Maxwell's demon

"[[Information theory|[I]nformation.]].. does enter into physics and has been in physics for a long time, in the most obvious way with ... [which] is able to use information about the motions of molecules to operate a shutter mechanism and put all the fast-moving ones on the left and the slow-moving ones on the right, thus establishing a temperature difference from which work can be extracted. You can run a heat engine, lift a weight [etc.]"

"One of the best established facts in thermodynamics is that it is impossible in a system enclosed in an envelope which permits neither change of volume nor passage of heat, and in which both the temperature and the pressure are every where the same, to produce any inequality of temperature or of pressure without the expenditure of work. This is the second law of thermodynamics, and it is undoubtedly true as long as we can deal with bodies only in mass, and have no power of perceiving or handling the separate molecules of which they are made up."

"But if we conceive of a being whose faculties are so sharpened that he can follow every molecule in its course, such a being, whose attributes are as essentially finite as our own, would be able to do what is impossible to us. For we have seen that molecules in a vessel full of air at uniform temperature are moving with velocities by no means uniform, though the mean velocity of any great number of them, arbitrarily selected, is almost exactly uniform."

"Now let us suppose that such a vessel is divided into two portions, A and B, by a division in which there is a small hole, and that a being, who can see the individual molecules, opens and closes this hole, so as to allow only the swifter molecules to pass from A to B, and only the slower molecules to pass from B to A. He will thus, without expenditure of work, raise the temperature of B and lower that of A, in contradiction to the second law of thermodynamics."

"It was... just a Gedanken-Experiment... in 1867, but just in recent years, engineers (nanotechnologists) have built real Maxwell demons, and this is now something of a cottage industry."

"[T]he demon... is transferring heat from a colder region to a warmer region in apparent defiance of the second law of thermodynamics. "And hold on," youre thinking, "doesnt my refrigerator do that?" Sure... a refrigerator... costs energy to run... but the demon is operating using information instead... The demon... runs without any energy expenditure."

"So in effect, information serves as a fuel, and this leads to the whole concept of information engines. Engines that will run on information power, and... there is an FQXi initiative on this..."

"Life was onto this... billions of years ago. Life uses many many nano-molecules which are, in effect, Maxwell demons. Our bodies are full of little Maxwell demons... doing the business of life. These little molecular machines are not quite perfect... but theyre coming pretty close to the theoretical limit, in terms of energy expenditure."

"s are the way in which, even now, you are thinking and paying attention, because the signals that travel between neurons, down the s, are controlled by the flow of s across the membranes of the axons... [T]hey are, in effect, little demons that sense the incoming signal and open and close the gates; and the ions flow. ...[T]his is so incredibly energy efficient that ...your brain, which is like a megawatt supercomputer, operates with the energy equivalent of a small light bulb."

"[I]n order to investigate this... [I]f you have a Maxwell demon or something like a Szilard engine in , could you use it, as Maxwell envisaged, to use information to extract energy from De Sitter space and lift a weight or do some sort of useful work? ...[T]he answer would seem to be, only if you can create a region of the De Sitter space that is screened out from that horizon, screened out from that thermal nature. If you put a reflective barrier around the demon, you then have De Sitter space, but with the horizon screened out. ...[T]hats a problem Im working on now ..."