Re: laws of thermodynamics

Jim,
    Your comment that "First, the 2nd law refers to a closed system (no net energy in or out) which our local situation (in universe address terms) is not." is a common misunderstanding of the 2nd law. The 2nd Law is actually universal in scope.

Allan,
    Thank you for the link to your well-written essay. Specifically your paragraph addresses Jim's comment very well: "It is worth mentioning here that the usual reply to creationists that "the second law doesn't apply to non-isolated systems" is not quite correct. The second law always applies; in fact, it was originally developed for non-isolated systems (the working fluid of a heat engine). The key point is that it is only in isolated systems that the second law takes the simplified "entropy must increase" form. For non-isolated systems, the second law still applies as a statement about heat flows and temperatures, just not in the form used in creationist arguments."

Of all the statements of the 2nd Law, my favorite is one I learned from George Uhlenbeck: "The second gradient of the free energy is positive" (which is much more elegant in equation form), meaning that the free energy is minimized in every physical process. The Free energy includes not only the well-known terms "U-TS" but also terms for pressure/volume, strain energy, chemical potential, magnetic potential, gravitational potential, etc. The overly-used "closed system" simplification keeps all the extra terms constant so that the remaining variable, entropy S, must be maximized to keep the free energy at a minimum.

Randy
Received on Tue Jan 4 21:20:45 2005