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Uncertain Principles

Physics, Politics, Pop Culture

Wednesday, November 26, 2003

The Meaning of "Favorite"

Bill Clinton, whose continued insistence on breathing serves as an endless source of outrage for a disturbingly large number of people, is catching some flack ar CalPundit and elsewhere for a list of 21 "favorite" books released by his presidential library. The complaints mostly center on the "calculated" nature of the list, which is heavy on Literature and serious non-fiction. People seem to think that there should've been a couple of trashy bestsellers on there, or soemthing.

Like most criticisms directed at Clinton, this is actually pretty stupid. For one thing, it's not inconceivable that it's a real list-- I do know a number of people who read almost exclusively Important Books. There's no a priori reason to find the list implausible on those grounds.

(As an aside, I'll also note that the people I know who read mostly Important Books also tend not to read all that many books. Whereas the people I know who read mostly genre fiction tend to read a lot. Which probably tells you... well, nothing much at all, given that I know those people precisely because they read, write, or edit the same sort of genre fiction I like. Sampling on the dependent vaiable, and all that.)

The bigger problem, though, is that "favorite books," like any "Best... Noun... Ever" list is kind of a slippery subject. I'm typing this in my "office" at home, surrounded by the hardcover portion of my book collection, and even here, I'd have trouble coming up with a good answer to "What are your favorite books?" I doubt I would come up with the same list twice.

The answer depends very strongly on who's asking, and why. There are lots of different kinds of "favorite books" lists out there. There are "the books I'm most likely to grab when I'm bored, and need something to read," which skews very heavily toward page-turning genre fiction. There are "the books I'd recommend to someone who reads the same sort of things I do," which would skew toward the more literary side of SF, and the more SF-nal side of "Manstream". There are "the books that made a really big impression on me, back in the day," which skews younger, and trashier. There wouldn't be a whole lot of overlap between those lists-- there might be two authors who would appear on all three (Brust and Westlake, at a guess), and a couple of others who would make two out of three, but they're fairly distinct categories.

The same thing holds for music-- there are records that I deem "perfect albums" that I hardly ever listen to, and some records in heavy rotation at any given time that I'll cheerfully acknowledge as trash. I don't agree with a lot of the Rolling Stone list Matt cited, but that's largely due to a different set of criteria (I would exclude "greatest hits" packages from a list of the best albums ever, for example).

In the case of Clinton's list of books, this is something prepared in conjunction with an exhibit of material from his presidential library. Which means that the category is something more like "favorite books which provide some insight into your thinking and career." Not being an especially important person, nobody's ever asked me for that sort of list, but if I were to construct one, it would contain more science books (Goedel, Escher, Bach, Gleick's Feynman biography) and less genre fiction than you might expect from my normal reading patterns. It would be a "calculated" list of favorites, in some sense, but it would also be an honest answer to the question that was actually being asked-- somebody who's trying to divine why I became a physicist from a list of my reading material might really enjoy Jhereg or Baby, Would I Lie?, but it wouldn't exactly provide much insight.

Posted at 4:49 PM | link | follow-ups | 2 comments

The Paper About the Thing by the Guy at the Place

Signal + Noise links to a paper claiming to be able to estimate the percentage of people citing a paper who have actually read it. I tend to agree with Chris that the authors are too quick to assume that mistaken citations are always the result of people not actually reading the paper in question-- I've certainly copied citations from other people's reference lists even though I'd read the actual article (generally because I wasn't sure how to abbreviate the journal name).

Of course, for someone coming from another discipline, the surprising result here may not be the propagation of errors, but just the mere existence of errors in published bibliographies. Back when I was a post-doc, and Kate was in law school, I was surprised to learn of the practice of "source-cites," where the student editors of law journals will get together in a library, and go through all the references in a submitted article, not just checking that the articles cited are cited properly, but also verifying that quoted material appears where the author says it does, and in the cited form.

This is an artifact of the practice of having law journals published by students, who are numerous, and need things to do. And who will work for food. Given the trouble that science journals have just locating referees, it's hard to imagine applying it anywhere else. But it probably works to dramatically reduce the number of erroneous citations in law review papers.

