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Galileo, Darwin, and HawkingThe Interplay of Science, Reason, and Religion
By PHIL DOWE
William B. Eerdmans Publishing CompanyCopyright © 2005 Wm. B. Eerdmans Publishing Co.
All right reserved.
Chapter OneCosmology and Scripture
As we have seen, one of the most potent images of conflict between science and religion in Western history is that of the trial of Galileo. We are tempted from our perspective to think of this as a fight between a lone scientist's attempt to replace outdated religious explanation and a desperate church's effort to retain its place of dominance within intellectual life. But this would be 'Whiggish' history - reading back into Galileo a modern naturalism that isn't in fact there. We need instead to understand the conflict in its context. Galileo was, of course, a scientist, but on all the evidence he was also a serious Catholic. There just was no one in the debate who was trying to replace religion with science.
One common Whiggish response to this fact is to say that figures such as Galileo 'had to' say that they believed in God because there would be political consequences if they didn't. But again, there just is no evidence that Galileo was insincere in his belief in God or in his membership in the church.
As we will see, the debate surrounding the Galilean controversy concerned the interpretation of Scripture on the one hand and science on the other. There was no question that either should be given up. The controversy concerned how to show their consonance; that is, how to give a unified understanding of science and religion. It centered on the issue of how we are to read Scripture, and what our understanding of the relation between Scripture and the discoveries of cosmology should be.
To understand the context of the conflict in which Galileo was involved we need to understand a little about the development of cosmology (in which Galileo played a significant part), a little about Genesis and the debate over how it is to be interpreted, and a little about the ways Galileo's predecessors, especially Augustine, construed the relation between science and religion. We start with an account of some of the various developments in cosmology leading up to Galileo.
Cosmology starts for our purposes with Eudoxus (408-353 B.C.) and Aristotle (384-322 B.C.). Aristotle was both a philosopher and a scientist, and his system included a remarkable synthesis of many fields of knowledge. In his cosmology Aristotle divided the subluminal area, or the earthly area, from the heavens, and according to his physics these two regions are fundamentally different. The heavens are perfect and are not subject to decay, but down on earth we have both imperfection and decay. Earthly things are made up of four basic elements: earth, air, water, and fire.
According to Aristotle's physics, things move in natural motions according to certain principles that are connected to those things' natures. In other words, the motions of an object depend on the kind of thing that object is. If that object's nature is earthy, its natural motion will tend towards the earth. This also applies to objects that possess a water nature, since water's nature is to move to the center of the universe, which is in fact the earth. On the other hand, objects whose natures are connected with air or fire have a different natural motion, namely to move away from the earth, that is, straight up. Violent motion is any motion that is not a natural motion. For example, pushing a physical object upwards, away from the earth, is a violent motion, since that goes against that object's natural motion. In Aristotle's physics, a violent motion requires a force to make it happen and continue to happen. To make a physical object keep moving in violent motion, one must continue applying a force to that object.
On the other hand, the so-called heavenly motions involve a different kind of motion, because the heavenly things are made of a different element, the fifth type of element, the ether. According to Aristotle, things that are made of the ether possess a perfectly circular, constant, continuous, and unforced motion. This idea is important in Aristotle's overall physics and cosmology.
Eudoxus, a friend of Aristotle's teacher Plato, had offered a schema for the movements of the heavenly bodies centered on the earth. Eudoxus' model depicts the universe as something like a beach ball, with the fixed stars painted on the inside and the earth in the exact centre. In the area between the earth and the fixed stars move what we would call the planets and the sun and the moon.
All these heavenly bodies move in spheres, which, being in the heavens, have the nature of ether and move in circles. The total system involves a series of concentric spheres. Saturn, Jupiter, Mars, Venus, Mercury, the sun, and the moon are all embedded in their own (sometimes interpenetrating) spheres, each sphere rotating slowly around the earth at its own speed. The fixed stars, on the other hand, rotate together once a day.
