Three Scientific Revolutions: How They Transformed Our Conceptions of Reality (7 page)

I do not believe that for exciting in us tastes, odors, and sounds, there are required in external bodies anything but sizes, shapes, numbers, and slow or fast movements; and I think that if ears, tongues, and noses were taken away, shapes and numbers and motions would remain but not odors or tastes or sounds. These, I believe, are nothing but names, apart from the living animal—just as tickling and titillation are nothing but names when armpits and the skin around the nose are absent.
²⁶

Since nothing was then known about the molecular, atomic, or subatomic structure of matter, he assigned the sizes, shapes, numbers, and movements to the “minute particles” or “corpuscles” that he believed constituted material objects. As examples, he says sounds “are created and are heard by us when . . . a rapid tremor of the air, ruffled into very minute waves, moves certain cartilages of a tympanum within our ear . . . that vision, the sense which is eminent above all others, is related to light . . . and that a multitude of minute particles having certain shapes and moving with certain velocities” striking the senses produce “the sensation which we call
hea
t
” (pp. 311–12).

These independent physical properties, later named “primary qualities,” versus the subjective “sensory qualities,” by John Locke in his
Essay Concerning Human Understanding
, became accepted scientific distinctions constituting Newton's corpuscular-mechanistic worldview. But the attempt to discover the actual nature of these particles and corpuscles and their properties, along with how they produce the sensory effects they do has been a major challenge of scientific research ever since. Thus it is fair to say that Galileo helped set the agenda of the physicists, chemists, physiologists, and microbiologists of modern science, along with the epistemological problems of Descartes and Locke, as well as most twentiethcentury philosophers.

Galileo himself was aware of his enormous originality and influence, immodestly listing his various books and their contributions in a letter to Belisario Vinta, a close scientific friend, seeking a better position. As again quoted by Drake, they consist of

two books on the system and constitution of the universe—an immense conception full of philosophy, astronomy, and geometry; three books on local motion, an entirely new science, no one else, ancient or modern, having discovered some of the very many admirable properties that I demonstrate to exist in natural and forced motions, whence I may reasonably call this a new science discovered by me from its first principles: three books on mechanics . . . and though others have written on this same material, what has been written to date is not one-quarter of what I write, either in bulk or otherwise. (p. 160)

Though not mentioned, he also asserted the valid principles of the uniformity of nature and the conservation of momentum.

This brings us to his most famous book, the English title of which is
Dialogue Concerning the Two Chief World Systems
—
Ptolemaic & Copernican
, whose renown is based on two factors: (1) it's astute arguments written in colloquial Italian and presented in dialogue form essentially showing the superiority of the heliocentric cosmology that made it the greatest scientific dialogue ever written; and (2) the scandalous conviction of Galileo of heresy by the Catholic Inquisition based on his alleged duplicity in writing the book, that has been called “the disgrace of the century.”

Having described in another work the contents of his book and the ensuing trial and conviction in greater detail, I shall focus mainly on the arguments he introduced to refute the objections to the movements of the earth. Taking place over four days, the dialogue is between three interlocutors, one of whom is Salviati, a Florentine aristocratic friend who has the role of an academician representing Galileo; another is Sagredo, a Venetian nobleman who acts as the moderator; and the third named Simplicius after a sixth-century scholastic who defends Aristotelianism and the connotations of whose name perhaps added to his selection as the opponent.

The first day's dispute concerns the distinction between the sublunar and translunar worlds. Salviati argues that while the distinction may have been warranted in Aristotle's day, new telescopic evidence such as Galileo's observations showing the moon's surface to be similar to the earth's; the discovery of four stars circulating Jupiter; the rectilinear trajectory of meteors; the detection of sun spots, novas, and new stars; along with Kepler's discovery of the elliptical shape of Mars's orbit is strong evidence that the distinction is no longer valid.

