Scientific American (august 2004)

GENETIC FUTURE OF CROPS • VIRTUAL REALITY BEATS FEAR AND PAIN The Pros and Cons of New Bunker-Busting Nuclear Missiles AUGUST 2004 WWW.SCIAM.COM Who needs rockets? Power and thrust from 25 miles of cable in space DYING FOR A DRINK Arsenic in Well Water Threatens Millions LAWRENCE M. KRAUSS On the Questions That Plague Physics COPYRIGHT 2004 SCIENTIFIC AMERICAN, INC. contents august 2004 SCIENTIFIC AMERICAN Volume 291 Number 2 features BIOTECHNOLOGY 42 Back to the Future of Cereals BY STEPHEN A. GOFF AND JOHN M. SALMERON Marrying traditional plant breeding with genetic insights, a technology called marker-assisted breeding could help launch a new green revolution. SPACEFLIGHT 50 Electrodynamic Tethers in Space 42 Better rice through smarter breeding BY ENRICO LORENZINI AND JUAN SANMARTÍN By exploiting fundamental physical laws, tethers may provide low-cost electrical power, thrust, drag, and artificial gravity for spaceflight. MEDICAL TREATMENTS 58 Virtual-Reality Therapy BY HUNTER G. HOFFMAN Patients can get relief from pain or overcome their phobias by immersing themselves in computer-generated worlds. NUCLEAR WEAPONS 66 Nuclear Bunker Buster Bombs BY MICHAEL LEVI New burrowing nuclear weapons could destroy subterranean military facilities—but their strategic and tactical utility is questionable. INFORMATION TECHNOLOGY 74 Next Stretch for Plastic Electronics BY GRAHAM P. COLLINS Organic semiconductor devices can make more than just bendable displays. They will find use in wearable electronics and innumerable other applications. COSMOLOGY 82 Questions That Plague Physics A CONVERSATION WITH LAWRENCE M. KRAUSS The physicist and best-selling author discusses th