"The Copernican Myths"

The ancient Greeks, although they were great philosophers and good at mapping the motions of stars and planets, tended to create models of the universe that were more influenced by philosophical, aesthetic, and religious considerations than by observation and experiment. The idea that Earth was the stationary center of the universe, and that the stars and planets were embedded in spheres that rotated around Earth, appealed to them because the circle and the sphere were the most perfect geometric shapes. In the Christian era, the model also pleased religious people because it gave pride of place to human beings - God's special creation. The prestige of Greek philosophers like Aristotle was so great, and commitment to religious doctrine so strong, that many scholars stubbornly tried to retain Ptolemaic astronomy even though increasingly complicated epicycles had to be added to make the system work even moderately well. So when Copernicus came along with the correct heliocentric system, his ideas were fiercely opposed by the Roman Catholic Church because they displaced Earth from the center, and that was seen as both a demotion for human beings and contrary to the teachings of Aristotle. Therefore the Inquisition persecuted, tortured, and even killed those who advocated Copernican ideas. Because of the church's adherence to philosophical and religious dogma, scientific progress was held back for a millennium. It was the later work of Tydto Brahe (1546-1601), Johannes Kepler (1571-1630), Galileo Galilei (1564-1642), and Isaac Newton (1642-1727) that finally led to the acceptance of heliocentrism.

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Problems with heliocentricity
Copernicus's heliocentric model, on the other hand, created all manner of difficulties. It required Earth to be in motion, but it did not say what caused it to move away from the center. If Earth was not stationary at the center but was midway in the sequence of planetary orbits around the Sun, how could you define "up" and "down"? Why would objects fall "down" if Earth were not at the center of the universe? How could objects thrown upward fall back to the same point if Earth was not at rest? Earth was still believed to be the most massive object in the universe. So if it was riot drawn to a fixed point at the center, did that mean that the universe had no center? Could that mean that the universe was infinite?

Kuhn argues that there were thus excellent reasons for rejecting the upstart Copernicus and retaining Aristotelian cosmology and its elaboration in Ptolemaic astronomy. Accepting Copernicus would not simply replace one astronomical model with another. It also meant that a whole class of physics problems that had been considered solved were now suddenly unsolved. Therefore much of the initial resistance came from within the physics and astronomy communities rather than from the church.
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In fact, awareness of Copernicus's work was at first largely restricted to the community of astronomers. Only they were interested in improving the calculation of planetary motions. Copernicus was widely respected as one of Europe's leading astronomers, and reports about his work, including his heliocentric hypothesis, had been circulating since 1515. So when his De Revolutionibus Orbium Coelestium (On the Revolutions of the Celestial Spheres) was published 28 years later, it was hardly a surprise to other astronomers. They accepted it as the most comprehensive account of celestial motions since Ptolemy.
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But most astronomers also felt that the Ptolemaic system, although complicated, could ultimately be made to work. So while they hailed Copernicus's work and used his tables and methods, they were skeptical of his central idea of a moving Earth. They dismissed it as an ad hoc trick (much as Max Planck's quantum hypothesis was initially viewed centuries later) that turned out to be a useful tool for calculations. The idea that the motion described by some artificial model was a convenient fiction was not unprecedented. Ptolemy himself had said that not all of his epicycles had to be considered physically real. Some were to be thought of as merely mathematical devices that gave sound results.

Galileo Galilei

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Initially, however, the Copernican system did not give better numerical results than the Ptolemaic. Part of the problem was that some of the existing astronomical observations were simply erroneous, a problem that plagued Ptolemaic and Copernican astronomy alike. Although better observations soon eliminated some of those problems, other problems remained obdurate for a long time. Furthermore, at the level of accuracy available to Copernicus, the introduction of ellipses in place of circular orbits would not have helped. What Copernicus needed to do, as historian Owen Gingerich puts it, was to "treat Earth and Mercury the same way as the other planets."

Kuhn says of Copernicus: "His full system was little if any less cumbersome than Ptolemy's had been. Both employed over thirty circles; there was little to choose between them in economy. Nor could the two systems be distinguished by their accuracy. When Copernicus had finished adding circles, his cumbersome sun-centered system gave results as accurate as Ptolemy's, but did not give more accurate results. Copernicus had failed to solve the problem of the planets."7
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Advantages
The Copernican model did have some aesthetic and qualitative advantages. It provided a more natural qualitative explanation for the zigzag motion of planets like Mars as observed from Earth, and it answered some important questions about the ordering of the planets. That's why heliocentrism was eventually accepted. As Kuhn puts it, "De Revolutionibus did convince a few of Copernicus' successors that sun-centered astronomy held the key to the problem of the planets, and these men finally provided the simple and accurate solution that Copernicus had sought." [see footnote 6]
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That's an important point about scientific revolutions. At the start, the new theory rarely gives convincingly better results than its predecessor. What usually happens is that it has some appeal, often aesthetic, that attracts others to work within the new model. And if, over time, the new model proves fruitful in resolving many puzzles, it gains adherents. [see footnote 7]

