The Philosophy of Physical Science (eBook)

CHAPTER II

SELECTIVE SUBJECTIVISM

I

Let us suppose that an ichthyologist is exploring the life of the ocean. He casts a net into the water and brings up a fishy assortment. Surveying his catch, he proceeds in the usual manner of a scientist to systematise what it reveals. He arrives at two generalisations:

(1) No sea-creature is less than two inches long.

(2) All sea-creatures have gills. These are both true of his catch, and he assumes tentatively that they will remain true however often he repeats it.

In applying this analogy, the catch stands for the body of knowledge which constitutes physical science, and the net for the sensory and intellectual equipment which we use in obtaining it. The casting of the net corresponds to observation; for knowledge which has not been or could not be obtained by observation is not admitted into physical science.

An onlooker may object that the first generalization is wrong. "There are plenty of sea-creatures under two inches long, only your net is not adapted to catch them." The ichthyologist dismisses this objection contemptuously. "Anything uncatchable by my net is ipso facto outside the scope of ichthyological knowledge, and is not part of the kingdom of fishes which has been defined as the theme of ichthyological knowledge. In short, what my net can't catch isn't fish." Or—to translate the analogy—"If you are not simply guessing, you are claiming a knowledge of the physical universe discovered in some other way than by the methods of physical science, and admittedly unverifiable by such methods. You are a metaphysician. Bah!"The dispute arises, as many disputes do, because the protagonists are talking about different things. The onlooker has in mind an objective kingdom of fishes. The ichthyologist is not concerned as to whether the fishes he is talking about form an objective or subjective class; the property that matters is that they are catchable. His generalization is perfectly true of the class of creatures he is talking about—a selected class perhaps, but he would not be interested in making generalizations about any other class. Dropping analogy, if we take observation as the basis of physical science, and insist that its assertions must be verifiable by observation, we impose a selective test on the knowledge which is admitted as physical. The selection is subjective, because it depends on the sensory and intellectual equipment which is our means of acquiring observational knowledge. It is to such subjectively-selected knowledge, and to the universe which it is formulated to describe, that the generalizations of physics— the so-called laws of nature—apply.

It is only with the recent development of epistemological methods in physics that we have come to realise the far-reaching effect of this subjective selection of its subject matter. We may at first, like the onlooker, be inclined to think that physics has missed its way, and has not reached the purely objective world which, we take it for granted, it was trying to describe. Its generalisations, if they refer to an objective world, are or may be rendered fallacious through the selection; But that amounts to condemning observationally grounded science as a failure because a purely objective world is not to be reached by observation.

Clearly an abandonment of the observational method of physical science is out of the question. Observationally grounded science has been by no means a failure; though we may have misunderstood the precise nature of its success. Those who are dissatisfied with anything but a purely objective universe may turn to the metaphysicians, who are not cramped by the self-imposed ordinance that every assertion must be capable of submission to observation as the final Court of Appeal. But we, as physicists, shall continue to study the universe revealed by observation and to make our generalizations about it; although we now know that the universe so reached cannot be wholly objective. Of course, the great mass of physicists, who pay no attention to epistemology, would have gone on doing this in any case.

Should we then ignore the onlooker with Ins suggestion of selection? I think not; though we cannot accept his remedy. Suppose that a more tactful onlooker makes a rather different suggestion: "I realise that you are right in refusing our friend's hypothesis of uncatchable fish, which cannot be verified by any tests you and I would consider valid. By keeping to your own method of study, you have reached a generalisation of the highest importance—to fishmongers, who would not be interested in generalisations about uncatchable fish. Since these generalisations are so important, I would like to help you. You arrived at your generalisation in the traditional way by examining the fish. May I point out that you could have arrived more easily at the same generalisation by examining the net and the method of using it?"

The first onlooker is a metaphysician who despises physics on account of its limitations; the second onlooker is an epistemologist who can help physics because of its limitations. It is just because of the limited—some might say, the perverted—aim of physics that such help is possible. The traditional method of systematic examination of the data furnished by observation is not the only way of reaching the generalizations valued in physical science. Some at least of these generalizations can also be found by examining the sensory and intellectual equipment used in observation. Epistemology thus presents physics with a new method of achieving its aims. The development of relativity theory, and the transformation of quantum theory from an empirical to a rational theory arc the outcome of the new method; and in it is our great hope of further fundamental advances.

II

We return to our fish to illustrate another point of great importance. No suggestion was offered as to the second generalisation— that all sea-creatures have gills—and, so far as we can see, it could not have been deduced from an examination of the net and its mode of use. If the ichthyologist extends his investigations, making further catches, perhaps in different waters, he may any day bring up a sea creature without gills and upset his second generalisation. If this happens, he will naturally begin to distrust the security of his first generalisation. His fear is needless; for the net can never bring up anything that it is not adapted to catch.

Generalisations that can be reached epistemologically have a security which is denied to those that can only be reached empirically.

It has been customary in scientific philosophy to insist that the laws of nature have no compulsory character; they are uniformities which have been found to occur hitherto in our limited experience, but we have no right to assert that they will occur invariably and universally. This was a very proper philosophy to adopt as regards empirical generalisations—it being understood, of course, that no one would be so foolish as to apply the philosophy in practice. Scientists, assured by their philosophy that they had no right to expectations, continued to cherish indefensible expectations, and interpreted their observations in accordance with them. Attempts have been made by the theory of probability to justify our expectation that if an occurrence (whose cause is unknown) has happened regularly hitherto it will continue to happen on the next occasion; but I think that all that has emerged is an analysis and axiomatisation of our expectation, not a defence of it.

The situation is changed when we recognise that some laws of nature may have an epistemological origin. These are compulsory; and when their epistemological origin is established, we have a right to our expectation that they will be obeyed invariably and universally. The process of observing, of which they are a consequence, is independent of time or place.

But, it may be objected, can we be sure that the process of observing3 is unaffected by time or place? Strictly speaking, no. But if it is affected—if position in time and space or any other circumstance prevents the observational procedure from being carried out precisely according to the recognised specification—we can (and do) call the resulting observation a "bad observation". Those who resent the idea of compulsion in scientific law may perhaps be mollified by the concession that, although it can no longer be accepted as a principle of scientific philosophy that the laws of nature are uncompulsory, there is no compulsion that our actual observations shall satisfy them, for (unfortunately) there is no compulsion that our observations shall be good observations.

What about the remaining laws of nature, not of an epistemological origin, and therefore, so far as we know, non-compulsory? Must they continue to mar the scheme as a source of indefensible expectations, which nevertheless are found to be fulfilled in practice? Before worrying about them, it will be well to wait till we see what is left of the system of natural law after the part which can be accounted for epistemologically has been removed. There may not be anything left to worry about.

The introduction of epistemological analysis in modern physical theory has not only been a powerful source of scientific progress, but has given a new kind of security to its conclusions. Or, I should rather say, it has put a new kind of security within reach. Whether the present conclusions arc secure is a question of human fallibility, from which the epistemologist is no more exempt than the classical theorist or the practical observer....