Miscellaneous Links

Posted on May 6, 2013 by woit
  • There’s an interesting discussion amongst philosophers at Brian Leiter’s blog about the effects of Templeton money (and I contributed my two cents…). In other Templeton news, they’re funding a new “literary science magazine” called Nautilus. Also via Leiter, they have awarded $3 million to two philosophers at Saint Louis University (“one of the largest grants SL has ever received in the areas of the humanities or the sciences”) for them to study the subject of intellectual humility.
  • In the category of rumors I’ve heard from so many reputable sources they must be true and I can’t really be violating confidentiality, W. Hugh Woodin is moving from Berkeley to Harvard, and Simon Donaldson from Imperial College to the Simons Center at Stony Brook.
  • Via Simon Willerton at the n-Category Cafe, Edinburgh now has a gallery with a wonderful collection of portraits of seventy mathematicians, including commentary from Michael and Lily Atiyah, an online version is here.
  • The publisher sent me a copy of Tony Zee’s new GR textbook, Einstein Gravity in a Nutshell, which I very much enjoyed looking through. Zee takes the textbook concept to new levels of informality, so it includes a wealth of interesting and amusing comments, spread throughout the text, footnotes and endnotes, including quite a few about quantum gravity. At over 800 pages, it’s a pretty huge book, including a lot of conceptual material (as in his QFT textbook), but more calculational detail than the QFT book. Undergraduate physics students should find this quite an approachable text (unlike the QFT one, which I think you need graduate level training to really follow).

    This definitely is a text for physicists, not mathematicians, with the geometry taking a back-seat. Differential forms and orthonormal frames don’t appear until nearly the end of the book. Personally I’ve found using the same language of connections on principal bundles to do gauge theory and gravity to make the most sense, but this involves getting familiar with quite a bit more formalism than most physicists are willing to deal with.

  • I’d been curious to hear more about recent work of Jacob Lurie and Dennis Gaitsgory on Tamagawa numbers, and had been waiting to see a paper from them. Turns out there’s something much better: Lurie has been teaching a course about this at Harvard this semester, with notes appearing here. For some indication of why you might take an interest in this if your interest is gauge theory, see here.
  • While about the only bipartisan agreement in Washington these days is that something must be done to deal with the terrible problem of the shortage of STEM graduates in the US, someone has noticed that there actually is no shortage, see here.
  • This past weekend there was a conference in honor of Bruno Zumino’s 90th birthday at Berkeley, and one can hope that some version of the talks might become available online here.
  • A hot topic in HEP remains that of when the failure of the SUSY picture that has been heavily over-sold for several decades will finally be acknowledged. From the list of titles at the Zumino conference, Maiani’s was “Supersymmetry: not time to give it up, yet”. Cormac O’Raifertaigh reports here that Nati Seiberg is saying “only certain aspects of minimal models had been ruled out so far. As for the future, who knows?”. (now corrected, see Cormac’s blog). Physics World has a story here, with Ben Allanach claiming that “data taken at the LHC have excluded roughly half of supersymmetry’s parameter space” and that now one has to wait until 2015 when, if SUSY is right, it will be found nearly immediately:

    “My hopes are pinned on the next run,” he says. “The energy jump now is going to make the big difference. And if supersymmetry is the correct theory of nature, I would be expecting to see a big signal within the first month. If it doesn’t crop up, I’ll then be getting pretty depressed.”

    Bill Murray of ATLAS makes the excellent point that

    “Proving [supersymmetry] wrong would be as important as proving it right,” he says. “Null results are hard to sell to newspapers, but they are really important to scientific progress.”

    Killing SUSY will be one of the great achievements of the LHC, and complaining about this might be kind of like being upset that Michelson-Morley didn’t find the ether.

Update: I’ve been pointed to an impressive photo of Robbert Dijkgraaf that unfortunately did not make the Atiyah Gallery.

Update: The New York Times has a story today about the new Templeton-funded science magazine Nautilus.

Update: The news from Britain is that Stephen Hawking has joined the academic boycott of Israel, cancelling plans to attend a conference there this month. Please discuss your views on the Israeli/Palestinian conflict elsewhere. There’s no way I’m going to moderate such a discussion, and there are now surely dozens of other sites carrying this story where comments are encouraged.

