CHAPTER VIIISCIENCE AND REALITY
SCIENCE AND REALITY
The Einsteinian absolute—Revelation by science—Discussion of the experimental bases of Relativity—Other possible explanations—Arguments in favour of Lorentz’s real contraction—Newtonian space may be distinct from absolute space—The real is a privileged form of the possible—Two attitudes in face of the unknown.
We approach the end of our work. Has reality, seen through the prism of science, changed its aspect with the new theories? Yes, certainly. The Relativist theory claims to have improved the achromatism of the prism and by this means improved the picture it gives us of the world.
Time and space, the two poles upon which the sphere of empirical data turned, which were believed to be unshakeable, have been dislodged from their strong positions. Instead of them Einstein offers us the continuum in which beings and phenomena float: four-dimensional space-time, in which space and time are yoked together.
But this continuum is itself only a flabby form. It has no rigidity. It adapts itself docilely to everything. There is nothing fixed, because there is no definite point of reference by means of which we could distribute phenomena; because on the shores of this great ocean in which things float there are none left of those solid rings to which mariners once fastened their vessels.
Up to this point the theory of Relativity well deserves its name. Butnow, in spite of it and its very name, there rises something which seems to have an independent and determined existence in the external world, an objectivity, anabsolutereality. This is the “Interval” of events, which remains constant and invariable through all the fluctuations of things, however infinitely varied may be the points of view and standards of reference.
From this datum, which, speaking philosophically, strangely shares the intrinsic qualities with which the older absolute time and absolute space were so much reproached, the whole constructive part of Relativity, the part which leads to the splendid verifications we described, is derived.
Thus the theory of Relativity seems to deny its origin, even its very name, in all that makes it a useful monument of science, a constructive tool, an instrument of discovery. It is a theory of a new absolute: the Interval represented by the geodetics of the quadri-dimensional universe. It is a new absolute theory. So true is it that even in science you can build nothing on pure negation. For creation you need affirmation.
The theory of Relativity has won brilliant victories, crowned by the decisive sanction of facts. We have given some astonishing instances of these in our earlier chapters. But to say that the theory is true because it has predicted phenomena that were afterwards verified would be to judge it from too narrowly Pragmatist a standpoint. It would also—there is real danger in this—be to close against the mind other paths where there are still flowers to cull. We will not do that.
It is therefore important, in spite of its successes—nay, on account of them—to turn the light of criticism upon the foundations of the newdoctrine. Even Cæsar, as he mounted the Capitol, had to listen to the jokes of the soldiers round his chariot and lower his pride. The theory of Relativity also, as it advances in all its magnificence along the Triumphal Way, must learn that it has its limits, perhaps its weaknesses.
But before we go further into it, before we turn the raw light upon it, let us make one observation.
Whatever be the obscurities of physical theories, whatever be the eternal and fated imperfection of science, one thing may be positively laid down here: scientific truths are the best established, the most certain, the least doubtful of all the truths we can know in regard to the external world. If science cannot reveal to us the nature of things in its entirety, there is nothing else that can do it as well. The truths of sentiment, of faith, of intuition, have nothing to do with those of science as long as they remain strictly truths of the interior world. They are on another plane. But the moment they claim to be measures of the external world—which would be their only cause of weakness—they subject themselves to the material reality, to the scientific investigation of the truth.
It is therefore nonsense to speak of a “bankruptcy of science” as contrasted with the certainty which other disciplines may give us respecting the external world. The bankruptcy of one would make all the others bankrupt. When it is not a question of the intimate oasis in which the serene realities of sentiment flourish, but of the arid and imperfectly explored desert of the material world, the scientific facts are the basis of all constructions. Destroy those and you destroyeverything. If you ram the ground floor of a house and bring it down, you bring down also the upper stories.
To say the truth, it would seem that nothing here below so much reveals the mystic presence of the divine as does the eternal and inflexible harmony that unites phenomena, and that finds expression in the laws of science.
Is not this science which shows us the vast universe well-ordered, coherent, harmonious, mysteriously united, organised like a great mute symphony, dominated by law instead of caprice, by irrefragable rules instead of individual wills—is this not a revelation?
