What Is Life (Canto Classics)

by Erwin Schrodinger

  The chief characteristics of sound perception are well understood in the mechanism of the ear, of which we have better and safer knowledge than of the chemistry of the retina. The principal organ is the cochlea, a coiled bony tube which resembles the shell of a certain type of sea-snail: a tiny winding staircase that gets narrower and narrower as it ‘ascends’. In place of the steps (to continue our simile), across the winding staircase elastic fibres are stretched, forming a membrane, the width of the membrane (or the length of the individual fibre) diminishing from the ‘bottom’ to the ‘top’. Thus, like the strings of a harp or a piano, the fibres of different length respond mechanically to oscillations of different frequency. To a definite frequency a definite small area of the membrane – not just one fibre – responds, to a higher frequency another area, where the fibres are shorter. A mechanical vibration of definite frequency must set up, in each of that group of nerve fibres, the well-known nerve impulses that are propagated to certain regions of the cerebral cortex. We have the general knowledge that the process of conduction is very much the same in all nerves and changes only with the intensity of excitation; the latter affects the frequency of the pulses, which, of course, must not be confused with the frequency of sound in our case (the two have nothing to do with each other).

  The picture is not as simple as we might wish it to be. Had a physicist constructed the ear, with a view to procuring for its owner the incredibly fine discrimination of pitch and timbre that he actually possesses, the physicist would have constructed it differently. But perhaps he would have come back to it. It would be simpler and nicer if we could say that every single ‘string’ across the cochlea answers only to one sharply defined frequency of the incoming vibration. This is not so. But why is it not so? Because the vibrations of these ‘strings’ are strongly damped. This, of necessity, broadens their range of resonance. Our physicist might have constructed them with as little damping as he could manage. But this would have the terrible consequence that the perception of a sound would not cease almost immediately when the producing wave ceases; it would last for some time, until the poorly damped resonator in the cochlea died down. The discrimination of pitch would be obtained by sacrificing the discrimination in time between subsequent sounds. It is puzzling how the actual mechanism manages to reconcile both in a most consummate fashion.

  I have gone into some detail here, in order to make you feel that neither the physicist’s description, nor that of the physiologist, contains any trait of the sensation of sound. Any description of this kind is bound to end with a sentence like: those nerve impulses are conducted to a certain portion of the brain, where they are registered as a sequence of sounds. We can follow the pressure changes in the air as they produce vibrations of the ear-drum, we can see how its motion is transferred by a chain of tiny bones to another membrane and eventually to parts of the membrane inside the cochlea, composed of fibres of varying length, described above. We may reach an understanding of how such a vibrating fibre sets up an electrical and chemical process of conduction in the nervous fibre with which it is in touch. We may follow this conduction to the cerebral cortex and we may even obtain some objective knowledge of some of the things that happen there. But nowhere shall we hit on this ‘registering as sound’, which simply is not contained in our scientific picture, but is only in the mind of the person whose ear and brain we are speaking of.

  We could discuss in similar manner the sensations of touch, of hot and cold, of smell and of taste. The latter two, the chemical senses as they are sometimes called (smell affording an examination of gaseous stuffs, taste that of fluids), have this in common with the visual sensation, that to an infinite number of possible stimuli they respond with a restricted manifold of sensate qualities, in the case of taste: bitter, sweet, sour and salty and their peculiar mixtures. Smell is, I believe, more various than taste, and particularly in certain animals it is much more refined than in man. What objective features of a physical or chemical stimulus modify the sensation noticeably seems to vary greatly in the animal kingdom. Bees, for instance, have a colour vision reaching well into the ultraviolet; they are true trichromates (not dichromates, as they seemed in earlier experiments which paid no attention to the ultra-violet). It is of very particular interest that bees, as von Frisch in Munich found out not long ago, are peculiarly sensitive to traces of polarization of light; this aids their orientation with respect to the sun in a puzzlingly elaborate way. To a human being even completely polarized light is indistinguishable from ordinary, non-polarized light. Bats have been discovered to be sensible to extremely high frequency vibrations (‘ultra-sound’) far beyond the upper limit of human audition; they produce it themselves, using it as a sort of ‘radar’, to avoid obstacles. The human sense of hot or cold exhibits the queer feature of ‘les extrêmes se touchent’: if we inadvertently touch a very cold object, we may for a moment believe that it is hot and has burnt our fingers.

  Some twenty or thirty years ago chemists in the U.S.A. discovered a curious compound, of which I have forgotten the chemical name, a white powder, that is tasteless to some persons, but intensely bitter to others. This fact has aroused keen interest and has been widely investigated since. The quality of being a ‘taster’ (for this particular substance) is inherent in the individual, irrespective of any other conditions. Moreover, it is inherited according to the Mendel laws in a way familiar from the inheritance of blood group characteristics. Just as with the latter, there appears to be no conceivable advantage or disadvantage implied by your being a ‘taster’ or a ‘non-taster’. One of the two ‘alleles’ is dominant in heterozygotes, I believe it is that of the taster. It seems to me very improbable that this substance, discovered haphazardly, should be unique. Very probably ‘tastes differ’ in quite a general way, and in a very real sense!

