Cosmos: Chapter 3 - The Harmony of Worlds
This is one of my favorite chapters. Here, Sagan recounts the lives of two of the most important scientists in history, Johannes Kepler and Issac Newton. In the process, Sagan draws an historical and philosophical line between the science of astronomy and the pseudoscience of astrology. Through these two men, the world made the transition from the Dark Ages, when astrology was the dominant view of cosmic affairs, to the Age of Enlightenment, when we began to use science to learn the true methods by which everything operates.
It is interesting to note that Sagan provides much more detail on Kepler's life and work than Newton's. In the book, Sagan devotes 14 pages to Kepler and only four to Newton. In the television series, this segment is devoted almost entirely to Kepler -- Newton's name is not even mentioned. It seems apparent that, in Sagan's opinion, Kepler has been shortchanged in traditional science education relative to Newton. Every educated person has heard of Issac Newton, but far fewer people are familiar with the name of Johannes Kepler. I believe that through Cosmos, Sagan hoped to correct that situation.
The chapter begins with a comparison of astronomy and astrology today. Sagan notes with sadness that most people are more familiar with the astrological model of the zodiac than with the fundamental facts of astronomy. He debunks the myth of astrology in two ways. First, he reads the horoscope entries from two newspapers for the same astrological sign on the same day and, lo and behold, they are quite different. Second, he points out that twins, born at the same place and time, often lead very different lives.
He traces the roots of astrology back to Ptolemy, who worked in the Library of Alexandria in the second century A.D. Ptolemy proposed a model of the solar system in which the planets and stars were attached to "crystal spheres" which rotated around the Earth. The Earth was considered to be the center of the solar system. This model was not seriously challenged until 1547, when Nicholas Copernicus postulated that the Sun was the center of the solar system and the planets orbited around it. Sagan does not dwell very much on Copernicus' work, except to say that his work did not disprove Ptolemy's model.
Sagan then takes us into the life of Kepler. His introductory paragraph is one of the book's most elegantly written:
"The epochal confrontation between the two views of the Cosmos -- Earth-centered and Sun-centered -- reached a climax in the sixteenth and seventeenth centuries in the person of a man who was, like Ptolemy, both astrologer and astronomer. He lived in a time when the human spirit was fettered and the mind chained; when the ecclesiastical pronouncements of a millennium or two earlier on scientific matters were considered more reliable than contemporary findings made with techniques unavailable to the ancients; when deviations, even on arcane theological matters, from the prevailing doxological preferences, Catholic or Protestant, were punished by humiliation, taxation, exile, torture or death. The heavens were inhabited by angels, demons and the Hand of God, turning the planetary crystal spheres. Science was barren of the idea that underlying the phenomena of Nature might be the laws of physics. But the brave and lonely struggle of this man was to ignite the modern scientific revolution."
Sagan describes Kepler's boyhood years, spent in seminary school, where he first began to contemplate God and the Cosmos:
"God became for him more than a divine wrath craving propitiation. Kepler's God was the creative power of the Cosmos. The boy's curiosity conquered his fear. He wished to learn the eschatology of the world; he dared to contemplate the mind of God. These dangerous visions, a first insubstantial as a memory, became a lifelong obsession. The hubristic longings of a child seminarian were to carry Europe out of the cloister of medieval thought. ... If the world was crafted by God, should it not be examined closely? Was not all of creation an expression of the harmonies in the mind of God? The book of Nature had waited more than a millennium for a reader."
Sagan explains how Kepler discovered Copernicus' hypothesis while studying at a university and, later, how he hit upon the idea that the size of the orbits of the six known planets at that time might be related to the five regular or "perfect" solids of the ancient Greeks. (Sagan gives a detailed discussion of these solids in an Appendix.)
"In these perfect forms, [Kepler] believed he had recognized the invisible supporting structures for the spheres of the six planets. He called his revelation The Cosmic Mystery. The connection between the solids of Pythagoras and the disposition of the planets could admit but one explanation: the Hand of God, Geometer."
Kepler devoted himself to an attempt to prove this idea, "but no matter how hard he tried, the solids and the planetary orbits did not agree well. The elegance and grandeur of the theory, however, persuaded him that the observations must be in error." Kepler then sought the assistance of a Danish nobleman, Tycho Brahe, who was "the greatest observational genius of the age." Brahe, however, was not eager to share his data with Kepler, whom he viewed as a rival. Sagan gives a dramatic description of their relationship: "Each knew that, alone, he would be unable to achieve the synthesis of an accurate and coherent world system, which they both felt to be imminent. ... The birth of modern science -- the offspring of theory and observation -- teetered on the precipice of their mutual distrust."
Kepler got access to the data after Brahe's death, but, after three years of calculations, he saw that his Cosmic Mystery was flawed, not only because it was based on the Pythagorean solids, but also because it assumed circular orbits. Sagan stresses how easy it would have been for Kepler to fudge his results, since it was common practice among "scholars" of the time and the margin of error was rather small:
"When Kepler found his long-cherished belief did not agree with the most precise observation, he accepted the uncomfortable fact. He preferred the hard truth to his dearest illusions, that is the heart of science. ... Kepler was shaken at being compelled to abandon a circular orbit and to question his faith in a Divine Geometer. Having cleared the stable of astronomy of circles and spirals, he was left, he said, 'with only a cartful of dung,' a stretched out circle something like an oval."
Kepler continued to work at the problem, however, and eventually discovered that the planets move in the path of an ellipse, with the Sun at one focus. This is the first of his three laws of planetary motion.
In addition, Kepler suggested that the planets were attracted to the Sun by some force similar to magnetism, pointing the way for Issac Newton to discover the law of universal gravitation. Sagan says, "[Kepler's idea] was the first nonmystical explanation of motion in the heavens; it made the Earth a province of the Cosmos. ... Kepler stood at a cusp in history; the last scientific astrologer was the first astrophysicist."
Sagan goes on to describe the life and work of Issac Newton, whom he calls "perhaps the greatest scientific genius who ever lived." He describes how, within the space of one year, Newton "occupied himself by inventing the differential and integral calculus, making fundamental discoveries on the nature of light, and laying the foundation for the theory of universal gravitation."
Sagan goes on to describe other aspects of Newton's life and work, including the law of inertia and the inverse square law. He then wraps up the chapter as follows:
"Kepler and Newton represent a critical transition in human history, the discovery that fairly simple mathematical laws pervade all of Nature; that the same rules apply on Earth as in the skies; and that there is a resonance between the way we think and the way the world works. They unflinchingly respected the accuracy of observational data and their predictions of the motions of the planets to high precision provided compelling evidence that, at an unexpectedly deep level, humans can understand the Cosmos."
Tom |
