Baby Pictures of the Universe
The poet only asks to get his head into the heavens. It is the logician who seeks to get the heavens into his head. And it is his head that splits.
—G. K. Chesterson
When I was a child, I had a personal conflict over my beliefs. My parents were raised in the Buddhist tradition. But I attended Sunday school every week, where I loved hearing the biblical stories about whales, arks, pillars of salt, ribs, and apples. I was fascinated by these Old Testament parables, which were my favorite part of Sunday school. It seemed to me that the parables about great floods, burning bushes, and parting waters were so much more exciting than Buddhist chanting and meditation. In fact, these ancient tales of heroism and tragedy vividly illustrated deep moral and ethical lessons which have stayed with me all my life.
One day in Sunday school we studied Genesis. To read about God thundering from the heavens, "Let there be Light!" sounded so much more dramatic than silently meditating about Nirvana. Out of naive curiosity, I asked my Sunday school teacher, "Did God have a mother?" She usually had a snappy answer, as well as a deep moral lesson to offer. This time, however, she was taken aback. No, she replied hesitantly, God probably did not have a mother. "But then where did God come from?" I asked. She mumbled that she would have to consult with the minister about that question.
I didn't realize that I had accidentally stumbled on one of the great questions of theology. I was puzzled, because in Buddhism, there is no God at all, but a timeless universe with no beginning or end. Later, when I began to study the great mythologies of the world, I learned that there were two types of cosmologies in religion, the first based on a single moment when God created the universe, the second based on the idea that the universe always was and always will be.
They couldn't both be right, I thought.
Later, I began to find that these common themes cut across many other cultures. In Chinese mythology, for example, in the beginning there was the cosmic egg. The infant god P'an Ku resided for almost an eternity inside the egg, which floated on a formless sea of Chaos. When it finally hatched, P'an Ku grew enormously, over ten feet per day, so the top half of the eggshell became the sky and the bottom half the earth. After 18,000 years, he died to give birth to our world: his blood became the rivers, his eyes the sun and moon, and his voice the thunder.
In many ways, the P'an Ku myth mirrors a theme found in many other religions and ancient mythologies, that the universe sprang into existence creatio ex nihilo (created from nothing). In Greek mythology, the universe started off in a state of Chaos (in fact, the word "chaos" comes from the Greek word meaning "abyss"). This featureless void is often described as an ocean, as in Babylonian and Japanese mythology. This theme is found in ancient Egyptian mythology, where the sun god Ra emerged from a floating egg. In Polynesian mythology, the cosmic egg is replaced by a coconut shell. The Mayans believed in a variation of this story, in which the universe is born but eventually dies after five thousand years, only to be resurrected again and again to repeat the unending cycle of birth and destruction.
These creatio ex nihilo myths stand in marked contrast to the cosmology according to Buddhism and certain forms of Hinduism. In these mythologies, the universe is timeless, with no beginning or end. There are many levels of existence, but the highest is Nirvana, which is eternal and can be attained only by the purest meditation. In the Hindu Mahapurana, it is written, "If God created the world, where was He before Creation? . . . Know that the world is uncreated, as time itself is, without beginning and end."
These mythologies stand in marked contradiction to each other, with no apparent resolution between them. They are mutually exclusive: either the universe had a beginning or it didn't. There is, apparently, no middle ground.
Today, however, a resolution seems to be emerging from an entirely new direction—the world of science—as the result of a new generation of powerful scientific instruments soaring through outer space. Ancient mythology relied upon the wisdom of storytellers to expound on the origins of our world. Today, scientists are unleashing a battery of space satellites, lasers, gravity wave detectors, interferometers, high-speed supercomputers, and the Internet, in the process revolutionizing our understanding of the universe, and giving us the most compelling description yet of its creation.
What is gradually emerging from the data is a grand synthesis of these two opposing mythologies. Perhaps, scientists speculate, Genesis occurs repeatedly in a timeless ocean of Nirvana. In this new picture, our universe may be compared to a bubble floating in a much larger "ocean," with new bubbles forming all the time. According to this theory, universes, like bubbles forming in boiling water, are in continual creation, floating in a much larger arena, the Nirvana of eleven-dimensional hyperspace. A growing number of physicists suggest that our universe did indeed spring forth from a fiery cataclysm, the big bang, but that it also coexists in an eternal ocean of other universes. If we are right, big bangs are taking place even as you read this sentence.
