UCB's Maxima Confirms Flat Universe, Inflation, Cosmological Constant
May 9, 2000
FOR IMMEDIATE RELEASE
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BERKELEY, CA--Astrophysicists have taken another major step in depicting the universe in its infancy. The first results from a balloon-borne experiment peering back to a time shortly after the big bang provide confirmation of a mysterious dark matter and dark energy that make up most of the cosmos.
Results of the experiment, an international collaboration called the Millimeter Anisotropy eXperiment IMaging Array (MAXIMA), directed by the University of California at Berkeley, are contained in two papers submitted Monday, May 8, to Astrophysical Journal Letters and scheduled for posting Tuesday on the internet at http://xxx.lanl.gov/list/astro-ph/new (papers #0005123 and #0005124).
The MAXIMA results confirm results announced last month by another group after analysis of data from a balloon-borne experiment called Balloon Observations Of Millimetric Extragalactic Radiation and Geophysics (BOOMERANG), and extend these results to smaller angular scales on the sky. The MAXIMA map is the highest resolution map of the cosmic microwave background yet published.
These results provide strong evidence that the universe is flat, with a large-scale geometry just like the Euclidean geometry everyone learns in high school. However, only about 5 percent of its mass and energy is comprised of ordinary matter--the stuff of which the Earth, the stars and humans are made. The remainder is either cold dark matter--the unseen mass that holds galaxies together, or dark energy, a mystifying pressure or repulsive force that seems to be accelerating the expansion of the universe. The dark energy is often referred to as the cosmological constant.
A subset of cosmological theories, those involving inflation, dark matter and a cosmological constant, fit our data extremely well, said team leader Paul Richards, UC Berkeley professor of physics. Inflation is the most popular cosmological theory describing the early history of the universe. This is a good confirmation of the standard cosmology, and a large triumph for science, because we are talking about predictions made well before the experiment, about something as hard to know as the very early universe.
The MAXIMA team, consisting of 22 collaborators from 13 institutions and five countries, is funded by the National Science Foundation and the National Aeronautics and Space Administration, with the Department of Energy supporting the data analysis.
Although some members are common both to the MAXIMA and to the BOOMERANG teams, the two analyses were done completely independently, noted Shaul Hanany, professor of physics at the University of Minnesota, Minneapolis, and first author of one of the papers. The fact that these independent experiments give such similar results is the best indication that we are both getting the science right.
These are extremely difficult experiments, and yet the data from MAXIMA and BOOMERANG show spectacular agreement, added cosmologist Adrian Lee, a leader of the MAXIMA project from the NSF Center for Particle Astrophysics and the Space Sciences Laboratory, both at UC Berkeley.
MAXIMA and BOOMERANG both measured the temperature variations of the cosmic microwave background, producing thermal maps of the universe 300,000 years after the big bang. The hot and cold spots vary by a few parts per 100,000 from the average background temperature of 2.7 Kelvin, or 454 degrees Fahrenheit below zero.
The size of the spots in the thermal map told the cosmologists immediately one important parameter of the universe, its geometry or curvature. Both experiments saw spots clustered in a size range of about one degree across, indicating a flat universe like the ancient Greek geometer Euclid described more than 2,300 years ago. That type of geometry, the most familiar to us, is characterized by parallel lines that always remain the same distance apart.
When combined with recent data on the universe obtained from studies of distant supernovas, the data also support the inflationary theory of the universe. Specifically, the experiments peg the amount of normal matter in the universe at about 5 percent; the amount of dark matter at about 30 percent; and the amount of dark energy--the cosmological constant--at about 65 percent.
Thats probably the most interesting result of all these experiments, Hanany said. The combination of our data with the data from supernovas is very powerful evidence that we need something like the cosmological constant to describe our universe. New physics may be required to explain the origin of the cosmological constant.
Richards noted that while the thermal map of the sky is a pretty picture, most of the information comes from a detailed statistical analysis of the sky data along with data at large angular scales from the COBE mission. Using supercomputers at the Department of Energys National Energy Research Scientific Computing Center (NERSC) at Lawrence Berkeley National Laboratory, the MAXIMA team calculated the power spectrum of the sky map, which is essentially the range of sizes of the hot and cold spots in the microwave background. Just as a cluster around one degree indicates a flat universe, clusters at smaller angular sizes are a hallmark of inflationary theories.
Though the MAXIMA results cannot unambiguously identify other peaks in the power spectrum, MAXIMA was able to derive other information that strongly supports inflation. Among these is a zero tilt, which essentially means that, immediately after inflation, the fluctuations in the energy in the universe were uniform over all size scales.
Inflationary theories make two main predictions, Lee said. One is a flat universe. The other is that the power spectrum has no tilt. MAXIMA supports both of these predictions.
Astronomers first became aware of the cosmic background radiation in 1965, with the accidental discovery of microwave emissions from all directions of the sky. This was taken as proof of the big bang, and theorists created numerous theories over the years to explain the evolution of the universe from its explosive birth.
In 1992, the Cosmic Background Explorer (COBE) satellite provided the first evidence that the microwave glow is not uniformly 2.7 Kelvin, but varies by as much as 100 millionths of a Kelvin above or below the average--evidence of clumps and wrinkles in the very early universe. These clumps of matter and energy presumably evolved into the clusters and superclusters of galaxies we see today.
Various small experiments since then have measured the size of these variations, hinting at a flat universe. But MAXIMA and BOOMERANG have given cosmologists far clearer evidence for this, Richards said. COBE obtained a low-resolution picture of the entire sky, accurately measuring the large-scale clumps, and is complementary to the MAXIMA data. MAXIMA looked with finer resolution at an area representing 0.3 percent of the sky--a spot about 11 degrees on a side, or 22 times broader than the full moon--in a northern region of the sky near the constellation Draco. While MAXIMA is more sensitive and can fly more frequently, BOOMERANG gathers data over a larger area of sky.
The data used for the analysis reported today were obtained from the first flight of MAXIMA on Aug. 2, 1998, out of the National Scientific Ballooning Facility in Palestine, Texas. The balloon, launched at sunset, flies at about 130,000 feet for one night, 7-10 hours, and is returned to the ground by a parachute. The 1.3 meter telescope focuses the microwave radiation on detectors cooled to one tenth of a degree Kelvin by high-tech refrigerators developed by Richards group. The detectors can sample the sky at angular resolutions from 5 degrees to 1/6 degree. COBE could get no smaller than 7 degrees.
MAXIMA 2 flew in June 1999 and observed roughly twice the area that MAXIMA 1 observed. MAXIMA 3 will fly in the fall of this year and will attempt to measure the polarization of the cosmic background radiation, which to date has never been observed. Continuing analysis of the data from MAXIMA 1 and 2, combined with the 1992 COBE data and eventually the BOOMERANG data, should provide better measurements of all the cosmological parameters, Lee said.
There is still a lot more we can get from the MAXIMA data. Were looking for gold in those Doppler hills, he said.
Paul Richards is in Paris on sabbatical. If you wish to speak with him, call or email Robert Sanders, 510-643-6998 or email@example.com.
Shaul Hanany is at (612) 626-8929 or firstname.lastname@example.org.
Adrian Lee can be reached at 510-642-8923 or email@example.com.
Additional information can be found on the MAXIMA web page: http://cfpa.berkeley.edu/group/cmb/.
A print-quality map of thermal fluctuations in the microwave background can be found at: http://cfpa.berkeley.edu/group/cmb/sanders/wmap300npix.gif or http://cfpa.berkeley.edu/group/cmb/sanders/wmap300npix.ps.