Nature at the energy frontier

Posted on June 12, 2013 by woit

Last week a symposium on Nature at the energy frontier was held at the ETH in Zurich, funded by the Latsis foundation. Videos of many of the talks have appeared here.

As part of the symposium, David Gross gave a public talk, available here. Gross is often invited to give such talks, and I’ve either attended or taken a look at the video for quite a few of them. The first substantive posting on this blog back in 2004 was about one such talk. Back then, Gross was claiming that in 3-4 years there would be a headline in the New York Times about the discovery of supersymmetry at the LHC (he was overly optimistic about how long it would take to get the machine working properly). I wondered at the time:

What will be interesting to see will be what Gross et. al. do when this doesn’t happen. Will they drop string theory?

In all of the talks I’ve seen since that time, Gross continued to express optimism, including willingness to bet significant sums of money on a discovery of superpartners at 50/50 odds. His talk at the Latsis symposium included a remarkable change of tone, featuring an Einstein quote I hadn’t seen him use before:

The successful attempt to derive delicate laws of nature, along a purely mental path, by following a belief in the formal unity of the structure of reality, encourages continuation in this speculative direction, the dangers of which everyone vividly must keep in sight who dares follow it.

He describes Einstein as both encouraging the kind of speculative path followed by string theory and SUSY, while at the same time warning of its dangers, and noted that Einstein himself devoted the latter part of his life to a speculative path that turned out to be a dead end.

In his explanation of the standard arguments for string theory and SUSY, Gross was much more cautious than in the past, careful to explain that these arguments were based on just speculative “clues”. These clues might just be coincidences, but the main reason for not giving up on them was that we don’t really have any others.

About the LHC results, Gross described them as having now ruled out the simplest SUSY models, which could be a clue that SUSY does not exist. He said that if SUSY is not seen at the LHC, we will learn for sure that theorists have been on the wrong track for many decades. According to him, this would “change a lot of our way of thinking”, since “we have been pursuing these clues for a long time.” He didn’t discuss how ways of thinking will change, although he is well known to strenuously reject one popular idea about this (anthropics and the multiverse).

Erik Verlinde gave an odd talk with a title that promised to address these issues, String Theory and the Future of Particle Physics. He explained the history of string theory and how the original hope was that it would tell us where the SM parameters came from, something which “looks differently now”. According to him, the idea of strings moving in a compactified 10d was the “old view”, now made obsolete by branes. The “present view” is all about gauge-gravity duality, which doesn’t say anything about those SM parameters. According to him the “future view” of string theory will somehow start from some new basic principles that we don’t know yet, providing an underlying microscopic description that will explain holography, and give an “emergent” explanation of space, time, matter, etc. There was no explanation at all of what these new principles were or what the new microphysical description would be. String theory itself would just be an “effective theory”, like the Standard Model.

After this introduction, Verlinde than moved on to something that seems to have nothing at all to do with string theory, giving a long explanation of how he thinks there are some new degrees of freedom out there that have dynamics at long time scales. These should be treated by the methods of polymer dynamics, and they will explain dark matter and dark energy. He produced lots of graphs of astrophysical data, and claimed that he has an “extension” of Newtonian gravity, better than MOND, which explains the astrophysical data. At the end of the talk there were a bunch of questions about the cosmological implications of this, I couldn’t tell if Verlinde had an answer. He has been talking about this idea in public talks for a couple years now, although as far as I can tell there is no paper. Also, as far as I can tell, no one else besides him takes this seriously.

The last talk of the conference was from Nima Arkani-Hamed, giving basically the same talk I’ve written about recently here and here. I confess to not listening to the whole thing, since it was quite familiar (although I did notice he addressed the question of the possibility there wasn’t really a hierarchy problem, saying people who raised that were “frustrating”, since he had thought about it for decades, and “trust me, there’s a hierarchy problem”). In the question session, he made the same point I often end up arguing with string theory proponents about, saying (1:14) that if “you can do experiments at the string scale, wouldn’t help you at all”. The idea that you would see string excitations on a compactified space he characterizes as a misguided old idea from the 1990s. If there’s a landscape, the possibilities are so complex for Planck scale behavior that you can’t predict what experiments at that scale would see. I’m glad to see that now instead of getting into arguments like this one, I can send people to go argue with Nima.

