COPERNICAN QUESTIONS

On May 24, 1543, Europe's foremost astronomer lay dying. The story goes that Nicholas Copernicus was on his deathbed when he received from the printer the first copies of his great work De Revolutionibus Orbium Caelestium—On the Revolutions of the Heavenly Spheres. This work proposed nothing less than a radical revision of the established view of the universe. Copernicus argued that the earth is not the immovable center of the universe but rather is part of a solar system. He proposed that the earth, along with its sister planets Mercury, Venus, Mars, Jupiter, and Saturn, are arrayed in a series of concentric circular orbits about the sun (or, to be precise, a point very close to the sun). Copernicus was not the first to make this startling suggestion; several thinkers in ancient Greece had entertained the notion of a heliocentric (sun-centered) cosmology. But by Copernicus's day, the geocentric (earth-centered) cosmology had gained the full support of science, philosophy, and, most important of all in those days, theology. So deeply entrenched was the geocentric view that Copernicus's system was inevitably regarded as shocking, absurd, or perhaps even heretical. Yet despite the opposition of scientists, philosophers, and the church—which famously condemned Galileo for defending the Copernican view—the heliocentric theory had won by about 1650.

The Copernican Revolution, like the Darwinian revolution of the nineteenth century, impacted not just science but something deep within the human psyche. Anyone who has followed the recent debates over "scientific creationism" or "intelligent design theory" knows that the Darwinism continues to elicit passionate feelings. In a sense, we are also still coming to terms with Copernicus.

WHAT WAS COPERNICUS'S REVOLUTION?

Just what was so radical about Copernicus's theory, and why did it shock so many of his contemporaries? Why did others find it so inspiring that it is fair to say that the whole Scientific Revolution began with Copernicus? To answer these questions we have to get deeper into the history. Merely to say that with Copernicus science moved from an earth-centered to a sun-centered cosmology is hardly adequate to understand the depth and breadth of a transformation so profound that it really marks the beginning of the modern world and the demise of the medieval one.

New theories do not arise in a vacuum. They are proposed in the face of established theories that have served long and honorably and have faced down many previous challengers. So, when new theories win, old theories lose. The fate of discarded theories is not pretty. They become the objects of mirth or pity as later generations find it hard to imagine how the universe could ever have been conceived in such terms.

Such condescension is inappropriate. As the saying goes, the past is another country, and when we disdain past views merely because they are old, we are behaving like someone who laughs at the customs and beliefs of other cultures. This does not mean that we must regard past theories—or even the customs and beliefs of other cultures—as equal to our own. The point is that theories accepted by people in previous centuries, including theories long since recognized as false, were in their day eminently reasonable views that explained the universe in ways that were rigorously logical, coherent, beautiful, satisfying, and comprehensive. The intellectual pillars of the late medieval worldview included the teachings of the church, of course, but also the doctrines of two eminent thinkers of pagan antiquity, the philosopher/scientist Aristotle and the astronomer Claudius Ptolemy.

Aristotle (384–322 BCE) is always ranked with Plato as one of the two greatest philosophical intellects of the ancient world. Aristotle studied under Plato, but he developed a distinct philosophy of extraordinary scope and power. He thought about everything and had important things to say about almost every conceivable topic. As opposed to Plato, whose mind ascended to the transcendent realm of eternal essences, Aristotle's intellect was focused on the physical world. The painting The School of Athens by the Renaissance master Raphael, depicts Plato and Aristotle as its two central figures. As they walk, engaged in animated debate, Plato is pointing heavenward while Aristotle gestures with his palm down and his arm forward and parallel to the ground, as if to emphasize his concern with...