Talk:Maxwell's demon
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see also vortex tube?
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A Suggestion
I find the idea more immediate if it's phrased like this:
- Suppose we have a demon with a little (frictionless) trapdoor between gas-filled bodies A and B. The demon is very smart, and can work out what the location of every particle is in both containers going forward in time. When he knows there is a particle moving from A -> B he opens the door, moving from B -> A he shuts the door. Pressure will increase on the B side. A contracting-minded person hooks up a turbine between container A and B, and hooks this engine up to half a ton of concrete. The concrete will be dragged up a hill. In this way we have converted "pure information" into very "concrete" work. It is as if "knowledge" and "work" are, at a base level, fundamentally the same stuff.
- Note this also works for probabilities - if the demon knows there is even an infinitessimally higher probability of a particle going from A->B than B->A he can get into the haulage buisness.
I realise this isn't quite the conventional explanation, but it seems to engage people a lot better. 129.94.6.28 08:34, 18 May 2005 (UTC)
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I wonder why the paragraph reading
- What is so fascinating about the demon is that if it existed, it would be able to break one of the most important laws of physics. If we could tame (or build mechanical) demons, ships for instance would no longer need fuel as they could simply use the heat of sea water as a source of available energy; indeed, it would solve all our energy problems. But at the same time, it is very hard to say why it could not be built. Maxwell's story seems plausible enough - can we yet save the second law by proving that in the actual world no demon can exist? The quest for this proof constitutes the history of Maxwell's Demon. Surprisingly, it is still hotly contested whether this quest has been completed or not.
was removed? In what sense does it add "nothing substansive"? Please rewrite it if you feel its badly done (I can imagine a word like 'fascinating' being considered non-encyclopedic), but pointing out (a) the relevance of the thought experiment and (b) that it is still a subject of controversy seems to me very relevant indeed. Victor Gijsbers 09:00, 26 Oct 2004 (UTC)
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Rewrote the description of why the demon doesn't work. It has little to do with quantum mechanics, but rather has more to do with information theory.
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Well - that is highly doubtful. Earman & Norton, two very eminent philosophers of physics, suggest in their 1998 article Exorcist XIV: The Wrath of Maxwell's Demon that information theory does not say anything useful about Maxwell's demon. -- Victor Gijsbers
Interesting. Are there any (eminent or significant) physicists who make the same claim?
BTW the link to the Hilsch apparatus needed to make clear that the clever device does not in any way violate the Second Law. You'll find that out if you read the page, but it's better not to raise false hopes. And the Fu & Fu article as of this date is in a "might have been posted by just anybody" status, more like a random Web page than a preprint from arXiv. Dandrake 04:27, May 18, 2004 (UTC)
I thought that diagram looked familiar. The page that describes the Hilsch tube is mostly lifted from "The Amateur Scientist" in Scientific American, November 1958, p. 145. While we're not legally liable for pointing to a copyvio, we shouldn't do it. So now we don't. Dandrake 06:33, May 26, 2004 (UTC)
I just read this article, and the description about why the demon wouldn't work (which references information theory) doesn't make much sense to me. Is there a way to re-write that explanation so it would make sense to the layman? K_R 20:05, 5 Sep 2004 (UTC)
Yes, I will rewrite this article sometime soon. I recently wrote my Master's thesis on Maxwell's Demon, so I hope I know what I'm talking about. ;) Victor Gijsbers 13:41, 23 Sep 2004 (UTC)
excellent - I'm looking forward to reading it K_R 02:43, 25 Sep 2004 (UTC)
"Likely heterosexual"?
I do not understand this at all- I understand entropy and thermodynamics, but Maxwell's demon is bizarre concrete terms for something abstract. Are the people taking the demon to literally? They disprove the theory by saying that the demon would not have enough memory? Are they not aware that demons do not exist, especially scientific men like themselves, and even if they did, how could it be small enough to open a door for molecules? Please help me! I am very confused!!!
The discussion of exorcism comes out of nowhere. Could someone who understands the topic please explain the meaning of "exorcism" in this context?
Why did I cut everything?
Before my edit, this article was a work in progress -- there were numerous headlines without content, and various notes for future revisions, with promises to flesh out more soon. I checked the history, and to the best I can tell, this semi-finished version has been up for months. It seems to me that an actual article, whatever it's limitations, is better than a worksheet, not least because the latter may intimidate people who have something to add, but feel that they should wait for the contributions of this other user, who has promised to return at some unspecified time.
