Two Views of the Cosmos

Two Views of the Cosmos

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 Sun 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.

Nicolaus Copernicus. 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)

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.

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stubborn, intelligent and fiercely independent, suffered two friendless years in bleak Maulbronn, becoming isolated and withdrawn, his thoughts devoted to his imagined unworthiness in the eyes of God.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.

Music of the Spheres

Music of the Spheres

Ptolemy’s aetherial spheres, imagined in medieval times to be made of crystal, are why we still talk about the music of the spheres and a seventh heaven (there was a “heaven” or sphere for the Moon, Mercury, Venus, the Sun, Mars, Jupiter and Saturn, and one for the stars).

In fact, 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?

With the Earth the center of the Universe, with creation pivoted about terrestrial events, with the heavens imagined constructed on utterly unearthly principles, there was little motivation for astronomical observations. Supported by the Church through the Dark ages, Ptolemy’s model helped prevent the advance of astronomy for a millennium. Finally, in 1543, a quite different hypothesis to explain the apparent motion of the planets was published by a Polish Catholic cleric named Nicholas Copernicus. Its most daring feature was the proposition that the Sun, not the Earth, was at the center of the universe. The Earth was demoted to just one of the planets, third from the Sun, moving in a perfect circular orbit (Ptolemy had considered such a heliocentric model but rejected it immediately; from the physics of Aristotle, the implied violent rotation of the Earth seemed contrary to observation).

The Earth Seen From the Moon. Our home planet is a large sphere rotating at the sound of music. Image : Illusion © Meg Jorgensen (Elena)

In Ptolemy’s Earth-centered system, the little sphere called the epicycle containing the planet turns while attached to a larger rotating sphere, producing retrograde apparent motion against the background of distant stars.

In Copernicus system, the Earth and other planets move in circular orbits about the Sun. As the Earth overtakes Mars, the latter exhibits its retrograde apparent motion against the background of distant stars.

It worked at least as well as Ptolemy’s spheres in explaining the apparent motion of the planets. But it annoyed many people. In 1616 the Catholic Church placed Copernicus’ work on its list of forbidden books “until corrected” by local ecclesiastical censors, where it remained until 1835 (in a recent inventory of nearly every sixteenth-century of Copernicus’ book, Own Gingerich has found the censorship to have been ineffective: only 60 percent of the copies in Italy were “corrected”, and not one in Iberia.

The Remains of the Sun

The Remains of the Sun

The Aztecs foretold a time “when the Earth has become tired… when the seed of Earth has ended”. On that day, they believed, the Sun will fall from the sky and the stars will be shaken from the heavens.

In the meantime, human beings will almost certainly have evolved into something quite different. Perhaps our descendants will be able to control or moderate stellar evolution. Or perhaps they will merely pick up and leave for Mars or Europa or Titan or, at last, as Robert Goddard envisioned, seek out an uninhabited planet in some young and promising planetary system.

Remains of the Sun. Every nebula is a token of a star in extremis. Image: © Megan Jorgensen

The Sun’s stellar ash can be reused for fuel only up to a point. Eventually the time will come when the solar interior is all carbon and oxygen, when at the prevailing temperatures and pressures no further nuclear reactions can occur. After the central helium is almost all used up, the interior of the Sun will continue its postponed collapse, the temperatures will rise again, triggering a last round of nuclear reactions and expanding the solar atmosphere a little. In its death throes, the Sun will slowly pulsate, expanding and contracting once every few millennia, eventually spewing its atmosphere into space in one or more concentric shells of gas. The hot exposed solar interior will flood the shell with ultraviolet light, inducing a lovely red and blue fluorescence extending beyond the orbit of Pluto. Perhaps half the mass of the Sun will be lost in the way. The solar system will then be filled with an eerie radiance the ghost of the Sun, outward bound.

When we look around us in our little corner of the Milky Way, we see many stars surrounded by spherical shells of lowing gas, the planetary nebulae (they have nothing to do with planets, but some of them seemed reminiscent in inferior telescopes of the blue-green discs of Uranus and Neptune. They appear as rings, but only because, as with soap bubbles, we see more of them at the periphery than at the center. Every planetary nebula is a token of a star in extremis. Near the central star there may be a retinue of dead worlds, the remnants of planets once full of life and now airless and ocean-free, bathed in a wraithlike luminance. The remains of the Sun, the exposed solar core at first enveloped in its planetary nebula, will be a smaller hot star, cooling to space, collapsed to a density unheard of on Earth, more than a ton per teaspoonful. Billions of years hence, the Sun fill become a degenerate white dwarf, cooling like all those points of light we see at the centers of planetary nebulae from high surface temperatures to its ultimate state, a dark and dead black dwarf.

We had the sky, up there, all speckled with stars, and we used to lay on our backs and look up at them, and discuss about whether they were made, or only just happened (Mark Twain, Huckleberry Finn). Image: © Megan Jorgensen.

Spherical Geometry

Spherical Geometry

Presumptive Galactic Cannibal

Some clusters of galaxies have their galaxies arranged in an unambiguously spherical geometry; they are composed chiefly of ellepticals, often dominated by one giant elliptical, the presumptive galactic cannibal. Other clusters with a far more disordered geometry have, comparatively, many more spirals and irregulars. Galactic collisions distort the shape of an originally spherical cluster and may also contribute to the genesis of spirals and irregulars from ellepticals. The form and abundance of the galaxies have a story to tell us of ancient events on the largest possible scale, a story we are just beginning to read.

The development of high speed computers makes possible numerical experiments on the collective motion of thousands or tens of thousands of points, each representing a star, each under a gravitational influence of all the other points.

Presumptive galactic cannibal. Zen Dark Sky. Image: © by Megan Jorgensen (Elena)

In some cases, spiral arms form all by themselves in a galaxy that has already flattened to a disk. Occasionally, a spiral arm may be produced by the close gravitational encounter of two galaxies, each of course composed of billions of stars.

The gas and dust diffusely spread through such galaxies will collide and become warmed. But when two galaxies collide the stars pass effortlessly by one another, like bullets through a swarm of bees, because a galaxy is made mostly of nothing and the spaces between the stars are vast.

Nevertheless, the configuration between the galaxies can be distorted severely. A direct impact on one galaxy by another can send the constituent stars pouring and careening through intergalactic space, galaxy wasted.

When a small galaxy runs into a larger one face-on it can produce one of the loveliest of the rare irregulars, a ring galaxy thousands of light-years across, set against the velvet of intergalactic spac. It is a splash in the galactic pond, a temporary configuration of disrupted stars, a galaxy with a central piece turned out.

Ptolemy as Astronomer

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 © 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.