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. But
now, 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, an _absolute_ reality. 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 new
doctrine. 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 destroy
everything. 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 of
the 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 the
direction 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.
* * * * *
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. About
the 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).
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 matter
and 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 the preceding 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 about
grammar; 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 the
house 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 him
the 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.