quarta-feira, 16 de outubro de 2013

Is the External World Real? by Max Planck

WE are living in a very singular moment of history. It is a moment of crisis, in the literal sense of that word. In every branch, of our spiritual and material civilization we seem to have arrived at a critical turning-point. This spirit shows itself not only in the actual state of public affairs but also in the general attitude towards fundamental values in per­sonal and social life.

Many people say that these symptoms mark the be­ginnings of a great renaissance, but there are others who see in them the tidings of a downfall to which our civilization is fatally destined. Formerly it was only religion, especially in its doctrinal and moral systems, that was the object of skeptical attack. Then the iconoclast began to shatter the ideals and principles that had hitherto been accepted in the province of art. Now he has invaded the temple of science. There is scarcely a scientific axiom that is not nowadays denied by somebody. And at the same time almost any non­sensical theory that may be put forward in the name of science would be almost sure to find believers and disciples somewhere or other.

In the midst of this confusion it is natural to ask whether there is any rock of truth left on which we can take our stand and feel sure that it is unassailable and that it will hold firm against the storm of skepticism raging around it. Science, in general, presents us with the spectacle of a marvelous theoretical structure which is one of the proudest achievements of constructive reasoning. The logical coherence of the scientific struc­ture was hitherto the object of unstinted admiration on the part of those who criticized the fundamentals of art and religion. But this logical quality will not avail us now against the skeptics’ attack. Logic in its purest form, which is mathematics, only coordinates and ar­ticulates one truth with another. It gives harmony to the superstructure of science; but it cannot provide the foundation or the building-stones.

Where shall we look for a firm foundation upon which our outlook on nature and the world in general can be scientifically based? The moment this question is asked the mind turns immediately to the most exact of our natural sciences, namely, Physics. But even physical science has not escaped the contagion of this critical moment of history. It is not merely that the claim to reliability put forward by physical science is questioned from the outside; but even within the province of this science itself the spirit of confusion and contradiction has begun to be active. And this spirit is remarkably noticeable in regard to questions that affect the very fundamental problem of how far and in what way the human mind is capable of coming to a knowledge of external reality. To take one instance: Hitherto the principle of causality was universally accepted as an indispensable postulate of scientific re­search, but now we are told by some physicists that it must be thrown overboard. The fact that such an extraordinary opinion should be expressed in respon­sible scientific quarters is widely taken to be significant of the all-round unreliability of human knowledge. This indeed is a very serious situation, and for that reason I feel, as a physicist, that I ought to put forward my own views on the situation in which physical science now finds itself. Perhaps what I shall have to say may throw some light on other fields of human activity which the cloud of skepticism has also darkened.

Let us get down to bedrock facts. The beginning of every act of knowing, and therefore the starting- point of every science, must be in our own personal experiences. I am using the word, experience, here in its technical philosophical connotation, namely, our direct sensory perception of outside things. These are the immediate data of the act of knowing. They form the first and most real hook on which we fasten the thought-chain of science; because the material that fur­nishes, as it were, the building-stones of science is received either directly through our own perception of outer things or indirectly, through the information of others, that is to say from former researchers and teachers and publications and so on. There are no other sources of scientific knowledge. In physical science we have to deal specially and exclusively with that material which is the result of observing natural phenomena through the medium of our senses, with of course the help of measuring instruments such as telescopes, oscillators and so on. The reactions thus registered in observing external nature are collated and schematized on the basis of repeated observations and calculations. This subject-matter of our scientific constructions, being the immediate reactions of what we see, hear, feel, and touch, forms immediate data and indisputable reality. If physical science could dis­charge its function by merely concatenating these data and reporting them, then nobody could question the reliability of its foundations.

But the problem is: Does this foundation fully meet the needs of physical science? If we may say that it is the business of physical science, solely and exclu­sively, in the most accurate and most simple way, to describe the order observed in studying various natural phenomena, then is the task of physical science ade­quately and exhaustively fulfilled? There is a certain school of philosophers and physicists who hold that this and this alone forms the scope of physical science. Many outstanding physicists have been induced to ac­cept this view because of the general confusion and insecurity that arises from the skeptical spirit of the times. They feel that here at any rate is a foundation that is impregnable. The school which puts forward this view is generally called the Positivist School; and in all that I have to say here I shall take the word Positivism in that sense. Since the time of Auguste Comte, the founder of Positivism, many meanings have been given to the word. Therefore I think it well to declare here at the outset that I am restricting its application to the definite meaning which I have already indicated. This happens also to be the meaning in which the word, Positivism, is most generally used.

