A Brief History of Time
Hawking also talks about light. He says that events can be described by light cones. The top of the light cone tells where the light from the event will travel. The bottom tells where the light was in the past. The center of the light cone is the event. Besides light cones, Hawking also talks about how light can bend. When light goes past a big mass, like a star, the light changes direction slightly towards the mass.