The laws of thermodynamics are special laws that sit above the ordinary laws of nature, as laws about laws or laws upon which the other laws depend. As noted above, the first law-the law of energy conservation-which says that all real world processes involve transformations of energy, and that the total amount of energy is always conserved, expresses time-translation symmetry. As far as the first law is concerned, nothing changes at all and this is just the definition of a symmetry, something that remains invariant, indifferent or unchanged given certain transformations. The remarkable point with respect to the first law is that it refers to that which is conserved (the quantity of energy) or remains symmetric under all transformations. Although intuited at least as early as the work of the Milesian physicists and in modem times particularly by Leibniz, the first law is taken to have been first explicitly "discovered" in the first part of the nineteenth century by Mayer, then Joule, and later Helmholz, with the demonstration of the equivalence of heat and other forms of energy. Discovery was completed in the twentieth century with Einsteins"s demonstration that matter is also a form of energy. FIGURE 3 shows the experiment Joule devised to demonstrate the law.
energy, conservation, Joule, rod swenson, Carnot, entropy, thermodynamics
FIGURE 4. The experiment devised by Joule to demonstrate the conservation of energy. When a constraint is removed, potential energy in the form of a suspended weight is converted into the kinetic energy of a moving paddle wheel in a container of water sealed against other inflow or outflow of energy. The moving paddle wheel heats the water by a precise amount consistent with the falling weight. (From Ref. 3, reproduced by permission of JAI Press.)
The second law was formulated in the middle of the eighteenth century by Clausius and Thomson following Carnot's earlier observation that, like the fall or flow of a stream that turns a mill wheel, it is the fall or flow of heat from higher to lower temperatures that motivates a steam engine. The key insight was that the world is inherently active and that whenever an energy distribution is out of equilibrium a potential or thermodynamic force (the gradient of a potential) exists that the world