Five Billion Years of Solitude (6 page)

During the nineteenth century, a series of incremental discoveries led to the breakthrough that enabled the bulk of modern astronomy: light emitted, absorbed, or reflected by matter changes its colors in a way that captures the matter’s chemical signature. Splitting up light into a spectrum to reveal those colors—a technique called spectroscopy—reveals those signatures, allowing astronomers to remotely measure the chemical composition of galaxies, stars, and planets. If they could somehow take a promising exoplanet’s picture by gathering enough of its reflected photons, researchers could use the resulting spectrum to investigate that world’s atmospheric chemistry. They could search for indicators of habitability, such as water vapor and carbon dioxide, as well as signs of life, like the free oxygen that filled and tinted our own planet’s skies. They could look for the glint of a parent star’s light shining off the smooth, flat surface of a planet’s oceans or seas, or even subtle changes in the color of land that would hint at photosynthetic plants. Astronomers using observations from satellites and interplanetary spacecraft had already performed all these measurements for the Earth, confirming that our living planet could, in theory, be studied from across the vast distances of interstellar space.
Even if any extraterrestrials didn’t advertise their presence to the universe at large, techniques like spectroscopy offered hope that we could still find and study their home worlds.

In the last decades of the twentieth century, as exoplanetology became a legitimate scientific field, planet hunters devised several ways to take planetary snapshots across the light-years. All involved one or more custom-built space telescopes designed to nullify a target star’s glare and reveal its retinue of planets. At a likely cost of several billion dollars, a single space telescope could be built capable of delivering images of worlds around nearby stars, each planet manifesting as a dot a few pixels wide—minuscule, but more than enough for atmospheric spectroscopy. If money were no object, a fleet of telescopes could be assembled in space or on the far side of the Moon to act as one giant instrument, yielding larger images of nearby exoplanets that, though still very low-resolution, could reveal a world’s shorelines, continents, and cloud patterns. Such telescopes would go a long way toward determining whether a planet was worthy of being anointed “Earth-like.” Based on a fragmented astronomical community, an apathetic public, a gridlocked political system, and a struggling global economy, however, none appeared likely to be built anytime soon—at least not by the federal government of the United States of America.

Drake felt that if something could happen, somewhere it would happen, even if not right here and now. He wondered whether, if advanced cultures existed around nearby stars, they might have been watching our planet for quite some time using large space telescopes of their own.

“I’m speculating far out on a limb here,” he said as we walked around his yard. “But I would guess that most every civilization with technological capabilities slightly beyond our own uses lenses on the order of a million kilometers in diameter to explore the universe and communicate between stars.”

Beginning in the late 1980s, Drake had begun exploring an idea that made a lunar far side dotted with telescopes seem like child’s play.
In retirement, the work had come to consume him, and now occupied much of his remaining time. He wanted to create a telescope that would surpass all others, one with a magnifying lens nearly a million and a half kilometers in diameter. Drake had found a way to transform the Sun itself into the ultimate telescope.

A consequence of the Sun’s immense mass is that it acts as a star-size “gravitational lens,” bending and amplifying light that grazes its surface. This effect, first measured during a solar eclipse in 1919 by the astronomer Arthur Eddington, was one of the key pieces of evidence that validated Einstein’s theory of general relativity. Simple math and physics, judiciously applied, show that our star bends light into a narrow beam aligned with the center of the Sun and the center of any far-distant light source. As first calculated by the Stanford radio astronomer Von Eshleman in 1979, the beam comes into focus at a point beginning some 82 billion kilometers (51 billion miles) away from the Sun, nearly fourteen times farther out than the orbit of Pluto, and extends outward into infinity. There are as many focal points and Sun-magnified beams as there are luminous objects in the sky—imagine a great sphere surrounding our star, its surface painted with amplified, high-resolution projected images of the heavens.

