There’s an article in this week’s Science magazine by Adrian Cho entitled Dreams Collide With Reality for International Experiment. It’s about DOE Undersecretary Orbach’s warning to HEPAP (mentioned here) that current plans were too optimistic about the time-scale for the ILC, leaving a potentially dangerously long period with few US HEP experiments in progress.
Some physicists who had proposals for experiments (BTeV and RSVP) that were canceled in favor of going ahead full steam with the ILC were not amused:
Meanwhile, Orbach’s call for a program of smaller projects evoked jeers from researchers whose experiments had been cut. “This is really stupid and very frustrating because we had a program,” says Sheldon Stone, a physicist at Syracuse University in New York who worked on an experiment called BTeV that would have run at the Tevatron collider at Fermilab.
While experimentalists are worrying about the short-term, string theorists seem to be taking the long view. In his talk on String Theory: Progress and Problems at the recent conference celebrating the centennial of Yukawa and Tomonaga, John Schwarz ends with the conclusion
Even if progress continues to be made at the current rapid pace, I do not expect the subject to be completely understood by the time of the Yukawa-Tomonaga bicentennial.
I don’t find his claims about a current rapid pace of progress very convincing, and the idea of the entire next century of theoretical particle physics being dominated by the kind of unsuccessful more and more complicated string theory constructions we’ve seen for the last 25 years doesn’t seem like something to look forward to.
Turning from the difficulties of the future, Howard Georgi gave a wonderful talk on The Future of Grand Unification at the same conference, which was actually mainly about the past, largely devoted to telling the story of how he and Glashow came up with the first GUT models. He emphasizes the kinds of manipulations of representations of Lie algebras that he and Glashow were masters of and used to construct many different kinds of models. There’s also an advertisement for his wonderful book on the subject, the text for his course where I first many years ago encountered this subject. This semester I’m teaching my own course on the same material, from a rather different point of view, emphasizing geometry. It remains one of the most beautiful and central parts of modern mathematics as well as physics.
Hi Peter,
I am surprised you are waxing so poetically about GUTs. GUTs
have no real successes, with the noteworthy exception that
experiments to detect proton decay were built (and found
something else). The GUT unification scale isn’t really all
that convincing as physics – it isn’t even completely clear
that there IS unification, since the matching of the Weinberg-Salam
and QCD scales is so rough. I remember the vanishing total
charge of each generation (for anomaly cancellation) was
considered a success. But later it was pointed out that it has
nothing to do with GUTs specifically.
Something’s there at higher energies, but why should it be a GUT?
Peter,
I thought Georgi’s talk was fascinating to read through, but that doesn’t mean I’m a huge fan of GUTs. One nice thing about the GUT story is that Georgi shows how particle theory is supposed to work: he and Glashow came up with a tolerably simple model which does offer some sort of explanation of some of the questions the standard model doesn’t answer (I do think the way fermions fit into the spinor representation of SO(10) is intriguing). They then made real predictions based on it (proton decay), and when these didn’t work out they gave up (Georgi points out that he stopped working on GUTs in the early 80s). What they didn’t do was keep coming up with more and more complicated models trying to evade failure. Once that seemed to be what was happening, I think they changed their attitude to “this doesn’t seem to be working. Maybe it’s true, but making more complicated models is a waste of time”, and went on to try other things.
The main problem with the GUT idea is that it’s not a very satisfactory sort of unification, since you’ve just moved many of your problems into a new Higgs sector. The electroweak Higgs sector is already the source of most trouble, adding a new Higgs sector with similar problems doesn’t seem like a promising way to make progress.
It is a wonderful mathematical exercise in Lie algebra technique, even if these higher rank groups don’t end up having anything to do with physics.
As to the ILC thingy…
I find it somekind strange that physicists want it.
The ministry of research in germany recently stated that it is unlikely for germany to apply for becoming Hamburg an ILC site.
Well, after some asking around why, it becomes clear, that there is research underway at various universities in germany to increase the energy of particle beams with many new techniques (some, in fact optical).
It seems that the german ministry of research has decided to leave the ILC to US america and then, after 20 years or such, build a new linar collider of much higher energy!
