Symmetry, Broken-Symmetry and the First and Second Laws ofThermodynamics
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 (Swenson & Turvey,
1991). It can be successfully shown that without the first and
second laws, which express symmetry properties of the world, there
could be no other laws at all. The first law or 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. Namely,
there is something that unifies the world (constitutes it as a
continuum) which if you go forward or backward in time remains
entirely the same. It is, in effect, through this conservation
or out of it that all real-world dynamics occurs, yet the first
law itself is entirely indifferent to these changes or dynamics.
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,
and 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 modern times particularly by Leibniz, the first law is taken to have been first explicitly "discovered" in the first part of the last century by Mayer, then Joule, and later Helmholz with the demonstration of the equivalence of heat and other forms of energy, and completed in this century with Einsteins's demonstration that matter is also a form of energy. Figure 2 shows a famous experiment devised by Joule to demonstrate it.
|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 Swenson, 1997a. Copyright 1997 JAI Press. Used by permission).|