Time
For Hawking, time is an interesting, complex and bewildering concept. He often refers to the pursuit of understanding what time really is, and whether it is possible to time travel. For example, he asks "if time travel is possible, where are the tourists from the future?" He also says that "only time (whatever that may be) will tell," which creates a humorous spin on his question of what time really is. He suggests that the majority of people take this for granted in their daily lives, but we should really question those concepts we think we understand, like space and time.
Tortoises
Hawking refers to a story where a scientist is asked an interesting question after a lecture: “A well-known scientist (some say it was Bertrand Russell) once gave a public lecture on astronomy. He described how the earth orbits around the sun and how the sun, in turn, orbits around the center of a vast collection of stars called our galaxy. At the end of the lecture, a little old lady at the back of the room got up and said: "What you have told us is rubbish. The world is really a flat plate supported on the back of a giant tortoise." The scientist gave a superior smile before replying, "What is the tortoise standing on?" "You're very clever, young man, very clever, " said the old lady. "But it turtles all the way down!"
Afterward, Hawking says that "most people would find the picture of our universe as an infinite tower of tortoises rather ridiculous, but why do we think we know better?" Here, Hawking uses tortoises to make us question and challenge what we passively understand to be the truth.
The mind of God
Hawking states that when we truly understand why humanity and the universe exist, we will understand "the mind of God." As he makes clear during the text, Hawking is not religious, and he therefore does not mean the Christian concept of God. Instead, the mind of God symbolizes omnipotence, and an entire understanding of the universe in the way that the God of the religion typically has.
