What Is Life (Canto Classics)
WHAT IS LIFE?
with
MIND AND MATTER
&
AUTOBIOGRAPHICAL
SKETCHES
WHAT IS LIFE?
The Physical Aspect of the Living Cell
with
MIND AND MATTER
&
AUTOBIOGRAPHICAL
SKETCHES
ERWIN SCHRÖDINGER
CAMBRIDGE UNIVERSITY PRESS
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Cambridge University Press
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What is Life? and Mind and Matter
© Cambridge University Press 1967
WHAT IS LIFE?
First published 1944
Reprinted 1945, 1948, 1951, 1955, 1962
MIND AND MATTER
First published 1958
Reprinted 1959
Combined reprint 1967
Canto edition with Autobiographical Sketches and
Foreword to What is Life? by Roger Penrose
© Cambridge University Press 1992
First printed 1992
14th printing 2013
Printed and bound by CPI Group (UK) Ltd, Croydon, CRO 4YY
ISBN 978-1-107-60466-7 Paperback
Cambridge University Press has no responsibility for the persistence or accuracy
of URLs for external or third-party internet websites referred to in this
publication, and does not guarantee that any content on such websites is,
or will remain, accurate or appropriate.
Contents
WHAT IS LIFE?
Preface
1 THE CLASSICAL PHYSICIST’S APPROACH TO THE SUBJECT
The general character and the purpose of the investigation
Statistical physics. The fundamental difference in structure
The naïve physicist’s approach to the subject
Why are the atoms so small?
The working of an organism requires exact physical laws
Physical laws rest on atomic statistics and are therefore only approximate
Their precision is based on the large number of atoms intervening. 1st example (paramagnetism)
2nd example (Brownian movement, diffusion)
3rd example (limits of accuracy of measuring)
The √ n rule
2 THE HEREDITARY MECHANISM
The classical physicist’s expectation, far from being trivial, is wrong
The hereditary code-script (chromosomes)
Growth of the body by cell division (mitosis)
In mitosis every chromosome is duplicated
Reductive division (meiosis) and fertilization (syngamy)
Haploid individuals
The outstanding relevance of the reductive division
Crossing-over. Location of properties
Maximum size of a gene
Small numbers
Permanence
3 MUTATIONS
‘Jump-like’ mutations – the working-ground of natural selection
They breed true, i.e. they are perfectly inherited
Localization. Recessivity and Dominance
Introducing some technical language
The harmful effect of close-breeding
General and historical remarks
The necessity of mutation being a rare event
Mutations induced by X-rays
First law. Mutation is a single event
Second law. Localization of the event
4 THE QUANTUM-MECHANICAL EVIDENCE
Permanence unexplainable by classical physics
Explicable by quantum theory
Quantum theory – discrete states-quantum jumps
Molecules
Their stability dependent on temperature
Mathematical interlude
First amendment
Second amendment
5 DELBRÜCK’S MODEL DISCUSSED AND TESTED
The general picture of the hereditary substance
The uniqueness of the picture
Some traditional misconceptions
Different ‘states’ of matter
The distinction that really matters
The aperiodic solid
The variety of contents compressed in the miniature code
Comparison with facts: degree of stability; discontinuity of mutations
Stability of naturally selected genes
The sometimes lower stability of mutants
Temperature influences unstable genes less than stable ones
How X-rays produce mutation
Their efficiency does not depend on spontaneous mutability
Reversible mutations
6 ORDER, DISORDER AND ENTROPY
A remarkable general conclusion from the model
Order based on order
Living matter evades the decay to equilibrium
It feeds on ‘negative entropy’
What is entropy? – The statistical meaning of entropy
Organization maintained by extracting ‘order’ from the environment
7 IS LIFE BASED ON THE LAWS OF PHYSICS?
New laws to be expected in the organism
Reviewing the biological situation
Summarizing the physical situation
The striking contrast
Two ways of producing orderliness
The new principle is not alien to physics
The motion of a clock
Clockwork after all statistical
Nernst’s Theorem
The pendulum clock is virtually at zero temperature
The relation between clockwork and organism
EPILOGUE. ON DETERMINISM AND FREE WILL
MIND AND MATTER
1 THE PHYSICAL BASIS OF CONSCIOUSNESS
The problem
A tentative answer
Ethics
2 THE FUTURE OF UNDERSTANDING
A biological blind alley?
The apparent gloom of Darwinism
Behaviour influences selection
Feigned Lamarckism
Genetic fixation of habits and skills
Dangers to intellectual evolution
3 THE PRINCIPLE OF OBJECTIVATION
4 THE ARITHMETICAL PARADOX: THE ONENESS OF MIND
5 SCIENCE AND RELIGION
6 THE MYSTERY OF THE SENSUAL QUALITIES
AUTOBIOGRAPHICAL SKETCHES
Translated by Schrödinger’s granddaughter Verena
WHAT IS LIFE?
