Kepler's Witch (8 page)

Twenty-first-century people often imagine that the Copernican controversy was about science against the church, but the reality was far more complex. Science as we know it did not yet exist, and the church, Protestant and Catholic alike, was in fact the normal place for intellectual discussion. Nevertheless, society itself was changing, all too fast for most people. As if under a magnet, complex social forces aligned, at once pushing Copernicus forward and shoving him back. Friends and enemies of the sun-centered universe gathered in colleges and cathedrals across Europe and shouted at one another, something that Copernicus himself described: “Since the newness of the hypotheses of this work—which sets the earth in motion and puts an immovable sun at the center of the universe—has already received a great deal of publicity, I have no doubt that certain of the savants have taken grave offense and think it wrong to raise any disturbance among liberal disciplines which have had the right set-up for a long time now.”
¹⁷

The changing cosmology scared people, affronted their sense of reason, a sense that derived its rationality, its worthiness for belief, from the single idea that God had set an order to things, an order to the heavens and an order to the earth. In the heavens, the stars and planets sailed on by force of the perfect divine will, the perfect divine law, which constrained them into circular orbits, the most perfect of all shapes. This was so, because it was the way things ought to be, the best of all possible worlds. On earth, the world was likewise ordered by divine will into church and state, into
hierarchies of religious and political power. Even when Luther rebelled against the order of the church, he did so by relying on the order of the state, by turning the princes and dukes into “emergency bishops,” so that the order of the whole might be maintained. Beyond this was chaos.

Who could imagine such a state? The medieval world that lingered in Kepler's day, although ancient and creaking, leaking oil and all too often rolling over the lives of peasants, overflowed with providence, with God's special care for trudging mortals doomed to die. What could possibly replace that? No wonder astronomers stepped lightly, not only out of fear of the church, though that fear was well founded. They stepped lightly out of fear of unraveling the cosmos, of pulling on the wrong string and having the whole order of the universe collapse at their feet. Nevertheless, the generation of astronomers before Kepler and Galileo, the generation of Michael Mästlin and Christoph Clavius, could see the value of the Copernican system. Its elegance and simplicity appealed to their reason as much as it did to Kepler's and Galileo's. Although Clavius was more conservative and more philosophically subtle, basing his resistance to Copernicus on the differences between reasonable hypotheses and proven fact, Mästlin was more willing to dig at the root of the problem. His criticisms of Aristotle were dangerous and he knew it, so he broadcast them carefully. Aristotle was the systematizer who had set Greek reason to the Babylonian cosmology of the Bible, and long use of his work to build a Christian cosmology had nearly identified him with Scripture itself. To reject Aristotle and his astronomical interpreter Ptolemy was to remove the cotter pins holding together the structure of rational Christianity. Mästlin never challenged Aristotle's value head on, but picked at the philosopher's mistakes from behind, showing how, contrary to common belief, his system did not support observation, but rather complicated it.

In Mästlin's lectures, the lectures that so influenced the life of Johannes Kepler, he traced the path that Aristotle had taken to create his system. “What happens to fire when it is lit?” he asked. “It rises.” In this, Aristotle too was following a long tradition set down by the Pre-Socratics, that heavy things fall and light things rise, just as air and water and earth mixed in a glass jar eventually settle with the earth at the bottom, the air
at the top, and the water in between. Heavy things separate from light things and wet things from dry things, hot things from cool things, and light things from dark things. Therefore, said Aristotle, the earth must be at the center of the universe, for, as anyone can see, the earth is heavy and the air, which extends outward into the sky, is light. In Aristotle's universe, and therefore in Ptolemy's, the heavens are made of clear crystal globes that gear against each other and groan in mystical harmonies. The spheres sing a song that perhaps only God can hear properly.

We are steeped in hundreds of years of Copernicanism, so we cannot see another way. In this, we are like the churchmen who condemned Galileo and the theological faculty at Tübingen who worried over Mästlin's lectures and later shook their heads over Kepler. But Ptolemy and his followers were not fools. They never tried to explain the heavens mechanically, but only to come up with a systematic account of all the phenomena that any observer could see by looking. The earth had to be the center of the universe, they argued, because otherwise the sky would seem different looking north and looking south or looking east and looking west, but it isn't—it is the same in all directions.
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The stars are different, of course, but the spheres appear to be the same distance from the earth no matter which way you look. Ptolemy assumed that the sky was an actual physical sphere, and not endless space, but that assumption came to him from Aristotle. Moreover, Ptolemy argued, the earth cannot move from its central position, because all things move toward the center of the universe as the heavy things sort themselves out from the light things. The earth, therefore, is a massive, bulky, weighty thing, while the heavens are light and ephemeral. So which makes more sense—that the adipose earth move from place to place or even spin, or that the aerie heavens, luminous and eternal, sailing through the sky as they do by the action of heavenly spirits, move? What later seemed so costly to Copernicus—that the entire universe would turn around the earth—seemed reasonable and natural to the followers of Ptolemy, based upon the relative weight of the two systems.

