The latest issue of Seed magazine (not yet available online, as far as I know), contains responses from various well-known physicists who were asked what they hoped to learn from the LHC. Here’s the gist of what they had to say:
Lisa Randall: The magnificent thing is that we know there should be an answer to the question of the weakness of gravity, and that it should be revealed at the LHC.
Leon Lederman: The long-simmering concern over the weakness of Einstein’s gravity may well be confronted. However, what is for sure is that the LHC, with its awesome reach, will answer all of our current astro-particle problems…
Alexander Vilenkin: If no trace of supersymmetry is found, this would be – necessarily indirect – evidence for the existence of the multiverse.
Sir Martin Rees: I’m hoping that it will clarify the nature of the particles that constitute the “dark matter” in the universe.
Edward Witten: The LHC wil tell us whether this notion [electroweak symmetry breaking] is correct, and if so how it works.
Max Tegmark: Our theory of particle physics has 26 pure numbers in it. Why do they have these particular values? How did the universe begin? Did it?
Leonard Susskind: I see only two possible outcomes of the LHC project – either there will be low energy supersymmetry or there won’t. … the big question is whether the gauge hierarchy fine-tuning is similar to the cosmological constant fine-tuning, or if it has a more conventional supersymmetric explanation.
Steven Weinberg: What terrifies theorists is that the LHC may discover nothing beyond the single neutral “Higgs” particle.. We fervently hope for some complicated discoveries.
John Schwarz: There are many speculative ideas for possible discoveries at the LHC. These include indications of extra dimensions, black holes, strings, magnetic monopoles, etc. I believe that all of these exist, and I would be thrilled to have experimental confirmation – but I am pessimistic about the prospects for finding them in the LHC’s energy range… I could be wrong. That’s why it is important that these experiments be carried out.
Sean Carroll: The beauty of science is that we don’t know what surprises may await us in these domains.
Gordon Kane: The LHC could discover the superpartners in a supersymmetric world. In addition to strong theoretical evidence for Higgs physics, there is strong experimental evidence that Higgs particles do exist with a mass implied by supersymmetry… Probably the main thing we have learned in the past two decades is that any understanding of nature at the most fundamental level (beyond a description) will require extending our thinking to embed our world in extra dimensions… An optimist (like me) can make the defendable argument that the LHC could test supersymmetry, establish string theory and move on to the remaining “why” questions.
My predictions: The LHC won’t see supersymmetry and won’t tell us anything about dark matter, dark energy or why gravity is weak. Witten has it exactly right, what the LHC will do will be to start to tell us what is causing electroweak symmetry breaking. It’s possible that Weinberg’s worry will be borne out, and, at LHC energies, we’ll just see what appears to be an elementary scalar, which will be depressing. But I think it’s equally likely that symmetry breaking is not coming from an elementary scalar, but from something much more interesting, quite possibly something we haven’t thought of, and the LHC may start to give us evidence for what this is.
I’ll also predict that we are still a few years from finding out what the LHC will tell us. These will be completely wasted years for particle theory if people just give up on looking for new ideas and sit on their hands (or wander pointlessly in the landscape), waiting for the LHC to revive the subject.
Yes, Witten gets it exactly right. But why do the others fail to answer right?
AR
Papal infallibility would be a cheap shot. Maybe he doesn’t have an obvious agenda, other than his work/research ethic?
I think that theoretical high energy physicists have speculated enough already. Time to wait for the data to come in. I suggest that, in the meantime, they should work on quantum computing. This would help balance their highly unbalanced Doritos diet. There was a time when theoretical physicists (Landau, Feynman, …) could chew gum and walk at the same time.
Can someone explain to me how one can find indications of magnetic
monopoles at LHC (John Schwarz’s comments)?
Thanks
By “why is gravity weak”, you should understand “why is the weak force strong,” a question that one hopes will be answered by the LHC. That is, is EWSB natural or is it finely-tuned?
I agree with EW, PW and AR, and what are those who think otherwise smoking?