Now let us ask, is the foundation which Positivism offers broad enough to support the whole structure of physical science? The best test that can be applied in finding an answer to this question is to ask where Posi­tivism would lead if we once were to accept it as offering the sole groundwork of physical science.

Suppose for the moment that we are positivists. And let us take the trouble to control ourselves so that we shall hold strictly to its logical implications and not allow commonplaces and considerations of sentiment to lure us from the logical train of positivist thought. Let us here and now decide that no matter what singular consequences we may encounter in deal­ing with the positivist line of thought we shall stick steadfastly to it. And we shall be sure that in doing so we cannot be faced with logical contradictions di­rectly emerging from the field of observation; because obviously two actually observed facts in nature can­not be in logical contradiction to one another. On the other hand as long as we remain positivists we must deal with every kind of experience and ignore no source of human knowledge whatsoever. Therein lies the strength of the positivist theory. As long as physi­cal science sticks to the positivist rule it occupies itself with all the problems that can be answered through direct observation. Every problem that has a meaning of definite importance comes within the ambit of physical science under the positivist rule. If we are to content ourselves with a direct observation of natu­ral phenomena and the recording of them, we shall obviously have no fundamental riddles to solve nor any obscure questions. Everything will lie in the open daylight. Thus far the state of affairs looks quite simple. But it is no simple matter at all to carry out the principle when we begin to deal with individual cases. Our daily habits of speech make it rather diffi­cult for us to observe the strict positivist rule. In ordi­nary life when we speak of an outer object—a table, for instance—we mean something that is different from the table as actually observed by physical science. We can see the table and we can touch it and we can try its firmness by leaning on it and its hardness and if we give it a thump with our knuckles we shall feel a hurt. In the light of positivist science the table is nothing more than a complex of these sensory perceptions and we have merely got into the habit of associating them with the word table.

Remove these sensory perceptions and absolutely nothing remains. In the positivist theory we must entirely ignore everything beyond what is registered by the senses and therefore we are impreg­nable in this clearly defined realm. For the positivist, to ask what a table in reality is has no meaning what­soever; and this is so with our other physical concepts. The whole world around us is nothing but an analogue of experiences we have received. To speak of this world as existing independently of these experiences is to make a statement that has no meaning. If a problem dealing with the external world does not admit of being referred immediately to some kind of sensory experi­ence and does not allow of being placed under observa­tion, then it has no meaning and must be ruled out. Therefore within the scope of the positivist system there is no place for any kind of metaphysics. If we glance upwards at the star-strewn firmament we see innumerable points or patines of light which move in a more or less regular way through the heavens. We can measure the intensity and the color of their rays. According to the positivist theory, these measurements are not merely the raw material of astronomy and astrophysics, but they are the sole and exclusive sub­ject-matter of these sciences. Beyond merely recording these measurements, astronomy and astrophysics have nothing more to say. If they draw any inferences from the measurements, these inferences cannot be con­sidered as legitimate science. That is the positivist standpoint. The mental constructions that we make in collating and selecting and systematizing the measure­ment data, and the theories which we advance to explain why they should be so and not otherwise, are an un­warranted human intrusion on the scene. They are mere arbitrary inventions of human reason. They may be convenient, just as the habit of thinking in similes is a convenient help to the mind, but we have no right to put them forward as representing anything that really happens in nature.

All we know is the bare result of the sensory meas­urements and we have no right to attach an ulterior significance to these.

Supposing we say, with Ptolemy, that the earth is the fixed center of the universe and that the sun and all the stars move around it; or supposing we say, with Copernicus, that the earth is a small particle of matter which is relatively insignificant in relation to the whole universe, turning on its axis once every twenty-four hours and revolving around the sun once in every twelve months—on the positivist principle the one theory is as good as the other, when con­sidered from the scientific viewpoint. They are merely two different ways of making a mental construction out of sensory reactions to some outer phenomena; but they have no more right to be looked upon as scientifically significant than the mental construction which the mystic or poet may make out of his sensory impressions when face to face with nature. It is true that the Copemican theory of astronomy is more widely accepted; but that is because it is a simpler way of formulating a synthesis of sensory observations and it does not give rise to so many difficulties about astronomical laws as would arise from the acceptance of the Ptolemaic theory. Therefore Copernicus is not to be judged as a pioneer discoverer in the realms of science, no more than a poet is to be judged as a pioneer discoverer when he gives fanciful and attractive expression to sentiments that are known to every human breast. Copernicus discovered nothing. He only formulated, in the shape of a fanciful mental construc­tion, a mass of facts that were already known. He did not add anything to the store of scientific knowledge already in existence. A tremendous mental revolution was caused by his theory and bitter battles were waged around it. For the logical consequence of it was to give an entirely different account of man’s place in the universe from that generally held at the time by the religion and philosophy of Europe. But for the positivist scientist all the fuss and trouble made over the Copernican theory were quite as senseless, from the scientific point of view, as if one were to quarrel with the rapture of a contemplative who gazes on the Milky Way and ponders over the fact that each star in that Milky Way is a sun somewhat like ours and that each spiral nebula is again a Milky Way from which the light has taken many millions of years to reach our earth, while the earth itself, with its human race on it, sinks away into an insignificant speck which is hardly discernible in the boundless space.

