The Sleepwalkers

by Arthur Koestler

Copernicus, Kepler, Galileo, and Newton: these were the guys who launched the scientific revolution. Through personal courage, genius, and endless toil, they overturned the old superstitions and set the Western world on the path to science, technology, and videogames. 


Not quite. It turns out that much of what you know about these heroes is wrong. Their successes were in some ways unintended, accidental, or just plain dumb luck.

There was no science
First, you must understand the context in which these people worked. Their entire worldview was quite different from our modern worldview, and it wasn’t because they were stupid. The worldview 500 years ago was the product of over a thousand years of debate involving thousands of scholars. It was most certainly NOT anything like superstition; it was a highly developed system of thought that had undergone endless poking, prodding, analysis, and debate.

The foundation for this worldview was the intellectual corpus created by Aristotle around 330 BCE. It is difficult for modern people to appreciate just how important Aristotle is to Western civilization. He launched us down the path of rigorous logical thinking, and applied that logical thinking to everything around him: politics, storytelling, astronomy, medicine, the human body, animals, plants, physics, and countless other subjects. The entire corpus of Aristotle’s work is humongous; few have read what remains of the entire corpus. If it were all assembled into a single piece, we’d call it an encyclopedia. What is most astounding about this opus is that it all fits together like the gears in a huge clockwork. The whole thing is logically consistent throughout. 

Christians didn’t realize just how vast Aristotle’s work was until after Thomas Aquinas had shown just how astounding it was. This was around the year 1200 CE. At first, they were excited over the possibility of using Aristotelian logic to prove the truth of Christian religion. In wrestling with that problem, they developed the radically new idea of a university as a place of debate and discussion. They also mined Aristotle’s other works to add substance to their arguments.

By the year 1500, they had produced a gigantic corpus of thought, integrating Aristotelian thought with Christian theology. The Aristotelian stuff acted like stiffeners for Christian theology, buttressing and strengthening it. 

Thus, they did not have our distinction between science and theology. They thought in terms of “philosophy” as a unified field of thought combining everything in a harmonic whole. Aristotle’s logic was part of it; so was the Bible; medicine, the sacraments, astronomy, prayer — everything was part of an integrated body of thought.

Aristotle’s model of the universe divided it into spheres. The lowest sphere was the earth, which was the center of the universe. Everything “wanted” to move toward the center of the universe, which explained what we now call gravity. Surrounding the earth were spheres holding the moon, the sun, and the planets. They were all in motion around the earth. The outermost sphere was the fixed stars. 

Everything on earth was corruptible, and everything in the spheres above the earth was pure and perfect. Aside from the motion of the spheres, nothing ever changed; because it was already perfect, there was no need for change. 

Astrology occupied a special place in this worldview. In the first place, there was no separation between astrology and astronomy; the two ideas were, as far as most people were concerned, the same. Indeed, the only reason anybody bothered with astronomy was to prepare more accurate tables of planetary positions for use in astrology. Although the Church was officially neutral about the merits of astrology, most people gave it credence. After all, the sun exercised absolute control over the seasons; the moon seemed connected to the menstrual periods of women; surely the other celestial bodies exercised some sort of influence over humanity — right?

This is the context in which Copernicus worked. Copernicus was motivated by a desire to make better tables of planetary positions for astrologers. He did not set out to solve grand cosmological problems; he just wanted more accurate predictions of planetary positions. That was his only goal; the heliocentric model was merely a necessary stepping stone to his goal.

Moreover, Copernicus did not invent the heliocentric model; that idea had been proposed nearly 2,000 years earlier by a number of Greek philosophers. Copernicus had just one simple idea: that a heliocentric model explained retrograde motion better than the geocentric model. For an explanation of retrograde motion, see my review of another book on the Copernican Revolution by Thomas S. Kuhn. 

That was Copernicus’ ONLY contribution to the history of ideas. And it didn’t work! Copernicus was still mired in the belief that the heavens were pure and perfect, and therefore the planets all orbited the sun in perfect circles. His model, using perfect circles, didn’t produce results any better than those of the old Ptolemaic system. In fact, Copernicus had to use even more epicycles (mathematical kluges) than the Ptolemaic system used. And his results still weren’t any better!

