- Person
- Leo Szilard
- Lived
- 1898–1964
- Field
- Nuclear physics
- From
- Hungarian-American
The story
Maxwell's demon is a famous thought experiment devised by the physicist James Clerk Maxwell in the nineteenth century. A tiny being sorts fast and slow gas molecules between two chambers, seemingly creating order for free and defying the second law of thermodynamics, which says that disorder, or entropy, in a closed system never decreases. Many physicists thought the puzzle insoluble.
Leo Szilard, a young Hungarian Jewish student in Berlin who attended lectures by Albert Einstein, Max Planck and Max von Laue, took it on. His doctoral thesis on thermodynamic fluctuations, praised by Einstein, won top honours in 1922. Soon afterwards he wrote a second paper, On the reduction of entropy in a thermodynamic system by the intervention of intelligent beings, which he used for his habilitation lecture in 1927 and published in 1929.
That paper introduced a thought experiment now called the Szilard engine, in which a single gas molecule in a box is used to do work once its position is known. Szilard showed that a real demon must measure the molecules, and that acquiring and using that information has an unavoidable cost in entropy, enough to save the second law. The paper also contained the first equation linking information with negative entropy.
This was the first time anyone of note had recognised the connection between thermodynamics and information. Szilard did not pursue the topic further, but the idea fed into the cybernetics of Norbert Wiener and the information theory of Claude Shannon in the 1940s and 1950s. John von Neumann pointed out that Szilard had been the first to equate information with entropy.
Later physicists, including Léon Brillouin, Rolf Landauer and Charles Bennett, refined the argument, showing in particular that erasing information carries a minimum energy cost. In 2012 experimenters measured that limit using a tiny particle, and in 2014 a team led by the physicist Pekola built a working Szilard engine.
The insight is central to modern research on the physical limits of computation, explaining why a computer must release at least a minimum amount of heat whenever it erases information.
Why it matters
Szilard's insight underlies today's understanding of the energy cost of computing and the physics of information.
About Leo Szilard
Physicist who conceived the nuclear chain reaction in 1933, drafted Einstein’s letter to Roosevelt, co-built the first reactor, then campaigned for the rest of his life against nuclear war.
More about Leo Szilard
- Szilard's advice helped clone the first human cellLeo Szilard gave essential advice that, according to Theodore Puck and Philip Marcus, made their 1955 cloning of a human cell a reality.
- Leo Szilard saw the chain reaction, and rescued scholarsWaiting at a London traffic light in September 1933, Leo Szilard conceived the nuclear chain reaction; that same year he helped found a group that found posts for 2,500 refugee scholars.
- Szilard found a way to make medical isotopesIn 1934 at St Bartholomew's Hospital, Leo Szilard and Thomas Chalmers discovered the Szilard–Chalmers effect, widely used to prepare medical isotopes.
- Szilard co-invented the chemostat for growing microbesAfter the war Leo Szilard and Aaron Novick invented the chemostat for growing microbes and discovered feedback inhibition, a key way cells control their chemistry.
- Szilard first proposed the cyclotron and electron microscopeLeo Szilard filed the earliest known patent applications for the electron microscope (1928) and the cyclotron (1929), and one for the linear accelerator (1928).
- Szilard and Einstein invented a silent refrigeratorBetween 1926 and 1930 Leo Szilard worked with Albert Einstein on a refrigerator with no moving parts, patented in the United States in 1930.
- Szilard petitioned Truman not to bomb without warningIn July 1945 Leo Szilard drafted a petition, signed by about 70 Manhattan Project scientists, urging President Truman not to use the atomic bomb on Japan without warning.
- Szilard fought for civilian control of the atomAfter the war Leo Szilard lobbied for changes to the Atomic Energy Act of 1946 that placed American nuclear energy under civilian rather than military control.
- Leo Szilard helped rescue 2,500 refugee scholarsIn 1933 Leo Szilard helped found the Academic Assistance Council in Britain, which by 1939 had found places for more than 2,500 refugee scholars.
Sources
- Leo Szilard Wikipedia
- Maxwell's demon Wikipedia
Another act of tikkun olam. This is part of tikkun olam, the Jewish idea of repairing the world, and every one of us can add to it.