Posted in Uncategorized | 37 Comments

Supersymmetry and Beyond

Posted on May 1, 2013 by woit

Back in the year 2000, Gordon Kane published Supersymmetry: Unveiling the Ultimate Laws of Nature, a popular book promoting supersymmetry and string theory. The thrust of the book was that there was already indirect evidence for SUSY, with confirmation by discovery of superpartners due to come soon from LEP (which was running at energies near 100 GeV/beam) and the Tevatron (where Run II at high luminosity and nearly 1 TeV/beam was to start in 2001). The LHC was also discussed, mainly as the place that would confirm and extend the LEP/Tevatron superpartner discoveries.

Thirteen years later, with no hint of SUSY showing up as promised, not only at LEP/Tevatron energies, but also at the much higher energies and luminosities of the 8 TeV LHC, Kane has a new popular book promoting supersymmetry and string theory, entitled Supersymmetry and Beyond. It includes his claim to have predicted the Higgs mass using string theory (see Matt Strassler’s take on this here, mine here). Much of the book though consists of exactly the same text as the 2000 version.

How does Kane handle the detailed failed predictions of the 2000 edition in the new 2013 version? Basically by editing them out, with no indication to the reader that this has been done.  What’s the right word to describe the result of an Orwellian exercise like this? You can make up your mind about that yourself, since I’ve gathered together here some examples of the book text, showing the edits that were done to create the new version.

Pages xvii/xviii

Supersymmetry is still an idea as this book is being written (mid-1999) in late 2012. There is considerable indirect evidence that it is a property of the laws of nature, but the confirming direct evidence is not yet in place. That is not an argument against nature being supersymmetric; rather, the accelerator collider facilitiesy that could confirm it (the LHC) are  is just beginning to cover the region where the signals could appear (Chapter 5)[about LEP and Fermilab].

Pages 2-3/3

If we understand supersymmetry and its implications correctly, direct experimental evidence for supersymmetry will be found in the next few years – possibly soon after this book is published (or, with great luck, even before).

Pages 13/16

Only now are colliders and detectors at laboratories are now achieving the energies and luminosities (amounts of data) and sensitivities needed to explicitly detect the superpartners explicitly, at least if our thinking about their properties is more or less right.

Pages 70-71/77-79

The manner in which supersymmetry explains the Higgs physics is elegant and has important consequences for how we expect to test supersymmetry experimentally. It is rather technical. A more detailed description is given in Appendix B; here I will give a short version. There are three parts…

Therefore, the supersymmetric Standard Model explanation of the Higgs mechanism would not make sense unless the some superpartner masses were not much larger than the Standard Model masses they explain. That gives us an estimate of the masses we should expect the superpartners to have as we search for them, and it tells us at what stage we should question the validity of the theory if the superpartners have not been detected. Such estimates are only approximate, but luckily the expected masses are small enough that they imply the superpartners should be detected soon.

Appendix B was deleted entirely, it contained the text (page 156)

Therefore, the superpartner masses cannot be very much larger than the Z boson mass if this whole approach is valid. This is the only place where we can use the theory to relate the unknown superpartner masses to known masses, so on the one hand, it is a major test of the correctness of the supersymmetry explanation of the Higgs physics, and on the other, it is the most significant reason whey we expect the masses of the superpartners to have values that allow them to be produced at Fermilab or even LEP. This connection also suggests that if the superpartner masses are much larger than the Z boson mass, then the apparent success of the supersymmetry theory in explaining the origin of the Higgs physics of the Standard Model could be an accident.

Pages 88-89/89

Several arguments imply that some sparticles are within the reach of Fermilab the LHC. The strongest One of the most appealing is based on the explanation supersymmetry gives for the Higgs mechanism of the Standard Model, as described in the last chapter Chapter 7. Basically the qualitative argument is that because since supersymmetry provides the Higgs mechanism that accounts for the masses of W and Z, the some sparticle masses cannot be much heavier than the W and Z masses themselves. Fermilab has already produced and detected thousands of W’s and Z’s. When this argument is framed put in a technical form, it implies that gluinos and probably charginos and neutralinos and stops should be in the Fermilab within the LHC reach. If they are not, the impressive successes of supersymmetry listed at the beginning of Chapter 4 may be meaningless coincidences. There are some arguments, both theoretical and phenomenological, suggesting that squarks and sleptons will be too massive to produce at the LHC.

Chapter 8, on SUSY implications for matter/anti-matter asymmetry, proton decay, rare decays like mu to e-gamma, and CP violation has been deleted. Appendix D, on large extra dimensions, has also been completely deleted.

