Life's Ratchet: How Molecular Machines Extract Order from Chaos by Peter M. Hoffmann Page A
Authors: Peter M. Hoffmann
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biology are purely one-way: Physics may explain biology, but biology has no bearing on physics. To cure such a misguided view of science, one should consider how Helmholtz came to argue for the law of energy conservation (or the conservation of force, as he called it). Helmholtz, trained as a physician, started his scientific career working on physiological experiments. It was these biological experiments that convinced him of the law of energy conservation.
Energy conservation had been in the air for a while. Descartes, Newton, and Leibniz had all argued for some quantity to be conserved in interactions between material corpuscles, although they could not agree on the type of conserved quantity (Newton argued for momentum or quantity of motion, while Leibniz argued for kinetic energy or vis viva [“the living force”]). Others had shown that work and kinetic energy could be converted into one another, for example, during free fall. Heat had been shown to be a type of motion, and it was already known that kinetic energy could be converted to heat through friction. In 1845, James Joule (1818–1889) showed that a fixed amount of work would result in a fixed amount of heat (what he called the mechanical equivalent of heat): “When equal quantities of mechanical effect are produced by any means whatever from purely thermal sources, or lost in purely thermal effects, then equal quantities of heat are put out of existence or are generated.”
Drawing on his own biological observations and diligent studies of mathematical physics, Helmholtz extended energy conservation to all types of energy, thus declaring energy conservation a fundamental law of the universe. He showed how the conservation of energy can be mathematically derived from simple assumptions. While the mathematical treatment was Helmholtz’s achievement alone, the idea of a universal law of energy conservation had been formulated some years earlier by another German scientist, Julius Robert von Mayer (1814–1878). Just like Helmholtz, Mayer was a physician venturing into physics and was also inspired by biology to proclaim the universal law of energy conservation. Helmholtz was unaware of Mayer’s 1841 paper when he published his own ideas six years later. In his paper, Mayer repudiated vital forces, asHelmholtz would do a short time later, and stated that “the cause of the chemical tension produced in the plant . . . is physical force.” This physical force, or energy, as we would say today, was the same as the energy that would be obtained if we were burning the plant. Furthermore, this energy had to come from somewhere. If we postulated a mysterious vital force— a force that would require no source—we would be “carried . . . into unbridled fantasy,” and all further investigation would “be cut off.” No, said Mayer, the real explanation had to be that energy and matter were only converted from one form to another, and “that creation of either one or the other never takes place.” In other words, even in something as complicated as a plant or an animal, energy was only transformed, but never created or destroyed. This is the universal statement of energy conservation.
In his famous essay of 1847, “Über die Erhaltung der Kraft” (“About the conservation of force”), Helmholtz, then only twenty-six, followed much the same line of argument that Mayer had set forth. Helmholtz felt that postulating mysterious vital forces added nothing to the investigation of how life works. Moreover, the presence of vital forces that could generate mechanical force from nothing would make it possible to construct a perpetuum mobile, a machine that generates energy from nothing. It was widely accepted that this was impossible. Energy conservation had to be correct, and special vital forces could not exist. Helmholtz showed that the law of energy conservation could be mathematically proven. He only needed to make the assumption that matter was made of
Energy conservation had been in the air for a while. Descartes, Newton, and Leibniz had all argued for some quantity to be conserved in interactions between material corpuscles, although they could not agree on the type of conserved quantity (Newton argued for momentum or quantity of motion, while Leibniz argued for kinetic energy or vis viva [“the living force”]). Others had shown that work and kinetic energy could be converted into one another, for example, during free fall. Heat had been shown to be a type of motion, and it was already known that kinetic energy could be converted to heat through friction. In 1845, James Joule (1818–1889) showed that a fixed amount of work would result in a fixed amount of heat (what he called the mechanical equivalent of heat): “When equal quantities of mechanical effect are produced by any means whatever from purely thermal sources, or lost in purely thermal effects, then equal quantities of heat are put out of existence or are generated.”
Drawing on his own biological observations and diligent studies of mathematical physics, Helmholtz extended energy conservation to all types of energy, thus declaring energy conservation a fundamental law of the universe. He showed how the conservation of energy can be mathematically derived from simple assumptions. While the mathematical treatment was Helmholtz’s achievement alone, the idea of a universal law of energy conservation had been formulated some years earlier by another German scientist, Julius Robert von Mayer (1814–1878). Just like Helmholtz, Mayer was a physician venturing into physics and was also inspired by biology to proclaim the universal law of energy conservation. Helmholtz was unaware of Mayer’s 1841 paper when he published his own ideas six years later. In his paper, Mayer repudiated vital forces, asHelmholtz would do a short time later, and stated that “the cause of the chemical tension produced in the plant . . . is physical force.” This physical force, or energy, as we would say today, was the same as the energy that would be obtained if we were burning the plant. Furthermore, this energy had to come from somewhere. If we postulated a mysterious vital force— a force that would require no source—we would be “carried . . . into unbridled fantasy,” and all further investigation would “be cut off.” No, said Mayer, the real explanation had to be that energy and matter were only converted from one form to another, and “that creation of either one or the other never takes place.” In other words, even in something as complicated as a plant or an animal, energy was only transformed, but never created or destroyed. This is the universal statement of energy conservation.
In his famous essay of 1847, “Über die Erhaltung der Kraft” (“About the conservation of force”), Helmholtz, then only twenty-six, followed much the same line of argument that Mayer had set forth. Helmholtz felt that postulating mysterious vital forces added nothing to the investigation of how life works. Moreover, the presence of vital forces that could generate mechanical force from nothing would make it possible to construct a perpetuum mobile, a machine that generates energy from nothing. It was widely accepted that this was impossible. Energy conservation had to be correct, and special vital forces could not exist. Helmholtz showed that the law of energy conservation could be mathematically proven. He only needed to make the assumption that matter was made of
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