This is why Copernicus held off publishing his results for so many years: his system didn’t work. He kept hoping that he could find some ideal combination of just a few epicycles that would produce useful results. But all his computational puttering around never gave him the answers he wanted. It was therefore a small miracle that Georg Rheticus fast-talked Copernicus into letting him publish the book, even though Copernicus knew that his work was still unfinished.

It is unlikely that Copernicus actually believed that his model represented physical reality. All those epicycles and deferents were just too much a kluge to command much credibility. That is what motivated the publisher of the book to insert the now-infamous preface disclaiming any pretension to physical reality by the book; it was merely a mathematical system that produced supposedly better results. 

Copernicus’ book didn’t convince anybody. A lot of readers thought that it *should* be correct; its simple geometric explanation of retrograde motion was so much more reasonable than the huge epicycles required by the Ptolemaic system. But the proof wasn’t there.

This is why Copernicus’s book was not placed on the Index of Prohibited Books; it wasn’t important enough to merit that attention. Around Europe, many scholars came to secretly accept the heliocentric system, but in the absence of proof, they knew that it was a matter of personal taste, not logical truth. 

The next actor in this tale is Johannes Kepler, definitely one of the weirder characters to stalk the halls of scientific history. Kepler was intellectually schizophrenic: on the one hand, he dreamed fabulous theories of pure cosmic geometries, and on the other, he was ruthlessly hard-headed in his insistence on the requirement that theory must conform to observations.

Kepler spent most of his life chasing a chimera: his belief that the planets were positioned so as to match the dimensions of the five regular solids (tetrahedron, cube, octahedron, dodecahedron, and icosahedron). Kepler knew in his bones that a nested arrangement of these solids just had to explain the positions of the planets. He never got it working, and he never gave up. Here’s a drawing of how these nested solids fit together. The spheres mark the orbits of the planets.


There’s no question that Kepler was one of the great geniuses of human history. This guy carried out immensely long calculations to test his ideas, and yet he had the intellectual integrity to throw out years of work because they produced an error of just eight minutes of arc in planetary positions. That’s one-quarter of the diameter of the full moon. He knew that his data had an observational error of about one minute of arc; if his predictions were off by eight minutes of arc, then they had to be wrong. So it was back to the drawing board.

Where Copernicus had just one idea (heliocentric model explains retrograde motion more satisfactorily), Kepler had three major insights — and the mathematical chops to prove them. His first big idea was actually published as his Third Law, and is the least bold of his three ideas. After much computational play, he realized that there is a fixed relationship between the size of the orbit of a planet and the amount of time it takes for the planet to complete one orbit. This required nothing more than a huge set of calculations, demonstrating true dedication on Kepler’s part, but not genius.

His first truly radical idea was abandoning the circular orbit for an elliptical one. Those of us who have been schooled to accept the elliptical orbit have difficulty appreciating just how radical a step this was. Kepler abandoned the whole idea of the geometric purety of the heavens, placing the sun at one focus of an ellipse — without saying anything about what might lie at the other focus. 

That in itself was a far more radical step than Copernicus had taken, but Kepler was just getting warmed up. His third big idea — a true stroke of genius — lay in observing that planets speeded up and slowed down as they orbited the sun. He expressed this as his Second Law, that planets sweep out equal areas in equal times as they orbit. It was really just a version of we now call the law of conservation of angular momentum. But figuring it out from the raw data was an act of brilliance far beyond my own creative powers. 

However, Kepler had his problems. His most detailed calculation, on the orbit of Mars, spanned 900 large pieces of paper. He miscalculated one of his steps in the middle — can you blame him? — which should have ruined his entire calculation. However, towards the end of the calculations, he just happened to make a second mistake that almost exactly cancelled out his previous mistake. In other words, his proof of the Second Law worked only because of a fluke. It was just dumb luck.

Galileo is rightly regarded as one of the giants of science. But much of his story, as known by the public, is mythology. The truth is, Galileo was an egotistical asshole and a bald-faced liar, and he got worse with age. He was also a genius, but his character flaws were the root of all his problems. 

