Number 44, August 8, 1991 by Phillip F. Schewe and Ben Stein IRON HYDRIDES ACTUALLY EXPAND WHEN SQUEEZED to pressures of 3.5 GPa or more. Scientists at the Carnegie Institution of Washington, D.C. (Russell Hemley, 202-966-0334) discovered that under the high pressures of a diamond anvil cell, iron samples immersed in a hydrogen fluid will swell by more than 17% in volume as hydrogen atoms fill up small pockets between the iron atoms. This sponge effect is of interest to materials scientists studying how hydrogen makes metals brittle and to geologists who seek to know whether hydrogen exists at the Earth's core. (Science, 26 July 1991.) INTERGALACTIC HYDROGEN CLOUDS are more numerous than was previously thought, based on observations made by the Hubble Space Telescope. The spectrum of quasar 3C 273 (2 billion light years away) exhibits various dips, several of which correspond to the absorption (at a particular wavelength, the so-called Lyman-alpha line) of quasar light by hydrogen atoms in intergalactic clouds along the light path to Earth. These absorption lines occur at wavelengths indicative of the clouds' redshift and consequently their distance from Earth. 3C 273 is one of the closest quasars and so the clouds are also relatively near, or, equivalently, young, at least in cosmological terms. Astronomers are therefore puzzled that such clouds could have persisted into present times without evolving much. (Astronomy, Sept. 1991.) STUDYING CP VIOLATION , with the help of accelerators devoted to the production of B mesons, is the best way to probe the standard model of particle physics, according to Cornell physicist Karl Berkelman (607-255-4198). At least until the SSC is built. Experiments have provided indirect evidence that certain decay modes of the B violate CP invariance; that is, the rate for these decays is slightly different for particles and antiparticles. Present accelerators, however, cannot produce enough of the short-lived B's to test for CP violation. Dedicated B factories (construction proposals for Cornell and Stanford and other labs around the world are now pending) would produce sufficient numbers of B's by colliding electron beams and positron beams at slightly different energies. The asymmetric beams would allow the B's to be produced not at rest but with a great forward velocity, a property which (by the laws of special relativity) extends their lifetime (and therefore their detectability) in the lab frame of reference. (Mosaic, Summer 1991.) A TOTAL OF 1183 PHYSICS PHD'S WERE GRANTED IN 1990 , up from 1112 the previous year. For the 1990-91 academic year the number of undergraduate physics majors at PhD-granting (172 institutions), terminal-master's degree (84 institutions), and bachelor's-degree-granting (491 institutions) colleges or universities was 14, 065; 325,000 students enrolled in their first introductory physics course. These facts are contained in a recent AIP report called "Enrollments and Degrees." (Contact Susanne Ellis, 212-661-9404.) PHYSICS NEWS UPDATE herewith goes on vacation for three weeks.