Pale Blue Dot: A Vision of the Human Future in Space - Carl Sagan, Ann Druyan (1997)
Chapter 2. ABERRATIONS OF LIGHT
If man were taken away from the world, the rest would seem to be all astray,
without aim or purpose … and to be leading to nothing.
—FRANCIS BACON, WISDOM OF THE ANCIENTS (1619)
Ann Druyan suggests an experiment: Look back again at the pale blue dot of the preceding chapter. Take a good long look at it. Stare at the dot for any length of time and then try to convince yourself that God created the whole Universe for one of the 10 million or so species of life that inhabit that speck of dust. Now take it a step further: Imagine that everything was made just for a single shade of that species, or gender, or ethnic or religious subdivision. If this doesn’t strike you as unlikely, pick another dot. Imagine it to be inhabited by a different form of intelligent life. They, too, cherish the notion of a God who has created everything for their benefit. How seriously do you take their claim?
“SEE THAT STAR?”
“You mean the bright red one?” his daughter asks in return.
“Yes. You know, it might not be there anymore. It might be gone by now—exploded or something. Its light is still crossing space, just reaching our eyes now. But we don’t see it as it is. We see it as it was.”
Many people experience a stirring sense of wonder when they first confront this simple truth. Why? Why should it be so compelling? On our little world light travels, for all practical purposes, instantaneously. If a lightbulb is glowing, then of course it’s physically where we see it, shining away. We reach out our hand and touch it: It’s there all right, and unpleasantly hot. If the filament fails, then the light goes out. We don’t see it in the same place, glowing, illuminating the room years after the bulb breaks and it’s removed from its socket. The very notion seems nonsensical. But if we’re far enough away, an entire sun can go out and we’ll continue to see it shining brightly; we won’t learn of its death, it may be, for ages to come—in fact, for how long it takes light, which travels fast but not infinitely fast, to cross the intervening vastness.
The immense distances to the stars and the galaxies mean that we see everything in space in the past—some as they were before the Earth came to be. Telescopes are time machines. Long ago, when an early galaxy began to pour light out into the surrounding darkness, no witness could have known that billions of years later some remote clumps of rock and metal, ice and organic molecules would fall together to make a place called Earth; or that life would arise and thinking beings evolve who would one day capture a little of that galactic light, and try to puzzle out what had sent it on its way.
And after the Earth dies, some 5 billion years from now, after it is burned to a crisp or even swallowed by the Sun, there will be other worlds and stars and galaxies coming into being—and they will know nothing of a place once called Earth.
IT ALMOST NEVER FEELS like prejudice. Instead, it seems fitting and just—the idea that, because of an accident of birth, our group (whichever one it is) should have a central position in the social universe. Among Pharaonic princelings and Plantagenet pretenders, children of robber barons and Central Committee bureaucrats, street gangs and conquerors of nations, members of confident majorities, obscure sects, and reviled minorities, this self-serving attitude seems as natural as breathing. It draws sustenance from the same psychic wellsprings as sexism, racism, nationalism, and the other deadly chauvinisms that plague our species. Uncommon strength of character is needed to resist the blandishments of those who assure us that we have an obvious, even God-given, superiority over our fellows. The more precarious our self-esteem, the greater our vulnerability to such appeals.
Since scientists are people, it is not surprising that comparable pretensions have insinuated themselves into the scientific worldview. Indeed, many of the central debates in the history of science seem to be, in part at least, contests over whether humans are special. Almost always, the going-in assumption is that we are special. After the premise is closely examined, though, it turns out—in dishearteningly many cases—that we are not.
Our ancestors lived out of doors. They were as familiar with the night sky as most of us are with our favorite television programs. The Sun, the Moon, the stars, and the planets all rose in the east and set in the west, traversing the sky overhead in the interim. The motion of the heavenly bodies was not merely a diversion, eliciting a reverential nod and grunt; it was the only way to tell the time of day and the seasons. For hunters and gatherers, as well as for agricultural peoples, knowing about the sky was a matter of life and death.
