The Universe Around Us quotes

On the evening of January 7, 1610, a fateful day for the human race, Galileo Galilei, Professor of Mathematics in the University of Padua, sat in front of a telescope he had made with his own hands.

More than three centuries previously, Roger Bacon, the inventor of spectacles, had explained how a telescope could be constructed so as “to make the stars appear as near as we please.”

In estimating his position in the universe, man had up to now been guided mainly by his own desires, and his self-esteem; long fed on boundless hopes, he had spurned the simpler fare offered by patient scientific thought.

Inexorable facts now dethroned him from his self-arrogated station at the centre of the universe; henceforth he must reconcile himself to the humble position of the inhabitant of a speck of dust, and adjust his views on the meaning of human life accordingly.

The adjustment was not made at once. Human vanity, reinforced by the authority of the Church, contrived to make a rough road for those who dared draw attention to the earth’s insignificant position in the universe. Galileo was forced to abjure his beliefs.

When we are able to put a question in such a definite form that either of these answers could be given in reply, we are generally already in a position to supply the answer ourselves.

Science advances rather by providing a succession of approximations to the truth, each more accurate than the last, but each capable of endless degrees of higher accuracy.

To the question, “where does man stand in the universe?” the first attempt at an answer, at any rate in recent times, was provided by the astronomy of Ptolemy: “at the centre.” Galileo’s telescope provided the next, and incomparably better, approximation:

… even to-day the astronomer is largely occupied with foretelling the future movements of the heavenly bodies, although not of human affairs—a considerable part of the present book will consist of an attempt to foretell the future, and predict the final end, of the material universe.

Where the astrologers went wrong was in supposing that terrestrial empires, kings and individuals formed such important items in the scheme of the universe that the motions of the heavenly bodies could be intimately bound up with their fates.

As soon as man began to realise, even faintly, his own insignificance in the universe, astrology died a natural and inevitable death.

Where the astrologers went wrong was in supposing that terrestrial empires, kings and individuals formed such important items in the scheme of the universe that the motions of the heavenly bodies could be intimately bound up with their fates.

As soon as man began to realise, even faintly, his own insignificance in the universe, astrology died a natural and inevitable death.

The utilitarian aspect of astronomy has by now shrunk to very modest proportions.

A gain of astronomical knowledge may add to our knowledge of physics and chemistry, and vice versa. The stars have long ago ceased to be treated as mere points of light.

Each is now regarded as an experiment on a heroic scale, a high temperature crucible in which nature herself operates with ranges of temperature and pressure far beyond those available in our laboratories, and permits us to watch the results.

In so doing, we may happen upon properties of matter which have eluded the terrestrial physicist, owing to the small range of physical conditions at his command.

Many even of those who seek after knowledge for its own sake, driven by that intellectual curiosity which provides the fundamental distinction between themselves and the beasts, find their main interest in astronomy, as the most poetical and the most aesthetically gratifying of the sciences.

They want to exercise their faculties and imaginations on something remote from everyday trivialities, to find an occasional respite from “the long littleness of life,” and they satisfy their desires in contemplating the serene immensities of the outer universe.

To many, astronomy provides something of the vision without which the people perish.

Finally its outer crust solidifies, rocks and mountains forming a permanent record of the irregularities of its earlier plastic form. Vapours condense into liquids, and rivers and oceans come into being, while the “permanent” gases form an atmosphere.

Gradually the earth assumes a condition suited to the advent of life, which finally appears, we know not how, whence or why.

It is not easy to estimate the time since life first appeared on earth, but it can hardly have been more than a small fraction of the whole 2000 million years of the earth’s existence.

The evidence favours a period of about 300,000 years ago for this last event. Thus life has inhabited the earth for only a fraction of its existence, and man for only a tiny fraction of this fraction.

To put it in another way, the astronomical time-scale is incomparably longer than the human time-scale—the generations of man, and even the whole of human existence, are only ticks of the astronomer’s clock.

Most of the 10,000 or so of generations of men who connect us up with our ape-like ancestry must have lived lives which did not differ greatly from those of their animal predecessors.

He began to experiment with metals and herbs, and with the effects of fire and water.

He began to notice, and try to understand, the motions of the heavenly bodies, for to those who could read the writing in the sky, the nightly rising and setting of the stars and planets provided evidence that beyond the confines of the earth lay an unknown universe built on a far grander scale.

In this way the arts and sciences came to earth, bringing astronomy with them.

Quite recently Pettit and Nicholson have measured the amount of heat received on earth from the warmed hemisphere, and find that its temperature must be about 350° Centigrade or 662° Fahrenheit, thus confirming that the planet always turns the same face to the sun.

Its warm hemisphere is at a temperature which melts lead; the other hemisphere, eternally dark and unwarmed, is probably colder than anything we can imagine.

The Milky Way in the neighbourhood of the Southern Cross

And, as might be expected, the proper interpretation of this great belt of faint stars has proved to be fundamental in understanding the architecture of the universe.

If stars were scattered uniformly through infinite space, we should at last come to a star in whatever direction we looked, so that the sky would appear as a uniform blaze of intolerable light.

It is true that this would not be the case if light were dimmed or blotted out after travelling a certain distance, but even then, the sky would appear the same in all directions, for there would be no reason why one part of the …

Yet an eye-piece which magnifies 60 times, or any greater number of times, can never make a star look as large as the moon. No magnification within our command causes any star to appear as anything other than a mere point of light.

The stars are of course enormously larger than Jupiter, but they are also enormously more distant, and it is the distance that wins.

N.G.C. 1501

Here and there this cloud may be denser than usual; here and there again it may be lighted up and made to incandesce by the radiation of the stars within it.

In other places it may be entirely opaque to light, lying like a black curtain across the sky.

The variations of density, opacity and luminosity in combination produce all the fantastic shapes and varied degrees of light and shade we see in the galactic nebulae.

When a speaker broadcasts from London his voice takes longer to travel 3 feet from his mouth to the microphone as a sound wave, than it does to travel a further 560 miles to Berlin or Milan as an electric wave.

Wireless listeners in Australia hear the music of a broadcast concert sooner than an ordinary listener at the back of the concert hall who relies on sound alone; they hear it a fifteenth of a second after it is played.

Yet light, or wireless waves travelling with the same speed as light, takes 4·27 years to reach the nearest star, so that the inhabitants of Proxima Centauri would be over four and a quarter years late in hearing a terrestrial concert.