There you have the only means of reconciling the minds which are devoted to external realities and those which bow to metaphysical mystery. To talk of bankruptcy of science—if it means anything more than to point out human weakness, which is, alas! obvious enough—is really to calumniate that part of the divine which is accessible to our senses, the part which science reveals.
In sum, the whole Einsteinian synthesis flows from the issue of the Michelson experiment, or at least from a particular interpretation of that issue.
The phenomenon of stellar aberration proves that the medium which transmits the light of the stars to our eyes does not share the motion of the earth as it revolves round the sun. This medium is known to physicists as ether. Lord Kelvin, who was honoured by being buried in Westminster Abbey not far from the tomb of Newton, rightly regarded the existence of interstellar ether as proved as fully as the existence ofthe air we breathe; for without this medium the heat of the sun, mother and nurse of all terrestrial life, would never reach us.
In his theory of Special Relativity, Einstein, as we saw, interprets phenomena without introducing the ether, or at least without introducing the kinematic properties which are usually attributed to it. In other words, Special Relativity neither affirms nor denies the existence of the classic ether. It ignores it.
But this indifference to or disdain of the ether disappears in the theory of General Relativity. We saw in a previous chapter that the trajectories of gravitating bodies and of light are directly due, on this theory, to a special curvature and the non-Euclidean character of the medium which lies close to massive bodies in the void—that is to say, ether. This, therefore, though Einstein does not give it the same kinematic properties as classic science did, becomes the substratum of all the events in the universe. It resumes its importance, its objective reality. It is the continuous medium in which spatio-temporal facts evolve.
Hence in its general form, and in spite of the new kinematic attitude which is ascribed to it, Einstein’s general theory admits the objective existence of ether.
Stellar aberration shows that this medium is stationary relatively to the orbital motion of the earth. The negative result of Michelson’s experiment tends, on the contrary, to prove that it shares the earth’s motion. The Fitzgerald-Lorentz hypothesis solves this antinomy by admitting that the ether does not really share the earth’s motion, but saying that all bodies suddenly displaced in it are contracted in thedirection of the movement. This contraction increases with their velocity in the ether, which explains the negative result of the Michelson experiment.
Lorentz’s explanation seemed to Einstein inadmissible on account of certain improbabilities which we pointed out, and especially because it assumes that there is in the universe a system of privileged references which recalls Newton’s “absolute space.” Einstein, taking his stand on the principle that all points of view are equally relative, does not admit that there are in the universe privileged spectators—spectators who are stationary in the ether—who could see things as they are, whereas these things would be deformed for every other observer.
Then, while preserving the Lorentz contraction and the formulæ in which it is expressed, Einstein says that this contraction, while it really exists, is only an appearance, a sort of optical illusion, due to the fact that the light which shows us objects does not travel instantaneously, but with a finite velocity. This spread of light follows laws of such a nature that apparent space and time are changed in precise accordance with the formulæ of Lorentz. That is the foundation of Einstein’s Special Relativity.
Hence the two immediate possible explanations of the negative result of the Michelson experiment are:
1. Moving objects are contracted in the stationary ether, the fixed substratum of all phenomena. This contraction is real, and it increases with the velocity of the body relatively to the ether. That is Lorentz’s explanation.2. Moving objects are contracted relatively to any observer whatsoever. This contraction is only apparent, and is due to the laws of the propagation of light. It increases with the velocity of the moving body relatively to the observer. That is Einstein’s explanation.
1. Moving objects are contracted in the stationary ether, the fixed substratum of all phenomena. This contraction is real, and it increases with the velocity of the body relatively to the ether. That is Lorentz’s explanation.
2. Moving objects are contracted relatively to any observer whatsoever. This contraction is only apparent, and is due to the laws of the propagation of light. It increases with the velocity of the moving body relatively to the observer. That is Einstein’s explanation.
But there is at least one other possible explanation. It introduces new and strange hypotheses, but they are by no means absurd. Indeed, it is especially in physics that truth may at times seem improbable. This explanation will show how we may account for the result of the Michelson experiment apart from either Lorentz or Einstein.