Now this system of Eudoxus' encountered several problems in accounting for all the data of astronomy. The biggest problem concerned what were known as the 'wandering stars' (that is, the planets). When astronomers observed Mars move, say, for six months, they noticed that it appears to travel forward and then loop back on itself, and then go forward again. Such phenomena needed to be explained within the concentric circles schema.
Aristotle attempted to solve this problem by introducing more spheres of movement, moving in different directions. The looping motions are explained if the planet transfers to a different sphere of motion (moving at the same distance from the center), and back again, just as if two trains are passing each other in opposite directions you can have a looping trajectory by jumping from one train to the other, and then back again. Aristotle's hope was that these additional spheres might help to explain the actual observations of the wandering stars. In all, Aristotle had to posit the existence of fifty-five spheres of motion, a system far more complicated than the original scheme proposed by Eudoxus.
There was, however, another problem with the Eudoxus/Aristotle model. According to this system, all the planets or wandering stars should appear to be the same brightness at all times because they are traveling in perfect circles. But according to observation the planets vary in brightness as though they are actually closer and further away at different times of the year. Aristotle's system had no obvious way of explaining this anomaly.
The Greek astronomer Ptolemy (a.d. 100-170) didn't question Aristotle's physics, but he did offer a new, more sophisticated mathematical system to explain the looping motion and the variation in brightness of the planets. He introduced several new devices. One was the epicycle. Ptolemy, like Aristotle, worked under the assumption that cosmology could be explained in terms of circular motions, and took this to be the basic motion of the heavenly bodies. However, Ptolemy added another smaller circular motion, or epicycle on that basic circle, on which the planet's motion is the sum of these two circles. This device allowed Ptolemy to explain the motions of the wandering stars and the variations in apparent brightness, by arranging various epicycles in the right way.
However, Ptolemy found that to account for observations he had to allow the planetary motions to be eccentric, meaning that the earth is not exactly in the center of the motion of the planetary spheres. He recognized that if the earth is not quite in the center of the circular motions of the planets, then Aristotle's fundamental principle of constant motion about the earth is violated. So Ptolemy introduced the notion of the equant to preserve this principle of constant motion, and to make his system more consistent with observation of the planets. The equant is a point near the earth, and also not quite at the center of the planetary revolution, but from which point the major epicycle of that planetary motion has constant angular velocity.
Followers of Ptolemy, and even Ptolemy himself, were equivocal about whether this system was intended to be a mathematical device for explaining observation, or a physical hypothesis about the way things really are. Aristotle, on the other hand was clear on this point. He maintained that his system was intended to be a physical hypothesis and explanation of the way that the cosmos really works.
By the time of Nicholas Copernicus (1473-1543), the Ptolemaic system had been the dominant view for more than a thousand years, although in the Renaissance it again became an ongoing, developing project. Copernicus was a priest in the Roman Catholic Church and a sincere, dedicated member of the church. His main work, On the Revolutions of the Celestial Spheres, is dedicated to the Pope. In that dedication, Copernicus also feels a need to offer ancient support for his theories, and so goes to great lengths to name Greek philosophers (among them Pythagoras and others of Heraclitus' followers) who had held heliocentric views similar to his own.
Copernicus' interest in cosmology arose within an ecclesiastical (church) setting. A church council had been convened to reform the calendar, which was based on predictions of the motions of the planets. The council determined that it was incapable of facilitating this reform, as not enough was known at that point about cosmology. This, then, became Copernicus' vision: to provide a cosmology adequate for the ecclesiastical reform of the calendar. Thus he saw his work in astronomy as being part of his service to the church.
But Copernicus found the Ptolemaic system most unpalatable, a "monster," a mish-mash of bits and pieces with no clear unifying concept. In particular, since it deals with the motions as they appear from the equant point, it gives no insight into the way the world really is. Further, the different cycles have their own principles of operation and epicycles, leaving the system with no unifying principle that explains how all the motions work as a whole. To Copernicus, Ptolemy's theory appears
as if someone were to collect hands, feet, a head, and other members from various places, all very fine in themselves, but not proportionate to one body, and no single one corresponding to others, so that a monster rather than a man would be formed from them.