Posted in Uncategorized | 33 Comments

Simons 75th Birthday Conference

Posted on June 3, 2013 by woit

Last week the CUNY Graduate Center hosted a conference in honor of the 75th birthday of Jim Simons. It was organized by Dennis Sullivan as a set of expository “mini-courses” on various topics related to Simons’ mathematical work. I was able to attend the morning talks, which were of a uniformly high quality, and focused on the Chern-Simons 3d QFT, as well as the “differential characters” of Cheeger and Simons. Video of most of the talks is available online here. In particular, Witten’s talk, which was a very simple physical introduction to use of the Abelian Chern-Simons term in condensed matter, is available here (followed by Deligne on Deligne-Beilinson cohomology). Talks by Robbert Dijkgraaf on Chern-Simons-Witten theory are here and here. The second Dijkgraaf talk was followed (go to 1:05) by some informal comments by Simons himself, explaining the history of how Chern-Simons came about. Mike Hopkins gave two wonderful talks, the first about differential characters in general and about his recent article with Dan Freed, the second about his work with Singer that used generalized differential cohomology.

The talks I missed were likely just as good, I’m starting to catch up on them on video now….

Posted in Uncategorized | 5 Comments

Snowmass on the Pacific

Posted on June 1, 2013 by woit

Due to popular demand from the comment section, I spent some time this afternoon taking a look at the talks now posted from the KITP Snowmass on the Pacific conference held the past few days. This is part of an ongoing project for a US HEP Community Summer Study that will culminate at a meeting in Minneapolis later this summer. The US HEP community faces serious questions about what priorities for the future should be in an environment of flat-to-declining budgets, no energy frontier projects in the US, and discouraging news from the LHC about no evidence for BSM physics.

The KITP talks cover a wide range of topics, and I haven’t had a chance to look at very many of them. For theorists, one interesting session was the Wednesday panel on Structural Issues for Theorists, which featured presentations by and discussions with the people at DOE and NSF responsible for HEP theory grants (Simona Rolli and Keith Dienes). There’s a lot of information about the situation of US theory grants there, but I was a bit struck by the impression that despite the large problems faced by HEP in the US, for theorists things look much like they always have:

  • Budgets are pretty flat. As salaries go up with inflation, and as new young people come into the system applying for grants, it’s harder and harder for people to get the grants and grant amounts they would like.
  • The split between DOE and NSF funding of often exactly the same thing doesn’t make much sense and leaves people sometimes confused.
  • There’s always a problem finding grant support for the number of students who want to do theory, leaving theorists trying to justify to their colleagues why their students should get more of the few TA positions available. The situation of funding about 180 theory Ph.D students in an environment where there are maybe 10 tenure track jobs/year in the country isn’t deemed even worthy of comment.

Some numbers from the presentations:

  • The DOE spends roughly \$25 million/year on positions at government labs, another \$25 million/year on grants to universities (the bulk going to pay grad students/postdocs/summer salary). The NSF spends \$13-14 million/year on grants to universities, another $6 million on Frontier Centers, some of which have an HEP theory component.
  • DOE funds 49 PIs at labs, 221 PIs at universities, NSF funds 186 PIs at universities.
    The DOE split by field is 128 Phenomenologists, 73 “Formal” (often “string theory”), 42 Cosmology, 27 Lattice Gauge Theory.
  • DOE funds 123 postdocs, NSF funds 50 of them. DOE funds 130 grad students in theory, NSF 50 of them.

This stable system of government funding has been crucial in determining the structure of HEP theory in the US for the past few decades, and the academic system is built around it. I keep wondering what the effect will be as new sources of money come into the system from private sources, on scales approaching that of government funding. As a somewhat extreme example that is likely a one-time thing, last year the string theorists in Princeton got \$15 million in checks from Yuri Milner, a number somewhat larger than the entire NSF $13-14 million/year budget for HEP theory.

Posted in Uncategorized | 26 Comments

A Tale of Two Oxford Talks

Posted on May 28, 2013 by woit

Last week (for more, see here) Eric Weinstein gave a talk at Oxford about his ideas about “Geometric Unity”, with positive coverage from the Guardian, leading to various critical commentary. I agree completely with the main point of most of the commentary: if he wants to be taken seriously, Eric needs to disseminate the details of his ideas about this, as a paper, slides of a talk, multimedia web-site, or whatever. As AJ put it here succinctly: “Paper, or it didn’t happen.”

