For the first time, scientists have observed long-sought relics of the "Big Bang," the primeval explosion that some believe created the universe 15 billion years ago.
Those relics, massive wisps of gas more than 500 million light years long, are the largest and oldest structures ever observed, astrophysicist George Smoot of California's Lawrence Berkeley Laboratory said yesterday at a meeting of the American Physical Society in Washington.
The structures provide the answer to a question that has plagued cosmologists for decades: How did the widely dispersed primordial gases produced by a Big Bang coalesce into stars and galaxies?
It now seems clear that gravitational forces within these huge ripples in space and time were the key driving force, slowly drawing the thin gases into dense clumps that evolved into all existing matter, Mr. Smoot said.
"It's one of the major discoveries of the century," said physicist Joel Primack of the University of California, Santa Cruz. "In fact, it's one of the major discoveries of science."
The discovery is "unbelievably important," physicist Michael Turner of the University of Chicago said. "The significance of this cannot be overstated. They have found the holy grail of cosmology. . . . If it is, indeed, correct, this certainly would have to be considered for a Nobel Prize."
The temperature and size of the structures discovered by Mr. Smoot and his colleagues also provide strong confirmation of the theorythat as much as 90 percent of the matter in the universe is so-called cold, dark matter. Cold, dark matter is invisible to the most powerful telescopes but provides a strong enough gravitational field that the universe will eventually collapse back in upon itself in a reversal of the Big Bang.
Photographs of the structures were taken by instruments aboard Cosmic Background Explorer, an astronomical satellite launched into polar orbit in November 1989 by the National Aeronautics and Space Administration.
The Big Bang is perhaps one of the most difficult physics concepts for laymen to accept. Its chief assumption is that 15 billion years ago all matter in the universe was compressed into an unimaginably dense sphere smaller than the period at the end of this sentence.
The ball exploded at a temperature of trillions of degrees, launching all matter on the expansionary course it continues to follow today. Within the first millionth of a second after the explosion, quarks and other exotic particles combined to form protons and neutrons, most of which were just as rapidly annihilated by collisions with antiprotons and antineutrons, releasing their energy in the form of light waves.
It is this light, now spread ineffably thin by the continued expansion of the cosmos, that Mr. Smoot and his colleagues have been studying with the COBE satellite. Its faint glow, detected as microwave radiation, corresponds to a temperature of just 2.7 degrees above absolute zero (minus 455 degrees Fahrenheit).
This cosmic microwave background radiation was discovered in 1964 by physicists Arno Penzias and Robert Wilson of Bell Laboratories, for which they won the 1978 Nobel Prize for physics.
But the problem has been that, at the limits of detectability, this background radiation has been found to be uniform throughout the universe in every study conducted over the past 28 years.
For stars and other matter to condense from the gaseous cloud formed in the Big Bang, however, there must have been small irregularities in density, and hence in the radiation. Those irregularities would act like "seeds" around which more matter would condense.
The previous failure to find such irregularities has called the Big Bang theory into question. The discovery by Mr. Smoot and his colleagues thus provides strong support for cosmologists who support the theory.
What Mr. Smoot and his colleagues have found are large regions of the sky in which the temperature is very slightly different, as little as one one-hundred-thousandth of a degree, from that of the areas around them. Such variations had been predicted by some scientists but had never been observed.
Despite the small size of the observed temperature difference, the researchers are confident of its accuracy because it is derived from hundreds of millions of measurements.
The regions encompassed by the variations are immense. The smallest span 500 million light years, about 2.9 billion trillion miles. The largest span two-thirds of the known universe, or 10 billion light years.
Until now, the biggest known structure in the universe was a 200-million-light-year-long arc of galaxies called the "great wall."
"What we have found solves a major mystery, revealing for the first time the primeval seeds that developed into the modern universe," said cosmologist John C. Mather of NASA's Goddard Space Flight Center in Greenbelt, Md.