Image (detail) courtesy of NASA
THE EYE HAS LONG BEEN thought the jewel of human anatomy. In Mesopotamia, fount of civilization and astronomy, Sumerians worshipped small gods of clay and marble, featureless but for the stare of large eyes. The ancient Egyptians, famous for economy of expression, had seven different hieroglyphs for the eye. In his Metaphysics, Aristotle called seeing the noblest faculty of man. Not even modernity has scrubbed the eye of its metaphysical sheen. James Russell Lowell dubbed it the notebook of the poet, and among the religious, its mere existence is said to refute Darwin. Yet, for all this tribute, the human eye remains a limited technology, seeing only the rainbow of visible light, a thin slice of the electromagnetic spectrum. And, even in this realm, it falls short of other mammals, for whom nightfall is no curfew; to have squinted into the dark and seen the glimmer of raccoon eyes is to have felt the chill of this truth. Human vision fails to encompass the horse's panoramic field of view or the brilliant ultraviolet shades seen by birds of prey. Even the insect, lower still on the totem pole of consciousness, absorbs a gushing, flood-like cinema — some 250 frames per second.
Hence, the human toolmaker has had to compensate, and vigorously. First by pouring new light into the world with fire and electricity, then by dreaming up technologies to complement the eye. Like early stone tools, these began crudely: chips of crystal unearthed and shaped into small magnifiers. In Rome, Nero was said to have peered through an emerald at gladiators fighting in the distance. It would take until 1608 for the telescope to be invented, and another year still until one was pointed at the night sky. Light from the moons of Jupiter fell down that telescope and into the mind of Galileo, who deduced from it that not all heavenly bodies circled the Earth — the first in a series of fresh cosmologies wrought by the telescope. In the 19th century, William Herschel would use a large wooden telescope to find and catalogue thousands of "nebulae," single stars then thought to be surrounded by clouds of luminous fluid. A century later, at the Mt. Wilson Observatory, Edwin Hubble took a closer look at Herschel's nebulae. Hubble discovered that Herschel had been right in thinking that nebulae contained stars, but that he was seriously mistaken about the number. We now have a new word for nebulae: galaxies.
The 400 years since Galileo have marked a revolution in seeing unlike anything since the Cambrian explosion, when light sensitivity first rippled through the food chain, remaking it wholesale. In that time, the telescope has divided and grown, mutating from a single modest tube to a multitude of enormous, landscape-dominating forms. It has assumed the ways of an ascetic, leaving civilization for more solitary, contemplative environments: deserts, the shoulders of volcanoes, exotic islands, even space itself. The camera and the computer have given the telescope a memory, freeing it from constant attachment to the human eye. Most importantly, it has become a refined aesthete, keen to the entire electromagnetic palette, including a species of energy especially prized by astronomers: infrared light. A telescope sensitive to infrared light can see into thick clouds, where new stars and planets lurk. And in the chill of deep space, freed from the distorting shimmer of the atmosphere, an infrared telescope can see nearly all of time.
In 1993, just three years after the launch of the Hubble Space Telescope, NASA began to lay the groundwork for its successor, an all-infrared instrument then called the Next Generation Space Telescope. Congress first approved funding for the Hubble in 1978, expecting it to launch five years later, at a cost of $400 million. Engineering setbacks plagued its early development, however, resulting in delays and cost overruns. Then, in 1986, the Challenger disaster halted all shuttle work at NASA for nearly three years. When at last the Hubble lifted off in 1990, the final bill for its construction had ballooned to over $2.4 billion, and it was still years away from being fully operational. After its inaugural images arrived back at Earth blurrier than expected, distorted by an improperly shaped mirror, the public began to lose patience with the Hubble. In a popular film, it was even compared to the Hindenburg, a fact shocking to consider from the vantage point of the present, a time in which the Hubble is revered as nothing short of a national, indeed an international, treasure. A solution to the blurry images would have to wait until the Hubble's first servicing mission in 1993, when astronauts visited the telescope in orbit and installed a specially designed instrument — a contact lens of sorts — to correct its vision. The servicing mission succeeded and came to be regarded as one of the finest hours of NASA's much-maligned shuttle program. Indeed its lead astronaut, John Grunsfeld, was recently tapped to head science operations at NASA. It had taken 15 years, but at last the Hubble was able to begin its work in earnest.