The second day begins with Simplicius defending, as was commonly believed at the time, the complete authority of Aristotle's writings: “There is no doubt that whoever has this skill will be able to draw from his books demonstrations of all that can be known; for every single thing is in them.”
²⁷
But previously Galileo had Sagredo express his firm belief in the limits, at the time, of knowledge: “there is not a single effect in nature, even the least that exists, such that the most ingenious theorists can arrive at a complete understanding of it” (p. 101).

But turning to the main dialogue of the day, as Galileo had argued, rather than accept the usual explanation that the apparent rising and setting of the sun was caused by the entire universe revolving from east to west in a single day, Salviati points out that the same appearance could be explained more simply and harmoniously by attributing a diurnal rotation to the much smaller earth from west to east. Not only was it incongruous to have the sphere of the fixed stars, at the farthest distance from the earth, complete their revolution in one day while the closer planets completed theirs in a much longer time, the westward revolution attributed to the fixed stars was contrary to the eastward revolution of the planets. Thus Salviati concludes that “by making the earth itself move, the contrariety of motions is removed, and the single motion from west to east accommodates all the observations and satisfies them all completely” (p. 117).

Salviati then addresses the counter argument that despite its simplicity, attributing the diurnal rotation to the earth cannot be true because then one would see clouds, birds, or other aerial objects displaced to the west as the earth revolved eastward. The example of dropping an object from the masthead of a ship is introduced, declaring that during the fall the object would descend at an angle inclined further from the masthead rather than parallel to it, even affirming that the experiment had been performed and shown the described result.

Salviati replies that this could not be true because when he had performed the experiment a solid object dropped from the masthead of a
uniformly moving
ship fell parallel to the masthead. He reinforces his argument by pointing out that in the cabin of a uniformly moving ship (as in an airplane today) everything happens as if the ship were stationary; objects dropped or thrown have the same trajectory as if the cabin were at rest. Since the objects partake of two motions, that of the uniformly moving container and the downward fall, the former cancels out leaving only the falling object as visible. Thus an object dropped from a tower falls parallel to the tower despite the rotation of the earth during the fall. As Salviati concludes:

With respect to the earth, the tower, and ourselves, all of which keep moving with the diurnal motion along with the stone, the diurnal movement is as if it did not exist; it remains insensible, imperceptible, and without any effect whatever. All that remains observable is the motion which we lack, and that is the grazing drop to the base of the tower. (p. 171)

While the second day's dialogue addressed the opposition to the earth's rotary motion, the third day deals with Simplicius' dissent to the earth's annual revolution around the sun based on the ordinary experience of seeing the sun circle the earth and the fact that as a terrestrial heavy body the earth naturally should be in the center of the cosmos. Salviati first responds by pointing out that Simplicius' argument presupposes that the cosmos is a finite sphere, yet it has not been proven whether that is its shape or whether it is “infinite and unbounded.” But as indicated previously, because Giordano Bruno was burned at the stake by order of the Holy Office partially for advocating an infinite universe, this argument is not pursued further.

Instead, Salviati offers Kepler's second two astronomical laws based on the sun's gravitational force as evidence of its central position and Galileo's telescopic evidence of Mars's radical deviation from a circular orbit, as seen from the earth, as refuting the Aristotelian view that all the planetary orbits are circular. As Salviati states regarding several orbital trajectories:

This approach and recession is of such moment that Mars when close looks sixty times as large as when it is most distant. Next, it is certain that Venus and Mercury must revolve around the sun, because of their never moving far away from it, and because of their being seen now beyond it and now on this side of it, as Venus's changes of shape conclusively prove. (p. 322)

He next cites Galileo's telescopic observations showing that the obits of Mercury and Venus are below Earth's while those of Mars, Jupiter, and Saturn are above it. When Simplicius refers to the anomaly in the Copernican system of only the Moon revolving around Earth while all the other planets revolve around the Sun, Salviati replies that this anomaly has been mitigated by the discovery of the four satellites circling Jupiter. Sagredo then brings up two other objections, the observed retrograde, loop-like motion of the five planets as seen from the earth and the absence of parallax when observing the stars. As for the first, Sagredo refers to a diagram by Galileo showing that “these stoppings, retrograde motions, and advances,” are illusions produced by the annual revolution of the earth around the sun (p. 342).