  Let us now return to the case of light and probe a little deeper into the way it is produced and into the fashion in which the physicist makes out its objective characteristics. I suppose that by now it is common knowledge that light is usually produced by electrons, in particular by those in an atom where they ‘do something’ around the nucleus. An electron is neither red nor blue nor any other colour; the same holds for the proton, the nucleus of the hydrogen atom. But the union of the two in the atom of hydrogen, according to the physicist, produces electro-magnetic radiation of a certain discrete array of wave-lengths. The homogeneous constituents of this radiation, when separated by a prism or an optical grating, stimulate in an observer the sensations of red, green, blue, violet by the intermediary of certain physiological processes, whose general character is sufficiently well known to assert that they are not red or green or blue, in fact that the nervous elements in question display no colour in virtue of their being stimulated; the white or grey the nerve cells exhibit whether stimulated or not is certainly insignificant in respect of the colour sensation which, in the individual whose nerves they are, accompanies their excitation.

  Yet our knowledge of the radiation of the hydrogen atom and of the objective, physical properties of this radiation originated from someone’s observing those coloured spectral lines in certain positions within the spectrum obtained from glowing hydrogen vapour. This procured the first knowledge, but by no means the complete knowledge. To achieve it, the elimination of the sensates has to set in at once, and is worth pursuing in this characteristic example. The colour in itself tells you nothing about the wave-length; in fact we have seen before that, for example, a yellow spectral line might conceivably be not ‘monochromatic’ in the physicist’s sense, but composed of many different wave-lengths, if we did not know that the construction of our spectroscope excludes this. It gathers light of a definite wave-length at a definite position in the spectrum. The light appearing there has always exactly the same colour from whatever source it stems. Even so the quality of the colour sensation gives no direct clue whatsoever to infer the physical property, the wave-length, and that quite apart from the comparative poorness of our discrim
ination of hues, which would not satisfy the physicist. A priori the sensation of blue might conceivably be stimulated by long waves and that of red by short waves, instead of the other way round, as it is.

  To complete our knowledge of the physical properties of the light coming from any source a special kind of spectroscope has to be used; the decomposition is achieved by a diffraction grating. A prism would not do, because you do not know beforehand the angles under which it refracts the different wave-lengths. They are different for prisms of different material. In fact, a priori, with a prism you could not even tell that the more strongly deviated radiation is of shorter wave-length, as is actually the case.

  The theory of the diffraction grating is much simpler than that of a prism. From the basic physical assumption about light – merely that it is a wave phenomenon – you can, if you have measured the number of the equidistant furrows of the grating per inch (usually of the order of many thousands), tell the exact angle of deviation for a given wave-length, and therefore, inversely, you can infer the wave-length from the ‘grating constant’ and the angle of deviation. In some cases (notably in the Zeeman and Stark effects) some of the spectral lines are polarized. To complete the physical description in this respect, in which the human eye is entirely insensitive, you put a polarizer (a Nicol prism) in the path of the beam, before decomposing it; on slowly rotating the Nicol around its axis certain lines are extinguished or reduced to minimal brightness for certain orientations of the Nicol, which indicate the direction (orthogonal to the beam) of their total or partial polarization.

  Once this whole technique is developed, it can be extended far beyond the visible region. The spectral lines of glowing vapours are by no means restricted to the visible region, which is not distinguished physically. The lines form long, theoretically infinite series. The wave-lengths of each series are connected by a relatively simple mathematical law, peculiar to it, that holds uniformly throughout the series with no distinction of that part of the series that happens to lie in the visible region. These serial laws were first found empirically, but are now understood theoretically. Naturally, outside the visible region a photographic plate has to replace the eye. The wave-lengths are inferred from pure measurements of lengths: first, once and for all, of the grating constant, that is the distance between neighbouring furrows (the reciprocal of the number of furrows per unit length), then by measuring the positions of the lines on the photographic plate, from which, together with the known dimensions of the apparatus, the angles of deviation can be computed.

  These are well-known things, but I wish to stress two points of general importance, which apply to well-nigh every physical measurement.

  The state of affairs on which I have enlarged here at some length is often described by saying that, as the technique of measuring is refined, the observer is gradually replaced by more and more elaborate apparatus. Now this is, certainly in the present case, not true; he is not gradually replaced, but is so from the outset. I tried to explain that the observer’s colourful impression of the phenomenon vouchsafes not the slightest clue to its physical nature. The device of ruling a grating and measuring certain lengths and angles has to be introduced, before even the roughest qualitative knowledge of what we call the objective physical nature of the light and of its physical components can be obtained. And this is the relevant step. That the device is later on gradually refined, while remaining essentially always the same, is epistemologically unimportant, however great the improvement achieved.

