- #36
AdrianMay
- 121
- 4
I also agree that we don't care about equilibrium - that's for PM machines to worry about, not us.
I'd still like to quibble this enormous temperature business. If we don't care about equilibrium, I can use balls from the fridge. They don't have to move very fast so there's no relativistic doppler effect to worry about, so I think they will look to the demon like normal cool balls. He won't see them glowing like a quasar.
You guys keep saying "the entropy of the demon will increase." I'd like to see one piece of evidence for that which does not use the 2nd law as an assumption. This is E+N's point, and apparently Bennet accepts it. Without using the second law, there's no argument saying that there will be any increase of entropy anywhere. All that stuff (whether you think observing or forgetting is associated with +ve or -ve entropy or whatever) sits on top of the assumption that the demon does not break the 2nd law, so you can hardly turn it around and use it to defend the 2nd law.
I think Ken is saying there will be something else defending the 2nd law from the demon if we think hard enough about it, and then all that information theory will be valid. But my mind is blank. Yes we must examine the whole system including the demon's brain, and we'd be home and dry if we could prove (without invoking the 2nd law) that this brain must increase entropy somewhere else. But how? I'm at a loss as to how this should work. Presumably there's some light in the system so he can see what's coming, but I think I can let that light be totally disordered from start to finish, so no problem there. I think I can make his brain a steady state so no problem there either.
I think it might be helpful to get the whole temperature thing out of the way because it's just causing distraction. How about a gas of aromatic molecules in a mixture of left handed and right handed forms. We don't give a monkey's about the temperatures - we just want to sort the two forms. The chemical reflects circularly polarised light in the matching handedness. (A bit of detail is called for here but I think it can work.) So if the demon sees a lot of right-circular light in his vicinity he opens he door. We can use oodles of light because we no longer care about the temperature.
If there are no losses to the environment, the light energy won't get lost but it will tend to turn from a few high energy photons to a large number of low energy photons. But I think we can probably arrange for the interesting mode (the one where the chirality plays a role) to be the lowest frequency mode available. Failing that, we only need to show that we can sort a molecule without degrading a useful photon into two lower energy ones.
If this light stuff fails we can also make a chemical detector, like a nose.
I'm back to square one now - there may be losses, but I don't see how I can equate them with the entropy reduction without invoking the 2nd law.
I'd still like to quibble this enormous temperature business. If we don't care about equilibrium, I can use balls from the fridge. They don't have to move very fast so there's no relativistic doppler effect to worry about, so I think they will look to the demon like normal cool balls. He won't see them glowing like a quasar.
You guys keep saying "the entropy of the demon will increase." I'd like to see one piece of evidence for that which does not use the 2nd law as an assumption. This is E+N's point, and apparently Bennet accepts it. Without using the second law, there's no argument saying that there will be any increase of entropy anywhere. All that stuff (whether you think observing or forgetting is associated with +ve or -ve entropy or whatever) sits on top of the assumption that the demon does not break the 2nd law, so you can hardly turn it around and use it to defend the 2nd law.
I think Ken is saying there will be something else defending the 2nd law from the demon if we think hard enough about it, and then all that information theory will be valid. But my mind is blank. Yes we must examine the whole system including the demon's brain, and we'd be home and dry if we could prove (without invoking the 2nd law) that this brain must increase entropy somewhere else. But how? I'm at a loss as to how this should work. Presumably there's some light in the system so he can see what's coming, but I think I can let that light be totally disordered from start to finish, so no problem there. I think I can make his brain a steady state so no problem there either.
I think it might be helpful to get the whole temperature thing out of the way because it's just causing distraction. How about a gas of aromatic molecules in a mixture of left handed and right handed forms. We don't give a monkey's about the temperatures - we just want to sort the two forms. The chemical reflects circularly polarised light in the matching handedness. (A bit of detail is called for here but I think it can work.) So if the demon sees a lot of right-circular light in his vicinity he opens he door. We can use oodles of light because we no longer care about the temperature.
If there are no losses to the environment, the light energy won't get lost but it will tend to turn from a few high energy photons to a large number of low energy photons. But I think we can probably arrange for the interesting mode (the one where the chirality plays a role) to be the lowest frequency mode available. Failing that, we only need to show that we can sort a molecule without degrading a useful photon into two lower energy ones.
If this light stuff fails we can also make a chemical detector, like a nose.
I'm back to square one now - there may be losses, but I don't see how I can equate them with the entropy reduction without invoking the 2nd law.