Talk:Brownian ratchet

History Error

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)

I am altering the article from "Feynman invented" to "idea made famous by Feynman". I will not add Smoluchowski without a reference. 131.111.8.96 (talk) 22:33, 8 December 2009 (UTC)

Glad you caught that. I looked up the references and added Lippmann and Smoluchowski's contributions. Thanks. --Chetvorno^TALK 22:38, 15 January 2010 (UTC)

Could someone explain simply why a brownian ratchet is self defeating?

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)

This article makes a claim that ratchet slippage somehow prevents the ratchet device from producing work. The article should reference such a claim as an unproven theory until an appropriate reference is included in the article showing proof that slippage prevents the ratchet device from performing any work. Being one who has written many of simulations, include a trapdoor simulation, I believe such slippage is merely a technological issue, not a limitation. Thanks.--PaulLowrance (talk) 18:41, 28 May 2008 (UTC)

Good point. I added the reference. Feynmann works out the mathematics of the slippage in Lectures on Physics. --Chetvorno^TALK 14:47, 1 July 2008 (UTC)

I added fact noted by Feynman that wheel would rotate in the other (backwards) direction if the temperature difference were reversed, as well as the parallel to why electrical diodes cannot extract useful work by rectifying thermal noise in a circuit at constant temperature.CharlesHBennett (talk) 04:07, 30 March 2010 (UTC)

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could someone add a picture to this page? I found a couple (including an animated one here: http://web.mit.edu/8.592/www/lectures/lec20/ (hover over the pic to see the animation)) but I didn't add them to the article because I wasn't sure of the copyright stuff.

The picture would be clearer if the ratchet were drawn with unsymmetrical teeth, with a gentle ramp leading up to a sudden drop, as in Feynman's drawing.CharlesHBennett (talk) 04:07, 30 March 2010 (UTC)

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could someone add a picture to this page? I found a couple (including an animated one here: http://web.mit.edu/8.592/www/lectures/lec20/ (hover over the pic to see the animation)) but I didn't add them to the article because I wasn't sure of the copyright stuff.

Thanks. -PB

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scale

On a small scale brownian motion could be seen a lots of pools of different temperature. -Jeff

Pawls are not fundamental

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. --Chetvorno^TALK 00:00, 1 July 2008 (UTC)

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)

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. --Chetvorno^TALK 00:31, 3 July 2008 (UTC)

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)

I sure hope you're right; we certainly need new sources of energy. --Chetvorno^TALK 03:45, 4 July 2008 (UTC)

Remove claim that Brownian motors extract work from noise?

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? --Chetvorno^TALK 09:54, 30 August 2008 (UTC)

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)

Good luck with your research. Meanwhile, I'm going to remove the unsupported Brownian motor claim. --Chetvorno^TALK 19:49, 11 September 2008 (UTC)

I know I am late to this debate but. Noise would need to be defined before stating whether or not the claim is possible or not. For example, equilibrium thermal noise cannot be used to do work; however, non-equilibrium noise can be used to do work. If the fluctuations are random but higher than the ambient thermal noise then yes they can be used to do work. This is how wrist watches work that neither have batteries nor a wind-up mechanism inside. — Preceding unsigned comment added by 128.32.166.162 (talk) 23:32, 13 November 2012 (UTC)

Granular gas section mis-represents the experiment

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)

Massless rod

"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)

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. --Chetvorno^TALK 07:40, 14 August 2011 (UTC)

Removed it. --Chetvorno^TALK 07:24, 18 August 2011 (UTC)