Witten’s preface has been edited:

Experimental clues suggest that the energy required to produce the new particles is not much higher than that of present accelerators. If supersymmetry plays the role in physics that we suspect it does, then it is very likely to be discovered by the next generation of particle accelerators, either at Fermilab in Batavia, Illinois, or Large Hadron Collider (LHC) or its upgrades, at CERN in Geneva, Switzerland.

Posted in Book Reviews | 51 Comments

Arkani-Hamed Colloquium

Posted on April 30, 2013 by woit

Nima Arkani-Hamed was here at Columbia yesterday to give the physics colloquium, which clocked in at a bit over 1 hour and 45 minutes. He did reveal the secret of why his talks are this long: when invited to give a 1 hour colloquium, he plans on talking for at least 1 hour 30 minutes. The content of the talk was similar to many others he has given recently that are available on the web, see for instance this one at the IAS, this recent one at BNL, or for a written version, see here.

As a performer, he’s a powerful speaker: smart, vigorous, and supremely self-confident. His arguments lead to “inevitable” conclusions, not just implying results but “nailing” them. It’s clear why he’s the most influential person in the field these days. With most theorists made worried and unsure by 40 years of failure to get anywhere in their efforts to improve on the Standard Model, he knows exactly what he thinks and will tell you forcefully what you should think. The fact that none of the ideas about BSM physics he is famous for (large extra dimensions, split SUSY, Little Higgs, etc…) have ever worked out doesn’t seem to slow him down, and he has a professorship at the IAS and a $3 million prize from Yuri Milner to back him up.

Despite his long-time advocacy of SUSY, according to Arkani-Hamed, the negative results from the LHC are “not making many of us worried about SUSY”. He (accurately) points out that he’s not one of those like Gordon Kane who for decades has been predicting the discovery of superpartners to be six months away. It has long been clear that the simplest versions of SUSY should have shown up at LEP and the Tevatron, and pre-LHC the lack of any indirect evidence for SUSY indicated to him that it was unlikely to show up at the 8 TeV LHC. So, by his lights, there’s no reason that LHC results so far should cause any new worries about SUSY, beyond those he already had pre-LHC. On the more limited question of whether a “natural” version of SUSY will work out, one where the superpartner masses just barely avoid large amounts of fine-tuning, a year ago (see here) he was saying we were at the “eleventh and a halfth hour” for this possibility. Now that the 8 TeV results are here (and negative), he argues that it is only with the 2015 data that the results will be decisive. The current wisdom about “natural SUSY” I guess is summarized in slide 8 here: Keep Calm and Wait for 14 TeV.

The main point of the talk was one that Arkani-Hamed has been consistently making for nearly a decade, that the role of the LHC is to decide between two possible futures for fundamental physics:

  • The small value of the Higgs mass (in Planck units) has a “natural” explanation, most likely using SUSY, in which case we spend the rest of our lives unraveling the complexities of a SUSY-extended Standard Model.
  • The small value of the Higgs mass (in Planck units) indicates “fine-tuning” that can only have an anthropic explanation, just like the one for the CC. In that case, we live in a multiverse, with physics determined by something like the string theory landscape. About this whole conceptual framework, he says the “ideas are so poorly defined, not clear if they make any kind of mathematical sense”, and it’s “not clear progress will happen anytime soon” but, no need to worry or get discouraged, since this is an “attractive problem”.

Based on the LHC results so far, it looks like all evidence is that we’re headed to the second alternative.

Arkani-Hamed’s talk was structured so as to present a long chain of argument (needing at least 1h 30 min to explain) leading to these two alternatives. One of the alternatives (SUSY naturalness) is essentially already dead, with the die-hards intent on hanging on a couple more years. The other is essentially what David Gross has called “giving up”: you just announce that the problems you haven’t been able to solve can never be solved. In this vision, the 20th century with its huge success at finding a highly predictive, mathematically beautiful fundamental theory was an aberration caused by only being able to see physics at energies way below the Planck scale. In this new 21st century physics, you just postulate that at higher energies things are much more complicated, in ways we can’t hope to ever know, and theorists devote their lives to making excuses, not predictions. Witten may end up being right that “string theory is 21st century physics that fell into the 20th century”, in a much more negative way than he intended.

