The first project is to build an artificial brain from scratch that can pass a high school science test. It sounds simple enough, but trying to teach a machine not only to respond but also to reason is one of the hardest software-engineering endeavors attempted — far more complex than building his former company’s breakthrough Windows operating system, said to have 50 million lines of code.

The second project aims to understand intelligence by coming at it from the opposite direction — by starting with nature and deconstructing and analyzing the pieces. It’s an attempt to reverse-engineer the human brain by slicing it up — literally — modeling it and running simulations.