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

by Arthur Koestler

On 21 March, Ciàmpoli relayed further assurances by Cardinals Bellarmine and del Monte, that Galileo had nothing to fear so long as he kept to the province of physics and mathematics, and refrained from theological interpretations of Scripture.

Dini also warned again, in the same vein: ‘One may write freely as long as one keeps out of the sacristy.’28 Galileo answered these admonitions in a letter to Dini dated 23 March. His answer was to refuse any compromise on the Copernican system. Copernicus did not mean it to be understood merely as a hypothesis. It was to be accepted or rejected absolutely. He agreed that the reinterpretation of Holy Scripture in the light of Copernicus should be left to the theologians, but he cannot help it if he has been forced on theological grounds, and since Bellarmine had quoted Psalm 19 to Dini, the passage that the sun ‘rejoiceth as a strong man to run his course’, Galileo ‘in all humility’ undertook to refute Bellarmine’s interpretation of the Psalm.

Third, I say that, if there were a real proof that the Sun is in the centre of the universe, that the Earth is in the third sphere, and that the Sun does not go round the Earth but the Earth round the Sun, then we should have to proceed with great circumspection in explaining passages of Scripture which appear to teach the contrary, and we should rather have to say that we did not understand them than declare an opinion to be false which is proved to be true. But I do not think there is any such proof since none has been shown to me. To demonstrate that the appearances are saved by assuming the sun at the centre and the earth in the heavens is not the same thing as to demonstrate that in fact the sun is in the centre and the earth in the heavens. I believe that the first demonstration may exist, but I have very grave doubts about the second; and in case of doubt one may not abandon the Holy Scriptures as expounded by the holy Fathers …30

Bellarmine had placed the burden of proof for the Copernican system back where it belonged: on the advocates of the system. There were only two possibilities left to Galileo: either to supply the required proof, or to agree that the Copernican system should be treated, for the time being, as a working hypothesis. Bellarmine had, in a tactful way, reopened the door to this compromise in the opening sentence of his letter, where he pretended that Galileo had ‘contented himself with speaking hypothetically and not absolutely’, had praised his prudence, and acted as if the Letters to Castelli and the Grand Duchess, which were before the Inquisition, did not exist. But Galileo was by now beyond listening to reason. For, by accepting the compromise, he would disclose to the world that he had no proof, and would be ‘laughed out of court’. Therefore he must reject it. It was not enough to be allowed, and even encouraged, to teach the superiority of the Copernican over the Ptolemaic hypothesis. He must insist that the Church endorse it, or reject it, absolutely – even at the risk of the latter alternative, which Bellarmine’s letter, Dini’s and Ciàmpoli’s warnings must have made clear to him. But how can he motivate his rejection of compromise? How can he refuse to produce proof and at the same time demand that the matter should be treated as if proven? The solution of the dilemma was to pretend that he had the proof, but to refuse to produce it, on the grounds that his opponents we...

But how can I do this, and not be merely wasting my time, when those Peripatetics who must be convinced show themselves incapable of following even the simplest and easiest of arguments?

The truly staggering thing in this passage is not its contemptuous arrogance, but the fact that while talking of ‘Peripatetics’ it is in fact aimed at Bellarmine; for it is on him and not on the backwoodsmen, that the decision depends, and it was Bellarmine who had challenged him to produce proof.

Galileo’s style is again so convincing that one is apt to forget the facts: that Copernicus’ book was only ‘accepted by the Church’ with the qualifications that we know; that Caccini, who had preached against it, was reprimanded by the Preacher General of his Order; and that, according to the accepted rules of the game, the scriptural objections could not be refuted on scriptural grounds, only by the scientific proofs which Bellarmine demanded and which Galileo was unable to supply.

