Summarising, we may say that in relativity, as in classical science, the sophisticated rules given for the determination of a simultaneity of external events presuppose that we possess the innate ability to differentiate between a simultaneity and a succession of sense impressions. These fundamental recognitions then serve as a basis for future discovery; and the sophisticated rules are used merely to allow us to pass from the recognition of a simultaneity which is a priori to those which cannot be determined a priori. As for the rules themselves, those suggested by relativity constitute but a refinement of the ones entertained by classical science. Aside from this purely quantitative difference, no change in method is involved.
It is therefore obvious that Dr. Whitehead’s criticism, when interpreted as referring to psychological simultaneity, appears to be totally unwarranted. Let us see whether it would possess any greater merit when interpreted as referring to a simultaneity of external events. The criticism would then have the following significance: Our recognition of the simultaneity of external events is fundamental. We know that two events, one on the sun and the other on the earth, are simultaneous, when we perceive them simultaneously. Physical measurements are irrelevant to the problem. Einstein’s theory fails to recognise this fact.
Now there is no doubt that the theory of relativity does fail to recognise the type of simultaneity presented in this last interpretation of Dr. Whitehead’s criticism. Hence the man who might have this understanding in mind would be perfectly justified in dissenting from a theory which would characterise his conception of simultaneity as altogether indefensible. But, for that matter, so would classical science. Both sciences refuse to agree that we possess any a priori means of determining a simultaneity of external events. Both sciences claim that in all such cases we are compelled to appeal to physical measurements of one kind or another. In other words, both sciences refuse to accept that bizarre doctrine known as “neo-realism” which consists in confusing the event that, occurs with the event that we sense.
According to neo-realism as championed by Whitehead, and by a number of other philosophers, vision is a matter of direct apprehension[57] Events would thus be simultaneous with the instants of their perception. In the same spirit, the neo-realist speaks of events occurring behind a mirror, or of the space he sees behind the mirror, or of the convergence of the rails on the embankment. No distinction in terminology is made between the status of such perspectives and that of the physical entities existing in the objective world of science. In ancient times Æsop warned his countrymen against the dangers of neo-realism when he composed his fable of the dog mistaking the bone for its reflection in the water. Indeed, for the plain man there appears to be no difference between the attitude of the neo-realist and that of the unsophisticated infant or primitive savage who views a mirror for the first time.
In order to extricate himself from the paradoxes in which he finds himself involved, the neo-realist is finally compelled to agree that the objects behind the mirror, etc., are not quite the same things as physical objects. So he calls them sensa or sense-objects. When requested to justify his belief in these mysterious, shadowy existents, he tells us that sensa and sense-objects certainly exist, for otherwise how could a round coin ever be seen as an ellipse? Obviously (so he maintains) in addition to the round physical object, there must be an “elliptical sensum” present, and it is this that we are sensing.
It is scarcely necessary to say that no scientist could be in sympathy with such loose arguments, and accept as sound this arbitrary materialisation of qualities. Forms and colour sensations are all that we are conscious of visually. It is only by inference, as a result of a co-ordination of sensations, that we are finally led to believe in the existence of a round coin in the objective world. After we have reached this stage of knowledge it is a simple matter to account for the elliptical impression we receive of the coin, since an image of this shape can be proved to have been formed on the retina. An application of the laws of geometrical optics, and a slight knowledge of the eye’s structure, suffice; and the “sensa” and “sense-objects” of the neo-realist can be discarded as perfectly useless hypotheses.
A more detailed study, which we shall spare the reader, would convince us that neo-realism, when taken literally, rests on a confusion between inferences and direct recognitions, and leads to contradictions when an attempt is made to conceive of an objective world transcending our private views. On the other hand, if taken with a grain of salt, mitigated, as occasion demands, by such palliatives as “pseudo” or “peculiar sort of” or “not quite the same as,” it resolves itself into a mere play on words, into a giving of the same name to things which even the neo-realist would concede to be essentially different.
Physical science, it must be remembered, deals with a common objective world. This world is not apprehended directly, but issues from a long, laborious, ever-widening synthesis of private views. Primarily, all we are aware of is a complex of sensations. Even the crude knowledge of the savage is therefore itself the result of a highly complex synthesis. But science must pursue the synthesis still farther, taking the results of previous syntheses as the elements of its more sophisticated ones. And so what was formerly the synthetic view becomes the private one when we rise to a higher plane. Thus, if we consider the aspect of the earth’s surface, viewed from any one spot, our private view would suggest that the earth was flat. Only a synthesis of a number of private views and experiences can lead us to assert that the earth is round; and science accordingly speaks of the rotundity of our planet and ignores its flatness. To put it in more technical language, the search for the objective world is similar to that of the search for the invariants or invariant equations of a group of transformations. In this illustration, each transformation corresponds to the passage from one private perspective to another, whereas the invariants correspond to the entities of the objective world with which science deals. The discovery of the space-time universe, to be discussed in a future chapter, illustrates the procedure.
To be sure, in many instances the private view may be of greater interest than the collective one. This will be the case if an artist wishes to paint a landscape on his canvas. He will, of course, draw distant objects on a smaller scale and make the rails converge. But, in contradistinction to the artist, the scientist is not particularly interested in the private view except as a means to an end. His ultimate goal is the common objective world.
The only charge that might be directed against the scientific attitude (which in this case is also that of the man in the street) is that this objective world resolves itself into a series of inferences, a mere mental construct, hence cannot possess the same measure of reality as the impressions we experience directly. The majority of scientists would grant the justice of this charge if by “what we experience directly” we mean our awareness of sensations. But they would strenuously oppose the claims of the neo-realist who endeavours to extend the meaning of these words so as to embrace the existence of his sensa and sense-objects; these represent nothing but inferences which he has drawn from his awareness of sensations. And this is precisely the error into which the neo-realist falls when, on perceiving a red flash in the sky, he talks of a star bursting into prominence “there-now.” If he wishes to avoid inferences, he should confine himself to saying: “I experience ‘here-now’ a luminous impression on a dark background.” For all he knows, the luminous impression may be due to an aviator’s light, or to a firefly, or to a purely subjective hallucination.