The scientist Rolf Landauer captured this idea with the phrase “information is physical.” All forms of information require a change in the physical universe. Written words require marks to be made on a physical medium of some kind. But even a spoken word requires the movement of vocal cords, which make air molecules vibrate. Similarly, a thought requires electrochemical changes in the neurons in our brains. In this sense, information entropy is constrained by thermodynamic entropy. As physical systems decay, so does any information they carry. Imagine writing your name in the sand on a beach.
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