sciencehabit writes: What is time? And how would you explain it to an 11-year-old? That's the question actor Alan Alda has posed to scientists in the second Flame Challenge—so named because the question in last year's competition was, "What is a flame?" The challenge aims to spur scientists to think about how they can better communicate with the public. Scientists have until 1 March to submit their answers, which will be judged by 11-year-olds around the world. Organizers will announce the winner at the World Science Festival in New York City on 1 June.