Posing the question to one hundred and fifty of the world's leading scientists and thinkers, this collection of responses reveals what about the present or the future worries each of them the most.

"EDGE.ORG presents original ideas by today's leading thinkers"--Cover.

The real risk factors for war / Steven Pinker -- MADness / Vernor Vinge -- We are in denial about catastrophic risks / Martin Rees -- Living without the Internet for a couple of weeks / Daniel C. Dennett -- Safe mode for the Internet / George Dyson -- The fragility of complex systems / Randolph Nesse -- A synthetic world / Seirian Sumner -- What is conscious? / Rimo Hannay -- Will there be a singularity within our lifetime? / Max Tegmark -- "The singularity" : there's no there there / Bruce Sterling -- Capture / Charles Seife -- The triumph of the virtual / Mihaly Csikszentmihalyi -- The patience deficit / Nicholas G. Carr -- The teenage brain / Sarah-jayne Blakemore -- Who's afraid of the big bad words? / Benjamin Bergen -- The contest between engineers and druids / Paul Saffo -- "Smart" / Evgeny Morozov.