Biology Reference
In-Depth Information
a small number of atoms to enrol themselves according to any
recognisable laws. Only in the co-operation of an enormously large
number of atoms do statistical laws begin to operate and control
the behaviour of these assemblies with an accuracy increasing as the
number of atoms involved increases. It is in that way that the
events acquire truly orderly features”
(WIL p.10).
In other words, order in macroscopic physical systems
13
arises
from molecular disorder. Atoms and individual molecules behave
randomly. If any order is produced it is solely due to the law of
large numbers,
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which reduces variability to a negligible level in the
immense populations of particles making up physical objects.
Schrödinger gives several examples of this general principle, the
most important of which, for biology, concerns Brownian motion
and diffusion.
Owing to thermal agitation, atoms and molecules are continu-
ally bumping into each other and moving about randomly, which
causes diffusion. This phenomenon can be described, despite the
probabilistic character of the movement of each individual atom, by
deterministic equations on the macroscopic scale. Indeed, if you put
a drop of a coloured product in a glass of water and then analyse
the concentration, you will find after a certain time that it is uni-
form throughout the glass. If the experiment is repeated in identi-
cal conditions, the phenomenon of diffusion will be repeated in
exactly the same way despite the random movement of each atom
of coloured product. This is due to the huge number of atoms
involved in this phenomenon. The variance is so small from one
experiment to another that in practice we only observe the mean
effect of all random individual movements (WIL pp. 14, 15).
The question then arises of whether order in biological systems
may proceed from such random dynamics, in which variability would
be eliminated in the same way through the law of large numbers.
Schrödinger accepts the very strong determinism postulated by the
13
Those existing at our level of observation.
14
See previous chapter (Sec. 1.1.2)
