by     Reginald O. Kapp


Chapter 8 - Introduction to Part Three

In the remainder of this book the Principle of Minimum Assumption in general, and the inference from it that I have called the Symmetrical Impermanence of Matter, will be tested by the criterion of explanatory power. It will be shown that one can infer from this principle the answers to a number of questions about our galaxy and those extragalactic bodies that resemble it closely enough also to be called galaxies. It will also be shown in Part Four that one can infer the characteristic properties of gravitation from the same basic principle.

Among the questions to be raised and partly answered are:

Why does the space within our galaxy contain very diffuse hydrogen? Why does some of the matter in the universe occur in the form of concentrations similar to our galaxy?
Why do the masses of all galaxies lie between finite upper and lower limits?
Why do stars and galaxies rotate ?
Why do many galaxies resemble one another in having the charac- teristic structure for which a dense central core is surrounded by spiral arms all in the same plane ?
Why do the galaxies contain stars ?
(A similar list of the questions about gravitation will be provided in Chapters 21 and 22.)

Not so very long ago the search for answers to such questions would have appeared meaningless. It was thought that stars, nebulae and galaxies just were, and it was taken for granted that they always had been like that. Questions about their origin seemed idle and not worth asking.

A new outlook occurred when it was first appreciated that many processes are irreversible, so that every physical system undergoes certain unidirectional changes. Such a system must have one form or state at its beginning and tend steadily towards another terminal form or state.

With this new understanding of the nature of the physical world questions about the origin and evolution of the galaxies acquired a new meaning. It was realized that these, like all other objects, must be in a process of unidirectional change and so it became natural to want to know as much as possible about the beginning of the process as well as about its development and all subsequent states. In short, we are today no longer satisfied merely to observe the objects that are revealed by our telescopes; we want also to explain them and to discover their past and future histories.

By 'explain' we mean here 'account for in terms of basic physical principles'. When we speak of explaining a phenomenon we mean that the phenomenon can be inferred; that, given certain accepted facts and principles one could predict the phenomenon without needing to observe it. In this sense Dirac predicted the positron, it will be remembered from Chapter 2, and would have been said to have explained it if its discovery had preceded his deductive reasoning. Thus a satisfactory explanation of the particular way in which ponderable matter is distributed must be based on more than an ingenious ad hoc hypothesis. It must be based on a sound philosophy, logical inference and a minimum of speculation.

Every one of the nine possible combinations from the (A) and (B) lists that occur at the beginning of Chapter 3 is speculative, though some may regard some of them as more speculative than others. Any such judgements would, however, be merely subjective and depend on the temperament of the person concerned. On an objective assessment one cannot grade the nine combinations into those that are more and those that are less speculative. But the question arises whether, having made one's choice among these nine possibilities, one will need to speculate further. Can one infer from one of the combinations, without the need for any additional hypo- theses, a cosmological model that resembles actuality?

In the rest of this book I shall develop the cosmological model that one infers if one adopts the philosophy expressed by what I have called the Principle of Minimum Assumption, the principle according to which the minimum assumption is always the true generalization about the physicist's world. To meet this principle the model must be based on the combination of (A3) with (B3), on the Hypothesis of the Symmetrical Impermanence of Matter.

It will be found that this model does seem to resemble actuality, where- as every other one, including the model based on the combination of (A3) with (Bl) fails completely.

I have to say 'it seems to', for I cannot exclude the possibility that there may be errors in the reasoning, which will of course have to be checked for these. But if there are errors, they will be of the kind that arises from faulty logic and mathematics, not of the kind that arises from indulgence in unjustifiable speculation.

Let me express the task in a different way. It is to show that all the facts about which the above questions are asked could be discovered with the help of a sound philosophy and accurate reasoning by the inhabitants of a planet permanently enveloped in cloud.

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