THE PHYSICAL ASPECT OF THE LIVING CELL
Based on lectures delivered under the auspices of the Dublin Institute for
Advanced Studies at Trinity College, Dublin, in February 1943
To
the memory of
My Parents
Foreword
When I was a young mathematics student in the early 1950s I did not read a great deal, but what I did read – at least if I completed the book – was usually by Erwin Schrödinger. I always found his writing to be compelling, and there was an excitement of discovery, with the prospect of gaining some genuinely new understanding about this mysterious world in which we live. None of his writings possesses more of this quality than his short classic What is Life? – which, as I now realize, must surely rank among the most influential of scientific writings in this century. It represents a powerful attempt to comprehend some of the genuine mysteries of life, mad
e by a physicist whose own deep insights had done so much to change the way in which we understand what the world is made of. The book’s cross-disciplinary sweep was unusual for its time – yet it is written with an endearing, if perhaps disarming, modesty, at a level that makes it accessible to non-specialists and to the young who might aspire to be scientists. Indeed, many scientists who have made fundamental contributions in biology, such as J. B. S. Haldane and Francis Crick, have admitted to being strongly influenced by (although not always in complete agreement with) the broad-ranging ideas put forward here by this highly original and profoundly thoughtful physicist.
Like so many works that have had a great impact on human thinking, it makes points that, once they are grasped, have a ring of almost self-evident truth; yet they are still blindly ignored by a disconcertingly large proportion of people who should know better. How often do we still hear that quantum effects can have little relevance in the study of biology, or even that we eat food in order to gain energy? This serves to emphasize the continuing relevance that Schrödinger’s What is Life? has for us today. It is amply worth rereading!
Roger Penrose
8 August 1991
Preface
A scientist is supposed to have a complete and thorough knowledge, at first hand, of some subjects and, therefore, is usually expected not to write on any topic of which he is not a master. This is regarded as a matter of noblesse oblige. For the present purpose I beg to renounce the noblesse, if any, and to be freed of the ensuing obligation. My excuse is as follows:
We have inherited from our forefathers the keen longing for unified, all-embracing knowledge. The very name given to the highest institutions of learning reminds us, that from antiquity and throughout many centuries the universal aspect has been the only one to be given full credit. But the spread, both in width and depth, of the multifarious branches of knowledge during the last hundred odd years has confronted us with a queer dilemma. We feel clearly that we are only now beginning to acquire reliable material for welding together the sum total of all that is known into a whole; but, on the other hand, it has become next to impossible for a single mind fully to command more than a small specialized portion of it.
I can see no other escape from this dilemma (lest our true aim be lost for ever) than that some of us should venture to embark on a synthesis of facts and theories, albeit with second-hand and incomplete knowledge of some of them – and at the risk of making fools of ourselves.
So much for my apology.
The difficulties of language are not negligible. One’s native speech is a closely fitting garment, and one never feels quite at ease when it is not immediately available and has to be replaced by another. My thanks are due to Dr Inkster (Trinity College, Dublin), to Dr Padraig Browne (St Patrick’s College, Maynooth) and, last but not least, to Mr S. C. Roberts. They were put to great trouble to fit the new garment on me and to even greater trouble by my occasional reluctance to give up some ‘original’ fashion of my own. Should some of it have survived the mitigating tendency of my friends, it is to be put at my door, not at theirs.
The head-lines of the numerous sections were originally intended to be marginal summaries, and the text of every chapter should be read in continuo.
E.S.
Dublin
September 1944
Homo liber nulla de re minus quam de morte cogitat; et ejus sapientia non mortis sed vitae meditatio est. SPINOZA’S Ethics, Pt IV, Prop. 67
(There is nothing over which a free man ponders less than death; his wisdom is, to meditate not on death but on life.)
CHAPTER 1
The Classical Physicist’s
Approach to the Subject
Cogito ergo sum.
DESCARTES
THE GENERAL CHARACTER AND THE PURPOSE OF
THE INVESTIGATION
This little book arose from a course of public lectures, delivered by a theoretical physicist to an audience of about four hundred which did not substantially dwindle, though warned at the outset that the subject-matter was a difficult one and that the lectures could not be termed popular, even though the physicist’s most dreaded weapon, mathematical deduction, would hardly be utilized. The reason for this was not that the subject was simple enough to be explained without mathematics, but rather that it was much too involved to be fully accessible to mathematics. Another feature which at least induced a semblance of popularity was the lecturer’s intention to make clear the fundamental idea, which hovers between biology and physics, to both the physicist and the biologist.