Reviewing Eshleman’s calculation, Drake had discovered that, due to electromagnetic interference generated by ionized gas in the Sun’s outer layers, ideal seeing conditions for this ultimate telescope weren’t at 82 billion kilometers, but almost twice as far out, at a distance of 150 billion kilometers (93 billion miles), a thousand times our distance from the Sun. For perspective, in June of 2011, humanity’s fastest and most-distant emissary, the
Voyager 1
spacecraft launched in 1977, was just under 18 billion kilometers from the Sun, a bit more than a tenth of the distance to Drake’s ideal focus. It had taken thirty-five years to get that far from Earth. Clearly, utilizing our solar system’s ultimate telescope was a goal that could potentially take centuries to achieve. But the payoff might be worthwhile. Placed at any distant
object’s given focal point, a light-gathering telescope on the order of 10 meters (33 feet) in size could beam images back to Earth about a million times higher in resolution than what a network of large telescopes on the lunar far side could deliver. If, for instance, we wished to examine a potentially habitable planet orbiting one of the two Sun-like stars in Alpha Centauri, the Sun’s nearest neighboring stellar system, a 10-meter telescope aligned with the Sun–Alpha Centauri gravitational focus could resolve surface features such as rivers, forests, and city lights. Put another way, a gravitational lens at Alpha Centauri could easily see the coastline of Monterey Bay, its tree-covered hills, and the bright lights of nearby big cities like San Francisco and Los Angeles.

“One of the beauties of gravitational lenses is that since the lensing object bends space, all light traveling through is equally affected,” Drake said, squinting into the sunlight beneath one of his lemon trees. “Gravitational lenses are achromatic—they work the same for optical light, infrared, everything. I like to think of what they could do for radio. If you had two civilizations around different stars in communication and aware of each other, they could use gravitational lensing to set up transmission and receiving stations on each end. You look at the numbers, and at first it seems totally insane, but this is real. You could transmit, let’s see, high-bandwidth signals from here to Alpha Centauri using only one watt of power. . . .”

He looked at me expectantly, but I could think of nothing to say.

“That’s the transmitting power of a cell phone,” he finished. “There’s a quote I sometimes use when I talk about this, from a French play called
The Madwoman of Chaillot
: ‘I know perfectly well that at this moment the whole universe is listening to us—and that every word we say echoes to the remotest star.’ The capabilities of gravitational lenses make that sort of paranoia almost justified. If there’s enough capability out there to build these things, you could have a kind of ‘galactic internet,’ with everyone monitoring and talking to each other, all with very high bandwidth and very low power.”

•   •   •

A
fter a half hour of outdoor ambling, we found ourselves standing before Drake’s trio of greenhouses. They were where he spent much of his time when he wasn’t caught up in his SETI work. He opened the door to the nearest one, and the hum of ventilation fans and a blast of humid, loamy air flowed out over the grass. Stepping inside, he let out a peaceful sigh. Like the other two greenhouses alongside it, this one was filled with orchids. Orchids hung from the translucent roof in pots of sphagnum moss, orchids stretched in rows on long wooden tables strewn with watering cans, and orchids sprouted from plastic buckets beneath lamps and irrigation tubes. Drake said he had about 225, but most were dormant. I counted only about a dozen blooms across the three greenhouses. He had picked up the hobby in the 1980s, about the same time he began seriously thinking about using the Sun as a gravitational lens. He did it for the challenge, he said, of nurturing the sometimes temperamental plants into full bloom, and for the satisfaction of seeing beautiful new morphological varieties emerge. Over millions of years, natural selection had shaped orchid flowers into a rich diversity of shape and color, each variety typically tuned to one or two species of pollinators. “Insects, mostly beetles,” Drake said. “They blindly shape the flowers. But the hybrids, of course, are chosen and bred by humans.”

Drake flipped on a grow lamp overhead, and in its pinkish light showed me a few blossoming hybrids, some cultivars he had cross-pollinated by hand. Each was wildly different from the others. One bore tiny flowers with trailing white petals and anthers heavy with yellow pollen. Another had five tubular, drooping purple blooms, each surrounded by a starburst of red-tinted curly leaves.

Drake turned to what he said was his current favorite, a single orange bloom with three angular petals that tapered to sharp, blood-red
points. They looked like fangs. “This one’s a hybrid of two different genuses,
Dracula
and
Masdevallia
,” he said. “Cold-growers from the Andes. No one’s seen one like this before, with this red. It wasn’t blooming yesterday. Some of these only blossom one day out of the year, and the next day they’re gone. You’re lucky to be here right now—the flowers aren’t long for this world.” He touched the petals with reverence.

“They die, but they have reincarnation,” Drake went on. “In principle, well-tended orchids are immortal. They reproduce by putting out new growths. Here’s one.” He gestured at a plant that bore no blooms but had several yellowish bulbous shoots hanging from its encasing pot. “This one is quite old. It’s outgrown its container—I should probably transfer it. You can see its new growth in these pseudobulb leads. Once you have two or three of these, you can cut one off and plant it in fertile soil. It becomes a new plant, and that plant will make more, and those plants will make more still. Each one doesn’t live forever, it lives maybe three or four years, but the organism moves on like a wave, constantly generating new growth.”

