2: Fundamental Notions about an Ether

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2: Fundamental Notions about an Ether
How matter is held together, and how we see it.

Apollonius of Tyana is said to have asked the Brahmins of what they supposed the Cosmos to be composed.

"Of the five elements."

"How can there be a fifth," demanded Apollonius, "beside water and air and earth and fire?"

"There is the ether," replied the Brahmin, "which we must regard as the element of which the gods are made; for just as all mortal creatures inhale the air, so do immortal and divine natures inhale the ether."

THE first thing to realise about the Ether is its absolute continuity. Let me explain. Matter is discontinuous; it consists of portions with gaps between. You see this clearly enough in the stars; they are bodies separated by wide empty spaces, they are not massed together. There must be a reason for this; the reason is partly known, but is not easy: we will be satisfied with the fact that it is so. Matter is full of discontinuity; it consists mostly of empty space: the portions of matter in space are all well separated from each other in proportion to their size. Fire an infinitely long-range projectile into the sky, and the chances are it will not hit anything: Lord Kelvin reckoned that the chance of hitting anything by such a projectile was about the same as the chance of hitting a bird if you fired a gun at random. That is one of the first things to realise about matter: there are great gaps between its particles.

You may say, That is all very well for the sky and the stars and planets; but what about the earth? What about a piece of rock, or furniture, or any solid object? Do you mean to say that the particles of a body like that are widely separated, with great spaces between them in proportion to their size, and that a straight line might penetrate them deeply without encountering a particle? Yes, I do: that is what I mean by the discontinuity of matter. It is discontinuous on a small scale as well as on a large scale. It does not appear so, but that is only because our senses are not fine enough to tell us about things on a small scale: we can only see things on a big scale. A microscope is of some assistance, but nothing like sufficient: no microscope, however powerful, can show us an atom, still less can it show us how an atom is composed and how far apart its ultimate particles are: we know this otherwise and indirectly. It is however common knowledge, now, that matter is built up of minute electric charges, both negative and positive, which are called electrons and protons. It is also known that these electric units are so extremely minute that they are separated from one another like the planets in the solar system: the greater part of the atom is empty space, just like the sky on a small scale. Or, more clearly, if we could take a solid body and magnify it sufficiently (which is impossible) we should see it something like the night sky.

Since the particles of matter are thus separated from each other and never in contact, it would seem to follow that they are all independent of each other, disconnected, nothing uniting them,---the particles completely separated by empty space. If there were nothing existent but matter, that would be so; there would be no unification, no binding force, no family relationship, nothing but separate independent particles: that is what would happen if Space were really empty; and the universe would be not a cosmos but a chaos.

We know better than that; we know that the stars are not independent of each other; they are bound together into systems: there is a unifying and connecting force between them, which is called Gravitation, though it is not fully understood. Hence the space between them cannot be really empty; the interspaces must be filled up somehow: there must be something which is without gaps, something really continuous, something which combines the whole together, welding all the separate bodies into a cosmos.

The same thing is true inside any solid body: the separated particles cohere, they are not independent of each other; there is no chaos to be found anywhere. The solid has a definite size and shape; and if it is a crystal its shape may be beautiful and very definite. There is evidently law and order reigning among the particles: however great the interstices between them, they must be full of something: space is not really empty, though it is empty of matter. Matter exists as separate particles, here one, there another. But the uniting "something" is not composed of particles at all; it is continuous: it unites the particles with a force which is known as Cohesion.

What you choose to call this unifying "something" is of no consequence. The Ancients sometimes spoke of the "Ether," possibly as an addition to the usual four elements, and Sir Isaac Newton adopted this term for the connecting medium. The optical medium connects the particles together in a solid or a liquid, and the same medium connects the Heavenly Bodies together into systems and clusters and constellations and nebulæ and Milky Way.

All pieces of matter and all particles are connected together by the Ether and by nothing else. In it they move freely, and of it they may be composed. We must study the kind of connexion between matter and Ether.

The particles embedded in the Ether are not independent of it, they are closely connected with it, it is probable that they are formed out of it: they are not like grains of sand suspended in water, they seem more like minute crystals formed in a mother liquor. The mode of connexion between the particles and the Ether is not known; it is earnestly being sought but the fact that there is a connexion has been known a long time. We know it, because a particle cannot quiver or move without disturbing the medium in which it is. A boat cannot oscillate on the surface of water without sending off waves or ripples; a bell cannot vibrate in air without sending out waves of sound; a particle cannot vibrate in Ether without sending out waves akin to those of light.

So the second thing to learn about the Ether is its property of conveying light. It seems curious to call it a "second" property, because historically it was the first,---the first discovered and the first on which attempts were made at elaboration. The Physics of the early part of the Nineteenth Century was almost wholly occupied with it: the highest genius was devoted to the theory of Ether waves, and the climax was reached by Clerk Maxwell. The whole of the immense Science of Optics is involved and grew out of it; but as with everything else it is difficult completely to understand and to realise clearly what is happening: certain things can be stated with apparent simplicity, but the full explanation is not yet attained.

