What is Maxwell's demon: Definition and 30 Discussions

Maxwell's demon is a thought experiment that would hypothetically violate the second law of thermodynamics. It was proposed by the physicist James Clerk Maxwell in 1867.In the thought experiment, a demon controls a small massless door between two chambers of gas. As individual gas molecules (or atoms) approach the door, the demon quickly opens and closes the door to allow only fast-moving molecules to pass through in one direction, and only slow-moving molecules to pass through in the other. Because the kinetic temperature of a gas depends on the velocities of its constituent molecules, the demon's actions cause one chamber to warm up and the other to cool down. This would decrease the total entropy of the two gases, without applying any work, thereby violating the second law of thermodynamics.
The concept of Maxwell's demon has provoked substantial debate in the philosophy of science and theoretical physics, which continues to the present day. It stimulated work on the relationship between thermodynamics and information theory. Most scientists argue, on theoretical grounds, that no practical device can violate the second law in this way. Other researchers have implemented forms of Maxwell's demon in experiments, though they all differ from the thought experiment to some extent and none have been shown to violate the second law.

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  1. N

    Particle Maxwell's demon full experiment description

    Hey! Does anyone have the large/full description of Maxwell's demon thought experiment? I've read it on Wikipedia, but I was wondering if someone knows a better source I can reach legally. Thanks.
  2. Eric Bretschneider

    Is Maxwell's Demon Limited by Energy Required for Door Movement?

    Physics students are taught about Maxwell's demon and how by opening and closing a door between two chambers filled with gas. If the demon opens and closes the door to "concentrate" low energy molecules on one side and high energy molecules on the other side he can create a temperature...
  3. iVenky

    I Maxwell's Demon and the Uncertainty Principle

    Maxwell's demon measures the position and velocity of the particle. How can it do that when it violates the uncertainty principle? Does that mean uncertainty principle is unavoidable otherwise we will violate II law of thermodynamics as in the case of Maxwell's demon?
  4. T

    Other Far from equilibrium statistics

    Hello! I would like your help to study Science graduate level books and articles, in the following subjects: 1. Far from equilibrium statistics. 2. Information theory and entropy. 3. Negentropy. 4. And Maxwell's demon. My main goal is to be able to understand and explore the Maxwell's demon...
  5. P

    Is this another Maxwell's demon?

    A though experiment: We have two gas chambers at the same temperature and pressure, separated by a wall punctuated by very small pores. Let's say small enough to allow the pass of only a few gas molecules at a time (so, no complex interactions between gas molecules inside the pore). These...
  6. M

    Ending global warming with Maxwell's demon

    As a start for discussion I'd like to make the following bold claim: Both the problems of enough usable energy and global warming can be resolved by implementing Maxwell's demon on a large scale. To justify this bold statement somewhat, I'd like to point to a (relatively) recent...
  7. Deepblu

    Maxwell's Demon Paradox: Solving the Puzzle Without Memory Requirements

    The resolution for Maxwell's demon paradox is that the demon has limited memory and the demon will eventually run out of information storage space and must begin to erase the information it has previously gathered. Erasing information is a thermodynamically irreversible process that increases...
  8. bland

    I have a problem with Maxwell's demon

    The problem I have is that I fail to see how it caused so much consternation. The way I understand it the demon could passively allow or not allow particles of gas to pass or not pass, and thus gradually create a more ordered state free of charge. I have learned that the problem with the demon...
  9. R

    Is Maxwell's Demon Still an Unsolved Mystery?

    https://en.wikipedia.org/wiki/Maxwell%27s_demon, Is this solved, or any new ideas about it?
  10. H

    An Implementation of Maxwell's Demon

    http://physics.aps.org/articles/v8/127 It uses energy so it doesn't break any laws.
  11. KMote

    Does Maxwell's Demon violate the 2nd Law of Thermodynamics

    I'm a newbie (obviously), but I just read this recent paper describing an "experimental realization of an autonomous Maxwell’s demon" (along with this review). I think I understand the general concept of Maxwell's thought experiment well enough (from a layman's perspective), but I'm having...
  12. fezster

    Where Can I Find Good Books on Maxwell's Demon?

    Can anyone recommend any good reading on Maxwell's demon? I'm mostly looking for things at the undergraduate level, but I don't mind something less rigorous or more advanced. (Apologies to the mods if this is in the wrong forum.)
  13. M

    Extracting Ambient Thermal Energy Without Gradients

    It seems possible to extract energy from the ambient air without temperature gradients (or at least with very small local gradients that will always be available). Being curious about this, I checked out some other threads and did not really find the specific question. (I did find some...
  14. S

    Maxwell's demon - a new concept

    Could somebody disprove the following concept of a Maxwell's demon: Let's say we have a very small container, the size and a form of a nanotube, similar to ellipse, and only two gas molecules randomly flying inside. According to probability we will quite often find molecules in the different...
  15. L

    Scaling Maxwell's Demon Experiment: Macro-Level Rigid Ball Suspension

    I had the concept of scaling up Maxwells' demon experiment to a marco scale. Replacing molecules of gas with light, rigid, balls. Perhaps coated in magnets with varying poles so they never touch (non-interacting). Would suspend them in a thin fluid with neutral buoyancy.
  16. K

    Maxwell's Demon: would a cone work?

