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.