You gotta love Vilenkin’s reasoning: Prob( Landscape | No SUSY at LHC & String Theory ) > Prob( Landscape | SUSY at LHC & String Theory ), therefore Prob( Landscape | No SUSY at LHC ) > Prob( Landscape | SUSY at LHC ). Because of course Prob( String Theory ) = 1.
… Gordon Kane’s answer is the best one because it maximizes the product of “interesting content” times “good motivation”. SUSY is going to be seen, and obnoxious critics of physics will finally be annihilated. Others either give overly speculative and unlikely answers or uninteresting answers …
http://motls.blogspot.com/2006/06/lhc-predictions-gordon-kane-wins.html
ED:
That would be interesting except that Vlienkin isn’t a string theorist. As Sean mentioned in his recent post, many cosmologists are landscapists without any need for string theory.
This must fall from the same sort of logic that derives that evidence that we’re not here by accident is evidence that we are.
I see that the list of experts does not include Carlo Rubbia (in fact, other than Lederman there are no expt physicists quoted). People forget that Rubbia did in fact discover supersymmetry (UA1 monojets), also the top quark (Mt = 44 GeV, anyone remember?). Put CR in charge of an LHC expt and there would be monopoles + strings + multiverse in a week.
But, really, only 1 expt physicist in the list?
sunderpeeche:
Experimentalists give boring answers, because they have a realistic sense of the machine’s limitations. Similarly, the lack of collider phenomenologists except Gordy Kane, who in his zeal tends to exaggerate what can be done.
So the choice is: talk nonsense or be boring? (I think Witten and Weinberg gave good answers, although not “exciting” ones.)
I favour the scenario:
They find nothing at all. No Higgs. No susy. No monopoles. No nothing.
Dear B,
what you write violates the rule of logic that the total probability of alternatives equals 100%. It is not possible to find nothing at 1 TeV, not even Higgs, because it violates unitarity of the WW WW scattering. Without the Higgs, the Standard Model gives you too high a prediction for the cross section of this process that would make the total probability of scattering greater than 100%.
Best
Lubos
Theorists already predicted everything LHC can see.
Aaron,
You’re right, I just looked him up at the arxiv. I suppose it’s possible he thinks Prob( SUSY | Not String Theory ) is not small, in which case his reasoning would be more complicated. Hard to tell.
Lubos Motl Says:
what you write violates the rule of logic
Dear Lubos,
whether that conclusion is one of logic depends on the validity of the axioms you use to draw the conclusion. I agree with your argument though.
Best, B.
Lubos said: It is not possible to find nothing at 1 TeV, not even Higgs
Care to place a wager on this, Dr. Motl?
Gordon Kane: The LHC could discover the superpartners in a supersymmetric world.
For many years, I was cautiously positive about string theory. It always bugged me that it apparently was in complete disagreement with experiments, but OTOH the math was cool and obviously relevant for statphys, which was the kind of physics I cared most about. An article by Gordon Kane in Physics Today in 1997, entitled “String theory is not only testable, but super-testable”, changed all that. It made it clear to me that string theory is not only wrong but evil, because it has the power to transform senior scientists into babbling crackpots, as is manifest already from the title; IIRC the body of the article was far worse.
But in retrospect Kane’s article appears as quite sane compared to the landscape stuff.
I read in an online physics book the prediction:
LHC will discover that the Higgs particle is composite,
not elementary, as there cannot be any elementary
spin 0 particles.
John,
That’s definitely one possibility. But composites of what? Bound together how? And will the composite nature only show up at much higher energies than those accessible at the LHC? There has been a lot of work on some models of this kind (e.g. Technicolor).
You statement really is amusing and ironic, Thomas. The thing is, Gordy Kane has never been a string theory partisan. In fact, he’s always been a supersymmetry partisan which is something different.
As with the above comment Vilenkin, not all that ails the world can be laid at the feet of the horrible string theorists, it seems.
