THERE is a story, it may be fictitious, about a professor of a past generation who had a sense of dramatic effect and a rare capacity for cogent illustration. Every year at the beginning of one of his lectures he would rush into the classroom holding a pair of scissors in bis hand. With these he cut the string by which a weight was suspended. As the weight fell to the floor he exclaimed: "Gentlemen, you have just witnessed one of the great unexplained mysteries of science."

Some of the students knew at once what their professor meant, others were puzzled. These thought that there can be no mystery in an occurrence so familiar and so expected as the falling of a weight. They would only have spoken of a mystery if the weight had not fallen. Yet the professor had not called the falling of the weight only a mystery. He had called it an unexplained mystery. The professor looked from face to face humorously, a challenge in his eye. "You all think you can explain it," he said. "You want to tell me that the weight falls because it is heavy." Then he continued a little fiercely: "That is no explanation at all." Someone ventured that the weight fell because it was attracted by gravity towards the centre of the earth.

"That, too, is no explanation, that is only the cause," was the reply. "What is gravitation?" Clasping his hands behind his back under his long frock-coat and leaning forward a little, impressively, he continued: "You cannot explain gravitation. I cannot explain it. No one can explain it."

This anecdote illustrates the meaning which a physicist attaches to the word "explain". For him the word is not equivalent to a statement of cause. For others it sometimes is. A Shakespearian scholar who explains the indecision of Hamlet will show how Hamlet's complex character prevented him from pursuing the line of action which his intelligence clearly revealed to be right. Without the help of the Shakespearian scholar, Hamlet's conduct may appear to us as an inexplicable mystery. Similarly a historian will explain a war by stating the political and economic causes which led to it. A meteorologist will explain bad weather by telling us that it has been caused by a depression over Iceland. An engineer explains how a machine works by demonstrating the interaction between its moving parts. A biologist who has to explain the salivation of dogs may tell us of the chemical and physiological processes which cause the appearance of saliva.

We must not forget, however, that the biologist may use the word "explain" with quite another meaning, namely as a statement of survival value. When he proves that saliva is necessary for the dog's digestion he may say that he is "explaining" salivation. For him an unexplained mystery is a phenomenon of which the survival value cannot be perceived. The biologist might reserve this expression for the huge, cumbersome antlers of the stag. They appear to be more burden than help.

The word "explain" has really four distinct meanings. The first is psychological. We call a man's character an inexplicable mystery until we have succeeded by an effort of empathy and introspection in "understanding" him. We then realize that the man has something in common with ourselves. The second meaning is a statement of cause. The third is a statement of survival value. The fourth is the meaning used by physicists. This is the demonstration that a fact is deducible.

When the professor called the falling of the weight an unexplained mystery he did not mean that no one can understand the psychology of a thing which strives to reach the centre of the earth. Yet the suggestion that he might have meant this is not as absurd as may be thought. For physicists did apply psychological explanations to natural events until a few centuries ago. They did this when they attributed suction to nature's horror of a vacuum and planetary paths to a cosmic urge towards perfection. To the non-scientific mind such explanations must have appeared more satisfying than those found to-day. Men felt that they could understand phenomena which were explained in this way. They, too, knew what horror is and they, too, could appreciate the beautiful symmetry of a circle. There are those who feel that physics never explains anything nowadays. These will find the theory that Matter tends to fall into the form of organisms more acceptable than scientists can. Being human beings they are natural organizers and can feel kinship with Matter when informed that this is a natural organizer too.

This, however, is a digression. We must return to the falling of the weight. The professor did not use the word "explain" with its second meaning. He did not wish to imply that the cause could not be stated. Everyone knew that this was gravity. Nor did the professor mean that no one could say what good it did the weight to fall. Discussion of survival value has only a meaning when applied to living things.

What the professor did mean was that no one had succeeded in deducing gravitation from more general and fundamental laws. Gravitation appeared, in the language coined in the last chapter, as a kurma fact, and to the physicist every kurma fact is an inexplicable mystery. He is not content until he has turned it into a testi fact. This is what happened fairly recently to the laws of chemical combination. The discovery of the structure of atoms enabled these laws to be turned from kurma into testi facts. Newton did the same to the observation that apples fall. He "explained" this observation in terms of gravitation. The professor of our anecdote was impressing on his students that gravitation appeared as a kurma fact and that they must not be content to leave matters there, if they would be good scientists. He urged the class to seek to find some still more general principle from which gravitation could be deduced. He was insisting that, in physics, it does not suffice to answer questions beginning with "how". The question "why" must be answered as well.

