171–179 of 179 posts
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Strangely not. You can do CS on paper, no need for a single bit-flipping device. Turing did half the field in his head / a thought experiment.
And input and ouput devices ...
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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 y…
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 Bor…
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.
The author is a well-known crank. See post #10 here, for instance: https://www.physicsforums.com/threads/strand-model-published... Proceed with caution.
I liked the original post at https://www.motionmountain.net/9lines.html , except for a couple of words I point out below. 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, geo…
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.
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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 Bor…
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 docoher…
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.
The author is a well-known crank. See post #10 here, for instance: https://www.physicsforums.com/threads/strand-model-published... Proceed with caution.
"Today is the first of April. Imagine strands as fluctuating, scaled-down, uncuttable, massless, endless, knot-free, cooked spaghetti"
The author is a well-known crank. See post #10 here, for instance: https://www.physicsforums.com/threads/strand-model-published... Proceed with caution.
Further down in the thread, crank or not, I found this note on their 'strand' theory very convincing from a FSM perspective: "Today is the first of April. Imagine strands as fluctuating, scaled-down, uncuttable, massless, endless, knot-free, cooked spaghetti"
“ bosons, quarks and leptons – with their charges and properties make up everything.” The empty space between the bosons, quarks and leptons is not made up of any of these particles, yet the space ‘exists’ - without it, everything in the universe would just be a big clump.
In general relativity, space is not a thing.
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In general relativity, space is not a thing.
I meant to thank you for this comment earlier - it’s led to a whole bunch of interesting stuff I did not know.