When it comes to UFOs, most scientists prefer to just say "no." Tackling the issue without damaging his credibility, astronomer William A. Alschuler wrote The Science of UFOs to explore how popular beliefs about aliens and spacecraft intersect with our current understanding of physics and biology. Though guaranteed to enrage extremists on both sides of the belief spectrum, he is careful to be fair to witness and investigator alike. The text is engaging, even fun, as Alschuler dives head-first into geek-out discussions of wormholes, antigravity effects, and alien DNA. He has this to say about Star Trek-style warp-drive ships: A watcher in the ship's wake would likely see the sky around the ship waver like a desert mirage as the ship accelerated away. If it happened at night or in space, the stars in the sky might appear to draw in around the ship, and as the stars crowded together this area might for a time look like a bright ring of sky. As the ship became more distant, this luminous doughnut would shrink in radius. Drawing plenty of analogies from popular science fiction, Alschuler explains his ideas clearly and forcefully. Though his conclusion--that we probably haven't been visited by extraterrestrials traveling in physical interstellar craft--is neither surprising nor especially satisfying, the process he uses to reach it is challenging, imaginative, and open-minded. These are good scientific values, well worth absorption by