I’ve only the vaguest notion of what Eric’s ideas are, so no way to evaluate them. From this standpoint of ignorance I should comment that I’m quite skeptical he has a viable unified theory, with reports of “very large multiplets of as yet undiscovered particles, and he has no idea of their masses” not confidence inspiring. But on the other hand, the current situation in fundamental theory is one of a serious lack of any new ideas at all. If he has been working on some very different ideas that haven’t gotten attention before, he could have something interesting or even important. But, again, until details are available, there’s no way to know one way or another. By the way, I should disclose that at one point I remember having a conversation with Eric about his plans to give a talk and make public his ideas. I tried to encourage him to do this, emphasizing though that I thought his main problem would be that he wouldn’t be able to get anyone to pay attention. Shows how little I know…

Surprisingly to me, before it was clear what was going on, there was a quick and hostile reaction from some to the Guardian piece about Eric and his work. Yes, it’s a bad idea for the press to publish overly optimistic material about grandiose and poorly supported claims from physicists, but this does happen all the time, and usually people (other than me…) don’t bother getting worked up about it. Very quickly New Scientist (not known for its general policy of only reporting on carefully vetted research) had a piece from an Oxford cosmologist denouncing Marcus du Sautoy for organizing Weinstein’s talk and not inviting any physicists:

Hosting a lecture in a university physics department without inviting any physicists is, at best, an unforgivable oversight. As my colleague Subir Sarkar put it, “It’s surprising that the organisers did not invite the particle physicists to attend – if indeed the intention was to have a discussion.”

Soon New Scientist was joined by Jennifer Ouellette at Scientific American and PZ Myers, all outraged at the unprofessional behavior of du Sautoy. Reading the New Scientist piece, for about 5 seconds I thought “wow, that du Sautoy sure is a piece of work”, before realizing “wait a minute, how likely is that?” Any experience with academic departments and dissemination of information like this should be enough to make one suspicious that the most likely course of events was that du Sautoy tried to get word out, but this didn’t happen very effectively. Yes, departments and groups have mailing lists, but the ones people pay attention to are shielded from use by outsiders. After a couple days, it came out that the true story was that du Sautoy did contact people in the physics department trying to get their help advertising the talk, sent them posters, etc., exactly as one would have expected.

What I find most remarkable about this story though is the contrast to the one that I wrote about the day before here. This involved a Sunday Times report about Laura Mersini-Houghton’s “hard evidence” for the multiverse, which she had found by analyzing the latest Planck CMB data. She plans to give a public talk about this at the Hay Festival on Friday, and a talk at Oxford is scheduled for June 11 (this talk is part of a workshop funded by the Templeton Foundation as part of their “establishing the philosophy of cosmology” effort). I assume physicists will get an invitation to the Oxford talk, but, at least at the moment, there’s no paper that I’m aware of backing up Mersini-Houghton’s claims. There is a 2008 paper about what Planck should have seen, but the Planck team reported nothing of the sort predicted in that paper.

This all leaves me rather curious about the question of why people got outraged about Eric Weinstein getting too much press attention for his undocumented claims and Oxford talk, when the same people as far as I can tell seem to have no problem with Mersini-Houghton and her undocumented claims + Oxford talk. To me it seems a lot more problematic that people have been reading in the press that hard evidence has been found for the multiverse than that they have read that Eric Weinstein has a theory of everything. Others seem to see things the other way around.

Update: Eric will be giving another talk at Oxford, this Friday, see here.

Update: To the extent you can call what’s on Twitter “information”, there’s information about today’s Oxford talk there, see for instance here and here.

Update: Denunciations of du Sautoy continue, see for instance here. For a response from him, see here. From the various very fragmentary accounts available online of the Friday talk, it sounds to me like Eric is far from having a viable TOE. Still no paper or details available, which is what is needed to see if he has a promising idea.

Meanwhile, on the BBC, it’s multiverse-mania as usual, with Mersini-Houghton,

a cosmologist at the University of North Carolina in Chapel Hill whose theory of the origin of the visible universe has attracted a lot of attention for its strong observational predictions.

explaining that

the recently released data from the Planck telescope lend particular support.

As far as I can tell, cosmologists and physicists think this kind of thing is just fine, or maybe they are way too busy being outraged about du Sautoy’s attack on the very fundamentals of science.

Update: Laura Mersini-Houghton and Richard Holman sent me the following which I’m adding here so that readers can have their point of view on this.

As avid readers of your blog, we were a bit dismayed to see your post lumping our work together with Weinstein’s. Unlike his case, we HAVE had not just one, but a series of papers where our calculations and predictions are laid out for all too see and argue about.

