A report from one of last Saturday’s events at the World Science Festival has string theorists Brian Greene and Shamit Kachru admitting that they’d be surprised to see experimental evidence for string theory in their lifetimes:

John Hockenberry, the panel’s moderator, asked Greene if he thought experimental evidence would come during his lifetime.

“I’d be surprised,” said Greene.

“And in your lifetime?” Hockenberry asked Kachru.

“…I’d be surprised,” conceded the young physicist reluctantly.

For more reports about the same panel discussion, see here and here.

Ludwig Boltzmann saw no evidence for the atomic hypothesis in his lifetime, underlying his work on kinetic theory, microstates and entropy and the Maxwell-Boltzmann distribution.

And he committed suicide.

Which is one way to guarantee that one won’t see results in one’s lifetime.

A role model for the ages?

The moderator seems to have avoided the obvious follow-up question, i.e. “Why the f*** are you still working on it, then?”

For the vast majority of theorists the fact their theories cannot be verified in their life time is a blessing!

Only a tiny amount of theoretical ideas turn out to be correct in the end. If verification were straightforward almost all theorists would see their vacuous ideas butchered by experiments.

The fact there is no way to separate the wheat from the chaff brought progress in fundamental physics to a halt.

Boltzmann saw no evidence of the atomic hypothesis? The man pioneered statistical mechanics! Just because there was still resistance to the atomic hypothesis does not mean there was no evidence–Dalton saw evidence of the atomic hypothesis before Boltzmann was even born.

I expect to see the disproof of supersymmetry, and thus indirectly of string theory, at the LHC in my lifetime.

Can we even see a

defining equationof string theory within our lifetime?The real power of String theory is that it *explains* things in a consistent way and does not just describe them. This is essential for a TOE. If someone could give a better explanation for the origin of the field content in 4D for example then we could compare the two approaches. Until then String theory is the only viable explanation and thus it would be very interesting to see where it can lead.

Giotis,

I keep hearing this, and I keep asking how string theory explains the black hole information paradox (how does information get out of a black hole?), and I keep getting completely incoherent answers. Maybe I’m dumb, but it certainly doesn’t explain everything to me.

@giotis:

The real power of String theory is that it *explains* things in a consistent way and does not just describe them.

While I’m not dead keen on a lot of what she says, Nancy Cartwright in one of her books notes that explanatory success accompanied by descriptive failure is a bad way to do science, at least over the long haul. Given its detachment from any observable context which could constitute an empirical test, it’s hard to see any descriptive efficacy in ST. And we’ve yet to be given any real reason to believe that the theories in physics which *do* connect with observation fall out as theorems from ST. So exactly what is the explanatory triumph you appear to be attributing to ST which redeems its descriptive failure ?

Let me play the devil’s advocate for this once.

The question involved the time the two scientists think -or are willing to state they expect- to live, together with the time before they think a first evidence for string theory will concretize. So they had to give a statement on the ratio R=T_s/T_d between the time to an evidence for string theory and the time to their death, and they both said they would be suprised if this ratio R turns out to be smaller than 1.

If you consider it this way, claiming that sihce they believe that R>1 they should work on something else makes as much sense as saying that the Tevatron should not search for the Higgs boson, given that the expected reach on the ratio R between the observable Higgs rate and the expected SM one is larger than unity…

Cheers,

T.

Or maybe they think that we will all be eaten by a black hole before we get to the energies we need to test string theory 🙂

/gets coat & sneaks away

I think that what is more relevant than specific estimates of the distance to the goal of string theory unification is the time evolution of these estimates.

1985: String theory enthusiasts were very excited, many were convinced that evidence would be found within a few years, say less than five.

2000: A typical estimate might be more like 20 years to go. See

http://www.longbets.org/12 where in 2002 Kaku and others were willing to bet money on superstring unification before 2020.

2010: Given normal life expectancies, we’re now talking about more than 40 years from now as an estimate from string enthusiasts about when they will have evidence.

@Thomas Larsson – how would LHC DISPROVE SUSY? If SUSY is not seen couldn’t that be consistent with a breaking scale above LHC energies?

Are there genuine particles or phenomena the LHC could plausibly see, such as technicolor, or Top-quark assisted technicolor, 4 generations of SM, preons, higgless EW breaking, or the non-detection of SUSY partners such as little Higgs, that would definitively discredit SUSY?

I spent the last month studying something out of string theory – the F-theory GUT models – because they very clearly have a chance of looking like reality. It seems inevitable either that the F-theory program will issue in the discovery of string-theory backgrounds which are completely consistent with experiment and cosmological observation, and in which all Standard Model parameters have a concrete explanation in terms of compactification, brane configuration, and various “fluxes”; or that the program will result in an impossibility theorem, to the effect that such models can’t do the job after all. I’d expect one outcome or the other within a few years, and obviously it’s big news either way.

So I struggle a little to understand what Greene and Kachru are thinking. But the panel discussion was about extra dimensions, so probably they were talking about direct experimental evidence for extra dimensions, such as missing energy. The F-theory models prove that you can already interpret particle physics in terms of specific higher-dimensional phenomena, so I would have thought there’s a very good chance that we’ll have indirect arguments for extra dimensions very soon.