The eye can only measure distances between astronomical objects by the help of an intricate machinery of cross-wires, screws and verniers; the photographic plate records distances automatically.

The eye, betrayed by preconceived ideas, impatience or hope, can and does make every conceivable type of error; the camera cannot lie.

And so it comes about that if we try to pick out landmarks in twentieth-century astronomy we find that, in a sense, it consists of nothing but landmarks;

Actually we find that the weights of the stars are mostly fairly equal, very few stars having weights greatly dissimilar from that of the sun.

This seems to indicate that a star is a definite species of astronomical product, not a mere random chunk of luminous matter.

LUMINOSITY. The last column of the table on p. 48 gives the “luminosities” of the stars, which means their candle-power as lights, that of the sun being taken as unity.

The light-fluctuations are so distinctive as to make the stars easy of detection. There is a rapid increase of light, followed by a slow gradual decline; then again the same rapid increase and slow decline as before.

It is as though someone were throwing armfuls of fuel on to a bonfire at perfectly regular intervals.

One other class of variable stars, generally known as “long-period variables,” shews somewhat similar light-fluctuations, but the two classes are easily distinguished by their very different periods of light-fluctuation.

7006, being about ten times as remote, at a distance of 220,000 light-years. At such distances the parallactic method of measuring distances would of course fail hopelessly.

The parallactic orbit of a star at 220,000 light-years’ distance is about the size of a pin-head held at a distance of 4000 miles; no telescope on earth could detect, still less measure, such an orbit.

The mere figure of 220,000 light-years can convey but little conception of the distance of this remotest of star-clusters from us.

The galactic system, with its hundreds of millions of stars, no more contains all the stars in space than one house contains all the inhabitants of Great Britain.

There are millions of other houses and millions of other families of stars.

THE EXTRA-GALACTIC NEBULAE. We have already spoken of the faint nebulous objects which Herschel described, somewhat conjecturally, as “island universes.” These are the other houses in which other families of stars are to be found.

For all but a 500th part of its long journey, the light by which we see this remotest of visible nebulae travelled towards an earth uninhabited by man.

Just as it was about to arrive, man came into being on earth, and built telescopes to receive it.

So at least it appears when viewed on the astronomical scale.

The 200-inch telescope, which it is hoped will shortly be built, having twice the aperture of the present 100-inch, ought to probe twice as far into space, and so may perhaps be expected to shew about eight times as many, or 16 million, nebulae.

So far every increase of telescopic power has carried us deeper and deeper into space, and space has seemed to expand at an ever-increasing rate.

We may well ask whether this expansion is destined to go on for ever: are there any limits at all to the extent of space?

Yet, as we know, he would necessarily be reduced in time to repeating his own tracks.

As a result of its curvature, the earth’s surface, although unlimited, is finite in extent.

Through his theory of relativity, Einstein claims to have established that space also, although unlimited, is finite in extent.

51). On de Sitter’s cosmology, the two displacements are not entirely independent, for it is an essential feature of this cosmology that near bodies should tend to move further apart from one another.

Just as bits of straw thrown together into a stream tend to get separated as they float down the stream, so objects in de Sitter’s universe move further apart as they float down the stream of time.

Thus on de Sitter’s theory a displacement of spectral lines to the red cannot be interpreted as evidence either of motion or of distance; it is a mixture of both.

If so, we see the fronts of two objects when we look at M 33 and M 31, and the backs of the same two objects when we point our telescopes in exactly the opposite directions and look at h 3433 and M 83.

No doubt this is only a conjecture, and perhaps rather a wild one, but many more startling conjectures have been made in astronomy, and subsequently proved to be true.

All these discussions of the structure of space are of course highly speculative, but they agree in suggesting the general conclusion that, if we cannot yet see the whole of space, we can at least survey an appreciable fraction of it.

Yet we may try to see all these distances in proper proportion relative to one another by the help of a model drawn to scale.

We can escape the effort of trying to imagine unimaginably great distances by keeping the scale very small.

The earth, travelling 1200 times faster than an express train, makes a journey of 600 million miles around the sun every year. Let us represent this journey by a pin-head ¹/₁₆ of an inch in diameter. This fixes the scale of our model;

we are approaching the confines of the galaxy. In the galactic plane itself we build out for about 7000 miles before we come to the farthest globular cluster, and still we are inside the galactic system.

With our earth’s long yearly journey round the sun as a pin-head the whole galactic system is about the size of the American continent.

It may be well to pause and try to visualise the relative sizes of a pin-head and of the American continent, before we go on with our mental model-building.

it takes no account of the immense empty stretches between one system of stars and the next. On averaging throughout the whole of the model, the mean distance of a speck of dust from its nearest neighbour proves to be something like 80 miles.

The universe consists in the main not of stars but of desolate emptiness—inconceivably vast stretches of desert space in which the presence of a star is a rare and exceptional event.

Let us in imagination take up a position in space somewhere near the sun, and watch the stars moving past with speeds about 1000 times that of an express train.

If we build our model in this way, we obtain a vivid picture of the emptiness of space.

Empty Waterloo Station of everything except six specks of dust, and it is still far more crowded with dust than space is with stars.

This is true even of the comparatively crowded region inside the galactic system; it takes no account of the immense empty stretches between one system of stars and the next.

Put in another form, the calculation shews that any one star may expect to move for something of the order of a million million million years before colliding with a second star.

The stars move blindly through space, and the players in the stellar blind-man’s-buff are so few and far between that the chance of encountering another star is almost negligible.

We shall see later that this concept is of the profoundest significance in our interpretation of the universe.

We can divide it into drops, but then each drop can be subdivided into smaller drops, and there seems to be no reason, on the face of things, why this process of subdivision should not be continued for ever.

The question which agitated the Greek philosophers was, in effect, whether the water of the ocean or the sand of the sea-shore gave the truest picture of the ultimate structure of the substance of the universe.

The school of Democritus, Leucippus and Lucretius believed in the ultimate discontinuity of matter; they taught that any substance, after it had been subdivided a sufficient number of times, would be found to consist of hard discrete particles which did not admit of further subdivision.

If they were scattered over the whole land surface of the earth, there would be nearly 100 million molecules to every square inch of land.

If we think of the molecules as tiny seeds, the total amount of seed needed to sow the whole earth at the rate of 100 million molecules to the square inch could be put into a pint pot.

