Bill Gates and Warren Buffett have had immeasurable impact on the world, but what would they do if they lost everything and had to start over? Gates, who dropped out of Harvard to start Microsoft in the 1970s, says that if he were to begin again, he would devote himself to either artificial intelligence, energy or biology. "The work in artificial intelligence today is at a really profound level," says Gates, speaking at a Facebook live event broadcast from Columbia University and moderated by Charlie Rose . "It is going to be phenomenal, so anything connected with that I think would be an exciting lifetime career." The planet needs to find reliable, cheap and clean energy, Gates says, so "the innovations there will be profound."