Liver cancer is one of the most difficult cancers to detect, but synthetic biologist Tal Danino had a left-field thought: What if we could create a probiotic, edible bacteria that was "programmed" to find liver tumors? His insight exploits something we're just beginning to understand about bacteria: their power of quorum sensing, or doing something together once they reach critical mass. Danino, a TED Fellow, explains how quorum sensing works -- and how clever bacteria working together could someday change cancer treatment.

Subtle motion happens around us all the time, including tiny vibrations caused by sound. New technology shows that we can pick up on these vibrations and actually re-create sound and conversations just from a video of a seemingly still object. But now Abe Davis takes it one step further: Watch him demo software that lets anyone interact with these hidden properties, just from a simple video.

In the United States, two institutions guide teenagers on the journey to adulthood: college and prison. Sociologist Alice Goffman spent six years in a troubled Philadelphia neighborhood and saw first-hand how teenagers of African-American and Latino backgrounds are funneled down the path to prison — sometimes starting with relatively minor infractions. In an impassioned talk she asks, “Why are we offering only handcuffs and jail time?”

Five things you need instead.