Thursday, April 23, 2015

Anecdote 1: The Qual

A key aspect of a good graduate education is realizing, more than ever, that to be competitive you'll have to raise your game.

My cohort of physics grad students arrived at Stanford in a sunny, dry September of 1993, and we were an interesting bunch.  Four out of the twenty of us were Russian (or from the recently former Soviet Union), and for this story it's important to understand that these folks were incredibly well-prepared in terms of academic physics training.  Growing up in the Soviet system, they basically decided for you when you were something like 14 years old if you were going to be trained as a physicist.  We all got together at a mixer in a crummy graduate apartment, and I still remember a bunch of us standing around the drinks table, chatting about our undergrad schools and what we'd studied.  One person had been a kicker for the Northwestern football team!  One person had been into rock climbing and had done a fun summer program at Los Alamos.  Then one of the Russians said that he'd studied conformal field theory.  For fun.  Kind of set the stage a bit.

At the time the department had a "qualifying exam" that was one of a series of tasks students had to complete in order to (eventually) receive doctoral candidacy.  In this case, the qual was a two-day, six hours each day, written exam with a total of eight problems, basically on advanced Stanford-level undergrad material, administered early in the fall quarter.  Two of the questions were "general physics", meant to test your ability to think on the fly and reason quantitatively as a physicist - these tended to be hard, since they didn't really seem like the kinds of questions you're usually asked in a standard undergrad physics class.  As I later learned from serving as the student rep on the department's qual committee, the point of the test was not to act as a filter to weed out weak students, or some kind of check on admissions.  The intent, at least for the 30% of the faculty who really thought this was a good idea, was that this was an assessment tool.  For example, if you passed overall but did badly on the quantum question, you would be strongly encouraged to think about taking (or grading) the undergrad quantum course.  You had two tries to pass the written exam, and if you were well prepared, you were strongly encouraged to give it a shot as soon as you got started in the program - why wait?  A strong showing on the qual could also ease the process of finding a rotation slot with a would-be thesis adviser.  Still, like any formal exam when the stakes are high, the process was fraught with tension.

Getting a really good qual exam together is very challenging, particularly if you want the problems to be solvable yet not be rehashed from books or other common sources.  This particular year, Bob Laughlin was chairing the qual committee, and he had lost patience with some of his colleagues and decided to put together much of the exam himself.   (Laughlin is a well-known, larger-than-life person who figures in a couple of other stories I may get around to telling.)  The previous year he'd written a question about heat capacity and thermal conductivity involving the cooking of a pot roast.  This problem was sufficiently infamous that he thought it would be funny to write another problem our year about pot roast (though he spelled it "potroast", prompting one Russian to ask, "Vot is this 'po-tro-ast'?").  He wrote a question spoofing "Brilliant Pebbles" (pdf!), a missile defense concept that he found completely ridiculous and impractical.  The exercise was about "brilliant pot roast", with the idea of de-orbiting 2 kg pieces of beef as kinetic kill weapons to take out missiles.   This included giving your opinion and a physics justification of whether the pot roast would splatter on the outside of the missile or punch a cartoonish pot roast-shaped hole through the missile.  He concluded the problem by saying "Don't worry if the numbers you find for this are absurd.  We'll just delete them and replace them with happier numbers.  This is called 'government science'."

We took the test in a big lecture room in one of the buildings ringing Stanford's main quad.   Chalkboards up front, lots of wood, afternoon sunlight slanting through narrow windows near the high ceiling.  The room had somewhat shallow tiered seating and long, curved tables rather than desks, so that everyone taking the exam (probably 30 people or so) could spread out and have plenty of room.   Stanford's honor code meant that the exam was unproctored, but Laughlin was sitting outside doing some reading, in case we had questions about the wording of the test.

Around 5 hours into day 1 (if I recall correctly), Laughlin came into the room, looking somewhat agitated.  "May I have your attention please?  It's been brought to my attention that there is a typographical mistake on the exam."

[groan from frustrated, tired students]

"On the time-dependent quantum problem, these two frequencies \( \omega_{0} \) and \( \omega \) are both supposed to be \( \omega_{0} \).  It may not be analytically solvable as written."

[angry muttering from bitter, aggravated students who had been wasting critical time on this]

"No," says a clear, Russian-accented voice from the back of the room, the same fellow who had studied conformal field theory, "Is difficult, but can be solved.  Have done."

[combination of disbelief, resignation, and semi-desperate laughter from the crowd]

Welcome to physics grad school.


Anonymous said...

Do you think the rigorous training of students from the former Soviet Union had an impact on the career outcomes of these students? For example, given the headstart they had, were they more likely to graduate with superior theses and end up with faculty positions at top schools?

Anonymous said...

Fantastic story! Resonates on a number of levels, especially since my graduate advisor is a Soviet product of the same era. Looking forward to more anecdotes from the series.

Anonymous said...

More importantly, did you pass the qual in that first try?

Douglas Natelson said...

Anon@12:56, interesting question. Considering several years' worth.... On the one hand, those who actually wanted to get faculty positions seemed to do very well. On the other hand, a few went into serious finance jobs, and a couple of them seemed just tired of physics after having been doing it for so long.

Anon@3:54, thanks!

Anon@7:44, yes, thankfully.

JonB said...

This is a great story. Thanks Doug.

A few months ago I read Masha Gessen's book "Perfect Rigour" about the life of Grigori Perelman and the aftermath of the Fields Medal announcement. Your story reminded of how, through a large network of good mathematics teachers and maths clubs, bright students could be identified and trained to be the next superstars in the Maths Olympiads and do great mathematics. I could easily imagine that physics was treated in a similar way.

Was your Russian colleague an International Physics Olympiad Medallist?

Anonymous said...

What was the correct answer for the potroast defense system? Would it splatter or make a hole through missiles?

Douglas Natelson said...

JonB, Google seems to say that he was not, but it would not have surprised me if he had been.

Anon@7:03, I think (and the exam graders seemed to like it) that it depends on (relative speed of pot roast and missile)/(speed of sound in both pot roast and missile material). If that ratio is quite a bit smaller than 1, then the pot roast should splat on the missile surface. If that ratio is much larger than 1, the pot roast should punch through the missile (launching shock waves into the missile casing), not unlike a BB punching a cone-shaped hole through a piece of glass. If the ratio is around 1, then the situation is messy.

gilroy0 said...

I hope someday we'll get your version of our musical episode. :)