NEW YORK -- Two Americans were awarded the Nobel Prize in physics yesterday for measuring the oldest light in the heavens, a feat described as ``one of the greatest discoveries of the century" that convinced skeptics of the big bang theory of the universe's origin.
George F. Smoot, 61, of Lawrence Berkeley National Laboratory in Berkeley, Calif., and John C. Mather, 60, of NASA's Goddard Space Flight Center in Greenbelt, Md., will share the $1.4 million prize equally for their groundbreaking work.
They were the chief architects of a NASA satellite observatory named COBE, for cosmic background explorer. Launched in 1989, the spacecraft measured feeble remnants of light that originated early in the history of the universe, about 380,000 years after the big bang. Until then the universe was opaque to light, making it impossible to directly observe anything older.
Smoot and Mather's findings revealed the ancient seeds of stars, galaxies, and other celestial objects.
``It's the farthest out we can see in the universe and it's the furthest back in time," said Phillip F. Schewe, a spokesman for the American Institute of Physics.
The big bang theory predicts that this primordial light should display a classic ``blackbody" spectrum, an indicator that the whole universe started out at a uniform temperature before expanding into the much less homogeneous state we now observe. That is exactly what COBE found.
``It's just a magnificent verification of the big bang," said Lawrence Krauss, a professor of physics at Case Western Reserve University in Cleveland.
The measurements also revealed tiny ripples in the light's intensity, representing ``lumps" no more than 0.001 percent richer in matter than the space around them. From those humble origins arose massive galaxies and galactic superclusters hundreds of millions of light-years across.
In announcing the prize, the Royal Swedish Academy of Sciences noted that life itself depends on the existence of those tiny fluctuations, because without them matter would be spread uniformly and thinly throughout space.
``It is one of the greatest discoveries of the century. I would call it the greatest," said Per Carlson, chairman of the Nobel physics committee. ``It increases our knowledge of our place in the universe."
``We did not know how important this was at the time when it happened. We only knew it was important," Mather said.
Smoot and Mather battled tight budgets, technical challenges, and launch delays caused by the 1986 explosion of the space shuttle Challenger, which was originally supposed to carry COBE into space. After more than a decade of development, the satellite was finally launched in 1989.
``It's vindication for an awful lot of people's faith in us," Mather told reporters who gathered at his suburban Maryland home yesterday morning.
Across the country in California, Smoot called the award ``a great thrill. It's not quite the same thrill as making the discovery."
The significance of the two scientists' achievement is reflected in the swiftness with which the Swedish academy chose to recognize it. Nobel prizes are typically awarded decades after the work that they commemorate, but both of the prizes announced so far this year were for research completed in the last 15 years.
The physics prize is also the second this year to go to a pair of Americans. On Monday, Andrew Z. Fire of Stanford University and Craig C. Mello of the University of Massachusetts Medical School in Worcester received the Nobel prize in medicine for discovering a way to block the activity of genes that has proved useful to both researchers and clinicians.
Americans have so dominated the Nobels in recent times that at least one US scientist has been a recipient in one of the three science categories every year since 1992. In two recent years -- 1998 and 2004 -- seven American laureates have been named in the sciences and economics.