Stephen Hawking's final paper: Not a fan of the multiverse

According to the last paper published by Stephen Hawking, our universe is simpler than previously imagined. The paper went by the name "A Smooth Exit from Eternal Inflation?" and it was authored by Stephen Hawking and Thomas Hertog. In this paper, Hawking and Hertog describe a reality in which our observable universe emerged from a larger, unobservable universe dictated by eternal inflation.

Much like popular explanations of multiple iterations of characters in comic books, theorists suggest the possibility of infinite universes – the multiverse. This theory isn't so simple as it's made in comics – it's not as if we've just got a bunch of versions of our Earth floating around out there somewhere. Instead, these multiverses likely have different rules of physics, and their own, smaller-scale inflation might still be occurring.

"The usual theory of eternal inflation predicts that globally our universe is like an infinite fractal, with a mosaic of different pocket universes, separated by an inflating ocean," said Hawking in an interview in the latter half of the year 2017. "The local laws of physics and chemistry can differ from one pocket universe to another, which together would form a multiverse."

The paper produced by Hawking and Hertog suggests the possibility of a limited number of universes in our multiverse. Their theory also suggests that the start of our universe (the one we're in right now, not the larger eternal inflation) is finite – and that we're not really meant to be working with the infinite fractal structure suggested by eternal inflation on our smaller universe's scale.

"We are not down to a single, unique universe," said Hawking, "but our findings imply a significant reduction of the multiverse, to a much smaller range of possible universes." That'd mean a testable set of predictable, observable elements with which to test this theory.

It doesn't mean we've got a comic book multiverse – but it does mean it's possible we've got the possibility of observable elements that COULD support this new theory. As Hawking and Hertog suggest in the paper, "The detailed exit from eternal inflation is encoded in the coupling between the field theory degrees of freedom on the exit surface and the classical bulk dynamics."

In other words – more work needs to be done. This remains a theory, and until we've got the ability to time-trip through the multiverse on a comic book-like level, we won't know for sure!

For more information on this data, have a peek at ARXIV in the Cornell University Library where the paper "A Smooth Exit from Eternal Inflation?" can be found. This paper was authored by Stephen W Hawking and Thomas Hertog, and can be found with code arXiv:1707.07702v3 [hep-th] (that's version 3).