@DanielSank, although I plan to try that out myself, but is the electron in a noisy bath conceptual question a meaningful one. I a not sure if I understood measurement correctly for that?
2. Electron in a noisy bath. Consider confining an electron prepared in the spin up state. Start subjecting the electron with a magnetic field that is changing in some random fashion for all points in space. Will this constant, random measurement by the magnetic field causes the electron's wavefunction to be projecting to e.g. spin state A, followed by spin state B, followed by spin state C etc., thus overall, the measured spin state along any direction will have the expectation value of zero?
Ah. Well first of all, are you interested in the case where the magnetic field is quantized, or do you want to think about a semiclassical picture where the magnetic field is classical but the spin is quantum?
If I understood correctly, if two quantum objects interact, then a measurement can happen. Therefore consider an electron in a box, subjected to a magnetic field which vary in space and time in some really erractic manner.
(I'm pretty sure that if the magnetic field is in a coherent state then the semiclassical picture is actually correct even in the case where the field is quantized. Not 100% sure though)
If the field is semiclassical then the field does not really "measure" the electron.
In that case, you have a random walk problem, although a bit complex because you're doing a random walk on the surface of a sphere (because the states of an electron spin are points on the surface of the Bloch sphere).
Hmm it seems my intuition is not off, I do kinda predict the spin vector will jittering around like crazy, I thought I think about the problem too classically
but it seems I am on the right track in treating as if the spin vector being knocked around by the magnetic field
People who are studying alone, like me, can get a wrong impression of a subject by the books they are reading. I was studying Physics from a very dull book until recently when I browsed another book and thought "this is actually talking to me like a human and that makes the subject so much more i...
@AccidentalFourierTransform For reasons not entirely clear to me, 10k users see the number of total flags ending review. If you already did your part of reviewing them (but the reviews are not completed), then the queue will look empty for you but the number won't be 0.
@Slereah Ah, yes - the momentum operator itself can only act on the dense subset. However, its unitary exponential a la Stone's thoerem is defined on the entire Hilbert space, and you cannot say whether or not that exponential maps the dense subset to itself, in general, time evolution being the prime example
@AccidentalFourierTransform The answer is usually "caching".
@BernardoMeurer It's not clear to me why 1) the press sets off the fireworks (although in some cases it looks like they burned the fuse and the press was there just for show), and 2) why they didn't film this at night.
@AccidentalFourierTransform Also: "Reputation changes from bounties, votes (both up and down), and acceptances on deleted posts (including answers to a deleted question) are nullified. (Exception: Reputation earned for posts with a score of three or higher, and where the post has been visible on the site for at least 60 days, is retained)."
Reading the blog post where this is explained, it appears to have been introduced to appease people on SO throwing tantrums beause they lost rep when their "fun" questions and answers were deleted :P
@AccidentalFourierTransform Well, you can only delete five of your posts per day and if you go on a deleting spree deleting upvoted content, the moderators will politely ask you to stop
In chapter 80, The Primary, Neal Stephenson has one of his character describe how the drives of a computer carried through a door (by the police, who where raiding the facility) will have been erased.
Basically, there's an enormous electromagnet around the door frame:
Cantrell is now drawing ...
You could certainly damage some drives, especially older ones, with a hugely powerful door magnet, but the fatality rate from pocket pens going through heads would be a tad steep...
Thorough, truly unrecoverable disk erasure requires powerful fields very close to the surface. Of course, there is always microwaving...
Forensic recovery looks for the random edges of bit regions that didn't quite get erased. More of that occurs, and is recoverable, than one might at first imagine. That's why full erasure protocols do so many re-writes. A door magnet could never replicate that.
Of course you could oscillate the door magnet field to prevent the pen fatalities... and likely replace them with exploding personnel from heating effects... hr might object to both strategies... :)
I recall that some time ago before I send my computer for repairs, I rewritten some of my downloaded journal articles from the campus license and some company confidential files multiple times to esure they canno be recovered
Confidential and restricted access materials are kinda sensitive...
@BernardoMeurer Ge is making a comeback, the holes are much faster than in the 3-5 stuff everyone has been focusing on for decades. Plus you don't need that much total per chip. Still has a heat issue, though, a hot day make Ge awfully metallic.
Hey, can anyone suggest a mathematical physics textbook that'll get one started with Jackson? I'm basically inquiring for a book that should be considered as a pre-req for Jackson's book. I'm not much of a big applied math buff, hence I have run away from studying these math methods book.
I found Methods of Theoratical Physics (Volumes I and II) by Morse but that's TOO long for the time being. Any (novel) suggestions instead of the usual: Arfken, Boas etc (the book I tend to run away from as I like more abstract math books)
@ACuriousMind Eraser got taken over by a different author who completely rewrote it and introduced some quite novel bugs, e.g. for a while it erased the target of a link instead of erasing the link itself, oh my, my oh my. It's better but every time I try it I still want to scream. The older version, Eraser 5.8.8, still works beautifully, is faster, safer, and available if you look for it.
@Shing it has small tidbits the book are missing! But the main coverage is I think the same. There are stupid things like undefined terms in the book that Feynman literally never said.
@BernardoMeurer I don't recall the current min estimates, but we are definitely getting closer to some hard limits. Rearranging how to do things keeps changing those limits, though.
@BernardoMeurer yep, that's really Feynman's original argument from "Plenty of room a the bottom." It's interesting, he also kicked off quantum computing, but for the purpose of emulating quantum effects to make them calculable in finite time. He never thought of encryption etc, that was Peter Shor (nice guy, Dr Shor).
@BernardoMeurer dude, as long as it's Elmer's, it's got better nutrition than some cafeteria meals... :)
@BernardoMeurer I got to interact with Dr Shor shortly after his paper, talking about emulation of the multi-state, non-temporal aspects of his algorithms using, well, basically old-school analog computing that uses hidden multistate via Fourier decomposition of the wave forms.
I have seen an uncommon derivation of the virial theorem and need some help understanding the physical aspects and interpretation.
For an integral form of an equation,
$$I = \int_{V(t)} \alpha d^3 x $$
where $\alpha$ is any single-valued scalar, vector or tensor field and $V(t)$ is a finite vol...
@BernardoMeurer at least when Duffield is accusing me of peddling nonsense he isn't naked. At least ... I don't think so. But then ... oh my God that's an image I'm going to struggle to get out of my mind!
@Shing I finally caved and bought mine Feynman audio CDs years ago. That Brooklyn accent is amazing! And while the fellows who transcribed him were smart and very respectful, they definitely just did not "get" some of his finer points and more subtle emphases, such as how an event is quantum iff no information on its status exists anywhere in spacetime.
I never got video critiqued, but the CMU Software Engineering Institute once banned me from all conferences on pain of them not attending if I was invited. After hyperventilating a bit one fellow noted it was kind of an honor. Bill Gates tried to get me fired once too. Gee, that was fun!!
@JohnRennie Yes, I did. That was on Cosmology and I could sustain for considerably long time in comparision to my age. He explains things wonderfully, slowly.
Can someone solve question number 2?
In chapter 80, The Primary, Neal Stephenson has one of his character describe how the drives of a computer carried through a door (by the police, who where raiding the facility) will have been erased.
Basically, there's an enormous electromagnet around the door frame:
Cantrell is now drawing ...
I have seen an uncommon derivation of the virial theorem and need some help understanding the physical aspects and interpretation.
For an integral form of an equation,
$$I = \int_{V(t)} \alpha d^3 x $$
where $\alpha$ is any single-valued scalar, vector or tensor field and $V(t)$ is a finite vol...