To recap, we made use of a particular model of the landscape of string theory, the one derived in the Douglas-Denef paper 2004, constructed the effective density matrix for observables in our patch and then used that to derive our predictions. Within the context of this model, we showed that the scale of SUSY breaking would be far above the reach of the LHC and thus no super-partners would be seen. We also calculated how the back reaction from the other parts of the landscape modifies the gravitational perturbations in such a way that the following would be true

a. the cold spot of 10 degrees in the sky at about z~1,

b. another highly underdense/void like region aka a suppression of power at k~1 which would give rise to:
c. a suppression by 30% of TT spectra of CMB at the lowest l<6 (k=1)
d. a modification of quadrupole, dipole and octopole (lowest l’s) which induces alignment of quadrupole and octopole, (axis of evil)
e. a preferred direction due to induced dipole power
f. the power asymmetry between the 2 hemispheres which are determined by the preferred direction (again the k~1 suppression shows as lack of structure at dipole/quadrupole level which suppresses structure in 1 hemisphere)

g. an overall suppression of sigma_8 due to the same correction to Newtonian potential by 30%.

Hints of all of these had been found by WMAP, but PLANCK confirms ALL of these (Paper 13 in the Planck series).

The two papers where predictions were derived are:

http://arxiv.org/pdf/hep-th/0612142

http://arxiv.org/pdf/hep-th/0611223

The full theory in 2005 for which these predictions are made is developed here

http://arxiv.org/pdf/hep-th/0511102

This theory was and remains the only one that uses quantum cosmology to derive the selection criterion from the landscape multiverse and that calculated every single prediction from an underlying fundamental physics formalism, without resorting to anthropics or any other conjectures. Silence does not imply ignorance.
While there is certainly room to argue with us (is our model of the landscape truly reflective of its actual behavior? How robust are our results to changes such as in the inflationary potential used?), we have striven to be above board in all we’ve written and said.

We also made predictions for a bulk flow that was argued for by Kashlinski et al. There has certainly been some dispute about the existence of this flow and a PLANCK paper argued that the flow is not statistically significant in their data but the jury is still out on that. However, the situation is not as clear cut as this. We are aware there was a paper by Pierpaoli et al stating they do not make a significant detection of the dark flow and another paper by Barandela et al., also a Planck team member, stating that the dark flow is definitely there and the filters used by Pierpaoli et al. were incorrect. Our current feeling is that it would be premature to say our theory is incorrect on the basis of a result awaiting conclusion while 8 of its major predictions have just been confirmed. Perhaps you are not aware that a bulk flow always arises when the CMB frame and the expansion frame in the universe do not coincide. On the other hand, should this discussion finally be resolved against us we are ready and willing to acknowledge this and move on. At least we have predictions that COULD be wrong!

It is true that there has been considerable media coverage for the last 7 years around this theory and its predictions but that is not surprising considering we made predictions for a theory of the origins of the universe based on fundamental physics. Don’t let the media coverage divert you from the science. The key issue is that we have a theory based on a well known fundamental physics formalism and we made predictions for the anomalies in 2006 that are currently in accord with ALL of the data (modulo the pending dark flow results). That is 8 predictions confirmed and one to go. As we said before, you might want to argue with the underpinnings of our ideas and we are more than willing to enter into such discussions. But we have calculated within our framework, derived physical predictions from these calculations and await further data to fully confirm or refute our model. We think that this how science should be done.

In light of this, we would appreciate it if you could revise your post to reflect these facts.

Best

Laura Mersini-Houghton

Rich Holman

Posted in Multiverse Mania, Uncategorized | 72 Comments

The “Unnatural” Standard Model

Posted on May 25, 2013 by woit

The Standard Model is a physical theory of a spectacularly successful sort. It is built on beautiful and deep mathematics, covers almost all known physical phenomena, and agrees precisely with the result of every single experiment ever done to test it. It leaves open a very small number of questions: why this specific combination of small symmetry groups and their representations? What determines the parameters of the model (18 if you ignore neutrino masses, 7 more if you include them)? What about gravity? Does it need to be extended to account for dark matter?

For several decades now, there has been a very active and heavily advertised field of “Beyond Standard Model” physics, the study of extensions of the standard model that remain consistent with experimental bounds. While BSM models have played a role in guiding experimentalists towards things to look for that are not already ruled out by what is known, they have never come anywhere near fulfilling the hope that they might provide some insight into the SM itself. They provide no explanation of the unexplained aspects of the Standard Model, instead adding a great deal of additional unexplained structure. Perhaps the simplest and most widely studied example is the minimal supersymmetric extension of the SM, which not only explains none of the 25 undetermined SM parameters, but adds more than 100 additional such parameters to the list.