After the passage, that I have already quoted, about the stupidity of his opponents, Galileo went on: Yet I should not despair of overcoming even this difficulty if I were in a place where I could use my tongue instead of my pen; and if I ever get well again so that I can come to Rome, I shall do so, in the hope of at least showing my affection for the holy Church. My urgent desire on this point is that no decision be made which is not entirely good. Such it would be to declare, under the prodding of an army of malign men who understand nothing of the subject, that Copernicus did not hold the motion of the earth to be a fact of nature, but as an astronomer merely took it to be a convenient hypothesis for explaining the appearances …

I have quoted some samples of Galileo’s superb technique in his written polemics. According to his contemporaries, he was even more effective when he used ‘his tongue instead of his pen’. His method was to make a laughing stock of his opponent in which he invariably succeeded, whether he happened to be in the right or in the wrong.

It was an excellent method to score a moment’s triumph, and make a lifelong enemy. It did not establish his own point, but it destroyed his opponent’s. Yet by the force of circumstances, these were the only tactics that he could adopt: to demonstrate the absurdity of Ptolemy’s epicycles and to pass in silence over the absurdity of Copernicus’ epicycles.

Even Bellarmine had incurred Paul’s displeasure. He and the other leading dignitaries – Cardinals Barberini, Dini and del Monte, Piccolomini and Maraffi – knew how to treat him. They were anxious to avoid committing the Church to any official decision on the Copernican system, until the astronomers were able to shed more light on it, and to preserve the status quo as defined in Bellarmine’s letter, ignoring Galileo’s ‘incursion into the sacristy’. But they knew that if the Pope learnt about the scandal, a showdown would be inevitable. That was probably why Bellarmine had advised against Galileo’s visit to Rome.

We come to the last episode before the blow fell. Galileo had repeatedly hinted that he had discovered a decisive physical proof of the Copernican theory, but had so far refused to disclose it. When he began to feel that arguing about the miracle of Joshua and the ludicrousness of Ptolemy was no longer of avail, and that his position was becoming impossible, he produced, as a last card, his ‘conclusive physical proof’. It was his theory of the tides.

In all these ‘dangerous innovations’ astronomers of the Jesuit Order, of which Bellarmine was the General, had played a prominent part. They had quietly abandoned Ptolemy, and progressed to the Tychonic system: the planets circle the sun, and with the sun the earth (just as the four ‘Medicean stars’ circle Jupiter, and with Jupiter, the sun). This is as far as both metaphysical prudence and scientific caution permitted them to go – even if some Jesuits were Copernicans at heart. The reasons for metaphysical prudence were theological; the reasons for scientific caution empirical: so long as there existed no observable stellar parallax, no apparent displacement in the position of the fixed stars caused by the earth’s motion through space, that motion remained unproven. Under these circumstances, the system of the universe which seemed to agree most closely with observed fact, was the Tychonic system. It also had the advantage of a compromise; by making the sun the centre of planetary motion, it prepared the way for a complete heliocentric system, should a stellar parallax be found, or some other discovery tilt the balance in its favour. But that, as we shall see, was another compromise that Galileo rejected.

The third document is a minute in the Vatican files which seems to contradict the previous two by alleging that Galileo was formally forbidden ‘to hold, teach, or defend in any way whatsoever, verbally or in writing’52 the Copernican doctrine. This minute, of doubtful reliability, has given rise to one of the most embittered controversies in the history of science, which has now been raging for nearly a century. It may be thought that to attribute such importance to the difference between an absolute injunction and an admonition is splitting hairs. But there is, in fact, a world of difference between the admonition not to ‘hold or defend’ a doctrine, and the command not to teach or discuss it ‘in any way whatsoever’. In the first case, it could be discussed as before, in terms of a mathematical hypothesis; in the second case, not (see note 52a).52a

The fallacy in Galileo’s reasoning is that he refers the motion of the water to the earth’s axis, but the motion of the land to the fixed stars. In other words, he unconsciously smuggles in the absent parallax through the back door. No effect of the earth’s annual motion relative to the fixed stars could be found. Galileo finds it in the tides, by bringing the fixed stars in where they do not belong. The tides became an Ersatz for parallax.

The point to be established is that the attitude of the Collegium Romanum and of the Jesuits in general changed from friendliness to hostility, not because of the Copernican views held by Galileo, but because of his personal attacks on leading authorities of the Order.