How lucky for us that the Sun, the Moon, the planets, and the stars are part of some elegantly configured cosmic clockwork! It seemed to be no accident. They were put here for a purpose, for our benefit. Who else makes use of them? What else are they good for?
And if the lights in the sky rise and set around us, isn’t it evident that we’re at the center of the Universe? These celestial bodies—so clearly suffused with unearthly powers, especially the Sun on which we depend for light and heat—circle us like courtiers fawning on a king. Even if we had not already guessed, the most elementary examination of the heavens reveals that we are special. The Universe seems designed for human beings. It’s difficult to contemplate these circumstances without experiencing stirrings of pride and reassurance. The entire Universe, made for us! We must really be something.
This satisfying demonstration of our importance, buttressed by daily observations of the heavens, made the geocentrist conceit a transcultural truth—taught in the schools, built into the language, part and parcel of great literature and sacred scripture. Dissenters were discouraged, sometimes with torture and death. It is no wonder that for the vast bulk of human history, no one questioned it.
It was doubtless the view of our foraging and hunting ancestors. The great astronomer of antiquity, Claudius Ptolemaeus (Ptolemy), in the second century knew that the Earth was a sphere, knew that its size was “a point” compared to the distance of the stars, and taught that it lay “right in the middle of the heavens.” Aristotle, Plato, St. Augustine, St. Thomas Aquinas, and almost all the great philosophers and scientists of all cultures over the 3,000 years ending in the seventeenth century bought into this delusion. Some busied themselves figuring out how the Sun, the Moon, the stars, and the planets could be cunningly attached to perfectly transparent, crystalline spheres—the big spheres, of course, centered on the Earth—that would explain the complex motions of the celestial bodies so meticulously chronicled by generations of astronomers. And they succeeded: With later modifications, the geocentric hypothesis adequately accounted for the facts of planetary motion as known in the second century, and in the sixteenth.
From there it was only a slight extrapolation to an even more grandiose claim—that the “perfection” of the world would be incomplete without humans, as Plato asserted in the Timaeus. “Man … is all,” the poet and cleric John Donne wrote in 1625. “He is not a piece of the world, but the world itself; and next to the glory of God, the reason why there is a world.”
And yet—never mind how many kings, popes, philosophers, scientists, and poets insisted on the contrary—the Earth through those millennia stubbornly persisted in orbiting the Sun. You might imagine an uncharitable extraterrestrial observer looking down on our species over all that time—with us excitedly chattering, “The Universe is created for us! We’re at the center! Everything pays homage to us!”—and concluding that our pretensions are amusing, our aspirations pathetic, that this must be the planet of the idiots.
But such a judgment is too harsh. We did the best we could. There was an unlucky coincidence between everyday appearances and our secret hopes. We tend not to be especially critical when presented with evidence that seems to confirm our prejudices. And there was little countervailing evidence.
In muted counterpoint, a few dissenting voices, counseling humility and perspective, could be heard down through the centuries. At the dawn of science, the atomist philosophers of ancient Greece and Rome—those who first suggested that matter is made of atoms—Democritus, Epicurus, and their followers (and Lucretius, the first popularizer of science) scandalously proposed many worlds and many alien life forms, all made of the same kinds of atoms as we. They offered for our consideration infinities in space and time. But in the prevailing canons of the West, secular and sacerdotal, pagan and Christian, atomist ideas were reviled. Instead, the heavens were not at all like our world. They were unalterable and “perfect.” The Earth was mutable and “corrupt.” The Roman statesman and philosopher Cicero summarized the common view: “In the heavens … there is nothing of chance or hazard, no error, no frustration, but absolute order, accuracy, calculation and regularity.”
Philosophy and religion cautioned that the gods (or God) were far more powerful than we, jealous of their prerogatives and quick to mete out justice for insufferable arrogance. At the same time, these disciplines had not a clue that their own teaching of how the Universe is ordered was a conceit and a delusion.
