What Is Life?

Summary

What Is Life? The Physical Aspect of the Living Cell is a short book based on public lectures that Erwin Schrödinger gave at Trinity College Dublin in February 1943, under the auspices of the Dublin Institute for Advanced Studies. Writing as a physicist who admits he is not a biologist, Schrödinger asks how the events inside a living organism can be accounted for by physics and chemistry. In the first chapter he explains why ordinary physical laws are statistical: they hold reliably only because they describe enormous numbers of atoms, and their precision improves roughly with the square root of the number involved. That is why organisms must be large compared with atoms. Yet heredity seems to defy this rule. In the second and third chapters he reviews the hereditary mechanism, chromosomes, meiosis and Mendelian inheritance, and the mutations described by Hugo de Vries, and uses estimates from X-ray mutation experiments to argue that a gene may contain only about a million atoms or fewer, far too few for statistical reliability. How, then, do hereditary traits remain unchanged over many generations? His answer, in the fourth and fifth chapters, comes from quantum mechanics. Drawing on the 1935 work of N. W. Timoféeff-Ressovsky, K. G. Zimmer and Max Delbrück, he describes the gene as a large molecule whose configurations are separated by energy thresholds, so that it stays stable at body temperature and changes only by rare quantum jumps, which are the mutations. He calls the chromosome an aperiodic crystal: unlike a periodic crystal that merely repeats a pattern, it is an irregular structure that can carry a code-script specifying the whole development of the organism, as a Morse-like code can carry endless meanings with a few signs. The sixth chapter turns to thermodynamics. A living thing avoids decay to equilibrium by drawing order from its surroundings, feeding, in his phrase, on negative entropy, which plants obtain from sunlight. In the seventh chapter he contrasts two ways of producing order: order from disorder, the statistical regularity of physics, and order from order, the new principle by which the organism's small, stable structures govern its life, like the clockwork that runs by quasi-static mechanism. He concludes that living matter, while obeying the laws of physics so far established, probably involves other laws of physics hitherto unknown. A short Epilogue, On Determinism and Free Will, offers his personal view, drawn from the Upanishads, that the conscious self which feels itself directing the body's atoms is one with the universal mind. Cambridge University Press published the book in 1944, and later editions add a note to Chapter 6 on free energy.

Top Lessons

• Asking a large question well

  Schrödinger turns the vague question what is life into precise ones: why atoms are small, how a tiny gene can be stable, and how an organism avoids decay. His book shows how a question from one field can be sharpened by the tools of another.

• Information in matter

  The idea of an aperiodic crystal carrying a code-script anticipated the discovery that DNA stores hereditary information in a sequence of chemical units. Schrödinger saw that the important feature was not substance but arrangement.

• Order sustained against decay

  A living thing stays alive only by taking order from its surroundings and releasing disorder. The picture of the organism as constantly sustained from outside gives a physical meaning to the old observation that life must be fed.

• Science and the self

  In the Epilogue Schrödinger moves beyond physics to the question of who directs the motion of the atoms, offering a personal answer from Hindu philosophy. Readers can see a great scientist marking where his science ends and his metaphysics begins.

Verified Quotes

Medical Lens

For the history of medicine the book marks the point at which heredity began to be conceived as stored molecular information, the conceptual root of molecular genetics and of later genetic medicine. Schrödinger discusses mutation as a rare physical event in a single molecule, its induction by X-rays according to the dose, and the fact that most mutations are disadvantageous and recessive, so that they can be carried hidden in a population; these arguments drew on the radiation genetics of the 1920s and 1930s. His picture of the organism maintaining itself by taking in order from food and sunlight became a common way of describing metabolism. The Epilogue's argument about the self that directs bodily processes speaks to the mind-body problem, but as philosophy rather than medicine.

• Chapters 2-3

  Mendelian inheritance, recessive mutations carried without effect in heterozygotes, and X-ray induced mutation rates used to estimate gene size.

• Chapter 4

  The permanence of hereditary traits across many generations explained by the quantum stability of the gene molecule.

• Epilogue

  The body as a mechanism obeying natural law, set against the direct experience of directing its motions, resolved in the identity of the self with universal consciousness.