by Gene Callahan by Gene Callahan
Recently, after looking in an introductory biology textbook for a description of meiosis, I browsed through its introduction. There, I came upon the following passage:
“For 2,000 years prior to [the Renaissance], scholars had accepted the writings of Aristotle and other ancient philosophers, as well as certain Church doctrines, to be unfaltering truths about the natural world. It took some of the greatest minds in history, including Copernicus, Galileo, and Newton, to shake this dominion of dogma and to replace it with theories and laws based on direct observation of nature. Nicholaus Copernicus, and later Galileo, made calculations that the Earth and other planets circle the sun…” (Wessells and Hopson, 1988, p. 11).
Many science textbooks contain similar one-or-two-paragraph histories of how modern science miraculously emerged from the dark swamp of ignorance we call the Middle Ages. The main problem with such stories is that they are almost entirely false. Let’s compare the picture painted above with the current understanding of scholars studying the history of the Scientific Revolution.
The first assertion, quite a commonplace one, is that from the time of the ancient Greeks until the Renaissance, the European mind was in the thrall of a dogmatic worldview, based only on authority, and made no progress toward a better understanding of the natural world. It is certainly true that scientific ideas developed much less rapidly during most of the period in question than they have in recent centuries. (Even admitting that much, the figure of “2000 years” in the quote above still seems to overshoot the mark, since it includes the time of pioneers like Archimedes and Ptolemy within its scope.) During the “Dark Ages,” in the centuries immediately after the fall of Rome, Western Europe did not challenge the received wisdom in science primarily because it did not do much science at all. People were struggling to survive, and intellectual life fell into abeyance. In fact, contrary to the view expressed in the biology textbook, for most of that period, Aristotle’s writings were lost to the West, so that they could hardly have been accepted as “unfaltering truths”!
But as Western European intellectual life revived, scholars began reconsidering the ideas of the ancients. As Bede’s Library has it:
“When Aristotle was rediscovered in the West, it was soon established that when there were clear conflicts between his philosophy and the Christian faith, the latter should always prevail. This was not much of a handicap, as on the subject of physical science, faith did not really have a lot to say. The bible could be read non-literally where necessary, as Augustine himself allowed, so William of Conches could even call the creation account in Genesis figurative. Nearly everyone agreed that the earth was a sphere even though the Bible implied a flat earth. But where Aristotle and faith were in clear conflict, such as his claim that the world was uncreated and eternal, it weakened his authority and allowed his ideas to be challenged. This opened the door to the idea of a developing body of knowledge, which is often assumed to have been absent from the medieval outlook.”
For example, in the fourteenth century, a group of philosophers, most of them at the University of Paris, developed the impetus theory of motion. It was both a break with one of the central ideas of Aristotle’s physics, and a step toward the modern theory of inertia. They also disputed the prevailing belief that the movement of each planet was guided by a conscious being:
“Although the theory of celestial intelligences became a central doctrine in Hellenic, Arabic and scholastic cosmology, it was attacked during the fourteenth century by several scholars, and most incisively in the work of Jean Buridan (died c. 1358) and his pupil Nicole Oresme (1320–1382).”
Nevertheless, Aristotelian physics did remain the primary means of explaining most physical phenomena well into the Scientific Revolution. There is a very good reason for that, which brings us to our next point. The textbook cited above claims that scientists such as Copernicus, Galileo, and Newton were able “to shake this dominion of [Aristotelian] dogma” with “theories and laws based on direct observation of nature.” Once again, the authors are repeating a commonplace view, one that appears in a multitude of popular accounts of the rise of science. The scholastic philosophers who dominated the medieval universities, enraptured with their elaborate metaphysical speculations, ignored the plain facts of the physical world, which were accessible to them if they had simply looked around. The great figures of the Scientific Revolution relied instead on observation, which led them to develop the theories that replaced Aristotelian physics.
But this story, inspiring though it is, runs afoul of the fact that Aristotle was a masterful observer, one whose physical theories are closely based on the world as it appears to the unaided senses. Knowledge, he held, begins with our observations of the world around us. Similarly, Ptolemy constructed his Earth-centered model of the cosmos to accurately reflect the best astronomical observations available to him.
