The first large object ever accurately measured was Earth, accomplished in the third century B.C. by Eratosthenes, a geographer who ran the Library of Alexandria. From travelers, Eratosthenes had heard the intriguing report that at noon on the summer solstice, in the town of Syene, due south of Alexandria, the sun casts no shadow at the bottom of a deep well. Evidently the sun is directly overhead at that time and place. (Before the invention of the clock, noon could be defined at each place as the moment when the sun was highest in the sky, whether that was exactly vertical or not.) Eratosthenes knew that the sun was not overhead at noon in Alexandria. In fact, it was tipped 7.2 degrees from the vertical, or about one-fiftieth of a circle—a fact he could determine by measuring the length of the shadow cast by a stick planted in the ground. That the sun could be directly overhead in one place and not another was due to the curvature of Earth. Eratosthenes reasoned that if he knew the distance from Alexandria to Syene, the full circumference of the planet must be about fifty times that distance. Traders passing through Alexandria told him that camels could make the trip to Syene in about 50 days, and it was known that a camel could cover 100 stadia (almost 11½ miles) in a day. So the ancient geographer estimated that Syene and Alexandria were about 570 miles apart. Consequently, the complete circumference of Earth he figured to be about 50 × 570 miles, or 28,500 miles. This number was within 15 percent of the modern measurement, amazingly accurate considering the imprecision of using camels as odometers.
As ingenious as they were, the ancient Greeks were not able to calculate the size of our solar system. That discovery had to wait for the invention of the telescope, nearly 2,000 years later. In 1672 the French astronomer Jean Richer determined the distance from Earth to Mars by measuring how much the position of the latter shifted against the background of stars from two different observation points on Earth. The two points were Paris (of course) and Cayenne, French Guiana. Using the distance to Mars, astronomers were also able to compute the distance from Earth to the sun, approximately 100 million miles.
A few years later, Isaac Newton managed to estimate the distance to the nearest stars. (Only someone as accomplished as Newton could have been the first to perform such a calculation and have it go almost unnoticed among his other achievements.) If one assumes that the stars are objects similar to our sun, equal in intrinsic luminosity, Newton asked, how far away would our sun have to be in order to appear as faint as nearby stars? Writing his computations in a spidery script, with a quill dipped in the ink of oak galls, Newton correctly concluded that the nearest stars are about 100,000 times the distance from Earth to the sun, about 10 trillion miles away. Newton’s calculation is contained in a short section of his Principia titled simply “On the distance of the stars.”
Newton’s estimate of the distance to nearby stars was larger than any distance imagined before in human history. Even today, nothing in our experience allows us to relate to it. The fastest most of us have traveled is about 500 miles per hour, the cruising speed of a jet. If we set out for the nearest star beyond our solar system at that speed, it would take us about 5 million years to reach our destination. If we traveled in the fastest rocket ship ever manufactured on Earth, the trip would last 100,000 years, at least a thousand human life spans.
But even the distance to the nearest star is dwarfed by the measurements made in the early twentieth century by Henrietta Leavitt, an astronomer at the Harvard College Observatory. In 1912 she devised a new method for determining the distances to faraway stars. Certain stars, called Cepheid variables, were known to oscillate in brightness. Leavitt discovered that the cycle times of such stars are closely related to their intrinsic luminosities. More luminous stars have longer cycles. Measure the cycle time of such a star and you know its intrinsic luminosity. Then, by comparing its intrinsic luminosity to how bright it appears in the sky, you can infer its distance, just as you could gauge the distance to an approaching car at night if you knew the wattage of its headlights. Cepheid variables are scattered throughout the cosmos. They serve as cosmic distance signs in the highway of space.
Using Leavitt’s method, astronomers were able to determine the size of the Milky Way, a giant congregation of about 200 billion stars. To express such mind-boggling sizes and distances, twentieth-century astronomers adopted a new unit called the light-year, the distance that light travels in a year—about 6 trillion miles. The nearest stars are several light-years away. The diameter of the Milky Way has been measured at about 100,000 light-years. In other words, it takes a ray of light 100,000 years to travel from one side of the Milky Way to the other.
