ARTIFICIAL VACUUMS ON EARTH. Inside his trap for antiparticles, Gerald Gabrielse of Harvard achieves a vacuum of 5 x 10^-17 torr, corresponding to about 2 atoms per cm³. By comparison, the atoms between stars are spaced a centimeter apart; in the gaseous halo of our galaxy the spacing is about 10 cm; and for intergalactic voids, it's up to 10 m, the lowest density (or highest vacuum) ever measured, at least indirectly. (New Scientist, 25 April.)