Theorists have traditionally followed what has been described as “Albert Einstein’s dream that the laws of nature are sublimely beautiful, inevitable and self-contained”, and the SM is our closest approach so far to Einstein’s dream. If you shared this dream, the known BSM models would never have much appealed to you, since they just added complexity and extra unexplained parameters. You also would not have been at all surprised by the strong negative results about such models that are one of the two major achievements so far of the LHC (the other is the Higgs discovery). If you’re a follower of Einstein’s dream, the obvious reaction to the LHC results so far would be to rejoice in the vindication of this dream, welcome the triumph of the simplicity of the SM, and hope that further study of the Higgs sector will somehow provide a hint of a better idea about where the SM parameters come from (almost all of them are Higgs couplings).

Remarkably, a very different story is being sold to the public by those who had a great deal invested in now failed BSM models. In this story, the BSM models were the ones of Einstein’s dream: they were “natural”, and their failure leaves us with the “unnatural” Standard Model.

An article entitled Is Nature Unnatural? is the source of the above quote about Einstein, and it tells us that

Decades of confounding experiments have physicists considering a startling possibility: The universe might not make sense…

In peril is the notion of “naturalness,” Albert Einstein’s dream that the laws of nature are sublimely beautiful, inevitable and self-contained. Without it, physicists face the harsh prospect that those laws are just an arbitrary, messy outcome of random fluctuations in the fabric of space and time…

“The universe is impossible,” said Nima Arkani-Hamed, 41, of the Institute for Advanced Study, during a recent talk at Columbia University [more about this talk here].

What is behind this sort of claim that down is up is abuse of the English word “naturalness”, which in this particular case has been adopted by theorists to refer a technical property better described as “not quadratically sensitive to the cut-off scale”. There’s a lot to be said (and a lot that has been said on this blog) about the precise technical issue here. It’s a real one, and likely an important hint about the true nature of the Higgs sector of the SM and where all those undetermined parameters come from. Getting rid though of this technical problem by invoking hundreds of new undetermined parameters is not the sort of thing Einstein was dreaming about. He would see the LHC results as vindication and encouragement: as we investigate new energy scales we find the universe to be as simple as possible. It’s remarkable to see this great discovery being promoted as telling us that we have to give up on Einstein’s dream and adopt a pseudo-scientific research program based on the idea that physical “laws are just an arbitrary, messy outcome of random fluctuations in the fabric of space and time”.

Update: The Science News story has now appeared at Scientific American, with the title New Physics Complications Lend Support to Multiverse Hypothesis. The “New Physics Complications” are the LHC only seeing pure SM behavior. If the LHC had seen a complicated SUSY spectrum, that would have been “natural”, but somehow seeing the simplest possibility has become a new “Complication”. It is a “complication”, but a sociological not physics one. SUSY theorists do have an answer for the complication of their ideas failing: the Multiverse did it.

Posted in Multiverse Mania | 58 Comments

Various Links

Posted on May 25, 2013 by woit
  • The Smithsonian has a long article about Lisa Randall here.
  • The Wall Street Journal has a shorter article about Randall’s high school classmate Brian Greene here. Brian’s World Science Festival will start here in New York on Wednesday.
  • I’ll probably skip the World Science Festival in favor of an event at the CUNY Graduate Center: a conference on the work of Jim Simons, in honor of his 75th birthday. The conference will start off Tuesday morning with talks by Witten and Deligne (for a recent piece about Deligne and the Weil conjectures by Ed Frenkel, see here)
  • One of many worthwhile things funded by Simons is Simons Science News, which now carries some of the best science journalism around. There’s a new interview with David Gross, who talks about the way QFT overcame those who wanted to do away with it in the sixties. About string theory:

    String theory is not as revolutionary as we once hoped. Its principles are not new: They are the principles of quantum mechanics. String theory is part and parcel of quantum field theory.

    About the multiverse:

    There are frustrating theoretical problems in quantum field theory that demand solutions, but the string theory “landscape” of 10500 solutions does not make sense to me. Neither does the multiverse concept or the anthropic principle, which purport to explain why our particular universe has certain physical parameters. These models presume that we are stuck, conceptually.

    About the current situation “Sometimes, he says, science is just plain stuck until new data, or a revolutionary idea, busts the status quo.”

    The latest article at Simons is one by Natalie Wolchover, who was at the same Nima Arkani-Hamed talk I recently attended. See her take here, mine here. Will write yet again about “naturalness” and some of the content of this article in a separate posting.

