The Sleepwalkers: A History of Man's Changing Vision of the Universe

by Arthur Koestler

Now at last, at long last, after six years of incredible labour, he held the secret of the Martian orbit. He was able to express the manner in which the planet’s distance from the sun varied with its position, in a simple formula, a mathematical Law of Nature. But he still did not realize that this formula specifically defined the orbit as an ellipse.* Nowadays, a student with a little knowledge of analytical geometry would realize this at a glance; but analytical geometry came after Kepler. He had discovered his magic equation empirically, but he could no more identify it as the shorthand sign for an ellipse than the average reader of this book can; it was nearly as meaningless to him. He had reached his goal, but he did not realize that he had reached it.

The result was that he went off on one more, last, wild goose chase. He tried to construct the orbit which would correspond to his newly discovered equation; but he did not know how, made a mistake in geometry, and arrived at a curve which was too bulgy; ...

What next? We have reached the climax of the comedy. In his despair, Kepler threw out his formula (which denoted an elliptic orbit) because he wanted to try out an entirely new hypothesis: to wit, an elliptic orbit. It was as if the tourist had told the waiter, after studying the men...

By now he was convinced that the orbit must be an ellipse, because countless observed positions of Mars, which he knew almost by heart, irresistibly pointed to that curve; but he still did not realize that his equation, which he had found by chance-plus-intuition, was an ellipse. So he discarded that equation, and constructed an ellipse by a different geometr...

Copernicus had a one-track mind; he never flew off at a tangent; even his cheatings were heavy-handed. Tycho was a giant as an observer, but nothing else. His leanings toward alchemy and astrology never fused, as in Kepler, with his science. The measure of Kepler’s genius is the intensity of his contradictions, and the use he made of them. We saw him plod, with infinite patience, along dreary stretches of trial-and-error procedure, then suddenly become airborne when a lucky guess or hazard presented him with an opportunity.

Yet even toward the end of the book (in chapter 60), long after he had found the correct law, Kepler speaks of the inverse ratio postulate as if it were true not only for Earth, but also for Mars. He could not deny, even to himself, that the hypothesis was incorrect;he could only forget it. Which he promptly did. Why? Because, though he knew that the postulate was bad geometry, it made good physics to him, and therefore ought to be true. The problem of the planetary orbits had been hopelessly bogged down in its purely geometrical frame of reference, and when Kepler realized that he could not get it unstuck, he tore it out of that frame and removed it into the field of physics. This operation of removing a problem from its traditional context and placing it into a new one, looking at it through glasses of a different colour as it were, has always seemed to me of the very essence of the creative process.35 It leads not only to a revaluation of the problem itself, but often to a synthesis of much wider consequences, brought about by a fusion of the two previously unrelated frames of reference. In our case, the orbit of Mars became the unifying link between the two formerly separate realms of physics and cosmology.

I have tried to show that without his invasion into the territory of physics Kepler could not have succeeded. I must now discuss briefly Kepler’s particular brand of physics. It was, as to be expected, physics-on-the-watershed, half-way between Aristotle and Newton. The essential concept of impetus or momentum, which makes a moving body persist in its motion without the help of an external force, is absent from it; the planets must still be dragged through the ether like a Greek oxcart through the mud. In this respect Kepler had not advanced further than Copernicus, and both were unaware of the progress made by the Ockhamists in Paris.

Newton, in fact, could only get over the ‘absurdity’ of his own concept by invoking either an ubiquitous ether (whose attributes were equally paradoxical) and/or God in person. The whole notion of a ‘force’ which acts instantly at a distance without an intermediary agent, which traverses the vastest distances in zero seconds, and pulls at immense stellar objects with ubiquitous ghost-fingers – the whole idea is so mystical and ‘unscientific’, that ‘modern’ minds like Kepler, Galileo, and Descartes, who were fighting to break loose from Aristotelian animism, would instinctively tend to reject it as a relapse into the past.

And that formulation Newton deduced from the discoveries of Kepler – who had intuitively glimpsed gravity, and shied away from it. In such crooked ways does the tree of science grow.

The very concept of a physical ‘force’ devoid of purpose, which we take so much for granted, was only just emerging from the womb of animism, and the word for it – virtus or vis – betrays its origin. It was (and is) indeed much easier to talk about a ‘simple, magnetic, material force’ than to form a concrete idea of its working.

