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Joule, and later Helmholtz in the first half of the nineteenth century with various demonstrations of the equivalence of heat and other forms of energy (e.g., see Thomson, 1852b; Singer, 1959; Schneer, 1960; Swenson, in press-c). The law was completed in this century with Einstein's demonstration that matter is also a form of energy. The first law says that (a) all real-world processes consist of transformations of one form of energy into another (e.g., mechanical, chemical, or electrical energy or energy in the form of heat), and that (b) the total amount of energy in all real-world transformations always remains the same or is conserved (energy is neither created nor destroyed).

The first law was not fully understood until the second law was formulated by Clausius and Thomson in the 1850's. What Carnot had observed some twenty-five years earlier was that, as he explained it, like the fall of a stream that turns a mill wheel, it was the "fall" of heat from higher to lower temperatures that motivates a steam engine. With the recognition that it was the potential to "fall" from hot to cold, or from a higher to lower place that motivated the flow of the stream, the turning of the mill wheel, or the motion of the steam engine, came the recoginition that with these actions the potential was irreversibly destroyed, or dissipated, as Thomson (1852b) would put it. Realizing that the active principle, if based on dissipation, could not be energy, which is conserved, Thomson and Clausius recognized that there were two fundamental laws in operation and showed how they were related. Clausius coined the word "entropy" to refer to the dissipated potential, and the second law states in its most fundamental form that all natural processes proceed so as to maximize the entropy (or equivalently minimize or dissipate the potential of a system), while, at the same time, energy is entirely conserved.

The first and second laws of thermodynamics are thus symmetry principles that sit above the other laws of nature, as, in effect, laws about laws, or laws on which the other laws are dependent (Swenson, 1991b; Swenson & Turvey, 1991). The first law expresses the time translation symmetry of all natural processes, that which remains the same in all past, present and future states, and the second law expresses the broken-symmetry of the natural world, providing, in a world which is out of equilibrium, as our expanding universe is, a nomological basis for distinguishing past, present, and future. The balance equation of the second law, expressed as DS > 0, says that in all real world processes entropy always increases.

In sharp contrast to the "dead" mechanical world view of Descartes and Newton, the active, end-directed nature of the world was stressed by Clausius' (1865, p. 400) in his statement of the first two laws of thermodynamics: "The energy of the world remains constant," he said, while "[t]he entropy of the world strives to a maximum" (italics added). Entropy maximization supplies what can be thought of as a final cause, in Aristotle's terms, of all natural processes-"the end to which everything strives and which everything serves" or "the end of every motive or generative process" (Bunge, 1979, p. 32)(see Salthe, 1994; Swenson, 1990b, 1991b; Swenson & Turvey, 1991). The active, end-directed (going towards an end, no "director" implied) nature of the second law is intuitively easy to grasp and empirically easy to demonstrate.

Consider a glass of hot liquid placed in a room at a cooler temperature. The temperature gradient or difference in temperatures in the glass-room system constitutes a potential, and a flow of energy in the form of heat, a "drain" on the potential, is spontaneously produced from the glass (source) to the room (sink) until the potential is minimized (the entropy is maximized) and the liquid and the room are at the same temperature. At this point, all flows and thus all entropy production stops and the system is in thermodynamic equilibrium. The same principle applies to any system where any form of energy is out of equilibrium with its surrounds (e.g., whether mechanical, chemical, electrical or energy in the form of heat): a potential exists that the world acts spontaneously to minimize. It spontaneously produces dynamics that work to minimize the potential and stop when it is minimized. In this precise and rigorous sense the world is inherently active and end-directed.

Boltzmann's Hypothesis and the Second Law as a Law of Disorder:
Why 'Organic Evolution' Was Thought to Negate 'Physical Evolution'

Dennett's idea that living things exist in a struggle against the apparent universality of physical law, that they defy the second law, or live in a battle against it, and so on, follows from Boltzmann's hypothesis of the second law which was quite different in a number of ways from the universal physical statement of the second law due to Thomson and Clausius (see Swenson, in press-c for further discussion). When the second law was first explicitly recognized, its active macroscopic nature presented a profound blow to the dead mechanical world view. Boltzmann's hypothesis, or theory about the second law, grew out of his attempt to save the mechanical view by reducing the second law to the stochastic collision of mechanical particles-to a law of probability. Modelling colliding gas molecules in a box as billiard balls, Boltzmann, following Maxwell, showed that nonequilibrium velocity distributions (groups of molecules moving at the same speed and in the same direction) would become increasingly disordered with each collision leading to a final state of macroscopic uniformity and maximum microscopic disorder. Boltzmann recognized this state as the state of maximum entropy (where the macroscopic uniformity corresponds to the dissipation of all field potentials or energy gradients). Generalizing the results to the world as a whole, the second law, he said, was simply the result of the fact that in a world of mechanically colliding particles, disordered states are the most probable.

There are so many more possible disordered states than ordered ones, Boltzmann argued, that a system will almost always be found either in the state of maximum disorder-the macrostate with the greatest number of accessible microstates such as a gas in a box at equilibrium-or moving towards it. A dynamically ordered state, with molecules moving "at the same speed and in the same direction", he (Boltzmann, 1886/1974, p. 20) wrote, "is the most improbable case infinitely improbable configuration of energy,"(italics added) and from this conception-from the extrapolation of a near-equilibrium gas in a box to the world-came the idea of the second law as a law of disorder. Although Boltzmann (1896/1964) himself acknowledged that his hypothesis had been demonstrated only for the case of a gas in a box near equilibrium, the science of his time (and until quite recently) was dominated by linear, near-equilibrium, or equilibrium, thinking, and his hypothesis became widely accepted. In fact, it came to be taken by many to be the second law, and in this sense Dennett's view represents a common and widespread misconception that has persisted from the time of Boltzmann right up to the present.