Number 54, November 4, 1991 by Phillip F. Schewe and Ben Stein
TWO-PHOTON BOUND STATES might occur in extremely nonlinear optical materials, materials in which the amount of output light is not linearly proportional to the amount of input light. Ze Cheng, a physicist at Huazhong University in China, suggests that photons can pair off in nonlinear crystals via the exchange of virtual phonons and that the resultant "superlight" would propagate without scattering attenuations (Physical Review Letters, 11 November 1991). Cheng compares this "superguiding" effect to low-temperature superconductivity, in which electron pairs (Cooper pairs formed by the exchange of phonons) link up to constitute a supercurrent. According to Richard Slusher of AT&T Bell Labs (908-582-4094), an expert on the properties of light in nonlinear media (including squeezed light), the degree of nonlinearity---and hence the intensity of the light entering the crystal---needed to produce the exotic pairing effect is probably beyond present experimental techniques. Nevertheless, Raymond Y. Chiao of the University of California at Berkeley (510-642-4965) and his group are also seeking two-photon states. They feel that such states exist theoretically and should be detectable experimentally. (Physical Review Letters, 9 September 1991.)
THE FIRST GLOBAL MAP OF VENUS , constructed by computers from radar data gathered by the Magellan spacecraft, shows that the planet has been completely resurfaced by volcanic eruptions in the course of time. In fact, the dark lava flow on one volcanic peak, Maat Mons, appears to be less than ten years old. Although the Magellan survey is complete, new measurements will continue to be made. At a NASA news conference on October 29, the mission's chief scientist, Stephen Saunders of the Jet Propulsion Lab, asserted that "We probably have a better global map of Venus now than we have of Earth because most of the ocean basins on Earth are so poorly mapped." (The New York Times, 30 October 1991.)
ELECTRON-PROTON COLLISIONS AT HERA have begun. While there are several electron-positron and proton-antiproton colliders around, HERA, the 6.3-km-diameter machine located at the DESY lab in Hamburg, Germany, is the only accelerator which collides electrons and protons. In this preliminary test, the two beams were steered into a collision course without the proton-beam magnets disrupting the trajectories of the electrons, which travel around the accelerator in their own beampipe. Actual particle physics experiments should begin next summer. (New Scientist, 2 November 1991.)
HOW COULD A PLANET BE ORBITING A PULSAR? Scientists at the University of California at Santa Cruz (Stan Woosley, 408-459-2976) suggest that the 10-Earth-mass planet orbiting pulsar 1829-10 is not a pre-existing planet which happened to have survived the supernova that gave birth to 1829-10. Instead, they believe, it formed from supernova debris falling back (at first) to a disk; from this, later, several 100-km planetesimals formed and later still these coagulated into a planet. A rival theory, presented by Julian H. Krolick (301-338-7926) at Johns Hopkins, holds that the pulsar companion began as a star, much of whose bulk was ablated through its interaction with the pulsar. (Nature, 31 October 1991.)
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