Meanwhile, plans for the Next Generation Space Telescope grew ever more ambitious. In 1997, the Space Telescope Science Institute issued a report recommending a massive eight-meter mirror for the new telescope. The mirror used by the Hubble measures eight feet in diameter, and until last year it was the largest of any in space. As the budget for the project began to take shape, it became clear fiscal restraints would require something more modest than the eight-meter improvement. By 2002, the project had a new, permanent name, the James Webb Space Telescope, and a smaller mirror measuring just six meters in diameter, still 2.75 times larger than the Hubble. The name was a nod to the glory days of space exploration, the 1960s, when James Webb, a lawyer not a scientist, had served as the administrator of NASA. Webb initiated development of the iconic Apollo missions and was also an early champion of the agency's more scientific endeavors, including its first interplanetary probes. Webb's legacy embodies NASA's most exalted idea of itself: competent, sturdy, capable of both scientific rigor and inspiring spectacle.
The launch of the James Webb will require technological cunning unequaled in the post-Apollo era. The base of the telescope, a six-layer sunshade, is roughly as long and wide as a tennis court. It will sit well beyond the moon, in a special pocket of gravity one million miles from Earth. Rather than orbit the Earth and whirl daily into the hot face of the sun, the Webb will use the combined gravity of the two to hide in a fixed position within the Earth's shadow. Its 18 hexagonal mirrors, made of beryllium and coated in 24-carat gold, will operate at temperatures near absolute zero — the point at which all motion ceases — in order to remain sensitive to the faint infrared emanations of deep space. In this way movement in the heavens may be likened to sound, of which Emerson wrote, "Let us be silent, that we may hear the whispers of the gods." Upon arriving in space, the Webb will attempt an unprecedented feat of reverse origami: It will emerge bundled from the tip of an Ariane rocket and slowly unfurl its shade, mirrors, and instruments, becoming in the process the world's largest space observatory, its seeing power 100 times that of the Hubble. The stakes for this metamorphosis are high, for even with tomorrow's technology, repair at such a remove from Earth will be impossible. If for any reason the Webb should fail after launch, it will be left to idle in space, out of reach, a stillborn in the void.
The costs associated with preventing such a ruinous malfunction have earned the Webb its share of critics on Capitol Hill. In July of last year a House Appropriations Subcommittee voted to kill the project outright, citing gross mismanagement and a ballooning budget. When the telescope was first conceived, NASA expected it to cost no more than $2 billion to construct, yet just last year that figure had risen to $6.5 billion and may still reach $8 billion. If this trend continues, the Webb could surpass the Large Hadron Collider as history's most expensive scientific instrument. Like the Hubble before it, the Webb is also woefully behind schedule. Launch was originally set for 2011, but is now expected no sooner than 2018. In an increasingly thrifty political environment, there is a question as to how long NASA can keep Congress at bay, especially when the project has also taken friendly fire from within the scientific community. In recent years, a small but vocal group of astrophysicists have criticized the Webb, complaining that its cost overruns have swallowed the funding for other projects in astronomy. In 2010, Nature published an article about the Webb entitled "The Telescope That Ate Astronomy." The criticism is not without merit: Congress's latest batch of funding for the telescope, approved in November 2011, requires NASA to cut over $300 million from other programs.