The first to realize the significance and implications of Kepler’s discoveries, were neither his German compatriots, nor Galileo in Italy but the British: the traveller Edmund Bruce, the mathematician Thomas Harriot, tutor of Sir Walter Raleigh; the Reverend John Donne, the astronomical genius Jeremiah Horrocks, who died at twenty-one; and lastly, Newton.

Wackher, though a Catholic convert, believed in the plurality of worlds; accordingly, he thought that Galileo’s discoveries were planets to other stars, outside our solar system. Kepler rejected this idea; but he equally refused to admit that the new heavenly bodies could be revolving round the sun, on the grounds that since there were only five perfect solids, there could only be six planets – as he had proved to his own satisfaction in the Cosmic Mystery. He accordingly deduced a priori, that what Galileo had seen in the sky could only be secondary satellites, which circled round Venus, Mars, Jupiter, and Saturn, as the moon circled round the earth. Once again he had guessed nearly right for the wrong reasons: Galileo’s discoveries were indeed moons, but all the four of them were moons of Jupiter.

The personalities of these ‘mutants’ already foreshadowed the discrepancy in the next development of man: the intellectual giants of the scientific revolution were moral dwarfs. They were, of course, neither better nor worse than the average of their contemporaries. They were moral dwarfs only in proportion to their intellectual greatness. It may be thought unfair to judge a man’s character by the standard of his intellectual achievements, but the great civilizations of the past did precisely this; the divorce of moral from intellectual values is itself a characteristic development of the last few centuries.

Thus moral assessments are thought to be essential in the case of Cromwell or Danton, but irrelevant in the case of Galileo, Descartes, or Newton. However, the scientific revolution produced not only discoveries, but a new attitude to life, a change in the philosophical climate. And on that new climate, the personalities and beliefs of those who initiated it had a lasting influence. The most pronounced of these influences, in their different fields, were Galileo’s and Descartes’.

It is, therefore, hardly surprising that the fame of this outstanding genius rests mostly on discoveries he never made, and on feats he never performed. Contrary to statements in even recent outlines of science, Galileo did not invent the telescope; nor the microscope; nor the thermometer; nor the pendulum clock. He did not discover the law of inertia; nor the parallelogram of forces or motions; nor the sunspots. He made no contribution to theoretical astronomy; he did not throw down weights from the leaning tower of Pisa, and did not prove the truth of the Copernican system. He was not tortured by the Inquisition, did not languish in its dungeons, did not say ‘eppur si muove’; and he was not a martyr of science. What he did was to found the modern science of dynamics, which makes him rank among the men who shaped human destiny. It provided the indispensable complement to Kepler’s laws for Newton’s universe: ‘If I have been able to see farther,’ Newton said, ‘it was because I stood on the shoulders of giants.’ The giants were, chiefly, Kepler, Galileo, and Descartes.

Why, in contrast to Kepler, was he so afraid of publishing his opinions? He had, at that time, no more reason to fear religious persecution than Copernicus had. The Lutherans, not the Catholics, had been the first to attack the Copernican system – which prevented neither Rheticus nor Kepler from defending it in public. The Catholics, on the other hand, were uncommitted. In Copernicus’ own day, they were favourably inclined towards him – it will be remembered how Cardinal Schoenberg and Bishop Giese had urged him to publish his book. Twenty years after its publication, the Council of Trent re-defined Church doctrine and policy in all its aspects, but it had nothing to say against the heliocentric system of the universe.

Thus legend and hindsight combined to distort the picture, and gave rise to the erroneous belief that to defend the Copernican system as a working hypothesis entailed the risk of ecclesiastical disfavour or persecution. During the first fifty years of Galileo’s lifetime, no such risk existed; and the thought did not even occur to Galileo. What he feared is clearly stated in his letter: to share the fate of Copernicus, to be mocked and derided; ridendus et explodendum – ‘laughed at and hissed off the stage’ are his exact words.

In fact, the opposite is true: the trouble with Galileo was not that he appropriated Kepler’s discoveries – but that he ignored them, as we shall see.

