The Gravity of Gravity

A Quick Look at Astronomy and Its Relevance

What was so amazing about Newton anyway? An apple falls, and he’s a genius? Everyone has always known that things fall. As one of my students said about something, “It’s as obvious as gravity.” And yet it was revolutionary? To understand a revolution, you have to understand from what it revolted.

 

Like most of the Quadrivium, Astronomy has lost its place in today’s classical liberal arts curriculum. In this talk, Dr. Seeley will give a brief introduction to Astronomy when it was a liberal art, and indicate how its developments remain a crucial part of the story of our civilization.

The historian Paul Johnson begins his work on the twentieth-century, Modern Times, in this surprising way.

The modern world began on 29 May 1919 when photographs of a solar eclipse, taken on the island of Principe off West Africa and at Sobral in Brazil, confirmed the truth of a new theory of the universe. It had been apparent for half a century that the Newtonian cosmology was in need of serious modification. It had stood for more than two hundred years. It was the framework within which the European Enlightenment, the Industrial Revolution, and the vast expansion of human knowledge, freedom and prosperity which characterized the nineteenth century, had taken place. . . . The public response to relativity was one of the principal formative influences on the course of twentieth-century history. It formed a knife, inadvertently wielded by its author, to help cut society adrift from its traditional moorings in the faith and morals of Judeo-Christian culture.

Johnson was referring to the dramatic confirmation of Einstein’s theory of relativity, which predicted that the light of stars would be bent by the gravitational field of the sun twice as much as was predicted by Newtonian theory. Johnson, a writer with a flair for the dramatic, made dramatic claims about the societal impact of two astronomers. Newton’s ideas about gravity provided a framework for the Enlightenment? The Industrial Revolution? The growth of democracy? How could that be? What use could knowledge of gravity be for a pre-space age society? My daughter says, “Gravity is my enemy.” There is nothing you can do about it. How could Einstein’s theories about the relativity of space and time, which only are detectable on a cosmological or atomic scale, contribute to undermining Judeo-Christian culture?

Johnson sees Newton and Einstein as examples of a more general truth: “Great scientific innovators . . . change our perception of the physical world and increase our mastery of it. But they also change our ideas. The second effect is often more radical than the first.” I think this is a fascinating claim in itself, and at this conference we want to encourage in ourselves a love of learning interesting things just for their own sake, apart from what use you might make of them in the classroom. But, if true, it also points out how today’s classical liberal arts curriculum, in which history so often plays the integrating role, should stretch itself to include an understanding of the scientific and mathematical developments which characterize ages and cultures.

What was so amazing about Newton anyway? An apple falls, and he’s a genius? Everyone has always known that things fall. As one of my students said about something, “It’s as obvious as gravity.” And yet it was revolutionary? To understand a revolution, you have to understand from what it revolted. In this case, that means going back to the ancient view of the cosmos, and the work of the 2nd century astronomer, Claudius Ptolemy. Ptolemy was to ancient astronomy what Euclid was to geometry. He gathered together and perfected all that the Greeks had learned about the sky that shone so brilliantly at night in the eons before cities and their lights erased it from ordinary experience.[1] According to the internet, over 80% of the human race cannot see the stars. When the 1994 Northridge earthquake wiped out lights in Los Angeles, concerned citizens made 911 calls about strange lights in the sky.

I would never have really seen the night sky except for visiting my grandparents’ farm in Michigan. There I saw the Man in the Moon, the Big Dipper, and, my personal favorite, Orion (Tolkien’s Menelvagor, the Swordsman of the Sky). That was about all. Those who lived on the farm knew much more about the night sky; my aunt would point things out, but I had a hard time seeing them.[2] It’s like staring at stuff under a microscope or looking at ultrasounds—it’s all just a blur to me, though the experienced eye sees everything distinctly.

Thankfully, my college’s commitment to liberal education demanded a serious encounter with the whole Quadrivium. At the beginning of Sophomore year, I spent two weeks systematically observing the sky with the naked eye, then studied Ptolemy, Copernicus, Kepler, Galileo, Newton, and Einstein over the next three years. Not only was I introduced to the historical developments of science, but I came to see the reasons why we believe that the Earth moves, and that all things are heavy. More than that, I was able to enter into Dante’s imaginative vision of the cosmos, and understand the ways in which St. Thomas used astronomy to help understand the science of theology.