In 1993, just before the repair of the Hubble, Dr. Robert Williams, a former professor of astrophysics at the University of Arizona, took over as director of the Space Telescope Science Institute in Baltimore. The institute is responsible for the operation of the Hubble and also for awarding research time to professional astronomers who wish to use it. The director of STScI is given discretion to award 10 percent of the telescope's research time to projects of his or her choosing, with the rest awarded by way of committee. Over 1,000 proposals for its use are submitted each year. Williams was familiar with this practice, having spent eight years as director of the National Optical Astronomy Observatory in Chile. He had returned to the states reluctantly at the urging of his wife, who wished to be closer to the couple's adult son. Williams preferred the visceral feel of working with the ground telescope in Chile, particularly the long nights in the Andes, alone with the instrument and sky. He had fallen for astronomy as a young boy when a teacher showed him a small photograph of Mars in a textbook. The image affected him so profoundly he brought a magnifying glass to school the next day, hoping to see the red planet in greater detail. Dissatisfied when the magnified image resolved into blurry dots, Williams took up a paper route in order to earn money to buy his first telescope. The first thing he did with that telescope, a refractor with a two-inch diameter lens, was point it at the farthest, dimmest object he could see - a trick he would repeat to astonishing effect with the Hubble.
On a rainy day this last November, I sat down with Williams in a private room atop the Smithsonian Museum of Air and Space in Washington, D.C. In his seventies now, Williams seems more like an ex-astronaut than an astronomer. A former runner, he remains tall and sturdy, his brown hair flecked only occasionally with gray. I asked him if he could recall when the Hubble was still unpopular, and he laughed, saying his son used to call him at STScI to ask how the "rubble space telescope" was doing. Williams, a self-described risk-taker, had gambled when he agreed to take on the Hubble prior to its dramatic repair. His peers knew the telescope had tremendous potential but feared it would continue to disappoint and that Williams, entering the prime of his career, would be asked to turn out the lights. However, after the successful servicing mission, Williams began planning an audacious experiment with which to test the Hubble's reach. He wondered what the telescope might find if it were pointed at a dark patch of sky and left to run an extended, multiday exposure. Williams sought counsel about the experiment from several eminences within the field of astrophysics. Among them was the late John Bahcall, to whom the Hubble owed its very existence, so fervent was his advocacy for the telescope. Bahcall opposed the idea of a Deep Field, as the experiment would come to be called, even going so far as to visit Williams at STScI to try and talk him out of it. He reasoned that whatever lay beyond the Hubble's expected range was probably too dim to be observed, and further that the telescope could not withstand another public disappointment should the Deep Field fail to yield results.
Undeterred, Williams assembled a team of 13 scientists from the institute, intent on going forward with the Deep Field. Each morning, the group would meet over coffee to discuss how the shot might be accomplished. Some suggested the Hubble be pointed toward distant objects already known to exist, with the hope of capturing unseen satellite galaxies. Williams was more ambitious, insisting the group aim for a dark, unexplored corner of the sky, away from the bright plane of the Milky Way galaxy. The team settled on just such a patch, in the region of sky above the Big Dipper. On December 18, 1995, the exposure began, set to run for 10 days. A blizzard struck midway through, forcing the group to climb through a snowbank to reach the institute. Some of the younger scientists hauled air mattresses into their offices to avoid being snowed out as the data began to accumulate.
Over 10 days the Hubble grabbed over 300 exposures, thin layers that Zoltan Levay, head of imaging at the institute, would painstakingly assemble into a final color image. Not much could be seen when the first layers arrived, but there were early indications that the data was good. When at last a discernible draft emerged, Levay sat back in his chair, registering the shock of seeing a vision of time never before glimpsed by human eyes. Over two centuries earlier, John Playfair had accompanied the geologist James Hutton to southern Scotland to search for an angular unconformity: a discontinuity in sedimentary rock that would prove the immense scale of geological time. Playfair would later say that to see the unconformity, laid bare against an otherwise unremarkable riverbank, was to be carried back in time to remote epochs:
The palpable evidence presented to us, of one of the most extraordinary and important facts in the natural history of the Earth, gave a reality and substance to those theoretical speculations, which, however probable, had never till now been directly authenticated by the testimony of the senses ... Revolutions still more remote appeared in the distance of this extraordinary perspective. The mind seemed to grow giddy by looking so far into the abyss of time.
