COSMOLOGY38 Is the Universe Leaking Energy? By Tamara M. Davis As the cosmos expands, light seems to lose energy, in violation of the laws of physics. What gives?MEDICINE48 DNA Drugs Come of Age By Matthew P. Morrow and David B. Weiner New vaccines and medicines in human trials offer hope for fighting HIV, influenza and other maladies. transportation54 The Dirty Truth about Plug-in Hybrids By Michael Moyer Cars that draw electricity from the grid may not be as clean as you think. The key factor? Where you live.ROBOTICS56 War of the Machines By P. W. Singer Thousands of robots now operate in Iraq and Afghanistan. They mark the most profound transformation of warfare since the atom bomb.ENERGY64 Clean Energy from Filthy Water By Jane Braxton Little California cities are pumping their treated wastewater underground to create electricity.EVOLUTION70 Winged Victory By Gareth Dyke Modern birds, long thought to have arisen after the dinosaurs perished, actually lived alongside them.PSYCHOLOGY76 How Babies Think By Alison Gopnik Even the youngest children know, experience and learn far more than scientists ever thought possible.ENVIRONMENT82 The Drillers Are Coming By Mark Fischetti A process for extracting natural gas is expanding despite concern over risks to drinking water.