More evidence of a flat universe.

Another balloon-borne experiment recording relic radiation from the Big Bang has found evidence that the universe is flat. The experiment, known as MAXIMA (Millimeter Anisotropy Experiment Imaging Array), detected tiny fluctuations in the temperature of the cosmic microwave background. That's the radiation associated with the explosive birth of the universe. Over billions of years, this radiation has cooled to microwave energies.

During a 1998 flight over Palestine, Texas, MAXIMA mapped the temperature of the microwave background over a small patch of sky. It found the greatest variations in temperature when comparing spots in the sky about 1 [degrees] across, roughly twice the size of the full moon. This result matches predictions for a flat universe--one that has just the right density of matter and energy to expand forever instead of collapsing in a Big Crunch.

The MAXIMA results confirm those of another experiment, BOOMERANG, that scanned a different patch of sky (SN: 4/29/00, p. 276). "It's humbling and gratifying" that the two experiments agree, says Andrew E. Lange of the California Institute of Technology in Pasadena, a member of both the BOOMERANG and MAXIMA teams.

An analysis of both experiments reveals that ordinary matter--material made of neutrons and protons--makes up 5 to 7 percent of the mass of the universe, says theorist Max Tegmark of the University of Pennsylvania in Philadelphia. Models of the amount of material forged in the Big Bang suggest the number is 4 percent. Tegmark says that he marvels that the theory and experiments yield such similar values.

The MAXIMA team has posted its findings at http://xxx.lanl.gov/abs/astro-ph/, numbers 0005123 and 0005124.