There are galaxies beyond our own. They have names like Andromeda (one of the nearest), Sculptor, Messier 87, Malin 1, IC 1101. The average distance between galaxies, again determined by Leavitt’s method, is about twenty galactic diameters, or 2 million light-years. To a giant cosmic being leisurely strolling through the universe and not limited by distance or time, galaxies would appear as illuminated mansions scattered about the dark countryside of space. As far as we know, galaxies are the largest objects in the cosmos. If we sorted the long inventory of material objects in nature by size, we would start with subatomic particles like electrons and end up with galaxies.
Over the past century, astronomers have been able to probe deeper and deeper into space, looking out to distances of hundreds of millions of light-years and farther. A question naturally arises: Could the physical universe be unending in size? That is, as we build bigger and bigger telescopes sensitive to fainter and fainter light, will we continue to see objects farther and farther away—like the third emperor of the Ming Dynasty, Yongle, who surveyed his new palace in the Forbidden City and walked from room to room to room, never reaching the end?
Here we must take into account a curious relationship between distance and time. Because light travels at a fast (186,000 miles per second) but not infinite speed, when we look at a distant object in space we must remember that a significant amount of time has passed between the emission of the light and the reception at our end. The image we see is what the object looked like when it emitted that light. If we look at an object 186,000 miles away, we see it as it appeared one second earlier; at 1,860,000 miles away, we see it as it appeared ten seconds earlier; and so on. For extremely distant objects, we see them as they were millions or billions of years in the past.
Now the second curiosity. Since the late 1920s we have known that the universe is expanding, and that as it does so it is thinning out and cooling. By measuring the current rate of expansion, we can make good estimates of the moment in the past when the expansion began—the Big Bang—which was about 13.7 billion years ago, a time when no planets or stars or galaxies existed and the entire universe consisted of a fantastically dense nugget of pure energy. No matter how big our telescopes, we cannot see beyond the distance light has traveled since the Big Bang. Farther than that, and there simply hasn’t been enough time since the birth of the universe for light to get from there to here. This giant sphere, the maximum distance we can see, is only the observable universe. But the universe could extend far beyond that.
In his office in Santa Cruz, Garth Illingworth and his colleagues have mapped out and measured the cosmos to the edge of the observable universe. They have reached out almost as far as the laws of physics allow. All that exists in the knowable universe—oceans and sky; planets and stars; pulsars, quasars, and dark matter; distant galaxies and clusters of galaxies; and great clouds of star-forming gas—has been gathered within the cosmic sensorium gauged and observed by human beings.
“Every once in a while,” says Illingworth, “I think, By God, we are studying things that we can never physically touch. We sit on this miserable little planet in a midsize galaxy and we can characterize most of the universe. It is astonishing to me, the immensity of the situation, and how to relate to it in terms we can understand.”
The idea of Mother Nature has been represented in every culture on Earth. But to what extent is the new unive
rse, vastly larger than anything conceived of in the past, part of nature? One wonders how connected Illingworth feels to this astoundingly large cosmic terrain, to the galaxies and stars so distant that their images have taken billions of years to reach our eyes. Are the little red dots on his maps part of the same landscape that Wordsworth and Thoreau described, part of the same environment of mountains and trees, part of the same cycle of birth and death that orders our lives, part of our physical and emotional conception of the world we live in? Or are such things instead digitized abstractions, silent and untouchable, akin to us only in their (hypothesized) makeup of atoms and molecules? And to what extent are we human beings, living on a small planet orbiting one star among billions of stars, part of that same nature?