These molecules move with very high speeds; in the ordinary air of an ordinary room, the average molecular speed is about 500 yards a second. This is roughly the speed of a rifle-bullet, and is rather more than the ordinary speed of sound.

Here we have energy taking three different forms in rapid succession.

All the life of the universe may be regarded as manifestations of energy masquerading in various forms, and all the changes in the universe as energy running about from one of these forms to the other, but always without altering its total amount.

Such is the great law of conservation of energy.

… rare, most common substances being formed out of the combinations of about 14 different atoms, say hydrogen (H), carbon (C), nitrogen (N), oxygen (O), sodium (Na), magnesium (Mg), aluminium (Al), silicon (Si), phosphorus (P), sulphur (S), chlorine (Cl), potassium (K), calcium (Ca), and iron (Fe).

In this way, the whole earth, with its endless diversity of substances, is found to be a building built of standard bricks—the atoms.

And of these only a few types, about 14, occur at all abundantly in the structure, the others appearing but rarely.

All the changes of the universe were supposed to amount to nothing more drastic than a re-arrangement of permanent indestructible atoms; like a child’s box of bricks, these built many buildings in turn.

The story of twentieth-century physics is primarily the story of the shattering of this concept.

It was towards the end of the last century that Crookes, Lenard, and, above all, Sir J. J. Thomson first began to break up the atom.

112 below), nature herself provides an endless supply of small particles charged with positive electricity, and moving with very high speeds, in the α-particles shot off from radio-active substances. Rutherford’s method was in brief to fire these into atoms and observe the result.

And the surprising result he obtained was that the vast majority of these bullets passed straight through the atom as though it simply did not exist.

It was like shooting at a ghost.

Rutherford’s method was in brief to fire these into atoms and observe the result. And the surprising result he obtained was that the vast majority of these bullets passed straight through the atom as though it simply did not exist.

It was like shooting at a ghost.

Yet the atom was not all ghostly. A tiny fraction—perhaps one in 10,000—of the bullets were deflected from their courses as if they had met something very substantial indeed.

As we pass the whole structure of the universe under review, from the giant nebulae and the vast interstellar and internebular spaces down to the tiny structure of the atom, little but vacant space passes before our mental gaze.

We live in a gossamer universe; pattern, plan and design are there in abundance, but solid substance is rare.

ATOMIC NUMBERS. The number of electrons which fly round in orbits in an atom is called the “atomic number” of the atom. Atoms of all atomic numbers from 1 to 92 have been found, except for two missing numbers 85 and 87.

the α-particle is the shot fired, the β-particles are the smoke, and the γ-rays are the flash. The atom of lead which finally remains is the unloaded gun, and the original radio-active atom, of uranium or what not, was the loaded gun.

And the special peculiarity of radio-active guns is that they go off spontaneously and of their own accord.

All attempts to pull the trigger have so far failed, or at least have led to inconclusive results; we can only wait, and the gun will be found to fire itself in time.

The weight of this energy is relatively small, so that the weights of the atoms may be expected to be approximately integral multiples of that of the hydrogen atom, and this expectation is confirmed, but they will not be so exactly.

The exact weight of our atomic building is not simply the total weight of all its bricks; something must be added for the weight of the mortar—the electromagnetic energy—which keeps the bricks bound together.

Thus the normal atom consists of protons, electrons, and energy, each of which contributes something to its weight.

The series of concepts which we now approach are difficult to grasp and still more difficult to explain, largely, no doubt, because our minds receive no assistance from our everyday experience of nature[11].

It becomes necessary to speak mainly in terms of analogies, parables and models which can make no claim to represent ultimate reality; indeed it is rash to hazard a guess even as to the direction in which ultimate reality lies.

The laws of electricity which were in vogue up to about the end of the nineteenth century—the famous laws of Maxwell and Faraday—required that the energy of an atom should continually decrease, through the atom scattering energy abroad in the form of radiation, and so …

it might have one, two, three, four or any other integral number of units of energy, but no intermediate fractional numbers, so that gradual changes of energy were rendered impossible.

The vibrator, so to speak, kept no small change, and could only pay out its energy a shilling at a time until it had none left.

Not only so, but it refused to receive small change, although it was prepared to accept complete shillings.

In 1917, Einstein put the concept into the more precise form which now prevails. According to a theory previously advanced by Professor Niels Bohr of Copenhagen, an atomic or molecular structure does not change its configuration, or dissipate away its energy, by gradual stages.

Gradualness is driven out of physics, and discontinuity takes its place.

An atomic structure has a number of possible states or configurations which are entirely distinct and detached one from another, just as a weight placed on a staircase has only a possible number of positions;

After about a thousand-millionth part of a second the nucleus and the electron would run into one another, and the whole atom would probably disappear in a flash of radiation.

By prohibiting any emission of radiation except by complete quanta, and by prohibiting any emission at all when there are no quanta available for dissipation, the quantum theory succeeds in keeping the universe in existence as a going concern.

It is difficult to form even the remotest conception of the realities underlying all these phenomena.

The recent branch of physics known as “wave-mechanics” is at present groping after an understanding, but so far progress has been in the direction of co-ordinating observed phenomena rather than in getting down to realities.

Indeed it may be doubted whether we shall ever properly understand the realities ultimately involved; they may well be so fundamental as to be beyond the grasp of the human mind.

It is just for this reason that modern theoretical physics is so difficult to explain, and so difficult to understand. It is easy to explain the motion of the earth round the sun in the solar system. We see the sun in the sky;

So we agree to make a sort of model in which the electron and proton are represented by the simplest things known to us, tiny hard spheres.

The model works well for a time and then suddenly breaks in our hands.

In the new light of the wave-mechanics, the hard sphere is seen to be hopelessly inadequate to represent the electron. A hard sphere has always a definite position in space; the electron apparently has not.

Thus as we make a substance hotter and hotter, it emits light of ever shorter wave-length, and runs in succession through the whole rainbow of colours—red, orange, yellow, green, blue, indigo, violet.

We cannot command a sufficient range of temperature to perform the complete experiment in the laboratory, but nature performs it for us in the stars.

THE EFFECTS OF HEAT. We have already seen that radiation of short wave-length is needed to break up an electric structure of small dimensions.

we now wish to go exploring in time. Man’s individual span of life, and indeed the whole span of time covered by our historical records—some few thousands of years at most—are both far too short to be of any service for our purpose.

