The Scientific Revolution was predicated on the idea that knowledge of how the universe worked was acquired through a combination of careful observations, controlled experiments, and the formulation of general laws, expressed in mathematical terms. New scientific instruments capable of making precise empirical observations underpinned some of the most important breakthroughs of the period. Perhaps no single invention produced more dramatic discoveries than the telescope, the first of which were produced in the early seventeenth century by Dutch eyeglass makers.

The impact of new instruments depended on how scientists employed them. In the case of the telescope, it was the brilliant Italian mathematician and astronomer Galileo Galilei (1564–1642) who unlocked its potential when he used it to observe the night sky. Within months of creating his own telescope, which improved on earlier designs, Galileo made a series of discoveries that put into question well-established understandings of the cosmos. He observed craters on the moon and sunspots, or blemishes, moving across the face of the sun, which challenged the traditional notion that no imperfection or change marred the heavenly bodies. Moreover, his discovery of the moons of Jupiter and many new stars suggested a cosmos far larger than the finite universe of traditional astronomy. In 1610, Galileo published his remarkable findings in a book titled The Starry Messenger, where he emphasized time and again that his precise observations provided irrefutable evidence of a cosmos unlike that described by traditional authorities. “With the aid of the telescope,” he argued, “this has been scrutinized so directly and with such ocular certainty that all the disputes which have vexed the philosophers through so many ages have been resolved, and we are at last freed from wordy debates about it.”19

Galileo’s empirical evidence transformed the debate over the nature of the cosmos. His dramatic and unexpected discoveries were readily grasped, and with the aid of a telescope anyone could confirm their veracity. His initial findings were heralded by many in the scientific community, including Christoph Clavius, the Church’s leading astronomer in Rome. Galileo’s findings led him to conclude that Copernicus (1473–1543), an earlier astronomer and mathematician, had been correct when he had advanced the theory that the sun rather than the earth was at the center of the solar system. But Galileo’s evidence could not definitively prove Copernicus’s theory to the satisfaction of critics, leading Galileo to study other phenomena, such as the tides, that could provide further evidence that the earth was in motion.

When the Church condemned Copernicus’s theory in 1616, it remained silent on Galileo’s astronomical observations, instead warning him to refrain from teaching or promoting Copernicus’s ideas. Ultimately, though, Galileo came into conflict with church authorities when in 1629 he published, with what he thought was the consent of the Church, the Dialogue Concerning the Two Chief World Systems, a work sympathetic to Copernicus’s sun-centric system. In 1632, Galileo was tried by the Roman Inquisition, an ecclesiastical court charged with maintaining orthodoxy, and convicted of teaching doctrines against the express orders of the Church. He recanted his beliefs and at the age of sixty-nine was sentenced to house arrest.

Although Galileo was formally convicted of disobeying the Church’s order to remain silent on the issue of Copernicus’s theory, the question most fundamentally at stake in the trial was “What does it mean, ‘to know something’?”21 This question of the relationship between scientific knowledge, primarily concerned with how the universe works, and other forms of “knowledge,” derived from divine revelation or mystical experience, has persisted in the West. Over 350 years after the trial, Pope John Paul II spoke of Galileo’s conviction in a public speech in 1992, declaring it a “sad misunderstanding” that belongs to the past, but one with ongoing resonance because “the underlying problems of this case concern both the nature of science and the message of faith.” Addressing the central question of what it means to know something, the pope declared scientific and religious knowledge to be compatible: “There exist two realms of knowledge, one which has its source in Revelation and one which reason can discover by its own power…. The distinction between the two realms of knowledge ought not to be understood as opposition…. The methodologies proper to each make it possible to bring out different aspects of reality.”22

Strangely enough, Galileo himself had expressed something similar centuries earlier. “Nor is God,” he wrote, “any less excellently revealed in Nature’s actions than in the sacred statements of the Bible.”23 Finding the place of new scientific knowledge in a constellation of older wisdom traditions proved a fraught but highly significant development in the emergence of the modern world.

Question: What can Galileo’s discoveries with his telescope and his conviction by the Inquisition tell us about the Scientific Revolution?