About That Smoking Gun…

Posted on May 13, 2015 by woit

Aeon magazine has just published a long piece on the current state of cosmology by Ross Andersen. One focus is on Paul Steinhardt and his claims that the popular multiverse/eternal inflation scenario doesn’t explain what it is supposed to, and is compatible with almost any experimental result. The BICEP2 fiasco, where multiverse proponents first claimed a “smoking gun” vindication from B-modes, then went on to claim that no B-modes was just as good for their theory once they disappeared, is the main topic of the article (for a previous posting about this, see here).

That’s why Steinhardt was surprised to see inflationary theorists clinking glasses when BICEP2 announced a high swirls figure. ‘They declared victory,’ he told me. ‘They said it was smoking-gun proof! Just what they expected!’

But then a few months passed and BICEP2’s interpretation started to look wobbly. In June, Linde told New Scientist that he didn’t like the way BICEP2’s swirls were being treated as a smoking gun for inflation. In July, Guth made similar statements to the Washington Post. Steinhardt was furious. He thought it was flip-flopping. He began to wonder if any data would disturb the serene certainty of inflationary theorists. ‘It was Andre Linde who used the “smoking gun” language in the first place,’ he told me. ‘Now he says it doesn’t make a difference what BICEP2 says. How can it be that not seeing gravitational waves is fine, and then seeing them is a smoking gun, and then not seeing them is fine again?’

Steinhardt explains that the underlying problem is that the underlying problem is an inherently untestable paradigm, compatible with anything:

The theory’s weaknesses can be explained away with the same glib shrug that accompanies the retort: ‘God just made it that way.’

A dominant, infinitely flexible multiverse theory could make it easy not to strain for the next leap forward. It could lead to a chilling effect on new ideas in cosmology, or worse, a creative crisis. Steinhardt thinks we’re already there. ‘Andre Linde has become associated with eternal inflation because he thinks the multiverse is a good idea,’ he told me. ‘But I invented it, too, and I think it’s a horrible idea. It’s an emperor’s new clothes story. Except in that story, it’s a child who points out that the Emperor has no clothes. In this case, it’s the tailors themselves telling us that the theory is not testable. It’s Guth and Linde.’

His hope for how the subject will get saved from itself is with help from philosophers:

‘The outside community isn’t recognising the problem,’ he said. ‘This whole BICEP2 thing has made some people more aware of it. It’s been nice to have that aired out. But most people give us too much respect. They think we know what we’re doing. They take too seriously these voices that say inflation is established theory.’

I asked him who might help. What cavalry was he calling for?

‘I wish the philosophers would get involved,’ he said.

That might help, but I think other ideas are needed…

Posted in Multiverse Mania | 33 Comments

The Admiral of the String Theory Wars

Posted on May 7, 2015 by woit

The science magazine Nautilus this month has a profile of me, under the title The Admiral of the String Theory Wars. The writer, Bob Henderson, spent a lot of time talking to me and other people around here, including attending my class. I think he did a very good job of handling the complex topic of the debate over string theory, not so easily done in the context of this kind of personal story. Then again, I guess I would think that since he was mainly hearing my point of view, others may see this very differently…

Talking to Henderson brought back memories of a lot of the very odd things that happened during this period, now nearly ten years ago. I also recently realized that this week is the 10th anniversary of the date on which I sent off the final version of “Not Even Wrong” to the publisher (it then went to copy editing, was published a year later). Looking back at it now, I don’t see much that I’d change. The earliest version of the manuscript written around 2003 didn’t discuss the landscape and multiverse business, which only really got going in 2004. By 2005 I did add a chapter on this, but at the time thought doing this might be a bit unfair to string theorists. Surely they were all aware this was obvious nonsense and would quickly themselves put a stop to it. I was very wrong about that and, oddly, it’s over this argument (where I would have thought my point of view was uncontroversial) that I’ve gotten the most grief from certain prominent string theorists (e.g. Polchinski).

For the latest in the string wars, you can watch last night’s Perimeter Institute public lecture by Amanda Peet. It was a promotional effort that reminded me a lot of the kind of thing you see on late night TV, with an inspirational speaker selling a product to a rapt studio audience. The main selling points for string theory were that it “would blow your mind”, that branes explain black hole entropy (the Strominger/Vafa calculations of 20 years ago), and that the world is a hologram (Maldacena from nearly 20 years ago).

