Theoretical physicist Brian Greene reveals why string theory could explain everything, whether we're living in a simulation, and why humanity's brief window of consciousness in cosmic history gives life profound meaning. From time travel possibilities to AI consciousness to the ultimate heat death of the universe, Greene explores the biggest unsolved questions in science and philosophy with accessible clarity. String theory proposes that reality's fundamental building blocks are vibrating filaments called strings, with different vibration patterns producing all particles and forces in the universe.