We must find far longer measuring rods with which to sound the depths of past time and to probe forward into the future.

Our general method will be one which the study of geology has already made familiar.

Undeterred by the absence of direct historical evidence, the geologist insists that life has existed on earth for millions of years, because fossil remains of life are found to occur under deposits which, he estimates, must have taken millions of years to accumulate.

As he digs down through different strata in succession, he is exploring in time just as truly as the geographer who travels over the surface of the earth is exploring in space.

A similar method can be used by the astronomer. We find some astronomical effect, quality, or property, which exhibits a continual accumulation or decrease, like the sand in the bottom or top half of the hour-glass;

More valuable information can be obtained from the accumulation of sediment washed down by the rain.

Every year that passes witnesses a levelling of the earth’s surface.

Soil which was high up on the slopes of hills and mountains last year has by now been washed down to the bottoms of muddy rivers by the rain and is continually being carried out to sea.

Geological methods suffice to shew that the earth must be hundreds of millions of years old, but to obtain more definite estimates of its age, the more precise methods of physics and astronomy must be called in.

Fortunately the radio-active atoms discussed in the previous chapter provide a perfect system of clocks, whose rate so far as we know does not vary by a hair’s breadth from one age to another.

We have seen how, with the lapse of sufficient time, an ounce of uranium disintegrates into 0·865 ounce of lead and 0·135 ounce of helium. The process of disintegration is absolutely spontaneous;

This method of estimating geological time has been described as the “Geological hour-glass.”

We see how much sand has already run, we notice how fast it is running now, and a calculation tells us how long it is since it first started to run.

The method suffers from the usual defect of hour-glasses, that there is no guarantee that the sand has always run at a uniform rate.

Even earlier than this, Leslie and others had used this method to determine the relative weights of different molecules, although without fully understanding the underlying theory.

Thus it may be accepted as a well-established law of nature that no molecule is allowed permanently to retain more energy than his fellows; in respect of their energies of motion, a gas forms a perfectly organised communistic state in which a law, which they cannot evade, compels the molecules to share their energies equally and fairly.

Subject to certain slight modifications, the same law applies also to liquids and solids. In liquids and gases, we can actually perform an experiment analogous to that of projecting our imaginary cannon-ball into the hail of molecule-bullets, and watch events.

A powerful microscope shews that these super-molecules are not brought completely to rest, but retain a certain liveliness of movement, as they are continually hit about by the smaller and quite invisible true molecules.

It looks for all the world as though they were affected by a chronic St Vitus’ dance, which shews no signs of diminishing as time goes on.

These movements are called “Brownian movements,” after Robert Brown, the botanist, who first observed them in the sap of plants.

These movements are called “Brownian movements,” after Robert Brown, the botanist, who first observed them in the sap of plants.

Brown at first interpreted them as evidence of real life in the small particles affected by them, an interpretation which he had to abandon when he found that particles of wax shewed the same movements.

In a series of experiments of amazing delicacy, Perrin not only observed, but also measured, the Brownian movements of small solid particles as they were hit about by the molecules of air and other gases, and deduced the weights of the molecules of these gases …

… from the single supposition that the motions of the stars are governed by either of these laws of gravitation—or, for the matter of that, by any other not entirely dissimilar law—we can prove the theorem of equipartition of energy to be true for these motions.

No subtle statement of exact conditions is required; the mere law of gravitation, together with the supposition that the stars cannot exercise free-will as to whether they obey it or not, is enough.

It is important to understand quite clearly what precisely the theorem asserts when applied to the stars. It does not of course assert that all the stars in the sky have equal energies.

… the high speeds of the latter just about making up for the smallness of their weights, and so suggested that the velocities of the stars, like those of the molecules of a gas, might be found to conform to the law of equipartition of energy.

It appeared to be a case of Brownian movements on a stupendous scale.

Since then a great deal more observational evidence has accumulated, and an exhaustive investigation made by Dr Seares of Mount Wilson in 1922 leaves very little room for doubt that the motions of the stars shew a real, and fairly close, approximation to equipartition of …

There is of course no such power-station.

The sun is entirely dependent on its own resources; it is a ship on an empty ocean.

And if, like such a ship, the sun carried its own store of coal, or if, as Kant imagined, its whole substance were its store of coal, so that its light and heat came from its own combustion, the whole would be burnt into ashes …

THE PAST HISTORIES OF THE SUN AND STARS. Let us carry on the multiplication. Two hundred and fifty million tons a minute is 360,000 million tons a day.

Thus the sun must have weighed 360,000 million tons more than now at this time yesterday, and will weigh 360,000 million tons less at this time to-morrow.

And 360,000 million tons a day is 131 million million tons a year. We can dig as far into the past as we like in this way and can probe as far as we like into the future.

the fraction is more like an eighth. This consideration extends the future life of the sun, and indeed of all the stars, almost indefinitely.

A sort of parsimony seems to creep over the stars in their old age; so long as they have plenty of weight to squander, they squander it lavishly, but they contract their scale of expenditure when they have little left to spend.

The sand runs slowly through the hour-glass when there is little left to run.

A sort of parsimony seems to creep over the stars in their old age; so long as they have plenty of weight to squander, they squander it lavishly, but they contract their scale of expenditure when they have little left to spend.

The sand runs slowly through the hour-glass when there is little left to run.

In the same way, the average star of double the sun’s weight does not merely radiate twice as much energy as the sun; it radiates about eight times as much. We must keep this in view in estimating the past life of the sun;

The two fundamental corner-stones of nineteenth-century physics, the conservation of matter and the conservation of energy, are both abolished, or rather are replaced by the conservation of a single entity which may be matter and energy in turn.

Matter and energy cease to be indestructible and become interchangeable, according to the fixed rate of exchange of 9 × 10²⁰ ergs per gramme.

Yet, looked at from another angle, the hypothesis only carries physics one stage further along the road it has already trodden in the past. Heat, light, electricity have all in turn proved to be forms of energy;

The first bottling took place millions of millions of years ago, before either sun or earth was in being, when the energy was first penned up in protons and electrons.

Instead of thinking prosaically of our sun as a mere collection of atoms, let us think of it for a moment as a vast storehouse of bottles of energy which have already lain in storage for millions of millions of years.

