Many thanks to Sabine Hossenfelder for her efforts to debunk the attempt to use Hawking’s death as a platform for multiverse hype. See her posting at Backreaction for a good explanation of what is going on here.
To summarize the problem, there are loads of news stories out there telling the public that Stephen Hawking’s ‘breathtaking’ final multiverse theory completed two weeks before he died, Stephen Hawking’s Final Paper Proposes Way to Detect the ‘Multiverse’, etc., etc. Cosmologist Carlos Frenk and theorist Thomas Hertog seem to be among those encouraging this nonsense.
This is all based on this recent paper by Hawking and Hertog, which contains nothing like a way to “detect the ‘Multiverse'”. It’s a toy model of bubble universe formation, one the authors admit they can’t even solve:
However, the setup we have considered does not allow us to describe the transition from the quantum realm of eternal inflation to a universe in the semiclassical gravity domain. This is because our duals are defined in the UV and live at future infinity. It therefore remains an open question whether the conjectured smoothness of global constant density surfaces impacts the eternity of eternal inflation. To answer this will require a significant extension of holographic cosmology to more realistic cosmologies
Their calculations inspire them to state: “… we conjecture that eternal inflation produces universes that are relatively regular on the largest scales”, but this is just an extremely vague conjecture without much backing it. Using it to get press stories published claiming to have found a way to “detect the ‘Multiverse'” is just absurd, and it’s sad to see Hawking’s passing memorialized with a cloud of ridiculous hype.
Update: Another detailed explanation of what is going on here, from Ethan Siegel. His summary:
There are no observable consequences; there is nothing to measure; there is nothing to test. There’s no prediction about the end of the Universe, and there are no robust conclusions we can draw about its beginning. There are tremendous limitations to the implications of this work, and there are few compelling reasons to believe that their toy model has relevance for our physical Universe. It is a seed of an idea that itself is controversial, based off of an also-controversial foundation, and this is a very small step in its development. Furthermore, all of what they do is based on the Hartle-Hawking no-boundary conjecture, which is still not generally accepted as true. The authors go so far as to admit, in the discussion of this paper, that even within their toy model, they have not shown that there is a non-Multiverse-inducing exit to eternal inflation:
“It therefore remains an open question whether the conjectured smoothness of global constant density surfaces impacts the eternity of eternal inflation.”
Right up there with claims by certain religious groups that Hawking, an avowed atheist, had a death-bed conversion to Christianity.
I think this one should win the theoretical physics equivalent of the Razzie Awards for the years best (most shameless) hype.
I’ve lost all trust in sound (or text) bites culled from interviews without seeing the full transcript, so I’m not sure what to conclude about Hertog. It’s common to see mountains made of molehills, but can’t remember so much popsci press about literally nothing in quite a while. Powerful is the dead celebrity.
I would have figured a claim that the multiverse is perhaps less profligate and more prosaic than some models suggest could fuel plenty of Mania without the added layer of fabrication. Apparently that’s not enough for the necrophiles out there.
“Right up there with claims by certain religious groups that Hawking, an avowed atheist, had a death-bed conversion to Christianity.”
I would argue that Hertog’s claims are worse than the death-bed conversion stories. First of all, nobody takes those deathbed conversion stories seriously. They don’t undermine who the person portrayed themselves as being. Hawking’s earlier works used a lot of language that indicated he was open to some kind of deism or pantheism (see A Brief History of Time). Later on, he disavowed himself of any religious belief or agnosticism and claimed that his physics research completely ruled out the possibility of a belief in God. So he was an atheist. He knew he was, we knew he was.
This paper, however, is crap and it undermines people’s confidence in the scientific enterprise. Nobody really cares if you believe in God. Some physicists do, some physicists don’t, and many simply just don’t care one way or the other. This bizarre, and bogus, multiverse claims subject the scientific discipline to ridicule. It’s worse than bad science fiction, because we are at a crossroads in society where there is a real risk that people will stop believing in science.
LMMI,
From the press stories, hard to tell what Hertog’s role in this is. But Hossenfelder’s posting has an extensive quote from him (not sure of source, email to her?) which explicitly makes the sort of claims that led to the bogus headlines.
It’s rather weird how a paper whose abstract says “the exit from eternal inflation does not produce an infinite fractal-like multiverse” becomes a whoooo multiverse! story. Sure, they’re arguing for a multiverse of their own flavor (“a much more limited set of possible universes”), but from a distance, it looks like a bucket of cold water on the idea that an extravagance of bubble universes is the natural and inevitable conclusion from orthodox cosmology. The headline could just as well have been, “In final paper, Hawking cuts multiverse down to size”.
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