Hi, I'm Peter Adamson and you're listening to the History of Philosophy podcast, brought to you with the support of the philosophy department at King's College London and the LMU in Munich.

Online at historyofilocity.net. Today's episode, the harder they fall, Galileo and the Renaissance.

In the last episode, I suggested that we tend to overestimate or at least misjudge the psychological impact of Copernicus removal of the Earth from the center of the universe.

By contrast, I believe that we tend to underestimate another feature of the new science of the heavens.

Around this time, it became increasingly clear that these celestial bodies are not as aerosol would have it, perfect and unchanging substances made from a fundamentally different kind of matter from that found in our earthly sphere.

The new science of the 16th and 17th centuries instead offered a single unified physics, applicable to both the heavens and the things around us in our everyday experience.

Things up there are made of more or less the same stuff as things down here, and as we now know, outer spaces full of changing and unexpected phenomena like comets, supernovas, and Sandra Bullock.

Unification of physics was already propounded by Telezio and Campanella. On their theory, the whole universe is made from one kind of matter, with everything from stars to stones being governed by the simple principles of heat and cold.

But what they offered was indeed only theory. It was at the beginning of the 17th century that another Italian scientist offered what he at least considered to be direct proof.

I refer, of course, to Galileo Galilei. He showed that the moon is not perfectly spherical, but covered with irregularities and mountains, on the basis of shadows he could see on the moon's surface using the new technology of the telescope.

With that same instrument, he discovered that there are spots moving across the surface of the sun itself.

Galileo also demonstrated that ANOVA that appeared in the night sky must lie beyond the moon, another example to show that things in this celestial world do change.

Furthermore, his telescope delivered powerful confirmation of the Copernican theory, especially in the case of Venus. This planet could now be seen to have phases of illumination, just like our moon, something that could be explained only by saying that it orbits the sun and not the earth.

Galileo also found four of Jupiter's moons, which were clearly orbiting around it. This was not a direct proof of Copernicus' heliocentrism, but undermined a powerful argument for the ancient cosmology given that the moon at least goes around the earth, surely everything else does, too.

Given the presence of bodies orbiting Jupiter, it was now easier to believe that the earth, too, might be circling the sun while having another heavenly body, the moon, circling it.

Thanks to these and other discoveries, Galileo is rightly seen as a truly pivotal figure in the history of European science and philosophy. He literally saw things that no one had ever seen before, and as a result, the universe as a whole came to be seen in a new light.

If it takes one revolutionary thinker to appreciate another fully, then we might pay heed to the words of Immanuel Kant.

In his critique of pure reason, which famously presents itself as performing a Copernican turn of its own within philosophy, he claimed that Galileo introduced an innovative scientific method, according to which,

reason has insight only into that which it produces after a plan of its own. It must itself show the way with principles of judgment based upon fixed laws, constraining nature to give answer to questions of reason's own determining.

Now, unlike Giordano Bruno, I would not insist that there is nothing new under the sun, but it's a guiding principle of this podcast series that intellectual developments do not come out of nowhere like the debris that caused all that trouble for Sandra Bullock in the movie Gravity.

One reason it is worth our time to learn about supposedly minor authors is that it puts us in a better position to understand the achievement of more famous figures. And so it is here.

There's good reason to see Galileo's breakthroughs, which he mostly made in the early 17th century, as a continuation of trends we have learned about from the 16th century.

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