A new theory of the universe, twenty years in the making, by Stephen Hawking and his close collaborator Thomas Hertog.
Perhaps the biggest question Stephen Hawking tried to answer in his extraordinary life was how the universe could have created conditions so perfectly hospitable to life.
Pondering this mystery led Hawking to study the big bang origin of the universe, but his early work ran into a crisis when the maths predicted many big bangs producing a multiverse - countless different universes, most of which were far too bizarre to harbour life.
Holed up in the theoretical physics department at Cambridge, Stephen Hawking and his friend and collaborator Thomas Hertog worked shoulder to shoulder for twenty years on a new quantum theory of the cosmos. As their discoveries took them deeper into the big bang, they were startled to find a deeper level of evolution in which the physical laws themselves transform and simplify until particles, forces, and even time itself fades away. Once upon a time, perhaps, there was no time. This led them to a revolutionary idea: the laws of physics are not set in stone but are born and co-evolve as the universe they govern takes shape.