Philosophy and religion presented mere opinion—opinion that might be overturned by observation and experiment—as certainty. This worried them not at all. That some of their deeply held beliefs might turn out to be mistakes was a possibility hardly considered. Doctrinal humility was to be practiced by others. Their own teachings were inerrant and infallible. In truth, they had better reason to be humble than they knew.
BEGINNING WITH COPERNICUS in the middle sixteenth century, the issue was formally joined. The picture of the Sun rather than the Earth at the center of the Universe was understood to be dangerous. Obligingly, many scholars were quick to assure the religious hierarchy that this newfangled hypothesis represented no serious challenge to conventional wisdom. In a kind of split-brain compromise, the Sun-centered system was treated as a mere computational convenience, not an astronomical reality—that is, the Earth was really at the center of the Universe, as everybody knew; but if you wished to predict where Jupiter would be on the second Tuesday of November the year after next, you were permitted to pretend that the Sun was at the center. Then you could calculate away and not affront the Authorities.*
“This has no danger in it,” wrote Robert Cardinal Bellarmine, the foremost Vatican theologian in the early seventeenth century,
and suffices for the mathematicians. But, to affirm that the Sun is really fixed in the center of the heavens and that the Earth revolves very swiftly around the Sun is a dangerous thing, not only irritating the theologians and philosophers, but injuring our holy faith and making the sacred scripture false.
“Freedom of belief is pernicious,” Bellarmine wrote on another occasion. “It is nothing but the freedom to be wrong.”
Besides, if the Earth was going around the Sun, nearby stars should seem to move against the background of more distant stars as, every six months, we shift our perspective from one side of the Earth’s orbit to the other. No such “annual parallax” had been found. The Copernicans argued that this was because the stars were extremely far away—maybe a million times more distant than the Earth is from the Sun. Perhaps better telescopes, in future times, would find an annual parallax. The geocentrists considered this a desperate attempt to save a flawed hypothesis, and ludicrous on the face of it.
When Galileo turned the first astronomical telescope to the sky, the tide began to turn. He discovered that Jupiter had a little retinue of moons circling it, the inner ones orbiting faster than the outer ones, just as Copernicus had deduced for the motion of the planets about the Sun. He found that Mercury and Venus went through phases like the Moon (showing they orbited the Sun). Moreover, the cratered Moon and the spotted Sun challenged the perfection of the heavens. This may in part constitute the sort of trouble Tertullian was worried about thirteen hundred years earlier, when he pleaded, “If you have any sense or modesty, have done with prying into the regions of the sky, into the destiny and secrets of the universe.”
In contrast, Galileo taught that we can interrogate Nature by observation and experiment. Then, “facts which at first sight seem improbable will, even on scant explanation, drop the cloak which had hidden them and stand forth in naked and simple beauty.” Are not these facts, available even for skeptics to confirm, a surer insight into God’s Universe than all the speculations of the theologians? But what if these facts contradict the beliefs of those who hold their religion incapable of making mistakes? The princes of the Church threatened the aged astronomer with torture if he persisted in teaching the abominable doctrine that the Earth moved. He was sentenced to a kind of house arrest for the remainder of his life.
A generation or two later, by the time Isaac Newton demonstrated that simple and elegant physics could quantitatively explain—and predict—all the observed lunar and planetary motions (provided you assumed the Sun at the center of the Solar System), the geocentrist conceit eroded further.
In 1725, in an attempt to discover stellar parallax, the painstaking English amateur astronomer James Bradley stumbled on the aberration of light. The term “aberration,” I suppose, conveys something of the unexpectedness of the discovery. When observed over the course of a year, stars were found to trace little ellipses against the sky. But all the stars were found to do so. This could not be stellar parallax, where we would expect a big parallax for nearby stars and an indetectible one for faraway stars. Instead, aberration is similar to how raindrops falling directly down on a speeding auto seem to the passengers to be falling at a slant; the faster the car goes, the steeper the slant. If the Earth were stationary at the center of the Universe, and not speeding in its orbit around the Sun, Bradley would not have found the aberration of light. It was a compelling demonstration that the Earth revolved about the Sun. It convinced most astronomers and some others but not, Bradley thought, the “Anti-Copernicans.”