Other great scientists, including Newton, became embroiled in bitter polemics. But these were peripheral to their work, skirmishes around a solidly established position. The particular tragedy of Galileo was that his two major works were only published after his seventieth year. Up to then, his output consisted in pamphlets, tracts, manuscripts circulated privately, and oral persuasion – all of it (except the Star Messenger) polemical, ironically aggressive, spiced with arguments ad hominem. The best part of his life was spent in these skirmishes. Until the end he had no fortress in the form of a massive and solid magnum opus to fall back upon. The new conception of science and philosophy which he brought into the world is diffused in passages here and there among the polemics of the Letters on Sunspots or The Assayer – hidden between tangles of barbed wire, as Kepler’s laws were among his harmonic labyrinths.

The third day is concerned with the astronomical arguments for and against Copernicus, and here Galileo is downright dishonest. He first shows that the Copernican system is superior to the Ptolemaic by the familiar arguments from the Jupiter moons and the phases of Venus. He then explains that to ‘save’ the planets’ apparent stations and retrogressions, Ptolemy had to introduce ‘very great epicycles’ with which Copernicus was able to dispense ‘with one single motion of the earth’. But he breathes not a word about the fact that Copernicus, too, needs a whole workshop full of epicycles; he keeps silent about the eccentricity of the orbits, the various oscillations and librations, the fact that the sun is neither in the centre of the motions, nor lies in their plane; in a word, he deliberately evades the real problems of astronomy which had started Tycho and Kepler on their quest. The planets all move in perfect circles at uniform linear velocities around the sun (which, for instance, would make Saturn’s period twenty-four years instead of thirty).15 All problems appear solved ‘with admirable facility’; for ‘in the Ptolemaic hypothesis there are the diseases, and in the Copernican their cure’.16

His panic was due to psychological causes: it was the unavoidable reaction of one who thought himself capable of outwitting all and making a fool of the Pope himself, on suddenly discovering that he has been ‘found out’. His belief in himself as a superman was shattered, his self-esteem punctured and deflated. He returned to the Tuscan Embassy, in Niccolini’s words ‘more dead than alive’. From then on he was a broken man.

Contrary to legend, Galileo never spent a day of his life in a prison cell.

From the purely legal point of view the sentence was certainly a miscarriage of justice. If one works through the maze of verbiage, it appears that he was found guilty on two counts: firstly, of having contravened both Bellarmine’s admonition, and the alleged formal injunction of 1616, and having ‘artfully and cunningly extorted the licence to print by not notifying the censor of the command imposed upon him’; and secondly, of having rendered himself ‘vehemently suspect of heresy, namely, of having believed and held the doctrine which is contrary to sacred Scripture that the sun is the centre of the world’. Concerning the first count, no more need be said about the dubious character of the document referring to the alleged absolute injunction; as for the second, the sun-centred universe had never been officially declared a heresy, since neither the opinion of the Qualifiers, nor the decree of the Congregation of 1616, had been confirmed by infallible pronouncement ex cathedra or by Ecumenic Council. Had not Urban himself said that the Copernican opinion ‘was not heretical but merely reckless’?

His epitaph was written for him by posterity: eppur si muove – the famous words which he never uttered at his trial.

If one had to sum up the history of scientific ideas about the universe in a single sentence, one could only say that up to the seventeenth century our vision was Aristotelian, after that Newtonian. Copernicus and Tycho, Kepler and Galileo, Gilbert and Descartes lived in the no-man’s-land between the two – on a kind of tableland between two wide plains; they remind one of stormy mountain streams, whose confluence finally gave rise to the broad, majestic river of Newtonian thought.

