A number of comments refer to the “supernatural” while others raise the notions of entropy, suggesting that the thought experiment is about getting something for nothing.

Even from the very early days, both notions were laughable, and both missed the point. The question has to do more with what sort of entity/agent/machine the demon would be, what its physical characteristics would be.

Since Bennett’s work of 1982, building on Landauer’s work of 1961 (both mentioned in the article), we know that the demon is an information processing machine, observing and recording state, occasionally acting, and occasionally erasing its state records.

The question is how efficient can we make the machine, how passive or active it needs to be.

Potential applications include more efficient cooling systems and advances in the theory and mathematics of information processing.