After the talk the first question read to her was the obvious one about testing these ideas experimentally. Remarkably, she claimed that string theory was testable, that published work of 10 years ago showed that it could be tested at accelerators, and so far it had passed the tests. What she was referring to was one of the weirder stories of the string wars. At the time Jacques Distler and collaborators wrote a paper entitled Falsifying String Theory Through WW Scattering, which I discussed here. They also wrote to the Wall Street Journal about this (see here). A few months later their paper was accepted by Physical Review Letters, with their claims about string theory removed, I assume at the insistence of a referee (see here). In a spectacular display of chutzpah, when the PRL paper appeared, the authors had their institutions put out press releases claiming that “Physicists Develop Test for String Theory” (see here), exactly the claim that PRL would not let them make in print. It’s this claim that Peet is now using to mislead the public at Perimeter. I think it’s their responsibility to look into this and issue a public correction. Or do they really feel that it is all right for their public lecture series to be used to mislead the public about science?

Update: I see that the Nautilus piece is part of an issue on “Error”, which also includes interesting articles about the OPERA superluminal neutrino story and about Vladimir Voevodsky.


Update: I probably should have included the relevant question and answer exchange with Peet, here it is:

Q: Any predictions or comments on how and when string theory might be able to be proven experimentally?

A:… there are experiments that can be done, this is published work that has been around for almost ten years now, that you can do experiments in nature in the lab without having to invent equipment that you haven’t invented yet that would test whether or not the assumptions of string theory are true or false. So far none of those experiments has shown a red flag that says string theory is wrong.


Update: Ethan Siegel has a blog entry and live-blogging about the Peet talk. He was hoping that Peet would discuss some sort of connection between string theory and observable physics, didn’t hear any (he seems to have missed the bogus claim about the LHC). Siegel gives an argument that string theory is in principle falsifiable, since it predicts space-time supersymmetry superpartners, although with no prediction for the mass scale. I’ve never heard this before, and I don’t know of any argument that such superpartners must appear in the spectrum of a string theory.

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First Collisions of Run 2

Posted on May 5, 2015 by woit

This morning in Geneva saw the first collisions in the revamped LHC, there’s an event display from ATLAS here, CMS here.

These collisions are just at the injection energy of 450 GeV/beam, but over the past few weeks beams have been successfully ramped up (without intentional collisions, although see page 23 here) to the planned 6.5 TeV/beam. 6.5 TeV beams have been accelerated not just with probe intensity, but with nominal bunch intensity and squeeze. They are roughly halfway through a planned 8 week beam commissioning process and on schedule, with stable beams for physics collisions still planned for around June 1. For quite a while now, 6.5 TeV/beam collisions have been possible, but no word yet on when this is planned for, I assume there will be some sort of media event at that time.

Update: Something about this from CERN here.

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Einstein’s Dice and Schrödinger’s Cat

Posted on May 2, 2015 by woit

I’ve written a review for the Wall Street Journal of Paul Halpern’s new book
Einstein’s Dice and Schrödinger’s Cat (It’s here, unfortunately now behind a paywall [commenter advice is try googling “The Half-life of physicists” and using the Google link]).
I liked the book quite a bit, and learned many things about some history I already thought I knew well. The most dramatic section of the book is the story of the 1947 trouble between Schrodinger and Einstein caused by Schrödinger’s publicity campaign for a supposed breakthrough in the search for a unified theory, and Halpern writes about that here.

The title of the book emphasizes their misgivings about the probabilistic interpretation of quantum mechanics, and describes how Schrödinger’s cat arose out of discussions with Einstein. More of the book though is actually about their efforts to generalize GR and find a unified geometrical theory of gravity and electromagnetism. This began almost as soon as the field equations for GR were in place (1915). The book’s stories of media hype for bad ideas, involving physicists given rock-star academic positions at institutes set up for them make clear that some contemporary problems go back much further than I’d ever realized.

Einstein’s later work is, for good reason, dismissed as misguided, since it ignored quantum theory. He and Schrödinger did however have good reasons for skepticism about the Copenhagen interpretation of quantum mechanics. The measurement problem has turned out to be a very subtle one, with the cat experiment a very good way of making clear the problem. Their enthusiasm for ideas about unification that weren’t working was also way ahead of their time…

Update: For some other reviews of the book, see Jennifer Ouellette in the New York Times, and Denis Weaire in Physics World.

Posted in Book Reviews | 15 Comments

Dreams of a Final (or Better) Theory

Posted on May 1, 2015 by woit

John Horgan has an interesting interview with Steven Weinberg here. Weinberg isn’t very optimistic about possible progress these days:

Horgan: In 1995 you told me that it’s a “terrible time for particle physics.” Are you feeling any better about your field now? Are there any particular advances that give you hope?

Weinberg: I’m not much more cheerful.
…
Horgan: Do you still believe in the attainability of a “final theory” of physics, one that ends what you called “the ancient search for those principles that cannot be explained in terms of deeper principles”?

Weinberg: I still expect there to be a final theory, but I’m less confident that humans will discover it in this century.