So enormous is the sun’s supply of these bottles, and so great the amount of energy stored in each that, even after radiating light and heat for 7 or 8 million million years, it still has enough left to provide light and heat for millions …

… the light and heat which keep the earth warm and grow our food, and the stored up sunlight in the coal and wood we burn, if traced far enough back, are found to originate out of the annihilation of electrons and protons in the sun.

The sun is destroying its substance in order that we may live, or, perhaps we should rather say, with the consequence that we are able to live.

The atoms in the sun and stars are, in effect, bottles of energy, each capable of being broken and having its energy spilled throughout the universe in the form of light and heat.

The sun is destroying its substance in order that we may live, or, perhaps we should rather say, with the consequence that we are able to live.

The atoms in the sun and stars are, in effect, bottles of energy, each capable of being broken and having its energy spilled throughout the universe in the form of light and heat.

Most of the atoms with which the sun and stars started their lives have already met this fate; the remainder are doubtless destined to meet it in time. Scientific writers of half a century ago delighted in the picturesque description of coal as “bottled sunshine”;

The combustion of a ton of the best coal in pure oxygen liberates about 5 × 10¹⁶ ergs of energy; the annihilation of a ton of coal liberates 9 × 10²⁶ ergs, which is 18,000 million times as much.

In the ordinary combustion of coal we are merely skimming off the topmost cream of the energy contained in the coal, with the consequence that 99·999999994 per cent. of the total weight remains behind in the form of smoke, cinders or ash.

Annihilation leaves nothing behind; it is a combustion so complete that neither smoke, ash, nor cinders is left.

In the ordinary combustion of coal we are merely skimming off the topmost cream of the energy contained in the coal, with the consequence that 99·999999994 per cent. of the total weight remains behind in the form of smoke, cinders or ash.

Annihilation leaves nothing behind; it is a combustion so complete that neither smoke, ash, nor cinders is left.

If we on earth could burn our coal as completely as this, a single pound would keep the whole British nation going for a fortnight, domestic fires, factories, trains, power-stations, ships and all;

of the total weight remains behind in the form of smoke, cinders or ash. Annihilation leaves nothing behind; it is a combustion so complete that neither smoke, ash, nor cinders is left.

If we on earth could burn our coal as completely as this, a single pound would keep the whole British nation going for a fortnight, domestic fires, factories, trains, power-stations, ships and all; a piece of coal smaller than a pea would take the Mauretania across the Atlantic and back.

Purely astronomical evidence has led to the conclusion that atoms are continually being annihilated in the sun and stars. Here we have a piece of the puzzle which fits perfectly on to those we tentatively fitted together in the last chapter.

In real space the unit of aggregation is the star, and an average star contains about 10⁵⁶ molecules—a number so large that it is quite useless to try to imagine it.

The emptiness of space does not originate from any paucity of molecules; it originates from the circumstance that, apart from those which form the tenuous clouds of gas stretching from star to star, the molecules are aggregated together in the huge colonies we call stars, with about 10⁵⁶ members to each.

Why should the molecules in space herd together in this way, when the molecules in the rooms in which I am writing and you are reading do not?

it originates from the circumstance that, apart from those which form the tenuous clouds of gas stretching from star to star, the molecules are aggregated together in the huge colonies we call stars, with about 10⁵⁶ members to each.

Why should the molecules in space herd together in this way, when the molecules in the rooms in which I am writing and you are reading do not?

Following a well-tried scientific method, we may attempt to discover why these aggregates have formed, by first examining what keeps them together now that they have formed. The earth’s atmosphere consists of about 10⁴¹ molecules.

In so doing, we double the gravitational pull tending to increase the condensation, but we also double the excess pressure which tends to dissipate it; we double the weights on each side of the balance, but the balance still swings in the same direction.

If once conditions are favourable to its growth, a condensation goes on growing automatically until there are no further molecules left for it to absorb.

The greater the extent in space of a condensation, the more favourable conditions are to its continued growth.

Thus, the larger a condensation is the more likely it is to go on growing, and by passing in imagination to larger and larger condensations we must in time come to condensations of such a size that they are bound to keep on growing.

Nature’s law here is one of unrestricted competition.

Nothing succeeds like success, and so we find that condensations which are big to start with have the capacity of increasing still further, while those which are small merely dissipate away.

Nature’s law here is one of unrestricted competition.

Nothing succeeds like success, and so we find that condensations which are big to start with have the capacity of increasing still further, while those which are small merely dissipate away.

Suppose now that an enormous mass of uniform gas extends through space for millions of millions of miles in every direction. Any disturbance which destroys its uniformity may be regarded as setting up condensations of every conceivable size.

Such an argument overlooks the way in which the gravitational pull of a small body acts throughout the universe. The moon raises tides on the distant earth, and also tides, although incomparably less in amount, on the most distant of stars.

Each time the child throws its toy out of its baby-carriage, it disturbs the motion of every star in the universe.

So long as gravitation acts, no disturbance can be confined to any area less than the whole of space.

The moon raises tides on the distant earth, and also tides, although incomparably less in amount, on the most distant of stars. Each time the child throws its toy out of its baby-carriage, it disturbs the motion of every star in the universe.

So long as gravitation acts, no disturbance can be confined to any area less than the whole of space.

The more violent the disturbance which creates them, the more intense the condensations will be to begin with, but even the smallest disturbance must set up condensations, although these may be of extremely feeble intensity.

And we have seen that the fate of a condensation is not determined by its intensity but by its size.

No matter how feeble their original intensity may have been, the big condensations go on growing, the small ones disappear.

In time nothing is left but a collection of big condensations. The mathematical analysis already referred to shews that there is a definite minimum weight such that all condensations below this weight merely dissipate away into space.

… enough approximation for our present purpose, this minimum weight is such that if a tenth of this weight of gas were isolated in space, and all the rest of the gas annihilated, the molecules would just and only just fail to escape from its surface[20].

We may say that the original uniformly distributed mass of gas was “unstable” because any disturbance, however slight, causes it to change its configuration entirely; it had the dynamical attributes of a stick balanced on its point, or of a soap-bubble which is just ready to burst.

PRIMAEVAL CHAOS. These general theoretical results may now be applied to any mass of gas we please. Let us begin by applying them to Newton’s hypothetical “matter evenly disposed throughout an infinite space.”

Although these densities are about a thousand million times as great as the estimated density of the original primaeval nebula of space, they are still almost inconceivably low.