If a long, complicated argument leads you to the conclusion that the only viable alternative is to give up, then it seems to me you have two choices: give up, or examine more carefully your argument. A much more interesting and more useful talk than Arkani-Hamed’s would be one less devoted to forcefully insisting on the conventional chain of argument based on the technical problem of sensitivity of the Higgs potential to the cut-off, instead looking carefully for weaknesses in the argument (one possibility is discussed here). Arkani-Hamed is a brilliant physicist, but this may be a time when what is needed is not self-confidence in the power of one’s arguments, but instead a suspicion that one has been making a mistake somewhere for quite a while now.

Posted in Favorite Old Posts, Uncategorized | 45 Comments

Time Reborn

Posted on April 23, 2013 by woit

Lee Smolin’s new book, Time Reborn, is out today. For more about the ideas in the book, see video of a talk here, and an interview here.

While I mostly vehemently agreed with what Smolin had to say in his last book, The Trouble With Physics, I find myself equally vehemently in disagreement with this one. On some of the topics covered, I’m indifferent to his arguments mostly as a matter of taste. While my views on human society are likely similar to Smolin’s, I’ve never found the scientific insights of fundamental mathematics or physics to have anything significant to tell me about this part of life. Similarly, while I’ve spent some time studying philosophy, I’ve mostly found this of little help in gaining deeper understanding of math or physics. Others though have a very different experience than me, and I’m not about to argue against people looking for enlightenment wherever they happen to find it.

On some of the scientific issues dealt with in the book, again I’m mostly just indifferent. Smolin accurately explains how the lack of predictivity makes typical multiverse models empty, but I’m not convinced that his favored alternative (“cosmological natural selection”) does much better. While I understand well the human appeal of wondering about what came before the big bang, I’ve yet to see any specific models of this that carry enough explanatory power about anything to make them particularly attractive or interesting.

Many of the ideas Smolin is arguing for are clearly labeled as what they are: speculative challenges from a very much minority point of view to some of the received wisdom of this kind of science. Unfortunately, parts of his argument that are most problematic are ones which are in danger of becoming the new received wisdom of the subject. The refusal to admit the failure of the idea of string/M-theory unification has left many of our most prominent theorists pushing the idea that fundamental physics is based on some new and very different degrees of freedom, with dynamics that just happens to be too complicated to allow them to find vindication by seeing how the Standard Model emerges at low energies. For his own reasons, Smolin signs on to a version of this point of view, writing:

I’m inclined to believe that just about everything we now think is fundamental will also eventually be understood as approximate and emergent: gravity and the laws of Newton and Einstein that govern it, the laws of quantum mechanics, even space itself…

A large part of the elegance of general relativity and the Standard Model is explained by understanding them as effective theories. The beauty is a consequence of their being effective and approximate. Simplicity and beauty, then, are the signs not of truth, but of a well-constructed approximate model of a limited domain of phenomena.

The notion of an effective theory represents a maturing of the profession of elementary-particle theory. Our young, romantic selves dreamed we had the fundamental laws of nature in our hands. After working with the Standard Model for several decades, we are now simultaneously more confident that it’s correct within the limited domain in which it has been tested and less confident of its extendability outside that domain.

This notion that the SM is “just an effective theory”, with its fascinating and deep mathematical structures nothing but an artifact of low-energy approximation has become the reigning ideology of the last few decades. One impetus for this has been string/M-theory, with its conjectured very different physics at short distances. This has been put together with our modern understanding of renormalization, according to which non-renormalizable theories make perfect sense as effective theories. The argument is then made that this is all there is to the SM, neglecting to note that to a large degree the SM couplings are asymptotically free, meaning that (most of) the quantized geometric degrees of freedom make perfectly good sense at all energy scales.

Smolin’s view that the recent history of particle physics makes us “less confident of its [the SM’s] extendability outside that domain [where it has been tested]” is one I strongly disagree with. Despite endless “naturalness” and “fine-tuning” predictions based on the “nothing but an effective theory” argument, the SM has not only been vindicated at the LHC over a large new energy range, but the discovery of the Higgs has shown it to have just the right characteristics to make perfectly good sense up to extremely high energies, far beyond anything we can test.

I’ve been teaching a course this past year on quantum mechanics for mathematicians, emphasizing the role of Lie groups, unitary representations and symmetries in providing not only useful calculational methods, but governing the underlying structure of the theory. Smolin argues instead that, based on Leibniz’s “identity of the indiscernibles”, symmetries cannot be fundamental (although a footnote says this doesn’t apply to gauge symmetries):

Symmetries are common in all the physical theories we know. Several of the most useful tools in the physicist’s toolbox exploit the presence of symmetries. Yet if Leibniz’s principles are right, they must not be fundamental.

