Bill Joy says he thinks the probability of a “civilization-changing event” is most likely in the double digits, perhaps as high as 50 percent.

He doesn’t merely ascribe these odds to terrorism; he suggests a pandemic disease might arise from a sudden accident or as a consequence of cutting-edge research. For disquieting evidence, he points out that a couple of years ago scientists assembled polio in a lab.

He says he believes that businesses doing research in areas deemed risky by their peers should be forced to take out insurance against catastrophes. He also says that science guilds should have the authority to limit access to potentially dangerous ideas.