This may be old news, but I just recently noticed that talks given at the IAS in Princeton last fall to celebrate its 80th anniversary are now available on-line here. They include talks by Voevodsky on the foundations of mathematics, Zaldarriaga on cosmology, Wilczek on supersymmetry and quantum computing, and Arkani-Hamed on Fundamental Physics in the 21st Century.

According to Arkani-Hamed, the 21st century will be all AdS/CFT, all the time, using it to justify:

the slogan is that string theory/quantum gravity is particle physics…

There is a less interesting but amusing sociological fact associated with this, that since this realization there aren’t really different camps in theoretical physics any more. There aren’t string theorists and particle theorists, there’s one big structure “Good Ideas in Theoretical Physics”, OK. That structure has many different facets and you can work on different parts of it, but it’s all connected. You can really see it in the way the field developed since the late 90s, we’re much, much more one big happy family than was the case in the 1980s. I should say of course there are still people that do bad theoretical physics, but they’re not at the Institute. So all good ideas in theoretical physics are combined in one very big structure that no longer is there such a big difference between strings, QFT…

This puts into practice Nati Seiberg’s 2005 prediction:

“Most string theorists are very arrogant,” says Seiberg with a smile. “If there is something [beyond string theory], we will call it string theory.”

Both Wilczek and Arkani-Hamed advertise supersymmetry, with Arkani-Hamed making the peculiar claim that physicists need to throw space-time out the window, but for some reason, before doing so it is important that they add supersymmetry to it. Wilczek states definitively that if superpartners don’t show up at the LHC, as far as he is concerned the idea will be gone.

The minimal supersymmetric standard model is an important pillar of the “Good Ideas in Theoretical Physics” that those at the Institute cling to, despite efforts to use them to unify physics failing miserably over the last 25 years. If the LHC doesn’t see supersymmetry and Wilczek and others give up on the idea, it will be interesting to see if the IAS faculty revise their point of view and start to develop more of an interest in what they now claim is “bad theoretical physics”. I suppose though that when they do, they’ll call whatever they change over to “string theory”.

**Update**: By the way, for the latest on what initial results from the LHC are saying about extra dimensions and supersymmetry, see this talk given today at CERN by Alessandro Strumia.

Crystal ball gazing is a popular pastime, no matter that it has regularly failed. The title of Stephen Hawking’s inaugural lecture as Lucasian Professor (1979) was “Is the end in sight for theoretical physics?” (The reason being, of course, the imminent arrival of the Theory of Everything.) So Arkani-Hamed 2010 is no wider off the mark than Hawking 1979. Physics – including “bad theoretical physics” and the Theory of Everything – will move forward on its own merry way.

I’ve always wondered whether or not pure mathematicians dismissively refer to string theory as mere applied algebraic geometry.

Geoff,

No. Mathematicians are well aware that, whatever string theory might be, it’s not a subfield of algebraic geometry.

However, some mathematicians undoubtedly enjoy this xkcd comic:

http://xkcd.com/435/

Peter See nima’s recent colloquium at Perimeter

Yeah, yeah… H.264 encoder needed. IAS doesn’t care …

crying_indian.jpg

Shantanu,

Unfortunately at the IAS talk he never got to the much more interesting material of the Perimeter colloquium.

As a non-physicist, I do not understand why adS/CFT generates so much excitement given that the CC is known to be positive, not negative. Is there a simple explanation?

neo,

Besides that AdS/CFT tells you about gravity with the wrong sign of the CC, you might also want to worry that it tells you about gravity in the wrong dimension…

AdS/CFT is certainly interesting, but I do find the claim that all good theoretical physics is related to it just bizarre.

Frank Wilczek’s talk (http://video.ias.edu/stream&ref=409) is as usual pretty good. He also talks about aliens straight from a Greg Egan novel!

Is he last man standing who likes Spin(10) GUT?

I wonder why the speakers need to start off at super-low level. What kind of audience do these talks have? Hell, give me an equation in the first minute, amaze me!

