December 2, 1999

Berkeley Lab Science Beat

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Berkeley Lab scientists played a major role in organizing the "Cosmic Genesis and Fundamental Physics" conference held at Sonoma State University recently, which gathered well over a hundred cosmologists, astronomers, particle physicists, and others, from string theorists to giant telescope builders.

Elliott Bloom, a particle astrophysicist with the Stanford Linear Accelerator Center who welcomed the crowd, urged scientists to look "beyond the Standard Model" of fundamental particles and interactions, proposing future collaborative experiments to search for particles and fields yet undiscovered and extra dimensions yet unobserved, and to find new ways to explore cosmic origin, structure, and fate.

In response to a challenge issued in May by NASA administrator Dan Goldin at the "Inner Space/ Outer Space" symposium at Fermilab, the Department of Energy, NASA, and the National Science Foundation supported the Sonoma conference with the intent of making the research dollar stretch farther -- or, as one participant phrased it, getting "more Big Bang for the buck."


Examples of experiments already approved or on the drawing board include the Constellation X orbiting X-ray observatory, described by NASA astrophysicist Nicholas White. Designed to meet Goldin's challenge "to image a black hole, where space and time cease to exist," the Constellation X array will launch four independent telescopes to fly in formation in Earth orbit, with resolving power 100 times greater than any yet achieved in X radiation; more modules would result in even higher resolution.

Formation flying also figures in the design of LISA (Laser Interferometer Space Antenna), described by University of Colorado physicist Peter Bender. Three spacecraft would form an equilateral triangle five million kilometers on a side. Gravitational waves from the collapse of black holes, for example, would be detected by variations in the distance between spacecraft of only a fraction of a wavelength of laser light.

While gravity becomes infinitely strong at the center of a black hole, it is many orders of magnitude weaker than the other forces of nature. Berkeley Lab theorist Nima Arkani-Hamed and Savas Dimopoulos of Stanford outlined a scheme that explains gravity's apparent weakness by invoking extra spatial dimensions.

If our world is confined to a wall, or `brane, in a multidimensional "bulk," the strong nuclear force and electro-weak force may be confined to three dimensions; then gravity would appear weak to us because gravitons, the bosons that convey gravity (analogous to the photons that convey electromagnetism) travel to us through at least two extra dimensions. University of Colorado experimentalist John Price described the table-top gear with which he is seeking to measure gravitation across distances of a few dozen microns, which is a long way, as string-theoretical dimensions go. If the theorists are right, at this range extra-dimensional gravity could be millions of times stronger than the gravity we are used to.

On a much larger scale -- that of the entire universe -- Saul Perlmutter, leader of the international Supernova Cosmology Project headquartered at Berkeley Lab, discussed last year's revolutionary discovery that the expansion of the universe is accelerating. Perlmutter noted two thrusts of future research: a search for nearby type Ia supernovae, in order to calibrate them as "standard candles;" and the proposed SuperNova/Acceleration Probe (SNAP) satellite, to gather many more distant supernovae under ideal conditions. SNAP is a paradigm of the sort of cooperative venture among DOE, NASA and NSF that the conference was meant to illuminate.

One imperative is to explain the energy that drives acceleration, a question debated throughout the three-day conference. Whether a form of the cosmological constant, or quintessence (a sort of inconstant cosmological constant), or some other scheme, "dark energy" will be a fertile field of theory and observation for years to come.

A major source of data on the shape of the universe will come from measurements of the anisotropy of the cosmic microwave background. Caltech's Jason Glenn teased conference participants with high-resolution sky maps obtained by the 10-day BOOMERanG balloon flight around the South Pole last January; but he withheld the all-important "CMB power spectrum," an analysis now underway at NERSC. The position of peaks in the spectrum will reveal whether the universe is open, closed or flat. (Since the conference, data from the 1997 BOOMERanG test flight has been published.)

Berkeley astrophysicist George Smoot, who pioneered studies of CMB anisotropy, also briefed the gathering on the proposed IceCube neutrino observatory at the South Pole. A cubic kilometer of ice near the existing AMANDA detector, IceCube will search for the neutrino signatures of high-energy events both in and beyond the Galaxy, including the origin of ultra-high-energy cosmic rays.

Robert Streitmatter from NASA reported on a score of cosmic rays of energy so high they were thought forbidden by theory -- the Fly's Eye detector in Utah has captured an event packing 51 joules of energy. In a separate talk, Angela Olinto of the University of Chicago speculated on possible sources of ultra-high-energy cosmic rays such as neutron star winds. "We need full-sky coverage and we need to know the composition of the cosmic rays," she said, "before we can relate their apparent origins in the sky to their actual origins."

Concluding the conference, Fermilab cosmologist Edward "Rocky" Kolb noted that whereas the computer industry has Moore's law, which predicts that computing power doubles every 18 months, particle physicists have the Livingston graph, charting increasing accelerator power since the 1930s. "At this rate we'll reach the Planck scale in 2138," Kolb said dryly -- which would require an increase in energy by some 15 orders of magnitude.

"The slope is sagging," he confessed. "Maybe we can come up with new technologies. Alternately, we can go for natural accelerating processes" -- for example, whatever is accelerating those cosmic rays.

Kolb's message was that a new unification of inner space and outer space studies is essential to carry on the work of fundamental physics, the elucidation of nature itself. The process will continue in Aspen, Colorado, in February, and thereafter move to concrete proposals. While it promises to be a long journey, the first step has been auspicious.

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