To experience the final, full-color Deep Field is an experience not unlike Playfair's epiphany upon the riverbank. At first glance, one might mistake it for gemstones scattered across black velvet, but a closer look reveals that each smudge of light, 2,600 in all, is a galaxy dense with billions of star-fired worlds, pinwheeling in deep time. To that point, astronomy had imaged objects only four billion light years away, and poorly at that. Here a telescope reached 11 and a half billion light years into space and delivered an image legible to the layman: an unprecedented expansion of human vision. Much of the light caught by the Deep Field traveled to the Hubble from across nearly the entire universe, from stars that burned out before the Earth had even begun to form. The oldest, most distant galaxies within the image have a chaotic, fragmentary structure, whereas the closer, brighter galaxies are symmetrical, marked with the familiar swirl of the Milky Way. From this progression, this cosmic vista, new notions about the evolution of galaxies have emerged. Gazing at the Deep Field is like mainlining the whole of time through the optic nerve, like counting by fingertip the tree rings of the universe.
Since its release in 1995, over 800 scientific papers have cited the Hubble Deep Field, making it one of the most valuable research projects in the history of astronomy. You would expect an image so intellectually significant, so visually breathtaking, to become synonymous with the instrument that produced it. But the Deep Field is only one of the signature achievements of the prolific Hubble. In its two decades in space, the telescope has captured an astonishing range of images, from the glowing ring of the Sombrero Galaxy to the ghostly arabesques of the Eagle Nebula. It has also confirmed a number of theoretical phenomena, including dark energy, the mysterious force pushing the universe apart at ever increasing speeds. Historically, discoveries of pure science are slow to reach the mainstream compared with those of the applied sciences, which noisily announce themselves with new medicines and gadgets. The Hubble has proved an exception, remaking, in a single generation, the popular conception of the universe. It has accomplished this primarily through the aesthetic force of its discoveries, which distill the difficult abstractions of astrophysics into singular expressions of color and light, vindicating Keats's famous couplet: "Beauty is truth, truth beauty." Though philosophy has hardly registered it, the Hubble has given us nothing less than an ontological awakening, a forceful reckoning with what is. The telescope compels the mind to contemplate space and time on a scale just shy of the infinite. With luck, the James Webb will stretch it further and faster still.
After it reaches space and flowers into full operational form, astronomers will point the Webb into some dark corner of the sky, hoping to conjure a new Deep Field, imaged in infrared, the sliver of the spectrum alive with ancient light. As the universe expands, distant objects recede from view, causing light from those objects to stretch, or shift, into the infrared. Thus, to glimpse the far recesses of the universe in infrared is like seeing through the ground to the oldest layer of sedimentary rock, the original, fossil-encrusted skin of Earth. Astronomers will zoom in on the earliest collections of stars, the faint galactic shards first imaged by the Hubble Deep Field. In doing so, they expect to answer a chicken-and-egg question that has vexed modern cosmology: For some time astronomers have wondered if black holes, collapsed stars, pulled oceans of stars into orbit, forming the first galaxies, or if they emerged later, as products of those galaxies. Some hope to see back to an even more spectacular, more primordial dawn: Genesis 1:3, "let there be light" — the first stars winking alive in the gloom after the Big Bang. Locally, the Webb will search for newly forming solar systems, infant stars, and planets glowing dim and cool in dusty discs of gas, opaque to telescopes constrained to just visible light.
