In an experimental Session 6, Bill Gates hosted and guest-curated the speaker lineup.

David Christian charts our course from the Big Bang to today: “To understand complexity, you have to survey the whole history of the universe. So let’s do it.”

Amina Az-Zubair on the UN Millennium Development Goals in Nigeria: “We are making progress. 20m more people now have access to safe drinking water, especially in schools and hospitals.”

“Polio is still a devastating disease,” says epidemiologist Bruce Aylward, “it’s just happening in another part of the world.”

Salman Khan describes the Khan Academy’s underlying philosophy: “Learn math the way you learn everything: fall off the bicycle. We encourage you to failure, but we do expect mastery.”

Photos: TED / James Duncan Davidson