Part 11/23:
He employs a metaphor from Hawking: beyond the North Pole, asking for a "further north" makes no sense—the same logic applies to time at the universe's origin. If time began at the Big Bang, then asking what came before is a category error. Alternatively, if a larger multiverse exists, then our universe may be just one bubble in an infinite expanse.
Dark Energy, Cosmic Expansion, and the Role of Gravity
Greene explains that Einstein's equations accommodate the possibility of repulsive gravity—an idea with enormous implications for the universe's evolution. Observations since 1998 reveal that the universe's expansion is accelerating, driven by a mysterious form of energy called dark energy.