The success of the Copernican model was aided by the work of the Danish astronomer Tycho Brahe, who died a few years before the invention of the telescope. Tycho is considered the greatest of the naked-eye observers. His wide ranging and accurate observations had an enormous impact.
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Although Tycho's pivotal role is recognized, what is less well known is that he, like most astronomers at the time, rejected Copernicus's ideas of a movin8 Earth. It created more problems, he thought, than it solved. But despite Tycho's opposition, his observations provided two major benefits for the heliocentric model: They got rid of some erroneous old data that had plagued all the earlier models and thus helped to remove some of the anomalies that the Copernican system couldn't explain. More important, the precision of Tycho's data provided puzzles that enabled Kepler, a convert to Copernicanism, to come up with the key idea that the motions of the planets were not circular - as Ptolemy; Copernicus, and Tycho had all assumed - but elliptical.

In the folklore that surrounds Copernicus, the introduction of elliptical orbits is rightly recognized as a crucial development that led to ultimate acceptance of his model. The pre-Keplerian astronomers, however, are unfairly characterized as insisting on circular motion because of aesthetic considerations, slavish adherence to the authority of the Greeks, and so forth. But at the time, the reasons for assuming circular motions were quite sensible. Because there were no good theories of force or gravity, one needed to have an explanation of motion. Circular motion could be explained by a plausible hand-waving argument. One could say that it was an initial condition - that once an object had been set in circular motion it would, if w1disturbed, continue circling forever.
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More complicated motions like elliptical orbits would mean that the planets' speeds and distances from the Sun were constantly changing. But that required a dynamical theory that simply did not exist in those pre-Newtonian times. Just introducing the idea of a moving Earth created all kinds of unsolved problems for the physical theories of the day. Adding noncircular motion would have compounded those problems, providing even stronger grounds for rejecting Copernicus.

Kepler's innovative idea of elliptical orbits, coupled with his law of areas, did let the Copernican, model dispense with cumbersome epicycles. But his accurate Rudolphine Tables for planetary motion, published in 1627, were difficult to use. It was Newton's theories of motion and gravity, not published until 60 years later, that sealed the scientific case in favor of Copernicus by putting his model on a firm theoretical footing.
Religious objections The actual religious reaction to the heliocentric model also differs from the folklore. For one thing, Copernicus did not seem to fear religious opposition to his ideas. After all, he was a reputable cleric himself. He even dedicated his book to Pope Paul ill with a letter in which he apologized for the seeming outlandishness of his suggestion that the Earth moved. He explained that he was forced to that hypothesis by the inadequacy of the Ptolemaic system for constructing calendars and predicting the positions of stars. A cardinal and a bishop were among those who urged him to publish his book. In fact, for 60 years after Copernicus's death just two months after its publication, De Reuolutionibus was read and at least partially taught at leading Catholic universities.
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In 1600 the church did burn at the stake the philosopher Giordano Bruno, an adherent of Copernicus, for heresy. But Bruno was condemned for other heresies against Christian doctrine rather than explicitly for being a Copernican. However, the fact that Bruno had been an advocate and popularizer of heliocentrism may have led to the later perception that he was the first martyr of the new science.

"Frontispiece of a 1566 edition of Copernicus's De Revolutionibus Orbium Coelestium, published in Basil, Switzerland. The work was first published a few months before the author's death in 1543"

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For many years after the publication of De Reuolutionibus, while Copernicus's ideas remained within the mathematical astronomy community, authors of more popular books on astronomy and cosmology were either unaware of his work or chose to ignore it. A few nonastronomers did ridicule it - not for being heretical but for promulgating the patently absurd idea of a moving Earth.

It was through popularizers, some of them poets, that Copernicus's ideas eventually became more widely known and began to spark religious opposition. But here too, the actual history is surprising. Opposition arose initially among Protestant groups rather than from the Roman Catholic Church.
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Kuhn suggests that this was because Martin Luther (1483-1546) and other leaders of the Reformation were emphasizing the Bible as the fundamental source of Christian knowledge and authority. And there were manifest contradictions between the Bible and Copernicus. The Catholic Church), by focusing more on doctrinal issues, actually had greater flexibility in dealing with science.