The Ptolemaic portion, especially grounded in the two weeks of observations, made me a friend of the night skies for the rest of my life. The observations involved watching the sky at different times through the night, and watching it at the same time every night for awhile, noting especially what was rising and what was setting. It set up a habit of keeping track of the sky, which was natural in our rural campus setting. In a place like that, the first thing you notice is how beautiful and overwhelming the lights in the night sky are. Then, in the profusion of lights, you might notice some clumping of stars, some brighter, some less bright, and the Moon standing out in size, shape, and brightness. If you spend some time outside on a starry night, you should be able to see the Moon and stars move, slowly but perceptibly over an hour or so, from east to west, just like the Sun, covering the entire sky in the course of one night. All the stars stick together, moving as one, but the Moon, if you pay attention, shifts its position slowly, falling behind the stars noticeably. As you get to know the sky over many months, you might be struck by the way in which most of the stars never change their positions to one another, though they are always moving. Orion is the same, day and night, forever; his faithful dog, Sirius, remains always at his side. But they start their night journey at different places, higher in the sky with each passing day. One month, Orion is high in the Southern sky as the night opens up, another month, much further to the right and coming down, another month and he is low in the West, a few months later, he has disappeared altogether. But the Moon drifts the other way, falling behind more each night, and changing shape, too, getting larger as its sunset position gets lower in the East, until it rises beautifully full as the Sun sets in the West.

The Moon is a wanderer among the stars. And if you pay attention over months to some of those brighter stars, you might notice them wandering, too. Not Sirius, the dog-star, one of the brightest, but Venus and Jupiter and Mars the red.  But though the Moon always drifts behind the star flow at the same steady pace, Venus falls back away from the setting sun for a while, then stalls about 45 degrees away, then slowly starts to catch up until it disappears. Coincidentally, soon a bright star appears in the early morning in the East, performing the same away-and-back-again motion. You might soon come to suspect that the Evening and Morning Stars are really the same planet (the Greek word for “wanderer”). Jupiter’s backward drift is not limited like Venus’s, but neither is it steady like the Moon’s. It will fall behind for awhile, then catch up a bit, then fall behind more, and catch up a little, and fall behind more.

These are some of the basic night sky movements that all civilizations seem to have come to know from the beginning: the never-varying nightly movement of the whole sky from East to West, the change of first evening positions of the constellations, the steady drift backward of the Moon, the cyclical back-and-forth drifting of the planets. Through devoted observations over centuries, they realized that, though the heavens are always in motion, their motions are absolutely predictable, and they can guide religion, agriculture, navigation.

When a fascinating chaos has been observed enough to reveal patterns that allow prediction, the human mind is ready to ask, “Why?” Ptolemy shared the common conviction of human beings watching the stars over millennia—the heavens are so different from the earth! They are always the same. Though the mountains may fall and the hills turn to dust, cities and empires come and go, Orion is always there, exactly the same for Ptolemy as for the first recorded observers. Like all the stars, he moves, but always in the same way, always with the same even, never-varying pace, always in conjunction with almost all the rest of the heavenly panoply. And though the planets wandered among the stars, observations revealed how tantalizingly predictable their wanderings were. So different from the movements of birds, or horses, or arrows, or volcanoes. According to thousands of years of human observations, the heavenly bodies were eternal, they always were, they always will be, world without end. They were immortal, divine, yet visible, and moving with what must be mathematical precision. The hope of drawing close to God by uncovering the mathematical elegance and precision of the divine heavens is what attracted Ptolemy to devote his life to studying the heavens.

Meditating that only the mathematical, if approached enquiringly, would give its practitioners certain and trustworthy knowledge with demonstration both arithmetic and geometric resulting from indisputable procedures, we were led to cultivate most particularly as far as lay in our power this theoretical discipline. And especially were we led to cultivate that discipline developed in respect to divine and heavenly things as being the only one concerned with the study of things which are always what they are.

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