B I O T E C H N O L O G Y42 Back to the Future of Cereals BY STEPHEN A. GOFF AND JOHN M. SALMERONMarrying traditional plant breeding with genetic insights, a technology called marker-assisted breeding could help launch a new green revolution.S P A C E F L I G H T50 Electrodynamic Tethers in Space BY ENRICO LORENZINI AND JUAN SANMARTÍNBy exploiting fundamental physical laws, tethers may provide low-cost electrical power, thrust, drag, and artificial gravity for spaceflight.M E D I C A L T R E A T M E N T S58 Virtual-Reality Therapy BY HUNTER G. HOFFMANPatients can get relief from pain or overcome their phobias by immersing themselves in computer-generated worlds.N U C L E A R W E A P O N S66 Nuclear Bunker Buster Bombs BY MICHAEL LEVINew burrowing nuclear weapons could destroy subterranean military facilities—but their strategic and tactical utility is questionable.I N F O R M A T I O N T E C H N O L O G Y74 Next Stretch for Plastic Electronics BY GRAHAM P. COLLINSOrganic semiconductor devices can make more than just bendable displays. They will find use in wearable electronics and innumerable other applications.C O S M O L O G Y82 Questions That Plague Physics A CONVERSATION WITH LAWRENCE M. KRAUSSThe physicist and best-selling author discusses the puzzles of dark energy, black hole evaporation, extra dimensions and more.P U B L I C H E A L T H86 Arsenic Crisis in Bangladesh BY A. MUSHTAQUE R. CHOWDHURYArsenic in drinking water could poison 50 million people worldwide. Strategies now being tested in Bangladesh might help prevent the problem.