I’m heading up to Rochester this evening, will give a colloquium talk there in the physics department on Wednesday at 3:45. I’ll put up a link to the slides after the talk, for now, here’s the abstract:
Particle theory: a view from a neighboring field
High energy particle physics faces a challenging future, largely because of the overwhelming success of the Standard Model. The LHC discovery of a Higgs particle with exactly the predicted properties, coupled with the lack of evidence there for “Beyond the Standard Model” physics, has led some to characterize this as a “crisis”.
In this talk I’ll consider the current situation from a somewhat unusual point of view, that of someone who began his career in physics departments doing particle theory, but then moved to mathematics departments. The field of mathematics has complex and close ties to fundamental physical theory, and the cross-cultural perspective it provides may be of interest.
Update: Apologies for the earlier mistake (I had “Thursday” instead of “Wednesday” above). The slides for the talk are available here.
I’ve been struggling to find an answer to this question, would you be willing to help?
The highly successful physics paradigms of today were largely in place by what year?
1973
If anyone from Perimeter institute is reading this, Could you give this talk at PI, so that it will be recorded? I don’t think Rochester records the colloquium
Peter, it would be great if the talk could be videoed and perhaps posted on Youtube later: Can you arrange this?
Good food in Rochester: Sticky Lips has great barbeque. Guida’s has great pizza. If you like thick crust ask Guida’s if they have any slices of Grandma’s Red.
Dr. Woit,
Your blog post says the colloquium talk is on Thursday but the University of Rochester website says Wednesday. Is it over? If so, could you please post a link to the slides?
Thanks
Talk just finished, sorry about the mistaken day given in the posting. No recording, I have added a link to the slides.
What questions did you get?
This may be a semantic issue, but I tend to disagree that Mathematics is a non-empirical science (as stated in the slides). For example:
The Taniyama-Shimura Conjecture (based on empirical observation of the characteristic numbers of elliptic curves and modular forms) led to Andrew Wiles’ proof of Fermat’s Last Theorem (as discussed in Simon Singh’s “Fermat’s Enigma”).
Scott Aaronson on a mathematical breakthrough in complexity theory: “It’s yet another example of something I’ve seen again and again in this business, how there’s no substitute for just playing around with a bunch of examples.” – http://www.scottaaronson.com/blog/?p=2325
Greg Chaitin, co-founder of Kolmogorov -Chaitin Information Theory:
“For years I’ve been arguing that information-theoretic incompleteness results inevitably push us in the direction of a quasi-empirical view of math, one in which math and physics are different, but maybe not as different as most people think. As Vladimir Arnold provocatively puts it, math and physics are the same, except that in math the experiments are a lot cheaper!” http://www.rutherfordjournal.org/article020103.html
lun,
The questions were mostly about the multiverse business, and the more I had to say there was just more of the usual if you read this blog.
JimV,
I don’t want to start a discussion of this here, but while, yes, mathematical advances often proceed by working out examples, finding patterns, conjecturing and then proving general theorems, the activity of working out examples is something quite different than a physics experiment. In one case you’re investigating the world of mathematical structures, in the other physical reality.
“mathematical ideas originate in empirics. But, once they are conceived, the subject begins to live a peculiar life of its own and is … governed by almost entirely aesthetical motivations. In other words, at a great distance from its empirical source, or after much “abstract” inbreeding, a mathematical subject is in danger of degeneration. Whenever this stage is reached the only remedy seems to me to be the rejuvenating return to the source: the reinjection of more or less directly empirical ideas.”
John Von Neumann
On slide 9 : “Experimental study of quantum gravity seems out of reach.”
Your fellow blogger Sabine Hossenfelder seems to disagree, for instance she writes:
“I am cautiously hopeful that within my lifetime we will succeed in experimentally demonstrating that gravity is quantized”
http://nautil.us/issue/45/power/what-quantum-gravity-needs-is-more-experiments
Any comment on what’s the root cause of this disagreement?
I honnestly have to say that this talk and this way to see the future of fundamental physics are not very optimistic, especially for young people like me.
