We cannot ourselves go and find out what the sun, moon or stars consist of, but our huge telescopes will, in a sense, bring them near to us, which comes to much the same thing. Thus the whole of space lies open for our exploration, at any rate until we are confronted by opaque substances which no telescope can penetrate. Even then the calculations of the mathematician are ready to carry on the story; for instance, quite a lot of work has been done in recent years on the constitution of the interiors of the stars. Telescopic observation and mathematical theory between them furnish us with a sort of magic rocket which will take us almost anywhere in space we desire to go.

Out in Space

Let us enter this magic rocket and persuade someone to shoot us towards the sun. We need only start with speed enough to carry us a short distance away from the earth—about 7 miles a second will do—and the sun's huge gravitational pull will do the rest. It will drag us down into the sun whether we like it or not. If we start at 7 miles a second, the whole journey will take about ten weeks.

Even in the first few seconds of our flight, we notice strange changes; the whole colour-scheme of the universe alters with startling suddenness.

Now that our rocket has brought us safely back to the earth of to-day, let us consider in more detail the small colony, almost completely isolated in space, which we believe to be the shattered fragments of what was once an ordinary star. It contains a great variety of objects, large, medium-sized, small and very small, which we must discuss in turn.

The Nine Planets

First let us look at its largest members, the nine principal planets. These move round the sun in almost circular paths, rather like circus horses trotting or galloping round the ring-master. They all go round in the same direction, and this must of course be the direction in which the wandering star, which brought them into being, moved round the sun. Because of the way it came into existence, the solar system has only one-way traffic—like Piccadilly Circus. The traffic nearest the centre moves fastest; that further out more slowly, while that at the extreme edge merely crawls—at least by comparison with the fast traffic near the centre. It is true that even the furthest and slowest of the planets covers nearly three miles every second, which is about 200 times the speed of an express train, but this is a mere crawl in astronomy. The planets Mercury and Venus, which constitute the fast traffic near the centre, move, the former ten and the latter seven, times as fast.

We inhabitants of the earth enjoy a piece of good fortune to which we give very little thought, which, indeed, we take almost as much for granted as the air we breathe—I mean the fact that we have a transparent atmosphere. Some of the other planets, for instance Venus and Jupiter, have atmospheres which are so thick with clouds as to be totally opaque. If we had been born on Venus or Jupiter, we should have lived our lives without ever seeing through the clouds, and so should have known nothing of the beauty and poetry of the night sky, and nothing of the intellectual excitement and joy of trying to decipher the meaning of the vast panorama of lights which are scattered round us in all directions in space.

It will not form a bad approach to our subject, if we imagine that until to-night our earth had also been covered in by an opaque blanket of clouds. Suddenly this is rolled back, and we see the glory, and the tantalising puzzle, of the night-sky for the first time.

Our first impression would probably be that the stars were some sort of illumination of lamps or lanterns suspended above our heads, perhaps at only a few miles, or even yards, distance—rather like the lights in the roof of a vast tent or hall.

We have seen how, when little was known about astronomy, it was natural to imagine that the stars went on for ever and ever, so that, however far one probed into space, one merely came to more stars. It was only like the town-bred child imagining that the lamp-posts go on for ever and ever. Yet we now know that if we go far enough out into space, we come to regions where the stars first begin to thin out, and then disappear altogether: we are now out in the depths of space beyond the Milky Way. The stars are like the lights of a vast city, but no city, however great, extends for ever, and if we go far enough, we get out of the city, and come at last to the dark open country beyond.

Yet this is not the whole story. We now know that the wheel-shaped system of stars bounded by the Milky Way is not the only system of stars in space. Far beyond the Milky Way are other cities, each with its own system of lights. The dark open country which surrounds our own city is not the end of everything; if we persevere through it for long enough, we shall come in time to another city whose lights are stars similar to those surrounding our sun. Let me explain the evidence for this statement.