This applies to the very structure of quantum mechanics:

Quantum mechanics, too, is likely an approximation to a more fundamental theory.

since it is linear, and he bets thus just a linear approximation to some fundamentally non-linear theory. Again, mathematical simplicity is seen as an artifact of approximation, not indication of something fundamental.

Smolin ends with a vision that is pretty much the exact opposite of mine, one with a vastly diminished role for mathematics in understanding the nature of reality:

The most radical suggestion arising from this direction of thought is the insistence on the reality of the present moment and, beyond that, the principle that all that is real is so in the present moment. To the extent that this is a fruitful idea, physics can no longer be understood as the search for a precisely identical mathematical double of the universe. That dream must be seen now as a metaphysical fantasy that may have inspired generations of theorists but is now blocking the path to further progress. Mathematics will continue to be a handmaiden to science, but she can no longer be the Queen.

Unfortunately it seems possible that Smolin’s arguments about mathematics will resonate well with the current backlash against sophisticated mathematics that one sees at many physics departments in the wake of the failure of string theory. In a footnote he explicitly argues that the problem with string theory was too much symmetry:

Indeed, we see from the example of string theory that the more symmetry a theory has, the less its explanatory power.

I don’t understand this argument at all. The problems with string theory are something I’ve written about endlessly here, but too much symmetry is not one of these problems.

Smolin has been quite right to point out in recent years that fundamental physical theory is in a state of crisis, but I think his diagnosis in this book is the wrong one. Abandoning the search for a more powerful mathematical understanding of the world because the huge success of this in the past has made further progress more difficult is the wrong lesson to draw from recent failures (the nature of which he lucidly described in his previous book).

My own interpretation of the history of the Standard Model is that progress came not from finding more, larger symmetries, but from a deeper appreciation of the various ways in which gauge symmetry could be realized (spontaneous symmetry breaking, confinement, asymptotic freedom). The arrival of string theory pushed the study of gauge symmetry into the background, and these days one often hears arguments against its fundamental nature, such as this one from Arkani-Hamed

What’s as a misnomer called gauge symmetry, whose beauty is extolled at length in all the textbooks on the subject, is completely garbage. It’s completely content free, there’s nothing to it.

Smolin’s arguments against the fundamental nature of symmetries, even if gauge symmetry is let off the hook in a footnote, just reinforce some of the attitudes at the root of our present-day crisis. The problems that remain in fundamental theory are difficult, but denigrating now the powerful ideas that have led to success in the past won’t help find a way forward.

Update: For more about this, there’s a review in the NYRB, and a piece at edge.org (with responses).

Posted in Book Reviews | 83 Comments

Anderson on Anderson-Higgs

Posted on April 16, 2013 by woit

Philip Anderson was here at Columbia yesterday, and gave a very interesting talk, mostly discussing what was going on in the late 50s and early 60s at the intersection of condensed matter and particle physics. This has attracted a lot of interest around the question of who first came up with what is now called the “Higgs mechanism” and who first predicted a “Higgs particle” (I’ve written a long blog posting about this here).

After the discovery of the BCS model of superconductivity, Anderson did important work on understanding the “gauge problem” of how gauge symmetry acts in such a theory, publishing a series of papers on this in 1958. He joked that he was “pretty naive about field theory” at the time, so much so that the spelling he was using was “guage”. He had the advantage of regularly talking with Bardeen and with Nambu, and he described some of Nambu’s work on the so-called “Nambu-Jona-Lasinio” model. His 1958 work explained how one avoids getting massless Goldstone bosons in superconductors due to the singular long range nature of the Coulomb force. His talk included an anecdote about escaping from handlers in the Soviet Union to get a chance to explain this to Shirkov during a visit there (he wasn’t allowed to meet Bogoliubov).

He was at Bell Labs in the summer of 1962, and talked to J.G. Taylor, who told him that the problem of massless Goldstones was something those in particle theory were actively worrying about. Taylor also gave him a copy of Schwinger’s Gauge invariance and mass paper, which had been published that January. This led to Anderson’s Plasmons, gauge invariance, and mass paper, finished in November, and published in April 1963. This paper clearly explains the nature of what is now generally referred to as the “Higgs mechanism”, in the Yang-Mills case, not just the Abelian case, ending with the very modern point of view

We conclude, then, that the Goldstone zero-mass difficulty is not a serious one, because we can probably cancel it off against an equal Yang-Mills zero-mass problem.