This third explanatory hypothesis is as follows. Every material body bears along with it, as a sort of atmosphere, the ether that is bound up with it. There is, in addition, a stationary ether in the interstellar spaces; an ether insensible to the motion of the material bodies that move in it, and which we may, to distinguish it from the ether bound up with bodies, call the “super-ether.” This super-ether occupies the whole of interstellar space, and near the heavenly bodies it is superimposed upon the ether which they bear along. The ether and the super-ether interpenetrate each other just as they penetrate matter, and the vibrations they transmit spread independently. When a material body sends out series of waves in the ether which surrounds it, these move relatively to it with the constant velocity of light. But when they have traversed the relatively thin stratum of ether bound up with the material body, which merges gradually in the super-ether, they spread in the latter, and it is relatively to this that they progressively take their velocity.
It is like a boat crossing the Lake of Geneva at a certain speed. Aboutthe middle of the lake it has this speed relatively to the narrow current which the River Rhone makes there, and then it resumes it relatively to the stationary lake.
In the same way the luminous rays of the stars, although they come from bodies which are approaching or receding from us, have the same velocity when they reach us, and this will be the common velocity which the super-ether imposes upon them. Thus also, on the other hand, the stellar rays that reach our telescopes will be transmitted to us by the super-ether, without the very thin stratum of mobile ether bound up with the earth being able to disturb their propagation.
These hypotheses explain and reconcile all the facts: (1) the fact of stellar aberration, because the rays which reach us from the stars are transmitted to us unaltered by the super-ether; (2) the negative result of the Michelson experiment, because the light which we produce in the laboratory travels in the ether that is borne along by the earth, where it originates; (3) the fact that, in spite of the approach or recession of the stars, their light reaches us with the common velocity which it had acquired in the super-ether, shortly after it started.
However strange this explanation may seem, it is not absurd, and it raises no insurmountable difficulty. It shows that, if the result of the Michelson experiment is a sort of no-thoroughfare, there are other ways out of it besides Einstein’s theory.
To resume the matter, we have offered to us three different ways of escaping the difficulties, the apparent contradictions, involved in our experience—the antinomy arising from aberration and the Michelson result—and they are reduced to these alternatives:
1. The contraction of bodies by velocity is real (Lorentz).2. The contraction of bodies by velocity is only an appearance due to the laws of the propagation of light (Einstein).3. The contraction of bodies by velocity is neither real nor apparent: there is no such thing (hypothesis of super-ether connected with ether).
1. The contraction of bodies by velocity is real (Lorentz).
2. The contraction of bodies by velocity is only an appearance due to the laws of the propagation of light (Einstein).
3. The contraction of bodies by velocity is neither real nor apparent: there is no such thing (hypothesis of super-ether connected with ether).
This shows that the Einsteinian explanation of phenomena is by no means imposed upon us by the facts, or is at least not absolutely imposed by them to the exclusion of any other explanation.
Is it at least imposed by reason, by principles, by the evidential character of its rational premises, or because it does not conflict with our good sense and mental habits as the others do?
One would suppose this at first, when one compares it with the teaching of Lorentz; and, in order to relieve this discussion, I will for the moment leave out of account the third theory which I sketched, that of a super-ether.
What seemed most difficult to admit in Lorentz’s hypothesis of real contraction was that the contraction of bodies was supposed to depend entirely upon their velocity, not in any way upon their nature; that it was supposed to be the same for all bodies, no matter what was their chemical composition or physical condition.
A little reflexion shows that this strange suggestion is not so clearly inadmissible. We know that the atoms are all formed of the same electrons, and they differ, and differentiate bodies, only in their number and arrangement. If, then, the electrons common to all matterand their relative distances experience simultaneously a contraction due to velocity, it is natural enough to suppose that the result maybe the same for all objects. When an iron grating of a given length is dilated by heat, the extent to which a temperature of a hundred degrees dilates it will be the same whether it counts ten or a hundred steel bars to the square yard, provided they are identical.
Hence it is not really here that we find the improbability which caused Relativists to reject the Lorentz theory. It is in the principles of the theory. It is because the theory admits in nature a system of privileged reference—the stationary ether relatively to which bodies move.
Let us examine this more closely. It has been said that Lorentz’s stationary ether is merely a resuscitation of Newton’s absolute space, which the Relativists have so vigorously attacked. That is very far from the truth. If, as we supposed in thepreceding chapter, our stellar universe is only a giant globe of ether rolling in a space that is devoid of ether—one of many such globes that will remain for ever unknowable to man—it is obvious that the drop of ether which represents our universe may very well be moving in the environing space, which would then be the real “absolute space.”