When asked about when string theory should be abandoned as a dead end he ignores that part of the question:

Horgan: In your new book, To Explain the World, you write that “scientific theories cannot be deduced by purely mathematical reasoning.” Doesn’t that principle apply to string theory? At what point, if ever, should string theory be abandoned as a dead end?

Weinberg: String theory may be inspired by mathematical reasoning, but not deduced, and certainly not confirmed.

He defends the multiverse with

Further, if we find some future theory that does make successful predictions about a lot of things, which turn out to be true rather than false, and if that theory also predicts the existence of a multiverse, then we should take that prediction seriously even though it can’t be tested directly.

which is true enough, but doesn’t address the fact that there is no such theory. The string theory landscape “prediction” of a multiverse is exactly the opposite sort of thing, not a corollary of successful predictions, but something being invoked as an excuse for failure to make predictions about anything at all.

For something more substantive, I recommend Alessandro Strumia’s theory summary for Moriond 2015. It has a lot of interesting commentary about a range of phenomenological topics. On the multiverse and anthropics he takes a quite different point of view than Weinberg:

Nobody talked about anthropics at Moriond 2015. This has an anthropic interpretation: Moriond is not in California. Clearly, social factors are playing a role, as always when experiments cannot set the issue. On one side, `having discovered the multiverse’ is physically indistinguishable from `having pursued a failed unification program’, but sounds much better. On the other side, future physicists could consider us as crazy for not having immediately accepted anthropic arguments.

He discusses “naturalness” extensively, including explaining why anthropics is no solution, since it doesn’t explain an unnaturally small Higgs mass.

Posted in Multiverse Mania | 21 Comments

Things Have Changed

Posted on April 24, 2015 by woit

I’ve been busy with other things, but after taking a look today at various new things related to quantum gravity, I was struck by how much things have changed sociologically in that subject over the last few years. Back in the days of the “string wars”, debates about quantum gravity were fiercely polarized. Oversimplifying and caricaturing the situation a bit, the two sides of the quantum gravity debate were:

  • Those interested in loop quantum gravity as well as other more exotic attempts to reformulate the problem of quantum gravity. These people just considered pure quantum gravity and devoted a lot of effort to analyzing the deep conceptual issues that arise. They sometimes considered highly speculative hypotheses, trying out abandoning the usual basic axioms, for instance replacing fundamental axioms of quantum mechanics. Lee Smolin was an influential figure, and the Perimeter Institute a major center for this research.
  • String theorists, who argued that the appearance of spin-two massless mode in the quantized string spectrum showed that string theory was the only way to understand quantum gravity. They claimed that they had a single, very specific and highly technical mathematical structure to study, which obeyed the conventional quantum theory axioms. Their efforts were devoted to specific computations in this theory, and they seemed to regard the other side of the debate as woolly thinkers, caught up in meaningless ill-defined philosophical speculation. The KITP at Santa Barbara, led by David Gross and Joe Polchinski, was a major center for this side of the debate.

These days, things have changed. If you’re at Perimeter, prominent activities include:

On the other hand, it you’re in Santa Barbara these days, you might be participating in a KITP conference on Quantum Gravity Foundations. This is featuring very little about the technical issues in superstring theory being discussed at Perimeter, but a lot of discussion of deep conceptual issues in quantum gravity. There’s also a lot of willingness to throw out standard axioms of physics, maybe even quantum mechanics. They’re even letting Carlo Rovelli talk.

The sort of speculation going on at the KITP is featured on the cover of this month’s Scientific American, and this week Quanta magazine will be publishing a series of pieces on something related, the “ER=EPR” conjecture. There’s debate whether anyone really understands this and whether it is consistent with standard quantum mechanics. It also features a diagram that people call the “octopus” diagram. Back in the day it was Lee Smolin who was getting grief for an “octopus” diagram (see here), yet another way in which things have changed.

For a more balanced view of quantum gravity issues, you might want to spend your time in France, where the IHES recently hosted an interesting series of surveys of the subject (see here), and the Quantum Gravity in Paris conference featured more specialized talks. In the category of quantum gravity topics I wish I had more time to learn about, Kirill Krasnov’s talk was presumably related to this recent work, which looks intriguing.

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The Lady Gaga of French Mathematicians Comes Stateside, and Other News

Posted on April 15, 2015 by woit

Cédric Villani is in town today, giving a talk at the French consulate. He’ll discuss his book, recently translated into English (I wrote a bit about it here). Yesterday, despite the lack of suitable bread and cheese, he was in Princeton, where he gave a public lecture at the IAS. The New Yorker has a story about him by Thomas Lin, entitled The Lady Gaga of French Mathematicians Comes Stateside.

If you’re not listening to Villani tonight, you could be watching a PBS Nova program on mathematics, The Great Math Mystery. Among the mathematicians interviewed will be my colleague Dusa McDuff. As for the question on the PBS site:

Is math a human invention or the discovery of the language of the universe?

the answer is the latter.