In 1964 the papers by Brout-Englert-Higgs-Guralnick-Hagen-Kibble appeared that have drawn the most attention as earliest instances of the Higgs mechanism, but Anderson had the correct idea a couple years earlier. He described the situation as one where he and the 1964 authors all had the right explanation for why the W and Z have mass, although none of them (including him) had the actual physical Higgs particle, which he claimed first appears in a 1966 paper of Higgs.

The main point of his talk was the fruitful nature of research at the intersection between problems in condensed matter and particle theory, with the 50s-60s a happy period of such work. He ended with some comments on “supersolids”, see his recent paper about this here. Anderson will be 90 years old later this year (he’s almost exactly the same age as Freeman Dyson) and it was great to see him still going strong.

Update: See here for a write-up by Anderson of a talk a few years ago covering much the same material as yesterday’s Columbia talk (including the story of meeting Shirkov).

Update: A commenter points to this recent talk by Guralnik at Brown and mentions some comments that might be about Frank Close.

I just watched the talk, and he explicitly refers to this exchange in the London Times. I don’t see how when he says

the person involved as far as we can tell has no understanding whatsoever of mass renormalization and how these things work.

this can refer to anyone except Close (about whom it is completely absurd). The point of contention here is a very simple one. Guralnik’s paper (unlike Higgs’s) has no potential term for the scalar field. In his talk he says this is because it was the practice at Harvard not to write such terms down, while knowing they had to appear to renormalize the theory. Close’s point I think is just that Higgs went further than the other authors at the time in terms of exhibiting what would be needed to study the dynamics of the physical mode of the scalar field. From what I can tell, of course everyone writing these papers knew about potential terms for the scalar and how they worked, but the whole issue is a bit irrelevant: none of the people involved at this period seem to have thought seriously about this physical mode that describes the Higgs particle itself. They were thinking about something entirely different, the mass of the gauge field, and in any case these are Abelian models that have nothing to do with the real non-Abelian model that describes the Higgs particle.

The main point of Guralnik’s talk as far as this controversy goes I think is his explicit and repeated claim (which seems to me debatable) that Higgs’s paper was just wrong for technical reasons, in the sense of reaching correct conclusions by an incorrect argument. This appears to be Guralnik’s argument for why he and his collaborators should be preferred to Higgs as candidates for a Nobel, and is made much more strongly here than in other places (such as here, where he doesn’t use the term “wrong”, emphasizes more why Higgs’s argument was “incomplete”).

Leon Cooper was in the audience, and asks Guralnik about the Anderson explanation for why the Goldstone theorem is violated here: the long range nature of the Coulomb potential. Guralnik seems to acknowledge that this is the right physical way to understand what is going on, but says that relativity makes things more complicated. He explicitly acknowledges that he understood not at all Anderson’s arguments, saying

we were woefully ignorant, had barely heard of superconductivity.

About the crucial question of priority, the fact that his competitor’s papers were published earlier, were read by him before submission of his paper, and explicitly referenced in his paper, all he says is

as we published it, we found out about other papers.

which really doesn’t do justice to the situation. In this piece, written after the Higgs discovery, he describes the history as

We finally submitted our paper to PRL with the proof of the general mechanism to avoid the Nambu Goldstone theorem (the only work to have this) and the special example. We were surprised to discover that two very different but related papers, with parts of the example, one by Englert and Brout and the other by Higgs also existed. All three papers appeared in the same volume of PRL in 1964.

which is highly misleading.

Posted in Uncategorized | 54 Comments

To Mars and Beyond

Posted on April 14, 2013 by woit

I’m not sure either of these stories from the past week is particularly important in and of itself, but since I try and keep up on trends in theoretical physics, and two is a trend, here’s some news from two of the greats of the field:

  • There’s an interview here (via John Baez) with Gerard ’t Hooft about his role as “ambassador” for the Mars One project, which plans to send people on a one-way trip to Mars in 2023. This will be financed with an associated reality TV show, and already 40,000 people have signed up for a chance to get to go.
  • Stephen Hawking has even more radical ideas, which he talked about in a visit to Cedars-Sinai in LA last week. He believes humanity is guaranteed to trash this planet, so our best hope is to use M-theory to find a way to move on to another one:

    For him, the answers to the largest and tiniest questions lie in M-theory.