There is still only about one molecule to the cubic inch, and a single breath from the lungs of a fly could fill a large cathedral with air of this density.

On proceeding to calculate the weights of the smallest condensations which could form and persist in a gas of this low density, we obtain the results shewn in the following table.

On the other hand, we not only know that the stars exist: we also know that the masses of gas exist out of which theory shews that stars must necessarily be born. They are the tenuous equatorial fringes of the great nebulae.

Our telescopes shew us both the nebular fringes and the stars, and we can almost study the actual process of birth.

THE GALACTIC SYSTEM OF STARS. If this is the true account of the birth of the stars, then our sun and its companions in space must have been born out of a rotating nebula. Observation gives strong support to this conclusion.

Yet the same statistical methods which give us useful information as to the properties of a gas may be applied to studying the motions of the stars.

There are so many stars that we do not trouble about individuals at all, we just treat them all together as a crowd.

To treat them as individuals would be as though the railway company tried to forecast the Bank Holiday traffic from London to Brighton by considering the finances, habits and psychology of each individual Londoner.

There are so many stars that we do not trouble about individuals at all, we just treat them all together as a crowd.

To treat them as individuals would be as though the railway company tried to forecast the Bank Holiday traffic from London to Brighton by considering the finances, habits and psychology of each individual Londoner.

The Nebula M 101 in Ursa Major

The same principle of “conservation of angular momentum” now requires that, as a star shrinks, its speed of rotation shall increase.

In brief, as a star ages, it spins faster and faster.

Now rotation was the essential factor in the birth of the stars out of the parent nebula.

all bodies having more than this critical amount of central condensation follow the sequence shewn in fig. 12. Thus when this critical degree of central condensation is reached there is a sudden swing over from fig. 11 to fig. 12.

In brief, every rotating body conducts itself either as if it were purely liquid, or as if it were purely gaseous; there are no intermediate possibilities.

There is not a single star in the sky of which we can say: here is a star which has certainly started to break up by fission, and will certainly end as a binary system.

It is perhaps not altogether surprising.

The breaking up process is in all probability of very short duration by comparison with the lives of the stars, so that in any case we should have to investigate a great many stars before catching one in the act of breaking into two.

Recently criticisms have accumulated, of so vital a nature as to make it clear that the hypothesis must be abandoned.

The sun, according to Laplace, broke up and gave birth to planets through excess of rotation.

Yet both theory and observation indicate quite clearly the fate in store for a star which rotates too fast for safety; it does not found a family, but merely bursts, like an overdriven fly-wheel, into parts of nearly equal size.

These photographs exhibit a process taking place before our eyes, which is essentially identical with that imagined by Laplace, except for a colossal difference of scale.

Everything happens qualitatively as Laplace imagined, but on a scale incomparably grander than he ever dreamed of.

In these photographs the primitive nebula is not a single sun in the making, but contains substance sufficient to form hundreds of millions of suns; the condensations do not form puny planets of the size of our earth, but are themselves suns;

In the same way, the molecules left behind by the slow shrinkage of a sun (assuming this for the moment to rotate rapidly enough to leave molecules behind) would not condense, because at any instant there would be too few of them available for condensation.

They would be shed by driblets, and a driblet of gas does not condense but scatters into space.

A mathematical calculation decides the question definitely, and the decision is entirely adverse to the hypothesis of Laplace. Apart from minor details, the process imagined by Laplace explains the birth of suns out of nebulae; it cannot explain the birth of planets out of suns.

The twin Nebulae N.G.C. 4567-8

If the approach is very close indeed, the tides may assume an entirely different aspect from the feeble tides which the sun and moon raise in our oceans; they may take the exaggerated forms of high mountains of matter moving over the surface of the star.

An even closer approach may transform these mountains into long arms of gas drawn out from the body of the star.

they may take the exaggerated forms of high mountains of matter moving over the surface of the star.

An even closer approach may transform these mountains into long arms of gas drawn out from the body of the star.

If, as will generally be the case, the two stars are of unequal weights, the lesser will in general suffer more disturbance than the weightier.

Nevertheless, the resisting medium appears to have existed for long enough to make the orbits, both of the planets and of their satellites, very nearly circular for the most part.

The exceptional cases are fully as significant as the cases of conformity.

Comparatively elongated orbits still exist in just those regions where we should expect the primaeval resisting medium to have been most sparsely spread in space, namely on the outermost confines of the solar system and of the various satellite system.

… the plane in which the outer planets now move must record the position of the plane in which the two stars, the sun and the wandering star, the second parent of the sun’s family of children, described orbits about one another 2000 million years ago.

It is the only clue the latter has left of his identity, and is of course far too slight to make identification possible after this long lapse of time.

To sum up, we have seen that the normal mechanism by which the greater part of the universe has been carved out is the birth of successive generations of astronomical bodies through the action of “gravitational instability.”

We can easily see how larger bodies might be broken up into swarms of meteors. We have supposed the sun to have been broken up, at least to the extent of ejecting a family of planets, by the tidal pull of a passing star.

What would have happened if the passing star had not passed, but had come to stay?

So long as it remained within a certain distance of the sun, its tidal forces were pulling the sun to pieces.

We can imagine how a longer visit from it would have resulted in a greater upheaval in the sun, and the birth of a larger family of planets.

Finally a visit of unlimited duration would have shattered the sun into fragments.

In 1850 Roche gave a mathematical investigation of this process of tidal break-up. His discussion dealt only with solid or liquid bodies, but the underlying mechanism is the same whether the bodies are solid, liquid or gaseous.

This distance is generally known as Roche’s limit.

A satellite can with safety describe a circular orbit about its primary so long as this orbit lies beyond Roche’s limit, but it is broken into fragments as soon as it trespasses within the limit.

The following figures confirm Roche’s mathematical analysis:

… loss of weight, and this again is all give and no take, the weight of any stray matter the star may sweep up out of space, like that of any radiation it receives, being quite inappreciable in comparison with the weight it loses by radiation.

Without unduly straining the facts, the normal object in the sky may be idealised as a solitary body, alone in endless space, which continually pours out radiation and receives nothing in return.

In the present chapter we shall consider the sequence of changes which such a star may be expected to experience during the course of its life.

Fig. 16. Distribution of radiation into visible and invisible.

If our eyes were suddenly to become sensitive to all kinds of radiation, and not to visual light alone, the appearance of the sky would undergo a strange metamorphosis.