Luther spoke out against heliocentrism in 1539, saying that the idea of a moving Earth going around a stationary Sun clearly went against the account in the book of Joshua that says Joshua commanded the Sun to stand still. Luther's deputy Philipp Melanchthon followed up by finding other biblical verses that described Earth as stationary.
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The conflict between scripture and Copernicanism was not limited to verses that involved the motion of Sun or Earth. The realization was growing that acceptance of Copernicanism raised other profound theological difficulties as well. As Kuhn points out, the problems just kept multiplying:

When it was taken seriously, Copernicus' proposal raised many gigantic problems for the believing
Christian. If, for example, the Earth were merely one of six planets, how were the stories of the Fall and of the Salvation, with their immense bearing on Christian life, to be preserved? If there were other bodies essentially like the Earth, God's goodness would surely necessitate that they, too, be inhabited. But if there were men on other planets, how could they be descendants of Adam and Eve, and how could they have inherited the original sin?...Again, how could men on other planets know of the Savior who opened to them the possibility of eternal life?
Or, if the Earth is a planet and therefore a celestial body located away from the center of the universe, what becomes of man's intermediate but focal position between the devils and the angels? If the Earth; as a planet, participates in the nature of celestial bodies, it cannot be a sink of iniquity from which man will long to escape to the divine purity of the heavens. Nor can the heavens be a suitable abode for God if they participate in the evils and imperfections so dearly visible on a planetary Earth. Worst of all, if the universe is infinite, as many of the later
Copernicans thought, where can God's Throne be located? In an infinite universe, how is man to find God or God man? [see footnote 6]

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"Giordano Bruno, burned at the stake as a heretic in 1600, was honored in 1887 with the erection of this statue at the site of his execution in Rome's Campo dei Fiori. Although Bruno was condemned by the Inquisition primarily for theological heresies rather than for his advocacy of heliocentrism, he is widely regarded as the first martyr of the scientific revolution"

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As time went on, Copernicus's ideas were seen as seriously disturbing to Christianity; they had to be countered.
Soon the Bible became the main weapon used against Copernicus. Protestant and Catholic clerics in the 17th century started combing through it for ammunition. People started calling the Copernicans infidels and atheists and urged their repression. But the new Protestant churches did not have the powers of suppression and enforcement that the long established Catholic Church had.
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Kuhn argues that it was probably the menace of burgeoning Protestantism that caused the Catholic hierarchy in 1616 to switch abruptly from tolerance of Copernicanism to repression. "Copernican doctrines were, in fact, condemned during the Counter Reformation, just when the Church was most convulsed by internal reforms designed to meet Protestant criticism. Anti-Copernicanism seems, at least in part, one of these reforms. Another cause of the Church's increased sensitivity to Copernicanism after 1610 [the year Galileo first turned a telescope to the heavens] may well have been a delayed awakening to the fuller theological implications of the Earth's motions. In the 16th century those implications had rarely been made explicit." [see footnote 6]

The idea of the Copernican model being a demotion for humanity probably first developed around 1650, after the scientific community had already accepted heliocentrism. Religious bodies undertook what was essentially a propaganda war against Copernicus. What probably happened was that after the heliocentric model had been well established, the location of the Sun did come to be perceived as a privileged place. So people read back into history the newly believed excellence of the center and attributed that belief respectively to the pre-Copernicans. The demotion idea may have been introduced as part of the effort to rally nonscientific religious people to turn against Copernicanism by appealing to their pride as human beings.
Atheism and science
The Protestant churches abandoned their opposition to Copernicanism fairly quickly when it - became clear that the evidence in favor of a Sun-centered system was overwhelming. But the Catholic Church, being a much larger and more tradition - bound and bureaucratic institution, was left clinging to its anti-Copernican views for a long time. Its ban on Copernicus remained until 1822, and his book remained on the forbidden list until 1835. In fact it was only in 1992 that Pope John Paul n lifted the edict of inquisition against Galileo. Thus the Roman Catholic Church is now generally regarded as the principal villain in perhaps the most notorious episode in the history of science.

What can we learn from all this? The story of the Copernican revolution shows that the actual history of science often bears little resemblance to the popular capsule versions that are learned in school or college or portrayed in textbooks and the popular media. Steven Weinberg calls them "potted history." The true story is much more complicated, but it's also a lot more interesting.
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My thanks to Owen Gingerich for an enlightening discussion and many helpful suggestions.

1. 1. Mano Singham is director of the University Center for Innovation in Teaching and Education and adjunct associate professor of physics at Case Western Reserve University in Cleveland, Ohio. December 2007 Physics Today - © 2007 American Institute of Physics)
   
2. 2. See, for example, P. Fishbane, S. Gasiorowicz, S. Thornton, Physics for Scientists and Engineers, 2nd ed., Prentice Hall, Upper Saddle River, NJ (1996), pp. 1, 320, 321
   
3. 3. D. R. Danielson, Am. J. Phys. 69, 1029 (2001)
   
4. 4. M. Singham, Phi Delta Kappan 88, 590 (2007)
   
5. 5. J. B. Russell, Inventing the Flat Earth: Columbus and Modern Historians, Praeger, New York (1991)
   
6. 6. T. Kuhn, The Copernican Revolution: Planetary Astronomy in the Development of Western Thought, Harvard U. Press, Cambridge, MA (1957)
   
7. 7. L Lakatos, The Methodology of Scientific Research Programmes, Cambridge U. Press, New York (1978)