Hugo-winner Egan (Schild’s Ladder
), champion of ultra-hard SF, devotes most of this slim novel to the efforts of the Arkmakers, who live in a neutron star’s accretion disk at the center of the galaxy, to develop orbital physics from first principles and save the artificial world created by their more sophisticated ancestors. Meanwhile, Rakesh, a more or less human member of a distant posthuman society, sets off on an unrelated quest to find the Arkmakers and is soon trying to save them from their current danger. Whole chapters are devoted to physics problems and include a variety of diagrams and cited sources. Egan’s briefly sketched characters and cultures are interesting, but this one is all about the science and won’t have much interest for those without at least some understanding of celestial mechanics. (Oct.)
