Every branch of science has made stunning advances in the twentieth century. The very foundations of physics have been revolutionized by the special and general theories of relativity, and by quantum mechanics. It was in this century that the nature of atoms—with protons and neutrons in a central nucleus and electrons in a surrounding cloud—was first understood, when the constituent components of protons and neutrons, the quarks, were first glimpsed, and when a host of exotic shortlived elementary particles first showed up under the ministrations of high energy accelerators and cosmic rays. Fission and fusion have made possible the corresponding nuclear weapons, fission power plants (a not-unmixed blessing), and the prospect of fusion power plants. An understanding of radioactive decay has given us definitive knowledge of the age of the Earth (about 4.6 billion years) and of the time of the origin of life on our planet (roughly 4 billion years ago). In geophysics, plate tectonics was discovered—a set of conveyer belts under the Earth's surface carrying continents from birth to death, and moving at a rate of about an inch a year. Plate tectonics is essential for understanding the nature and history of landforms and the topography of the sea bottoms. A new field of planetary geology has emerged in which the land-forms and interior of the Earth can be compared with those of other planets and their moons, and the chemistry of rocks on other worlds—determined either remotely or from returned samples brought back by spacecraft or from meteorites now recognized as arising from other worlds—can be compared with the rocks on Earth. Seismology has plumbed the structure of the deep interior of the Earth and discovered beneath the crust a The Twentieth Century • 253
semi-liquid mantle, a liquid iron core, and a solid inner core— all of which must be explained if we wish to know the processes by which our planet came to be. Some mass extinctions of life in the past are now understood by immense mantle plumes gushing up through the surface and generating lava seas where solid land once stood. Others are due to the Impact of large comets or near-Earth asteroids igniting the skies and changing the climate. In the next century, at the very least we ought to be inventorying comets and asteroids to see if any of them has our name on it.
One cause for scientific celebration in the twentieth century is the discovery of the nature and function of DNA, deoxyri-bonucleic acid—the key molecule responsible for heredity in humans and in most other plants and animals. We have learned to read the genetic code and in increasing numbers of organisms we have mapped all the genes and know what functions of the organisms most of them are in charge of. Geneticists are well on their way to mapping the human genome—an accomplishment with enormous potential for both good and evil. The most significant aspect of the DNA story is that the fundamental processes of life now seem fully understandable in terms of physics and chemistry. No life force, no spirit, no soul seems to be involved. Likewise in neurophysiology: Tentatively, the mind seems to be the expression of the hundred trillion neural connections in the brain, plus a few simple chemicals.
Molecular biology now permits us to compare any two species, gene by gene, molecular building block by molecular building block, to uncover the degree of relatedness. These experiments have shown conclusively the deep similarity of all beings on Earth and have confirmed the general relations previously found by evolutionary biology. For example, humans and
254 • Billions and Billions chimpanzees share 99.6 percent of their active genes, confirming that chimps are our closest relatives, and that we share with them a recent common ancestor.
In the twentieth century for the first time field researchers have lived with other primates, carefully observing their behavior in their natural habitats, and discovering compassion, foresight, ethics, hunting, guerrilla warfare, politics, tool use, tool manufacture, music, rudimentary nationalism, and a host of other characteristics previously thought to be uniquely human. The debate on chimpanzee language abilities is still ongoing. But there is a bonobo (a "pigmy chimp") in Atlanta named Kanzi who easily uses a symbolic language of several hundred characters and who has also taught himself to manufacture stone tools.
Many of the most striking recent advances in chemistry are connected with biology, but let me mention one that is of much broader significance: the nature of the chemical bond has been understood, the forces in quantum physics that determine which atoms like to link up with which other atoms, how strongly, and in what configuration. It has also been found that radiation applied to not implausible primitive atmospheres for the Earth and other planets generate amino acids and other key building blocks of life. Nucleic acids and other molecules in the test tube have been found to reproduce themselves and reproduce their mutations. Thus substantial progress has been made in the twentieth century toward understanding and generating the origin of life. Much of biology is reducible to chemistry and much of chemistry is reducible to physics. This is not yet completely true, but the fact that it is even a little bit true is a most important insight into the nature of the Universe.
Physics and chemistry, coupled with the most powerful computers on Earth, have tried to understand the climate and general circulation of the Earth's atmosphere through time. This
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powerful tool is used to evaluate the future consequences of the continued emission of CO2 and other greenhouse gases into the Earth's atmosphere. Meanwhile, much easier, meteorological satellites permit weather prediction at least days in advance, avoiding billions of dollars in crop failures every year. At the beginning of the twentieth century astronomers were stuck at the bottom of an ocean of turbulent air and left to peer at distant worlds. By the end of the twentieth century great telescopes are in Earth orbit peering at the heavens in gamma rays, X rays, ultraviolet light, visible light, infrared light, and radio waves.
Marconi's first radio broadcast across the Atlantic Ocean occurred in 1901. We have now used radio to communicate with four spacecraft beyond the outermost known planet of our Solar System, and to hear the natural radio emission from quasars 8 and 10 billion light-years away—as well as the so-called black body background radiation, the radio remnants of the Big Bang, the vast explosion that began the current incarnation of the Universe.
Exploratory spacecraft have been launched to study 70 worlds and to land on three of them. The century has seen the almost mythic accomplishment of sending 12 humans to the Moon and bringing them, and over a hundred kilograms of moon rocks, back safely. Robotic craft have confirmed that Venus, driven by a massive greenhouse effect, has a surface temperature of almost 900° Fahrenheit; that 4 billion years ago Mars had an Earth-like climate; that organic molecules are falling from the sky of Saturn's moon Titan like manna from Heaven; that comets are made of perhaps a quarter of organic matter. Four of our spacecraft are on their way to the stars. Other planets have recently been found around other stars. Our Sun is revealed to be in the remote outskirts of a vast, lens-shaped galaxy comprising some 400 billion other suns. At the begin-256 • Billions and Billions ning of the century it was thought that the Milky Way was the only galaxy. We now recognize that there are a hundred billion others, all fleeing one from another as if they are the remnants of an enormous explosion, the Big Bang. Exotic denizens of the cosmic zoo have been discovered that were not even dreamt of at the turn of the century—pulsars, quasars, black holes. Within observational reach may be the answers to some of the deepest questions humans have ever asked—on the origin, nature, and fate of the entire Universe.
Perhaps the most wrenching by-product of the scientific revolution has been to render untenable many of our most cherished and most comforting beliefs. The tidy anthropocentric proscenium of our ancestors has been replaced by a cold, immense, indifferent Universe in which humans are relegated to obscurity. But I see the emergence in our consciousness of a Universe of a magnificence, and an intricate, elegant order far beyond anything our ancestors imagined. And if much about the Universe can be understood in terms of a few simple laws of Nature, those wishing to believe in God can certainly ascribe those beautiful laws to a Reason underpinning all of Nature. My own view is that it is far better to understand the Universe as it really is than to pretend to a Universe as we might wish it to be. Whether we will acquire the understanding and wisdom necessary to come to grips with the scientific revelations of the twentieth century will be the most profound challenge of the twenty-first. CHAPTER 19
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