For its first 300,000 years, the Universe was filled with hot ionized gases as opaque as the center of the sun. Cosmologists generally believe that as the Universe expanded, the boiling cloud cooled and thinned until the charged particles were drawn together into neutral atoms of hydrogen and helium. At this point, the thermal radiation was unveiled, freed to travel across the Universe. Billions of years later, astronomers perceive this energy as the cosmic microwave background radiation (CMBR)--the ghost of the moment when matter began to form in the Universe.
Theories suggest that this phantom of the Universe should be slightly uneven, with ripples superposed on a smooth background. Recent satellite images of the CMBR provide us with our first view of these primordial ripples. According to computational astrophysicist Ed Bertschinger, they capture the afterglow of the Big Bang.
Bertschinger, a professor of physics at MIT, cannot calculate backwards from this pattern to the beginning of time in order to determine its source, because there are too many unknowns in the early Universe. Instead, he uses the IBM RS/6000 Scalable POWERparallel Systems (SP) at the Cornell Theory Center to evolve his own, parallel universe based on a variety of theories. He then compares the patterns that emerge from the simulations with recorded images of the actual radiation. While presented at a much higher resolution than the COBE images, Bertschinger's simulated picture of the primordial ripples are statistically consistent with the images from space.
Observed patterns for this research come from the Cosmic Background Explorer (COBE) satellite, launched by NASA in 1989. COBE images of the CMBR support the Big Bang theory while also adding to the evidence that another form of matter, so-called dark matter, accounts for most of the mass in the Universe. Extremely accurate measurements by astronomers using COBE, as well as balloon-borne and ground-based experiments, reveal patterns that represent the seeds of the stars and galaxies populating today's night sky.
Bertschinger and his associates believe that very small variations (one thousandth of one percent) in the density of the primordial cloud created during the first small fraction of a second of its existence likely produced the ghostlike ripples in the CMBR observed today. Given the time scale (15 billion years, give or take a few billion), the formation of stars, galaxies, and larger structures may also be explained by these same minute variations in the density of the plasma and the dark matter.
"The subject doesn't end with COBE," says Bertschinger. "COBE opened up the field." Astronomers have proposed launching new observational satellites that will examine the early Universe at finer scales. Bertschinger's models will keep pace with these efforts, adding to and balancing the basic ingredients of his cosmic cloud, as he strives to identify the range of theories to be tested in upcoming experiments.