TOWARDS A UNIFIED COSMOLOGY

by     Reginald O. Kapp

PART III - THE ORIGIN AND EVOLUTION OF GALAXIES

Chapter 16 - Observation, Inference And Speculation


It will be convenient if I summarize very briefly the conclusions that have just been reached. They are as follows.

One should expect a cosmological model based on Symmetrical Impermanence to contain some extensive clouds of very tenuous gas. In an expanding universe these would begin to form as soon as the distance between adjacent galaxies exceeded a certain critical value. At first these clouds would grow rapidly in extent, while they still remained so tenuous that the gas between stars within our galaxy would have to be called dense in comparison. But when these extragalactic clouds had acquired a substantial gravitational field of their own, they would capture hydrogen from their surroundings and would also shrink under the influence of their own gravitational fields. Hence they would become more dense. But in spite of their smaller volume they would also become more massive, for loss from matter falhng out of the cloud would cease and be replaced by gain from the matter that fell into it.

These clouds would bear but little resemblance to the spiral nebulae. Nor will the closer study of their formation that is to follow shortly improve the resemblance. On the contrary. It will be found that the incipient clouds must differ from spiral nebulae quite significantly in shape, in size, in the way matter within them is distributed, in their own intrinsic motion.

Can it then be inferred that the cloud will eventually develop into a spiral nebula, into a galaxy similar to those with which astronomers are familiar? If one cannot infer this, the cosmological model that is based on Symmetrical Impermanence does not resemble actuality and this basic hypothesis must be abandoned and with it the even more basic Principle of Minimum Assumption. Much depends on whether one can infer from established knowledge and this principle that the extragalactic cloud can develop into a familiar spiral nebula.

For this reason it now becomes necessary to consider in detail what one should expect to happen to an extragalactic cloud after it has begun to form on an astronomical summit. But such consideration can with ad- vantage be preceded by an appreciation of the task that it involves, and this will be most easily obtained, be it at the cost of some repetition, if I recall what has been said in Chapter 2 about scientific method.

To infer from established knowledge what happens to an extragalactic cloud is comparable to what engineers do when they infer the performance of machines that have been designed but not yet made machines that may embody entirely new principles and that may be quite different from anything that has been made before.

To draw such inferences taxes the engineer's powers of logical reasoning considerably. It calls for great care lest some decisive factor be overlooked; it may require the use of some new mathematical tool; the design may have to be preceded by much experimental research of which the purpose is to extend the range of established knowledge. But in engineering the new machine does not have to be manufactured and tried out before anything is known of its performance. The designer knows, of course, that some mistake or unforeseen circumstance may falsify his predictions, so his performance figures include margins, technically known as tolerances. When there is some doubt, a prototype may precede mass production. But these precautions do not imply that the engineer lacks all faith in his own powers of calculation and logical inference; and in the great majority of cases experience shows a close agreement between inference and eventual performance.

Amateur scientists and philosophers often fail to appreciate this. The technique of inference, which is a commonplace in engineering, appears to them as unpardonable speculation. A consequence of this is that both scientific and philosophical conclusions are too often assessed by the wrong criterion. When a conclusion is arrived at by a process of inference, the proper course is to examine the reasoning that has led to the conclusion. This may have been faulty and can then be exposed by better reasoning. But the history of science abounds in occasions when this obvious duty has been neglected. For one critic of Darwin who examined his reasoning in the early days of evolutionary theory a hundred dismissed the theory by quite different, and far less sound, criteria.

There are sundry reasons for this and one is man's natural intellectual indolence. The detection of faulty reasoning requires a substantial mental effort, while other criteria can be applied with little or none. One of these false criteria is applied when the result of inference from established knowledge is dismissed as 'mere speculation'. If this happens more often than one should expect, it is because the difference between inference and speculation tends to be obscured.

Confusion sometimes arises from giving a false status to observation. There are schools of philosophy in which the validity of any statements about unobservables is denied. These schools find ready adherents, for the notion seems superficially plausible that one cannot say anything valid about something that one has not and cannot observe. However, the plausibility evaporates when one remembers the everyday work of scientists and engineers.

A machine that has never been made is certainly unobservable at the time when the designer makes statements about its performance, and so the philosophers of this school would have to say that such statements could not be justified scientifically. These philosophers advocate a kind of empiricism that would make the engineer's task impossible. It is fortunate that most physicists, and all engineers, know better than to practise what is sometimes preached to them.

Cosmology is typical, but by no means unique, among the fields of study in which one cannot afford to listen to these schools. In cosmology inferences have to be drawn about systems that are just as unobservable as a machine that has not yet got past the blueprint stage. Predictions in this field require the same disciplined care as in engineering; if this care is exercised, they are just as valid; they are subject to the same kind of un- certainty. As often happens in engineering, moreover, inferences cannot be checked with the help of small-scale models.

All this applies to the present theme. We are here trying to draw inferences about the behaviour of masses of gas so enormous that their movement is largely governed by their own gravitational fields. Such masses are not at the disposal of the laboratory technologist. The telescope tells us a little about them, but by no means all that we need to know. If we are to extend our knowledge in the field of cosmology, we must adopt the engineer's technique of inference. There is no alternative and those who deprecate inference do not suggest one. One must either use this technique with the thoroughness and care of the machine designer, or abandon all hope of gaming a better insight into cosmological processes.

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