What some mathematicians might consider the “Great Math Mystery” is whether Mochizuki really has a proof of the abc conjecture. There finally will be the topic of a workshop involving experts in the field, to be held this December in Oxford. Still no paper from Go Yamashita about this, but here you can find some photographs of the boards from his talks in Kyoto last month. Mochizuki himself has a new paper, inspired by conversations with Fesenko.

Also in New York this week, Bjorn Poonen will be speaking on Thursday. His topic is a heuristic argument that there is a finite bound on the rank of elliptic curves. For notes from a talk of his about this last year, see here.

Update: The Villani IAS talk is available here.


Update: At David Mumford’s blog he has a long and very interesting posting about the state of mathematical research publishing.

Update: One more piece of math news. Dan Rockmore has set up a public version of his Concinnitas Project, which lets people post, with explanation, a picture of their choice of a “most beautiful mathematical expression”. See here for details.

Posted in Uncategorized | 25 Comments

LHC News

Posted on April 9, 2015 by woit

The LHC has just ramped up for the first time to 6.5 TeV, and has a probe beam circulating in one direction, the highest energy protons humans have ever accelerated. You can follow what’s happening here.

The BBC has gotten very excited about this whole LHC thing.


Update: Now it’s two beams at 6.5 TeV. They just need to be careful to avoid beam collisions until the press event is organized…

Update: Maybe they weren’t careful enough. The Monday morning beam commissioning reports “Possibly first collisions”. No confirmation of this from the experiments, or officially from CERN.

Posted in Uncategorized | 17 Comments

News of the Multiverse

Posted on April 8, 2015 by woit

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.

Posted in Multiverse Mania | 35 Comments

Various News

Posted on March 31, 2015 by woit

Some news from all over:

  • The problem with a short in the LHC seems to have been resolved (one can follow progress here), looks like they’ll be ready to inject a beam in a few days. Also looks like they’re not likely to spend their Easter Sunday doing this, so, maybe it will be next Monday?
  • Cambridge has finally gotten around to choosing a new Lucasian professor (the last two were Michael Green and Stephen Hawking). Michael Cates will take the position July 1.
  • Grothendieck’s death last year was sad to hear about, but a positive result is that the Grothendieck Circle is back in the business of making available resources concerning his work. There’s a comment at the top of the website that

    With the agreement of Grothendieck’s family, the work of the Circle to bring Grothendieck’s unique story and writings to the public has resumed.

  • There was a workshop this past month devoted to Mochizuki’s work, but I haven’t found anyone who knows what happened there. Minhyong Kim has taken to trying to write about Mochizuki’s ideas on MathOverflow, see here.
  • The Toronto Star has a long article about Langlands.
  • At the KITP this week a new program on quantum gravity is starting. This month’s Scientific American has a Joe Polchinski cover story on Burning Rings of Fire. Maybe some of the KITP talks will be enlightening, but the small amount of time I’ve spent trying to follow the past two years of debate on this has just left me mystified, struggling to see how the very general framework people seem to be working in can possibly lead to a resolution of the questions they’re concerned with.
  • Frank Wilczek has a speculative article about Physics in 100 years. A commenter here suggests comparing it to Wilczek’s version of nearly fifteen years ago. The last fifteen years have not been kind to Wilczek’s hopes for vindication of SUSY or SUSY GUTs, but he’s not giving up yet. It will be interesting to see what his reaction will be if the next fifteen years are equally discouraging.

    I do very much like one thing in the new version, the section about possible unification of ideas of quantization and of symmetry, where he speculates:

    Quantization and fundamental symmetry will not appear as separate principles, but as two aspects of a deeper unity.

    That’s pretty much one of the main motivations of the book I’m writing (see here).

Update: There are rumors going around tonight that there’s been a hoax perpetrated on the arXiv, something like the Sokal hoax. This has to do with an hep-th posting entitled Riding Gravity Away from Doomsday, which has appeared under the name of a very prominent string theorist, Ashoke Sen, winner of the $3 million Milner Fundamental Physics Prize. What I’m hearing is that no one can believe that Sen could possibly have seriously written something this silly, so it must be some sort of hoax. Speculation is that the hoax could have been carried out to make the hep-th moderators look bad, by showing that they’ll agree to anything, no matter how absurd, if it invokes the Landscape and the multiverse. Some think that Sen’s account must have been hacked and then used to post the nonsense paper, others think that Sen himself is behind the hoax, having had enough of the Landscape business. I’ll update this as more information becomes available.

Update: At least some papers on the arXiv still are serious.

Update: Beams are back in the LHC, successfully circulated at 450 GeV on Easter Sunday (live blog here). Next step, ramp up to 6.5 TeV.

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