In this issue:
"Dark Worlds": A shadow cosmos, woven silently into our own, may have its own rich inner life.
"Controlling the Brain with Light": A new technique called optogenetics is enabling researchers to see how the nervous system works – in unprecedented detail.
"Halting the World's Most Lethal Parasite": A new malaria vaccine and other interesting ideas for vanquishing this killer.
"How to Build the Supergrid": The U.S. needs a new electric transmission system to deliver cleaner, more reliable power nationwide.