Two Views of the Cosmos

Two Views of the Cosmos

Ptolemy as Astronomer

The study of the heavens brought Ptolemy a kind of ecstasy. “Mortal as I am”, he wrote, “I know that I am born for a day. But when I follow at my pleasure the serried multitude of the stars in their circular course, my feet no longer touch the Earth…”.

Ptolemy believed that the Earth was at the center of the universe; that the Sun, Moon, planets and stars went around the Earth. This is the most natural idea in the world. The Earth seems steady, solid, immobile, while we can see the heavenly bodies rising and setting each day. Every culture has leaped to the geocentric hypothesis. As Johannes Kepler wrote, “It is therefore impossible that reason not previously instructed should imagine anything other than that the Earth is a kind of vast house with the vault of the sky placed on top of it; it is motionless and within it the Sun being so small passes from one region to another, like a bird wandering through the air.”

But how do we explain the apparent motion of the planets – Mars, for example, which had been known for thousands of years before Ptolemy’s time? (One of the epithets given Mars by the ancient Egyptians was sekded-ef em khetkhet, which means “who travels backwards,” a clear reference to its retrograde or loop-the-loop apparent motion).

With the Earth the center of the Universe, there is little motivation for astronomical observations. Image: Neon Light Planet © Meg Jorgensen (Elena)

Ptolemy’s model of planetary motion can be represented by a little machine, like those that, serving a similar purpose, existed in Ptolemy’s time. For example, four centuries earlier, such a device was constructed by Archimedes and examined and described by Cicero in Rome, where it had been carried by the Roman general Marcellus, one of whose soldiers had, gratuitously and against orders, killed the septuagenarian scientist during the conquest of Syracuse.

The problem was to figure out a “real” motion of the planets, as seen from up there, on the “outside”, which would reproduce with great accuracy the apparent motion of the planets, as seen from down here, on the “inside”.

The planets were imagined to go around the earth affixed to perfect transparent spheres. But they were not attached directly to the spheres, but indirectly, through a kind of off-center wheel. The sphere turns, the little wheel rotates, and, as seen from the Earth, Mars does its loop-the-loop. This model permitted reasonably accurate predictions of planetary motion, certainly good enough for the precision of measurement available in Ptolemy’s day, and even many centuries later.

Copernicus

Martin Luther described Copernicus as “an upstart astrologer… This fool wishes to reverse the entire science of astronomy. But Sacred Scripture tells us that Joshua commanded the Sunt to stand still, and not the Earth.” Even some of Copernicus’ admirer argued that he had not really believed in a Sun-centered universe but had merely proposed it as a convenience for calculating the motions of the planets.

The epochal confrontation between the two views of the Cosmos – Earth-centered and Sun-centered – reached a climax in the sixteenth and seventeenth centuries in the person of a man who was, like Ptolemy, both astrologer and astronomer. He lived in a time when the human spirit was fettered and the mind chained; when the ecclesiastical pronouncements of a millennium or two earlier on scientific matters were considered more reliable than contemporary findings made with techniques unavailable to the ancients ; with deviations, even on arcane theological matters, from the prevailing doxological preferences, Catholic and Protestant, were punished by humiliation, taxation, exile, torture or death.

The heavens were inhabited by angels, demons and the Hand of God, turning the planetary crystal spheres. Science was barren of the idea that underlying the phenomena of Nature might be the laws of physics. But the brave and lonely struggle of this man was to ignite the modern scientific revolution.

In an inventory of nearly every sixteenth-century copy of Copernicus’ book, Owen Gingerich has found the censorship to have been ineffective : only 60% of the copies in Italy were “corrected”, and not one in Iberia. Image : Spicy Pink and Lilac Fractals © Megan Jorgensen (Elena)

Johannes Kepler was born in Germany in 1571 and sent as a boy to the Protestant seminary school in the provincial town of Maulbronn to be educated for the clergy. It was a kind of boot camp, training young minds in the use of theological weaponry against the fortress or Roman Catholicism. Kepler, stubborn, intelligent and fiercely independent, suffered two friendless years in bleak Maulbronn, becoming isolated and withdrawn, his thoughts devoted to his imagined unworthiness in the eyes of God. He repented a thousand sins no more wicked than another’s and despaired of ever attaining salvation.

But God became for Kepler more than a divine wrath craving propitiation. Kepler’s God was the creative power of the Cosmos. The boy’s curiosity conquered his fear. He wished to learn the eschatology of the world; he dared to contemplate the Mind of God. These dangerous visions, at first insubstantial as a memory, became a lifelong obsession. The hubristic longings of a child seminarian were to carry Europe out of the cloister of medieval thought.