Aristotle's physics, on the other hand, had that unity, for in it all of the planets move by constant, circular motion.
On the Revolutions of the Celestial Spheres was published in 1543, although the ideas put forward in this work had been formulated by Copernicus as early as 1512. The essence of the Copernican system is that the center of the cosmos is not the earth but (more nearly) the sun, and that the earth, and the heavenly bodies (except the moon) circle the sun. This enabled Copernicus to rescue the idea that the motion in the heavens is constant and circular, and, he claimed, to bring all of cosmology back to simpler motions.
But the Copernican system immediately causes problems for Aristotelian physics. If the earth is moving around the cosmos, loose objects will fly off (that is, be left behind), clouds will necessarily float toward the west, and a body in free fall next to a tower will land to the west of the tower. None of this in fact occurs. Worse still, the Copernican system makes the earth a heavenly body, when its nature is not to be in motion, and it places a heavenly body, the sun, at the centre of the cosmos and not strictly in the heavens.
It should also be noted that Copernicus' system did not make things particularly simpler. To make the system fit in with astronomical observation, Copernicus also introduced the epicycle. In fact, he introduced epicycles on epicycles on epicycles, resulting in a system even more complex than that of Ptolemy. (Real simplification did not come until the work of Kepler in 1609, who recognized that the planetary motions are better described by the ellipse.)
We now turn to Galileo's contribution. Galileo (1564-1642), who grew up in Pisa and taught in Padua and Florence, was a vocal defender of the Copernican system and equally vocal critic of Aristotelianism. (He was more impressed by philosophers such as Archimedes than by Aristotle.)
One of Galileo's chief contributions was to appreciate how the Copernican theory required a new physics, and he argued vigorously for a version of the 'impetus theory.' By the time of Isaac Newton this impetus theory had solved many of the physical problems or 'absurdities' facing the Copernican system - such as the fact that bodies in free fall fall in a straight line toward the earth - by utilizing the radical dynamic principle of impetus. In opposition to the Aristotelian notion that violent motion needs a sustaining force, the impetus theory (in the version of interest here) says that without interference a 'violent' motion remains constant and rectilinear. The reason, therefore, why a ball dropped from a tower lands at the base of the tower and is not left behind as the earth moves on is that it already has the 'violent' motion and that motion continues in virtue of the impetus of the object. In other words, physical bodies show no effect of the earth's motion in virtue of their participation in the earth's motion.
On first glance the impetus theory appears to be contrary to the evidence. If I knock a ball, causing it to roll along the ground, then the ball eventually stops unless I continue to apply the force. Galileo himself solves this by distinguishing actual empirical motion and natural motion in an ideal sense. By ideal motion Galileo meant motion in which all external influences, such as friction and air resistance, are discounted. The natural ideal motion of the ball is to continue in motion, but empirically the ball stops because it is acted on by frictional forces.
In 1610 Galileo published his major work, The Starry Messenger, in which he reports his observations of the heavens made with a telescope. The telescope had been in use for some time before Galileo, but only in either a commercial or military capacity. Galileo was the first to direct his telescope towards the heavens, and his discoveries made him a celebrity overnight. One of these was the fact that the moon is not a perfect sphere, immune to decay or change, but rather has a landscape that includes mountains and valleys. Other discoveries included the moons of Jupiter and a vast number of new stars that had never before been seen, which challenged the Aristotelian picture of a fixed, small universe with stars embedded in the outer shell like a beach ball.
While Galileo's discoveries made him a celebrity, they also put him in conflict with the Aristotelians, who were mainly centered in the universities, and sections of the church, as we will see in subsequent sections.
Excerpted from Galileo, Darwin, and Hawking by PHIL DOWE Copyright © 2005 by Wm. B. Eerdmans Publishing Co.. Excerpted by permission.
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