Greg Egan is an Australian with a worldwide perspective--seven of the ten stories in this fine and thoughtful collection appeared in Britain's premier SF magazine Interzone and the rest in America's Asimov's SF Magazine. In a time when it's frequently claimed that SF holds no more surprises Egan casts a coldly innovative eye on old themes like the problem of consciousness: where in the human brain's intricate mess does the "I" actually live? He delivers shocking body-blows to received ideas in thought- experiment stories that like Jorge Luis Borges's philosophical squibs are booby- trapped with terrible truths and paradoxes. Standouts here include the title piece where a supercomputer built from pure light explores a defect in known mathematics that could smash not only the theoretical but the physical universe; "Silver Fire", an unspeakably bleak examination of our need for superstition, however irrational; "Reasons To Be Cheerful", exploring with chilling logic the implications of the likelihood that human emotions are "only" chemical states; "Cocoon", testing liberal sentiments to destruction with a biotechnology that might let parents choose only heterosexual kids; and "The Planck Dive", a one-way trip into a black hole that makes most previous SF versions of this ultimate bungee-jump seem naive. Egan's visions of the future glow with gloomy intellectual fire. Luminous indeed. --David Langford