Of course, these are just the low-hanging fruit, the natural, predictable extensions of today's astronomy. When I asked Lawrence Krauss, the renowned cosmologist and director of the Origins Initiative at Arizona State University, what he most looked forward to seeing through the eye of the Webb, he told me he reserves his deepest longings for what he doesn't expect to see, the discoveries he can't anticipate. "Whenever you open a new window on the universe," he said, "you're surprised at what you find, and this is an incredible new window." Each telescope sketches the cosmos in finer detail than its predecessors. The Hubble gave us the structure of the universe, but left it a twinkling, lifeless expanse. The James Webb Telescope will go a long way towards refining that structure, and, for an encore, may fill it with worlds.
There is poetry in the history of looking for new Earths. Around our own star, we call the most Earthlike of planets Venus, for the Roman goddess of love and beauty. Before that she was Ishtar in Babylon and Aphrodite in Greece. Venus is the only planet named after a goddess, and to this day when new hills, craters, and canyons are discovered on her surface, they are given feminine names. Of course, the ancients who named Venus could not have known that she shared, roughly, the Earth's volume and mass, but they might have deduced that as its closest neighbor, she stood a decent chance of sharing its extraordinary fertility. Venus's thick atmosphere has long shielded it from study, allowing the myth of life on its surface to persist well into the 20th century. Radar images have since revealed the Venusian surface to be a sulfurous hell, its temperatures exceeding 400 degrees Celsius: too hot to host the kind of dynamic environments thought to give rise to life. Likewise, probes to Earth's next closest neighbor, Mars, have found barren deserts beneath an atmosphere erased by time. Further afield are the gas giants, a strange collection of worlds marked by extreme temperatures and hundred-year storms. Throughout the space age, NASA has deployed increasingly sophisticated machines across the solar system in pursuit of the Earthlike, each new technology pushing the search radius outward. While a few stones remain unturned - most promising, the ice-covered ocean of Jupiter's moon Europa - there is a growing sense that Earth is an only child, the prized and spoiled daughter of the sun. Sic itur ad astra: Thus to the stars. But this is easier said than done. The closest star to the sun, Proxima Centauri, sits over four light years away, too far to reach with current propulsion technologies.
Today SETI, the Search for Extraterrestrial Intelligence, is our most promising means of finding life outside the solar system. SETI uses radio telescopes to monitor distant stars, hoping to detect an intelligible signal, a radio transmission beamed into space. The scope of its search is narrow: Elephants do not send radio signals, and neither do forests or, for that matter, bacteria. Nor is it clear that we ought to be looking for radio waves at all; it's possible the galaxy is rich with advanced civilizations, each of which cast aside radio technology eons ago. In 50 years of searching, employing increasingly powerful telescopes, SETI has come up empty. Some have even suggested that given its slim odds of success, SETI is not science at all, but rather a cultural activity, a reassurance that someone is looking. Meanwhile, the human yearning to find life has found fertile ground elsewhere, particularly in science fiction, where it has generated an entire literature of alien encounters. It's easy to see why. Science fiction thrives in the quiet periods between scientific revolutions, when the imagination can sense the shape, but not the details, of a new paradigm. As our understanding of the universe and its scale have progressed, UFO sightings, abductions, and other dubious extraterrestrial phenomena have proliferated, hinting that a deep cosmic loneliness afflicts modern humans. In some of its forms, that loneliness can seem like a religious impulse, a wishful dissatisfaction with the imaginative frontiers of our home planet. At last, it may have found a scientific outlet.