Besides, the discoveries announced in the Star Messenger were not quite as original as they pretended to be. He was neither the first, nor the only scientist, who had turned a telescope at the sky and discovered new wonders with it. Thomas Harriot made systematic telescopic observations and maps of the moon in the summer of 1609, before Galileo, but he did not publish them. Even the Emperor Rudolph had watched the moon through a telescope before he had heard of Galileo. Galileo’s star maps were so inaccurate that the Pleiades group can only be identified on them with difficulty, the Orion group not at all; and the huge dark spot under the moon’s equator, surrounded by mountains, which Galileo compared to Bohemia, simply does not exist.

It is curious to note that Copernicus’ Book of Revolutions had created little stir for half a century, and Kepler’s Laws even less at their time, while the Star Messenger, which had only an indirect bearing on the issue, caused such an outburst of emotions. The main reason was, no doubt, its immense readability. To digest Kepler’s magnum opus required, as one of his colleagues remarked, ‘nearly a lifetime’; but the Star Messenger could be read in an hour, and its effect was like a punch in the solar plexus on those grown up in the traditional view of the bounded universe.

Canon Koppernigk had been a kind of invisible man throughout his life; nobody who met the disarming Kepler in the flesh or by correspondence, could seriously dislike him. But Galileo had a rare gift of provoking enmity; not the affection alternating with rage which Tycho aroused, but the cold, unrelenting hostility which genius plus arrogance minus humility creates among mediocrities.

Without this personal background, the controversy which followed the publication of the Sidereus Nuncius would remain incomprehensible.

Here, too, emotion and prejudice combined with technical difficulties against clear-cut conclusions. And here, too, it was not unreasonable for self-respecting scholars to refuse to look at the photographic ‘evidence’ for fear of making fools of themselves. Similar considerations may be applied to the refusal of otherwise open-minded scholars to get involved in the ambiguous phenomena of occult seances.

Yet, while Galileo boasted about Kepler’s letter to the Grand Duke and his correspondents, he neither thanked Kepler nor even acknowledged it.

Galileo had transformed the Dutch spy-glass from a toy into an instrument of science, but he had nothing to say in explanation of why and how it worked. It was Kepler who did this.

The Harmony of the World is the continuation of the Cosmic Mystery, and the climax of his lifelong obsession. What Kepler attempted here is, simply, to bare the ultimate secret of the universe in an all-embracing synthesis of geometry, music, astrology, astronomy, and epistemology. It was the first attempt of this kind since Plato, and it is the last to our day.

The heavenly motions are nothing but a continuous song for several voices (perceived by the intellect, not by the ear); a music which, through discordant tensions, through sincopes and cadenzas, as it were (as men employ them in imitation of those natural discords), progresses towards certain pre-designed, quasi six-voiced clausuras, and thereby sets landmarks in the immeasurable flow of time. It is, therefore, no longer surprising that man, in imitation of his creator, has at last discovered the art of figured song, which was unknown to the ancients. Man wanted to reproduce the continuity of cosmic time within a short hour, by an artful symphony for several voices, to obtain a sample test of the delight of the Divine Creator in His Works, and to partake of his joy by making music in the imitation of God.15

Unlike his First and Second Laws, which he found by that peculiar combination of sleepwalking intuition and wide-awake alertness for clues – a mental process on two levels, which drew mysterious benefits out of his apparent blunderings – the Third Law was the fruit of nothing but patient, dogged trying.

He had been searching for this Third Law, that is to say, for a correlation between a planet’s period and its distance, since his youth. Without such a correlation, the universe would make no sense to him; it would be an arbitrary structure. If the sun had the power to govern the planets’ motions, then that motion must somehow depend on their distance from the sun; but how? Kepler was the first who saw the problem – quite apart from the fact that he found the answer to it, after twenty-two years of labour. The reason why nobody before him had asked the question is that nobody had thought of cosmological problems in terms of actual physical forces. So long as cosmology remained divorced from physical causation in the mind, the right question could not occur in that mind. Again a parallel to the present situation imposes itself: there is, one suspects, a fragmentation in the twentieth-century mind which prevents it from asking the right questions. The offspring of a new synthesis is not a ready solution, but a healthy problem crying lustily for an answer.

To change metaphors once more: the three Laws are the pillars on which the edifice of modern cosmology rests; but to Kepler they meant no more than bricks among other bricks for the construction of his baroque temple, designed by a moon-struck architect. He never realized their real importance. In his earliest book he had remarked that ‘Copernicus did not know how rich he was’; the same remark applies to Kepler himself.

