The LHC is the cover story on this week’s issue of Science magazine, with three articles on the topic here, here and here.
Also in this week’s Science is an article about the “spin puzzle”, the fact that accelerator experiments with polarized particles give results for protons that are different than what one would expect from a naive quark model. The general assumption seems to be that this is a QCD effect, one that is tricky to calculate. I’ve always wondered if there is any chance that there is some sort of spin-dependent behavior of quarks different than that predicted by QCD. I don’t know of any work by people trying to come up with such models, but maybe it’s out there. I’d love to hear from some expert on this about whether the experimental results really do point to a serious possibility of something going on other than standard QCD.
A new book of interviews of scientists has recently appeared, Candid Science VI by Istvan and Magdolna Hargittai. It contains interviews with David Gross and Frank Wilczek. The authors ask both of them about their interactions with Wigner, and what they think of various other famous Hungarian scientists. Wilczek explains why he has made various moves over his career, that he was quite influenced by Peter Freund as an undergraduate, why he thinks it took so long to get the Nobel prize, and that his motivation for working on the beta-function calculation was to know if the electroweak model had the same Landau pole problem as QED.
Gross talks about his background and relation to Judaism, and also about his Nobel prize work. He remains enthusiastic about string theory, and characterizes opposition to string theory in many physics departments as due to people not wanting to learn it because it is hard work, as well as fear that if they hire string theorists, all the good graduate students will go work with them. There may be something to what he says, but I think it’s out of date, and times are changing.
I hear from David Derbes, who put together Dyson’s 1951 Lectures on Advanced Quantum Mechanics that were mentioned here earlier, that World Scientific is publishing them as a book this month. Profits will go to the New Orleans Public Library, where David grew up.
The two new Fields medalist bloggers each have fascinating blog entries on Millenium problems. Terry Tao writes a long explanation of Why Global Regularity for Navier-Stokes is Hard. He also comments about the recent New York Times piece about him and about math education issues. The comment sections of his postings have some very interesting discussions going on.
Alain Connes has a wonderful posting about Le reve mathematique, especially his mathematical dream of proving the Riemann hypothesis using non-commutative geometry. He notes that the first goal is to come up with a non-commutative geometry version of a proof for the function field case. More about this in a recent posting on the same blog by David Goss.
I was delighted to hear that David Derbes, who put Dyson’s 1951 Lectures on Advanced Quantum Mechanics into LaTex was contributing the proceeds to the New Orleans Library. I met David when I taught at Tulane University. He wrote his PhD under the direction of Higgs. He was teaching at the high school in N.O. from which he graduated, as a form of service. I was quite impressed by his knowledge and his discription of particles as broken symmetries help me in my work.
description, not discription.
I am certainly not an expert on this, but I know that the so called “proton spin crisis” has been discussed for many years (at least since the 90s) and there are tons of papers and various proposals about it. You find them e.g. by searching for “proton spin crisis” on the arxiv or at Google scholar. I was always surprised that this “crisis” did not get much attention outside of the lattice-QCD and related communities, because (as you already wrote) it might very well indicate that something is wrong with QCD as we know it.
I’ve also noticed papers on this over the years, periodically tried to read more about it to see if there was any chance there was something wrong with QCD. Never got far with this, so I was hoping to find a real expert who had some feel for the situation. I agree that it’s surprising this problem has not attracted more attention in the particle theory community. Even if it’s not evidence that will upend the standard model, it seems to be one of the least understood corners of particle physics, with experimental anomalies to guide one to better understanding, and new data coming in.
Quote from a web page on the standard model of particle physics:
“So far every experiment test of the standard model has confirmed the predictions of the theory.”
I think I’ve seen similar statements on this blog. In light of what was initially called the proton “spin crisis,” which has not gone away, how can this be said?
A first principles calculation of how the spin of the proton is distributed among its constituents would be extremely difficult. So there is no really good prediction coming just from QCD to compare things to. Assuming that almost all the spin is on the valence quarks (or rather, appropriately dressed “constituent quarks”) turns out to give quite good predictions for such things as the neutron/proton magnetic moment ratio. But if you look at the scattering off the quark spin, this model gives wildly wrong answers. So this very simple-minded model is wrong. What are needed (and what people have worked on developing) are calculationally tractable models that capture more of the essential features of QCD and explain why very simple models can give accurate results for specific quantities.