In the year 2000, fresh off completing a doctorate in astronomy at Harvard, Sara Seager headed to the United Kingdom to attend the General Assembly of the International Astronomical Union in Manchester. The IAU General Assembly is the world's largest annual meeting of professional astronomers, drawing over 2,000 astronomers from around the globe. Seager was slated to present a pair of papers before the symposia on cosmology and exoplanets. Up to that point in her career, she had focused most of her research on cosmology, doing theoretical work on recombination, a crucial period beginning just 400,000 years after the Big Bang, when electrons and protons first joined to form hydrogen. Alongside her work on the early universe, she had nurtured an interest in exoplanets, or planets that exist outside of our solar system. In 1995, astronomers robustly detected the first such planet orbiting the star 51 Pegasi, just 50 light years from Earth. Researchers have since developed several ingenious ways to look for exoplanets. Some track the movements of a star as seen from Earth, looking for tiny wobbles that suggest an orbiting planet. Others look for periodic dips in a star's brightness, evidence that an orbiting object is passing in front of it. By 2000, the field was growing rapidly, offering fresh research opportunities to young astronomers willing to forgo safe careers within more established disciplines. Seager, now a professor of planetary sciences and astrophysics at MIT, was one such young astronomer. What's more, she had begun devising a promising new method for looking in to the atmosphere of an exoplanet. And all it required was a gleam of reflected starlight.
When sunlight passes through the Earth's atmosphere and then through a prism — such as water — it splits into a spectrum, a rainbow. A closer look at that spectrum reveals dark, microscopic lines interspersed throughout it, like the black keys on a piano. Those lines correspond to the molecules in the Earth's atmosphere that absorb light, giving what remains a passport stamp rich in chemical information. By splitting reflected starlight from a distant planet into a spectrum, astronomers can see what molecules are in its atmosphere, and even the relative densities of those molecules. If you know what the air is like on a planet, you can tell if the air can be breathed, and, more tantalizing, you can tell, with a high degree of accuracy, whether it is being breathed. To find a habitable planet, astronomers will first examine an exoplanet spectrum for evidence of water vapor, but the existence of water vapor only indicates life could exist on a given planet. To know whether or not life actually exists on the planet, astronomers need to find what Seager calls biosignature gases: high concentrations of molecules that don't occur within naturally occurring chemical equilibriums. If, for instance, a planet were covered in plants, you would expect to see a noticeable excess of oxygen, a product of photosynthesis. Methane, when combined with oxygen, is an especially strong sign that life is lurking upon a planet's surface. If in the near future interstellar photons bring news of lush extraterrestrial jungles, Seager will take on a unique role in the history of astrobiology: She will have successfully predicted how information about life would first travel between stars.
When I spoke to Dr. Seager in December of last year, data from a different space telescope was beginning to reach the public. In 2009, NASA launched the Kepler Space Telescope in order to search for planets in a single starry patch of the Milky Way. The Kepler stares at a particular group of stars and records the tiny dips in brightness that occur as planets pass in front of those stars. In order to see a large number at once, a distant group was chosen, with the result that the data collected by Kepler is statistical in nature. It will suggest whether exoplanets are common or rare and whether any sit in the habitable zones around their stars, but it won't provide images of those planets or data about their atmospheres. Seager called it, elegantly, a census of the Milky Way.
This census is still underway. The Kepler can only confirm a planet candidate once it has passed in front of a star three times. The third transit allows astronomers to verify the interval between the first two and confirms the same object is responsible for all three. The time required to see three transits can be quite long — for Earth, it would be three years — with the consequence that the earliest confirmed candidates will be hot, uninhabitable planets with tight orbits. In its first two years the Kepler has spotted over 2,000 planet candidates, including 48 that reside in the habitable zone around their stars. The most promising candidates are confirmed with the aid of ground-based telescopes. In December, a spectacular confirmation was announced: A large Earthlike planet, Kepler 22b, resides in the habitable zone around a star 600 light years from Earth. The early extrapolations from this data are hopelessly incomplete, but there are hints that over two billion habitable planets may exist in the Milky Way alone.
