Talk:Brownian ratchet

message: This ratchet is also a restatement of Maxwell's Demon more or less.  Feynman may have made this idea famous but he did not invent it...  It was being discussed by Smoluchowski in 1912. Less full out incorrect statements on Wikipedia please. — Preceding unsigned comment added by 128.32.166.162 (talk) 23:27, 13 November 2012 (UTC)
replies: text: Glad you caught that.  I looked up the references and added Lippmann and Smoluchowski's contributions. Thanks.  --ChetvornoTALK 22:38, 15 January 2010 (UTC)

text: It's not an incredibly scientific explaination, but I did add sort of a plausibility argument for its failure that I've heard at talks on Brownian motors. Laura Scudder 01:13, 17 Feb 2005 (UTC)

text: Good point.  I added the reference.  Feynmann works out the mathematics of the slippage in Lectures on Physics. --ChetvornoTALK 14:47, 1 July 2008 (UTC)
thread_title:  History Error 

message: It is not absolutely neccesary to use a pawl or even to have the machine rotate in one preferential direction to do work. An simple electric generator will output power no matter if the rotor goes one way or the other, AC currents carry useful energy even if they are null on average. Also at the brownian scale there are instantaneous large temperature fluctuations between the pawl and the ratchet even if they average over time.-Felix
:The generator example is a good alternate illustration. If, for example, the generator is used to do work by sending current through a resistor at the same temperature as the generator, the random AC current from the generator will be no bigger than the random fluctuations of thermal Johnson noise current in the resistor.  The resistor will act like a 'generator' itself some of the time, driving current through the generator.  So on average, an equal amount of noise power will travel both ways, and no net power will flow into the resistor.  On the other hand, if the resistor is at a lower temperature than the generator, it will produce less Johnson noise current, so net power will flow from the generator to the resistor, acting like a normal heat engine. --ChetvornoTALK 00:00, 1 July 2008 (UTC)
replies: text:  I think the microscopic generator idea Felix was describing is an attempt to produce rectification of such thermal energies, and therefore resistance from the resistor would merely help. Such a hypothetical microscopic generator would convert higher frequency thermal energies to lower frequency energies. If a 1MHz signal is modulated by the same 1MHz signal the result is DC plus 2MHz. I believe that is the basis of rectification for diodes, but I'm uncertain as to the details of what Felix is referring to. --PaulLowrance (talk) 01:26, 1 July 2008 (UTC)
replies: text: I'm not totally clear on what you and Felix were referring to, but the diode is an electronic analog of the ratchet, and a circuit with a diode and a resistor is an exact electrical analog of Feynmann's experiment, and fails to generate power at equilibrium for the same reasons.  The exponential torque vs. velocity equation Feynmann derives for his brownian ratchet is exactly the same as the voltage/current relation in a diode.  See eq.46-1, p.46-4 Lectures on Physics, compare to Schockley diode equation in Diode.  --ChetvornoTALK 00:31, 3 July 2008 (UTC)
replies: text:  Hi. I am well aware of such data, as I have spent years studying the possibility of diodes rectifying thermal energy. I am studying highly shielded measurements on 50GHz ZBD (Zero Bias Diodes) conducted out in the California desert that is showing DC voltage conversions from natural ambient thermal energy. It is well known that at microscopic levels vast temperature gradients always exist in all matter. In fact, it is impossible to get rid of such thermal fluctuations. Several years ago I spent a great deal of time measuring small *macro* temperature gradients at room temperature. There's no size scale at which natural thermal fluctuations vanish, but the fluctuations are greater at small scales. In terms of theory, the micro to macro scale occurrences in real semiconductor matter are vast and too difficult to compress into a nice little hand written equation. The quantum physics of diodes is based on mathematical approximations. One could write a book on just how controversial the math and science is behind diodes at thermal equilibrium rectifying ambient thermal energy. There's even question how to properly mathematically model thermal and shot noise. For example, there are papers that mathematically prove Gaussian thermal noise violates 2LoT. So from a distance, yes, it may appear conventional physics dictates that a diode cannot rectify thermal energy at thermal equilibrium, but when one becomes evolved in dirty details, present research from various scientists, etc. things become questionable. IMO in ~ a decade technology will reach a level where devices will convert thermal AC noise energy as sustained by the Sun into usable DC energy. Theoretically such devices would work day and night at any hospitable location. --PaulLowrance (talk) 16:29, 3 July 2008 (UTC)
replies: text: I sure hope you're right; we certainly need new sources of energy.  --ChetvornoTALK 03:45, 4 July 2008 (UTC)
replies: text: We figured it out how to extract limitless energy that graphene generates. It’s only a little power, but limitless energy nonetheless. Walid.Miran (talk) 12:37, 24 February 2021 (UTC)
replies: text: See WP:NOTFORUM. --Hob Gadling (talk) 15:53, 24 February 2021 (UTC)
thread_title: Pawls are not fundamental

message: I don't know of any support for the claim that Brownian motors extract useful work from thermal noise.  Since this seems to violate the 2nd Law, and the 'citation needed' tag has been on a while, I think it should be removed.  Comments? --ChetvornoTALK 09:54, 30 August 2008 (UTC)
replies: text: I don't know who placed the claim you are talking about, but I would like to just pop in (no debating for now please) and say that my research in this field is showing that it is merely an interpretation and a failed one at that to say thermodynamics claims it is impossible to extract usable energy from natural ambient thermal energy. The following link is not an attempt at self-promotion. I do not sell anything and I do not accept $ donations, as it's 100% self funded. It's merely an outline, so the mathematics is excluded from the site for now until time permits --> http://aemcomp.googlepages.com  --PaulLowrance (talk) 15:16, 30 August 2008 (UTC)
replies: text: Good luck with your research.  Meanwhile, I'm going to remove the unsupported Brownian motor claim. --ChetvornoTALK 19:49, 11 September 2008 (UTC)
thread_title:  Remove claim that Brownian motors extract work from noise? 