The first and most definite fact, on which there is complete agreement, is the rate at which Ether waves travel, the thing ordinarily called "the velocity of light." This speed is the most fundamental and absolute thing in the physical universe, and it is evidently related to some fundamental or constitutional velocity, the full meaning of which has still to be discovered. Meanwhile we can make elementary statements about what has been observed in connexion with it.

The speed is measured by timing the interval required by light to travel a certain measured distance, whether it be a distance measured on the earth or a greater distance measured in the heavens. The results all agree, and there is no doubt that all Ether waves, however else they differ, travel at the same pace. The speed of light is not only the speed of that by which we see things, but it is the speed with which every disturbance travels in the Ether of Space. Such disturbances may be the great waves (akin as it were to Atlantic rollers) which we employ in radio telegraphy; or they may be the small ripples which, when they break upon the shore of matter, excite heat; or they may be the minuter tremors which in enormous numbers enter the eye and operate the curious receiving mechanism there, so as to disturb the nerves and give us the sense of sight, or, by rearranging the chemicals on a glass plate or film, can reproduce the likeness of the objects which have emitted them; or they may be the still minuter tremors---small almost beyond imagination, and beyond the power of any microscope to utilise,---fearfully rapid tremors or ether vibrations which can be excited electrically in a form which we know as X-rays. But whether big or small, they all travel at the same pace, with a speed far beyond anything in our experience, a speed which it seems impossible even for the Ether to over-top.

Imagine a thread wrapped round the Equator of the world, crossing all the continents and oceans; stretch such a thread out into a straight line---that is the distance which light can travel in the seventh part of a second. To get the distance traversed by light in a second, the thread would have to be wrapped round the world seven times and then stretched out; such a thread would reach nearly to the moon. The light of the moon takes a second and a quarter to reach the earth: from the Sun it takes eight minutes: from the stars, even the bright stars, it takes years or even centuries: while some of the dim and distant objects revealed in a large telescope we see only as they were a hundred-thousand years ago. So immense is the scale of the Universe!

All this is well and even popularly known: the difficulties do not lie here, they lie in determining the exact nature of the waves and the way in which they are produced. We have to work by analogies for the most part. As a vibrating bell or string or tuning-fork excites waves in the air, so a vibrating electron excites waves in the Ether: the processes are analogous, not identical; and if we tried now to enter into more detail we should get beyond our depth.

Meanwhile if ripples are travelling from distant objects, there must be something which is rippling. You cannot imagine Space being thrown into Vibration; there must be something in space which vibrates, and that "something" extends to the furthest visible object. This was our first idea of the Ether of Space: it is more than a century old, and the argument was as valid in 1825 as it is to-day. The Ether was therefore called "the luminiferous Ether," the light-carrier, the vehicle of light. Nor of light only, but of every other link between the worlds and between the atoms; the vehicle of Gravitation, as Sir Isaac Newton suspected; the vehicle of Cohesion too, as we now know; the unifying and connecting mechanism which welds together the disconnected atoms of matter and makes cosmos out of chaos.

However evasive the ether is to our senses it is a great reality and we continually use it. The waves emitted by a radio-aerial will get to the Antipodes, say New Zealand, in the 1/14th part of a second. How far will sound waves travel in the same time? Sound in air takes five seconds to go a mile. Consequently in the 1/14th part of a second they go the 1/70th part of a mile, which is 25 yards, that is to the back of a hall in which one might be speaking. Ether waves travel just about a million times as quickly as sound waves: consequently if the waves were of the same length, the vibrations would be a million times as rapid. But the Ether waves by which we see are not of the same length: sound waves are a few feet long: whereas a series of 50,000 light waves is only an inch long. Consequently the rate of vibration which the eye perceives is 500 million-million per second---a quite incredible number! But in dealing with the Universe we must not be afraid of large numbers: the magnitudes we deal with are many of them appalling, some of them appalling for size, others for smallness, some for rapidity, others for unknown and mysterious properties. We have as yet very little acquaintance with the Universe; sometimes we seem to know a great deal, at other times we realise that we hardly know anything. The mystery of it all escapes us, the possibilities of it are beyond our conception: many of them we could not apprehend if they were explained to us, we have not the terms or ideas to understand them. Meanwhile we grope along as best we can, and do our daily work and have a keen expectation of the future; and he is wisest who denies least of the mystery which surrounds us and the possibilities ahead. To assert requires knowledge, to deny requires much more knowledge. Let us be satisfied with positive knowledge, so far as it has been vouchsafed to us, and leave negations to the self-sufficing and the omniscient. We can deny the self-contradictory and the absurd, but in the Unknown and the Mysterious, denials have no legitimate place: our business is carefully and cautiously to ascertain what is. We are surrounded by infinity, infinities of various kinds; and the wealth of existence is such as to justify a Faith in our highest conceptions, a Hope in the possibilities which lie before us, and a Charity which enables us to do our daily work and to love our fellow men.