The second law of thermodynamics (the entropy
law or law of entropy) was formulated in the middle of the last
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 acts spontaneously to dissipate or minimize. All real-world
change or dynamics is seen to follow, or be motivated, by this
law. So whereas the first law expresses that which remains the
same, or is time-symmetric, in all real-world processes the second
law expresses that which changes and motivates the change, the
fundamental time-asymmetry, in all real-world process. Clausius
coined the term "entropy" to refer to the dissipated
potential and the second law, in its most general form, states
that the world acts spontaneously to minimize potentials (or
equivalently
maximize entropy), and with this, active end-directedness or
time-asymmetry
was, for the first time, given a universal physical basis. The
balance equation of the second law, expressed as S > 0, says
that in all natural processes the entropy of the world always
increases, and thus whereas with the first law there is no time,
and the past, present, and future are indistinguishable, the second
law, with its one-way flow, introduces the basis for telling the
difference.
The active nature of the second law is intuitively easy to grasp
and empirically demonstrate. If a glass of hot liquid, for example,
as shown in Figure 3, is placed in a colder room a potential exists
and a flow of heat is spontaneously produced from the cup to the
room until it is minimized (or the entropy is maximized) at which
point the temperatures are the same and all flows stop.
A glass of liquid
at temperature TI is placed in a room at temperature
TII such that . The disequilibrium produces a field
potential
that results in a flow of energy in the form of heat from the
glass to the room so as to drain the potential until it is
minimized
(the entropy is maximized) at which time thermodynamic equilibrium
is reached and all flows stop. refers to the conservation of
energy in that the flow from the glass equals the flow of heat
into the room. (From Swenson, 1991a. Copyright 1991 Intersystems
Publications. Adapted by permission).
Figure 4 shows various other potentials and
the flows they would produce. Of important theoretical interest
for this paper is the fact that Joule's experiment (Figure 2)
while designed to
show the first law unintentionally demonstrates
the second too. As soon as the constraint is removed the potential
produces a flow from the falling weight through the moving paddle
through the thermometer. This is precisely the one-way action
of the second law and the experiment depends upon it entirely.
The measurement of energy only takes place through the lawful
flow or time-asymmetry of the second law, and the point to underscore
is that the same is true of every measurement process. In addition,
every measurement process also a demonstrates the first law as
well since the nomological relations that hold require something
that remains invariant over those relations (or else one could
not get invariant or nomological results). The first and second
laws are thus automatically given in every measurement process
for the simple fact, in accordance with the discussion above,
that they are entailed in every epistemic act (Swenson, in press
a, b; see also Matsuno, 1989, in press on generalized measurement).