Pascal,
I’m no expert on this, but most of the discussions of possible quantum gravity experiments seem to aim at little more than checking that gravity obeys general laws of quantum mechanics (and it’s not clear if they can achieve that). What seems to me to be inaccessible is any experimental access to the study of quantum gravity beyond checking that at low energies there is the kind of consistency of gravity and quantum mechanics expected. In simpler terms, it’s the questions about quantum gravity at the Planck scale that really mystify theorists, and that I don’t see experiments telling us anything about.
Amami, about the prospect in particle physics, and about 1973 in particular (reference to Peter’s comment about 1973), I happened to be in a place to cook a steak for Feynman in that year. We were hosting him at our college and later in our off-campus apartment. He was very gracious with his time and various jokes and comments.
I asked him straigtht out what he thought the prospects for particle physics were, and what he might suggest people study instead if in fact particle physics are starting to dry out.
He said he did indeed think it was starting to dry out, that most things had basically been figured out (this was slightly before the Standard Model was mostly finalized, but a lot of things were known).
His advice? Computer science or pure mathematics.
I elected not to go to grad school and instead joined Intel Corporation. A lot of fun physics. Not exactly figurring out the nature of spacetime–not many do–but fun and I retired when I was 34. (Kept doing other things, just not on a 9-5 schedule dictated by other things.)
A physics education, even up to just a Bachelors, for those gifted in physics, is actually very useful in a lot of areas of high tech. I was hired by and worked for he guy who went on to become the President, CEO, and Chairman of Intel (Craig Barrett).
(Not so gifted, no. And even those with Ph.D.s who are not gifted, well, I worked with a lot of these types and they were not very successful in my experience.)
Meaning, if you are good at physics, keep at it. As to whether you may figure out the Theory of Everything, not too likely. And it was not too likely in 1973. Or in 1955. It never was.
Things were more easy to do experiments on in earlier times. For obvious reasons. So a Dirac saw his antimatter prediction confirmed a year or two later. And so on. Today, a prediction might take 200 years to test…simple log energy graphs.
If you are really good at math, keep at it as well. A couple of my roommates in college have had long and distinguished careers in math. I think the influence of the physicists in the house may have had an effect, and I strongly suspect the supper with Feynman did.
Fun talk, Peter. Surprised how many of the initial slides were essentially an overview of your version of the current state of experimental HEP.
For some of us, the theoretical motivations have always been a minority portion of the motivations for doing particle physics. Given all the experimental slides you included, odd you didn’t mention that. Your talk, though, you are of course free to cover whatever you feel is important.
Can’t agree with: “Technological barriers are starting to make it impossible to make progress on HEP physics as before.” (slide 31). All the technological barriers at the energy frontier are doing is slowly refocusing experimental effort away from that frontier, on to other frontiers.
The energy frontier has of course the most important source of breakthroughs, but it hasn’t accounted for a lopsided portion of the breakthroughs in particle physics.
A list… the discovery of the neutron (could have been done in 1919 when Rutherford started to disintegrate nuclei, took until 1932 due to not doing the right experiment); the neutrino (the great Ellis and Wooster experiment); neutron-induced radioactivity and all of its consequences including the bomb, medical isotopes, and nuclear reactors (Fermi and his Nobel); the measurement of the proton magnetic moment (1930’s, indicated proton substructure); the pi/mu distinction (Fermi’s old group in Rome during WWII); parity violation (the tau-theta puzzle); K0-K0bar mixing (off the frontier); the nu_mu/nu_e distinction (1962 off the frontier); CP violation in K0-K0bar system (off the frontier); the solar neutrino deficit; the J/Psi (the ISR was the energy frontier, missed charm); both the tau and the bottom (again, off the energy frontier, which was then too dirty; better detectors have improved it); the long b-life and B-mixing; atmospheric neutrino mixing; KAMLAND and Daya Bay/RENO narrowing down the neutrino mixing matrix.
A list so long it gets boring. But I must say: by omitting the rich realm of particle physics discovery that did not occur at the energy frontier (while simultaneously acknowledging the great importance the frontier) you incorrectly, IMO, imply that experimental discovery is over in HEP.