Physicists and astronomers around the world are now speculating about what these parallel worlds may look like, what laws they may obey, how they are born, and how they may eventually die. Perhaps these parallel worlds are barren, without the basic ingredients of life. Or perhaps they look just like our universe, separated by a single quantum event that made these universes diverge from ours. And a few physicists are speculating that perhaps one day, if life becomes untenable in our present universe as it ages and grows cold, we may be forced to leave it and escape to another universe.
The engine driving these new theories is the massive flood of data that is pouring from our space satellites as they photograph remnants of creation itself. Remarkably, scientists are now zeroing in on what happened a mere 380,000 years after the big bang, when the "afterglow" of creation first filled the universe. Perhaps the most compelling picture of this radiation from creation is coming from a new instrument called the WMAP satellite.
THE WMAP SATELLITE
"Incredible!" "A milestone!" were among the words uttered in February 2003 by normally reserved astrophysicists as they described the precious data harvested from their latest satellite. The WMAP (Wilkinson microwave anisotropy probe), named after pioneering cosmologist David Wilkinson and launched in 2001, has given scientists, with unprecedented precision, a detailed picture of the early universe when it was a mere 380,000 years old. The colossal energy left over from the original fireball that gave birth to stars and galaxies has been circulating around our universe for billions of years. Today, it has finally been captured on film in exquisite detail by the WMAP satellite, yielding a map never seen before, a photo of the sky showing with breathtaking detail the microwave radiation created by the big bang itself, what has been called the "echo of creation" by Time magazine. Never again will astronomers look at the sky in the same way again.
The findings of the WMAP satellite represent "a rite of passage for cosmology from speculation to precision science," declared John Bahcall of the Institute for Advanced Study at Princeton. For the first time, this deluge of data from this early period in the history of the universe has allowed cosmologists to answer precisely the most ancient of all questions, questions that have puzzled and intrigued humanity since we first gazed at the blazing celestial beauty of the night sky. How old is the universe? What is it made of? What is the fate of the universe?
(In 1992, a previous satellite, the COBE [Cosmic Background Explorer satellite] gave us the first blurry pictures of this background radiation filling the sky. Although this result was revolutionary, it was also disappointing because it gave such an out-of-focus picture of the early universe. This did not prevent the press from excitedly dubbing this photograph "the face of God." But a more accurate description of the blurry pictures from COBE would be that they represented a "baby picture" of the infant universe. If the universe today is an eighty-year-old man, the COBE, and later the WMAP, pictures showed him as a newborn, less than a day old.)
The reason the WMAP satellite can give us unprecedented pictures of the infant universe is that the night sky is like a time machine. Because light travels at a finite speed, the stars we see at night are seen as they once were, not as they are today. It takes a little over a second for light from the Moon to reach Earth, so when we gaze at the Moon we actually see it as it was a second earlier. It takes about eight minutes for light to travel from the Sun to Earth. Likewise, many of the familiar stars we see in the heavens are so distant that it takes from 10 to 100 years for their light to reach our eyes. (In other words, they lie 10 to 100 light-years from Earth. A light-year is roughly 6 trillion miles, or the distance light travels in a year.) Light from the distant galaxies may be hundreds of millions to billions of light-years away. As a result, they represent "fossil" light, some emitted even before the rise of the dinosaurs. Some of the farthest objects we can see with our telescopes are called quasars, huge galactic engines generating unbelievable amounts of power near the edge of the visible universe, which can lie up to 12 to 13 billion light-years from Earth. And now, the WMAP satellite has detected radiation emitted even before that, from the original fireball that created the universe.
