Physics News Update, Number 425

Number 425, April 28, 1999 by Phillip F. Schewe and Ben Stein

THE COSMIC NEUTRINO BACKGROUND can in principle be detected. There are almost as many neutrinos loose in the universe as photons, and almost as much energy vested in neutrinos as in photons. Yet, owing to the extreme reticence of neutrinos to interact with other particles, detecting the neutrino background is not easy as detecting the cosmic photon (microwave) background. Indeed, dedicated neutrino detectors struggle just to record a handful of incoming neutrinos from potent nearby sources like the sun. Nevertheless, there might be a chance to map the background indirectly. The pattern of lumps in the microwave background, which will be measured by the upcoming MAP and PLANCK orbiting detectors, encodes information about the neutrino background. Scott Dodelson of Fermilab (630-840-2426), Michael Turner and Robert Lopez of the University of Chicago, and Andrew Heckler of Ohio State show these measurements will accurately establish the time at which slow-moving matter (protons and later atoms) became predominant over fast-moving radiation (photons and neutrinos), and that this in turn determines precisely how much early annihilation energy (arising from electrons and positrons smashing up) was apportioned among photons and neutrinos. (Lopez et al., Physical Review Letters, 17 May 1999.)

PROGRESS TOWARDS A DICK TRACY WATCH. Introduced in a Jan. 13, 1946 comic strip, the Dick Tracy watch is a techie's dream: it is a two-way, voice-activated video phone that fits around a wrist. In work that may lead to some components for a real-life Dick Tracy watch, Peter Gammel and his colleagues at Bell Labs/Lucent Technologies have constructed a tiny (100-micron) pyramid-shaped microphone on a silicon chip. According to Gammel, this is the first microphone built by surface micromachining techniques, in which various thin films are deposited on a silicon surface and some of the features are etched away to result in movable parts. This process is to be distinguished from bulk micromachining, in which features are carved out of a silicon surface itself. The researchers have also built a very small rf filter, which blocks unwanted radio frequencies and prevents signals from a phone's transmitter from disrupting its receiver. Made of aluminum nitride on a silicon surface, it is 100 times smaller than conventional ceramic filters, by far the largest single component in a cell phone. The Bell Labs researchers also built a micron-scale version of an inductor, a simple loop of wire that helps determine the proper frequency for communications. Most important of all, these components can all be built on the same silicon chip. Describing these results at the New York State section meeting of the APS held at Lucent last week, Gammel speculates that all of the components for a Dick Tracy watch should be technologically available by 2005. (See figure at Physics News Graphics)

APS CENTENNIAL PHOTOGRAPHS. The American Physical Society (APS) Centennial meeting in Atlanta, Georgia, March 20-26, 1999 was attended by 11,400 physicists, making it the largest physics meeting in history. Highlights included the presence of more than 40 Nobel laureates, a talk by Stephen Hawking, the unveiling of the Centennial physics wall chart, an international banquet attended by physicists from over 60 nations, a series of public lectures on everyday physics, and numerous symposia and press conferences on some of the most important physics topics of the day. A gallery of photographs from these events can be viewed at: /png/html/aps100/apsphoto.html