message: As far as I can see, this experiment is mis-quoted or mis-described. The abstract in phys rev lett does not describe any ratchet at all, the symmetry breaking is provided by the vanes having different coating (soft, i.e. energy-absorbing inelastic) on the clockwise side. Furthermore, the phrasing at the beginning ("despite being theoretically proven") is a gross overstatement; the original paper does not claim to provide thermal equilibrium but explicitly refers to the "necessary" out of equilibrium environment given by the shaking of the gas. The experiment is probably worth mentioning but it should be done accurately. 207.172.169.230 (talk) 14:56, 10 September 2010 (UTC)
thread_title:  Granular gas section mis-represents the experiment 

message: :"The ratchet is connected by a massless and frictionless rod to a paddle wheel that is immersed in a fluid of molecules at temperature T1."
This implies that other parts of the apparatus, notably the paddle and cog wheel, need not be massless. If that is so, and since these parts are all connected and moving in unison, why does it matter that the rod is massless? 86.160.83.115 (talk) 01:16, 14 August 2011 (UTC)
replies: text: I agree.  I have never, in any description of the thought experiment, come across a requirement that the shaft be massless and frictionless.  I think it should be removed.  Good catch.  --ChetvornoTALK 07:40, 14 August 2011 (UTC)
replies: text: Removed it.  --ChetvornoTALK 07:24, 18 August 2011 (UTC)
thread_title:  Massless rod 

message: Hello fellow Wikipedians,
I have just modified  on Brownian ratchet. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
*Added archive https://web.archive.org/web/20031206054642/http://monet.physik.unibas.ch:80/~elmer/bm/ to http://monet.physik.unibas.ch/~elmer/bm/#why
When you have finished reviewing my changes, please set the checked parameter below to true or failed to let others know (documentation at ).
Cheers.—InternetArchiveBot (Report bug) 13:29, 9 November 2016 (UTC)
thread_title:  External links modified 

message: Even if the brownian ratchet were to work (i.e. it were to do useful work), it would not satisfy the definition of a perpetual motion machine: "A perpetual motion machine is a hypothetical machine that can do work indefinitely without an energy source."
The energy source is the ambient temperature of the air.  This is a finite resource, and the ratchet would eventually reduce the air temperature via reducing the velocity of gas particles.
Therefore, it is not an "aparrent perpetual motion machine".  This phrase should be removed.  ----Cowlinator (talk) 22:03, 20 February 2020 (UTC)
replies: text: No, because all forms of energy, in particular the mechanical energy produced by the ratchet, are eventually degraded to ambient heat (random motion of molecules), which is the power source of the ratchet.  So if the ratchet could work it would be a true perpetual motion machine.  A perpetual motion machine that uses ambient heat is called a perpetual motion machine of the second kind. --ChetvornoTALK 01:40, 21 February 2020 (UTC)
thread_title:  Not an apparent perpetual motion machine. 

message: I think the article should probably contain some information on this study. It may also be relevant to other articles (which?). It's currently featured in 2020 in science in short form like so:
A rippling graphene-based energy-harvesting circuit with the potential to deliver "clean, limitless, low-voltage power for small devices" if adequately incorporated into a chip is demonstrated.
Additional news report here. From this report of Physics World:
In the early 1960s, the Nobel laureate Richard Feynman popularized a thought experiment known as the “Brownian ratchet”, which had been conceived in 1912 by the Polish physicist Marian Smoluchowski. This involves a paddle wheel that is connected by an axle to a ratcheted gear. Both the paddle wheel and the ratchet are immersed in fluids. The system is imagined as being small enough so that the impact of a single molecule is sufficient to turn the paddle. Because of the ratchet, the paddle can only turn in one direction and therefore it appears that the Brownian motion of the paddle can be harnessed to do the work of turning the axle.
However, Feynman showed that if the two fluids were at the same temperature, collisions throughout the system would prevent this from happening. The only way work could be done, argued Feynman, is if the fluids are a different temperature, making the Brownian ratchet a heat engine.
In their new study, University of Arkansas physicist Paul Thibado and colleagues replaced the paddle with a freestanding sheet of graphene – a single layer of carbon atoms.
--Prototyperspective (talk) 10:25, 4 December 2020 (UTC)
thread_title:  Please update with: "Fluctuation-induced current from freestanding graphene" 

message: I've undone the removal the "failed verification" tag on the passage that claimed Magnesco proved there was no net motion regardless of the shape of the teeth of the ratchet.  The tag originally pointed to #History Error section but that does not seem to have any relevant discussion.  I can't find any of the words "teeth", "tooth", or "shape" anywhere in the paper.  Now Magnesco talks about periodic "potential functions" which we can interpret as the teeth of the ratchet, but I'm not seeing a claim either that any shape protential function will result in no net motion.  Indeed, the whole thrust of the paper is that "net drift speed" is possible in some circumstances.  If you think that this paper does support the claim, then please specify exactly where it does so before removing the tag again. SpinningSpark 14:16, 26 September 2022 (UTC)
thread_title:  Shape of teeth