Talk:Maxwell's demon

Further explanation of Experiment

The explanation does not account for the input of work required to open and close the door and how this impacts the entropy of the system. — Preceding unsigned comment added by 92.0.252.207 (talk) 23:07, 10 November 2017 (UTC)

I just wanted to add exactly this. To open and close the door, the system it requires work. Thank you. — Preceding unsigned comment added by 5.170.8.48 (talk) 23:51, 23 May 2020 (UTC)

Right, it all seems to depend on the existence of a massless door that can deflect matter, i.e., a magic force field that can be made arbitrarily strong with no input of energy. How is this not a trivial refutation? 71.183.27.86 (talk) 23:28, 5 November 2023 (UTC)

Even if the door did have mass, moving it back to its starting position and back to rest would entail 0 Joules of work. Work is the integral of force applied over distance. 71.178.19.78 (talk) 20:34, 9 November 2023 (UTC)

You could presume the door was made of a very light substance, and as noted above mount it on a spring which would return most of the energy when the door was opened again. The part of the experiment that actually requires an unavoidable energy loss (entropy increase) is measuring the velocity of the approaching particle. This requires shining a light on it or bouncing something off it. --Chetvorno^TALK 22:45, 9 November 2023 (UTC)

A good reference to work in

Has anyone considered this reference produced by the Springer? "Challenges to the Second Law of Thermodynamics: Theory and Experiment" by Vladislav Cápek, Charles University, Prague, Czech Republic and Daniel P. Sheehan, University of San Diego, California, U.S.A. The front page and other relevant references can be found here: http://webspace.qmul.ac.uk/rocornwall/Thermo.htm

Could highly reflective paint that acts as passive cooling count as a maxwell's demon?

Xiulin Ruan, a professor of mechanical engineering at Purdue University, and his students came up with a white paint that reflects 98.1 percent of solar radiation. The white paint emits more infrared heat than it absorbs. For example, previous experiments showed this paint cooling a surface by 8 degrees Fahrenheit versus the surroundings under noon sunlight. At night, the ultra-white material can keep things 19 degrees Fahrenheit cooler. Wouldn't this functionally be a form of Maxwell's Demon?

No. The heat is still moving from hot to cold. You are only considering the immediate surroundings. The heat sink in this case is the 2.7K of the CMB. 108.7.187.43 (talk) 07:03, 13 August 2023 (UTC)

References

re original thought experiment

Passage:

"The demon must allow molecules to pass in both directions in order to produce only a temperature difference; one-way passage only of faster-than-average molecules from A to B will cause higher temperature and pressure to develop on the B side."

To maintain equal pressure, the total number of molecules on the cool side must be larger than on the hot side. But that could even be done in a way that does not change the energy balance. 172.59.89.255 (talk) 20:40, 3 September 2024 (UTC)