Incidentally we must remind ourselves that to look at nature in this way is to look at it from the sesthetic and ethical standpoints. These, of course, have no direct relation to physical science. Therefore they are excluded. But in excluding them there is a fundamental difference between the attitude of the non-positivist and that of the positivist physicist. The ordinary scientist, who does not believe in the positivist attitude, admits the validity of the sesthetic standpoint and the ethical standpoint; but he recognizes these as belonging to another way of looking at nature. Such a way does not come within the province of physical science. On the other hand, the positivist does not admit any such values as real at all, even in other provinces than physical science. For him a beautiful sunset is merely a sequence of sensory impressions. Therefore, as I said at the beginning, as long as we logically pursue the positivist teaching we must exclude every influence of a sentimental, sesthetic or ethical character from our minds. We have to keep to the logical track. That is the indispensable guarantee of certainty which the positivist teaching has to offer. And here I may remind the reader once again that we are examining a system which has been put forward with the very laudable motive of furnishing a sure basis for the reliability of science. Therefore the whole position must be dis­cussed entirely objectively and free from any polemical feeling.

In the positivist way of looking at nature sensory impressions are the primary data and therefore signify immediate reality. From this it follows that in principle it would be a mistake to speak of the senses themselves being deceived. What under certain circumstances can be deceptive are not the sensory impressions themselves but the conclusions we so often draw from them. If we plunge a straight stick into water and hold it slant­wise, and notice the apparent bend at the point of im­mersion, we are not deceived by the sense of sight into thinking that the stick is thereby bent. There is an actual bending present as an optical perception; but that is quite a different thing from concluding that the stick itself is bent. The positivist will not allow us to conclude anything. We have a sensory impression of the part of the stick that is in water and a contiguous sensory impression of the part that is in air; but we have no right to say anything about the stick itself. The most that the positivist principle will allow us to say is that the stick looks “as if” it were bent. If we explain the whole phenomenon by saying that the light rays which are reflected in the air from the stick to the eye pass through a less dense medium than that through which the rays pass when reflected from the part of the stick immersed in water, and that therefore the latter are more strongly deflected, that way of stating the case is useful from many points of view but it is no closer to reality than to say that the senses perceive the stick “as if” it were bent.

The essential point here is that, from the standpoint of Positivism, both ways of stating the case are funda­mentally of equal validity. And there would be no sense in attempting to judge their rival validities by asking how far one is more appropriate than the other, by appealing to the sense of touch to rectify the ap­parent anomaly of a stick which was straight in air being bent in water. In the positivist system there would be no meaning in a decision one way or another; be­cause a strictly logical positivist science would have to be content with merely noting the sensory impressions and leaving the matter at that. We could say that the stick looks “as if” it were bent. In practice, of course, anything like a serious attempt at an all-round appli­cation of this “as if” theory would lead to ridiculous consequences. But here we are not testing the positivist theory by any such grounds. We are considering it on its own chosen ground of logical consistency, which is its bedrock foundation. It must stand or fall by the consequences that would result for physical science by the logical application of the positivist premises.

What I have said here in regard to the stick applies equally to all the surrounding objects of inanimate nature. In the positivist view a tree is nothing more than a complex of sense-impressions. We can see it grow. We can hear the rustle of its leaves and inhale the perfumes of . its blossoms. But if we take away all these sensory impressions then nothing remains to cor­respond to whait may be called the “tree in itself.”

