From Copernicus to Darwin, to current-day thinkers, scientists have always promoted theories and unveiled discoveries that challenge everything society holds dear; ideas with both positive and dire consequences. Many thoughts that resonate today are dangerous not because they are assumed to be false, but because they might turn out to be true. What do the world's leading scientists and thinkers consider to be their most dangerous idea? Through the leading online forum "Edge" (www.edge.org), the call went out, and this compelling and easily digestible volume collects the answers. From using medication to permanently alter our personalities to contemplating a universe in which we are utterly alone, to the idea that the universe might be fundamentally inexplicable, "What Is Your Dangerous Idea?" takes an unflinching look at the daring, breathtaking, sometimes terrifying thoughts that could forever alter our world and the way we live in it.

Political scientists often ask themselves what might have been if history had unfolded differently: if Stalin had been ousted as General Party Secretary or if the United States had not dropped the bomb on Japan. Although scholars sometimes scoff at applying hypothetical reasoning to world politics, the contributors to this volume--including James Fearon, Richard Lebow, Margaret Levi, Bruce Russett, and Barry Weingast--find such counterfactual conjectures not only useful, but necessary for drawing causal inferences from historical data. Given the importance of counterfactuals, it is perhaps surprising that we lack standards for evaluating them. To fill this gap, Philip Tetlock and Aaron Belkin propose a set of criteria for distinguishing plausible from implausible counterfactual conjectures across a wide range of applications. The contributors to this volume make use of these and other criteria to evaluate counterfactuals that emerge in diverse methodological contexts including comparative case studies, game theory, and statistical analysis. Taken together, these essays go a long way toward establishing a more nuanced and rigorous framework for assessing counterfactual arguments about world politics in particular and about the social sciences more broadly.