In fact, it was the pioneers of the Scientific Revolution who had to overcome the commonsense view of the world revealed by direct observation in order for their theories to gain acceptance. The most obvious discrepancy between the reports of our senses and the new ideas is that the Earth seems quite plainly to be standing still, while the heavenly bodies clearly appear to be rotating around it. Renaissance man had no experience of, for instance, traveling in an airplane at 600 miles per hour yet feeling as though he wasn’t moving. When he moved rapidly, such as on horseback, he could feel that he was moving. And to account for the apparent motions of the heavenly bodies, the Earth would have to rotate at what, for him, was a truly astonishing rate. (At the equator, the actual speed is over 1000 miles per hour.)
What’s more, if the Earth was spinning around that rapidly, it seemed that we ought to be able to detect that motion in many ways. For example, if you dropped a rock from a tower, it should fall some distance from the tower’s base, in the direction opposite to the Earth’s rotation, since the ground would have moved under it as it was falling. The Earth’s atmosphere would also be left behind, so that there would be a continuous wind sweeping from east to west at hundreds of miles per hour.
On a more technical level, a major reason that Copernicus’s heliocentric (sun-centered) theory was rejected by many leading astronomers of the sixteenth century was the absence of any observed parallax in the “fixed stars.” Parallax is the astronomical term for the fact that objects will appear to change their location when observed from different places. If the Earth revolves around the sun, the stars should appear to move slightly during the course of the year, but astronomers observed no such phenomena. (The explanation for that failure is that the stars are much farther away from the Earth than anyone at that time suspected, so that the parallax was too minute for their instruments to detect.)
Copernicus handled the difficulty that presented for his theory with an ad hoc hypothesis, declaring that the sphere of the stars was ten times farther from the Earth than had previously been believed. Not only was the hypothesis ad hoc, it was also, as a Popperian would put it, unfalsifiable: there were no instruments available at the time to measure a parallax as small as the new distance implied. And if a geocentric astronomer had developed a device capable of measuring such a slight change in observed position, Copernicus could (and undoubtedly would) have simply moved the stellar sphere ten times farther away still.
Copernicus also "was puzzled by the variations he had observed in the brightness of the planet Mars. [But] Copernicus's own system was so far from answering to the phenomena in the case of Mars that Galileo in his main work on this subject praises him for clinging to his new theory though it contradicted observation…" (Butterfield, 1949, p. 23).
What’s more, as we noted above, Copernicanism violated many of the principles of the Aristotelian physics of his time. Copernicus could not explain why objects didn't fly off the rotating Earth, why the Earth didn't spin itself apart, why dropped objects fell straight to the ground, or what kept celestial objects going in their orbits if not the motion transmitted from sphere to sphere in the Ptolemaic/Aristotelian model. Aristotelian physics explained all of those phenomena in ways that made sense of the observational experience then available. As Butterfield writes:
"In fact, you had to throw over the very frameboard of existing science, and it was here that Copernicus clearly failed to provide an alternative. He provided a neater geometry of the heavens, but it was one which made nonsense of the reasons and explanations that had previously been given to account for the movements in the sky" (1949, p. 27).
Of course, Aristotelian physics had difficulties of its own, but Copernicanism introduced a whole host of new problems, while only eliminating a few: "Most of the essential elements by which we know the Copernican Revolution — easy and accurate computations of planetary position, the abolition of epicycles and eccentrics, the dissolution of the spheres, the sun a star, the infinite expansion of the universe — these and many others are not to be found anywhere in Copernicus's work" (Kuhn, 1957, p. 135).
Nor does the frequent assertion that Copernicus's theory was significantly simpler than Ptolemy’s stand up to scrutiny. As Lakatos notes:
"The superior simplicity of the Copernican theory was just as much of a myth as its superior accuracy. The myth of superior simplicity was dispelled by the careful and professional work of modern historians. They reminded us that while Copernican theory solves certain problems in a simpler way than does the Ptolemaic one, the price of the simplification is unexpected complications in the solution of other problems. The Copernican system is certainly simpler since it dispenses with equants and some eccentrics; but each equant and eccentric removed has to be replaced by new epicycles and epicyclets…. he also has to put the centre of the universe not at the Sun, as he originally intended, but at an empty point fairly near to it."
The suggestion that Galileo had all of the evidence on his side in his battle against the Aristotelians and the Church is also erroneous. In his book Two Systems one of the major pieces of evidence he advanced for the Copernican model was the existence of tides. Galileo explained them as arising from the motion of the Earth rocking the oceans back and forth, much as a swinging a bucket containing water will slosh the water up one side of the bucket and then the other.
