The same objection applies to the allegation, that infinite space is full of ether, air, gas, nebulæ, or any other kind of matter. It is an assertion incapable of proof; and therefore thoroughly unscientific; as all Infidel theories are. But if it could be proven that every part of space accessible to our telescopes is full of an ether whose undulations transmit light, as we believe it can, that would be only a proof of the finitude of matter. That ether consists of parts whose movements can be measured and numbered; and no possible multitude of such parts can amount to the infinite.
While reason thus enables us to show this dogma of the infinity of the universe to be theoretically improbable, and logically irrational, science has lately taken a more decisive step, and demonstrated it to be actually false. The universe has boundaries, and we have seen them. The proof is simple, and easily demonstrable. That broad band of luminous cloud which stretches across the heaven, called the Milky Way, consists of millions of stars, so small and distant that we can not see the individual stars, and so numerous that we can not help seeing the light of the mass; just as you see the outline of the forest at a distance, but are unable to distinguish the individual trees. Besides this mass of stars to which our solar system belongs, there are thousands of smaller similar clouds in various parts of the heavens, which have successively been shown to consist of multitudes of stars. But all around these star-clouds the clear blue sky is discovered by the naked eye.
Now, it is easy to perceive, that if all the regions of infinite space were filled either with self-luminous suns, or planets capable of reflecting light, or luminous nebulæ, or comets of gaseous consistency, at such distances as the Milky Way, or any other star-cloud demonstrates to be safe and practicable, we should see no blue sky at all; but the whole vault of heaven would present that whitish light resulting from the mingling of the rays of multitudes of stars, planets, and comets, which the Milky Way does actually exhibit. No matter how small or how distant these stars, if they were only infinitely numerous, it is impossible that there could be any point in the heavens unilluminated by their rays, even although the stars themselves were invisible to our eyes, or even to our telescopes. The whole heaven would be one vast Milky Way. Or rather, as Humboldt reasons, "If the entire vault of heaven were covered with innumerable strata of stars, one behind the other, as with a widespread starry canopy, and light were undiminished in its passage through space, the sun would be distinguished only by its spots, the moon would appear as a dark disc, and amid the general blaze not a constellation would be visible."[186] It would appear also to follow, as a necessary consequence, that such an infinite multitude of blazing suns must generate a heat compared with which the general conflagration would be cool and comfortable.
But the telescope shows us a state of matters vastly different from this. It shows us, in fact, that space, so far from being occupied with suns and stars, is mostly empty. Our universe is only a little island in the great ocean of infinite space.
Though the telescope discovers multitudes of stars where the naked eye sees none, yet they are, in far the greater number of instances, "seen projected on a perfectly dark heaven, without any appearance of intermixed nebulosity."[187] And even through the Milky Way, and the other nebulæ, the telescope penetrates, through "intervals absolutely dark, and completely void of any star, of the smallest telescopic magnitude."[188] It may assist us to understand the full import of this declaration, to remember that Lord Rosse's large telescope clearly defines any object on the moon's surface as large as the Custom House. Its power of penetrating space surpasses our power of imagination, but is represented by saying, that light, which flashes from San Francisco to London quicker than you can close your eye and open it again, requires millions of years to travel to our earth from the most distant star-cloud discoverable by this telescope.[189] If a galaxy like this of ours existed anywhere within this amazing distance, that telescope would discover its existence. It has, in fact, augmented the universe visible to us, 125,000,000 times, and thus made us feel that not merely this world, which constitutes our earthly all, and yon glorious sun, which shines upon it, but all the host of heaven's suns, and planets, and moons, and firmaments, which our unaided eyes behold, are but as a handful of the sand of the ocean shore compared with the immensity of the universe. But ever, and along with this, it has shown us the ocean as well as the shore, and revealed boundless regions of darkness and solitude stretching around and far away beyond these islands of existence. The telescope, then, enlarges and confirms our views of the extent of the unoccupied portions of space.
If there were only one dark point of the heavens no larger than the apparent magnitude of the smallest star, this one unoccupied space would sufficiently disprove the infinity of the universe, inasmuch as there would be a portion of space of boundless length, and of a diameter not less than the diameter of the earth's orbit, say 190,000,000 miles, in which stars might exist, as they do in its borders, but yet do not. But the argument becomes utterly overwhelming, when the attempt is made to calculate the proportion of space occupied by the stars to that left unoccupied. Whether we take Herschel's computation, that the nebulæ cover one two hundred and seventieth part of the superficies of the visible heaven,[190] or Struve's supposition of the existence of a star subtending no measurable angle, in every part of the visible sky as large as the surface of the moon, the vast disproportion of the universe, to the space in which it is placed, forces itself upon our notice. For, upon the largest of these computations, the proportion of existence to empty space is mathematically proved to be not greater than as the cube of one to the cube of two hundred and sixty-nine; that is to say, there is room for 19,395,109 such universes as this of ours in that small part of infinite space open to the view of Herschel's telescopes. But when we come to consider the vastness of these regions of darkness, over which no light has traveled for twenty millions of years, and remember also that astronomers have looked clear through the nebulæ, and find that they bear no more cubical proportion to the infinite darkness behind them than the sparks of a chimney do to the extent of the sky against which they seem projected, so far from imagining the universe to be infinite, we stand confounded at its relative insignificance, and are convinced that it bears no more proportion to infinite space than a fishing-boat does to the Atlantic Ocean.
There is no possible evasion of this great fact, by any contradictory hypothesis. It can not be objected "that stars may exist at infinite distances, whose light has not yet reached the limits of our universe." If they do, they did not exist from eternity, for there is no possible distance over which light could not have traveled, during eternal duration. But their eternal existence is the very thing which the Atheist is concerned to prove. Grant that infinite space is filled with worlds which had a beginning, and their necessary existence instantly falls, and we are compelled to seek for a cause of their beginning of existence; that is to say, a Creator.
Nor will it answer the purpose to say, "that for anything we know to the contrary, these dark regions may be filled with dark stars."
If the fact were so, it is equally fatal to the dogma of self-existence. Some stars shine; others are dark. Why so? Wherefore this difference? Variety is an effect, and demands a prior cause. Were there only two stars in the sky, or two substances on the earth, and those unlike in any particular, that plurality, and that variety, would prove that they could not be infinite or self-existent, but dependent upon some cause for their existence, and for their variety of form.
But we do know many things contrary to the notion that the dark regions of infinite space may be full of dark stars. Light is not the only indication of the presence of a star. The attraction of gravity, which is wholly independent of light, is a proof quite as certain and satisfactory to the astronomer. The presence of stars and planets too faint to be discovered by the naked eye, and of one, the planet Neptune,[191] as far distant from the planet disturbed by its attraction as the earth is from the sun, was ascertained, and its place pointed out by Adams and Le Verrier, before it was seen. If the dark interplanetary spaces, then, were full of dark attracting bodies, the perturbations of the other planets would discover their existence. So the presence of some invisible stars at much greater distances from their visible associates has been discovered by Bessel,[192] and it is quite possible that a dark firmament may yet be discovered, containing as great a number of dark stars as we now behold of luminaries; another group of islets in the ocean of infinite space. But the very facts which will prove their existence will disprove their infinity; for we can know their presence only by their perturbation of the proper motions of the visible stars; but if infinite space were full of dark bodies, the visible stars would have no room to move at all. It is easily demonstrable, that if infinite space were filled with dark stars, the equilibrium and coherence of our galaxy, and of all other clusters of stars, would be destroyed. The existence of nebulæ, and clusters, and the revolutions of the binary stars, are conclusive proof that the dark parts of infinite space are not full of dark attracting bodies.