    “To understand the universe at the deepest level, we have to understand why is there something rather than nothing,” Hawking said, speaking through a computer program that converts his eye and cheek movements into spoken speech. “Why do we exist? Why this particular set of laws, and not some other? I believe the answers to all of these things is M-theory.”

    The theory, he said, combines multiple ideas about math and physics. It suggests that there are multiple dimensions or universes, and offers solutions for the behavior of super-massive black holes and the properties of the fabric of space-time. M-theory is a work in progress, but Hawking said he believes that it’s the most promising lead to a unified theory.

    The payoff to solving M-theory, Hawking said, is understanding where we fit in — and, perhaps, how we can thrive.

    “We must continue to go into space for humanity,” Hawking said. “We won’t survive another 1,000 years without escaping our fragile planet.”

Update: On Tuesday Hawking gave a talk to students at Caltech, with a report here that includes smuggled audio of the talk. Evidently Hawking told students that they don’t need God, but they do need M-theory and anthropics:

During his talk, he cited M-Theory — a wide-ranging and as-yet-incomplete explanation of the universe that attempts to unite the factions within String Theory — as the only workable theory going forward that can explain the true nature of the cosmos.

M-Theory suggests that the multi-dimensional “strings” of the universe are bound together by a strange material sometimes called membranes, but also known by other names. It suggests that matter, space, time and every possible history exists simultaneously across dimensional planes that were created out of nothing at the moment of the Big Bang some 13.8 billion years ago. Only in very few of these dimensions can a species like humanity come into being.

Posted in Uncategorized | 45 Comments

This Week’s Hype

Posted on April 3, 2013 by woit

The award for this week’s hype goes to the people at CERN, who normally are pretty good about this, but somehow thought it was a good idea to spin the AMS-02 results in a way that makes it sound as if they provide significant evidence for dark matter. The press release has:

The international team running the Alpha Magnetic Spectrometer (AMS1) today announced the first results in its search for dark matter….

These results are consistent with the positrons originating from the annihilation of dark matter particles in space, but not yet sufficiently conclusive to rule out other explanations….

One possibility, predicted by a theory known as supersymmetry, is that positrons could be produced when two particles of dark matter collide and annihilate. Assuming an isotropic distribution of dark matter particles, these theories predict the observations made by AMS…

which, is inconclusive if you read it carefully, but sure makes it sound like this was an announcement of significant evidence for dark matter if you don’t. As one might expect, this immediately led to press stories about how:

A $2 billion particle detector attached to the International Space Station has detected the potential signature of dark matter annihilation in the Cosmos, scientists have announced today…

By doing a tally of electrons and positrons, physicists hope the AMS will help to answer one of the most enduring mysteries in science: Does dark matter exist?

And today, it looks like the answer is a cautious, yet exciting, yes.

the kind of thing which, as usual, made it to Slashdot.

I won’t bother explaining here why this is nonsense, since this has been done much better and at length by Jester and Professor Matt Strassler.

Posted in This Week's Hype | 22 Comments

Various Links

Posted on April 2, 2013 by woit
  • The AMS-02 experiment results will be announced tomorrow, 1700 CERN local time, webcast here. The normally reliable Jester says rumor is no dark matter. For this kind of astrophysics news, you should find a site with an expert to interpret the results, I’ll try and provide a link here.
  • Weird. The Templeton Prize was supposed to be announced on Thursday, but they’ve changed their announcement to read “April 2013 (exact date to be determined)”. Did someone turn it down or something?
  • There’s a very long oral history transcript here of an interesting interview with Joe Polchinski. It covers a lot of ground of the history of what went on in particle theory during an era which included the rise of string/M-theory. The interview took place in 2009, and has a certain amount of “string wars” sort of material, since that was the period when this was winding down. Someone should fix the proper names in the transcript though…
  • As part of his Einstein Chair at CUNY, Dennis Sullivan has run a seminar for many, many years, with quite a few interesting speakers. There’s now video online of many of the talks.
  • Howard Burton, who was the founding director of the Perimeter Institute now has a multimedia magazine called Ideas Roadshow, with one of the first programs a long interview with Nima Arkani-Hamed (access free for to this if you sign up).
  • I keep on finding out about more math blogs worth a look, for instance Chromotopy and DZB’s blog (via Motivic Stuff).
  • Eckhard Meinrenken’s book Clifford Algebras and Lie Theory is now out. The book is online here if your institution is paying Springer.

Update: A live blog from the AMS talk is here. See the comment from “M” here which has an abstract of the talk giving some of its main conclusions.

