Indeterminacy.....................................

Turing was particularly interested in the math at the core of quantum physics, which described how events at the subatomic level are governed by statistical probabilities rather than laws that determine things with certainty.  He believed (at least while he was young) that this uncertainty and indeterminacy at the subatomic level permitted humans to exercise free will - a trait that, if true, would seem to distinguish them from machines.  In other words, because events at the subatomic level are not predetermined,  that opens the way for our thoughts and actions not to be predetermined.

-Walter Isaacson,  The Innovators:  How a Group of Hackers, Geniuses, and Geeks Created the Digital Revolution