When the infant universe was a mere 300,000 years old, it was a thinning fog of protons and electrons - no stars, no galaxies, not an oxygen or carbon atom to be found anywhere. To enter this domain, astrophysicists say, was to enter a vast expanse of plasma glowing yellow hot as it roiled at a searing 5,000 degrees Fahrenheit.
Tomorrow afternoon, the United States is set to launch a spacecraft to peer back in time and make the most detailed images yet of this nascent universe. These images come encoded in a faint bath of microwave radiation - all that reaches human instruments after the plasma's radiation has hurtled through space at the speed of light for some 14 billion years.
"This is one of the most important and one of the most exciting missions that NASA has ever conceived in space science," says Alan Bunner, science director for NASA's program to study the structure and evolution of the universe. "We will take the ultimate baby picture."
The $95 million spacecraft, scheduled for launch from the Kennedy Space Center in Florida, is called the Microwave Anisotropy Probe (MAP). It is designed to measure tiny differences in the microwave background radiation left over from the big bang, the primordial explosion that astrophysicists say gave rise to the universe.
Orbiting a point in space roughly 1 million miles from Earth, where gravity from Earth and from the sun cancel each other, MAP will measure these variations over the entire sky and at a level of precision - differences of millionths of a degree - that will allow researchers to zero in on some of the most fundamental properties of the universe.
"We're looking at the oldest light in the universe," says Charles Bennett, an astrophysicist at the Goddard Space Flight Center in Greenbelt, Md., and MAP's lead scientist. "Tiny patterns in the light hold the key for understanding the history, content, shape, and ultimate future" of the cosmos.
The mission comes at a time when the study of the universe's evolution is at a watershed.
"We're witnessing a revolution," says University of Chicago astrophysicist Stephan Meyer, another MAP scientist who also has used balloon-borne experiments to measure the microwave background. He explains that cosmology has reached a point where its theories are refined enough to make precise predictions that can be tested with increasingly precise instruments.
The notion that the universe burst into being through an enormous release of energy confined in an infinitesimally small space emerged following observations in the 1920s that galaxies are hurtling away from each other at ever-increasing velocities.
In 1965, researchers serendipitously discovered the cosmic microwave background - the "afterglow" predicted by the big bang theory, at the expected temperature of 3 degrees above absolute zero. But the big bang theory alone couldn't explain the structure of the universe - from galaxies to superclusters of galaxies, which themselves stretch in vast, arching sheets to surround enormous "bubbles" of empty space.
In the late 1970s, the idea of an inflationary universe - one that experienced exponential growth during its first few fractions of a second - emerged as a refinement to the big bang theory. Among its predictions, inflation posited the existence of subtle variations in the cosmic microwave background. These variations were held to reflect differences in density in the early universe. The densest regions would become the seeds for the larger structures astronomers see today.
In 1992, NASA's Cosmic Background Explorer (COBE) spacecraft first detected broad variations in the microwave background. The inflation theory's stock has been rising ever since. Over the past three years, balloon- and ground-based experiments have improved on COBE's results for small patches of sky, detecting patterns in the irregularities and hints of further patterns that MAP is expected to pull into greater focus.
Combined with results from other observations, these recent measurements describe a universe just dense enough to expand forever - as opposed to collapsing eventually under the influence its collective gravity. Ordinary matter and energy account for about 4 to 5 percent of that density, recently discovered "dark energy" accounts for about 65 percent, and the balance is thought to be made up of as-yet-undetected "dark matter."
Yet if MAP is expected to provide more refined measures of already-known features, it also should yield surprises - another cause for excitement among astrophysicists.
"As an experimentalist, either confirming or disproving a theory is equally cool," adds Barth Netterfield of the University of Toronto, an investigator on one of the balloon-borne experiments.
(c) Copyright 2001. The Christian Science Monitor