Control Systems in the Living World - Building the Most Complex Structure on Earth - page 10

Figure 1.6 Mount Rushmore National Memorial.

thermodynamics, which, in the opinion of many scientists, may be the most universal
law governing the universe. Central to the second law of thermodynamics is the prin-
ciple of entropy. For the purpose of this discussion, a simple and classical definition
of the law is:

In an isolated system, only processes that are associated with increase of entropy
can occur.

The movement of molecules of a gas under moderate temperatures may be
described as disordered, but molecules of water are less so, while nitrogen bases in
DNA are highly ordered. Working on a mechanical theory of gases, Rudolf Clausius
(1822-1888) coined the term “transformation content” ( Verwandlungsinhalt ) or
entropy (from the Greek en + trope —“toward”+“turn”) for describing the direc-
tion of the flow of heat from a hotter compartment of a gas system to a colder one.
This leads to a state of equilibrium in the system where the temperature (the aver-
age speed of gas molecules in the whole system) equalizes. Reversion to the origi-
nal state (i.e., segregation of high-speed gas molecules from low-speed ones in the
system) cannot occur. Extrapolating this to the universe, Clausius concluded that the
entropy of the universe tends to be at a maximum. Later, Ludwig Boltzmann (1844-
1906) popularized the idea of entropy as a measure of disorder in a system. He tried
to explain why material systems tend to increase their entropy or states of disorder;
this is because the number of disordered states in a gas system is infinitely larger
than the ordered state . Accordingly, the stabler state is the one that the system has
the highest probability to reach.
Boltzmann tried to explain why the entropy increases in one direction only:
past→present→future. To account for this time asymmetry of entropy, he suggested
that in the endless universe, isolated spaces still exist, which have not reached the
equilibrium state (maximal entropy) and are still increasing their entropy. Boltzmann
reasoned that since the probability of disordered states in these “isolated spaces” is
incomparably higher than the ordered one, it follows that these spaces will continue