Assuming that Arkani-Hamed’s talk is the same as the last one I saw, his point (stripped of the propaganda) is that AdS/CFT is a useful mathematical model for describing various physical situations. In fact he explicitly compared it to the simple harmonic oscillator, which (also?) doesn’t exist in the real world.

Since he is modelling physics that is experimentally accessible, or at at least much more accessible than the Planck scale, presumably we’ll know soon whether AdS/CFT is a useful mathematical model or not.

In some sense, string theory is a unique way towards the theory of everything if it really exists. There are numerous reasons for that. Here i list some of them.

1 String theorists are smart

2 String theorists are hard-working

3 String theorists are not stubborn, namely always ready to absorb any important insight or development from other desciplines into their toolbox.

On the other hand, just like GR, when you learn AdS/CFT more, you will be intrigued by its beauty and power. With SUSY, AdS/CFT is a very powerful tool at least.

Peter wrote: Besides that AdS/CFT tells you about gravity with the wrong sign of the CC, you might also want to worry that it tells you about gravity in the wrong dimension…

I don’t understand why you wrote this.

If you are interested in 4-dimensional AdS space then you need a 3-dimensional CFT. There are plenty of those known, and now we also know that some of them are exactly dual to 4-dimensional AdS times a 7-dimensional Einstein space, like a 7-sphere. They are Chern-Simons theories, so you should like them. There has been lots of work on this since 2008. We also know that the critical 3-dimensional O(N) model is dual to a higher spin theory in AdS_4.

My main problem with AdS/CFT is that it’s an extremely technical subject, with by now about 10,000 papers or so dealing with it. This makes it hard for anyone to understand exactly what the state of the subject is, and this is made much harder by its proponents, who engage in an absurd level of hype. If you believe everything you read or hear, you learn that:

1. It’s the modern version of the harmonic oscillator, the central approximation method for solving physical problems that we teach all undergraduates.

2. It contains all good theoretical physics, theoretical physics not related to it is bad theoretical physics. Theorists at top institutions like the IAS are all in agreement about this.

3. It explains heavy-ion physics.

4. It explains high-Tc superconductivity.

5. According to people like Bob, those who work on it are hard-working geniuses, always open to new ideas from all sources. They have found the unique possible route to a theory of everything. It’s not their fault that this theory of everything turns out to predict nothing.

6. According to Arkani-Hamed and AdSCFTlover, this solves the problem of a realistic 4d quantum theory of gravity, that’s done and over now.

John Rennie has been led to believe that soon we’ll have definitive experimental tests of this wonderful subject. But it seems to me that we’re now nearly 15 years into this, and I’ve yet to see anything like a convincing way to confront these ideas with experiment. The most highly developed thing I’ve seen are the attempts to use AdS/CFT to do approximate calculations in QCD, but here it still looks to me like you have only a very crude approximation with little control of its accuracy.

To be honest, as to AdS/CFT, i do not think it is a HIGHLY technical object if one is assumed to be familiar with both GR and QFT, two pillars of fundamental physics in 20th century. In particular, the essential underlying idea is remarkably as simple as possible, but not simpler. So i do believe that an idiot can also understand it.

Concerning its contact with experiments, string theorists are trying their best to making it possible. But there is no doubt that this is a tough job. We should be patient with its progress along this direction.

In addition, i am not saying that string players are geniuses although definitely a few of them are.

PS: After i spent some time on studying AdS/CFT, i found there are many misunderstandings about string theory and AdS/CFT in Roger Penrose’s Road to Reality book. With this sort of experience, i realize that it is very dangerous to criticize something you are not very familar with.

Bob,

Sorry, but you’re really not changing my opinion that AdS/CFT has a problem with its proponents being fountains of hype.

Maybe there is some sort of hype in popular scientific articles related to string theory and ads/cft. But similar hype may also happen to other subjects.

But when you read any serious research paper by string theorists,

you will find that none claims that ads/cft has solved QCD problem. On the contrary, they are always saying that there is a long way to go for real QCD….

In addition, I prefer Nima’s slogan, namely physics makes progress by radical conservativists rather than conservative radicalists. String theorists belongs to the former.