Aaron, Gordy has been talking for a while about how to use LHC data to help pin down the underlying string theory construction.
dear Lubos,
ideally you are right. But in practice LHC is a dirty hadronic machine: it is not clear if LHC allows to test if WW WW scattering exceeds unitarity. What would an experimentalist really see, in that case?
Aaron,
Kane has written quite a lot promoting string theory. See for instance
http://feynman.physics.lsa.umich.edu/kane/Zing.htm
He explains there his relation to string theory:
“I am often asked what is the connection between string theory and supersymmetry. String theory is like a musical score. Supersymmetry is like the performance. If you can read the score and hear it in your head you don’t need the performance, but most of us do. Or, string theory is the recipe, supersymmetry is the cake.”
Several people,
Please, stop posting here advertisements for your unorthodox ideas about physics on the grounds that they are “LHC predictions”. If you want to discuss the topics covered in this posting fine, if you want to promote yourself and your own ideas that have nothing to do with this posting, do it elsewhere.
I’m not saying that Kane is anti-string theory. He obviously isn’t. He’s not a string theorist, though; he’s a phenomenologist. When I last saw him (a few years ago at TASI), I got the impression that string theory was interesting in as much as it told us something about supersymmetric model building. (Modulo unlikely things like weak scale gravity, of course.) Along those lines, hep-th/0509157 or hep-ph/0403040.
Giving that the Yukawa coupling of the top is 0.998 or so, a composite model explaining this phenomena is inviting, but I do not know any. A second question about composites is if it can be really claimed that they avoid the hierarchy problem (at least, it will depend on where do you put the compositeness scale).
To John Stanton
John, people say that fundamental scalars cannot exist because in a 4 dimensional renormalizable field theory, the coupling constant would flow to zero under the renormalization as the cutoff is taken to infinity. A similar thing will happen in dimensional regularization as the dimension 4 limit is taken.
Hence the only possible 4 dimensional scalar field theory would be a trivial noninteracting or free one if the the cutoff is infinite. If one considers the possibility that the cutoff is finite, the one can have scalars, but these are not considered fundamental as there must be something beyond the cutoff of the scalar field theory. Peter is right that the interesting thing is what, but unfortunately, that cannot be found unless one makes measurements at the scale of the cutoff or beyond.
Aaron, the article is too old to be available on-line, but the content of the February 1997 issue of Physics Today is available here:
“Superstring Theory Is Testable, Even Supertestable
Many believe that superstring theory, because of its extraordinarily tiny length scale and gargantuan energy scale, cannot be tested. That belief is a myth — Gordon Kane”
If you think my comment is so funny, maybe you could tell us how to supertest string theory.
I read the article. It’s available if the library has a subscription.
“Superstring Theory Is Testable, Even Supertestable
Many believe that superstring theory, because of its extraordinarily tiny length scale and gargantuan energy scale, cannot be tested. That belief is a myth — Gordon Kane”
From what has been cited here and in the blog text it seems evident that it is more the string physicists who have a reasonable opinion (because they know what they talk about), rather than the beyond-the-standard-model extra-dimensional phenomenologists, isn’t it? It’s them who keep the standards high.
BTW, any idea what the people who actually run the experiment and do all the work think about the outcome? I would think these should be asked in the first place. But probably they are all idiots and busy with pulling cables etc.
A question to the experts: are we completely, 100%, sure
that, in the case that the Higgs is composite,
the components and forces keeping the parts
togther must be new? In other words,
are we completely sure that this is not the strong
interaction, for example?
I read the article. It’s available if the library has a subscription.
Means what? That just because you have read a particular piece of propaganda, it is ridiculous to call that piece of propaganda by its right name?
Besides, you didn’t answer how string theory could be supertested. Or, since scientific theories only can be falsified, maybe I should ask for a doable experiment which would superfalsify string theory.
David, John: It should be stressed that the “triviality limit” is shown in most plots of new physics, specially the one from Chris Hillman that appears from time to time in the Review of the PDG, sometimes showing both the “triviality” and the “unitarity” bounds, as well as vacuum stability. In fact this plot is the main argument to claim we will find something at LHC energies.