But not until 1837 did direct observations of the stars prove in the clearest way that the Earth is indeed circling the Sun. The long-debated annual parallax was at last discovered—not by better arguments, but by better instruments. Because explaining what it means is much more straightforward than explaining the aberration of light, its discovery was very important. It pounded the final nail into the coffin of geocentrism. You need only look at your finger with your left eye and then with your right and see it seem to move. Everyone can understand parallax.
By the nineteenth century, all scientific geocentrists had been converted or rendered extinct. Once most scientists had been convinced, informed public opinion had swiftly changed, in some countries in a mere three or four generations. Of course, in the time of Galileo and Newton and even much later, there were still some who objected, who tried to prevent the new Sun-centered Universe from becoming accepted, or even known. And there were many who at least harbored secret reservations.
By the late twentieth century, just in case there were any holdouts, we have been able to settle the matter directly. We’ve been able to test whether we live in an Earth-centered system with planets affixed to transparent crystal spheres, or in a Sun-centered system with planets controlled at a distance by the gravity of the Sun. We have, for example, probed the planets with radar. When we bounce a signal off a moon of Saturn, we receive no radio echo from a nearer crystal sphere attached to Jupiter. Our spacecraft arrive at their appointed destinations with astonishing precision, exactly as predicted by Newtonian gravitation. When our ships fly to Mars, say, their instruments do not hear a tinkling sound or detect shards of broken crystal as they crash through the “spheres” that—according to the authoritative opinions that prevailed for millennia—propel Venus or the Sun in their dutiful motions about the central Earth.
When Voyager 1 scanned the Solar System from beyond the outermost planet, it saw, just as Copernicus and Galileo had said we would, the Sun in the middle and the planets in concentric orbits about it. Far from being the center of the Universe, the Earth is just one of the orbiting dots. No longer confined to a single world, we are now able to reach out to others and determine decisively what kind of planetary system we inhabit.
EVERY OTHER PROPOSAL, and their number is legion, to displace us from cosmic center stage has also been resisted, in part for similar reasons. We seem to crave privilege, merited not by our works but by our birth, by the mere fact that, say, we are humans and born on Earth. We might call it the anthropocentric—the “human-centered”—conceit.
This conceit is brought close to culmination in the notion that we are created in God’s image: The Creator and Ruler of the entire Universe looks just like me. My, what a coincidence! How convenient and satisfying! The sixth-century-B.C. Greek philosopher Xenophanes understood the arrogance of this perspective:
The Ethiopians make their gods black and snub-nosed; the Thracians say theirs have blue eyes and red hair … Yes, and if oxen and horses or lions had hands, and could paint with their hands, and produce works of art as men do, horses would paint the forms of the gods like horses, and oxen like oxen …
Such attitudes were once described as “provincial”—the naive expectation that the political hierarchies and social conventions of an obscure province extend to a vast empire composed of many different traditions and cultures; that the familiar boondocks, our boondocks, are the center of the world. The country bumpkins know almost nothing about what else is possible. They fail to grasp the insignificance of their province or the diversity of the Empire. With ease, they apply their own standards and customs to the rest of the planet. But plopped down in Vienna, say, or Hamburg, or New York, ruefully they recognize how limited their perspective has been. They become “deprovincialized.”
Modern science has been a voyage into the unknown, with a lesson in humility waiting at every stop. Many passengers would rather have stayed home.
*Copernicus’ famous book was first published with an introduction by the theologian Andrew Osiander, inserted without the knowledge of the dying astronomer. Osiander’s well-meaning attempt to reconcile religion and Copernican astronomy ended with these words: “[L]et no one expect anything in the way of certainty of astronomy, since astronomy can offer us nothing certain, lest, if anyone take as true that which has been constructed for another use, he go away from this discipline a bigger fool than when he came to it.” Certainty could be found only in religion.