The confusion was further increased by William Gilbert’s sensational theory that the earth was a giant loadstone, which induced Kepler to identify the sun’s action on the planets as a ‘magnetic’ force. It was quite natural, and indeed logical, that this confusion between magnetism and gravity should arise, for the loadstone was the only concrete and tangible demonstration of the mysterious tendency of matter to join matter under the influence of a ‘force’ which acted at a distance without contact or intermediaries. Hence the magnet became the archetype of action-at-a-distance and paved the way for universal gravity. Without Dr Gilbert, man would have been much less prepared to exchange the homely and traditional view that ‘weight’ meant the natural tendency of bodies to fall towards the centre for the adventurous notion that it meant the grappling of bodies at each other across empty space. Magnetism demonstrated that this grappling by ghostly fingers was a fact, that iron filings rushed to a magnet as by secret command, as stones rushed to the earth; and for about half a century the two phenomena were either identified, or regarded as Siamese twins.

Like Kepler who hit on the concept of gravity, then kicked it away, like Galileo who rejected even the moon’s influence on the tides, Descartes’ wide-open mind boggled in horror at the idea of ghost arms clutching through the void – as unprejudiced intelligence was indeed bound to do, until ‘universal gravity’ or ‘electromagnetic field’ became verbal fetishes which hypnotized it into quiescence, disguising the fact that they are metaphysical concepts dressed in the mathematical language of physics.

It is equally impossible to discover when and under what precise circumstances the cornerstone of the theory was laid – the Law of Gravity, which states that the force of attraction is proportionate to the attracting masses, and diminishes with the square of the distance. It had been suggested, but without concrete proof, as far back as 1645 by Boulliau. Perhaps it was derived by analogy from the diffusion of light which, as Kepler knew, also diminishes in intensity with the square of distance. Another suggestion is that it was deduced from Kepler’s Third Law; Newton himself says that he found the formula by calculating the force required to counterbalance the moon’s centrifugal force – but it does not sound entirely convincing.

It is inconceivable, that inanimate brute matter should, without the mediation of something else, which is not material, operate upon, and affect other matter without mutual contact … And this is one reason, why I desired you would not ascribe innate gravity to me. That gravity should be innate, inherent, and essential to matter, so that one body may act upon another, at a distance through a vacuum, without the mediation of anything else, by and through which their action and force may be conveyed from one to another, is to me so great an absurdity, that I believe no man who has in philosophical matters a competent faculty of thinking, can ever fall into it. Gravity must be caused by an agent acting constantly according to certain laws; but whether this agent be material or immaterial, I have left to the consideration of my readers.

Another appalling difficulty of this concept was that a universe filled with gravity ought to collapse, i.e., all the fixed stars should rush together and meet in a kind of final, cosmic super-explosion.* The difficulty was indeed unsurmountable, and Newton found no other solution than to assign to God the function of counteracting gravity and keeping the stars in their places:

Newton identified the Keplerian orbit of the moon with the Galilean orbit of a projectile, which was constantly falling downward towards the earth, but was unable to reach it, owing to its fast forward motion.

In order to carry out this operation, he must first of all know at what rate the earth’s gravity diminished with distance. The apple fell from the tree at a known acceleration of approximately ten yards added speed per second; but what would be the acceleration of the distant moon towards the earth? In other words, he had to discover the Law of Gravity – that the force diminishes with the square of distance. In the second place, he had to know the exact value of the moon’s distance. Thirdly, he had to decide whether it was legitimate to treat two huge globes like the earth and the moon in an abstract manner, as if their whole mass were concentrated in a single central point. Lastly, to reduce the mathematical difficulties, the moon’s orbit had to be treated as if it were a circle instead of an ellipse. As a result of all these difficulties, Newton’s first calculations only agreed ‘pretty nearly’ with the facts; and that was not good enough. For nearly twenty years he dropped the whole issue.