The main reason why he was unable to realize how rich he was – that is, to understand the significance of his own Laws – is a technical one: the inadequacy of the mathematical tools of his time. Without differential calculus and/or analytical geometry, the three Laws show no apparent connexion with each other – they are disjointed bits of information which do not make much sense. Why should God will the planets to move in ellipses? Why should their speed be governed by the area swept over by the radius vector, and not by some more obvious factor? Why should the ratio between distance and period be mixed up with cubes and squares? Once you know the inverse square law of gravity and Newton’s mathematical equations, all this becomes beautifully self-evident.

A fact, once discovered, leads an existence of its own, and enters into relations with other facts of which their discoverers have never dreamt.

One cannot escape the feeling [wrote Heinrich Herz] that these mathematical formulae have an independent existence and an intelligence of their own, that they are wiser than we are, wiser even than their discoverers, that we get more out of them than was originally put into them.

In his quarrels with Tycho and constant naggings at him, he displayed embarrassing pettiness. Yet he was curiously devoid of jealousy or lasting resentment. He was proud of his discoveries and often boasted of them (particularly of those which turned out to be worthless), but he had no proprietary feeling about them; he was quite prepared to share the copyright of the three Laws with the Junker Tengnagel and, contrary to the habits of the time, gave in all his books most generous credit to others – to Maestlin, Brahe, Gilbert, and Galileo. He even gave credit where none was due, for instance to Fabricius, whom he nearly saddled with the honour of having discovered the elliptic orbits. He freely informed his correspondents of his latest researches and naïvely expected other astronomers to part with their jealously guarded observations; when they refused, as Tycho and his heirs did, he simply pinched the material without a qualm of conscience. He had, in fact, no sense of private property concerning scientific research. Such an attitude is most unusual among scholars in our day; in Kepler’s day it seemed quite insane.

I measured the skies, now the shadows I measure Skybound was the mind, earthbound the body rests.

Objectivity is an abstract ideal in an age which has become ‘a divided house of faith and reason’; and more especially so when the episode to be treated is one of the historic causes of that division.

Among my earliest and most vivid impressions of History was the wholesale roasting alive of heretics by the Spanish inquisition, which could hardly inspire tender feelings towards that establishment. On the other hand, I find the personality of Galileo equally unattractive, mainly on the grounds of his behaviour towards Kepler.

is my conviction that the conflict between Church and Galileo (or Copernicus) was not inevitable; that it was not in the nature of a fatal collision between opposite philosophies of existence, which was bound to occur sooner or later, but rather a clash of individual temperaments aggravated by unlucky coincidences.

Within a brief period, Jesuit astronomers also confirmed the ‘earthly’ nature of the moon, the existence of sunspots, and the fact that comets moved in outer space, beyond the moon. This meant the abandonment of the Aristotelian doctrine of the perfect and unchangeable nature of the celestial spheres. Thus the intellectually most influential order within the Catholic Church was at that time in full retreat from Aristotle and Ptolemy, and had taken up an intermediary position regarding Copernicus. They praised and fêted Galileo, whom they knew to be a Copernican, and they kept Kepler, the foremost exponent of Copernicanism, under their protection throughout his life.

The inertia of the human mind and its resistance to innovation are most clearly demonstrated not, as one might expect, by the ignorant mass – which is easily swayed once its imagination is caught – but by professionals with a vested interest in tradition and in the monopoly of learning. Innovation is a twofold threat to academic mediocrities: it endangers their oracular authority, and it evokes the deeper fear that their whole, laboriously constructed intellectual edifice might collapse.

Incidentally, the famous experiment of dropping cannon balls from the leaning Tower of Pisa was carried out not by Galileo but by his opponent, the aforementioned Coressio, and not in refutation, but in confirmation of the Aristotelian view that larger bodies must fall quicker than smaller ones.

Kepler answered immediately. He recalled having himself observed a sunspot in 1607 ‘of the size of a meagre flea’, which he had mistakenly assumed to be Mercury passing in front of the sun.6 He laughed at his mistake, then quoted reports of similar observations dating back to the days of Charlemagne; then gave his opinion that the spots were a kind of dross, due to the cooling of the sun in patches. Galileo delayed his answer for more than three months, and then claimed the priority of the discovery for himself. He alleged having observed sunspots for about eighteen months, and having shown them a year before ‘to many prelates and gentlemen in Rome’, but did not name any of these witnesses.

