'Increasingly looking inward'
While Hawking spoke of his lack of belief in God during his life, several of his other answers are more surprising.
"There are forms of intelligent life out there," he writes. "We need to be wary of answering back until we have developed a bit further."
And he leaves open the possibility of other phenomena.
"Travel back in time can't be ruled out according to our present understanding," he says. He also predicts that "within the next hundred years we will be able to travel to anywhere in the Solar System."
"He realized that people specifically wanted his answers to these questions," the scientist's daughter, Lucy Hawking, who helped complete the book, told CNN.