Of course, this is quite different from our current understanding of tides as arising from the gravitational influence of the moon. But what is really surprising about Galileo’s hypothesis, given his common portrayal as a staunch empiricist, is that he had not even investigated the actual period of the tides before forwarding this argument! His theory required a 24-hour tidal cycle, while in fact it is 12 hours. When he learned that sailors in the Mediterranean reported high and low tides occurring every 12 hours, he explained this glaring discrepancy as resulting from local variations in the ocean bottom. (See Shea and Artigas, 2003.)
Galileo also failed to be a “good empiricist” when he ignored his ally Kepler’s theory that the planets orbit the sun in elliptical, rather than circular, paths. Kepler’s model fit the data much better than Galileo’s, yet Kepler’s letters to Galileo suggesting elliptical orbits never even solicited a response.
When one looks at the real history of the Scientific Revolution, it becomes apparent that observation was rarely the prime impetus for the development of the most important new theories. Instead, leading scientists drew their main inspiration from their beliefs about the kind of world they envisioned that God would create. Copernicus and Kepler were Neo-Platonists, and it seemed to them that the Sun, the most brilliant light in our world, was a more fitting center for God’s creation than the Earth. Copernicus was also dissatisfied with the Ptolemaic model of the heavens because it centered the orbits of heavenly bodies not on the Earth, the supposed center of the cosmos, but on a point called the equant, which was an empty spot in space near to the Earth. Newton was a deeply religious man, who believed that God’s work would naturally exhibit the sort of mathematical perfection he hoped to reflect in his own theories.
I came across another very common idea about the Scientific Revolution in browsing a recent issue of National Geographic. Speculating on the impact of the possible future discovery of other, earth-like planets, the article’s author writes: “It’s hard to overstate the excitement scientists feel at the prospect of seeing that faint blue dot. If it told of a watery, temperate place, humanity would face a 21st-century version of Copernicus’s realization nearly 500 years ago that the Earth is not the center of the solar system. The discovery would show ‘that were not in a special place, that we might be part of a continuum of life in the cosmos, and that life might be very common,’ says Michael Meyer, an astronomer at the University of Arizona.”
As a corollary of the above, it’s often suggested that many people in the sixteenth and seventeenth centuries rejected the idea of a sun-centered solar system because it displaced the Earth from its unique location at the center of the universe, and therefore seemed to make humanity less important in the scheme of creation. However, Professor John Milton, with whom I am studying the history of science at King’s College in London, notes that historians have discovered no evidence of any of the contemporaries of Copernicus or Galileo voicing such a concern. And that is not too surprising, when we consider that, in the prevailing cosmology of the time, the center of the cosmos was not a very prestigious place to be. Aristotle regarded it as the region to which gross and corrupt matter gravitated, distinctly inferior to the unchanging perfection exhibited by the heavens. And in Dante’s Divine Comedy, the occupant of the Earth’s center, and therefore at the precise center of the universe, was none other than Satan himself. To place the Earth in the heavens was to grant it a promotion.
None of what I have presented above is meant to claim that the conservatism typical of entrenched interests, for instance, of the Aristotelians who dominated the universities of the 16th and 17th centuries, did not present an extra-scientific hurdle that new conceptions of the physical world had to surmount, or that the Catholic Church never resisted the progress of science for dogmatic reasons.
But the common, popular version of the history of science, in which unselfish, heroic scientists do battle with the backward forces of religion, is a fairy tale, spun mostly by Voltaire and his followers, in order to discredit the religious belief that they despised. The real history of the Scientific Revolution is much more complex and nuanced than the simplistic morality play they made it out to be. If we are truly interested in understanding the roles that religion and science have played in creating our civilization, we should put aside the myth and attend to the reality.
- Appenzeller, T. (2004) “Search for Other Earths,” National Geographic, Dec. 2004, pp. 68–95.
- Butterfield, H. (1949) The Origins of Modern Science: 1300–1800, London: G. Bell and Sons Ltd.
- Kuhn, T.S. (1957) The Copernican Revolution: Planetary Astronomy in the Development of Western Thought, Cambridge, Massachusetts and London: Harvard University Press.
- Lakatos, I. (1978) The Methodology of Scientific Research Programmes: Philosophical Papers Volume 1, Cambridge, England: Cambridge University Press.
- Shea, W.R. and M. Artigas (2003) Galileo in Rome: The Rise and Fall of a Troublesome Genius, Oxford, England: Oxford University Press.
- Wessells, N.K and J.L. Hopson (1988) Biology, New York: Random House.
January 25, 2005