  The second point is that the observer is never entirely replaced by instruments; for if he were, he could obviously obtain no knowledge whatsoever. He must have constructed the instrument and, either while constructing it or after, he must have made careful measurements of its dimensions and checks on its moving parts (say a supporting arm turning around a conical pin and sliding along a circular scale of angles) in order to ascertain that the movement is exactly the intended one. True, for some of these measurements and check-ups the physicist will depend on the factory that has produced and delivered the instrument; still all this information goes back ultimately to the sense perceptions of some living person or persons, however many ingenious devices may have been used to facilitate the labour. Finally the observer must, in using the instrument for his investigation, take readings on it, be they direct readings of angles or of distances, measured under the microscope, or between spectral lines recorded on a photographic plate. Many helpful devices can facilitate this work, for instance photometric recording across the plate of its transparency, which yields a magnified diagram on which the positions of the lines can be easily read. But they must be read! The observer’s senses have to step in eventually. The most careful record, when not inspected, tells us nothing.

  So we come back to this strange state of affairs. While the direct sensual perception of the phenomenon tells us nothing as to its objective physical nature (or what we usually call so) and has to be discarded from the outset as a source of information, yet the theoretical picture we obtain eventually rests entirely on a complicated array of various informations, all obtained by direct sensual perception. It resides upon them, it is pieced together from them, yet it cannot really be said to contain them. In using the picture we usually forget about them, except in the quite general way that we know our idea of a light-wave is not a haphazard invention of a crank but is based on experiment.

  I was surprised when I discovered for myself that this state of affairs was clearly understood by the great Democritus in the fifth century B.C., who had no knowledge of any physical measuring devices remotely comparable to those I have been telling you about (which are of the simplest used in our time).

  Galenus has preserved us a fragment (Diels, fr. 125), in which Democritus introduces the intellect () having an argument with the senses () about what is ‘real’. The former says: ‘Ostensibly there is colour, ostensibly sweetness, ostensibly bitterness, actually only atoms and the void’, to which the senses retort: ‘Poor intellect, do you hope to defeat us while from us you borrow your evidence? Your victory is your defeat.’

  In this chapter I have tried by simple examples, taken from the humblest of sciences, namely physics, to contrast the two general facts (a) that all scientific knowledge is based on sense perception, and (b) that none the less the scientific views of natural processes formed in this way lack all sensual qualities and therefore cannot account for the latter. Let me conclude with a general remark.

  Scientific theories serve to facilitate the survey of our observations and experimental findings. Every scientist knows how difficult it is to remember a moderately extended group of facts, before at least some primitive theoretical picture about them has been shaped. It is therefore small wonder, and by no means to be blamed on the authors of original papers or of text-books, that after a reasonably coherent theory has been formed, they do not describe the bare facts they have found or wish to convey to the reader, but clothe them in the terminology of that theory or theories. This procedure, while very useful for our remembering the facts in a well-ordered pattern, tends to obliterate the distinction between the actual observations and the theory arisen from them. And since the former always are of some sensual quality, theories are easily thought to account for sensual qualities; which, of course, they never do.

  AUTOBIOGRAPHICAL SKETCHES

  I lived far apart from my best friend, actually the only close friend I ever had, for the greater part of my life. (Maybe that is why I have often been accused of flirtatiousness instead of true friendship.) He studied biology (botany to be exact); I physics. And many a night we would stroll back and forth between Gluckgasse and Schlüsselgasse engrossed in philosophical conversation. Little did we know then that what seemed original to us had occupied great minds for centuries already. Don’t teachers always do their best to avoid these topics for fear that they might conflict with religious doctrines and cause uncomfortable questions? This is the main reason for my turning against religion, which has n
ever done me any harm.

  I am not sure whether it was right after the First World War or during the time I spent in Zurich (1921–7) or even later in Berlin (1927–33) that Fränzel and I spent a long evening together again. The small hours of the morning found us still talking in a café on the outskirts of Vienna. He seemed to have changed a lot with the years. After all, our letters had been few and far between and of very little substance.

  I might have added earlier that we also spent our time together reading Richard Semon. Never before or after did I read a serious book with anyone else. Richard Semon was soon banned by the biologists, since his views, as they saw them, were based on the inheritance of acquired characteristics. So his name was forgotten. Many years later I encountered him in a book (Human Knowledge?) by Bertrand Russell, who devoted a thorough study to this genial biologist, stressing the significance of his Mneme theory.

  Fränzel and I did not see each other again until 1956. This time it was a very brief encounter in our flat in Vienna, Pasteurgasse 4, while others were present, so that those fifteen minutes are hardly worth mentioning. Fränzel and his wife lived across the border, our northern one, unhampered by the authorities, it seemed; nevertheless, leaving the country had become rather difficult. We never met again: two years later he died very suddenly.