The red stars Betelgeux and Antares, which are at present only 12th and 16th in order of brightness, would flash out as the two brightest stars in the sky, while Sirius, at present the brightest of all, would sink to third place.

STELLAR DIAMETERS. It is easy to measure the diameter of a planet, because this appears in the telescope as a disc of finite size. But the stars are too remote for their diameters to be measured in the same way.

No star appears larger in the sky than a pin-head held at a distance of six miles, and no telescope yet built can shew an object of this size as a disc.

All stars, even the nearest and largest, appear as mere points of light[24], so that their diameters can only be measured by roundabout methods.

Observation shews that the physical characteristics of the stars vary enormously, so that it is easy, as we shall soon see, to tell a sensational story by contrasting extremes, setting the brightest against the dimmest, the biggest against the smallest, and so on.

This would, however, give a very unfair impression of the inhabitants of the sky; it would be like judging a nation from the giants and dwarfs, the strong men and the fasting men, seen inside the showman’s tent.

We shall obtain a more balanced impression of the actual degree of diversity shewn by the stars as a whole if we consider the physical states of those stars which are nearest the sun.

The discussion of this sample of stars suggests that the majority of stars in space are smaller, cooler and fainter than the sun.

Stars exist which are far brighter than the sun, but they are exceptional, the average star in the sky being a small dull dim affair in comparison with our sun.

With this sample of the average population of the sky before us, we may proceed to discuss the various characteristics of stars in a systematic way, without fearing to mention extremes. Let us begin with their weights.

In comparison with the very moderate range of stellar weights, the range of luminosity is enormous; S Doradus is 15,000,000,000 times as luminous as Wolf 359.

If S Doradus is a lighthouse, Wolf 359 is something less than a firefly, the sun being an ordinary candle.

If the sun suddenly started to emit as much light and heat as S Doradus, the temperature of the earth and everything on it would run up to about 7000 degrees, so that both we and the solid earth would disappear into a cloud of …

… horse-power, the sun emits energy at the rate of 50 horse-power per square inch, a star with a surface-temperature of 1650 degrees emits only 0·35 horse-power per square inch, while Plaskett’s star, with a surface-temperature of 28,000 degrees, emits about 28,000 horse-power per square inch.

In plain English, each square inch of this last star pours out enough energy to keep an Atlantic liner going at full speed, hour after hour, and century after century.

And the energy emitted per square inch by the surfaces of various stars covers the whole range from the power of a liner to that of a man in a row-boat.

Let us break the atom up into its constituent parts, pack these together as closely as they will go, and we see the way in which matter is packed in van Maanen’s star.

Six wasps which can roam throughout the whole of Waterloo Station can nevertheless be packed inside a very small box.

GIANTS AND DWARFS. There is a continuous series of stars between the limits of weight we have mentioned, and the same is true of the limits of temperature (and so also of colour) and of size.

How is it done? As we shall shortly see, there is only one possible answer.

The atom consists mostly of emptiness—we compared the carbon atom to six wasps buzzing about in Waterloo Station.

Let us break the atom up into its constituent parts, pack these together as closely as they will go, and we see the way in which matter is packed in van Maanen’s star.

This completes our collection of observational material. We now turn to the far more difficult problem of discussing what it all means.

Here we leave the firm ground of ascertained fact, to enter the shadowy morasses of conjecture, hypothesis and speculation.

The questions we shall discuss are some of the most interesting in the whole of astronomy, to which it must be admitted that science has so far obtained only lamentably dusty answers.

The questions we shall discuss are some of the most interesting in the whole of astronomy, to which it must be admitted that science has so far obtained only lamentably dusty answers.

The reader who is hot for certainties may prefer to read something other than the remainder of the present chapter.

The foregoing collection of observational data has provided abundant proof that stars to certain specifications do not exist at all. To put the same thing in another way, there are certain regions in the Russell diagram which are wholly unoccupied by stars.

it would be like trying to build a house of cards in a hurricane.

A sun consisting of molecules of air proves to be an inconsistency, a contradiction; our hypothesis has defeated itself, and we must start again from the beginning.

We may start wherever we like, but the conclusion which we must finally reach is that, no matter what kind of molecules the sun consists of, the heat at the sun’s centre will break them up, either completely or nearly so, into their constituent nuclei …

The heat which flows away from the sun’s surface must first have been brought there from its interior. Heat only flows from a hotter to a cooler place, and a vigorous flow of heat is evidence of a steep temperature gradient.

The temperature must rise sharply as we pass from the sun’s surface towards its centre, and this rise, continued along the whole 433,000 miles to the centre, must result in a very high temperature indeed being reached there.

The calculated central temperature of 30 to 60 million degrees so far transcends our experience that it is difficult to realise what it means.

We have already seen that, on this view of the mechanism of generation of stellar energy, a star can only continue to shine steadily if its central regions are not in a purely gaseous condition.

A star built on foundations of highly compressible gas meets the same fate as a house built on sand: it collapses.

A purely gaseous star is a dynamically unstable structure, and must continually contract until the atoms in its central regions are so closely packed that their state can no longer be regarded as gaseous.

If this is altered, the carrying power of the radiation is altered, and this affects the whole structure of the star.

A star whose interior was entirely transparent could not retain any heat at all; its whole interior would be at a very low temperature and the star would be of enormous extent.

On the other hand, in a very opaque star, all energy would remain accumulated at the spot at which it was generated, so that the interior temperature would become very high and the star’s diameter would be correspondingly small.

A very similar method may be used to determine the atomic weights of the atoms of which the stars are composed.

A star is in effect nothing but a huge X-ray apparatus.

We know the weights of many of the stars, and the rate at which they are generating X-rays is merely the rate at which they are radiating energy away into space.

Seares’ diagram of stellar weights (p. 282) shews that this is a general property of the stars.

To repeat our former metaphor, the stars squander their substance lavishly in their youth, while they have plenty left to spend, but parsimony comes over them with old age.

Theoretical considerations have now given us an explanation of this phenomenon.

As a star ages and its weight decreases, it continually has to pick out new configurations such as make its emission of energy equal to its internal rate of generation of energy.

The same star may be a red giant, a main-sequence star and a white dwarf in turn.

Stripped of technicalities this means that a star continually adjusts its diameter to suit its varying rate of generation of energy.