Regarding the absence of parallax or displacement when viewing the stars from the different positions on the earth as it revolves around the sun, this can be explained by attributing a much greater distance to the stars than normally believed. The Aristotelian response was that for a star to be seen from such a great distance “it would have to be so immense in bulk as to exceed the earth's orbit—a thing which is, as they say, entirely unbelievable” (p. 372). Lacking any evidential rebuttal, Salviati gives the sensible answer that without knowing how the stars transmit their light from such a great distance it is impossible to draw a definite conclusion.

The day's dialogue ends with a summary of the evidence that Salviati (as Galileo) believes shows the greater credibility of the heliocentric system, which is one of the major reasons Pope Urban VIII later felt so strongly that he had been deceived and disobeyed when he had agreed to the publication, as long as Galileo treated both systems impartially.

See, then, how two simple noncontradictory motions assigned to the earth, performed in periods well suited to their sizes, and also conducted from west to east as in the case of all movable world bodies, supply adequate causes for all the visible phenomena. These phenomena can be reconciled with a fixed earth only by renouncing all the symmetry that is seen among the speeds and sizes of moving bodies, and attributing an inconceivable velocity to an enormous sphere beyond all the others, while lesser spheres move very slowly. Besides, one must make the motion of the former contrary to that of the latter, and to increase the improbability, must have the highest sphere [to] transport all the lower ones opposite to their own inclination. I leave it to your judgment which has the more likelihood in it. (p. 396)

Considering the acuteness of the arguments of the first three days, the fourth and last day's dialogue is disappointing and yet Galileo considered it one of the most convincing evidences of the earth's motions, even to the extent of intending to include it in the title of the book until prevented from doing so by Pope Urban VIII, who thought it presumptuous. Recall that Kepler had explained the tides as caused by the mutual gravitational force between the earth and the moon which was accepted by the scientific community.

Objecting that the explanation invoked a mysterious force acting at a distance similar to “occult powers,” Galileo dismissed it. Instead, he attributed the ebb and flow of the waves to the contrasting motions of the earth, similar to the undulations in the water in the bilge of a ship due to its pitching in rough seas. Thus he has Sagredo, the moderator, include this argument with the others in a concluding statement.

In the conversations of these four days we have, then, strong evidences in favor of the Copernican system, among which three have been shown to be very convincing—those taken from the stoppings and retrograde motions of the planets, and their approaches toward and recessions from the earth; second, from the revolution of the sun upon itself, and from what is to be observed in the sunspots; and third, from the ebbing and flowing of the ocean tides. (p. 462)

When published in February 1632, after two years of difficult negotiations, as was to be expected, the contrasting reactions were striking. As reported by Drake, Castelli, who was mentioned previously as his scientific friend and who had been sent a copy, replied: “I still have it by me, having read it from cover to cover to my infinite amazement and to my delight; and I read parts of it to friends of good taste to their marvel and always more delight, more to my amazement, and with always more profit to myself.”
²⁸

The reactions of the clergy, especially the Jesuits and Pope Urban VIII, were not only vivid, but livid. While the consequent trial of Galileo involved considerable misunderstandings and incriminations, that Galileo had previously “agreed” to the edict of February 26, 1616, “that he must not hold, defend, or teach in any way, orally or in writing,” the “motion of the earth and stability of the sun,” and did not inform the pope of this when he obtained permission from him to published the book, was one of the incriminating charges. As mentioned previously, the other was that the pope, having agreed to the publication provided Galileo “treat the evidence impartially,” yet having Salviati declare the “improbability” of the Aristotelian view in contrast to the Copernican system and having Sagredo state “in the conversations of these four days we have, then, strong evidence in favor of the Copernican system,” the pope decided that Galileo had deliberately disobeyed his admonition to treat them impartially.