  • For the state of SUSY, and particle physics in general, check out recent talks here, especially Matt Reece’s SUSY theory overview. I think a fair description of the current state of affairs is that the only SUSY theories standing are either “fine-tuned” (removing the main argument of LHC-scale SUSY), or highly contrived (e.g. by going beyond the MSSM in various ways to escape LHC negative results). For the latest experimental results about SUSY, watch for this CMS talk on Tuesday.
  • For the latest in speculative theorizing about HEP and cosmology, see this past week’s Planck 2013 conference.
Posted in Uncategorized | 6 Comments

Eric Weinstein on Geometric Unity

Posted on May 23, 2013 by woit

Eric Weinstein is a Harvard math Ph. D. who has been working as an economist here in New York for many years, and someone I’ve often enjoyed talking to over the years. Going back to his days as a graduate student, he has been working on some of his own far out of the mainstream ideas about geometry and physics (which I’ve never seen the details of). Eric has finally gotten to the point where he is willing to talk about these ideas publicly, and he is giving a lecture today in Oxford, something that was arranged by Marcus du Sautoy. The Guardian has a long article about him and his work here.

There’s a bit of an analogy with the Garrett Lisi physics outsider story here, although I think Eric will get less media attention since he doesn’t have the surfing angle going for him. Both he and Garrett are pursuing what seems to me one of the deepest questions around: what is the relationship between the SU(3)xSU(2)xU(1) geometry of the Standard Model, and the 4d pseudo-Riemannian geometry of space-time and general relativity? Garrett was trying to understand this in terms of E(8) symmetry, and I’m looking forward to seeing what Eric’s ideas about this are. I’m not sure when he’ll have a paper out on the arXiv, or whether some sort of version of his lecture will be available.

Update: The Guardian now has a very enthusiastic article about this by Marcus du Sautoy, while New Scientist has a skeptical take here.

Update: See Jennifer Ouellette for a critical take on the Guardian coverage.

Update: It seems that claims that physicists were not invited to Weinstein’s talk are not true: an announcement and posters were sent to the physics department, but did not get widely disseminated. For a small amount of info about the talk, see the comment here from “Leaker”.

Posted in Uncategorized | 76 Comments

Hard Evidence for the Multiverse Found, but String Theory Limits the Space Brain Threat

Posted on May 22, 2013 by woit

In recent years there have been many claims made for “evidence” of a multiverse, supposedly found in the CMB data (see for example here). Such claims often came with the remark that the Planck CMB data would convincingly decide the matter. When the Planck data was released two months ago, I looked through the press coverage and through the Planck papers for any sign of news about what the new data said about these multiverse evidence claims. There was very little there; possibly the Planck scientists found these claims to be so outlandish that it wasn’t worth the time to look into what the new data had to say about them. One exception was this paper, where Planck looked for evidence of “dark flow”. They found nothing, and a New Scientist article summarized the situation:

“The Planck team’s paper appears to rule out the claims of Kashlinsky and collaborators,” says David Spergel of Princeton University, who was not involved in the work. If there is no dark flow, there is no need for exotic explanations for it, such as other universes, says Planck team member Elena Pierpaoli at the University of Southern California, Los Angeles. “You don’t have to think of alternatives.”

One of those promoting the idea that “dark flow” was evidence for a multiverse was Mersini-Houghton, who in a 2008 paper with Holman wrote:

Our contention, then, is that these observations of bulk flow can be construed as evidence for the birth of the universe from the landscape multiverse imprinted on the superhorizon sized nonlocal quantum entanglement between our horizon patch and others that began from the landscape. When we calculate the size of the induced dipole in our theory and convert it into a bulk velocity dispersion, we will see that for the constrained values of our parameters we arrive at a velocity dispersion of order 670 km/sec, remarkably close to the observed value of 700 km/sec.

One might think that the refutation of their prediction by the Planck data would be a problem. Instead though, the Sunday Times reported a few days ago that Scientists believe they have found the first evidence that other universes exist. The story got picked up by other news outlets, and appeared in the Daily Mail as “The first ‘hard evidence’ that other universes exist has been found by scientists”. The source for the story was Mersini-Houghton:

Laura Mersini-Houghton, theoretical physicist at the University of North Carolina at Chapel Hill, and Richard Holman, professor at Carnegie Mellon University, predicted that anomalies in radiation existed and were caused by the pull from other universes in 2005.
Now that she has studied the Planck data, Dr Mersini-Houghton believes her hypothesis has been proven.
Her findings imply there could be an infinite number of universes outside of our own.
She said: ‘These anomalies were caused by other universes pulling on our universe as it formed during the Big Bang.
‘They are the first hard evidence for the existence of other universes that we have seen.’

She will be in Britain soon promoting this at the Hay Festival on May 31 and at Oxford on June 11.