I haven’t followed all the latest papers, but early on F-theory GUTs ignored all moduli stabilization problems, and had at best a hand-wavy argument for preferring (fairly high-scale) gauge mediation to gravity mediation. (My experience is that gauge mediation tends to be delicate — it’s difficult to stabilize all moduli and cancel the C.C. without breaking SUSY.) So there’s a long chain of tenuous arguments that end up predicting — minimal gauge mediation! Which, of course, predates F-theory GUTs by many years. Seeing it wouldn’t convince anyone of anything about high-scale physics, beyond the zeroth-order question of what scale SUSY is broken at.

I’d be surprised if string theory makes a definite prediction in my lifetime.

Even if you can’t get falsifiable

predictionsfrom string theory, you could still falsify some of the assumptions it is built upon. E.g. spin-2 gravitons seem to everyone to be logical and necessary and require some kind of stringy framework unlike the spin-1 vector bosons in the Standard Model, but suppose gravity doesn’t conform to the expectations of Pauli and Fierz, and isn’t spin-2. It’s looked logical to Ptolemy to model the sun and stars daily orbiting the Earth… things did not turn out to be that simple.Like Ptolemy’s epicycles, string theory is an ad hoc mathematical explanation for a widely held prejudice which still hasn’t a shred of experimental evidence behind it. Maybe we need a new Kepler.

OK, maybe string theory has not predicted anything definite about the real world yet. But via the AdS/CFT correspondence it has made many precise predictions about some gauge theories at strong coupling, like the N=4 supersymmetric Yang-Mills.

These predictions are testable. In fact, some of them have been tested by solving for some qauge theory quantities as functions of the coupling and comparing with string theory at strong coupling. It works!

Maybe this is not enough to satisfy some of you critics, but I find this amazing.

AdSCFTfan:Woit has been fairly consistent in saying that it’s stringunificationhe thinks hasn’t panned out, not all the mathematical developments associated with string theory.Dan, if no hint of susy were observed at the LHC it would mean, as you say, that its scale is significantly higher than 10 TeV. In that case it would lose most, if not all, of its phenomenological appeal.

Fluffy Eschaton:

Thanks for the clarification. Why is this blog still called `Not Even Wrong’ then? Them there harsh words…

Isn’t it time to admit that string theory gets some things right? Hey, you never know: the real world may budge next!

anon., what I anticipate is that a specific higher-dimensional effect may become the standard explanation for a specific unexplained feature of the Standard Model. The analogy is with SU(5) GUT explaining the weak mixing angle and supersymmetric GUTs providing exact unification of running coupling constants. For example, the F-GUT explanation of flavor hierarchies (arXiV:0906.0581).

Dan is right. Even if LHC falsifies SUSY in 4D it doesn’t mean that SUSY doesn’t exist in 10 or 11 dimensions i.e. in the energy realm of string/M theory. Supersummetry is inevitable in String theory for internal consistency reasons and not because it is a good candidate for physics beyond the standard model in 4D.

So even if LHC falsifies SUSY in 4D they could always construct models that break all the SUSY in 4D upon compactification. They will have to search for a different kind of vacua that’s all.

@ Remo, Michio Kaku, Lubos and other string partisans have argued that it is merely a limitation of collider technology that prevents experiments above 10 TEV scale. If SUSY is broken above 10 TEV, and there were colliders that could explore this scale, wouldn’t it be phenomenologically interesting? Maybe not stabilizing EW scale but perhaps DM candidates?

@ Giotis the successor to CDMS II is SuperCDMS. It evidentally has the sensitivity to detect neutralinos over its entire parameter space.

ref:

http://arxiv4.library.cornell.edu/abs/1005.0761

SUSY dark matter in light of CDMS II results: a comparative study for different models

Authors: Junjie Cao, Ken-ichi Hikasa, Wenyu Wang, Jin Min Yang, Li-Xin Yu (Submitted on 5 May 2010)

“(i) For each model the new CDMS limits can exclude a large part of the parameter space allowed by current collider constraints; (ii) The property of the allowed parameter space is similar for MSSM and NMSSM, but quite different for nMSSM; (iii) The future SuperCDMS can cover most part of the allowed parameter space for each model.”

If the LHC does not find neutralinos, and the future SuperCDMS (and other direct and indirect dark matter detection) also fails to detect neutralinos with sensitivity to detect them over its parameter space, is there a plausible SUSY model (4D or 11D, planck-scale, etc.) that could account for both null results?

Can SUSY be a symmetry of nature broken at any scale if neither LHC nor SuperCDMS detects them?

“Can SUSY be a symmetry of nature broken at any scale if neither LHC nor SuperCDMS detects them?”

From Frank Wilczek’s Future summary from 2001, p 20:

“Of course, the ultimate test for low-energy supersymmetry will be to produce some of the predicted new R-odd particles. Even in the focus point scenario, there must be several accessible to the LHC.”

@Dan

Yes of course. Supersymmetry has been well established by String theory as a theoretical concept at high energies.

Whether it would be observed at the low energies of LHC is not vital for Supersymmetry although psychologically this would be bad news for SUSY and String theory.

Moreover the vast majority (if not all) of String theory models have been constructed for N=1 SUSY in 4D so a failure in LHC would have I guess a significant impact in 4D model building.