CHAPTER I

_The Sciences Converge_

One of the most fascinating features in the history of thought is that on several occasions an important new idea has come simultaneously to independent minds. Thus after Euclid’s geometry had remained without a rival for two thousand years the conception of an alternative non-Euclidean system was reached separately by Gauss, Lobatschewsky, and Bolyai during the years 1820-30. Bolyai’s father, while ignorant of the fact that Gauss had already made the same discoveries, wrote to his son urging him to publish his results and used the following prophetic words:

“There is some truth in this, that many things have an epoch, in which they are found at the same time in several places, just as the violets appear on every side in the spring.”

Another example of the simultaneous emergence of an idea in the minds of different thinkers is given by Darwin in his introduction to the _Origin of Species_. He there calls attention to the fact that in 1794-5 the broad idea of the evolution of species--though not its cause--was simultaneously formulated by Goethe in Germany, St Hilaire in France, and his own grandfather, Dr Darwin, in England. Moreover Darwin himself had the remarkable experience of finding in an essay submitted to him in 1858 by A. R. Wallace a complete summary of his own unpublished theory of natural selection as the chief cause of the evolution of species.

The last few years constitute another critical period of a similar kind, since an idea, which when made precise will transform scientific thought, has already come independently to many thinkers. Since 1922 many scientists have felt that in studying the emission and absorption of light physics has come near to the problem of life.[1] Others have proposed that in order to straighten out its atomic problems physics will have to take a hint from biology, but what this hint should be has not yet been indicated. The following pages suggest a definite line of advance for physics, and interpret these isolated flashes of intuition as evidence of a special feature in the present situation of the sciences.

We stand at the eve of a new epoch. Physics, biology, and psychology are converging towards a scientific synthesis of unprecedented importance, whose influence on thought and social custom will be so profound that it will mark a stage in human evolution. For centuries science has concentrated its highest genius on the study of inanimate matter; to-day the three great sciences are at last reaching the problem of life. For their researches on matter, life, and mind are now overlapping at one common issue: the nature of the fundamental electrical processes which underlie radiation and chemical combination.

Thus physics is at present occupied with the changes that occur when an atom emits either light or electricity. Biology is at the same problem in studying the electrical processes which are the basis of all organic behaviour, whether in primitive forms of protoplasm or in the highly developed central nervous system of man. Meantime psychology is dealing with an identical process when it analyses the structure of mind, and considers the elementary changes of consciousness which are produced when light of a given colour falls on the retina and sends its influence to the brain.

As the result of these convergent researches, life and consciousness will soon be subject to the first stages of a theoretically-grounded control, compared with which the present tentative efforts of medicine and psychology will be looked back on much as we remember the haphazard work of the alchemists before the foundation of chemistry. But this development of human knowledge and powers will carry with it great responsibilities, and scientists have to prepare themselves for the new tasks that will very soon fall to them. By indicating the main ideas through which this broad scientific synthesis may come about, this essay aims at showing that this possibility has to be taken seriously. We shall first examine the situation in physics and then turn to consider the influence which future developments of physical theory may have on biology and psychology.

Two main types of process defy interpretation within the present scheme of physical conceptions: life itself, and the atomic processes of radiation and the building up of stable compounds. In organic processes on the one hand, and the energy-interchanges of atoms on the other hand, we find something happening which cannot adequately be explained as a change in the _structure_ of the system considered. By structure is meant a spatial pattern of particles, which are supposed to be permanent and to move about like cricket balls or planets. Systems with a structure of this kind could not display the purposive quality of organic behaviour, and when we try to make a structural model of the atom we find that it fails to explain why the atom radiates energy in the abrupt packets which are called ‘quanta’, instead of in a continuous wave. We shall return presently to the question of organisms, after making an endeavour to discover why the atom cannot be described in terms of a particle structure.

In 1911 Rutherford achieved remarkable success in accounting for the results of his own researches in radioactivity by adopting a model of the atom as a miniature solar system, with planetary electrons rotating rapidly around a nucleus. But in order to explain the fact that the spectrum of the light emitted by an atom shows a characteristic series of lines, Bohr suggested that an electron inside an atom could emit light only by making a discontinuous jump from one possible orbit to another quite distinct orbit. This apparent discontinuity in the motion of electrons has intrigued physicists for more than ten years, and the following interpretations have recently been offered for this puzzling behaviour:

1. Nature is made up of electrons, but neither space nor time is fundamentally discontinuous. The electron appears to have some freedom of choice, and to be able to reappear unexpectedly at forbidden places.

2. Nature is not discontinuous or arbitrary, but nevertheless something prevents us determining all the things we should like to know about an electron. For instance, if we try to determine exactly where it is, it behaves so that we cannot simultaneously measure its exact velocity. (Heisenberg.) This view may perhaps be interpreted to mean that we have made the atom model more complex than the atom itself is, and that consequently we have been using more quantities than are necessary for describing all we can observe of its behaviour.