For actually, in spite of the variety of topics involved, the whole enterprise is intended to convey one idea only – one small comment on a large and important question. In order not to lose our way, it may be useful to outline the plan very briefly in advance.
The large and important and very much discussed question is:
How can the events in space and time which take place within the spatial boundary of a living organism be accounted for by physics and chemistry?
The preliminary answer which this little book will endeavour to expound and establish can be summarized as follows:
The obvious inability of present-day physics and chemistry to account for such events is no reason at all for doubting that they can be accounted for by those sciences.
STATISTICAL PHYSICS. THE FUNDAMENTAL
DIFFERENCE IN STRUCTURE
That would be a very trivial remark if it were meant only to stimulate the hope of achieving in the future what has not been achieved in the past. But the meaning is very much more positive, viz. that the inability, up to the present moment, is amply accounted for.
Today, thanks to the ingenious work of biologists, mainly of geneticists, during the last thirty or forty years, enough is known about the actual material structure of organisms and about their functioning to state that, and to tell precisely why, present-day physics and chemistry could not possibly account for what happens in space and time within a living organism.
The arrangements of the atoms in the most vital parts of an organism and the interplay of these arrangements differ in a fundamental way from all those arrangements of atoms which physicists and chemists have hitherto made the object of their experimental and theoretical research. Yet the difference which I have just termed fundamental is of such a kind that it might easily appear slight to anyone except a physicist who is thoroughly imbued with the knowledge that the laws of physics and chemistry are statistical throughout.1 For it is in relation to the statistical point of view that the structure of the vital parts of living organisms differs so entirely from that of any piece of matter that we physicists and chemists have ever handled physically in our laboratories or mentally at our writing desks.2 It is well-nigh unthinkable that the laws and regularities thus discovered should happen to apply immediately to the behaviour of systems which do not exhibit the structure on which those laws and regularities are based.
The non-physicist cannot be expected even to grasp – let alone to appreciate the relevance of – the difference in ‘statistical structure’ stated in terms so abstract as I have just used. To give the statement life and colour, let me anticipate what will be explained in much more detail later, namely, that the most essential part of a living cell – the chromosome fibre – may suitably be called an aperiodic crystal. In physics we have dealt hitherto only with periodic crystals. To a humble physicist’s mind, these are very interesting and complicated objects; they constitute one of the most fascinating and complex material structures by which inanimate nature puzzles his wits. Yet, compared with the aperiodic crystal, they are rather plain and dull. The difference in structure is of the same kind as that between an ordinary wallpaper in which the same pattern is repeated again and again in regular periodicity and a masterpiece of embroidery, say a Raphael tapestry, which shows no dull repetition, but an elaborate, coherent, meaningful design traced by the great master.
In calling the periodic crystal one of the most complex objects of
his research, I had in mind the physicist proper. Organic chemistry, indeed, in investigating more and more complicated molecules, has come very much nearer to that ‘aperiodic crystal’ which, in my opinion, is the material carrier of life. And therefore it is small wonder that the organic chemist has already made large and important contributions to the problem of life, whereas the physicist has made next to none.
THE NAÏVE PHYSICIST’S APPROACH
TO THE SUBJECT
After having thus indicated very briefly the general idea – or rather the ultimate scope – of our investigation, let me describe the line of attack.
I propose to develop first what you might call ‘a naïve physicist’s ideas about organisms’, that is, the ideas which might arise in the mind of a physicist who, after having learnt his physics and, more especially, the statistical foundation of his science, begins to think about organisms and about the way they behave and function and who comes to ask himself conscientiously whether he, from what he has learnt, from the point of view of his comparatively simple and clear and humble science, can make any relevant contributions to the question.
It will turn out that he can. The next step must be to compare his theoretical anticipations with the biological facts. It will then turn out that – though on the whole his ideas seem quite sensible – they need to be appreciably amended. In this way we shall gradually approach the correct view – or, to put it more modestly, the one that I propose as the correct one.
Even if I should be right in this, I do not know whether my way of approach is really the best and simplest. But, in short, it was mine. The ‘naïve physicist’ was myself. And I could not find any better or clearer way towards the goal than my own crooked one.
WHY ARE THE ATOMS SO SMALL?
A good method of developing ‘the naïve physicist’s ideas’ is to start from the odd, almost ludicrous, question: Why are atoms so small? To begin with, they are very small indeed. Every little piece of matter handled in everyday life contains an enormous number of them. Many examples have been devised to bring this fact home to an audience, none of them more impressive than the one used by Lord Kelvin: Suppose that you could mark the molecules in a glass of water; then pour the contents of the glass into the ocean and stir the latter thoroughly so as to distribute the marked molecules uniformly throughout the seven seas; if then you took a glass of water anywhere out of the ocean, you would find in it about a hundred of your marked molecules.3