The unseen universe

by Balfour Stewart; Peter Guthrie Tait

It will be obvious now that an enormous increase of the so-called space-penetrating power of a telescope gives it in reality but a very feeble additional advantage, in fact, that, if there be absorption by the ether, we have already instruments capable of showing us, at the very least, half of the whole number of stars which any conceivable improvement of telescopes would enable us to see.

148. It would be out of place here to speculate on what becomes of the light thus supposed to be absorbed, for we have as yet no experimental bases on which to reason. We have not the least idea, for instance, what is the effect of change of temperature in the luminiferous ether. That it is practically incompressible we know; it is quite probable that it may not be sensibly compressed (if it be subject to gravity, of which we have no proof) even by the attraction of the mass of the whole earth—though, so great is the intensity of molecular or cohesive attraction, we may easily conceive that in the interior of bodies the ether may be considerably compressed. And it is not improbable that the ether, as a whole, may have, in virtue of its internal forces, a property (akin, as it were, to a liquid film) such that the gravitation action, which appears to be between particles of matter, may merely be the visible result of a tendency to a minimum of some affection of the fluid in which they are immersed.

Regard the ether as we please, there can be no doubt that its properties are of a much higher order in the arcana of nature than those of tangible matter. And as even the high-priests of science still find the latter far beyond their comprehension, except in numerous but minute and often isolated particulars, it would not become us to speculate further. It is sufficient for our purpose to know from what the ether certainly does that it is capable of vastly more than any one has yet ventured to guess.

149. If we review the attempts recorded in this chapter we see how the scientific mind is led from the visible and tangible to the invisible and intangible.

In the first place, we know that one body, such as the sun, can part with its radiant energy to another body, such as the earth, and observation and experiment alike lead us to acknowledge a stage in which the energy has left the one body and has not yet arrived at the other. But we have already seen that energy is always found associated with matter, never by itself. In fact we have spoken of matter as the ‘vehicle of energy.’ Hence it necessarily follows that there is something between the sun and earth capable of moving and transmitting energy, and therefore, from the very conception of energy, possessing mass—this something we agree to call the ethereal medium.

Again, we know that different masses of visible matter attract one another apparently at a distance. Our first attempt to analyse the nature of this force leads to the question:—Does it proceed from the surfaces of the attracting bodies, or does it penetrate their entire mass? This question was answered by Newton, who came to the conclusion that every particle of matter attracts every other particle with a force proportional to the product of their masses, and inversely proportional to the square of their distances.

But this drives the mystery of gravitation only from the mass to the particle, and here the same sort of questions again occur. A particle as truly as a mass occupies space, and we wish to know whether gravitation force proceeds from the surface of the particle or from its interior.

150. We likewise wish to know how this force is communicated between one particle and another? Before we can solve these questions we must have some definite conception of the nature of a particle and of the constitution of the surrounding medium. Sir W. Thomson, as we have seen, has attempted to advance towards the nature of an atom or particle in his supposition that atoms are vortex-rings generated out of a perfect fluid filling all space. While, however, this conception accounts for some of the properties of an atom it does not at all directly account for anything like gravitation, and hence he adopts in addition the hypothesis of ultra-mundane corpuscles, which he supposes to be only a finer form of vortices.

151. There is, however, one objection to the precise form of vortex-ring hypothesis introduced by Thomson which from our point of view is very strong. The act by which the atom was produced must surely on this hypothesis have been an act of creation in time ([Art. 133]), that is to say, an act impressed upon the universe from without, and it must therefore have denoted a breach of continuity ([Art. 85]); for if the antecedent of the visible universe be nothing but a perfect fluid, can we imagine it capable of originating such a development in virtue of its own inherent properties, and without some external act implying a breach of continuity?—we think most assuredly not. In the production of the vortex-atom from a perfect fluid we are driven at once to the unconditioned—to the Great First Cause; it is, in fine, an act of creation and not of development. But from our point of view ([Art. 86]) creation belongs to eternity and development to time, and we are therefore induced at least to modify the hypothesis so as to make it consistent with this view. We cannot, in fact, if we agree to hold at the same time the principle of unbroken continuity and the vortex-ring theory of formation of the visible universe, regard the material whose rotating parts are ordinary matter as an absolutely perfect fluid.

152. This way of regarding this supposed material is strengthened by the fact that the hypothesis which seems most likely to account for gravitation presumes the existence of ultra-mundane corpuscles: and the observations of Struve upon the extinction of starlight tend (whatever they are worth) towards the same conclusion, since the absorption of light is more compatible with a corpuscular constitution than with that of a perfect fluid. Finally, the mere fact that the velocity of light is finite, tends also in the same direction. But if the visible universe be developed from a material which is not a perfect fluid, then the argument deduced by Sir W. Thomson in favour of the eternity of ordinary matter disappears, since this eternity depends upon the perfect fluidity of that out of which it was developed. In fine, if we suppose the material universe to be composed of a series of vortex-rings developed from something which is not a perfect fluid, it will be ephemeral, just as the smoke-ring which we develop from air, or that which we develop from water, is ephemeral, the only difference being in duration, these lasting only for a few seconds, and the others it may be for billions of years.