The End

Monday, Jun. 25, 2001 By MICHAEL D. LEMONICK
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But it was more like seeing God through dirty Coke-bottle glasses: the satellite saw lumps but couldn't determine much about them. In April, though, scientists offered up much sharper images from a balloon-borne experiment called BOOMERANG (Balloon Observations of Millimetric Extragalactic Radiation and Geophysics), which lofted instruments into the Antarctic stratosphere; from another named MAXIMA (Millimeter Anisotropy Experiment Imaging Array, which did the same over the U.S.); and from a microwave telescope on the ground at the South Pole, called DASI (Degree Angular Scale Interferometer).

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All these measurements pretty much agreed with one another, confirming that the lumps scientists saw were real, not some malfunction in the telescopes. And two weeks ago, astronomers from the Sloan Digital Sky Survey confirmed that this primordial lumpiness has carried over into modern times. The five-year mission of the survey, to make a 3-D map of the cosmos, is far from complete, but scientists reported at the American Astronomical Society's spring meeting in Pasadena, Calif., that it is clearer than ever that galaxies cluster together into huge clumps that reflect conditions that existed soon after the Big Bang.

To the unaided eye, the images are meaningless. A statistical analysis, however, shows that the early lumps--actually patches of slightly warmer or cooler radiation--don't come at random but rather at certain fixed sizes. "It's as though you're studying dogs," says University of Pennsylvania astrophysicist Max Tegmark, "and you find out that they come in just three types: Labrador, toy poodle and Chihuahua."

That turns out to be enormously important. Knowing the characteristic sizes and also the temperatures, to a millionth of a degree, of these warm and cool regions gives theoretical physicists all sorts of information about the newborn cosmos. They were already pretty sure, from the equations of nuclear physics and from measurements of the relative amounts of hydrogen, helium and lithium in the universe, that protons, neutrons and electrons (the building blocks of every atom in the cosmos) add up to only about 5% of the so-called critical density--what it would take to bring the cosmic expansion essentially to a halt by means of gravity.

But when you add Tegmark's "dogs," plus the more esoteric equations of sub-nuclear physics, it turns out that an additional 30% of the needed matter most likely comes in the form of mysterious particles that have been identified only in theory, never directly observed--particles with quirky names like neutralino and axion. These are the mysterious dark matter, or most of it anyway. The cosmic background radiation itself began to shine when the universe was 300,000 years old, but the temperature fluctuations were set in place when it was just a split-second old. "It's pretty cool," says Tegmark, "to be able to look back that far."

THE FLAT UNIVERSE