What-is-life-(生命是什么)-by-薛定谔

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1、WHAT IS LIFE?ERWIN SCHRODINGERFirst published 1944What 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 ParentsPrefaceA scientist is supposed to

2、 have a complete and thorough I of knowledge, at first hand, of some subjects and, therefore, is usually expected not to write on any topic of which he is not a life, 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 th

3、e 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 to and throughout many centuries the universal aspect

4、has been the only one to be given full credit. But the spread, both in and width and depth, of the multifarious branches of knowledge by 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 t

5、ogether 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 who aim be lost for ever) than that some of us

6、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 notnegligible. One's native speech is a closely fitting garment,

7、 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

8、 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 o

9、riginally intended to be marginal summaries, and the text of every chapter should be read in continuo. E.S.Dublin September 1944Homo 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

10、a free man ponders less than death; his wisdom is, to meditate not on death but on life.)CHAPTER 1The Classical Physicist's Approach to the SubjectThis little book arose from a course of public lectures, delivered by a theoretical physicist to an audience of about four hundred which did not subs

11、tantially 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 hardlybe utilized. The reason for this was not that the subject was simple enoug

12、h to be explained without mathematics, but rather that it was much too involved to be fully accessible to mathematics. Another feature which at least1induced a semblance of popularity was the lecturer's intention to make clear the fundamental idea, which hovers between biology and physics, to bo

13、th 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

14、 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 endeavor to expound and establish can be summ

15、arized 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 W DIFFERENCE IN STRUCTUREThat would be a very trivial remark if it weremeant

16、 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, isamply accounted for. Today, thanks to theingenious work of biologists, mainly ofgeneticists, during the last t

17、hirty or forty years,enough is known about the actual materialstructure of organisms and about theirfunctioning to state that, and to tell preciselywhy present-day physics and chemistry could notpossibly account for what happens in space andtime within a living organism. The arrangementsof the atoms

18、 in the most vital parts of anorganism and the interplay of these arrangementsdiffer in a fundamental way from all thosearrangements of atoms which physicists andchemists have hitherto made the object of theirexperimental and theoretical research. Yet the difference which I have just termed fundamen

19、tal 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. For it is in relation to the statistical point of view that the structure of the vital parts of living

20、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. It is well-nigh unthinkable that the laws and regularities thus discovered should happen to apply immediately to the behav

21、iour 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 therelevance of the difference in statistical structure stated in terms so abstract as I have just used. To give the statement

22、 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

23、, these are very interesting and complicated objects; they constitute one of the most fascinatingand 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 th

24、at 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 cry

25、stal one of the most complex objects of his research, I had in mind the physicist proper. Organic chemistry, indeed, in investigating more and more complicated2molecules, has come very much nearer to that 'aperiodic crystal' which, in my opinion, is the material carrier of life. And therefor

26、e 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 NAIVE PHYSICIST'S APPROACH TO THE SUBJECTAfter having thus indicated very briefly the general idea -or rather the ultimate scop

27、e -of our investigation, let me describe the line of attack. I propose to develop first what you might call 'a naive 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 statisti

28、cal 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 contribut

29、ions to the question. It will turn out that he can. The next step must be to f 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

30、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 'naive physicist' was myself. And I could not find any better

31、 or clearer way towards the goal than my own crooked one.WHY ARE THE ATOMS SO SMALL? A good method of developing 'the naive physicist's ideas' is to start from the odd, almost ludicrous, question: Why are atoms so small? Tobegin with, they are very small indeed. Every little piece of mat

32、ter 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 glassi

33、nto the ocean and stir the latter thoroughly so as to distribute the marked molecules uniformly throughout the seven seas; if then you took aglass of water anywhere out of the ocean, you would find in it about a hundred of your marked molecules. The actual sizes of atoms lie between about 1/5000 and

34、 1/2000 the wave-length of yellow light. The comparison is significant, because the wave-length roughly indicates the dimensions of the smallest grain still recognizable in the microscope. Thus it will be seen that such a grain still contains thousands of millions of atoms. Now, why are atoms so sma

35、ll? Clearly, the question is an evasion. For it is not really aimed at the size of the atoms. It is concerned with the size of organisms, more particularly with the size of our own corporeal selves. Indeed, the atom is small, when referred to our civic unit of length, say the yard or the metre. In a

36、tomic physics one is accustomed to use the so-called Angstrom (abbr. A), which is the 10lOth part of a metre, or in decimal notation 0.0000000001 metre. Atomic diameters range between 1 and 2A. Now those civic units (in relation to which the atoms are so small) are closely related to the size of our

37、 bodies. There is a story tracing the yard back to the humour of an English king whom his councillors asked what unit to adopt -and he stretched out his arm sideways and said: 'Take the distance from the middle of my chest to my fingertips, that will do all right.' True or not, the story is

38、significant for our purpose. The king would naturally I indicate a length comparable with that of his own body, knowing that anything else would be very3inconvenient. With all his predilection for the Angstrom unit, the physicist prefers to be told that his new suit will require six and a half yards

39、 of tweed -rather than sixty-five thousand millions of Angstroms of tweed. It thus being settled that our question really aims at the ratio of two lengths -that of our body and that of the atom - with an incontestable priority of independent existence on the side of the atom, the question truly read

40、s: Why must our bodies be so large compared with the atom? I can imagine that many a keen student of physics or chemistry may have deplored the fact that everyone of our sense organs, forming a more or less substantial part of our body and hence (in view of the magnitude of the said ratio) being its

41、elf composed of innumerable atoms, is much too coarse to be affected by the impact of a single atom. We cannot see or feel or hear the single atoms. Our hypotheses with regard to them differ widely from the immediate findings of our gross sense organs and cannot be put to the test of direct inspecti