Aristotle and Ptolemy had invented a system anyone could see at work
in a glass jar, watching light things separate out from heavy. Then they could step outside and watch the heavens waltz across the sky like gods in evening wear, and they would say, “Of course!” But then there was this problem—the dances of the planets, the “wanderers” that didn't follow the expected pattern. They were eccentric, sweeping across the dance floor in arcs of perfect circles as expected, but during the time of their “opposition,” when they were on the other side of the sun from the earth, they stopped, hand-jived backward, then reversed course and waltzed on. Ptolemy explained this strange retrograde motion by inventing circles,
epicycles,
whose center moves along a larger circle, called the
deferent,
whose center was the earth. Moderns are often stymied at this idea, wondering what the planets are orbiting in their epicycles, what points of gravity were holding the epicycles together, keeping the planets moving round and round like dancers, but although everyone could see gravity at work on the earth—heavy things fall and light things rise—they could not imagine it for the heavens. These little circles were descriptive of the appearances, each planet circling through its epicycles, all inside the planet's crystalline sphere, in the space between the inner and outer walls. The spheres themselves rotated, moving the planets across the sky, but inside the sphere the planets circled on. The presence of epicycles in the system alone wasn't the problem, however. The problem surfaced when, with increased observation, Ptolemaic astronomers needed to add more and more epicycles to the system to keep it working. For a long time, they required only twenty-seven epicycles, but by Kepler's day, they needed nearly seventy—far too complicated.

Kepler saw this at once. Though he loved theology and Scripture, though he could read in four languages (German, Latin, Hebrew, and Greek) and write in two (German and Latin), he found himself drawn toward the study of the heavens. He had always been good at mathematics, and since the day his mother took him to see the comet back in 1577, his mind and heart had been pulled toward the stars. There was beauty, majesty, and grace there. There was harmony—he could feel it—and he longed for simplicity. Real harmony, he reasoned, can never be that complicated.

Eventually, Mästlin loaned him his own copy of Copernicus's
De Revolutionibus Orbium Coelestium, On the Revolutions of Heavenly Spheres.
This was quite an act of trust, for the book was rare and a little dangerous. Mästlin told Kepler how Copernicus had delayed publication, worried about the effect of his own ideas, and how on May 24, 1543, a friend put a newly arrived copy of the book into Copernicus's hand as he lay on his deathbed. In the preface, Mästlin said, Copernicus had stated that his ideas were merely a useful means for calculating celestial events, a mathematical hypothesis. This was the same argument that the Jesuit Clavius used when discussing Copernicus with Galileo. But that is not how the rest of the book reads. Many astronomers and mathematicians suspected that Copernicus believed what he wrote and that he wrote the preface out of timidity.
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In truth, Andreas Osiander, whom Copernicus put in charge of the book's publication, wrote the preface, and he did this without the permission of the author, which would likely have angered Copernicus, had he not been on his deathbed. The preface had the positive effect, however, of making Copernicus's book more palatable, so that men like Clavius, Mästlin, and Brahe could study it without fear, since the preface itself said that Copernicus's system was meant only as a device for calculation.
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Device for calculation or not, Copernicus's theory set Kepler's mind on fire. Here was the simplicity, the elegance of thought he longed for. Kepler was enough of a Platonist to believe that the universe was simple elegance and was best described by simple, elegant mathematics. Could a good and loving God, a rational God, all-wise and all-knowing, have created the epicyclic nightmare that the Ptolemaic system had become? Kepler doubted it, and yet he fretted. For all his excitement about Copernicus's cosmos, with its simplicity and elegance, the thought that the earth was no longer the center of the universe worried him. Even if Aristotle didn't think much of the earth, Christians did. Shouldn't the place where the Son of God had been born, had lived out his life, and died, the place where he was raised and from which he ascended to the Father be the center of things? Shouldn't the world of human beings, built in God's image, be the center? The answers he needed to these questions could not be found in mathe
matics, but in metaphysics and theology. Like Melanchthon, Kepler expected that the human mind and God's mind worked in roughly the same way, because God created humans in God's own image and likeness.

For all his doubts, however, Kepler was convinced enough to defend Copernicus to his fellow students, writing one disputation after another, first making physical arguments and then metaphysical ones. In all the emotional turmoil, in 1593 his health problems returned. He still struggled with poor eyesight, and his clumsy and somewhat malformed hands pained him. But now he had headaches, possibly migraines, as well. Emotionally, he felt that honors owed to him were being held back.

Resistance to the Copernican system was growing throughout Europe, in Catholic and Protestant countries alike. Except for Mästlin, the faculty at Tübingen was decidedly anti-Copernican. One of the favorite arguments of the objectors was that if the earth really moved, why couldn't the people living on the earth feel it? There should be some perceptual evidence of this motion, one way or another.

In 1593, Kepler wrote a short dissertation, supported by his friend Christopher Besold, imagining what the earth would look like to people living on the moon. This would be revised several times in his life and finally published as Kepler's
Somnium,
his
Dream,
after his death. The purpose of this dissertation was to demonstrate Copernicus's idea that the earth moves very rapidly, rotating and revolving around the sun, but the people living on the earth cannot see or feel this. Anyone who looks up at the sky from the earth can see the moon and its motions, so what would happen if someone were standing on the moon? Would they not see the motions of the earth, just as we see the motions of the moon?

Kepler wanted to present it as a disputation, but Vitus Müller wouldn't have it. Müller hated Copernicus's ideas and would not listen, nor would he let the thesis be heard. Though Müller never referred the incident to the general faculty, some of the professors had already begun to wonder if Kepler was suited to the ministry and whether he might be happier doing something else. Some people suspected him of being a crypto-Calvinist. Why did the boy have to go his own way all the time? And this Copernican
nonsense of his! Even Magister Mästlin did not go so far. Could the Kepler boy become an embarrassment?

Then, lucky day, a solution. The Lutherans in Graz were looking for a mathematics teacher. All the way in Austria. People would be sad to see him go. Many people liked the boy and wished him well. But, all the way to Austria.

L
ETTER FROM
K
EPLER TO THE
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HEOLOGY
F
ACULTY AT
T
ÜBINGEN
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EBRUARY
28, 1594