To describe the universe, cosmologists sometimes use the example of looking down from the top of the Empire State Building, which soars more than a hundred floors above Manhattan. As you look down from the top, you can barely see the street level. If the base of the Empire State Building represents the big bang, then, looking down from the top, the distant galaxies would be located on the tenth floor. The distant quasars seen by Earth telescopes would be on the seventh floor. The cosmic background measured by the WMAP satellite would be just half an inch above the street. And now the WMAP satellite has given us the precise measurement of the age of the universe to an astonishing 1 percent accuracy: 13.7 billion years.
The WMAP mission is the culmination of over a decade of hard work by astrophysicists. The concept of the WMAP satellite was first proposed to NASA in 1995 and was approved two years later. On June 30, 2001, NASA sent the WMAP satellite aboard a Delta II rocket into a solar orbit perched between Earth and the Sun. The destination was carefully chosen to be the Lagrange point 2 (or L2, a special point of relative stability near Earth). From this vantage point, the satellite always points away from the Sun, Earth, and Moon and hence has a totally unobstructed view of the universe. It completely scans the entire sky every six months.
Its instrumentation is state-of-the-art. With its powerful sensors, it can detect the faint microwave radiation left over from the big bang that bathes the universe, but is largely absorbed by our atmosphere. The aluminum-composite satellite measures 3.8 meters by 5 meters (about 11.4 feet by 15 feet) and weighs 840 kilograms (1,850 pounds). It has two back-to-back telescopes that focus the microwave radiation from the surrounding sky, and eventually it radios the data back to Earth. It is powered by just 419 watts of electricity (the power of five ordinary lightbulbs). Sitting a million miles from Earth, the WMAP satellite is well above Earth's atmospheric disturbances, which can mask the faint microwave background, and it is able to get continuous readings of the entire sky.
The satellite completed its first observation of the full sky in April 2002. Six months later, the second full sky observation was made. Today, the WMAP satellite has given us the most comprehensive, detailed map of this radiation ever produced. The background microwave radiation the WMAP detected was first predicted by George Gamow and his group in 1948, who also noted that this radiation has a temperature associated with it. The WMAP measured this temperature to be just above absolute zero, or between 2.7249 to 2.7251 degrees Kelvin.
To the unaided eye, the WMAP map of the sky looks rather uninteresting; it is just a collection of random dots. However, this collection of dots has driven some astronomers almost to tears, for they represent fluctuations or irregularities in the original, fiery cataclysm of the big bang shortly after the universe was created. These tiny fluctuations are like "seeds" that have since expanded enormously as the universe itself exploded outward. Today, these tiny seeds have blossomed into the galactic clusters and galaxies we see lighting up the heavens. In other words, our own Milky Way galaxy and all the galactic clusters we see around us were once one of these tiny fluctuations. By measuring the distribution of these fluctuations, we see the origin of the galactic clusters, like dots painted on the cosmic tapestry that hangs over the night sky.
Today, the volume of astronomical data is outpacing scientists' theories. In fact, I would argue that we are entering a golden age of cosmology. (As impressive as the WMAP satellite is, it will likely be dwarfed by the Planck satellite, which the Europeans are launching in 2007; the Planck will give astronomers even more detailed pictures of this microwave background radiation.) Cosmology today is finally coming of age, emerging from the shadows of science after languishing for years in a morass of speculation and wild conjecture. Historically, cosmologists have suffered from a slightly unsavory reputation. The passion with which they proposed grandiose theories of the universe was matched only by the stunning poverty of their data. As Nobel laureate Lev Landau used to quip, "cosmologists are often in error but never in doubt." The sciences have an old adage: "There's speculation, then there's more speculation, and then there's cosmology."
As a physics major at Harvard in the late 1960s, I briefly toyed with the possibility of studying cosmology. Since childhood, I've always had a fascination with the origin of the universe. However, a quick glance at the field showed that it was embarrassingly primitive. It was not an experimental science at all, where one can test hypotheses with precise instruments, but rather a collection of loose, highly speculative theories. Cosmologists engaged in heated debates about whether the universe was born in a cosmic explosion or whether it has always existed in a steady state. But with so little data, the theories quickly outpaced the data. In fact, the less the data, the fiercer the debate. --Ce texte fait référence à l'édition Broché .