The heavenly bodies were once considered divine, made of entirely different stuff from objects on Earth. Aristotle argued that all matter was constituted from four elements: earth, fire, water, and air. A fifth element, ether, he reserved for the heavenly bodies, which he considered immortal, perfect, and indestructible. It wasn’t until the birth of modern science, in the seventeenth century, that we began to understand the similarity of heaven and Earth. In 1610, using his new telescope, Galileo noted that the sun had dark patches and blemishes, suggesting that the heavenly bodies are not perfect. In 1687 Newton proposed a universal law of gravity that would apply equally to the fall of an apple from a tree and to the orbits of planets around the sun. Newton then went further, suggesting that all the laws of nature apply to phenomena in the heavens as well as on Earth. In later centuries, scientists used our understanding of terrestrial chemistry and physics to estimate how long the sun could continue shining before depleting its resources of energy; to determine the chemical composition of stars; to map out the formation of galaxies.
Yet even after Galileo and Newton, there remained another question: Were living things somehow different from rocks and water and stars? Did animate and inanimate matter differ in some fundamental way? The “vitalists” claimed that animate matter had some special essence, an intangible spirit or soul, while the “mechanists” argued that living things were elaborate machines and obeyed precisely the same laws of physics and chemistry as did inanimate material. In the late nineteenth century, two German physiologists, Adolf Eugen Fick and Max Rubner, each began testing the mechanistic hypothesis by painstakingly tabulating the energies required for muscle contraction, body heat, and other physical activities and comparing these energies against the chemical energy stored in food. Each gram of fat, carbohydrate, and protein had its energy equivalent. Rubner concluded that the amount of energy used by a living creature was exactly equal to the energy it consumed in its food. Living things were to be viewed as complex arrangements of biological pulleys and levers, electric currents, and chemical impulses. Our bodies are made of the same atoms and molecules as stones, water, and air.
And yet many had a lingering feeling that human beings were somehow separate from the rest of nature. Such a view is nowhere better illustrated than in the painting Tallulah Falls (1841), by George Cooke, an artist associated with the Hudson River school. Although this group of painters celebrated nature, they also believed that human beings were set apart from the natural world. Cooke’s painting depicts tiny human figures standing on a small promontory above a deep canyon. The people are dwarfed by tree-covered mountains, massive rocky ledges, and a waterfall pouring down to the canyon below. Not only insignificant in size compared with their surroundings, the human beings are mere witnesses to a scene they are not part of and never could be. Just a few years earlier, Ralph Waldo Emerson had published his famous essay “Nature,” an appreciation of the natural world that nonetheless held humans separate from nature, at the very least in the moral and spiritual domain: “Man is fallen; nature is erect.”
Today, with various back-to-nature movements attempting to resist the dislocations brought about by modernity, and with our awareness of Earth’s precarious environmental state ever increasing, many people feel a new sympathy with the natural world on this planet. But the gargantuan cosmos beyond remains remote. We might understand at some level that those tiny points of light in the night sky are similar to our sun, made of atoms identical to those in our bodies, and that the cavern of outer space extends from our galaxy of stars to other galaxies of stars, to distances that would take light billions of years to traverse. We might understand these discoveries in intellectual terms, but they are baffling abstractions, even disturbing, like the notion that each of us once was the size of a dot, without mind or thought. Science has vastly expanded the scale of our cosmos, but our emotional reality is still limited by what we can touch with our bodies in the time span of our lives. George Berkeley, the eighteenth-century Irish philosopher, argued that the entire cosmos is a construct of our minds, that there is no material reality outside our thoughts. As a scientist, I cannot accept that belief. At the emotional and psychological level, however, I can have some sympathy with Berkeley’s views. Modern science has revealed a world as far removed from our bodies as colors are from the blind.
