Number 82, June 2, 1992 by Phillip F. Schewe and Ben Stein SQUEEZED LIGHT has been used in the spectroscopic study of atomic cesium (E.S. Polzik et al., Phys. Rev. Lett. 18 May 1992). Quantum mechanics holds that a beam of light, even laser light, exhibits small energy irregularities (shot noise) owing to the effects of vacuum fluctuations (electromagnetic fields in the vacuum whose omnipresence is sanctioned by Heisenberg's uncertainty principle). Over the past decade physicists have been able partially to overcome this problem by reducing the noise in either the phase or the amplitude of the light at the expense of the other. The resultant "squeezed light," or at least that component of the light with a noise level lower than normally allowed by the uncertainty principle, is of interest, both in its own right, representing as it does a specimen of "nonclassical light," and as a potential high-precision probe of atomic physics. Scientists at Caltech (H. Jeffrey Kimble, 818-356-8340) have used a tunable beam of squeezed light over a wavelength range of 840-970 nm to measure, with half the usual noise, certain atomic transitions in cesium. (Science News, 30 May 1992.) THE EXTREME ULTRAVIOLET EXPLORER (EUVE) , a satellite expected to be launched this month, will map the sky at wavelengths between 100 and 900 angstroms, an energy range important for studying stellar atmospheres and white dwarfs. The EUV band is hard to observe, however, since it is largely absorbed by clouds of interstellar hydrogen atoms. This limits effective viewing to a region of space out to about 300 light years, a volume that is, fortunately, relatively free of hydrogen. Rosat, the German satellite, has also been mapping the sky at EUV (and at soft x-ray) wavelengths, but does not have the EUVE's ability to study the spectra of individual sources. (Science News, 23 May 1992.) HIGH ENERGY PHOTON-PHOTON INTERACTIONS can occur when electrons and positrons, racing past each other at a collider, communicate with each other through a complex web of virtual photons. According to quantum theory, these photons---which cannot be directly observed---can interact in a variety of ways, giving rise to various resonances and jets of particles, which can be detected. A meeting on photon-photon collisions held in San Diego in March revealed that most experimental results, at labs like Tristan and LEP, are in line with the predictions of quantum electrodynamics (QED) and quantum chromodynamics (QCD). At the meeting, V. Telnov of Novosibirsk suggested that a beam of high-energy real photons (virtual photons owe their fleeting existence to the vagaries of the uncertainty principle) could be made by scattering laser light from beams of electrons at a linear collider. (Nature, 28 May.) OXYGEN AND IRON , two of the most important elements of life on Earth, were not much present in the early phase of our galaxy: the metallicity (proportion of elements heavier than helium) for old stars is only 0.02%, while that of younger stars like our Sun (4.6 billion years) is 2%. Supernovas, the furnace for producing metals, spew heavy elements out into the interstellar medium, where they can be taken up in future generations of stars. A star's metallicity is usually pegged to its iron content because iron's complex spectrum is easier to detect than oxygen's. (Astronomy, July 1992.)