An excerpt from quantum physicist Erwin Schrodinger's "What Is Life?" (1944)
LIVING MATTER EVADES THE DECAY
TO EQUILIBRIUM
What is the characteristic feature of life? When
is a piece of matter said to be alive? When it
goes on 'doing something', moving, exchanging
material with its environment, and so forth, and
that for a much longer period than we would
expect of an inanimate piece of matter to 'keep
going' under similar circumstances. When a
system that is not alive is isolated or placed in a
uniform environment, all motion usually comes
to a standstill very soon as a result of various
kinds of friction; differences of electric or
chemical potential are equalized, substances
which tend to form a chemical compound do so,
temperature becomes uniform by heat
conduction. After that the whole system fades
away into a dead, inert lump of matter. A
permanent state is reached, in which no
observable events occur. The physicist calls this
the state of thermodynamical equilibrium, or of
`maximum entropy'. Practically, a state of this
kind is usually reached very rapidly.
Theoretically, it is very often not yet an absolute
equilibrium, not yet the true maximum of
entropy. But then the final approach to
equilibrium is very slow. It could take anything
between hours, years, centuries,... To give an
example -one in which the approach is still fairly
rapid: if a glass filled with pure water and a
second one filled with sugared water are placed
together in a hermetically closed case at constant
temperature, it appears at first that nothing
happens, and the impression of complete
equilibrium is created. But after a day or so it is
noticed that the pure water, owing to its higher
vapour pressure, slowly evaporates and
condenses on the solution. The latter overflows.
Only after the pure water has totally evaporated
has the sugar reached its aim of being equally
distributed among all the liquid water
available. These ultimate slow approaches to
equilibrium could never be mistaken for life, and
we may disregard them here. I have referred to
them in order to clear myself of a charge
of Inaccuracy.
IT FEEDS ON 'NEGATIVE ENTROPY'
It is by avoiding the rapid decay into the inert
state of 'equilibrium' that an organism appears so
enigmatic; so much so, that from the earliest
times of human thought some special
non-physical or supernatural force (vis viva,
entelechy) was claimed to be operative in the
organism, and in some quarters is still claimed.
How does the living organism avoid decay? The
obvious answer is: By eating, drinking, breathing
and (in the case of plants) assimilating. The
technical term is metabolism. The Greek word ()
means change or exchange. Exchange of what?
Originally the underlying idea is, no doubt,
exchange of material. (E.g. the German for
metabolism is Stoffwechsel.) That the exchange
of material should be the essential thing is
absurd. Any atom of nitrogen, oxygen, sulphur,
etc., is as good as any other of its kind; what
could be gained by exchanging them? For a
while in the past our curiosity was silenced by
being told that we feed upon energy. In some
very advanced country (I don't remember
whether it was Germany or the U.S.A. or both)
you could find menu cards in restaurants
indicating, in addition to the price, the energy
content of every dish. Needless to say, taken
literally, this is just as absurd. For an adult
organism the energy content is as stationary as
the material content. Since, surely, any calorie is
worth as much as any other calorie, one cannot
see how a mere exchange could help. What then
is that precious something contained in our food
which keeps us from death? That is easily
answered. Every process, event, happening -call
it what you will; in a word, everything that is
going on in Nature means an increase of the
entropy of the part of the world where it is going
on. Thus a living organism continually increases
its entropy -or, as you may say, produces
positive entropy -and thus tends to approach the
dangerous state of maximum entropy, which
is of death. It can only keep aloof from it, i.e.
alive, by continually drawing from its
environment negative entropy -which is
something very positive as we shall immediately
see. What an organism feeds upon is negative
entropy. Or, to put it less paradoxically, the
essential thing in metabolism is that the
organism succeeds in freeing itself from all the
entropy it cannot help producing while alive.
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