An example of the bad physics pursued by stupid people is described in hep-ph/0604254 where progress towards over-constraining the CKM parameters via a combination of experimental measurements and lattice QCD calculations is reviewed (no doubt out of date by now). Of course, only ignorant losers could possibly be interested in such an approach to determining new physics beyond the SM.

As usual, if ads/cft geniuses and other geniuses have anything interesting to say about physics, let them go publish it in Physical Review Letters.

Cheers from `amused’, after a few too many beers in Taipei. Happy Chinese New Year everyone.

V. Voevodsky’s talk is outrageously shallow. He definitely didn’t do his homework when analyzing Godel’s incompleteness theorems and Gentzen’s consistency proof.

The fact that the formalized version of 2nd incompleteness theorem is provable in arithmetic itself has far reaching consequences. It led (together with other developments) to an important class of logics called Provability logics (http://en.wikipedia.org/wiki/Provability_logic)

Voevodsky’s inability to answer E. Witten’s question [about impact on real numbers and the notion of continuum] makes one wonder if he’s even aware of the work on independence in set theory. For recent advances see Woodin’s review:

http://www.ams.org/notices/200106/fea-woodin.pdf

http://www.ams.org/notices/200107/fea-woodin.pdf

Let’s assume that Mr. Arkani-Hamed is aware of the fact that not all theoretical physics is theoretical particle physics, so let’s replace “theoretical physics” with “theoretical partical physics”.

But then this still means that if you work in theoretical particle physics, you either work on string theory or you’re a bad physicist. The way that Mr. Arkani-Hamed made this statement seems to indicate that it is not meant to be a joke.

Well, someone has to tell the non-stringy particle physicists that they’d better switch to string theory, if they are intellecutally capable to do so, that is. Maybe some of them can be redeemed.

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I have a question about the slides of Alessandro Strumia’s talk mentionned in the post: the physics is over my head, but the tone of the last few slides seems to be that SUSY is now very unlikely to be correct.

So I was wondering how much more data is needed to rule it out altogether (e.g. the little green area not yet excluded on slide 16), and whether this could happen before the 2013 shutdown. Thank you…

joestudent,

The LHC will never be able to completely rule out supersymmetry, since you can always push the masses of superpartners higher. However, if you accept the standard motivation for the subject (“solves the hierarchy problem”), then you get that the supersymmetry breaking scale should be of order 100 GeV. Making other assumptions, Strumia gets a probability distribution peaked there, falling off at higher energies. By this analysis, supersymmetry was already rather an unlikely hypothesis, and the LHC last year removed half of the remaining probability.

I don’t have a reference at hand, but talks by Atlas/CMS people projecting the reach of their experiments under various assumptions shouldn’t be hard to find. My very rough guess is that they should be able to get gluino mass limits in the range 1-1.5 TeV in the run beginning this year, would need more beam energy and/or a lot more data to get up to 2-3 TeV. Even with this though, there will always be some small amount of probability higher.

It’s going to be very interesting over the next few years to see at what point supersymmetry enthusiasts throw in the towel. By Strumia’s measure, already half of the possible places for supersymmetry to hide have disappeared. Probably half of the remaining half will vanish in the coming year. Based on my experience with string theory though, I’m wary of making any estimate for how much evidence it takes to convince someone a speculative idea they favor doesn’t work.

Those plots are for the CMSSM, which is a highly constrained version of the MSSM (although to be fair, the MSSM parameters are already highly constrained by experiment). But weak-scale SUSY does not even have to be the MSSM.

Quite simply, it is way too early to be trying to draw conclusions about the existence of supersymmetry at the weak scale. The next few years will tell. I for one, and I think many other people, will give up on low-energy SUSY if it is not found at the LHC, but the time to give up is not yet upon us!

Rhys (or any other supersymmetry optimists who care to comment),

You have to make some assumptions on supersymmetry-breaking parameters to even make any understandable statements about this subject, since there are over a hundred of them in the minimal version. If you’re not going to be convinced until the LHC nails down bounds on every corner of the parameter space, this could take a while.