    Maxwell's demon is the little guy who opens an atomic door to a container to let atoms fly in, but shuts it before an atom flies out, thus increasing the internal pressure. Suppose the walls of a container had several small cone-shaped holes built into it. The inside hole might be pretty...
  17. ThomasT

    Random thoughts on Maxwell's demon

    This just came into my head. I don't think I really understand the significance of Maxwell's demon. Please don't try to explain it to me. It's just a random thought.
  18. A

    What is the connection between Maxwell's Demon and Liouville's Theorem?

    Hi Folks, (Skip to next paragraph if you already know what M's D is.) Maxwell's demon was a counterargument to the second law of thermodynamics (and hence the first) involving two chambers of air connected by a trap door which this demon would open and close to let fast molecules go one way...
  19. W

    In regards to Maxwell's Demon

    In regards to "Maxwell's Demon" In regards to the Maxwell's Demon thought experiment and violation of the Second Law of Thermodynamics, I have a scenario that results in (a) question(s). First I won't pretend to have extensive knowledge of Thermodynamics so bear with me... Say we have two...
  20. B

    Maxwell's Demon via molecular reed valves can produce work?

    Well not literally The Maxwell's Demon... If a one-way reed valve can be brought down to size of only a few molecules, don't you think it could allow passage of a gas molecule across a barrier in one direction only? How I think it could work: -The small size (molecular) of the valve is...
  21. T

    Maxwell's Demon Thought experiment

    I recently just heard of this thought experiment where two rooms/resoviors whatever you want to call them are adjoined by a door that a little demon controls. Both rooms have the same temperature, The demon then opens this door when particles with higher kinetic energy are nearby to let them...
  22. K

    Maxwell's Demon: Exists, Hard at Work at Phase Interfaces

    In his famous thought experiment of 1867, James Clerk Maxwell postulated a creature (later called a “demon” by Lord Kelvin) who could discern the speeds of gaseous molecules and who could pass selected molecules through a partition or deny them passage on the basis of those speeds. The essence...
  23. W

    Maxwell's Demon: Chance of Violating the 2nd Law?

    http://en.wikipedia.org/wiki/Maxwell%27s_demon" when i read this i was wondering, what if the deamon accuires no information at all and just shoots blind by guessing wherever a approaching particle is A or B.. in most cases the demon would end up with a no separation, but if its lucky...
  24. fluidistic

    Understanding Entropy: Exploring the Variant of Maxwell's Demon

    Hi, I've not covered yet the Second's Law of thermodynamics so I don't understand it well. A friend of mine talked to me about Maxwell's demon and now I have the following question : Imagine a planet such that its escape velocity is about Earth's one, but without any atmosphere. Now imagine...
  25. R

    Maxwell's Demon: Clarifying Arguments Against 2nd Law

    With my little reading on the subject (after listen to the argument in Stat.Mech. class a year ago), I am asking for help on clarifying the following points: The arguments against such a system violating the 2nd law focus on the two processes that would increase the entropy of the system...
  26. Loren Booda

    Nanotechnological Maxwell's demon?

    Has nanotechnology had any success in mechanically separating "cold" atoms from "hot" ones, an application first dreamt up by Maxwell in the late 1800s?
  27. D

    Maxwell's Demon: Is it Worth the Read?

    Maxwell's Demon by Hans Christian and Von Baeyer, for those who've read it, is it worth reading?
  28. K

    Maxwell's Demon: What Do You Think?

    This came up in another topic, but rather than talk on about it there, I created a new thread as it would be too far off subject for the said other thread. I don't see the big deal about "Maxwell's Demon". Assuming the walls and everything in the system are perfect insulators, wouldn't...
  29. X

    Maxwell's Demon: An Energy Conversion Experiment

    Maxwell’s Demon An Energy Conversion Experiment in Contradiction to the Second Law We have performed successfully an experiment of energy conversion of a totally new type. Please see the attachment figures. The experiment relates to a special electronic tube, which has two similar and...
  30. S

    Maxwell's Demon Possibility?(Entropy)

    "Maxwell's Demon" Possibility?(Entropy) About a hundred years ago, James Clerk Maxwell imagined 2 adjacent chambers, each containing gas and both sealed to the outside world. The chambers are also sealed from one another, except for a single gate the size of a gas molecule. Guarding this gate...