Update: CERN has a press release with the results here.

… these features show evidence of a new physics phenomena.

The exact shape of the spectrum, as shown in Figure 2, extended to higher energies, will ultimately determine whether this spectrum originates from the collision of dark matter particles or from pulsars in the galaxy. The high level of accuracy of this data shows that AMS will soon resolve this issue.

Update: For a summary of the significance of this for dark matter, see Resonaances.

The paper is here. The delay in the public announcement was clearly caused by Ting’s decision, unusual these days, to not submit a preprint to the arXiv when the results were ready, but just quietly submit to a journal (PRL, on March 14th), and say nothing publicly until the paper was accepted and published.

Update: Better (as in free) link for paper.

Update: The Templeton Prize was announced today, April 4: Desmond Tutu.

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Strange connections to strange metals

Posted on April 2, 2013 by woit

In recent years much of the attention of string theorists has turned to applications of string theory (via AdS/CFT) to heavy-ion physics and condensed matter physics. Since I’m no expert on either topic, I’ve been curious to hear what experts think about this. In the case of heavy-ion physics, as far as I can tell, this doesn’t seem to have worked out very well, with string theory not of much use to say anything about heavy-ion physics at the LHC (although I’d be interested to hear from those more knowledgeable about this). There does still seem to be some promotional activity in this area, with Joe Polchinski last month giving a popular talk in which he claimed that

The quark-gluon liquid, produced at the RHIC accelerator in NY and by the LHC, is best modeled as a black hole, by applying AdS/CFT duality.

On the AdS/CMT front, one expert is now being heard from. In the latest Physics Today, Philip Anderson has a piece called Strange connections to strange metals, in which he responds to an earlier Physics Today article by Hong Liu, From black holes to strange metals, which claimed:

String theory relates gravity to the physics of a novel phase of matter observed above the superconducting transition temperature.

Anderson writes:

It [the earlier Physics Today article] is one of many quasi-journalistic discussions I have seen of results using the AdS/CFT (anti–de Sitter/conformal field theory) correspondence from quantum gravitation theory ostensibly to solve condensed-matter physics problems such as the “strange metal” in the cuprate (high Tc) superconducting metals. As the probable source of the buzzword phrase “strange metal” to describe the phenomena observed in the cuprates and of a theory that bids well to explain those phenomena in detail, I think I have a reasonable motivation to object to the publication of those claims, even though advanced tentatively, when so much is known about this particular phase.

He ends with a summary of what he sees as the problem with the whole AdS/CMT idea:

As a very general problem with the AdS/CFT approach in condensed-matter theory, we can point to those telltale initials “CFT”—conformal field theory. Condensed-matter problems are, in general, neither relativistic nor conformal. Near a quantum critical point, both time and space may be scaling, but even there we still have a preferred coordinate system and, usually, a lattice. There is some evidence of other linear-T phases to the left of the strange metal about which they are welcome to speculate, but again in this case the condensed-matter problem is overdetermined by experimental facts.

Hong Liu responds here.

Anderson will be here at Columbia to give a colloquium April 15 on The Discovery of the Anderson-Higgs Mechanism. I’ve written something about this history here, look forward to hearing about it from Anderson himself. There’s much speculation about a possible Nobel for the Anderson-Higgs mechanism this year, one wonders if the Nobel committtee has any AdS/CMT proponents…

Update: An additional comment about this just occurred to me: the criticism of Anderson’s work on the Anderson-Higgs mechanism has always been that he didn’t appreciate how different relativistic systems. Now he’s claiming the AdS/CMT proponents don’t appreciate how different non-relativistic systems are.

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Grothendieck News

Posted on March 30, 2013 by woit

On Thursday someone pointed out to me that it was Alexander Grothendieck’s 85th birthday. Hopefully he is well and celebrating appropriately. Coincidentally I just heard the following rumor. Supposedly a couple months ago the librarian at the IHES got a phone call from a man who said his name is Alexander Grothendieck, that he needed a specific book from the library and asked if he/she could mail it to him at a certain address somewhere in the south of France.

The librarian said that books are lent only to IHES members and no books are sent by mail. The man on the phone said something and the librarian said that he/she must consult with the director. The director then went ahead and had the book sent.

Perhaps someone can confirm this rumor. Of course the first question that comes to mind is: “What book was it???” (And yes, if I do find out, I suppose I shouldn’t blog the answer, to respect Grothendieck’s privacy…)

Posted in Uncategorized | 17 Comments