At this time then, you in the US will have a wonderful ILC without any value!
Whatever State wants to get the ILC site, I wonder what to do with this rather low energy collider, when not a single hint of supersymmetry can be found. Is it not likely, that this will be a machine, which will have almost nothing to measure?
If you don’t mind me asking, what would you say would be the level and nature of required background knowledge for this book?
As to peter, what he says about GUT: I think that is absolutely correct. Glashow and Georgy are very honest researchers of the good old school.
The behaviour of some theorists, everytime when an idea does not work (in Feynmans words) to come up with a “fix-up” and look what happens if you add a parallel-world, hyperspace or a new unobserved differend standard-modell as hidden sector is simply what would be considered as scientific misconduct in experimental science. Expecially when they overhype these theories in press releases and refuse to mention any of their problems. When one looks at the Susy and sting propaganda one simply gets scared, since they often do not mention even the obiousliest problems
This is the same behaviour as of an experimentalist, who measured something and before publication deletes all his data which might be problematic.
For example why after the appearance of
Phys. Rev. D 20, 403 – 408 (1979) http://prola.aps.org/abstract/PRD/v20/i2/p403_1 does anyone continue to write propaganda material like: http://arxiv.org/abs/hep-ph/0203114 where it is statet that there would exist “a consistent pictures of breaking susy” and let experimentalists in fact believe, that such a theory would exist?
Coin,
It’s a textbook for a graduate physics course, basically what a mathematician would call a physicist’s take on Cartan-Weyl theory, with lots of examples worked out. I took the course near the end of my undergraduate years, but I was a ridiculously ambitious student and took lots of courses that were over my head (this one was only a bit over my head… and Georgi was a good teacher).
The background needed to go through the book is basically quantum mechanics and a good grasp of how angular momentum and spin works in that subject.
Benni,
I think most people agree that the case for the ILC depends on the LHC first finding evidence of some new physics that can be studied at ILC energies. One reason I suspect Orbach is saying the ILC may take a while is that it may take a while for the LHC results to arrive. New accelerators and detectors often take a while to get working properly.
If the LHC does find something new that the ILC would be the right tool to study, it would make sense to build it, and building it in the US will solve the problem of what’s next for US HEP research. This is what people are preparing for, but it is a bit of a gamble. Things like laser acceleration technologies are a long ways off, I strongly doubt having an accelerator of that kind ready 20 years from now is feasible.
Thanks.
Peter,
*slightly offtopic*
What specific courses did you take in undergrad that were “over your head”? (Besides the Georgi group theory course).
JC,
By far the most ridiculous thing I did was take a quantum field theory course in my second year (taught by Roy Glauber). I did come in with advanced standing due to taking a lot of AP exams, so technically I was a junior, but still… That year I started out taking a classical mechanics course from Arthur Jaffe, and sitting in the QFT course to see what it was about. A few weeks into the semester I realized that the classical mechanics seemed boring and required doing lots and lots of hard problem sets that had to be handed in on time, whereas the graduate course just had a few problem sets due every so often. So I went to see my advisor (Shelly Glashow), who, when I asked him if I could drop one and enroll in the other, irresponsibly said “Sure, whatever you want, I don’t want you to be unhappy…”. He would sign pretty much anything, if you could find him.
This is definitely getting off-topic, enough about misspent youth.
Re: Schwarz’s attitude, I too was rather perturbed by it when I went to talk to him last term about frontiers in physics. He said he didn’t think we would have a Theory of Everything before he died, which seems to me to be overly pessimistic. Maybe it’s just the naivete of youth (I’m an undergraduate freshman), but it seems to me there are enough people poking around in the right directions that we should stumble upon something, and probably in the next 10–15 years. Maybe working on string theory for so long engenders pessimism, heh.
Domenic Denicola,
I use to think exactly like you 20+ years ago, when I was younger and naively bought into string theory. It took me a long time to eventually figure out that string theory wasn’t all that it was cracked up to be.
Domenic,
I’m about 15 years younger than Schwarz, so probably have a bit longer than him. If you extrapolate from the last 25 years, both Schwarz and I will be long gone before there’s serious progress towards a TOE.