What holds good for the world of plant life must also have meaning for the animal world. We speak of this world as a special and independent realm of being, but that is solely because it is a convenient way of thinking and talking. If we tread on a worm it squirms. That we can see. But there would be no sense in asking if the worm suffers pain thereby. For a man can feel only his own pain and he cannot with any certainty of knowledge extend that same feeling to the animal world. To say that an animal suffers pain is an assumption based on a summary of various char­acteristics that correspond to what happens in our own case under similar circumstances. In the case of a worm we notice a squirming or shrugging. In the case of other animals we notice contortions of the face and body. These are analogous to what happens in our case under like conditions. And there are certain cries in the animal world which are analogous to the sounds we utter when we suffer pain.

When we come from the animal world to the world of human beings we find the positivist scientists making a clear distinction between one’s own impressions and the impressions of others. One’s own impressions are the sole reality and they are realities only for oneself. The impressions of another person are only indirectly knowable to us. As objects of knowledge they signify something fundamentally different from our own im­pressions. Therefore in speaking of them we are merely following the same sort of useful analogy as when we speak of the suffering of animals. But, in the strict positivist view, we have no reliable knowledge what­soever of other people’s impressions. Because they are not a direct sensory perception, they do not furnish a basis for the certainty of our knowledge.

It is quite clear that the positivist outlook cannot be accused of logical inconsistency. So long as we stick closely to its principles we do not find ourselves up against any contradiction. That is the strong point of the whole system. But when we come to apply it as the exclusive foundation on which scientific research can be carried on we shall find that the result would be of very significant import for physical science. If the scope of physical science extends no further than the mere description of sensory experiences, then strictly only one’s own experiences can be taken as the object of such description; because only one’s own experiences are primary data. Now it is clear that on the basis of a mere individual complex of experience not even the most gifted of men could construct anything like a comprehensive scientific system. So we are faced with the alternative of either renouncing the idea of a com­prehensive science, which will hardly be agreed to even by the most extreme positivist, or to admit a compro­mise and allow the experiences of others to enter into the groundwork of scientific knowledge. But we should thereby, strictly speaking, give up our original stand­point, namely, that only primary data constituted a reliable basis of scientific truth. The sensory impressions of others are secondary and they are data for us only through the reports we have of them. This brings a new factor into play here, namely, the trustworthiness of oral and written information in scientific reports. Therewith we break at least one link of the logical chain which holds the positivist system together; for the foundational principle of the system is that only imme­diate perception can be considered as offering material for scientific certainty.

Let us, however, pass over this difficulty and let us assume that all reports furnished by scientific research­ers are reliable or at least that we have an infallible means of excluding those which are unreliable. In this case it is obvious that the reports furnished by the numerous scientists who were and are acknowledged as honorable and reliable both in the past and to-day must be taken into scientific consideration} and there are no grounds whereon some should be excluded in favor of others. It would be quite wrong to devaluate the claims of any investigators on the grounds that his findings have not been corroborated by others.

If we should stick to this idea then it would be diffi­cult to explain or to justify the conduct of physical science in regard to certain individual researchers. Let us take one instance as illustrative.

The so-called N-rays which were discovered by the French physicist, Blondlot, in the year 1903, and at that time studied on all sides, are to-day entirely ignored. Rene Blondlot, who was professor at the Uni­versity of Nancy, was admittedly an excellent and reliable investigator. His discovery was for him an ex­perience as great as that of any other physicist. We cannot say that he was fooled by his sense-perceptions; for in positivist physics, as we have seen, there is no such thing as delusion in sensuous perception. It would be only proper and right to look upon the N-rays as primary reality-data, something that directly struck the perception of one man. And if since the time of Blond­lot and his school no man throughout all the years between has succeeded in reproducing them, that is no reason for saying—at least from the positivist stand­point—that they will not one day, under some special circumstances, yet again become discernible.

Under the positivist test we should have to agree that the number of those researchers whose findings are of value for physical science is indeed very small. We should have to admit only those who devote themselves specially to this science, because the discoveries which outsiders have made in this field are more or less insignificant. Moreover, we must from the outset ex­clude all theoretical physicists; for their experiences are restricted essentially to the use of pen, ink, and paper and abstract reasoning. And thus we have only the experimental physicists remaining, and in the first line only those who confine themselves to the operation of extremely sensitive instruments for special investi­gation. Therefore in the positivist hypothesis only a small roll of specially qualified physicists come into the picture when we speak of the contributions of those who have devoted themselves to the progress of physical science.