If you are that other user, just revert my changes; your worksheet is still there in memory, and you can post your completed version when it's completed. Hope you get to it soon; I'd like to read it!
NoahB 18:41, 26 Apr 2005 (UTC)
Removed references
- Feynman, Richard P., Feynman Lectures on Computation (Perseus: 1996). ISBN 0201489910.
Nice introduction to thermodynamics, but Feynman uses the ratchet and pawl model instead. Maxwell's demon is mentioned very briefly (lecture 46, middle of page 5), so the explanation is not very clear or tight. Hardly a first choice for a reference.
- Grayce, Christopher J., "Maxwell's Demon (http://www.chem.uci.edu/education/undergrad_pgm/applets/bounce/demon.htm)". Educational Applets. University of California, Irvine, Irvine, CA.
404 Not Found
- First International Conference on Quantum Limits to the Second Law of Thermodynamics (http://www.ipmt-hpm.ac.ru/SecondLaw/index.en.html), San Diego, CA, July 2002
How is this helpful?!
- Xin Yong Fu and Zi Tao Fu, "Realization of Maxwell's Hypothesis : An Experiment Against the Second Law of Thermodynamics (http://arxiv.org/abs/physics/0311104)". Shanghai Jiao Tong University, Shanghai, P.R. China (arXiv.org is a site for pre-prints of scientific papers; but this paper is not endorsed or sponsored under arXiv's procedures by any known scientist including the authors.)
This paper didn't pass peer review, and for a good reason — it demonstrates lack of understanding of the 2nd law and the well-known solutions to the Maxwell's demon paradox. There are ample correct references in the book by Leff and Rex.
- Vlatko Vedral's Lengthy discussion of Maxwell's Demon (http://www.qubit.org/people/vlatko/Papers/maxwell2.pdf) (PDF)
This is the first chapter from the book by Leff and Rex, and now linked as such.
some problems with article
I'm not a mathematician or a physicist, and am certainly not an expert on Maxwell's Demon. However, in browsing around the internet and looking at some other sources, I think there are some serious problems with this article. First of all, the description of the Szilard experiment is vague and doesn't seem to jibe with other accounts I've looked at. I've tried my best to tweak it, but it's hard to know if I've succeeded since, as I said, I'm not an expert. Second, I separated the Bennett experiment from the Szilard experiment, but it too needs to be expanded on and better explained. Finally, the article suggests that Maxwell's Demon has been refuted, and that the Bennett experiment is final. From poking around the web a little, I don't think that's the case...though, again, I don't really have the background to know for sure. Anyone with more knowledge than me able to respond to these points? NoahB 13:53, 3 Jun 2005 (UTC)
How about Maxwell's demon disproving the SLTD?
Currently, the first line runs:
- Maxwell's demon is a character in an 1867 thought experiment by the Scottish physicist James Clerk Maxwell, meant to illustrate the second law of thermodynamics.
But shouldn't it say "...meant to disprove..." or, at least "...meant to complicate the second law ofr thermodynamics"? That's what Maxwell himself claimed it did. I'm ignorant, though, so maybe someone out there who knows more can make the change.
More References To Maxwell's Daemon
Look in Ken Kesey's Daemon Box - there's a notable regard to Maxwell's Daemon and Psycology
Oversight?
I am probably missing something, but isnt' Bennett's idea a little short-sighted? Who is to say that information storage space would eventually run out? Surely there must exist or will soon exist an information storage device large enough to catalogue the status of every molecule in a sufficiently small collection of molecules as either 'A' or 'B'.
- If you have a source where that objection is made, cite it and put it in the article. Otherwise it's original research, which Wikipedia usually tries to avoid. Also, you can sign your post by typing four tildes (~). NoahB 18:08, 16 Jun 2005 (UTC)
my mistake
I see what you're saying. I apologize; it's my nature to argue ;) Taurrandir 16:45, 18 Jun 2005 (UTC)
- No apology necessary. My goodness, go look at Wikipedians bashing each other on Talk:Mother Theresa or Talk:Abortion or any number of other places. You raised a legitimate question and presented it politely -- can't ask for more than that. NoahB 13:05, 20 Jun 2005 (UTC)