Inspired by the elegant efficiency of spider webs, researchers at NASA's Jet Propulsion Laboratory in Pasadena, Calif., have designed a tiny, web-shaped sensor that maps faint structures in the early universe, reinforcing theories that the cosmos is flat in its geometry.
(A NASA news release describing the overall results may be found at ftp://ftp.hq.nasa.gov/pub/pao/pressrel/2000/00-067.txt .)
Carried on an internationally sponsored balloon experiment called BOOMERANG (Balloon Observations of Millimetric Extragalactic Radiation and Geophysics), the dime-sized sensor known as a "micromesh bolometer" is a prime example of NASA's success in developing miniaturized, high-performance technologies for space missions.
"Just as spiders spin their webs with the least amount of silk possible, we were able to eliminate 99 percent of the material used by conventional bolometers," said Dr. James Bock, who led in the detector's development at JPL's Microdevices Laboratory. "The supporting material for our detector even has the same thickness as a strand in a spider's web -- about one micron thick, or one hundred times finer than a human hair."
Using advanced micro-machining techniques, each section of the sensor's web was designed to be smaller than the millimeter wavelength of radiation streaming in from the cosmic microwave background. Created when the first atoms formed in the early universe, the cosmic microwave background has cooled a thousand times from its original temperature -- comparable to the hot surface of the Sun -- to the cold, faint radiation seen today.
While the cosmic microwave background is almost perfectly uniform in all directions, the sensitivity of JPL's bolometer allows scientists to capture temperature variations of only 100- millionths of a degree (0.0001 C) in just a few seconds of observing time.
"That's sensitive enough to detect the heat given off by a coffee maker all the way from the Moon," said Bock.
By measuring one small patch of sky after another over several days of observation, the bolometers plot a map of the cosmic background radiation, providing a snapshot of the universe when the radiation formed about 300,000 years after the Big Bang. At this time, regions with a higher density of matter and energy left a record in the background radiation. Wherever dense regions existed, they left a faint imprint of slightly higher temperatures. These fluctuations in the background serve as a kind of fingerprint, allowing scientists to discriminate between theories of cosmic development.
With the bolometer's high level of sensitivity, the BOOMERANG project was able to reveal density patterns in the young universe that are consistent with an inflationary theory of cosmic development. This theory proposes that, in the first moments after the Big Bang, the universe went through a period of extreme, exponential inflation. The theory further predicts a "flat" geometry for the universe, because the immense stretching of space during an inflationary period would have removed any initially strong curvature in the smaller and denser early universe.
"Think of it this way," explains Bock. "If we were to balance on a large ball, we would certainly feel the curvature beneath our feet. Expand that ball to the size of the Earth, and we experience that space as flat. Now think about blowing up that ball to a cosmic scale, and you can imagine how inflation would vastly flatten the visible universe."
To test cosmic development theories even further, future JPL bolometers will fly on the European Space Agency's Far Infrared and Submillimetre Telescope (FIRST) and Planck missions, both scheduled for launch in 2007. Using bolometers with 10 times higher performance, Planck is expected to provide the definitive map of variations in the cosmic microwave background, while FIRST will survey some of the earliest galaxies. In the meantime, scientists will be studying the BOOMERANG map over the next few years to gain a better understanding of the nature and composition of matter in the universe.
The BOOMERANG results were obtained through a balloon experiment in 1998 that carried JPL's bolometer in a sensitive receiver 36 kilometers (23 miles) above the atmosphere in Antarctica. Because Antarctica provides 24-hour sunlight and winds that blow in a circular pattern around the continent, the balloon experiment was able to maintain continuous measurements over a 10-1/2 day period.
The scientific results will be published in the April 27 issue of Nature. Information on the BOOMERANG project can be found at http://www.physics.ucsb.edu/~boomerang and http://oberon.roma1.infn.it/boomerang . For images of JPL's micromesh bolometer and its results, see http://www.jpl.nasa.gov/pictures/boomerang .
The BOOMERANG Project was led by Dr. Andrew Lange of the California Institute of Technology and by Dr. Paolo DeBernardis of the University of Rome La Sapienza. Primary funding for BOOMERANG was provided by the National Science Foundation and NASA in the United States; the Italian Space Agency, the Italian Antarctic Research Programme and the University of Rome La Sapienza in Italy; and the Particle Physics and Astronomy Research Council in the United Kingdom. The Department of Energy's National Energy Research Supercomputing Center provided high-level computer analysis of the data.
The Microdevices Laboratory is a state-of-the-art research and technology-development facility in the Center for Space Microelectronics Technology at JPL. Funding for the micromesh bolometer came from JPL's Technology and Applications Programs Directorate. JPL is managed by Caltech on behalf of NASA.