Maxwell's Demon and the Nature of Information

[Chris]

This is pretty good about how information is subject to the laws of physics simply because memory is finite.


http://www.youtube.com/watch?feature=player_embedded&v=tqgvqeLybik

[Dr. Who]

I'm not a physicist so no doubt this really over my head, but I kept thinking that the demon was expending energy keeping track of the slow and fast moving particles and opening and closing the door, but turns out it was only deletions that was expending energy. Hmmm.

[Devil's Advocate]

I don't entirely buy their argument. They're focusing on the quantity, not quality, of information when it's deleted and overwritten.

Instead, information can be transformed similarly to how positive numbers are flipped to negative numbers when doing math. When a molecule goes from one side to the other, it doesn't have to be completely rewritten in the record. It can simply be turned around.

[Chris]

The idea of the thought experiment is the assumption that information is free because it's not subject to the laws of physics. But because memory is finite, eventually, even if you reformulate it, say as formulas that generate bits of data, you will have to delete something. Logically, we reach a self-contradiction. Therefore the assumption is false.Ergo, information must be subject to the laws of physics.

[Devil's Advocate]

The idea of the thought experiment is the assumption that information is free because it's not subject to the laws of physics. But because memory is finite, eventually, even if you reformulate it, say as formulas that generate bits of data, you will have to delete something. Logically, we reach a self-contradiction. Therefore the assumption is false.Ergo, information must be subject to the laws of physics.

This is what I'm disagreeing with. You don't need to delete something if you can turn it.

[Chris]

Turn it? You still have to store information, even if it's a formula, computer program, even a genetic algorithm. Storage is limited.

[Guerilla]

I think devils advocate may have been suggesting that the storage could be made more efficient if it could relay that info to the other side after the molecule passes, instead of deleting it. Then you exchange info instead of stockpiling and deleting it. At least that's how I've been understanding the conversation. Another thought; what if instead of storing the info and having some really fast accurate door - you just place a permeable wall between the two boxes. Have one side of the wall that passively allows something you want on that side to go through to the other, while simultaneously having the other side of the wall be permeable to a substance on that side that you want to be on the original side. I don't know where the hell you would find a wall like that - but, theoretically, it wouldn't require energy.