This week’s New Yorker has a quite good article on the LHC and the state of particle physics with the title Crash Course. One of the main themes of the article is that of the rivalry between experimentalists and theorists. There’s a quote from Leon Lederman:
If I occasionally neglect to cite a theorist, it’s not because I’ve forgotten,… It’s probably because I hate him.
CMS experimentalist Robert Cousins describes worries that triggers designed with too much attention paid to theorists could be disastrous:
There are famous high-energy-physics experiments that missed discoveries because they weren’t writing them to tape… This is why we try not to be too specific about which theoretical speculations we care about. We add up all the energy, and if it’s a huge number we write that event to tape. If on one side of the detector it’s a not-so-huge number, but there is nothing on the other side, so it’s a huge imbalance, we get excited about that, and we write that to tape, too.
The only theorist interviewed is Nima Arkani-Hamed, who, while consuming prodigious numbers of espressos, describes the perception of theorists by experimentalists as:
There is a sense among many experimentalists that theorists are a bunch of irresponsible little spoiled brats who get to sit around all day, having all these fun ideas, drinking espresso and goofing off, with next to no accountability.
and jokes that theorists will need to get a “Deep Throat” among experimentalists in order to get access to any raw LHC data.
As for the state of the LHC, the Resonaances blog at CERN describes rumors from “well-informed sources” that the low-energy test run scheduled for late this year is likely to be cancelled, with a physics run at full energy not likely until summer 2008.
I read in the article that
As of 2000, at least ten thousand scientific papers on supersymmetry, and several thousand more on string theory, had been written.
So what has been learned from those thousand and thousand of papers? What is the best review paper available?
Thanks,
Christine
Christine, Einstein said if 100 geniuses all believe in the same thing, at least one of them should be able to provide some solid reasoning, and if they can’t do that, you begin to wonder how ingenious they really are. That was in 1931 when 100 Authors Against Einstein was published. Supersymmetry is pretty similar. So many people can’t all be wrong in their prejudiced opinions, even though they have no solid evidence and furthermore – with the landscape problem – no conceivable way of ever getting any solid evidence. What’s been learned is that the landscape undermines the credibility of the subject, but the inertia of groupthink continues.
I am sure that quite a lot has been learned, but I doubt that any of it is relevant to the LHC.
Re: the New Yorker article, I am curious about some of the more wacko speculations as to what the LHC might produce, e.g. extra dimensions or mini black holes. How would one know? In the time-honoured particle physics tradition, all the LHC experiments use measured position and momenta of detectable particles to infer properties of the unstable particles that may have created them using relativistic kinematics. One may be able to enlarge the table of known particles by analysing these data, but how does one go from this to demonstrating the existence of extra dimensions or mini black holes? In these cases one would surely need to have a clear idea of how these esoteric ideas impacted the list of known particles and their properties first – something that at present is clearly lacking.
Maybe I am missing something here. Does the LHC have an experiment specifically designed (e.g.) for catching mini black holes? (other than in the funding, obviously).
Christine,
As far as attempts to use supersymmetry and string theory to connect to the real world, the three books I wrote about recently each review this. Dine is strongest on supersymmetric field theory, Becker-Becker-Schwarz on string theory. Lots has been learned about string theory and supersymmetry that is irrelevant to the real world, but there’s such a variety of things that I don’t know a single source that reviews them.
Chris,
There are “brane-world” models in which the quantum gravity scale is low and you can estimate cross-sections for producing black-holes, and what the experimental signatures would be if you produced them. There’s a whole industry of people doing this. Of course it’s pretty much completely unmotivated, there’s no reason at all to believe that the quantum gravity scale is around 1 TeV, carefully set so as to have zero effect at the Tevatron, but a dramatic effect at the LHC. Then there’s the problem that these things maybe should already have shown up in neutrino experiments.
As far as I can tell virtually no one believes that this kind of thing will be seen at the LHC, but a lot of people go on about how exciting it would be it this happens.
Supersymmetry is pretty similar. So many people can’t all be wrong in their prejudiced opinions, even though they have no solid evidence and furthermore – with the landscape problem – no conceivable way of ever getting any solid evidence.
There are many, many conceivable ways of getting solid evidence for supersymmetry. And what, exactly, does supersymmetry have to do with the landscape anyways? Can we please try to keep our attacks of various directions in high energy physics straight?
For Chris, in various extra dimension models, people have worked out the relevant accelerator signatures. As an example, for certain TeV scale gravity models, you can produce graviton that leaves the brane and thus manifests as missing energy. There are many others, but I’m not really up on this stuff. Similarly, small black holes have accelerator signatures as worked out, for example, by Giddings and Thomas (and again, probably many others).
Chris & Peter,
I heard Lisa Randall give a talk last year mod(details) when she said that some of the things in her book should be testable at the LHC. It might be interesting to have a guest posting to hear about the details.
Best,
David
David,
I think Lisa Randall is at one extreme of the spectrum in terms of believing in these models, since she is one of the people who came up with them. But from what I remember of her book, even she doesn’t claim a strong belief that these things will be seen at the LHC.
Nima Arkani-Hamed must know something if he mentions me like that. Maybe my throat is too deep….