From this standpoint how are we to explain the extraordinary impression made and the revolution which was created in the world of international science by the findings, for instance, of Oersted, who detected the influence of a galvanic current on the compass . needle, or of Faraday, who first discovered the effect of electromagnetic induction, or of Hertz, who discov­ered small electric sparks in the focus of his parabolic reflector by the use of the magnifying glass? How and why did these individual sensory impressions create such a furore and lead to such a world revolution in the theory and application of scientific methods? To this question the upholders of positivism can give only a roundabout and entirely unsatisfactory answer. They have to fall back upon the theory that these individual experiences, which were insignificant in themselves, merely opened up a viewpoint as a result of which other researchers were led to the discovery of a series of much greater and more portentous results. That is a rather lame answer but it illustrates very well the positivist position, because the upholder of positivism will admit nothing except a bald description of results experienced in research j and if we ask why it is that certain findings of a few obscure individuals, carried out under quite primitive conditions, had such an im­mediate and world-wide significance for all other physicists—that question has no meaning for physical science as viewed from the positivist standpoint

The reason for taking up this striking attitude is quite easy to understand. Those who lean towards the discipline that I have been describing deny the idea and the necessity of an objective physical science which is independent of the actually experiencing and sense- perceiving investigator. They cling to this attitude be­cause they are bound logically to acknowledge no other reality save that of the factual experience of the indi­vidual physicist. Now I think it is obvious here that if physical science as such were to accept this position, as the exclusive basis of its research, then it would find itself trying to support a huge structure on a very inadequate foundation. A science that starts off by pre­dicting the denial of objectivity has already passed sentence on itself. Of what value to the world are the sensory impressions of a mere individual? Yet that is the foundation to which in the last analysis physical science is reduced in looking for a basis for its struc­ture. This plot is entirely too small for such a building. It has to be extended by the addition of other ground. No science can rest its foundation on the dependability of single human individuals. And the moment we have made that statement we have taken a step which puts us off the logical pathway of the positivist system. We have followed the call of common sense. We have taken a jump into the metaphysical realm; because we have accepted the hypothesis that sensory perceptions do not of themselves create the physical world around us, but rather that they bring news of another world which lies outside of ours and is entirely independent of us.

And thus we strike out the positivist als-ob (As-If) and attribute a higher kind of reality than that of mere description of immediate sensory impressions to the practical discoveries that have been already mentioned —Faraday’s, etc. Once we take this step we lift the goal of physical science to a higher level. It is not restricted to the mere description of bare facts of ex­perimental discovery; but it aims at furnishing an ever increasing knowledge of the real outer world around us.

At this point a new epistemological (1) difficulty enters. The basic principle of the positivist theory is that there is no other source of knowledge except within the re­stricted range of perception through the senses. Now there are two theorems that form together the cardinal hinge on which the whole structure of physical science turns. These theorems are: (I) There is a real outer world which exists independently of our act of know­ing, and, (2) The real outer world is not directly knowable. To a certain degree these two statements are mutually contradictory. And this fact discloses the presence of an irrational or mystic element which ad­heres to physical science as to every other branch of human knowledge. The knowable realities of nature cannot be exhaustively discovered by any branch of science. This means that science is never in a position completely and exhaustively to explain the problems it has to face. We see in all modern scientific advances that the solution of one problem only unveils the mys­tery of another. Each hilltop that we reach discloses to us another hilltop beyond. We must accept this as a hard and fast irrefutable fact. And we cannot remove this fact by trying to fall back upon a basis which would restrict the scope of science from the very start merely to the description of sensory experiences. The aim of science is something more. It is an incessant struggle towards a goal which can never be reached. Because the goal is of its very nature unattainable. It is some­thing that is essentially metaphysical and as such is always again and again beyond each achievement.

But if physical science is never to come to an ex­haustive knowledge of its object, then does not this seem like reducing all science to a meaningless activity? Not at all. For it is just this striving forward that brings us to the fruits which are always falling into our hands and which are the unfailing sign that we are on the right road and that we are ever and ever drawing nearer to our journey’s end. But that journey’s end will never be reached, because it is always the still far thing that glimmers in the distance and is unattain­able. It is not the possession of truth, but the success which attends the seeking after it, that enriches the seeker and brings happiness to him. This is an acknowl­edgment made long ago by thinkers of deepest insight, even before Lessing gave it the classic stamp of his famous phrase.

1. Epistemology is the Science of the Nature of Knowledge.

In: Where is science going? The universe in the light of modern physics. New York, 1932, pp. 64-83.

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