With the James Webb, astronomers will zoom in on exoplanets orbiting nearby stars, with the hope of finding atmospheres rich with the exhalations of life. There are two ways the Webb might gather enough light from a planet to be able to determine the makeup of its atmosphere. First, it will look for a subset of exoplanets called super-Earths. As the name suggests, super-Earths are rocky planets like Earth, only larger. Large planets transiting small stars are easier to detect, in the same way that, from a distance, a ping-pong ball passing in front of a flashlight is easier to see than a marble crossing a floodlight. Astronomers are keen to find super-Earths with tight orbits around small stars, which will be easier to observe on account of their large, frequent transits. The habitable zones around small stars will be tighter than around our sun, because a smaller star produces less energy. A super-Earth's nearness to its star, however, does not bar it from potentially supporting life.
Still, even the awesome eye of the Webb will need to focus on stars close to the Earth in order to see the spectrum of a super-Earth atmosphere. And while the ongoing search for super-Earths is compelling, it lacks the paradigm-shifting oomph of finding a true Earth twin. In fact, a more ambitious project called the New Worlds Mission hopes to use a giant "starshade" with the Webb, in order to directly image a new Earth. The project emerged from the work of Webster Cash, professor of astrophysics and planetary science at the University of Colorado in Boulder. In 2005, Cash, electrified by the rush of new exoplanet research, wondered how his work on the optics of X-ray telescopes could be brought to bear on the search for a new Earth. He came up with the idea of pointing a space telescope at a nearby star, and using a starshade to block the star's light, so that the star's planets could be seen. The project faces a number of daunting technical hurdles, not the least of which is the shade's shape. It can't be a square or a circle because defraction would allow starlight to sneak around its edges, thus the actual shape resembles a massive flower, 50 meters across, where each elongated petal is rendered precisely, within nanometers or less. The positioning is more worrying: To use the starshade effectively, astronomers must be able to align it precisely with the Webb, in spite of the awesome distance — some 80,000 kilometers — between the two. One solution involves placing a small telescope in the center of the starshade in order to view the Webb against a backdrop of alignment-friendly stars. Cash estimates the project itself could cost close to $750 million to develop. NASA has been slow to make starshade research a funding priority, but Cash is hopeful that the pace of development will quicken under John Grunsfeld, a starshade enthusiast, and the new head of science operations at NASA. It is likely too late to develop a starshade to launch alongside the Webb in 2018, but 2021 remains a possibility. Once a starshade is in place, the Webb would need two years to survey the nearest hundred sunlike stars, where it would stand the best chance of seeing into alien atmospheres, and, likewise, the best chance of finding a second pale-blue dot — the first, of course, being among the most famous images in the history of space science: the portrait of Earth taken by the Voyager 1 spacecraft from the edge of the solar system.
Seager told me that a second blue dot would complete the revolution commenced five centuries ago, when Copernicus first dislodged the Earth from the center of the universe, by showing that it revolved around the sun. The naked eye, it turns out, bestows many false honors. Over time the telescope has reduced the sun and Milky Way to less than pixels in the cosmic scheme. And yet, on one front, the Earth has held her sway, for as far as we know she remains a goddess of fertility unequaled across the entire universe. A glimmer from a remote biosphere, a sister Earth, will leave only human consciousness to distinguish her, and even that may fall away in time.
Toward the end of our conversation, Seager told me the fate of the James Webb ought to turn on whether or not we as a society still believe in building marvelous things and in bearing the costs and disappointments that invariably attend such projects. It is a question uniquely addressed to Americans, for if we do not build the James Webb Space Telescope, no one else will. Already, NASA has asked the European Space Agency and the Canadian Space Agency to partner on the project, as neither agency on its own has the budget, or the capacity, to complete it. And while China has lately begun to pursue an ambitious space program, it has no plans for a telescope on the scale of the Webb. A scrapped or defunded Webb will mean that, for a time — a generation perhaps — astronomy will cease its beautiful revolutions. The search for life among the stars will hang suspended in the imagination, an impotent question posed to the sky. Science asks a mythic task of America: that she coil the strength of her economy and sling a golden mirror into cold space.