According to a New Scientist story just out, this hard evidence for the multiverse should be welcomed, since it (together with string theory) has just been shown to have the power to save us from “Legions of disembodied brains floating in deep space”. The story, which appeared in print as String Theory Limits Space Brain Threat starts with

LEGIONS of disembodied brains floating in deep space threaten to undermine our understanding of the universe. New mathematical modelling suggests string theory and its multiple universes may just provide our salvation – and that could win the controversial theory a few more backers.

It goes on to explain about Boltzmann brains and a recent paper by Bousso and Zukowski, and ends with news of yet another experimental success for string theory:

“This is potentially an added experimental success for string theory and eternal inflation,” says Daniel Harlow, a physicist at Princeton University. “We need to understand it better – [but] the fact that it potentially explains something is motivation to understand it better.”

Update: More here on how string theory will save us from the space brains.

Update: I’ve appended a response from Laura Mersini-Houghton and Richard Holman about this to a later posting, see here.

Posted in Favorite Old Posts, Multiverse Mania, This Week's Hype | 34 Comments

One Ring to Rule Them All

Posted on May 16, 2013 by woit

This week in Sweden the Nobel Foundation is running a symposium on LHC results. It’s invitation only, but the slides of the talks are available here.

One of the scheduled talks today was about string theory, and I was wondering how that would fit into the “LHC results” framework since string theory has nothing to say on the topic. Now that the slides are available I don’t see anything about the LHC, but there are some remarkable revelations. The first is that string theory is not science but “Magic”, with several slides describing the “Magic of String Theory”. The relationship to mathematics is that in string theory “No concept in Math remains unambiguous”, which I guess is about what you would expect when you’re dealing with magic.

An even bigger revelation comes later in the talk: string theory is Sauron’s Ring of Power! It is described as “Concentrated Power” and it seems that the markings on the ring are a SUSY Lagrangian. Part of the Ring Poem is quoted

One Ring to rule them all, One Ring to find them,
One Ring to bring them all and in the darkness bind them.

To put this back in context, recall that this is Sauron’s ring he created in order to control everything from Mordor. Here’s more of the poem, including the original language

Ash tug Shakhbûrz-ûr Ulîma-tab-ishi za,
Uzg-Mordor-ishi amal fauthut burgûli.
Ash nazg durbatulûk, ash nazg gimbatul,
Ash nazg thrakatulûk, agh burzum-ishi krimpatul
Uzg-Mordor-ishi amal fauthut burgûli.

One for the Dark Lord on his dark throne
In the Land of Mordor where the Shadows lie.
One Ring to rule them all, One Ring to find them,
One Ring to bring them all and in the darkness bind them
In the Land of Mordor where the Shadows lie.

This interpretation of string theory as Sauron’s ring I suppose could explain a lot…

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String Theory and the Scientific Method

Posted on May 14, 2013 by woit

There’s a new philosophy of science book out, Richard Dawid’s String Theory and the Scientific Method (available online here if your institution is paying Cambridge University Press appropriately or if you have a credit card). It comes with endorsements from string theorists David Gross and John Schwarz, with Schwarz writing:

Richard Dawid argues that string theory plays a novel role in the scientific process that has been neglected by philosophers of science. I believe that this book is a valuable contribution to the philosophy of science, which should interest practicing scientists as well as those who are more interested in the methodology of science.

Dawid is a particle theorist turned philosopher, and as you might guess from the endorsement, he approaches string theory from an enthusiast’s point of view. The fundamental question addressed is how one can reconcile string theory’s failure in terms of conventional methodology of science with its continuing hold on at least part of the physics community. He explains how the book came about as follows:

This book has been on my mind ever since I left physics and turned to philosophy in the year 2000. A core motivation for making that step at the time was my feeling that something philosophically interesting was going on in fundamental physics but remained largely unappreciated by the world outside the departments of theoretical physics – and underappreciated even within. Twelve years of grappling with the specification of that general idea have considerably changed my perspective on the issue but left the overall idea intact. This book is the attempt to present it in a coherent form.

Reading the book in an odd way reminded me of my recent experience reading Gordon Kane’s reissued book on supersymmetry and string theory written in 2000, especially Witten’s essentially unchanged introduction. The degree of self-confidence of string theorists at that time was much different than now: AdS/CFT was a new idea, with a solution to QCD on its way, SUSY a sure thing at the LHC if not at the Tevatron or LEP, and at least half of the new jobs in the field going to string theorists. No landscape or multiverse pseudo-science was around to sow dissension in the ranks. No failure of SUSY to show up anywhere. No discouraging numbers like those for the last two years which show, in the US at least, 9% of jobs going to string theorists, with more jobs going to lattice gauge theorists in 2011 than to string theorists. And of course, a uniformly positive press, with no naysayers like Smolin and Woit causing trouble.