You’re missing the point, Thomas. I’m not defending the article. I’m just amused that it was an article by a phenomenologist who focusses on supersymmetry that turned you off on string theory.
Hi all… Nice collection of comments I must say!
FWIW, I agree with Witten, Rivero, and (of course!) Peter Woit.
I am in CMS, but I think CMS and Atlas will see very little. They will do precision physics (t), unfortunately following the tradition of LEP (Z) and LEP2 (W). They will only find the Higgs, but only if they are lucky – not because I think there is none there, quite the opposite! Because CDF and D0 have a real chance to see it first!!
Why do I think that LHC won’t find any SUSY ? Because I don’t buy it. But also because CDF and D0 should have found something weird in their dataset by now!
In Run I, CDF saw a extremely unlikely event with two electrons, two high-Et photons, and significant missing energy (a neutrino, most likely – or two). I must confess that the eeggmet event was on the verge of changing my attitude toward SUSY, but then… With 10 times the statistics, CDF and D0 haven’t seen anything weird anymore; extensive searches (with more acceptance to anything weird) for parents of that event have seen nothing! So one is left with the feeling that the eeggmet event was a fluke anyways. In that case, a SM fluke is, by force of Ockham’s razor, to be preferred…
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What about the HyperCP events that claim they might be seeing a SUSY sgoldstino?
Does anyone know if anyone is going to try to recreate the experiment?
Fred
Aaron, I’m sorry that I misinterpreted you.
I think the best prediction is that we will learn more about the “notorious” question of the Higgs (or Higgses); none of us know precisely in what way.
In that sense Sean Carroll is right: the beauty of science is that this is unknown terrain.
And a terrain in a vast and unknown Landscape? Who knows? 😉
I find it wrong – and not even wrong – trying to do a cost-benefit analysis here, or to say that time will be waisted with the LHC.
Any other ideas? Trying to find answers by debunking string theory, or modern quantum field theory? Or trying to find a “background independent” answer?
Witten is certainly right that we will learn a lot about EWSB at the LHC. The betting odds are that a SM-like Higgs boson will be found, though this won’t by iteself provide clear evidence for low-energy supersymmetry. After that, one’s tastes in exotic physics determines what one expects/hopes to find. At that level there is no point in making a general statement about weak gravity or extra dimensions or SUSY or string theory (not to mention multiverses) – only the experiments will tell us what is there. Making pronouncements about what the LHC will find is worse than predicting who will win the world cup! If, as Bee predicts, there is no new physics and no Higgs boson (or its surrogate), then we cable tuggers will be very frustrated indeed, but the community will certainly have learned something big: the Standard Model and most models of physics beyond the Standard Model will essentially be ruled out, and all the enthusiasm over the last few decades about the Higgs mechanism will have been misplaced.
I certainly agree that SEED should have polled more experimenters, especially a couple out of the thousands who actually work on LHC experiments. How strange it would be to publish an article on the national economy based on comments from, say, applied mathematicians. Or even stranger, to write an article on the future of theoretical physics after talking to a dozen experimenters. I guess the lesson is that the star power resides in the theoretical community, so it is good for SEED circulation to tap there…
# robert Says: Papal infallibility would be a cheap shot. Maybe he doesn’t have an obvious agenda, other than his work/research ethic?
Hmm I’d better tell that Witten’s agenda, whatever it is, happens to coincide now with the real physicist agenda. In previous occasions Witten agenda seemed to be the use of his influence on mainstream research to promote interesting mathematical topics, as noncommutativity or K-theory, to name a couple ones. In most cases, the result has not been very happy, with a flood of string-oriented papers obscuring the mathematical and physical meaning of the concepts -mostly because they drank only from Witten’s papers-.
If the LHC doesn’t find superpartners, isn’t that in itself significant, as evidence against supersymmetry? (Or at least as evidence against SUSY at energy scales where it could be an answer to the hierarchy problem?)