What I’m really curious is, at what point would you be willing to give up on supersymmetry if the LHC sees nothing:

1. Late this year (say 3 inverse fb at 7 TeV)

2. Late 2012 (say 5-10 inverse fb at 7 or 8 TeV)

3. 2015? (say 10 inverse fb at 14 TeV)

or later? (will you wait for 100s of inverse fb at 14 TeV, and when nothing is seen then, say then thing to do is to wait for the higher luminosity of the S-LHC, or higher energies from higher field dipoles?).

Peter,

I think it’s only reasonable to wait until after the next two years of running to come close to drawing any conclusions about supersymmetry. As you’ve said, the expected SUSY spectra are dependent on different models of supersymmetry breaking, and there is currently still a lot of viable parameter space in different models. If supersymmetry is there, it will be found. If not, then there should be some other interesting physics to be discovered. I think it’s better to approach things with the optimism and excitement of potential discoveries rather than the pessimism and cynicism that is all too prevalent in your posts.

Eric,

Well, I’m optimistic that the LHC will tell us something interesting, but think it will be about electroweak symmetry breaking and the Higgs.

Still, I would like to hear from those who expect to see supersymmetry about when (in terms of amount/energy of data) they’re expecting to see it.

Peter,

I’ll think we may learn something new about EWSB as well, and I’m very excited to see what is discovered at LHC. I think everyone should try to get past being aligned with and fighting over particular theories and models, as if they were religious doctrines. I do think that supersymmetry plus Higgs is the most likely possibility, however I will rethink this if nothing shows up by the end of 2012.

Hi Peter,

I hope your question about when to give up is moot. If the LHC doesn’t find sparticles, then I desperately hope it finds some other new dynamics around the TeV scale, otherwise I will probably give up on high energy particle physics altogether.

Eric’s comments above are very sensible.

Wilczek in his talk presents a graph of 3 coupling constants, that intersect at high energy. To an uninformed person like me, it looked rather persuasive. Is that honest, or did they have to tweak free parameters to get those 3 lines to intersect?

Hi tristes_tigres,

The gauge coupling unification at high energies happens automatically (within experimental errors) in the minimal supersymmetric Standard Model. Whether or not this is a sign of supersymmetric grand unification or just a coincidence is currently unknown, but many people take it as a circumstantial bit of evidence in favor of TeV-scale SUSY.

tristes_tigres,

The coupling constant unification argument Wilczek gives is probably the best evidence for supersymmetry, but it is still rather weak evidence. The situation is more complex than the way it is usually advertised, for a detailed explanation, one place to look is

http://www.physics.ohio-state.edu/~raby/pdg.guts.revised05.pdf

My understanding is that things work best in a one-loop calculation, going to a more accurate two-loop calculation makes the agreement less accurate. There are many ways to parametrize the size of the disagreement, Raby gives it as 3 sigma. Note that this kind of calculation typically assumes no new physics between the TeV scale and the GUT scale, which most people find hard to believe.

Wilczek has a personal reason for being enthusiastic about this idea, since he was one of the co-authors of the original calculation of this kind.

“I think it’s better to approach things with the optimism and excitement of potential discoveries”

i for once think it has always payed off to approach new theory with extreme scepticism unless they explain all current experimental findings and make definite predictions for future ones.

“I desperately hope it finds some other new dynamics around the TeV scale, otherwise I will probably give up on high energy particle physics altogether.”

so you don’t follow Churchills advise. that might be really good for you and your future life. i for once am much more interested in how nature works and not so much in some particular theoretical idea. i wouldn’t dream of throwing the towel just because an experiment does not confirm my prejudices. but motivations for doing theoretical physics are different i guess.

“i for once am much more interested in how nature works and not so much in some particular theoretical idea.”

When did I say I was only interested in some particular idea?

If all the data from the LHC can be described perfectly well by the standard model with a fine-tuned Higgs, then it will be very difficult to motivate further experimental or theoretical work in high-energy particle physics.

That’s different to saying that there will be nothing to do in theoretical physics…

I think you seriously underestimate human inventiveness 🙂