But, unlike him, I’m more optimistic. What strikes me about the Standard Model is both how incredibly good it is and how much beautiful, deep mathematics it involves. Besides gravity, most of the problems it leaves unresolved have to do with electroweak symmetry breaking. If either the LHC tells us what is really going on there, or someone figures it out without experimental guidance, we may very well end up with a theory that deserves to be called a TOE.
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Undersecretary Orbach’s remarks is his ‘politically correct’ way of saying the ILC is dead. Kaput. So forget about it. There is simply no justification for such an expensive machine. It is the wrong machine for the wrong time. We can try again in 10 years’ time.
Maybe LHC will tell that ILC has a strong physics motivation. Today we have a strong argument against ILC (high-energy physics needs moving to more advanced technologies) and a strong argument in favor of ILC (it would keep the US high-energy physics community alive). Small experiments have been killed to emphasize the last argument (without explicitly mentioning it), but maybe it is not the best strategy.
It seems unavoidable that high-energy physics will become (for both experimentalists and for theorists) a part-time job: one big experiment every 30 years and in the meantime progress on astrophysics, neutrino physics, and whatever lower energy physics that happens to be interesting. Trying to do this transition in a smooth way could be the way of exploring physics up to the maximal possible energy.
Theorists often don’t like near-cost navigation, but being interested only in big projects (such as a Theory of Everything) can be suicidal.
In “Lie Algebras and Quantum Mechanics” (1970), Robert Hermann wrote theoretical physicists
“…are like greyhounds all chasing the same rabbit, never really catching it, but periodically convincing themselves that it is not worthwhile chasing this particular one any longer, and going off after another.” (p. x)
It looks like Schwarz has given up.
BTW: Peter, do you often speak with Glashow? Because in your book, where you write about symmetry principles and group representation theory, these chapters look, as if they could be written from Glashow himself (At least it looks like this, when one looks at what Glashow is trying now with group theory). It seems indeed as if your book belongs to somewaht that could be called a “Glashow-school”. Is this correct?
Benni,
I haven’t talked to Glashow since I was a student, and am definitely not a member of a “Glashow school”. I suspect that, other than agreeing with me about a lot of the problems of string theory, we see things very differently. In his book Georgi (who definitely is in the “Glashow school”) warns very explicitly about the seductive danger of making too much of representation theory, treating it as more than a device for doing approximate calculations. From his point of view, I’ve definitely gone too far and been seduced, since I see representation theory as a fundamental principle of physics. In general Georgi and Glashow are both pretty suspicious of abstract mathematics (one reason they didn’t become string theorists), quite the opposite of my belief that progress in particle theory will require more mathematics, not less.
Well now, Glashow does such things involving group theory:
http://arxiv.org/abs/hep-ph/0601236
(I for me, of course find this somewat misleading and wrong. But it is refreshing to see that some people try their own new ideas).
Peter,
How common is it for particle theorists to be suspicious of abstract mathematics? (Excluding string theorists).
Some of my previous colleagues who did string phenomenology, were not really interested in the overly abstract math stuff. On the other hand, a few other string colleagues were heavily into the abstract math stuff (ie. stuff related to mirror symmetry, etc …).
JC,
I think particle theorists are all over the map on this issue these days. Some are highly suspicious, some are quite enamored of abstract math. For something related, see my next posting….
Peter said
The main problem with the GUT idea is that it’s not a very satisfactory sort of unification, since you’ve just moved many of your problems into a new Higgs sector. The electroweak Higgs sector is already the source of most trouble, adding a new Higgs sector with similar problems doesn’t seem like a promising way to make progress.
This is exactly the point – embedding the gauge group is not the real problem, and that is why SU(5) seemed doomed to me from the beginning. In the “real” theory this embedding will be explained naturally and perhaps the heroic effort will be seen in a new light and will not simply be recorded as a failure. I think in some sense the failure of GUT, which was certainly unexpected, coming hard on the heels of the failure to find a UFT for light and gravity, demoralized the community of physicists, and so string theory had a fertile ground of disillusionment in which to take root.
-drl