I told Drake his orchids made me think of
L
, a technological civilization’s longevity, the greatest uncertainty in his equation. If it was too low, our galaxy could give birth to millions, even billions, of civilizations over its eons-long life, but each one, isolated on a lonely planet, would wither and fall unseen with no chance for cross-pollination. If
L
was high, then in-bloom civilizations could linger and eventually intermingle, hybridizing their cultures across the light-years. Stability could set in; some would perhaps gain a sort of immortality.

Drake smiled and nodded. The similarity had not escaped his notice.

•   •   •

B
ack inside, Drake fished a bag of cashews from his cupboard and offered me a bottle of Sam Adams beer. He opened a can of Coca-Cola, and we sat down on his living room couch to discuss what the future might hold for SETI. Drake said he still thought that a civilization’s
average longevity approached 10,000 years, and that some 10,000 alien cultures were probably sitting out there in the Milky Way, waiting to be discovered. He admitted his belief was somewhat faith-based.

“I think 10,000 is plausible, but my estimate shouldn’t be dignified by saying there’s observational evidence that could accurately lead you to that specific number,” he said between mouthfuls of cashews. “The factor of
L
still remains a total puzzle. We now know the rough fractions of stars with planets, and we’re closing in on the frequencies of habitable planets. Sooner or later we’ll know that number. But something like the lifetime of technological civilizations . . .” He trailed off, and stared for a long moment at the living room’s blue stained-glass window.

Bits of multicolored glass were fused within the window’s field of blue, forming a series of pictograms outlined in metal wire. Sunlight shining through gave the window a phosphorescent glow like an old analog television screen, and the colorful, blocky shapes looked very much like crude pixelated graphics from some lost, early-1980s video game. Drake had devised the design in 1974, when he was in the middle of a two-decade stint as a professor at Cornell University. Drake had initially been drawn to the job in 1964 because at the time Cornell managed the newly opened Arecibo Observatory, our planet’s largest and most powerful single-aperture radio telescope. Soon after arriving at Cornell, Drake became the director of Arecibo, a position he held until 1981. The observatory was built into an immense limestone sinkhole in the jungle of northern Puerto Rico and boasted a 305-meter-wide (thousand-foot) bowl-shaped aluminum dish—big enough, Drake once calculated, to hold more than 350 million boxes of corn flakes. It was also big enough to transmit messages across hundreds, even thousands of light-years. On November 16, 1974, Drake used the massive dish to blast his message on a focused pencil beam of modulated radio waves toward a star cluster called M13, located some 25,000 light-years away, in the constellation of Hercules. With an effective radiance of twenty million megawatts at its specific wavelength, for the three-minute duration of the transmission Drake’s beam outshone the Sun by a factor of 100,000.

The image’s low resolution was a functional necessity; its content was formed from a series of 1,679 frequency pulses in the transmission beam: 1,679 is the product of two prime numbers, 73 and 23. Thoughtful aliens, Drake hoped, would use this hint to correctly interpret the message’s pulses as forming a grid of 0’s and 1’s 73 units high and 23 wide. His stained-glass window displayed the resulting output: a top row of dots establishing a binary counting method, listing numbers one through ten, followed by a second row listing the atomic numbers of hydrogen, carbon, nitrogen, oxygen, and phosphorus, the key chemical elements of all life on Earth. A third section assembled the preceding atomic numbers into chemical formulas for the nucleotides in a molecule of DNA, followed by a schematic depiction of a DNA molecule’s distinctive double helix. A long vertical bar represented the DNA molecule’s sugar-phosphate backbone, and doubled as a binary depiction of 3 billion, roughly the number of nucleotide base pairs within the human genome. The molecule’s image hovered over the head of a stick-figure human being, which was sandwiched between two more binary numbers, 4 billion and 14. Four billion was meant to convey the world population in 1974, and 14, multiplied by the transmission’s wavelength of 12.6 centimeters, was intended to show that the human figure stands 176 centimeters high—just as tall, it turns out, as Frank Drake. The figure stood above the third of nine small dots extending out from one dot very much larger—a representation of our solar system and a hint that we lived on the third planet from our star. Finally, Arecibo itself was depicted as a simplified dish and antenna, with its gargantuan dimensions given in binary notation.