But there is at present insufficient observational evidence either for or against such a hypothesis.

Some pieces of the puzzle are missing, and we can only wait until they turn up.

WHITE DWARFS. Apart from these hypothetical massive white dwarfs, astronomers generally regard ordinary white dwarfs as the final stage in stellar evolution.

When we stand on the banks of a river and watch its current ever carrying water out to sea, we know that this water is in due course transformed into clouds and rain which replenish the river.

Is the physical universe a similar cyclic system, or ought it rather to be compared to a stream which, having no source of replenishment, must cease flowing after it has spent itself?

To this question, the wide scientific principle known as the second law of thermodynamics provides an answer in very general terms.

AVAILABILITY OF ENERGY. The second law of thermodynamics rules out any such possibility. Energy is indestructible as regards its amount, but it continually changes in form, and generally speaking there are upward and downward directions of change.

It is the usual story—the downward journey is easy, while the upward is either hard or impossible.

As a consequence, more energy passes in one direction than in the other. For instance, both light and heat are forms of energy, and a million ergs of light-energy can be transformed into a million ergs of heat with the utmost ease;

the passage is easy in one direction, impossible in the other. A human crowd may contrive to find a way round without jumping over turnstiles, but in nature there is no way round; this is the second law of thermodynamics.

Energy flows always in the same direction, as surely as water flows downhill.

Part of the downward path consists, as we have seen, of the transition from radiation of short wave-length into radiation of longer wave-length. In terms of quanta (p.

Our original answer “energy” is seen to be incomplete. Energy is no doubt essential, but the really complete answer is that it is the transformation of energy from a more available to a less available form; it is the running downhill of energy.

To argue that the total energy of the universe cannot diminish, and therefore the universe must go on for ever, is like arguing that as a clock-weight cannot diminish, the clock-hand must go round and round for ever.

Energy cannot run downhill for ever, and, like the clock-weight, it must touch bottom at last. And so the universe cannot go on for ever;

a universe in which the energy had no further availability to lose would be dead already. Change can occur only in the one direction, which leads to the heat-death.

With universes as with mortals, the only possible life is progress to the grave.

Even the flow of the river to the sea, which we selected as an obvious instance of true cyclic motion, is seen to illustrate this, as soon as all the relevant factors are taken into account.

trying to warm space by annihilating all the matter in it is like trying to warm a room by burning a speck of dust here and a speck of dust there.

As compared with any amount of radiation that is ever likely to be poured into it, the capacity of space is that of a bottomless pit.

Indeed, so far as scientific observation goes, it is entirely possible that the radiation of thousands of dead universes may even now be wandering round space without our suspecting it.

As compared with any amount of radiation that is ever likely to be poured into it, the capacity of space is that of a bottomless pit.

Indeed, so far as scientific observation goes, it is entirely possible that the radiation of thousands of dead universes may even now be wandering round space without our suspecting it.

Such is the final end of things to which, so far as present-day science can see, the material universe must inevitably come in some far-off age, unless the course of nature is changed in the meantime.

The table on p. 144 shews that radiation of the wave-length just mentioned might conceivably crystallise into electrons and protons, and finally form atoms.

If we want a concrete picture of such a creation, we may think of the finger of God agitating the ether.

We may avoid this sort of crude imagery by insisting on space, time, and matter being treated together and inseparably as a single system, so that it becomes meaningless to speak of space and time as existing at all before matter existed.

74). The universe now becomes a finite picture whose dimensions are a certain amount of space and a certain amount of time; the protons and electrons are the streaks of paint which define the picture against its space-time background.

Travelling as far back in time as we can, brings us not to the creation of the picture, but to its edge; the creation of the picture lies as much outside the picture as the artist is outside his canvas.

On this view, discussing the creation of the universe in terms of time and space is like trying to discover the artist and the action of painting, by going to the edge of the picture.

it implies merely a growing conviction that the ultimate realities of the universe are at present quite beyond the reach of science, and may be—and probably are—for ever beyond the comprehension of the human mind.

It is à priori probable that only the artist can understand the full significance of the picture he has painted, and that this will remain for ever impossible for a few specks of paint on the canvas.

It is for this kind of reason that, when, as in Chapter II, we try to discuss the ultimate structure of the atom, we are driven to speak in terms of similes, metaphors, and parables.

… efforts to understand the most minute processes of the universe (and it is the common everyday train of thought of those who are working in this field), then it must surely be still more applicable to our efforts to understand the universe as a whole.

Phenomena come to us disguised in their frameworks of time and space; they are messages in cypher of which we shall not understand the ultimate significance until we have discovered how to decode them out of their space-time wrappings.

Whatever may be thought about our final ability to decode the difficult messages we have recently received about the ultimate structure of the minutest parts of matter, it seems natural that we should feel some apprehension with regard to those about the structure of the …

By far the greater part of the matter of the universe is at a temperature of millions of degrees, so that its molecules are broken up into atoms, and the atoms are broken up, partially at least, into their constituent parts.

Now the very concept of life implies duration in time; there can be no life where atoms change their make up millions of times a second and no pair of atoms can ever stay joined together.

It also implies a certain mobility in space, and these two implications restrict life to the small range of physical conditions in which the liquid state is possible.

Now, to the best of our present knowledge, planets are very rare. We have seen how a single star cannot of itself produce planets.

A family of planets must have two parents; it only comes into being as the result of the close approach of two stars, and stars are so sparsely scattered in space that it is an inconceivably rare event for one to pass near to a neighbour.

On the Tidal Theory, explained on p. 236, planets cannot be born except when two stars pass within about three diameters of one another.

All this suggests that only an infinitesimally small corner of the universe can be in the least suited to form an abode of life.

Primaeval matter must go on transforming itself into radiation for millions of millions of years to produce a minute quantity of the inert ash on which life can exist.

Then by an almost incredible accident this ash, and nothing else, must be torn out of the sun which has produced it, and condense into a planet.

Is it the final climax towards which the whole creation moves, for which the millions of millions of years of transformation of matter in uninhabited stars and nebulae, and of the waste of radiation in desert space, have been only an incredibly extravagant preparation?

Or is it a mere accidental and possibly quite unimportant by-product of natural processes, which have some other and more stupendous end in view?

Or, to glance at a still more modest line of thought, must we regard it as something of the nature of a disease, which affects matter in its old age when it has lost the high temperature and capacity for generating high-frequency radiation with which …