And I doubt theorists would be able to do anything with “raw LHC data” anyhow. Probably they would get as far as to re-discover partons, but not much more. Raw LHC data will be as raw as the tail of a live cow can be called “rare filet”. Not easy to digest if you don’t kill the cow first.
Cheers,
DT
Deep Throat,
I think the LHC experiments should seriously consider providing “raw data” to any theorists who complain. The results might be amusing to watch.
Can someone please explain to me the reason for your skepticism about supersymmetry? String theory is one thing, but I think calling supersymmetry unmotivated and crazy is just plain wrong. Those of you who think this way must have never really studied particle physics. Otherwise, you would be aware of how simply and elegangly supersymmetry solves a hosts of problems.
Also, half the particle spectrum has already been observed, and about 20% of the couplings measured.
But it must be mentioned that at least one prominent staff theorist at CERN (who most certainly has studied particle physics) claims that the MSSM is minimal with respect to its credibility… We’ll see, in due time.
Dear Peter,
I know it’s forbidden to mention one’s own paper on your blog, but my paper arXiv:0704.1476 is definitely an attempt to take TeV-scale gravity very seriously. There’s unfortunately a very large amount of work still to do to have predictions ready for the LHC, but it’s doable, and I’m going as fast as possible.
The most generic prediction of TeV-scale gravity is that the effects will turn on extremely fast at a certain energy, due to the very rapid increase with energy of graviton effects. Below a certain energy, that could very well lie between 2 TeV and 14 TeV, there will be nothing detectable, and above that energy, a large fraction of the large transverse momentum processes selected at the LHC will see large fractions of missing energy as gravitons are radiated into the extra dimensions. In this respect it will be similar to the J/psi.
With regard to why it should happen at the LHC:
(1) TeV-scale gravity makes it easier to fit a small cosmological constant; and
(2) There’s a natural factor of 1/10 (a loop factor) between the topologically stabilized breaking of the Horava-Witten E8 to the Standard Model, and the radiative breaking of SU(2) x U(1) in modern versions of the Coleman-Weinberg mechanism, see e.g. hep-ph/0509122 by Chishtie, Elias, Mann, McKeon, and Steele.
With regard to neutrinos, Maltoni and Schwetz have shown in arXiv:0705.0107 that MiniBooNE and LSND can be in perfect agreement if there are two sterile neutrinos, i.e. a (3+2) scheme, due to a new CP violating phase. The E8 breakings in subsection 5.6 of 0704.1476 lead automatically to a number of Standard Model generations plus an unrelated number of sterile neutrinos, so can accomodate 3 + 2.
Best regards,
Chris
There are a number of reasons why high-energy experimentalists have hostile feelings towards theorists (as expressed by Lederman
in his book). Unlike, say, condensed-matter physics, there is rarely
much contact between experimentalists and any but the most
phenomenological theorists. That is because neither theorists
nor expermentalists are doing something which has serious
impact on the activities of the other group.
The experiments are very hard to do but produce no fundamental results (let’s hope that will change soon). Hence theorists work on problems with low stakes (like unifying particle physics with quantum gravity) alienating the experimentalists.
One can appreciate Michael Peskin’s recent effort to refocus the theorists attention to real world LHC issues, like finding traces of new particles in the rather complicated background of the jets.
(Although he lures them with an highly optimistic picture of finding both SUSY physics and dark matter particles at the 100 GeV scale.)
http://video.tau.ac.il/Lectures/Exact_Sciences/Physics/stringfest/OnDemand.html?6
(Needs Internet Explorer 5.5 or higher)
Regards, Hans
I heard Lisa Randall give a talk last year mod(details) when she said that some of the things in her book should be testable at the LHC. It might be interesting to have a guest posting to hear about the details.
Hi David,
regarding predictions of models with extra dimensions at the LHC, see
Extra Dimensions
and
Micro Black Holes
Best,
B.
Btw, Peter, thanks for the pointer to the article, it’s really well written and worth reading. I didn’t know that quotation by Wilson, I like it a lot.
am I the only one who finds the random comics in the middle of the page kind of disturbing?
Bee, certainly you are not. I totally agree with you.
“… while consuming prodigious numbers of espressos… ”
Apparently, Nima could gobble up “no less than six cups of espresso” during a 1.5-hour interview! Kolbert also reports a similar kind of feat.
Wow! Assuming it is not decaf, this is hell of a lot of caffeine in the bloodstream! This is almost literally turning oneself into a machine running on caffeine.
Now, I wonder whether this is the physics equivalent of the often-talked-about amphetamine intake of some mathematicians (if the latter is still happening).
Being a guy who gets paid to gather & analyze data I was most impressed by the amount of data that has to be massaged. Always the hardest problem is extracting information from the data. With that problem even the crudest model helps a lot. Even a bad theory is better than none — so I guess even a bad theorest is worthwhile.
Bee,
Thank you.
David
Tonight, the NY Times website has a link to an article about the LHC that apparently will run in Tuesday’s papers (the online version is dated May 15).
http://www.nytimes.com/2007/05/15/science/15cern.html
The Times article covers similar ground to the New Yorker one — i.e., both the physical construction and science of the LHC — and is similarly lengthy.