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Information is a concept first used to resolve the paradox of Maxwell's demon. About 150 years ago, the physicist J. C. Maxwell came up with an intriguing idea. He conceived a thought experiment, in which a little demon who operates a friction-free trap door to separate molecules of one type from the other (see Figure 01a), and finally arrives at a system with lower entropy. Such organizing entity of Maxwell's seems to violate the second law of thermodynamics as the demon only selects molecules but does no work. This paradox kept physicists in suspense for half a century until Leo Szilard showed that the demon's stunt really isn't free of charge. By selecting a molecule out of the alternative of 2 types, he creates something called information, which produces an amount of entropy (through mental processing in the brain, see Integrated Information Theory of Consciousness) exactly offsetting the decrement in the re-arrangement. The unit of this commodity is bit, and each time the demon chooses a molecule to shuffle, he shells out one bit of information for this cognitive act, precisely balances the thermodynamic accounts. The new concept has since shown its usefulness in communication and computer, but perhaps
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