9/5/2023 0 Comments Entropy magazine![]() “You need to pay,” said Gonzalo Manzano, a physicist at the Institute for Quantum Optics and Quantum Information in Vienna. According to Landauer’s erasure principle, the rise in entropy from the erasure would more than compensate for the decrease in entropy caused by the sorting of the particles. Periodically it would need to erase this information. ![]() He realized that Maxwell’s demon was at core an information-processing machine: It needed to record and store information about individual particles in order to decide when to open and close the door. In 1982, the American physicist Charles Bennett put the pieces of the puzzle together. ![]() “Information is physical,” he later proclaimed. Landauer’s erasure principle provided a tantalizing link between information and thermodynamics. The second vital piece of the puzzle was the principle of erasure. In 1961, the German American physicist Rolf Landauer showed that any logically irreversible computation, such as the erasing of information from a memory, would result in a minimal nonzero amount of work converted into heat dumped into the environment, and a corresponding rise in entropy. “The modern understanding of Maxwell’s demon was established by Shannon’s work.” “In the 19th century, no one knew about information,” said Takahiro Sagawa, a physicist at the University of Tokyo. In 1948, Shannon showed that the information content of a message could be quantified with what he called the information entropy. The first was by the American mathematician Claude Shannon, regarded as the founder of information theory. Two advances would be crucial to solving Maxwell’s demon. “He tried to prove a system where the entropy would decrease,” said Laia Delgado Callico, a physicist at King’s College London. Maxwell had created a system that appeared to defy the rise of entropy, and thus the laws of the universe. This isolated system would seem to grow more orderly, not less, because two distinguishable compartments have more order than two identical compartments. And every time a slow-moving particle approached from the right, the demon let it into the left-hand compartment.Īfter a while, the left-hand compartment would be full of slow, cold particles, and the right-hand compartment would grow hot. Every time it saw a fast-moving particle approaching from the left-hand side, it opened the door and let it into the right-hand compartment. What if, suggested Maxwell, a tiny imaginary creature - a demon, as it was later called - sat at the door. But at any given time, some particles will be moving more slowly than others. The average speed of the particles corresponds to the temperature of the gas - faster is hotter. Like all gases, this one is made of individual particles. In the thought experiment, Maxwell imagined splitting a room full of gas into two compartments by erecting a wall with a small door. And even after a solution was found, physicists have continued to use “Maxwell’s demon” to push the laws of the universe to their limits. A thought experiment devised by the Scottish physicist James Clerk Maxwell in 1867 stumped scientists for 115 years. So of course physicists are constantly trying to break it. Seen in this way, the inexorable rise in entropy, or disorder, as quantified by the second law of thermodynamics, takes on an almost mathematical certainty. If the universe chooses from all the possible states at random, you can bet that it’s going to end up with one of the vast set of disordered possibilities. ![]() But there are uncountable billions of permutations where the molecules spread out in different ways throughout the water. There’s another where, say, the molecules settle in a tidy clump at the pool’s bottom. ![]() There’s one possible state where the molecules are crowded into the thimble. Physicists quantify this tendency to spread by counting the number of possible ways the dye molecules can be arranged. All of those dye molecules are going to slowly spread throughout the water. Imagine, for example, dropping a thimbleful of red dye into a swimming pool. ![]()
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