Just about ten years ago, my April 1 posting here was a fantasy about the Stanford ITP getting major funding from the Templeton Foundation, using it to fund a program on the multiverse, and renaming themselves the Stanford Templeton Research Institute for Nature, God and Science. The last part hasn’t yet come true yet, but I just noticed the announcement last year of a $878K Inflation, the Multiverse, and Holography grant from Templeton to the SITP, the third part of “A three component Templeton Initiative at the Stanford Institute for Theoretical Physics.”
To get some idea of the scale of this funding, note that the entire NSF budget for theoretical HEP is about $12 million (the DOE spends about $50-60 million, but that supports groups at the labs, as well as computational hardware, and is decreasing). The Templeton Foundation has an endowment of over $3 billion (growing rapidly), and pays out over $100 million in grants/year (also growing rapidly). I don’t think my skills as a fantasist are good enough to imagine what this means for ten years from now in the future.
In other multiverse news, the Literary Review of Canada has published a review by David Orrell of the recent Unger/Smolin book, and an exchange of letters between him and Matthew Kleban. I wrote something about the book here, and I’m in many ways not very sympathetic to the point of view of Orrell and Unger/Smolin, especially about the role of mathematics in physics.
I’m more on Kleban’s side about mathematics, but the way he paints multiverse studies as the latest scientific descendant of the mathematics-driven successes of physics of the past is highly problematic. While this is a point of view favored at Stanford and at Templeton (Kleban has a $175,000 grant from them), I don’t think it’s a defensible one. Kleban’s arguments are
More to the point is the string landscape, a relatively concrete structure believed to follow from the mathematics of string theory.
Here “relatively” is a weasel word (relative to what?), masking the fact that we don’t at all know what the structure of the string landscape is.
contrary to Unger and Smolin’s assertions, recent work indicates that current or near-future cosmological observations – specifically, the detection of positive spatial curvature – would falsify the landscape (if it is false).
The situation with the measurement of spatial curvature is that recent Planck results give |Omega_K| less than 0.005 and the expectation is that it is zero to a much higher accuracy than that, way beyond anything measurable (this is considered one of the main arguments for inflation). This “prediction” isn’t “recent”. Susskind’s book on the multiverse ten years ago gave this one bit of sign information as the only prediction of the multiverse (see here). Shortly thereafter some authors were arguing that you could get positive curvature from the string landscape (see here). I have no idea if they’re right, but in a recent paper Kleban himself writes about this:
Positive curvature would probably not completely end discussion about a multiverse but it would be very bad news for the eternal inflation/CDL bubble nucleation framework.
and I think Orrell has it right that
I would be interested to see if the detection of positive spatial curvature actually falsified the theory – wouldn’t it just adapt?
Furthermore, the theory can be used to predict the signatures of cosmic bubble collisions: violent events where two previously separate “universes” collide.
There’s no evidence at all for such “signatures”, and I don’t think there’s any plausible argument for why they’ll appear in new data given that they haven’t been seen yet (I wrote here about Kleban’s Columbia talk about this). Final data from Planck on polarization are expected soon, but this is so implausible that I’m not sure Planck will even bother to look.
The problem with this kind of “testable prediction” is that it’s much like my claiming that my theory that the universe is controlled by a giant turtle is testable and predictive, since if you saw a big picture of a turtle in the CMB, that would be strong evidence for my theory. There was a reason Popper went on about falsifiability…
the standard model of particle physics combined with Einstein’s theory of general relativity – two of the most well-established theories in physics – predict a large landscape quite similar to that of string theory.
This one brings back the “string wars” era, since I haven’t heard anyone trying to use it (based on this) since 2007. Whenever people make a “string theory is just like the standard model” argument I’m never sure what to respond. How do you argue with someone trying to claim that the most successful physical theory ever, by far, is “quite similar” to a theory that has had zero success? It’s kind of like trying to argue with someone who wants to tell you that black is white, because they’re both kinds of grey. Surely they’re not serious?
In this case, sure, if you put the standard model on a complicated space-time background, added lots of fluxes, etc. to the background, maybe you could turn it into as useless a theory as string theory. This doesn’t mean it’s “quite similar”.
Update: Just noticed another recent essay about the multiverse, Marcelo Gleiser’s examination of whether Fairies live in the multiverse.