ATOM WAVES CAN BE USED TO DETECT ROTATIONAL EFFECTS, such as the revolution of the Earth, with as much sensitivity as most commercial laser gyroscopes, new experiments have demonstrated. David Pritchard (dave@amo.mit.edu) and his coworkers at MIT pass a beam of sodium atoms through an atom interferometer, a device which splits individual atoms into wavelets and recombines them to form interference patterns of light and dark fringes. Rotating the interferometer itself while the atom waves travel freely through the device makes the fringes shift from their usual positions. The MIT device can detect rotation rates as slow as one-hundredth of a degree per minute, comparable to the sensitivity of good-quality commercial laser gyroscopes used to detect rotational effects in autos and tanks, but only about one-tenth the sensitivity of laser gyroscopes used in inertial guidance systems in aircraft. With further improvements, atom interferometers may one day easily surpass the sensitivity of laser interferometers because atom wavelengths can be tens of thousands of times smaller (potentially making them more sensitive to smaller changes) and the atoms' much slower speeds compared to light means the interferometer has more time to rotate while the particles travel through the device and thereby can create more appreciable fringe shifts. (A.Lenef et al., Physical Review Letters, 3 February 1997.)

PHOTONS AND LEPTONS SHALL INHERIT THE UNIVERSE. The Copernican principle that the Earth does not occupy a privileged place in space can be extended to the time domain. Carbon-based homo sapiens live some 10^10 years after the big bang, but this is a mere preface to the vast timespan yet to come. Using the latest models of proton decay, stellar evolution, and black holes, Fred Adams and Greg Laughlin of the University of Michigan have prophesied a dim future for the cosmos. They have wound up the clock of the universe and let it tick forward in steps they call "cosmological decades," periods of tenfold increase in the number of years since the big bang. (They also assume the continuing cosmological expansion.) In the current "stelliferous" age (10^6--10^14 years along, or decades n=10-14) regular stars like ours are succeeded by longer-lived red and white dwarf stars. In the "degenerate era" (n=15-37) galaxies fall apart as their inhabitants are reduced to stellar remnants such as brown dwarfs and as more matter falls into black holes. Remnant stars are replenished somewhat by soaking up dark matter but ordinary baryonic matter inexorably disappears through proton decay (a white dwarf generates about 400 watts of energy via proton decay). In the next era (n=38- 100) even the last large repositories of mass, black holes, succumb to evaporation (whereby particle-pair production at the hole's event horizon allows some particles to escape): stellar- mass black holes evaporate in 10^65 years, galaxy-mass black holes in 10^98 years. In the "Dark Era" (n>100) almost nothing is left but electrons, positrons, neutrinos and photons, most of which are so spread out that encounters are rare. (Talks at the American Astronomical Society meeting and April issue of Rev. of Modern Physics.)

REMINDER ON SUBSCRIBING TO PHYSICS NEWS UPDATE: add or delete your address from our list automatically by sending a message to listserv@aip.acp.org. Merely specify either or in the body of the message.