3. Nature is not made up of electrons, but of waves. The atom must be considered as a system of electric waves spread over its whole volume. ‘Electrons’ are merely an inaccurate way of describing some of the properties of these waves. The wave picture of the atom is, however, to be considered only as a temporary expedient to be used until some better description of the atom can be invented, in which both the wave and the corpuscular properties of atoms will appear as aspects of some more profound physical property. (Schrödinger.)

The first alternative is a mere cry of despair, since it does not propose any line of advance. But the other two suggestions may be combined thus:

4. The view of the atom as a structure of Newtonian particles is wrong since it gives rise to discontinuities, and provides more quantities than we at present need. A new formulation of atomic processes must be found using fewer quantities which will explain why we find wave properties, and why sometimes the electron does behave like a small billiard ball though really it is some different sort of thing.

Now since the Newtonian mathematics of moving particles is inadequate for describing the changes that go on in the atom--just as it is for describing organic processes--there must be some assumption implicit in Newton’s laws which is valid neither for atom nor for organism. Such an assumption can be found very easily, though physics has never given it much attention. It is that the elementary processes in nature are _reversible_, or would be if they could be isolated. By reversible is here meant that the laws governing the process remain unchanged when the direction of time is reversed, i.e. when -t is substituted for +t. If the law is changed by this substitution so that the reversed process never occurs or is recognizably different, then the process is called irreversible. An irreversible process can therefore be used to yield an objective criterion of past and future, when these terms have been once defined.

To take an example. If I am standing behind a hedge and take a cinematograph film of a stone which suddenly rises in the air and disappears from sight, I could not tell from an examination of the film which way to wind it. Thus if it is wound one way the stone appears to rise, and if wound the other way to fall from the sky. To tell which was the right way I should have to use my subjective sense of the direction of time, i.e. remember the fact that I saw the stone low in the air before I saw it high up. This case, like every gravitational process, is reversible, and motions of this kind have provided the basis for modern physical conceptions.

But suppose that instead I had taken a film of a cup of tea as it was cooling. One end of the film would show the steam above the cup and the spoon changing in length as it changed in temperature. Passing along the film these effects would grow less marked until the successive photos showed no variation when the temperature of the tea was nearly that of the surrounding air. It would be obvious which way to wind this film, without using any subjective criterion supplied from memory of the individual process which had been photographed. This process is irreversible, but physics has hitherto assumed that all such processes are merely the statistical result of a chaos of molecular motions each of them perfectly reversible.

The assumption of reversibility seems to some physicists so fundamental that they think there could be no science without it. But that is a mere prejudice arising from the fact that Newton conceived one particular way of giving mathematical formulation to the measurable features of physical processes. By suggesting that all the laws of nature might take a form similar to his law of gravitation, he made the implicit assumption that all elementary processes were reversible. Gravitational motions are so, at any rate within the accuracy of Newton’s law, and as a consequence of the confirmation of his law and the fact that it has been taken as a model for the whole system of modern physical conceptions, the latter are only appropriate for reversible processes.

Apparent irreversibility, such as the cooling of a cup of tea, is attributed to statistical effects, and the second law of thermodynamics, which asserts that temperatures tend to uniformity, is treated as merely a statement of what is highly probable. This is probably quite legitimate, but even where no statistical effect can enter and the process is clearly irreversible physics usually adopts any measure rather than assume that a fundamental elementary process is irreversible.[2] We cannot be surprised at this, since if physics once admitted that any elementary process was irreversible it would have to give up the whole system of Newtonian conceptions. Matter, force, energy, action, and wave properties are all unsuitable for the treatment of irreversible effects since they all ultimately depend on Newton’s reversible law.

An entirely new set of ideas is necessary for describing processes which necessarily proceed in one direction, so that one particular state of the system must precede another state. It appears conceivable that an alternative set of conceptions to replace the Newtonian might be established by demanding the irreversibility of all natural laws, as well as the demands hitherto made by physics, i.e. the permanence of matter and the conservation of energy.

The question of the reversibility of natural processes provides the key to a great intellectual struggle which is now in progress behind the complexities of philosophic and scientific thought. The issue can be formulated thus:

Is there a real temporal process in nature? Is the passage of irreversible time a necessary element in any view of the structure of nature? Or, alternatively, is the subjective experience of time a mere illusion in the mind which cannot be given objective expression? These are not metaphysical questions that can still be neglected by science with impunity. For just as Einstein made his advance by analysing conceptions such as simultaneity, which had been thought to be adequately understood for the purposes of empirical science, so the next development of physical theory will probably be made by carrying on the analysis of time from the point at which Einstein left it. Moreover, the above questions may be put into precise scientific form by asking if the causal relations which are studied by science are symmetrical and reversible so that we cannot obtain from them any criterion by which to distinguish past and future. If, on the other hand, they are asymmetrical and irreversible, the laws of nature lead us on necessarily from what went before to what comes afterwards.