From this standpoint the Lorentzian ether cannot be identified with absolute space. To do so amounts to saying that the space called “absolute” by Newton does not deserve the name. If Newtonian space is only the physical continuum in which the events of our universe happen, it is anything but stationary.
In that case the whole fault one has to find with Newton is that he used a wrong expression: that he called something absolute which is merely privileged for a given universe. It would be a quarrel aboutgrammar; and such things have never succeeded in revolutionising science.
But the Relativists—at least those impenitent Relativists, the Einsteinians—will not be content with that. It is not enough for them that the Newtonian space with all its privileges may not be absolute space.
Our conception of the universe, as a moving island of ether, is well calculated to reconcile the pre-eminence of Newtonian space with that agnosticism which forbids us to hope to attain the absolute. But this again is not enough for the Einsteinians. What they mean to do is to strip of all its privileges the Newtonian space on which the structure of classical mechanics has been reared. They mean to reduce this space to the ranks, to make it no more than analogous to any other spaces that can be imagined and which move arbitrarily in reference to it.
From the agnostic, the sceptical, point of view this is a fine and strong attitude. But in the course of this volume we have so much admired Einstein’s powerful theoretical synthesis and the surprising verifications to which it led that we are now entitled to make some reserves. It is legitimate to call into question even the denials of doubters, because, after all, they are really themselves affirmations.
We believe that in face of this philosophic attitude of the Einsteinians—in face of what I should like to call their absolute relativism—we are justified in rebelling a little and saying something like this:
“Yes, everything is possible; or, rather, many things are possible, but all things are not. Yes, if I go into a strange house, the drawing-room clock may be round, square, or octagonal. But once I have entered thehouse and seen that the clock is square, I have a right to say: ‘The clock is square. It has the privilege of being square. It is a fact that it is neither round nor octagonal.’
“It is the same in nature. The physical continuum which contains, like a vase, all the phenomena of the universe, might have, relatively to me—and as long as I have not observed it—any forms or movements whatever. But as a matter of fact, it is what it is. It cannot be different things at the same time. The drawing-room clock cannot at one and the same time be composed entirely of gold and entirely of silver.
“There is therefore one privileged possibility amongst the various possibilities which we imagine in the external world. It is that which has been effectively realised: that which exists.”
The complete relativism of the Einsteinians amounts to making the universe external to us to such an extent that we have no means of distinguishing between what is real and what is possible in it, as far as space and time are concerned. The Newtonians, on the other hand, say that we can recognise real space and real time by special signs. We will analyse these signs later.
In a word, the pure Relativists have tried to escape the necessity of supposing that reality is inaccessible. It is a point of view that is at once more modest and much more presumptuous than that of the Newtonians, the Absolutists.
It is more modest because according to the Einsteinian we cannot know certain things which the Absolutist regards as accessible: real time and space. It is more presumptuous because the Relativist says that there is no reality except that which comes under observation. For himthe unknowable and non-existent are the same thing. That is why Henri Poincaré, who was the most profound of Relativists before the days of Einstein, used to repeat constantly that questions about absolute space and time have “no meaning.”
One might sum it up by saying that the Einsteinians have taken as their motto the words of Auguste Comte: “Everything is relative, and that is the only absolute.”
Newton, whose spatio-temporal premises Henri Poincaré vigorously refused to admit, and classical science take up an attitude, on the contrary, which Newton himself well described when he wrote: “I am but a child playing on the shore, rejoicing that I find at times a well-polished pebble or an unusually fine shell, while the great ocean of truth lies unexplored before me.” Newton says that the ocean is unexplored, but he says that it exists; and from the features of the shells he found he deduced certain qualities of the ocean, especially those properties which he calls absolute time and space.
Einsteinians and Newtonians are agreed in thinking that the external world is not in our time entirely amenable to scientific research. But their agnosticism differs in its limits. The Newtonians believe that, however external to us the world may be, it is not to such an extent as to make “real time and space inaccessible to us.” The Einsteinians hold a different opinion. What separates them is only a question of degree of scepticism. The whole controversy is reduced to a frontier quarrel between two agnosticisms.