Very recent scientific findings have added yet another dimension to the question of our place in the cosmos. For the first time in the history of science, we are able to make plausible estimates of the rate of occurrence of life in the universe. In March 2009, NASA launched a spacecraft called Kepler, whose mission was to search for planets orbiting in the “habitable zone” of other stars. The habitable zone is the region in which a planet’s surface temperature is not so cold as to freeze water and not so hot as to boil it. For many reasons, biologists and chemists believe that liquid water is required for the emergence of life, even if that life may be very different from life on Earth. Dozens of candidates for such planets have been found, and we can make a rough preliminary calculation that something like 3 percent of all stars are accompanied by a potentially life-sustaining planet. The totality of living matter on Earth—humans and animals, plants, bacteria, and pond scum—makes up 0.00000001 percent of the mass of the planet. Combining this figure with the results from the Kepler mission, and assuming that all potentially life-sustaining planets do indeed have life, we can estimate that the fraction of stuff in the visible universe that exists in living form is something like 0.000000000000001 percent, or one-millionth of one-billionth of 1 percent. If some cosmic intelligence created the universe, life would seem to have been only an afterthought. And if life emerges by random processes, vast amounts of lifeless material are needed for each particle of life. Such numbers cannot help but bear upon the question of our significance in the universe.
Decades ago, when I was sailing with my wife in the Aegean Sea, in the midst of unending water and sky, I had a slight inkling of infinity. It was a sensation I had not experienced before, accompanied by feelings of awe, fear, sublimity, disorientation, alienation, and disbelief. I set a course for 255 degrees, trusting in my compass—a tiny disk of painted numbers with a sliver of rotating metal—and hoped for the best. In a few hours, as if by magic, a pale ocher smidgen of land appeared dead ahead, a thing that drew closer and closer, a place with houses and beds and other human beings.
DAVID QUAMMEN
Out of the Wild
FROM Popular Science
IN JUNE 2008, a Dutch woman named Astrid Joosten left the Netherlands with her husband for an adventure vacation in Uganda. It wasn’t their first trip to Africa, but it would be more consequential than the others.
At home in Noord-Brabant, Joosten, forty-one, worked as a business analyst for an electrical company. Both she and her spouse, a financial manager, enjoyed escaping Europe on annual getaways. In 2002 they had flown to Johannesburg and, stepping off the airplane, felt love for Africa at first sight. On later trips they visited Mozambique, Zambia, and Mali. The journey to Uganda in 2008, booked through an adventure-travel outfitter, would allow them to see mountain gorillas in the southwestern highlands of the country as well as some other wildlife and cultures. They worked their way south toward Bw
indi Impenetrable Forest, where the gorillas reside. On one day, the operators offered a side trip, an option, to a place called the Maramagambo Forest, where the chief attraction was a site known as Python Cave. African rock pythons lived there, languid and content, grown large on a diet of bats.
Joosten’s husband, later her widower, is a fair-skinned man named Jaap Taal, a calm fellow with a shaved head and dark, roundish glasses. Most of the other travelers didn’t fancy this Python Cave offering, he told me in a subsequent interview. “But Astrid and I always said, ‘Maybe you come here only once in your life, and you have to do everything you can.’” They rode to Maramagambo Forest and then walked a mile or so, gradually ascending, to a small pond. Nearby, half concealed by moss and other greenery, like a crocodile’s eye barely surfaced, was a low, dark opening. Joosten and Taal, with their guide and one other client, climbed down into the cave.
The footing was bad: rocky, uneven, and slick. The smell was bad too: fruity and sour. Think of a dreary barroom, closed and empty, with beer on the floor at three A.M. The cave seemed to have been carved by a creek, or at least to have channeled its waters, and part of the overhead rock had collapsed, leaving a floor of boulders and coarse rubble, a moonscape, coated with guano like a heavy layer of vanilla icing. It served as a major roosting site for the Egyptian fruit bat (Rousettus aegyptiacus), a crow-size chiropteran that’s widespread and relatively abundant in Africa and the Middle East. The cave’s ceiling was thick with them—many thousands, agitated and chittering at the presence of human intruders, shifting position, some dropping free to fly and then settling again. Joosten and Taal kept their heads low and watched their step, trying not to slip, ready to put a hand down if needed. “I think that’s how Astrid got infected,” Taal told me. “I think she put her hand on a piece of rock, which contained droppings of a bat, which are infected. And so she had it on her hand.” Maybe she touched her face an hour later, or put a piece of candy in her mouth, “and that’s how I think the infection got in her.”
The Best American Science and Nature Writing 2013 Page 20
