In Adrian Cho’s interpretation at Science:
When Stephen Hawking died on 14 March, the famed theoretical physicist had a few papers still in the works. Today, the Journal of High Energy Physics published his last work in cosmology—the science of how the universe sprang into being and evolved. (Other papers on black holes are still being prepared.) In the new paper, Hawking and Thomas Hertog, a theoretical physicist at the Catholic University of Leuven (KU) in Belgium, attempt to stick a pin in a bizarre concept called eternal inflation, which implies—unavoidably, according to some physicists—that our universe is just one of infinitely many in a multiverse. Borrowing a concept from string theory, Hawking and Hertog argue that there is no eternal inflation and only one universe. But what they’re driving at is something even more basic: They’re claiming that our universe never had a singular moment of creation.
Most sources have focused on the “no Big Bang” aspect, probably because eternal inflation is Cool but the Big Bang is not. So this aspect of his theory is not so much discussed.
The problem with cosmic inflation:
At the most basic level, the existence of all these other universes wouldn’t affect our universe. They’re just too far away to have any connection with ours. On the other hand, the notion of eternal inflation and a multiverse may thwart cosmologists’ entire enterprise of explaining why the universe is the way it is, Hertog says. Things like the values of certain key physical constants could vary randomly among the pocket universes, he says, which would render moot any effort to explain why they have the values they do in our universe. They would be set by random chance, Hertog says, and that’s not very satisfying. More.
The jury is out on their solution, which gets rid of time as well as the Big Bang. Interesting to learn that there are other posthumous papers in the works.
See also: Stephen Hawking’s final theory scales back multiverse
Cosmic inflation theory loses hangups about the scientific method
Does the beginning of the universe require a cause? Alexander Vilenkin says no. William Lane Craig says yes.
The Big Bang: Put simply,the facts are wrong.
Hat tip: Ken Francis