Did Stephen Hawking prove the multiverse? That is what many media outlets have asked when introducing "A Smooth Exit From Eternal Inflation?" Hawking's final paper before he passed away on March 14, 2018.
His last 16-page work of quantum mechanics has been touted as something that either proves or disproves the existence of the multiverse, but it’s not as definitive as many news outlets would have you think. While “A Smooth Exit…” certainly discusses the multiverse, it’s purely from a theoretical standpoint.
The paper is more about creating a working model of a mathematical equation to measure the other universes hypothetically formed after the Big Bang. Rather than being a defining statement, Hawking’s final work is more of a question being posed to the scientific community.
So no, Hawking did not prove the multiverse, but that was never his intention in the first place. Instead, he was trying to help build a new model for the evaluation of those things which we cannot - and likely will not - ever be able to see.
Despite the reverence surrounding Hawking's final paper, there's very little definitive information included in it. The paper, co-authored with Thomas Hertog, a physicist at the Catholic University Leuven (KU Leuven) in Belgium, doesn't provide any solid answers so much as it provides a new possibility within an area in which Hawking was already working.
Hertog told Live Science Hawking was still wrestling with many of the theories and ideas he'd written about in the past. When Hawking contacted his co-author, he suggested they "try to tame the multiverse."
That's a great pull quote, but it's not exactly what the duo did. Instead, they worked on creating "a method to transform the idea of a multiverse into a coherent testable scientific framework."
Hawking's death was unfortunate and devastating for a multitude of reasons, and the fact he was still performing revisions on his final paper is just one of them. Hawking had already made a series of revisions to the paper a week before his death, and it's likely that he would have made another series of changes if he had the time.
The paper is available online (it's still in peer review as of this writing) and it's a fascinating, brief read. Knowing that Hawking had revised his work mere days before his death makes one wonder what else he was thinking about changing.
One of the most misleading things about all of the articles written about Hawking's final paper is the omission of the fact he wasn't the only scientist researching this kind of theoretical measuring tool; there's an entire group of scientists who are using the holographic principle to understand the boundaries of time and space.
In an interview with Discover Magazine, Clifford Johnson, a professor in the Physics and Astronomy Department at the University of Southern California, says the final Hawking paper is one of many that essentially say the same thing.
Johnson said, “It’s two very good researchers adding a paper to the many very good papers that have been incrementally moving this framework of ideas."
To say that "A Smooth Exit From Eternal Inflation?" disproves or proves anything is to miss the point of the paper, which is simply trying to define an abstract concept in terms humans can understand.
Hawking and Hertog scaffolded the idea of a multiverse by scaling back the number of worlds from infinite to just those that come from a "smooth" universe like ours. If the two were working off the theoretical universes that don't adhere to our universe's classical physics, the multiverse would lead to a paradox: with an infinite number of universes (and an infinite number of variations on classical physics laws, like the speed of light), nobody would be able to make scientifically testable predictions concerning any of the universes.
This method wasn't even created to say there aren't an infinite number of universes; it was applied in order to give the scientists a set of constraints from which they could go about predicting what the universes looked like. This is what Hawking meant by "taming the multiverse" - he was giving the science community the beginning of framework in which to work.