Primitive man must have found nature singularly puzzling and intricate. The simplest phenomena could be trusted to recur indefinitely; an unsupported body invariably fell, a stone thrown into water sank, while a piece of wood floated. Yet other more complicated phenomena shewed no such uniformity—the lightning struck one tree in the grove while its neighbour of similar growth and equal size escaped unharmed; one month the new moon brought fair weather, the next month foul. Confronted with a natural world which was to all appearances as capricious as himself, man's first impulse was to create Nature in his own image; he attributed the seemingly erratic and unordered course of the universe to the whims and passions of gods, or of benevolent or malevolent lesser spirits. Only after much study did the great principle of causation emerge. In time it was found to dominate the whole of inanimate nature: a cause which could be completely isolated in its action was found invariably to produce the same effect. What happened at any instant did not depend on the volitions of extraneous beings, but followed inevitably by inexorable laws from the state of things at the preceding instant. And this state of things had in turn been inevitably determined by an earlier state, and so on indefinitely, so that the whole course of events had been unalterably determined by the state in which the world found itself at the first instant of its history; once this had been fixed, nature could move only along one road to a predestined end.
Primitive man must have found nature singularly puzzling and intricate. The simplest phenomena could be trusted to recur indefinitely; an unsupported body invariably fell, a stone thrown into water sank, while a piece of wood floated. Yet other more complicated phenomena shewed no such uniformity—the lightning struck one tree in the grove while its neighbour of similar growth and equal size escaped unharmed; one month the new moon brought fair weather, the next month foul. Confronted with a natural world which was to all appearances as capricious as himself, man's first impulse was to create Nature in his own image; he attributed the seemingly erratic and unordered course of the universe to the whims and passions of gods, or of benevolent or malevolent lesser spirits. Only after much study did the great principle of causation emerge. In time it was found to dominate the whole of inanimate nature: a cause which could be completely isolated in its action was found invariably to produce the same effect. What happened at any instant did not depend on the volitions of extraneous beings, but followed inevitably by inexorable laws from the state of things at the preceding instant. And this state of things had in turn been inevitably determined by an earlier state, and so on indefinitely, so that the whole course of events had been unalterably determined by the state in which the world found itself at the first instant of its history; once this had been fixed, nature could move only along one road to a predestined end.
The new physics just described was still based largely on Newtonian ideas. Indeed, in its theoretical aspects, it might not unfairly be described as a final attempt to explain the world in materialistic terms—as particles being pushed and pulled about in space and time. Nevertheless, the new physics had found it necessary to abolish most of the forces of pushing and pulling, replacing the gradual changes of motion of the particles under these forces by sudden and unpredictable jumps. These appeared to involve violations of the law of causality, both in the disintegration of radioactive atoms and also in the internal changes of ordinary atoms. We seemed to see Fate defying this law as she picked out certain atoms for disintegration or collapse and, by her apparently capricious acts, sent the universe along one path or another according to her whim. On such lines the new physics had explained many phenomena which had hitherto seemed inexplicable, but it had by no means met with complete success. For instance, while it gave a perfect interpretation of the simplest spectrum of all, namely that of the hydrogen atom, it failed with more complex spectra. This was not necessarily a fatal objection; a few emendations and possibly a few new ad hoc assumptions might have effected a complete reconciliation, although this seems improbable.
The cover design is from a Greek bronze mirror, said to have come from Corinth, and is dated about 350-300 B.C.It shows Aphrodite and Pan playing fivestones.Originally a magical means for divining the future, the five-stones of this engraving is a game of chance.Its throws, like those of dice, are controlled by probabilistic laws.The behavior of elementary particles is also governed by probabilistic laws.As in the game of five-stones so in the world of particles, no event can be foretold as certain to happen, but only as likely to happen with a given degree of probability.The time of such a probabilistic universe is different from the time of ordinary human experience.It misses continuity, and nothing in its nature corresponds to our notions of now versus then, or to the related distinctions among future, past, and present.Aphrodite is seated on a stone slab next to Pan-the god of woods and pastures.Their bench is a sample of solid objects that are formed when elementary particles jell into massive matter.The universe of Newtonian physics comprises small as well as immense chunks of such matter.Events in that world are connected by deterministic rather than probabilistic laws, time is continuous, and a meaning may be assigned to the idea of well-defined instants.But it is still a universe without the kind of temporality that might be metaphorically described as flowing.The goose in front of the bench is a traditional attribute of Aphrodite-as are doves, swans, and dolphins.Let her small entourage represent the life process itself.It is the instant by instant internal coordination necessary for the maintenance of life that defines a now in the nowless world of inanimate matter.And, it is the biological needs of organisms that distinguish between future and past with reference to those present needs, and thereby identify a direction of time.The central figure is Aphrodite, the goddess of love, beauty, and fertility.According to Homer, "her enchantments came from this: allurement of the eyes, hunger of longing, and the touch of lips that steals all wisdom from the coolest men."Through her capacity to create designs for a long-term future and retain memories of a long-term past, the Aphrodite of this Arcadian image represents the complex time of the human mind.vii
Twentieth-Century Physics A century which has run less than a third of its course has already witnessed two great upheavals in physical science. These are associated with the words Relativity and Quanta, and have forced the physicist of to-day to view nature against a background of ideas which is very different from that of his nineteenth-century predecessor. The latter thought of nature as an assemblage of objects located in space and continually changing with the passage of time. It was something entirely detached from, and external to, himself; something which he could study and explore from a distance as the astronomer studies the surface of the sun through his telescope, or the explorer the desert from his aeroplane. He thought of the apparatus of his laboratory as the astronomer thinks of his telescope, or the explorer of his field-glass; it shewed him things which were there whether he looked at them or not, which had been there before the first man appeared on earth, and would still be there after the last man had been frozen to extinction. Finally he accepted a “common-sense” view of nature, believing that there was no great difference between appearance and reality; the possibility that things were not as they seemed might provide an admirable subject for a debating society of philosophers, but was of as little practical concern to the scientist as to the farm-labourer. Although he may not have realised it, this complex of beliefs constituted a philosophical creed in itself.
Abstract In the first quarter of this century physicists were slowly and somewhat reluctantly forced to realize that the view of the physical world, so painstakingly built up over the preceding four centuries, was in serious need of revision. In particular, the laws that governed the motion of particles on the atomic scale were not those of classical mechanics. Physics found itself catapulted into the strange new world of quantum theory in which the very notion of position or velocity of a particle became blurred and statistical laws dominated everything.
We have now concluded our summary of the findings of modern physics, and may turn to consider how these findings affect the practical problems of philosophy and of everyday life. But let us first recapitulate the conclusions we have reached in our scientific discussion. Recapitulation Because we are human beings and not mere animals, we try to discover as much as we can about the world in which our lives are cast. We have seen that there is only one method of gaining such knowledge—the method of science, which consists in a direct questioning of nature by observation and experiment. The first thing we learn from such questioning is that the world is rational; its happenings are not determined by caprice but by law. There exists what we have called a ‘pattern of events’, and the primary aim of physical science is the discovery of this pattern. This, as we have seen, will be capable of description only in mathematical terms. The new quantum theory explained in the preceding chapter has provided a mathematical description of the pattern of events which is believed to be complete and perfect. For it enables us—in principle at least—to predict every possible phenomenon of physics, and not one of its predictions has so far proved to be wrong. In a sense, then, we might say that theoretical physics has achieved the main purpose of its being, and that nothing remains but to work out the details.