With the publication of Newton’s Principia in AD 1687, cosmology became a disciplined science;

We are in the habit of visualizing man’s political and social history as a wild zigzag which alternates between progress and disaster, but the history of science as a steady, cumulative process, represented by a continuously rising curve, where each epoch adds some new item of knowledge to the legacy of the past, making the temple of science grow brick by brick to ever greater height. Or alternately, we think in terms of ‘organic’ growth from the magic-ridden, myth-addicted infancy of civilization through various stages of adolescence, to detached, rational maturity. In fact, we have seen that this progress was neither ‘continuous’ nor ‘organic’. The philosophy of nature evolved by occasional leaps and bounds alternating with delusional pursuits, culs-de-sac, regressions, periods of blindness, and amnesia. The great discoveries which determined its course were sometimes the unexpected by-products of a chase after quite different hares. At other times, the process of discovery consisted merely in the cleaning away of the rubbish that blocked the path, or in the rearranging of existing items of knowledge in a different pattern. The mad clockwork of epicycles was kept going for two thousand years; and Europe knew less geometry in the fifteenth century than in Archimedes’ time.

All we know is that mental evolution cannot be understood either as a cumulative, linear process, or as a case of ‘organic growth’ comparable to the maturing of the individual; and that it would perhaps be better to consider it in the light of biological evolution, of which it is a continuation.

New ideas are thrown up spontaneously like mutations; the vast majority of them are useless crank theories, the equivalent of biological freaks without survival-value. There is a constant struggle for survival between competing theories in every branch of the history of thought. The process of ‘natural selection’, too, has its equivalent in mental evolution: among the multitude of new concepts which emerge only those survive which are well adapted to the period’s intellectual milieu. A new theoretical concept will live or die according to whether it can come to terms with this environment; its survival value depends on its capacity to yield results. When we call ideas ‘fertile’ or ‘sterile’, we are unconsciously guided by biological analogy. The struggle between the Ptolemaic, Tychonic, and Copernican systems, or between the Cartesian and Newtonian views of gravity, was decided by those criteria. Moreover, we find in the history of ideas mutations which do not seem to correspond to any obvious need, and at first sight appear as mere playful whimsies – such as Apollonius’ work on conic sections, or the non-Euclidian geometries, whose practical value became apparent only later. Conversely, there are organs which have lost their purpose and are yet carried over as an evolutionary legacy: modern science is full of appendices and rudimentary monkey-tails.

When we look back at the grotesque decline of Aristotelian scholasticism, or the blinkered single-mindedness of Ptolemaic astronomy, we are reminded of the fate of those ‘orthodox’ marsupials, like the koala, who changed from tree-climbers into tree-clingers. Their hands and feet turned into hooks, their fingers no longer served to pluck fruit and explore objects but degenerated into curved claws with the sole purpose of fixing the animal to the bark of the tree to which it hangs on for dear life.

The ultimate criterion of the value of a functional whole is the degree of its internal harmony or integratedness, whether the ‘functional whole’ is a biological species or a civilization or an individual. A whole is defined by the pattern of relations between its parts, not by the sum of its parts; and a civilization is not defined by the sum of its science, technology, art, and social organization, but by the total pattern which they form, and the degree of harmonious integration in that pattern.

Each new departure, each reintegration of what has become separated, involves the breaking down of the rigid, ossified patterns of behaviour and thought. Copernicus failed to do so; he tried to mate the heliocentric tradition with orthodox Aristotelian doctrine, and failed. Newton succeeded because orthodox astronomy had already been broken up by Kepler and orthodox physics by Galileo; reading a new pattern into the shambles, he united them in a new conceptual frame.

A new evolutionary departure is only possible after a certain amount of de-differentiation, a cracking and thawing of the frozen structures resulting from isolated, over-specialized development.

Most geniuses responsible for the major mutations in the history of thought seem to have certain features in common; on the one hand scepticism, often carried to the point of iconoclasm, in their attitude towards traditional ideas, axioms, and dogmas, towards everything that is taken for granted; on the other hand, an open-mindedness that verges on naïve credulity towards new concepts which seem to hold out some promise to their instinctive gropings. Out of this combination results that crucial capacity of perceiving a familiar object, situation, problem, or collection of data, in a sudden new light or new context: of seeing a branch not as part of a tree, but as a potential weapon or tool; of associating the fall of an apple not with its ripeness, but with the motion of the moon. The discoverer perceives relational patterns of functional analogies where nobody saw them before, as the poet perceives the image of a camel in a drifting cloud.