To be certain, one of the great virtues of Americans is our suspicion of the grandiose. From Prometheus to the Tower of Babel to the Titanic, a whole mythology sits embedded in our culture, warning against technological hubris. Moreover, archaeology has revealed the sordid history of yesterday's grand, national projects, most of which stand atop the thrown-away bodies of slaves. Once revered, the great walls and pyramids of antiquity now seem like monuments to social control, megalithic echoes of former North Koreas, boy kings and all. Nor is it necessary to reach back to the edge of prehistory to grow suspicious of dazzling wonders pursued by the state, to become queasy at the thought of scientists joining forces with the public purse to affect brilliant discoveries. We moderns have our own monuments to consider: our burnt and leveled cities, our radioactive wastelands, the wrecked playgrounds of 20th-century physics.
But the telescope, the most sublime of human technologies, leaves a legacy of an entirely different character than the high-rise tomb or atom bomb. It blasts open new tunnels between the mind and The Other, tunnels not easily sealed by the censorious henchmen of fading paradigms. Just after the turning of the New Year, I visited a friend, an avid eclipse tourist, at his home in Southern California. After a meal and too much wine, he wheeled out his telescope, a 10-inch reflector, so we could have a look at the sky. It was a clear night, but terrible for stargazing; light pollution, both lunar and suburban, dimmed the stars to a few faint points of white. Jupiter, however, shone high and bright, and we resolved to make it our main object of study. My friend aligned the heavy tube of the scope while I hovered above the eyepiece, shifting to and fro until at last there it was: a dull, striped marble beset by a line of tiny twinkling moons, the same peculiar arrangement of photons glimpsed by Galileo through his telescope — his "perspicillum," as he called it. I stepped back to allow my host a turn. Blinking, I could still see the planet glowing against my eyelids. The afterimages of a telescope burn long after one averts the eyes, long after they are closed, long into history.
In its time the telescope has transformed the night sky from a decorative ceiling — a fixed sphere of glittering stick-figure gods — into a universe whose reaches carry the seeds of this Earth and new Earths still. Astronomers have compared this historical moment, this awakening, to Plato's "Allegory of the Cave." In it, a man is freed from a grim existence, from chains that kept him affixed to a cave wall, forced to stare at flickering shadows upon it, the shadows a product of unseen objects paraded before a distorting fire. He leaves the cave for a world, the world, of brilliant sunshine, his journey the original and best metaphor for intellectual discovery. Map Plato's fable onto the history of astronomy, and one sees it has many sequels, with more yet to be written. Every time we leave one cave we find ourselves in another, each a deeper reality, a more marvelously complex roaming ground for the intellect, but still a cave, the sum of human knowledge being always unequal to the universe.
Unlike the telescope, whose childhood has been recorded by many devoted chroniclers, the evolution of the eye is somewhat mysterious. We know that it first emerged in the 80 million years that make up the Cambrian explosion, but it's not clear if it burst rapidly into existence, or grew in fits and starts. Richard Dawkins has said that large mutations seldom survive in nature, but that geneticists love them anyway, because they are so easy to study. Perhaps, then, it's best to imagine the eye arising slow and steady, from photosensitive cell to functional whole. But it can be foolish to underestimate nature in this way. In January, biologists from the University of Minnesota were astonished when a single-celled yeast evolved multicellular bodies — resembling tiny snowflakes — in just two weeks time. Our history of seeing is thus incomplete; it yields no easy pattern for divining the future of the telescope.
Back in Washington, I asked Robert Williams if he envied future generations, if he despaired at not knowing what science will discover in a thousand years' time. "You have to be comfortable knowing we have limits," he said. "It's difficult to know when the light bulb will hit. In 1905, Einstein discovered relativity, Brownian motion, and mass-energy equivalence all in a single year — a truly mind-blowing spike in perception. But then he followed it with 20 years of nothing. And so I'm content. I don't have such a feeling of wishing that I knew the future."