Marvel-ing

I found Friday's Colloquium very interesting. I learnt a lot I did not know about the Federal Government's budget process. The speaker, Kevin Marvel, Executive Director of the American Astronomical Society, conveyed a lot of information, as well as a good take-home message, in his 50 minutes. He is obviously very well-practiced at doing this sort of thing! He does, after all, talk to persuade, for a living. I think of him as the Nick Nailor of science. And so it is no surprise that his talk was bang on 50 minutes, and entertaining to boot. Also, as one student said to me: "He was very well-dressed, not like a normal scientist at all".

I claim you could hear a sharp intake of breath in the room as he said "Science funding by the US government is optional". I believe it's really important to remember this. With 3 trillion dollars in the budget annually, it seems like the US has plenty of money to spend on science. But after you say that 50-60% of that needs to go to non-discretionary expenditure (e.g. Medicare, Social Security, interest on the national debt) and half of what's left goes to the Department of Defence, well, suddenly $3 trillion just doesn't go as far as it used to.

Science has always depended on patrons for its practice. Tycho Brahe had the King of Denmark, we have the US Federal Government. The non-defence part of R&D spending is about 2% of the budget: which is a higher fraction of GDP than most other (maybe all other?) countries. 2% doesn't sound like much, until you consider that this is competing with Foreign Aid (which receives an even smaller share of the budget than R&D), support for single mothers, road building, funding for schools, etc. etc. etc. Which should lead you to ask: Why does the US consider it worth its while to spend 10s of billions of dollars each year on scientific research?

And make no mistake, our Department benefits from that decision on a day-to-day basis. We
receives about $3 million annually in external funding, most of it from the Federal Government. We get 0.0001% of the total federal budget! Go us! But seriously, that money is crucial to the health of our program. It funds roughly 50% of the graduate students in the Department. It funds almost all the post-docs in the Department. And it funds about 20% of most faculty salaries. So the issues Dr Marvel was discussing are crucial to all of us. If the Federal Government decided tomorrow it could no longer afford to support scientific research many of you who are reading this blog would be out of a job. And your career prospects would take a huge nosedive. So what, then, should be our stance as regards this huge, somewhat capricious, organization with which all of our futures are interwoven?

Hadrons, quarks, and all that

In his comment, Inam asked the very sensible question "what makes people believe that quarks are point like particles when all they can observe is the hadronic state of quarks?". The answer is that although we detect only hadrons (which we think consist of confined quarks) in detectors, the way, for instance, high-energy electrons scatter from a proton, is very well described by a picture in which the electrons are scattering from three point-like objects (of charges +2/3, +2/3, and -1/3) within the proton. This discovery was made in experiments done at the Stanford Linear Accelerator in the 1960s, and won the Nobel Prize in 1990.

More generally, although at long distances quarks are not observed as free particles, quarks are 'asymptotically free' and so in any experiment that achieves high enough energies we can compute the outcome of the experiment using the fundamental theory of the strong interaction, QCD. In QCD the quarks are point-like, and the statement in Dr Cardman's talk was just that all experiments to date are consistent with that assumption, and no evidence for non-point-likeness has yet been seen. Note that there is a nice feature of QCD here: to look for non-point-like-ness (=composite-ness) of quarks you have to use a very-high-energy accelerator, so you can probe very short distances. But at very short distances quarks are almost free, so you can calculate the "standard QCD" effects (i.e. assuming point-like quarks) using perturbation theory. Bounds are then obtained by adding extra terms to the QCD Lagrangian and seeing what they would do to the data. (Summary of results available here.)

Inam's other question, about quark-hadron duality, is a little harder to answer. At its most basic level this is just a statement that a complete set of states with quark degrees of freedom and a complete set of states with hadron degrees of freedom are both, well, a complete set of states. So you can do the quantum mechanics using whichever basis you prefer. BUT you may find that things that are easy to describe in one basis are difficult to describe in another. I believe, although I am not sure, that similar phenomena occur in Condensed Matter systems (e.g. bases of 'fundamental' degrees of freedom or quasi-particles). The standard statement of duality is encapsulated in a 'folk theorem' due to Steven Weinberg: 'You can use whatever degrees of freedom you want to describe the system, but some choices will be more efficient than others'. (My paraphrase, since I couldn't find the original source.)

More specifically, Jefferson Lab has done some very nice experiments on a really interesting phenomenon called "local duality" which is a statement about averages of electron-scattering observables in which hadronic resonances are seen being equal to the result for the same observable if you compute it with quarks in the limit of very high energies where that description is more efficient.

Building nucleons and nuclei...

So last Friday's Colloquium was about the science program at Jefferson Lab. Jefferson Lab is an electron accelerator, located in Newport News, Virginia. The talk was presented by the Associate Director for Experimental Nuclear Physics (read powerful guy who decides when experiments get done), Dr Lawrence Cardman. Aside from the fact that I was distracted because his name makes me think of "South Park" I thought Dr Cardman gave a good talk. But I'd be interested to know what people who are less familiar with Jefferson Lab's scientific program thought. As Dr Cardman said, they've done 140 experiments now, so that's a lot of ground to cover. And he talked about a lot of different stuff in his one hour: probably each one of the experiments he talked about could've (and has in some cases!) had a whole Colloquium of its own.

I was also intrigued by the emphasis on "nuclear physics is to QCD what molecular physics is to QED". Do people find this to be a helpful analogy? If that's true what does it imply about what the important problems in nuclear physics are?

First thoughts

This blog is a place for people in the Ohio University Physics & Astronomy Department to blog about interesting talks they've heard recently, hot news in science, the tribulations of life as a physicist (or astronomer...) etc. etc. To provide some sort of structure we will try to talk each week about the Departmental Colloquium, the schedule for which can be found at http://www.phy.ohiou.edu/~phillips/Colloquium/colloquium.html. For those of you who are not familiar with the blog's title, to speak "colloquially" means to not use proper English. This is an attempt at humour, given the blog's Colloquium orientation. But more generally it means that informal discussion is encouraged. So please, go ahead, make a comment, even if it's only brief. Or it's critical. The goal is to have a decent online discussion about interesting physics.