Another pre-condition for basic discoveries to occur, and to be accepted, is what one might call the ‘ripeness’ of the age. It is an elusive quality, for the ‘ripeness’ of a science for a decisive change is not determined by the situation in that particular science alone, but by the general climate of the age.

Prophets and discoverers, painters and poets, all share this amphibial quality of living both on the contoured drylands and in the boundless ocean. In the history of the race as of the individual, both branches of the cosmic quest originate in the same source. The priests were the first astronomers; the medicine-men were both prophets and physicians; the techniques of hunting, fishing, sowing, and reaping were imbued with religious magic and ritual. There was division of labour and diversity of method in the symbols and techniques, but unity of motive and purpose.

The Galileo affair was an isolated, and in fact quite untypical, episode in the history of the relations between science and theology, almost as untypical as the Dayton monkey-trial was. But its dramatic circumstances, magnified out of all proportion, created a popular belief that science stood for freedom, the Church for oppression of thought. That is only true in a limited sense for a limited period of transition. Some historians, for instance, wish to make us believe that the decline of science in Italy was due to the ‘terror’ caused by the trial of Galileo. But the next generation saw the rise of Toricelli, Cavallieri, Borelli, whose contributions to science were more substantial than those of any generation before or during Galileo’s lifetime; the shift of the centre of scientific activity to England and France and the gradual decline of Italian science, as of Italian painting, was due to different historical causes.

Kepler, Descartes, Barrow, Leibniz, Gilbert, Boyle, and Newton himself, the generation of pioneers contemporary with and succeeding Galileo, were all deeply and genuinely religious thinkers. But their image of the godhead had undergone a subtle and gradual change. It had been freed from its rigid scholastic frame, it had receded beyond the dualism of Plato to the mystic, Pythagorean inspiration of God the chief mathematician. The pioneers of the new cosmology, from Kepler to Newton and beyond, based their search into nature on the mystic conviction that there must exist laws behind the confusing phenomena; that the world was a completely rational, ordered, harmonic creation. In the words of a modern historian, the aspiration to demonstrate that the universe ran like a piece of clock-work … was itself initially a religious aspiration. It was felt that there would be something defective in Creation itself – something not quite worthy of God – unless the whole system of the universe could be shown to be interlocking, so that it carried the pattern of reasonableness and orderliness.

Theology and physics parted ways not in anger, but in sorrow, not because of Signor Galileo, but because they became bored with and had nothing more to say to each other.

Consider this contrast: when Darwin or Einstein proclaim theories which modify our ideas, it is a triumph for science. We do not go about saying that there is another defeat for science, because its old ideas have been abandoned. We know that another step of scientific insight has been gained. Religion will not regain its old power until it can face change in the same spirit as does science. Its principles may be eternal, but the expression of those principles requires continual development …

Today there is a wide measure of agreement, which on the physical side of science approaches almost to unanimity, that the stream of knowledge is heading towards a non-mechanical reality; the universe begins to look more like a great thought than like a great machine. Mind no longer appears as an accidental intruder into the realm of matter; we are beginning to suspect that we ought rather to hail it as the creator and governor of the realm of matter

The medieval astronomers manipulated their epicyclic symbols as modern physics manipulates Schroedinger’s wave equations or Dirac’s matrices, and it worked – though they knew nothing of gravity and elliptic orbits, believed in the dogma of circular motion, and had not the faintest idea why it worked.

If there is a lesson in our story it is that the manipulation, according to strictly self-consistent rules, of a set of symbols representing one single aspect of the phenomena may produce correct, verifiable predictions, and yet completely ignore all other aspects whose ensemble constitutes reality:

Physics is mathematical not because we know so much about the physical world, but because we know so little: it is only its mathematical properties that we can discover.

If we knew the answer, we would, of course, also know the remedy; and once the answer is known, it will again appear as heartbreakingly obvious as the sun’s central position in the solar system. ‘We are indeed a blind race,’ wrote a contemporary scientist, ‘and the next generation, blind to its own blindness, will be amazed at ours.’26