§35. Moving Heaven and Earth
When Galileo’s advocacy of the Copernican hypothesis brought him to the attention of the Holy Office, friends excused him with the argument that the motion Copernicus attributes to the earth is merely hypothetical, a fiction for calculation, not a physical truth.
Galileo refused this defense, as had Copernicus, and even Ptolemy for his geocentric model. Copernicus ignored the Aristotelian dichotomy between physics and astronomy. What he says of the stars does not merely save the phenomena but describes nature just as physics does. Galileo too knew he saw something in the telescope and that it mattered. It could change the whole orientation of natural philosophy.94Before Galileo published there was no empirical evidence for the Copernican system. Mathematically it was somewhat simpler than simple versions of Ptolemy, but not enough to make its adoption compelling, especially in light of the paradoxical movement Copernicus attributes to the earth. Why do we not feel it? Why is there no terrestrial evidence of movement? Then Galileo turned his telescope to the sky. He observed a cycle of phases of Venus, which was predicted by Copernicus yet never observed; furthermore, the Ptolemaic system denied Venus full phases, yet there they were. The moons Galileo observed orbiting Jupiter implied that the universe could have more than one center of motion, and when viewed through the telescope the stars, unlike the moon, did not seem much larger, which would be expected if, as the Copernican system implies, their distance is very much greater.
The most controversial part of Copernicus’s theory was the motion imputed to the earth. In proposing this theory he contradicts the sensory evidence of the earth’s immobility and central position in favor of a rational construction. A sensible effect—stellar motion—is explained by a non-evident cause—terrestrial motion.
Now Galileo calls his contemporaries to the telescope to consider the observational evidence against all their observations. Copernicus published On the Revolutions of the Celestial Spheres in 1543, nearly seventy years before Galileo began observing the stars. There is little of the empiricist about Copernicus. He solves the problem of the planets (their paradoxical retrograde motion) not by studying the heavens but by working on his calculations. The success of his system cast doubt on the adequacy of perception in natural philosophy and destroyed the naive unity of the real and the visible. What is accessible to vision is an arbitrary section through the real. In Hans Blumenberg’s expression, Copernicus put the eyes in the wrong. Experience available to everybody merely by visual attention becomes irrelevant to astronomical research. Detached from observation, objectivity is invested in formality, a trend in epistemology that climaxes with Rudolf Carnap in the twentieth century (§66).95Empiricism is not—or not only—the idea that concepts and their knowledge originate in the senses. That is one empiricism, but neither the first nor most influential. Another empiricism, more durable and consistent, values the observable as evidence of things not observable and otherwise unsuspected. Rather than tie all knowledge to observation, this empiricism requires that the pursuit of knowledge concerning the unobserved be controlled by observation. Observation per se is less important than continuity with observation. We can infer the causal behavior of unobserved elements when they are continuous with what we observe. Maybe vision lost some former authority after Galileo, but natural philosophy remains empirical to the extent that postulation is controlled by experience and not mere logic.
That was the rule of the atomists, of Democritus and Epicurus. No one can see atoms, so they plainly introduce the non-evident, but do so to explain what is evident.
Logical consistency is not enough for natural science. It was not the atomists but Parmenides who violated experience, enjoining the adept not to “let ordinary experience in its variety force you along this way [of nonbeing], [allowing] the eye, sightless as it is, and the ear, full of sound, and the tongue to rule.” Epicurus felt the injustice of that and made respect for experience a principle of his natural philosophy. Maybe we cannot see the causes, but we feel the difference their detection makes, which is why Epicureans practice natural philosophy.96What led to the break with scholastic natural philosophy was not authority finally bending to experience; it was a new kind of experience, experience under controlled, highly artificial conditions—in a word, experimental experience. For ancient thought, reality is that which shows itself (the meaning of the word phenomenon). But after Copernicus and Galileo reality does not show itself; it has to be made to appear, to leave a trace and submit to measurement under the artificial conditions of an experiment. The fact that no one has perceived a thing becomes no reason to deny its reality. That is not a triumph of rationalism over empiricism. It is the triumph of experimental experience over experience unqualified, uncontrolled, come-by-chance.