Galileo’s central problem in life was his certainty that the Copernican system was correct, combined with his inability to prove it. Kepler had the intellectual integrity to acknowledge that he couldn’t claim as true what he couldn’t prove. Galileo, on the other hand, fervently believed in the Copernican system without any proof of it. But the Copernican system was inferior to the Keplerian system, which Galileo refused to recognize. There were three competing models of the solar system in Galileo’s day.

The first was the Copernican system, which placed the sun at the center of the solar system, with the earth and the other planets orbiting it in perfect circles, combined with lots of epicycles and other geometric kluges. The second was the Tychonic system, in which Venus and Mercury orbited the sun in perfect circles, but the sun and all the other planets orbited the earth in perfect circles. The third was the Keplerian system, in which all the planets orbited the sun in elliptical orbits. The Keplerian system is the one we now accept.

Being an egomaniac, Galileo refused to accept the Keplerian system, because Kepler was still alive and Galileo didn’t want to share an iota of glory. It was this “Me first” attitude that lay behind all his troubles. His basic attitude was “I am the only real scientist in the world; everybody is an ignorant idiot.” When other scientists, most notably a number of very capable Jesuits, extended Galileo’s observations, he ridiculed them. When they made new discoveries, Galileo insisted that the discoveries were his own, despite the complete absence of documentation to support his claims. He published embarrassingly ugly screeds denouncing everybody else. In the process, he managed to antagonize everybody.

By contrast, the Church comes out of the affair smelling like a rose. The Church really did want to do what was right, but Galileo made it impossible through his mean-spirited antics. The Church’s fundamental position was entirely reasonable: theology must bow to proven science, but retained priority over unproven science. Thus, the fact that Venus orbited the sun was enthusiastically embraced by the Catholic scientists, because Galileo had proven it with his observations of the way Venus went through phases just like the moon’s as it orbited the sun. Similarly, the Church abandoned one of the fundamental Aristotelian teachings (that the earth was corruptible but the heavens were perfect) when Galileo’s observations of the moon showed it to be pitted with craters. Again, the Church had no problem accepting scientific proof and modifying its position accordingly. But they insisted on sticking with theological positions that had not been disproven scientifically. What fault could anybody find in that position?

The opening round in the tragedy was a series of meetings in Rome with Galileo in which he was given, in writing, the following rules to follow:

1. He was forbidden to teach or defend the Copernican system, as it was as yet unproven.
2. He was free to “teach the controversy” — he could freely discuss the Copernican system as a working hypothesis. But he could not declare it to be true without proof.

Again, it is impossible to find any fault in these written instructions. Galileo toed the line for the next fifteen years, but grew increasingly restive as time passed. He was sure in his bones that he was right, but he simply couldn’t prove it. 

His problem here was “simple relativity” — not the Einsteinian form of relativity. Imagine yourself floating in space, and you see another object that appears to be circling around you. How can you prove that you are circling it and not the other way around? This turns out to be a very tricky problem to solve; the only proof available in Galileo’s time lay in Kepler’s complex calculations of the orbit of Mars. By assuming elliptical orbits, Kepler was able to make accurate predictions of the positions of the planets. The accuracy of those predictions was the best proof that the earth moves, but Galileo refused to admit that Kepler was his equal. Instead, he pig-headedly clung to an erroneous model: the Copernican model.

In 1632 his vanity overcame his better judgement and he published his landmark “Dialogue Concerning the Two Chief World Systems”. The whole thing was a crock, because he pitted the Copernican system against the Ptolemaic system, even though the Church knew that the Ptolemaic system was doomed. Until scientific proof was presented, however, the theological arguments retained priority. 

The book was a shambles. It presented a discussion between three people, one representing Galileo, another representing a yes-man, and the third representing his imagined opposition; he named this third actor “Simplicio”, a transparent pun on “simpleton”. He poured ridicule onto Simplicio, making him out to be a nitwit. Worse, he put the words of the Pope into Simplicio’s mouth. In other words, he insinuated that the Pope was a simpleton. 

