Indeed, the author's 2000-page online textbook, heavily promoted on the internet, is a classic trap for unwary students.
It looks alright at first: volume I is light on math, but full of neat examples. But it's full of intuitively plausible but slightly wrong statements which fall apart in more general situations, reflecting the author's lack of technical expertise. This problem steadily gets worse: volume IV is an oversimplified introduction to quantum mechanics which contains almost no math, and serious conceptual errors on almost every page. Volume V covers a bizarre mix of particle physics, consciousness, and sexual reproduction. And volume VI is the author's almost math-free personal theory of everything. Because the change is gradual, a student can get seriously misled without noticing, like the proverbial boiling frog.
On HN, people are always asking how to get started self-learning topics like physics. The tragedy is that this has been a completely solved problem for decades: the standard textbooks are excellent. But people don't hear that message because self-promoters pollute the discourse.
A caveat. Some years ago, at a first-tier university, some physicists and mathematicians were munching. A physics professor described how days earlier he thought he had found a case of a well-respected intro physics textbook saying something wrong. But, after some hours and days of thought, he realized the textbook was very carefully worded so as to not be incorrect. Yay. Most everyone smiled and agreed it was an excellent textbook.
A bit later, there was a quiet out-of-band question: So... if you're already an expert on the topic, and do a close read, after thinking about it for days, you will escape being misled... and this is a win??
There's an old physics education research joke: If you think your lectures are working, your assessment also isn't. I've found that to apply to much science education content as well.
Sorry, I have to disagree with this, at least with respect to quantum mechanics. The pedagogy of QM is atrocious because it generally focuses on the single-particle case and relegates entanglement to the sidelines while making a big deal out of the mystery of the measurement problem. This leaves students hopelessly confused. At least, it left me hopelessly confused for about ten years. Even today one hears physicists speak un-ironically of "quantum erasers changing the past" and other associated nonsense. If there's a standard text that inoculates against that, I have not seen it.
> Can you point to a standard textbook that does this?
That does what? Focus on the single-particle case and punt on measurement? My two poster children are the Feynman lectures and Griffiths.
> The ones I'm familiar with definitely don't shortchange multi-particle problems.
What does your reading list look like? Maybe things have changed since I last looked.
> the measurement problem not a mystery?
It might be a mystery, but it is not the mystery most commonly presented, namely, that particles change their behavior "when somebody looks." This is nonsense. Measurement has nothing to do with "somebody looking", it is just entanglement + decoherence. The only real mystery is the origin of the Born probabilities.
A) I don't consider the Feynman lectures a "standard textbook." I don't think there exists any university that uses them as the primary reference in their quantum course. They're fine, as far as they go, but I think modern pedagogy is better.
Concerning Griffiths, what do you feel it lacks? You've got the hydrogen atom, fermions, bosons, helium, and probably more stuff that I'm forgetting right now. What else would you stick in an intro course? Hartree-Fock?
B) Decoherence doesn't solve the measurement problem. Even the decoherence boosters admit this. See, for example, Adler's paper on this: https://arxiv.org/abs/quant-ph/0112095.
This isn't to say the decoherence program isn't important. I think it is. It just hasn't solved the measurement problem.
What Griffiths lacks is an explanation of what a measurement is. He, like many other authors, explicitly avoids this because he says that measurement is an ineffable mystery, but it isn't. A measurement is a macroscopic system of mutually entangled particles. The only real mystery is why the outcomes obey the Born rule.
Decoherence does not solve the whole measurement problem. Like I said, it does not explain the Born rule. But it does solve parts of the measurement problem. Decoherence explains why measurements are not reversible (they are reversible in principle but not in practice because you would have to reverse O(10^23) entanglements). It explains why only one outcome is experienced (because you are part of the mutually entangled system of particles that constitutes the measurement, and all of the particles in the system are in classical correlation with each other). I don't know of any standard text that discusses this at all.
