As usual, Daniel Nocera came in by the back door.

On a rainy night in April, as the trees on the Boston College campus were sending out their first tentative shoots of spring, Nocera arrived (slightly late) as the keynote speaker for a meeting of the American Physical Society, where he was about to discuss a decidedly inorganic variation on a vernal theme: the "artificial leaf," his invention that uses sunlight to generate an alternative form of energy.

Nocera made his way across a parking lot, went in the "Employees Only" entrance to the banquet hall, asked a bemused janitor for directions, and found himself in an elevator that deposited him right in the middle of the kitchen. "I'm the speaker