42、on. Must that be so? Is there an intrinsic reason for it? Can we trace back this state of affairs to some kind of first principle, in order to ascertain and to understand why nothing else is compatible with the very laws of Nature? Now this, for once, is a problem which the physicist is able to clea

43、r up completely. The answer to all the queries is in the affirmative.THE WORKING OF AN ORGANISMREQUIRES EXACT PHYSICAL LAWS If it were not so, if we were organisms so sensitive that a single atom, or even a few atoms, could make a perceptible impression on our senses -Heavens, what would life be lik

44、e! To stress one point: an organism of that kind would most certainly not be capable of developing the kind of orderly thought which, after passing through a long sequence of earlier stages, ultimately results in forming, among many other ideas, the idea of an atom. Even though we selectthis one poi

45、nt, the following considerations would essentially apply also to the functioning of organs other than the brain and the sensorial system. Nevertheless, the one and only thing of paramount interest to us in ourselves is, that we feel and think and perceive. To the physiological process which is respo

46、nsible for thought and sense all the others play an auxiliary part, at least from the human point of view, if not from that of purely objective biology. Moreover, it will greatly facilitate our task to choose for investigation the process which is closely accompanied by subjective events, even thoug

47、h we are ignorant of the true nature of this close parallelism. Indeed, in my view, it lies outside the range of natural science and very probably of human understanding altogether. We are thus faced with the following question: Why should an organ like our brain, with the sensorial system attached

48、to it, of necessity consist of an enormous number of atoms, in order that its physically changing state should be in close and intimate correspondence with a highly developed thought? On what grounds is the latter task of the said organ incompatible with being, as a whole or in some of its periphera

49、l parts which interact directly with the environment, a mechanism sufficiently refined and sensitive to respond to and register the impact of a single atom from outside? The reason for this is, that what we call thought (1) is itself an orderly thing, and (2) can only be applied to material, i.e. to

50、 perceptions or experiences, which have a certain degree of orderliness. This has two consequences. First, a physical organization, to be in close correspondence with thought (as my brain iswith my thought) must be a very well-ordered organization, and that means that the events that happen within i

51、t must obey strict physical laws, at least to a very high degree of accuracy. Secondly, the physical impressions made upon that physically well-organized system by other bodies from outside, obviously correspond to the4perception and experience of the corresponding thought, forming its material, as

52、I have called it. Therefore, the physical interactions between our system and others must, as a rule, themselves possess a certain degree of physical orderliness, that is to say, they too must obey strict physical laws to a certain degree of accuracy.PHYSICAL LAWS REST ON ATOMIC STATISTICS AND ARE T

53、HEREFORE ONL Y APPROXIMATEAnd why could all this not be fulfilled in the case of an organism composed of a moderate number of atoms only and sensitive already to the impact of one or a few atoms only? Because we know all atoms to perform all the time a completely disorderly heat motion, which, so to

54、 speak, opposes itself to their orderly behaviour and does not allow the events that happen between a small number of atoms to enrol themselves according to any recognizable laws. Only in the co-operation of an enormously large number of atoms do statistical laws begin to operate and control the beh

55、aviour 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. All the physical and chemical laws that are known to play an important part in the life of organisms are of this statistical kind; any o

56、ther kind of lawfulness and orderliness that one might think of is being perpetually disturbed and made inoperative by the unceasing heat motion of the atoms.THEIR PRECISION IS BASED ON THE LARGE OF NUMBER OF ATOMS INTERVENINGFIRST EXAMPLE (PARAMAGNETISM)Let me try to illustrate this by a few exampl

57、es, picked somewhat at random out of thousands, and possibly not just the best ones to appeal to a reader who is learning for the first time aboutthis condition of things -a condition which in modern physics and chemistry is as fundamental as, say, the fact that organisms are composed of cells is in

58、 biology, or as Newton's Law in astronomy, or even as the series of integers, 1, 2, 3, 4, 5, .in mathematics. An entire newcomer should not expect to obtain from the following few pages a full understanding and appreciation of the subject, which is associated with the illustrious names of Ludwig

59、 Boltzmann and Willard Gibbs and treated in textbooks under the name of 'statistical thermodynamics'. If you fill an oblong quartz tube with oxygen gas and put it into a magnetic field, you find that the gas is magnetized. The magnetization is due to the fact that the oxygen molecules are li

60、ttle magnets and tend to orientate themselves parallel to the field, like a compass needle. But you must not think that they actually all turn parallel. For if you double the field, you get double the magnetization in your oxygen body, and that proportionality goes on to extremely high field strengt

61、hs, the magnetization increasing at the rate of the field you apply. This is a particularly clear example of a purely statistical law. The orientation the field tends to produce is continually counteracted by the heat motion, which works for random orientation. The effect of this striving is, actual

62、ly, only a small preference for acute over obtuse angles between the dipole axes and the field. Though the single atoms change their orientation incessantly, they produce on the average (owing to their enormous number) a constant small preponderance of orientation in the direction of the field and p

63、roportional to it. This ingenious explanation is due to the French physicist P. Langevin. It can be checked in the following way. If the observed weak magnetization is really the outcome of rival tendencies, namely, the magnetic field, which aims at combing all the molecules parallel, and the heat m

64、otion, which makes for random orientation, then it ought to be possible to5increase the magnetization by weakening theimpact of one single molecule of those whichheat motion, that is to say, by lowering thehammer their surface in perpetual impacts. Theytemperature, instead of reinforcing the field.

65、Thatare thus knocked about and can only on theis confirmed by experiment, which gives theaverage follow the influence of gravity. Thismagnetization inversely proportional to theexample shows what funny and disorderlyabsolute temperature, in quantitative agreementexperience we should have if our senses werewith theory (Curie's law). Modern equipmentsusceptible to the impac