Whether or not Feynman is a "standard text" is quibbling over terminology. A lot of people learn QM from it (or at least try to).
I'm sorry, but your description of how decoherence purportedly solves parts of the measurement problem is incorrect.
Even decoherence researchers agree that docoherence theory does not do this. You can find references and details in the Adler paper I linked, or in Schlosshauer's "Decoherence, the measurement problem, and interpretations of quantum mechanics." (Schlosshauer is the author of a main reference on docoherence: http://faculty.up.edu/schlosshauer/index.php?page=books.)
So, the reason that Griffiths avoids giving the explanation of measurement you prefer is that it is wrong. It's a virtue of the book, not a fault. He does discuss decoherence on page 462 of the third edition, though.
> Even decoherence researchers agree that docoherence theory does not do this
Yes, but they are wrong. And it's not hard to see that they are wrong.
The crux of the argument is that the state predicted by QM:
|S1>|A1>|O1>|E1> + |S2>|A2>|O2>|E2>
where S is the system being measured, A is the measurement apparatus, O is the observer, and E is the environment, is not what is observed. What is observed is either:
|S1>|A1>|O1>|E1>
or
|S2>|A2>|O2>|E2>
neither of which is the predicted state above. Except that it is because |S1>|A1>|O1>|E1> is what is predicted to be observed by an observer in state |O1> and |S2>|A2>|O2>|E2> is what is predicted to be observed by an observer in state |O2>. It is not that the prediction is wrong, it is that you, a classical observer, are not sufficiently omniscient to see both observations. You can only see one or the other. And this too can be explained, though by quantum information theory rather than decoherence theory. In order to be a classical observer it is necessary to be able to copy (classical) information. The only way to do that is to discard some of the (quantum) information contained in the wave function. Being non-omniscient (i.e. being unable to directly observe a superposition) is a necessary precondition of being a classical observer.
After reading your comment I looked at the original post with a view to identifying its basic perspective.
https://www.motionmountain.net/9lines.html was clearly not written by a physicist, as it includes the line "The nine lines contain physics, chemistry, material science, biology, medicine, geology, astronomy, engineering and computer science. It appears that the nine lines contain all natural sciences!" which is not a physics type of statement.
Obviously, physics contains everything, just the way "bits contain all software". Observing that doesn't make someone a programmer, in my opinion.
Why stop at physics, chemistry, material science, biology, medicine, geology, astronomy, engineering and computer science (list provided).
However, it is kind of like saying text comprises all of the words of Shakespeare. Well, sure, but that doesn't mean that you get Shakespearean criticism from writing a text editor. It's two different fields.
However, the lines "Isn't this incredible?" and "Enjoy searching for answers." are sarcastic and disrespectful to the work actual physicists put into their discipline for decades and the author should be ashamed for this tone.
If they want to be a physicist they should observe and learn from physicists at every opportunity. (I'm not one, by the way.)
Ignoring the rude sarcasm, we can correctly summarize the document as "Physics governs everything. Period."
It's not a physics document. It is (or rather ought to be) a tribute to physicists and the unbreakable laws of physics.
Thank you for your candid feedback. I belong to those working in physics for decades. To avoid such misunderstandings in future, I improved a few lines.
One remark: the text is really meant to state that the specific 9 lines given do contain all of physics (and thus all other natural sciences).
The argument differs from "words and Shakespeare": the nine line describe nature exactly, within measurement precision. That is the central content of that page. It is not that physics governs everything. It is that those specific 9 lines describe all measurements, all observations, and contain all equations. This is a much stronger statement.
The Physical Review is a gigantic set of journals, and like anything of its size, many of its published results are wrong. At this very moment I'm writing a rebuttal to a PRD paper that arrived at nonsensical conclusions due to some basic algebra mistakes.
"Several"? Google Scholar shows two, one of which is an approximately 1-page comment on a rebuttal to the other one. Neither mentions "strand theory," the focus of the criticism in that link.
Proceed with caution.