[lisper]

> the standard textbooks are excellent

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.

[spekcular]

Can you point to a standard textbook that does this? The ones I'm familiar with definitely don't shortchange multi-particle problems.

And is the measurement problem not a mystery? If there's convincing explanation, that's news to me.

[lisper]

> 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.

See https://flownet.com/ron/QM.pdf for a complete discussion.

[spekcular]

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.

[lisper]

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).

[spekcular]

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.

[lisper]

> 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.