planck's notion of energy quanta (or energy quantization, of the light wave or in general) has remained in force.
We are interested how the thinking and ideas behind physics historically proceeded.
The important historical lesson is that Einstein had the correct idea and framework to think about light __at that time__ and advance physical theory, he wrote it down and people refused to accept it.
* 1900 Plank describes black-body radiation in a way where energy is quantized.
* 1905 Einstein describes light as having “corpuscular” nature and uses it to describe photoelectric effect.
* 1923 Compton effect discovered. Einsteins ideas about light quanta explain them perfectly. Everybody accepts that light is also a particle and Gilbert Lewis coins the word photon.
Isn't this somewhat simplified? The modern "proper" understanding/mechanistic explanation of the Quantization of (spin-1/2, massless - or symmetry groups etc.)fields resulting in photons came later still.
You have to think how the ideas proceeded historically, not to try to retrofit current understanding backwards in time. For example, Isaac Newton believed light was composed of a stream of corpuscles, but he lost his case in 1801 when Young presented his double slit experiment.
Einstein's idea at that time was more correct and provided better explanations and predictions.
Kinda hard to beat Whittaker's "A History of the Theories of Aether & Electricity" -the more recent things tell a rather more linear story than the actual history. There were some crazy ideas, most of which were quasi-mechanical or fluid mechanical.
The book I referenced discusses both the early hydrodynamic model maxwell used for electrostatics and a rather bizarre (and intriguing) mechanical model involving flywheels and gears.
Can't comment on whether it linearizes the history though.
These ideas were not original to Maxwell; virtually ALL of the pre-Maxwell theories of electricity and magnetism looked like that. The first chunk of Whittaker's book is all about these mostly forgotten ideas and the cool people who tought them up. It's really a classic.
I feel like this illustrates a problem with the world of physics today (and other areas). This paper sounds like it could be the beginning of something new/better. But the effort required to bring all of that together was probably significant, and I kept seeing "to first order" which indicates it's nowhere near complete.
I guess my point is that QM took a long time, and work from a lot of people to reach the point it has. Any replacement will likely need a lot of work by a lot of people, and there don't seem to be very many people working outside the box. Or perhaps that's just because nobody wants to publish half-baked ideas. I'd rather see new ideas published and get shot down than yet another experiment confirming spooky action at a distance in some new configuration.
Well, I'm always enthusiastic when I see such new developments and I'm certainly going to read through it later in the evening. That being said, I'm also more skeptical whether this has a chance to work, especially if it's a classical construction.
Why? Well, you'd probably need to study physics for a few years to really appreciate the answer, however I can sum it up quite simply:
At the beginning of the 20th century we realized that our models are allowed to contain whatever objects you can imagine (and put in a consistent mathematical form, of course).
In particular, theories are allowed to operate on objects which don't even take number values as long as they are objects which obey the defined rules. This realization is so refreshing, so liberating that it allowed for the construction of a number of magnificent things like quantum mechanics, field theory, standard model and strings.
However it's hard to convey this truth to someone who's mathematical education finished (even) at an engineer level. Thus, you see the media and half-physicists always focusing on the same stupid "paradoxes" when there was never one to begin with.
The insistence of many mediocre people against quantum mechanics (and modern physics in general) is analogous to an ancient Egyptian protesting that: "we should have a theory where everything is explained with natural numbers" which is the only object that his limited imagination can directly connect with reality. Another argument which people tend to use is that "QM is complicated", but nothing stands further from the truth. It might be hard to derive the solutions, but the postulates are really simple and there are no simple alternatives with the scope of validity of QM. The only real way of proceeding is to learn the lessons of quantum theory and build upon it, someday we may be lucky enough to find simple mathematical rules (but likely highly abstract) that govern the universe.
So as you see, I partially agree with you. The "spooky action" kind of experiments are stupid, but for the opposite reason!
Thanks for that. I am that engineer / half-physicist and I can appreciate my own ignorance in this area. I have my own interest where my depth seems to go beyond most people studying it, so I know your frustration if only a little.
>> "we should have a theory where everything is explained with natural numbers" which is the only object that his limited imagination can directly connect with reality.
That part though... Physics has a problem where the people practicing it can't even make a satisfactory connection to reality. Even from the outside we see this in debates about "interpretation" which go on among physicists. To be satisfied with the mathematics is one thing, to have a satisfactory connection back to reality is quite another. Don't let the beauty of the abstractions blind you to that.
It seems like you've really missed the crucial part.
The whole point is to have a theory which will mirror the relations of objects in the world not the objects themselves. The former leads to truth, the latter is silly.
All the interpretations stuff you read about is, unluckily (for the public image of physicists), a fools game. QM is as it was 100 years ago and no progress has ever been made in the "foundations of quantum mechanics", most people who work in this area are either philosophers or very confused physicists.
Who's to blame for this state of affairs? Well, there has been plenty of wrong stuff said about QM in media and even in academia. Part of the problem is that people still insist on using the old classical language in the description of quantum experiments.
Examples:
* "nonlocality" - quantum theory is a local theory, it's only when you assume that it's "classical in disguise" you get nonsense
* "delayed choice" - should have rather be called "post-factum reasoning"
As I said before if you really dig down deep, you'll realize that this is because our classical macroscopic quantities like "value of momentum", "magnetic moment" etc. are not the same things that exist "down there". The language of nature turns out to be much more subtle. Quantum Mechanics is really the best you can get when you try to hold on to the old classical ideas. Thus an alternative to QM would most likely have nothing to do with classical mechanics at all, it would need to be something entirely new.