In Dawid’s description, string theorists are still partying like it’s 1999:

String theory has attained a pivotal role in fundamental physics and has been treated as a well-established and authoritative theory for quite some time by the community of string theorists and by physicists in related fields. As we have described above, large parts of fundamental physics are influenced by string theoretical analysis. The string community is one of the largest communities in all of theoretical physics and for many years has produced the majority of the field’s top-cited papers. Moreover, many string theorists express a remarkably strong trust in their theory’s viability.

For the actual list of last year’s top-cited papers in HEP, see here, and “remarkably strong trust in their theory’s viability” seems to me more 2000 than 2013. He does go on to mention skeptics, but to him a majority of the field is behind string theory, with the skeptics only coming from outside particle theory:

On one side of the divide stand most of those physicists who work on string physics and in fields like inflationary cosmology or high energy particle physics model building, which are strongly influenced by string physics. That group represents a slight majority of physicists in theoretical high energy physics today. Based on an internal assessment of string theory and the history of its development, they are convinced that string theory constitutes a crucial step towards a better and more genuine understanding of the world we observe. On the other side stand many theoretical physicists of other fields, most experimental physicists and most philosophers of physics. They consider string theory a vastly overrated speculation.

Dawid’s main thesis is that string theory critics fail to recognize that a new paradigm of scientific methodology is now needed:

String theory thus should not be taken to announce an end of science but rather to represent a new phase of scientific progress. In this new phase, progress in fundamental physics is no longer carried by a sequence of limited, internally fully developed theories, but rather by the discovery of new aspects of one overall theoretical scheme whose general
characteristics identify it as a candidate for a final theory, yet whose enormous complexity bars any hope of a full understanding in the foreseeable future.

What is the reason you should accept this final theory that no one can understand? Obviously the lack of any empirical support is a problem, so Dawid turns his attention to a detailed study of the subject of “non-empirical theory assessment”: how do you assess scientific progress absent connection to experiment? This is a real and serious problem, which Dawid studies in detail, although from a point of view which just naively accepts all arguments made by string theorists. He considers three main reasons for studying a theory with no empirical support:

  • The No Alternatives Argument. This is the best argument for string theory: there aren’t a lot of viable unified theories out there. Of course, the way science progresses is that there always are unsuccessful ideas with no good alternatives, until the day someone come up with a better idea.
  • The Unexpected Explanatory Coherence Argument. This is the idea that if a theory holds together better after you start studying it and understand it better, that’s a good thing. Dawid repeats uncritically claims of some string theorists that this is the case for string theory. I think you could make an equally good case for string theory unification becoming a more and more dubious idea as it became better understood (see, the Landscape).
  • The Meta-Inductive Argument. Here the idea is that if a theoretical research program worked before, so will a similar later one. Dawid claims that the string theory research program is just like the research program that led to the Standard Model:

    Given the entirely theoretical motives for its creation, the lack of satisfactory alternatives and the emergence of unexpected explanatory inter-connections, the standard model can be called a direct precursor of string theory.

    Honestly, this I just find bizarre, and have no idea what he’s talking about, with the history of the Standard Model and the history of string theory two radically different subjects.

In one crucial respect, this book is very different though than Kane’s. Kane is well aware that the idea of an inherently experimentally untestable theory is something he can’t sell to his colleagues and the public, so he devotes his book and its argument for string theory to supposed experimental tests. More savvy string theorists than Kane though are seeing the writing on the wall: no SUSY at 8 TeV means almost surely no SUSY at 13 TeV, and thus no prospects for experimental evidence for SUSY during any of our lifetimes. To prop up the string theory unification program past SUSY null results from the 13 TeV LHC in 2016 is going to require relying on Dawid’s “non-empirical theory assessment” and convincing people that string theory and the multiverse represent a new paradigm for how to pursue fundamental science. This book will be welcomed by those pursuing such a goal.

Update: For a different take on the book you can see Lubos Motl’s review (as you might expect, he’s a big fan). The case of the most prominent string theorist blogger reminds me of one of the funnier things in the Dawid book that I forgot to mention, this footnote:

It should be emphasized that physicists on both sides of the divide are aware of the slightly precarious character of the “non-physical” arguments deployed in the debate. Lee Smolin has applied the concept of groupthink to the community of string physicists (which, incidentally, seems a quite accurate representation of what many critics of string physics do think about string physicists) but is careful not to present it as a core argument. String theorists, when entering a discussion with their critics (see e.g. Polchinski in his reasoning against Smolin), try to keep the debate at an entirely physical level.

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