It seems when a simple-minded calculation agrees with standard model, that’s taken as a vindication. If not, no crisis, we just need to do more work. Heads I win, tails we flip the coin again.
Ther is currently a paper that purports to disprove the RH, posted on the arXiv at
This has not received the media attention that the cataloguing of E8 has (though there has been a rustle in the hedgerow of the blogosphere); is this because it may be wrong (I am not qualified to judge, though the approach looks pretty much ‘old school’ to me) or perhaps down to the author’s lack of a good PR unit?
great blog but may I suggest that you put a description and some few key words in your html so that when searching on google you get an idea of what the blog is about – like lubos’s “The best theoretical physics blog that the search engine can offer you”.
Yes, but since we do not really know how to do bound states for QFT in general and the Standard Model in particular the proton spin crisis is only a crisis for ad hoc, string-and-sealing-wax models used to plug this gap in our understanding.
That paper on the RH has all of the hallmarks of a wrong paper: dramatic claims to do something no one else has been able to do in over a hundred years, no evidence of a new idea that other people haven’t looked at, a long technical argument, full of opportunities to go wrong. Remember, papers on the arXiv are not refereed, and even when they contain errors, the authors do not always acknowledge this and retract them. I have no idea if an expert has tried to go through that paper and the kind of problem most would expect to exist.
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Your comment reminds me of an item from the Feynman biography by Gleick:
When a historian of science pressed him on the question of unification in his Caltech office, he resisted. “Your career spans the period of the construction of the standard model,” the interviewer said.
” ‘The standard model,’ ” Feynman repeated dubiously. . . .
The interviewer was having trouble getting his question onto the table. “What do you call SU(3) X SU(2) X U(1)?”
“Three theories,” Feynman said. “Strong interactions, weak interactions, and the electromagnetic. . . . The theories are linked because they seem to have similar characteristics. . . . Where does it go together? Only if you add some stuff we don’t know. There isn’t any theory today that has SU(3) X SU(2) X U(1) — whatever the hell it is — that we know is right, that has any experimental check. . . . “
The spin puzzle is neither a verification or a disproof of QCD. In
the simple quark model, the quark masses in a nucleon are
consituent masses. These are much greater than the current
masses, which are actual masses. Most of the constituent
mass is glue and virtual quarks – which should have an effect
on any experiment measuring spin or magnetic moments. Nobody
has calculated how this works, I believe.
Peter – Frank Wilczek gave a talk yesterday at Rice, and I asked him about the QCD spin situation. I have a new blog posting discussing this. In short, he says there is no problem with the QCD calculations or measurements; both say that the proton ends up as spin-1/2. Rather, the problem is that people’s intuitions don’t like that the calculations say that much of that spin comes from the gluon field.
(His posting is at http://nanoscale.blogspot.com/2007/03/frank-wilczek-talk-part-two.html)
Navier Stokes Equations and Euler’s Equations.
It’s very brave of Penny Smith who persists in working on one of the hardest and still fruitless areas of mathematics–namely the Navier-Stokes and Euler’s. From what I know, there are now only a handful of mathematicians who are still working on it: Peter Constantin is the most stubborn one among them. If you look at Clay Math’s official problem description, you will notice that there are virtually no significant results. Humans have only moved a few steps in a thousand miles of the journey, yet, the problem seems to be that, the road doesn’t exist, and one has to find a road to move forward. Sadly, all those leading experts in this field now become inactive simply because of the difficulty posted by the problems. I admire Dr. Smith’s persistence. Her works are certainly good contributions to the field. I read about her papgers and preprints, left alone the mistakes, it doesnt seem to me that even the mistakes were abscent, each of the claims (correct or incorrect) still need to be proved, which is an extremely essential process. I, as well as my colleagues in Europe, don’t believe that the claims have any usefulness in resolving the Navier-Stokes Equations. But nevertheless, good efforts. It’s inspiring–hope more mathematicians would try it…