March 28, 1996
Vol. 15, No. 14

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    From end of the earth, a search for beginning of time

    It is the world's highest, driest, coldest desert. The average summer temperature is 18 below zero; in the winter, the mercury can plunge to 100 below. The vast, white, windblown plain is featureless, devoid of all but human life -- no plants, animals, insects or bacteria. It is impossible to sustain human life without extensive support systems. It is 800 miles from the nearest coast, 10,000 miles from Chicago. It is the South Pole, the end of the earth -- an ideal spot for studying the beginning of time.

    At the South Pole, the University manages the Center for Astrophysical Research in Antarctica (CARA), a multi-institutional National Science Foundation Science & Technology Center where astrophysicist Mark Dragovan and other scientists study, among other things, the origins of the universe.

    The South Pole's elevation (nearly 10,000 feet) and cold, dry climate make it one of the best places on earth for doing certain types of astronomy. Dragovan (A.B.'80, Ph.D.'86), Senior Scientist in Astronomy & Astrophysics and one of CARA's founders, has been making an annual trek to the Pole since 1987. He is a principal investigator on the Cosmic Background Radiation Anisotropy (COBRA) experiment, one of four astronomy experiments operated by CARA at the South Pole.

    Dragovan and his colleagues -- Giles Novak (Ph.D.'88), Steve Platt (Ph.D.'90), John Ruhl and John Kovac -- have been observing with COBRA's telescope, Python, a 0.75-meter-diameter radio telescope, for several seasons, even during the austral summer (November through February), when the sun is above the horizon at the South Pole 24 hours a day. Python is carefully shielded from direct sunlight, but the overall brightness of the sky doesn't affect its search, deep in the sky and back in time, to the beginning of the universe.

    What Python detects is the "cosmic microwave background radiation," radiation from 300,000 years after the Big Bang, dating back nearly 15 billion years. Imagine standing at the top of the Sears Tower, looking down with a pair of binoculars, and being able to see workers pour the initial foundations for the tower. Looking at the microwave background is as close as astronomers can get to seeing the construction of the universe.

    Over time, the radiation -- the remnants of the Big Bang's cosmic fireball -- has been stretched out and cooled with the expansion of the universe to just under 3 degrees Kelvin, so that it's now visible only in the microwave region of the electromagnetic spectrum.

    "If you looked at the sky with microwave eyes, you'd see a uniform glow across the sky," Dragovan explained. "If you had sensitive eyes, you would see that it's brighter in one direction than the other, due to our galaxy's motion relative to the background. And if you had really sensitive eyes, you would see brighter patches and darker patches, maybe about as big across as the full moon."

    Python is like a pair of eyeglasses that enables Dragovan to see in this way, allowing him to peer at the cosmic fabric of the universe and look for "lumps" -- the brighter and darker patches. These patches, anisotropies in the microwave background, are the origins of structure in the universe -- the galaxies, clusters and superclusters of galaxies that we see today. Small variations in the density of matter when the universe was 300,000 years old -- when protons, neutrons and electrons were cool enough to combine to form atoms -- were magnified by gravity over the next 15 billion years.

    "The cosmic background radiation is a snapshot of the universe at age 300,000 years," said cosmologist Michael Turner, Professor in Astronomy & Astrophysics. "If the universe had been uniform mush after 300,000 years, it would still be uniform mush today."

    The question that cosmologists want to answer is, how did the lumps get there in the first place? Research by Dragovan and his colleagues may provide the best clues yet to this cosmic mystery.

    At the time of the Big Bang, the universe was a hot, dense, smooth "soup" of fundamental particles -- quarks and leptons. Many cosmologists, including Turner, believe that the lumpiness arose during the first fraction of a second after the Big Bang, when the universe expanded more, proportionately, than it has in the 15 billion years since. Quantum-scale fluctuations may have been stretched out to astrophysical scales during this period, called "inflation," leading to some regions of space having slightly more or less matter than others.

    "These tiny density enhancements left their imprint on the microwave background in the form of hotter and colder areas," Dragovan said. The sizes of the temperature differences and the scales on which they occur, he said, will unlock the secrets of the first fractions of a second of the universe.

    Inflation is a major component of the "cold dark matter" theory of the origin of the universe, which predicts that the greatest temperature differences will occur on angular scales of about one degree on the sky, that is, between patches about twice the size of the full moon.

    Temperature differences are measured in mere millionths of a degree Kelvin. "These temperature differences we're trying to measure are so small, it's like trying to measure variations on the smooth surface of a ball bearing," Dragovan said.

    What's exciting to cosmologists is that the predicted size and angular scale of the variations in the cosmic microwave background radiation are extraordinarily sensitive to factors such as the rate of expansion of the universe and the amount of matter it contains. An accurate measurement of the cosmic microwave background radiation at a variety of angular scales, therefore, will provide an extremely accurate measurement of these hotly debated quantities.

    In 1992, a satellite called the Cosmic Background Explorer found the first evidence for temperature variations in the microwave background. But its beam was seven degrees on the sky, too wide to detect the smaller-scale variations that are of the greatest interest to cosmologists.

    So far, said Turner, COBRA has provided some of the best measurements of the cosmic microwave background at angular scales of about one degree and offered strong evidence that there are indeed one-degree-sized hot spots.

    Next year, a larger telescope, called Viper, will be shipped down to the Pole. Assembled at Carnegie Mellon University by one of Dragovan's colleagues, Jeff Peterson, Viper is a 2-meter telescope that will detect temperature differences on even smaller angular scales.

    Dragovan is already looking beyond Viper, though. He and colleague John Carlstrom, Assistant Professor in Astronomy & Astrophysics, are starting to build a telescope they call the Very Compact Array, or VCA. About the size of a hot tub, VCA will consist of 13 light-gathering "horns" and should provide the first-ever image of the microwave sky. They hope to take it to the South Pole in the austral summer of 1997-98.

    Carlstrom is unabashedly optimistic. "In 100 days of taking data, if it's working well," he said, "we'll have a lot of answers to our questions."

    Dragovan is hedging his bets and looking further ahead yet. He is a principal investigator on two of three satellite proposals currently being considered by NASA. If all goes according to plan, a new sun-orbiting satellite with the ability to detect tiny temperature variations on a wide variety of angular scales will be launched by 2001. Scientists involved in the project say that in six months they could collect enough data to answer, once and for all, some pivotal questions: How old is the universe? How fast is it expanding? How much matter is there? Will the universe continue expanding forever, or will it collapse in on itself?

    Until a new satellite is launched, however, the coldest place on earth will remain the hottest spot around for studying the origins of the universe.

    -- Diana Steele