Mathematical “experiments” concern observations of patterns in the outcomes of computations or other formal manipulations, where understanding the laws governing the physical substrate of the manipulations is not the issue. One can do arithmetic computations with pencil and paper (and a scheme for representing numbers and operations on them), a calculator, or a computer. By design, all these tools are facilitating the same manipulations.
In this sense, mathematics is not empirical.
Goleta Beach,
Thanks for the comment. The talk was intentionally provocative with one aim to explain the problem at the energy frontier (the severity of which I don’t think is widely appreciated outside of the field). I did give the caveat that there is still hope for other approaches, especially noting that neutrino physics is still poorly understood, but a serious discussion of that would have been another, different talk, one I’d be ill-equipped to give.
On your history, I don’t really agree that the charm/tau/bottom discoveries were not “energy frontier”. In particular, SPEAR in the mid-seventies I’d describe as an energy frontier machine (since it was at the highest e+/e- energy), just as I’d describe the ILC as an energy frontier machine if it ever gets built. About the neutrino results, yes, that’s true that those have generally not been energy frontier results and that will continue to be true.
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Is there some concensus on what theory should describe the low-energy behavior of quantum gravity (which you agree might be experimentally accessible with some luck and and hard work)?
Pascal,
Using the standard Einstein-Hilbert Lagrangian for gravity gives a perfectly sensible low-energy effective field theory, and that’s generally assumed to be what we would see in the low-energy limit if we could do experiments. The renormalizability problem, from the effective field theory point of view, just shows up at high energies (of order the Planck mass).
Hi Peter, perhaps in retrospect SPEAR was an “energy frontier” machine, but at the time two facts made contemporaries view it as off the frontier:
(1)ISR at CERN was at CM energy of 30 GeV, and NAL (now FNAL) was at 20 GeV (see Figure 15 of link below)… both hadron beams
(2)SPEAR’s CM energy was at 4.8 GeV, and the J/Psi was down at 3.1 GeV, and the tau-tau threshold was at 3.6 GeV. Richter, in late 1974, resisted going back down to the 3 GeV region to scan… internally it was sometimes said he was the first Nobel prize winner to lobby against the pursuit of the physics he was later awarded for. He acquiesced to a re-scan of the 3.1 GeV region a bit reluctantly, but he did agree. In any case, off the frontier, even SPEAR’s frontier.
Now we know all about partons and pdf’s and we know that the parton CM energy is well below that of the hadrons, so the ISR and NAL effective energies aren’t that different than SPEAR’s. But at the time no-one agreed with that view… even Richter in the link below thought the SPEAR data in the summer of 1974 contraindicated the quark/parton model.
At the time (and even now with ILC) e+e- is valued for its cleanliness and precision. ISR missed charm, after all, but could easily, with today’s detector technology, have seen charm. Or even with tech of the 1960’s and the right idea of pursuing charged leptons while ignoring the hadrons (perhaps). With the advances in hadron-collider detector abilities, it is very hard any more to call e+e- “energy frontier”…. that is, it is hard to imagine LHC missing stuff in the way the ISR did. Not impossible but hard. What the ILC could do… nail down Higgs couplings to great precision, and maybe indicated new physics somewhere “up there” in mass. But neutrino physics has already done that, and other low energy stuff like electric dipole moments are also probing “new physics” at pretty high masses for particles appearing in loops.
The problem will always be: knowing something is in a loop always has ambiguities and degeneracies. Knowing something is in a loop mainly provides support for a new energy frontier machine, and that is what the ILC could do. So could EDMs. I think the natural neutrino “new physics” scale is so high that no imaginable collider could get there, but probably that statement is not air-tight.
Link to summer-1974 Richter talk… http://slac.stanford.edu/pubs/slacpubs/1250/slac-pub-1478.pdf
On the b-quark discovery… really it was high resolution in the FNAL spectrometers, not center-of-mass energy, that made the upsilon discovery. When e+e- started to see the upsilon, it was DORIS and CESR, which were way behind the e+e- energy frontier, which was PETRA and PEP… the latter 2 had 3X the center-of-mass energy of the former.
Some places where the energy frontier was indeed crucial: antiproton discovery, Omega- discovery, W/Z, top quark, Higgs. Crucial stuff, of course.