Nobel laureate Steven Weinberg has
argued that science proceeds by finding "simple but impersonal
principles."iWe
agree and submit that the notion that "nature abhors a gradient" is
just such a principle. Although life is complex, understanding
it should be less so. At the same time, it should not be too simple:
replicating sets of algorithms in computer hard drives, sometimes called "artificial
life," are
just that—artificial. Oversimplification is a tendency in science.
Experimenters like to work with systems that show repeatable results,
and that leads them to discard systems that are too complex or that have
too many variables. Nonetheless, organisms move through many more states,
and do so far more subtly, than simulations on machines.
Classical thermodynamics studies the world under
highly specific conditions. The isolated system has no contact with
events outside its sealed walls. This idealization does allow for the
solution of many problems that otherwise would be intractable. Open
systems, although more interesting, have more variables—they are harder to understand. Thus, a crucial stage
in the transition from classical to open-system thermodynamics was the
study by energy scientists of closed systems. Closed systems, allowing
energy but not matter to be exchanged across their boundaries, possess
an intermediate number of variables. This makes them more realistic than
isolated systems, but not so difficult to study as more complex, open
ones. An example of a closed system is a chemical reaction in a closed
flask where excess heat from the reaction is permitted to move outside
the flask into the surroundings while the chemical by-products remain
behind in the vessel. By contrast, organisms and all known functioning
ecosystems—with the arguable exception of the biosphere itself—trade
both matter and energy across their boundaries. They are open systems.
Stars, burning nuclear fuel and producing high-quality light, are also
open systems. In cities too the materials (food, lumber, copper wire,
etc.) and energy (electricity, methane, oil, etc.) are constantly being
withdrawn from and returned across city limits. From stars to lovers
to the latest computer programs, the most fascinating systems in the
universe—and the most destructive ones, such as sharks, armies,
and exploding supernovas—are open.
Energy, heat, and work are key concepts in thermodynamics. Energy is
the capacity to do work. That work can be to carry a one-kilogram laundry
basket up some three meters of stairs, to pull a train over the Alps,
or to launch a rocket to Mars. Although the varieties of work are unlimited,
only a few kinds of energy exist: kinetic, potential-gravitational, magnetic,
electrical, chemical, and the energy in thermonuclear bonds. One kind
of energy can transform into another, as in the birth of stars from gravitationally
gathered clouds of cosmic debris. Matter itself, as Einstein's equation E = mc2
(energy = mass multiplied by the squared speed of light) shows, is a
vast potential reservoir of energy, although life has not evolved to
use it except in nuclear bombs and power plants. The first law of thermodynamics
suggests that energy subtly changes forms but never completely vanishes.
Heat
and work are processes or methods for transferring energy. A particle
can possess energy by virtue of its position (potential energy), or its
motion (kinetic energy). Work is a means of transferring energy
into coherent action. Heat, or rather heat flow, is
a means of transferring energy via temperature gradients. Thus, unlike
one kilogram of flour in a sack, or a pile of coal that can be burnt,
bought, or sold—which are things—heat flow and work are processes,
not things.
When work is done on a system, the transfer of
energy is via coherent motion. Consider a well-hit golf ball flying
eighty meters toward the green. All the atoms and molecules in the
golf ball travel together—they
are coherent. The club head transfers kinetic energy to the ball—and
there goes the ball.
When we heat a system, it is just the opposite. As energy transfers
from one body to another via warming, the thermal motions of the second
body become more chaotic. The energy is still stored as potential and
kinetic energy, but now the location and motion of the particles are
more difficult to detect; they are incoherent.
The several basic forms of energy can be converted
from one form to another via simple processes. Consider the three forms
of energy that occur during the swing of a pendulum (fig. 2.1). A pendulum,
at the top of its swing, has its highest potential energy. When it
is released, this gravitational potential energy converts into kinetic
energy and the pendulum descends. At the bottom of its swing, the pendulum
weight has its highest kinetic energy, highest velocity, and lowest
potential energy. In a swinging pendulum, kinetic energy transforms
back and forth into potential energy. Then the pendulum comes to rest—achieving
an end state of minimum kinetic energy and minimum potential energy.
What stills the pendulum, what makes it reach thermodynamic equilibrium,
is the second law: the friction of rubbing wears the system down—its
energy is lost to the environment, dissipated as heat. Frictional components
such as air resistance against the pendulum, or the gears in a grandfather
clock, generate minute amounts of heat flow into the surrounding environment.
Energy is not truly lost, just converted to heat. Although some heat
can be retrieved for useful purposes, the most important thermodynamic
trait of heat is that it is energy in its most useless form. Nonetheless,
it is energy. That energy will be conserved as it changes forms is known
as the first law of thermodynamics, or the law of the conservation of
energy.
Far from contradicting
evolution, thermodynamics is required to understand complex processes.
This applies to all complex processes, including networks based on informational
rules. The laws of thermodynamics, centering on nature's tendency to
conserve energy as it changes forms as well as to head toward molecular
disorganization, are human generalizations. Yet they reflect the behavior
of more than just computers; if the world is a cellular automaton spawned
by the mind of God, it is one in which the behaviors governed by the
second law have been given a peculiar primacy. From an idealistic informational
viewpoint, the second law may (like probability theory) be a measure
of, even a metaphor for, our ignorance; but from the point of view
of observation, the behaviors governed by the second law apply not
only to computers but to a vast array of real and imaginable systems
that naturally "figure out" how to come
to equilibrium with available materials. The activities of these systems,
sometimes quite complex, make complex thermodynamic systems de facto
computers—even if the operating manuals have not yet been unsealed
for human inspection.
In the meantime the second law reveals major aspects of evolutionary and
ecological processes.
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