A physicist only claims to have explained a fact when he has proved it to be the inevitable result of the operation of principles common to the whole of the Material Universe. Causality forms no part of such an explanation. A fact is not caused by the general principle which serves to explain it. The fact is implied in the principle. To the physicist explanation means not demonstration of causality but proof of deducibility.

A physicist will, for instance, hardly say that the elliptical orbits of planets are explained by the sun's attraction. He will prefer to say that the orbits are caused by the sun's attraction and explained by the Laws of Gravitation and Motion.

The physicist bases his work on belief in the universality of all laws and principles. What holds true at one place and at one time must also hold true at any other place and at any other time. In physics sauce for the goose is invariably sauce for the gander. Thus Newton refused to believe that there is one law for things that fall and another law for things that pursue their long journeys through the heavens. Discovery of atomic structure has proved that there is not one law governing the chemical behaviour of oxygen and another governing that of neon. The chemical behaviour of all substances is governed by one unifying principle and depends on the number of unit positive electric charges carried on the atomic nuclei. The General Theory of Relativity brought about a further unification. A weight resting on the table exercises a force on the table. There is also a force on the drawbar of a locomotive which is accelerating a train out of the station. At one time these two types of force seemed to be due to two distinct principles, of which one embodied the Laws of Gravitation, the other the Laws of Motion. Einstein proved that there is not one law for gravity and another for acceleration, but that both effects are the inevitable result of the geometry of space-time.

The General Theory of Relativity has done what the professor in our anecdote urged his students to attempt. It has "explained" gravitation. Were the professor alive to-day he would have to illustrate his point by a different example. It follows from what has been said in the preceding chapter that his choice would now be far more restricted than it was at one time. The number of "unexplained mysteries" confronting physics is no longer so great as it used to be.

But the choice would only be restricted so long as the examples had to be taken from the inorganic world. In the organic world the choice is practically unlimited. In biology most facts are kurma facts. These are never proved to be the inevitable result of the operation of principles common to the whole Material Universe. Causality and survival value are the only terms in which biological facts can be "explained". Though Newton disproved the theory that there is one law governing the falling of apples and another governing the motion of planets, no one has ever disproved or even tried to disprove the theory that there is one law governing the ripening of apples and another governing the motion of planets.

So any example taken from the domain of biology would have provided our professor with as good an illustration as the falling of the weight. He might have selected the salivation of dogs. Instead of cutting the string and letting the weight fall, he could have pointed to a slobbering dog and made exactly the same remark. He could have said: "Here, gentlemen, you witness one of the great unexplained mysteries of science. It is a mystery about which we know no more than we do about gravitation."

Pavlov, who made the salivation of dogs his life's study, never said this to his students. He may have thought it, but it would not occur to those biologists who claim philosophical significance for Pavlov's work. To these a thing is no mystery if both its cause and its survival value can be stated and understood. The expert on the behaviour of dogs knows what causes the salivation of the animal. This cause has received the name stimulus. The expert also knows a good deal about the chemical and physiological processes connecting stimulus with response. He has the same sort of knowledge as the professor's students had about the falling of the weight. But, unlike our professor, the biologist-philosopher is satisfied with this knowledge.

He has to be. if he were not, he would be so much obsessed by the unexplained mysteries surrounding him that he would never get any useful work done. For biologists are concerned all the while with facts which would puzzle any physicist. That an animal has teeth, that a tulip flower has three external petaloid sepals and three internal petals, that there is glucose in muscles, that a chicken hatches out of a hen's egg could all have been classed by our professor with gravitation as among the great unexplained mysteries. If the word "explain" had no other meaning than that given it by the physicist, biology would never explain anything.

The biologist proves satisfactorily that every observed fact is compatible with the laws of physics and chemistry. From this the materialist argues that an organism is governed wholly by these laws. If he omitted the word "wholly" he would be right. But to justify the insertion of this word it would be necessary to prove that biological facts are not only compatible with the laws of physics and chemistry but also that they are deducible from these laws. To be deducible, biological facts would have to be implicit in the great sweeping laws and principles of physics. It would have to be proved that, given as a basis, the Principle of Least Action, the geometry of space-time, quantum numbers, Matter would have no choice but to form "six-petalled" tulip flowers, to cause chickens to hatch out of hens' eggs, and dogs to secrete saliva on receipt of a suitable stimulus. There is not a shred of evidence to suggest this. No one has ever attempted to provide such evidence. In inserting the word "wholly" the materialist reveals a considerable capacity for self-deception. There is no stronger reason for the belief that biological facts are wholly governed by the laws of physics and chemistry than the hope of those who like to think so.

