The Moons of Jupiter

In this season of thanks, most of us are thankful for family and friends, for health and happiness, and for all other human values. Our lives are much safer and easier than our ancestors’ were a thousand years ago. We should be grateful for the benefits of civilization, despite the costs. What else should we be thankful for?

Physicist Sean Carroll has an unusual suggestion. “This year we give thanks for an historically influential set of celestial bodies, the moons of Jupiter.”  They played a crucial role in the development of astronomy, and so in the change from the pre-scientific medieval mind to our modern Secular Scientific Humanism. That shift began the split between what Wilfred Sellars called the Manifest Image and the Scientific Image (“Philosophy and the Scientific Image of Man” 1963). The Manifest Image is what pre-scientific common sense tells us about the way the world is. Carroll is thankful that common sense has been replaced by science, because science is true and pre-scientific common sense is (usually) false. Among the benefits of civilization is scientific truth. 

What did people think about astronomy in the middle ages, or as recently as 400 years ago when the moons of Jupiter were discovered? Basic science is now so much a part of modern common sense that it can be hard to imagine, though ordinary perceptual experience is not always wrong. Sometimes we hear that before Copernicus, people thought the world was flat. However, anyone who stared out at the ocean could see that they were standing on a huge sphere. On a clear day, the ocean horizon is a distinct sharp line, maybe 10 or 20 miles away if you are a few hundred feet above sea level. If the world were flat, there would be no horizon. The ocean would fade off into an indistinct haze. The sharp horizon looks exactly like what it is: the edge of a huge sphere. What could people who made this observation have thought about what was happening on the other side of the sphere?

Common sense did seem to show that the Earth was stationary and that the sun, moon, stars and planets orbited the Earth. When we stand on solid ground we do not feel as if we are moving. The ground seems stationary. The motions of heavenly bodies showed that the stationary Earth was at the center of the universe. Sean Carroll thinks we should be thankful to have overcome this illusion:

   Galileo discovered the four largest moons of Jupiter —Io, Europa, Ganymede, and Callisto —  in 1610, and wrote about his findings in Sidereus Nuncius (The Starry Messenger). They were the first celestial bodies to be discovered using that new technological advance, the telescope. But more importantly for our present purposes, it was immediately obvious that these new objects were orbiting around Jupiter, not around the Earth.

All this was happening not long after Copernicus had published his heliocentric model of the Solar System in 1543, offering an alternative to the prevailing Ptolemaic geocentric model. Both models were pretty good at fitting the known observations of planetary motions, and both required an elaborate system of circular orbits and epicycles — the realization that planetary orbits should be thought of as ellipses didn’t come along until Kepler published Astronomia Nova in 1609. As everyone knows, the debate over whether the Earth or the Sun should be thought of as the center of the universe was a heated one, with the Roman Catholic Church prohibiting Copernicus’s book in 1616, and the Inquisition putting Galileo on trial in 1633.

Strictly speaking, the existence of moons orbiting Jupiter is equally compatible with a heliocentric or geocentric model. After all, there’s nothing wrong with thinking that the Earth is the center of the Solar System, but that other objects can have satellites. However, the discovery brought about an important psychological shift. Sure, you can put the Earth at the center and still allow for satellites around other planets. But a big part of the motivation for putting Earth at the center was that the Earth wasn’t “just another planet.” It was supposed to be the thing around which everything else moved. (Remember that we didn’t have Newtonian mechanics at the time; physics was still largely an Aristotelian story of natures and purposes, not a bunch of objects obeying mindless differential equations.)

The Galilean moons changed that. If other objects have satellites, then Earth isn’t that special. And if it’s not that special, why have it at the center of the universe?




The Catholic Church of the 17th century thought something crucial was at stake. Why should it matter so much what orbits what? Our modern scientific common sense knows that the Earth orbits the sun, which is an average star, one of 200-400 billion in the Milky Way galaxy. Our galaxy is one of 200 billion to 2 trillion galaxies in the universe. That’s big. The universe is unimaginably vast. We are a small part. So what? Why worry about that when we have Trump and Putin to worry about? The Catholic Church seems to have foolishly faught a losing battle it did not need to fight, merely defending ignorant superstition against scientific enlightenment. Or was there more at stake?

The world of the middle ages was miserable, tortured by starvation, disease and warfare. But think how cozy it was. You are at the center of the universe. The universe literally revolves around you. You must be important. Your life must be meaningful. The God who created all this knows your value. You can have faith in Him and in your value. This is what Catholism represented.

The Church Fathers may have been right to worry about the “psychological shift” that threatened all this. The moons of Jupiter were a small insight into the cold reality that the universe does not revolve around us. The universe does not care about us or about anything else. It is not organized around us. The Earth, the sun, the stars, the planets, the moons of Jupiter and everything else are just “a bunch of objects obeying mindless differential equations.” There is no purpose to any of it. The Catholic Church saw Gallileo as the beginning of the end.

But we still have purpose, don’t we? Even if the stars merely obey mindless differential equations, and not pushed around by the intentions of God, we still have our own intentions, our own meanings, don’t we? BQTA contributor Rick Lenon, M.D. recently commented that “all human responses are determined by unconscious processes. Consciousness itself is a construction of preconscious processing.  Consciousness does not construct itself.” He is implying that the same mindless processes that control the galaxies also control us. Your mind is constructed and determined by the biological equivalent of “mindless differential equations.”  There is no more purpose to the bio-chemical reactions occuring inside your body than there is in the orbits of the moons of Jupiter. And your internal biochemistry determines your actions and constructs your feelings.

Sean Carroll is right to be thankful for Galileo and the moons of Jupiter. “Thus began one of the great revolutions in our understanding of our place in the cosmos.”  It’s better to know the truth than to live an illusion, no matter how pleasant.

So where does the purposefulness of our actions and feelings come from? We still have that, don’t we? How can the strength of our feelings be undiminished when their meaning has vanished?



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