Wednesday, July 27, 2011

The LHC makes me yawn

This post may just reflect my ill informed prejudices. Please correct me.
Sorry, but I cannot get excited about the Large Hadron Collider (LHC). I find it hard to see how it is going to reveal the secrets to the universe, or even to produce new scientific insights comparable to the expense and effort involved.

First, I find it hard to believe that the Higgs boson will not be found. My limited knowledge of particle physics and the standard model is that it just has to be there. Spontaneous symmetry breaking and the associated dynamical mass generation is well established in other areas of physics (e.g. the Meissner effect in superconductors can be viewed as photons acquiring mass, as first emphasized by Anderson). Hence, I won't be surprised if it also works / is present in the Standard model via the Higgs boson.

On the one hand, the LHC (search for the Higgs boson) is an experiment that should certainly be done, in a world in with almost unlimited resources for science.
On the other hand, I remain to be convinced that the LHC is a much better investment than "tabletop science." The latter has produced Graphene, violations of Bell inequalities, spin ice, fractional statistics in the quantum Hall effect, and cuprate superconductors. To me anyone of those is of comparable importance to confirming the Higgs boson is really there.

An earlier post considered the second of Two questions physics can no longer avoid, asked by Martin Gutzwiller in a Letter to Physics Today, published in August 1994.
His first question was, "Has particle physics fulfilled its promise?"


  1. I invariably get a little excited when I get to tell someone that condensed matter has Anderson-Higgs, Chern-Simons, anyons, nonabelions, or Majoranas. Usually they're just being polite, but it reminds me that condensed matter has a lot of cool stuff at, I imagine, a fraction of the price.

  2. I agree with you that confirmation of the Standard Model would hardly justify the construction of the LHC. But there is now substantial evidence (dark matter, neutrino oscillations, etc.) for tangible physics beyond the Standard Model. I am no expert either, and so I can't reproduce the arguments here quickly, but I've been convinced by discussions with colleagues that at one of the most likely dark matter candidates is a super symmetric particle found at a mass scale accessible by the LHC. Not being an expert, I can't say whether this is wishful thinking or not. But IMO this is much more exciting than the Higgs.

    I'm as jaded a CM physicist as one can find, but even I have to agree that it is a fantastically important unsolved physics problem is discovering what it is that makes up 20%+ of the stuff of the physical universe.

  3. It appears to be entirely possible that the LHC will find nothing - neither a Higgs boson, nor any deviation from the rest of the standard model. All the exclusions for the Higgs boson currently being announced apply only to the simplest model of the Higgs sector. An extended Higgs sector can apparently perform all the functions of the simplest Higgs model, while remaining completely undetectable at the LHC.

    The expectation of something besides the Higgs at the LHC comes from the "hierarchy problem" and the "little hierarchy problem". The hierarchy problem is the question of why the Higgs mass scale - or, less presumptively, the electroweak mass scale - takes the value it does. Naively, the Higgs mass should receive quantum corrections that make it much heavier. One way to avoid this, without exponentially improbable finetuning of parameters, is to have supersymmetry, but then supersymmetry has to be broken a little, since we haven't seen the superpartners. But as the susy-breaking scale increases, a new, much milder form of finetuning enters the picture. That is, if the superpartners exist at 1 TeV, that would be "natural", but if they are at 10 TeV, that would require (as I understand it) a 10% finetuning - and so on up the scale. The possibility of smaller-scale finetuning is the "little hierarchy problem", and it has motivated all sorts of models of supersymmetric physics "just around the corner" - at 1 TeV rather than 10 TeV.

    But the string theorist Lubos Motl argues, I think convincingly, that the little hierarchy problem was never very well-motivated. Certainly not, when compared to the original hierarchy problem, which potentially involves finetuning to one part in 10^15 or so. Lubos's informal sociological analysis is that particle physics phenomenologists were motivated to construct and hype these models which predicted "stuff" at the LHC (extra dimensions, micro black holes, new particles and forces) because it justified their work, and the little hierarchy "problem" offered a convenient rationale for this practice.

    Perhaps the best place to read about the confrontation between theory and experiment in the coming months will be the blog at