Galileo offered as proof of the heliocentric model the behavior of the tides. He maintained that they were driven by the motion of the earth around the sun. His argument was preposterous, because it worked just as well with a stationary earth as with a moving earth. Worse, it didn’t explain why there are two tides per day. He contemptuously rejected Kepler’s (correct) explanation that it was due to the moon. Kepler had come right up to the very edge of the idea of gravity, and had implied as much in explaining the tides, but Galileo scornfully rejected Kepler’s explanation as idiocy.

The book was loud and clear in its support for the Copernican model. There’s no question that it violated the prohibition against teaching the Copernican model as anything more than a hypothesis. And the abuse Galileo pours onto the Ptolemaic model would lead any reader to conclude that the book overwhelmingly supports the Copernican model.

The book was a slap in the face of the Church in general and the Pope in particular. Galileo was daring them to indict him. He was certain that he, Galileo, was simply too great a scientist to be challenged by the Church.

He was, of course, quite wrong. He had enjoyed the vast respect of all the upper echelons of the Church, but he had managed over the years to insult just about everybody. And yet, even after publication of the Dialogue Concerning the Two Chief World Systems, most Churchmen were reluctant to bring down the full weight of heresy charges against him. There were, as always, conservatives in the Church hierarchy who wanted to burn Galileo as a heretic. After some delay, the Pope opened the door for them to proceed — but kept a tight leash on him. 

Galileo was brought to Rome and indicted for heresy. Unlike every other person charged with heresy, he was allowed to stay in luxury at the palace of the Florentine ambassador. Even at one crucial phase, where the law absolutely required him to be held in the Vatican, he was given a luxurious five-room suite with servants to care for his every need. He never spent a single day in a jail or dungeon. 

The charge of heresy was drawn as narrowly as possible. It concerned only the written instructions that he had been given fifteen years earlier. They had enjoined him from teaching or defending the Copernican system, and his book had clearly taught and defended the Copernican model. It was an open and shut case. Yet Galileo insisted that this was not his intention; he had merely written too enthusiastically when laying out the case for the Copernican system, and had irresponsibly rushed through the section of the book supposedly critiquing. This was a bald-faced lie; the book was full of muscular support for the Copernican model, obviously faked criticism of it, and ferocious attacks on those who rejected the Copernican system. It was not so much a scientific treatise as a polemic. Yet Galileo stoutly testified that everybody was misreading his intentions. He repeatedly declared that he did not believe in the Copernican model. 

The inquisitors were taken aback by this patent lie. They had expected a more convincing defense, but this was simply absurd. They incredulously asked him endless variations on the basic question: did he really believe in the Copernican model? And every time Galileo answered by lying through his teeth. 

When a defendent was suspected of lying, standard procedure required that he be subjected to torture. There were three steps in the process. First, the defendent is warned that he will be subjected to torture if he continues to lie. If this doesn’t shake the truth loose (in the opinion of the inquisitors), the defendent is shown the instruments of torture and told in gruesome detail what will happen to him. If this doesn’t work, then the defendent is sent to the torture dungeon. Yet in Galileo’s case, they gave up after step one. Apparently the Pope had forbidden such a humiliation.

In the end, Galileo was found guilty. Anybody else would have been promptly burned at the stake. Galileo was forced to publicly declare his denial of the Copernican system, and was sentenced to house arrest for life. This was truly a slap on the wrist; at 70 years old, Galileo’s travelling days were already over. He was forbidden to write anything further on science. Yet somehow, four years later, he managed to smuggle out the manuscript for another book and get it published in Vienna.

Thus, the standard version you learn in school has it backwards: the Church was the Good Guy and Galileo was the Bad Guy. He lied, he abused everyone, he boasted of his genius, and acted like a world-class asshole. The Church bent over backwards to accommodate Galileo, to find a formula that permitted him to continue as a scientist without directly contradicting theology. Yet Galileo rejected every compromise, every tactful re-wording. He wanted a fight and, when he finally goaded the Church into indicting him, he lied repeatedly to show his contempt for the Church.

The book concludes with a short section on Newton. While Koestler wrote extensive analyses of the thinking of Copernicus, Kepler, and Galileo, he gave short shrift to Brahe and Newton.