The single existential risk that Tegmark worries about most is unfriendly artificial intelligence. That is, when computers are able to start improving themselves, there will be a rapid increase in their capacities, and then, Tegmark says, it’s very difficult to predict what will happen.

…

"Longer term—and this might mean 10 years, it might mean 50 or 100 years, depending on who you ask—when computers can do everything we can do," Tegmark said, "after that they will probably very rapidly get vastly better than us at everything, and we’ll face this question we talked about in the Huffington Post article: whether there’s really a place for us after that, or not." I imagined glances from nearby museum-goers.