The biologist wisely proceeds on the assumption that these facts are partly governed by other laws. He conducts his research as though these laws were distinct for each thing studied, as though there were one set of laws for the salivation of dogs, another for the structure of tulip flowers, another for the embryology of chickens.

Thus while the physicist finds that the whole of the Material Universe complies with one single Cosmic Statute Book revealed as a very meagre document if, indeed, it contains anything at all, the biologist, finds in the organic world a different and extremely elaborate set of requirements for each species of organism, if not for each individual. And while every discovery in physics has helped to whittle down the Cosmic Statute Book, every discovery in biology adds more clauses to the specified requirements for living forms. While the biologist discovers more laws, the physicist discovers fewer. The method adopted by each is justified by results.

The contrast in method is well illustrated by a comparison of the steps preferred in each science for verifying conclusions. Neither a biologist nor a physicist would draw a general conclusion from no more than one single observation. The biologist will repeat his observations many times before he dare embody them in a statement of law. To establish his theory of conditioned reflexes Pavlov made many experiments every day during many years on hundreds of dogs. Only after he had verified that the same stimulus produces the same response time after time did Pavlov feel sure that he could accurately predict a dog's behaviour.

The physicist sometimes employs this inductive method, but he prefers to verify his conclusions deductively. His method is best illustrated by a very elementary example. Suppose a primitive person wants to know the result of taking 117 oranges 29 times. If he has access to a sufficient number of oranges he can arrange them in 29 heaps of 117 oranges each and then undertake the laborious task of counting them all. When he has done the work he is in the position of a research worker who has conducted an experiment and made an observation. He cannot be quite sure that his observation is correct until he has checked it by counting the oranges again and again. But if his capacity for abstract thinking is a little higher he will realize that the result can be verified with the help of pencil and paper. He can then prove that the result could have been predicted without counting the oranges even once.

A physicist acts similarly when he has observed a new fact. Instead of repeating the experiment he sets to work with pencil and paper to find whether, with a greater capacity for abstract thinking, he could have predicted the result. When with the help of an experiment he makes a discovery, he does not regard his work as completed. Rather does he consider it as just begun. The next, and usually more important step is to find means of showing that the discovery could have been made without performing the experiment or making any observation. Thus Newton showed that the elliptical paths of planets could have been deduced with the use of pencil and paper even if no one had ever seen a planet.

Another striking example of the physicist's method was provided after Michelson and Morley had found with the help of the newly invented interferometer that a point on the earth's surface has no detectable motion relative to the medium in which light travels. This famous experiment was performed in the year 1887. It was not repeated for a generation. During this time scientists attempted to verify the result with pencil and paper. They sought to prove that the observation made by Michelson and Morley could have been predicted without any experiment. Their quest ended long before another experiment was made when Einstein "explained" the result in terms of the Restricted Theory of Relativity.

A physicist is so sure that his observations are implicit in basic laws and facts and principles that he hardly believes what he sees until he has proved it without seeing it by pure reasoning. Is then physics a purely deductive science like mathematics?

When we have asked physicists they have looked quite shocked at the question. ' 'Of course physics is an inductive science," they have replied. "Francis Bacon disposed long ago of the notion that any science is deductive." It seemed to us that the answer was substantially correct but required some qualification. In conversation, however, we never got any further. Only in the writings of Eddington have we been able to find any enlightenment.

We would like to suggest that inductive methods may have to be employed in physics for two excellent reasons. The first of these is due to the basic laws and facts and principles. If there are any such they are contained in the Cosmic Statute Book and the Cosmic Specification. If any laws or data constitute a specified selection between alternatives they can never be deduced by pure reasoning. Only the inductive methods of observation and experiment can reveal what they are. But if both these documents contain nothing but blank pages then every apparent kurma fact is really a testi fact, true only by definition and could, like everything in mathematics, be deduced with pencil and paper.

But a mistake might be made in the calculations. Unwarranted assumptions might creep in, unnoticed. The human mind has its limitations. Confronted with the complexities of our Material Universe the physicist is in the position of a savage who has been set the task of predicting the result of taking 117 oranges 29 times. Even when a physicist knows that a result can theoretically be predicted by pure deduction he wisely does not trust his predictions. He seeks to verify them with the help of observation and experiment. So a physicist, even if he does not believe in the Doctrine of Specified Requirements for the Inorganic World does still rightly believe in the usefulness of inductive method.

Top of Page