When we discussed the face of the sky in our first chapter, the stars were nothing to us but a distant background of points of light. This background enabled us to fix our bearings in space, and we saw how we could pick out our near neighbours, the planets and other members of the sun's family, by their rapid motion against it.

Since then we have examined what the stars really are, and have discussed their various physical characteristics. Amongst other things, we have found that they shew great variety in their candle-powers. While some are thousands of times more luminous than our sun, others are thousands of times fainter. If we compare our sun to an ordinary candle, some stars must be compared to searchlights, and some, at the other end of the scale, to glow-worms or fireflies.

It has only recently been discovered how great a range there is in the candle-powers of the stars. For a long time it was supposed that the stars all had pretty much the same intrinsic brightness—like a row of street lamps—so that when a star looked very dim, it was only because it was very distant. In 1761 the astronomer Lambert argued that as all the stars had been made to serve the same purpose, there was no reason why some should have been made fainter than others; if some appeared fainter it could only be that they were more distant.

We have seen how modern physics reduces the universe to systems of waves. If we find it hard to imagine waves unless they travel through something concrete, let us say waves in an ether or ethers. I believe it was the late Lord Salisbury who defined the ether as the nominative of the verb “to undulate.” If this definition will serve for the moment, we can have our ether without committing ourselves very far as to its nature. And this makes it possible to sum up the tendency of modern physics very concisely: modern physics is pushing the whole universe into one or more ethers. It will be well, then, to scrutinise the physical properties of these ethers with some care, since in them the true nature of the universe must be hidden.

It may be well to state our conclusion in advance. It is, in brief, that the ethers and their undulations, the waves which form the universe, are in all probability fictitious. This is not to say that they have no existence at all: they exist in our minds, or we should not be discussing them; and something must exist outside our minds to put this or any other concept into our minds. To this something we may temporarily assign the name “reality,” and it is this reality which it is the object of science to study.

Let us study in more detail this soap-bubble, blown of emptiness, by which modern science portrays the universe. Its surface is richly marked with irregularities and corrugations. Two main kinds may be discerned, which we interpret as radiation and matter, the ingredients of which the universe appears to us to be built.

Markings of the first kind represent radiation. All radiation travels at the same uniform speed of about 186,000 miles a second. If the train in Fig. 2 (p. 88) had travelled at a uniform speed of a mile a minute, its motion would have been represented by a perfectly straight line inclined at an angle of 45° to the vertical. A succession of trains all moving uniformly at a mile a minute would be represented by a lot of lines all parallel to this. Now let us change our standard speed from a mile a minute to 186,000 miles a second, and replace the one direction from London to Plymouth by all the directions in space. The diagram on p. 88 now becomes replaced by the four-dimensional continuum, and radiation is represented by a set of lines all making the same angle (45°) with the direction of time advancing.

Markings of the second kind represent matter. This moves through space at a variety of different speeds, but all are small in comparison with the speed of light.

Primitive man must have found nature singularly puzzling and intricate. The simplest phenomena could be trusted to recur indefinitely; an unsupported body invariably fell, a stone thrown into water sank, while a piece of wood floated. Yet other more complicated phenomena shewed no such uniformity—the lightning struck one tree in the grove while its neighbour of similar growth and equal size escaped unharmed; one month the new moon brought fair weather, the next month foul.

Confronted with a natural world which was to all appearances as capricious as himself, man's first impulse was to create Nature in his own image; he attributed the seemingly erratic and unordered course of the universe to the whims and passions of gods, or of benevolent or malevolent lesser spirits. Only after much study did the great principle of causation emerge. In time it was found to dominate the whole of inanimate nature: a cause which could be completely isolated in its action was found invariably to produce the same effect. What happened at any instant did not depend on the volitions of extraneous beings, but followed inevitably by inexorable laws from the state of things at the preceding instant. And this state of things had in turn been inevitably determined by an earlier state, and so on indefinitely, so that the whole course of events had been unalterably determined by the state in which the world found itself at the first instant of its history; once this had been fixed, nature could move only along one road to a predestined end.