Harriot seems to have been the first to observe them, but Fabricius was the first to publish, and Scheiner the second. Harriot, Fabricius, and Scheiner neither knew of the others’ parallel discovery, nor did they raise any particular claim to priority. Thus Galileo’s claim was untenable, firstly because Fabricius and Scheiner had been first to publish the discovery, and secondly because he could name no witnesses, or correspondents, to prove it – yet we remember how careful he was to protect his priority claims on previous occasions, by immediately sending out messages in anagram form. But Galileo had come to regard telescopic discoveries as his exclusive monopoly – as he himself stated on a later occasion: You cannot help it, Mr Sarsi, that it was granted to me alone to discover all the new phenomena in the sky and nothing to anybody else. This is the truth which neither malice nor envy can suppress.7 By his specious priority claim over the sunspots, followed by disguised attacks on Father Scheiner, Galileo had made the first enemy among the Jesuit astronomers, and started the fatal process which in the end would turn the Order against him.

The book won immediate and great popular acclaim. In so far as the Church is concerned, not only was no voice raised in opposition, but Cardinals Borromeo and Barberini – the future Urban VIII – wrote letters to Galileo expressing their sincere admiration.

There the matter could have rested, and probably would have rested, but for Galileo’s hypersensitivity to criticism, and his irrepressible urge to get involved in controversy.

After invoking Augustine’s authority once more, Galileo draws a distinction between scientific propositions which are ‘soundly demonstrated’ (i.e. proven) and others which are ‘merely stated’. If propositions of the first kind contradict the apparent meaning of passages in the Bible, then, according to theological practice, the meaning of these passages must be reinterpreted – as was done, for instance, with regard to the spherical shape of the earth. So far he has stated the attitude of the Church correctly; but he continues: ‘And as to the propositions which are stated but not rigorously demonstrated, anything contrary to the Bible involved by them must be held undoubtedly false and should be proved so by every possible means.’16

The burden of proof has been shifted. The crucial words are those in (my) italics. It is no longer Galileo’s task to prove the Copernican system, but the theologians’ task to disprove it. If they don’t, their case will go by default, and Scripture must be reinterpreted. In fact, however, there had never been any question of condemning the Copernican system as a working hypothesis. The biblical objections were only raised against the claim that it was more than a hypothesis, that it was rigorously proven, that it was in fact equivalent to gospel truth. The subtlety in Galileo’s manoeuvre is that he does not explicitly raise the claim. He cannot do so, for he had not produced a single argument in support of it.

For it must be remembered that the system which Galileo advocated was the orthodox Copernican system, designed by the Canon himself, nearly a century before Kepler threw out the epicycles and transformed the abstruse paper-construction into a workable mechanical model. Incapable of acknowledging that any of his contemporaries had a share in the progress of astronomy, Galileo blindly and indeed suicidally ignored Kepler’s work to the end, persisting in the futile attempt to bludgeon the world into accepting a Ferris wheel with forty-eight epicycles as ‘rigorously demonstrated’ physical reality.

As a result, Father Luigi Maraffi, Preacher General of the Dominican Order, wrote to him a sincere apology. ‘Unfortunately,’ wrote Maraffi, ‘I have to answer for all the idiocies that thirty or forty thousand brothers may or do actually commit.’19 The letter illustrates the contrast in attitude between the higher dignitaries of the Church and the ignorant fanatics among the lower echelons.

This was in November 1615. For the next eighteen years Galileo lived honoured and unmolested, befriended by Pope Urban VIII and an impressive array of cardinals. But the Letters to Castelli and to the Grand Duchess remained on the files of the Inquisition, and in the minds of the theologians. The text was so carefully worded that it could not be indicted as heresy, but the intent was unmistakable; it constituted a challenge which sooner or later had to be answered. The challenge lay in the implied claim that the Copernican system belonged to the category of ‘rigorously demonstrated’ physical truths to which the meaning of the Bible must be adapted; and that unless it was explicitly refuted and condemned, theological objections would become irrelevant and the case would go by default.