Which, of course, just means that you'll need to be more clever if you want to ferret out law professors who don't actually read the material they cite...

Posted at 4:18 PM | link | follow-ups | 1 comment

Tuesday, November 25, 2003

Show All Work For Full Credit

Here's the final exam I gave last week in my modern physics class. You have two hours to complete it, and can use a calculator and one 8.5" x 11" sheet of paper with any equations you think you may need.

Long Answer

1) A band of space rednecks pile into their battered Ford pickup rocketship (with a Confederate flag sticker), and head out of the solar system at 0.75 c.

a) If their ship has a rest length of 150 m, how long does it appear to an observer at rest with respect to the Sun?

b) On their way past Jupiter, they lob a beer can full of tobacco juice out the window of the ship. If they measure it to be moving at 0.5 c at a right angle to their direction of motion, what is the perpendicular component of the can's velocity according to a stationary observer?

c) What is the total speed of the can when it splatters all over one of Jupiter's moons?

d) Their cousins back on Earth celebrate by drinking beer and joyriding in pickup trucks. If the average speed of a rusty truck in a cornfield is 30 m/s, how far out of synch are the watches of one moving and one stationary redneck after the first minute of "Sweet Home Alabama" played in the truck? (Hint: You will need to use the binomial approximation to get a sensible answer.)

2) An electron is observed leaving a physics lab apparatus at 0.25 c.

a) What is the kinetic energy of the electron?

b) If the electron was initially at rest and was knocked loose by Compton scattering of a photon with λ=0.01 nm, what is the final wavelength of the scattered photon?

c) What scattering angle would the photon be detected at?

3) A particle trapped in a potential well has a wavefunction given by:

                  = 0            for x<-a
          ψ(x)    = A[1-(x2/a2)] for –a < x <+a
                  = 0            for x>a

a) What is the value of A that properly normalizes this wavefunction?

b) What is < p > for this wavefunction?

c) What is < p2 > for this wavefunction? (NOTE: This is not the same as < p >2)

Short Answer

4) You've discovered a new element, tentatively called "unobtanium." You produce 1000 atoms of unobtainium in the lab, then go off for a celebratory lunch. On returning one hour later, you find only 252 atoms are left. What is the half-life of unobtanium?

5) A hydrogen atom in the ground state absorbs a photon with λ = 102 nm. What is the principal quantum number of the final state?

6) Oxygen atoms have 8 protons, while mercury atoms have 80 protons.

a) Would you expect Oxygen-16 to be stable or unstable? Why?

b) Would you expect Mercury-160 to be stable or unstable? Why?

7) The diabolical Professor Schrödinger has kidnapped your beloved dog, and put him into a fiendish apparatus. An electron with total energy E is fired at a rectangular potential barrier with height Vo (>>E) and width Lo, so that there is a 50% chance that the electron will tunnel through the barrier. If the electron makes it through, your dog will be killed, if not, he will be set free. To make things a little more interesting, the mad professor offers you a choice: you can either double the height of the barrier (from Vo to 2Vo), or double its width (from Lo to 2Lo). Which of the two options will do the most to improve your dog’s chances, and why?

8) A light-emitting diode (LED) produces photons when electrons drop from the conduction band of a semiconductor down to the valence band. What is the minimum width of the band gap needed to make an LED that produces visible light? (Note: Visible light has wavelengths between 400 nm and 700 nm.)

Posted at 1:02 PM | link | follow-ups | 8 comments

Sunday, November 23, 2003

The World Has Changed

Quick Quiz: The following lines are from the first verse of a song. What's it about?

My city's still breathing (but barely it's true)
through buildings gone missing like teeth.
The sidewalks are watching me thinking about you,
all sparkled with broken glass.

You're wrong. It was recorded in early 2000.

One of the most tiresome repeated lines in the aftermath of the attacks of September 11th is that "everything has changed." Usually, this is said in support of some new outrage in the fields of civil liberties and foreign policy, often by people who ought to know better. And, ironically, that's where it's least true. There is no level of wanton murder, no number of innocent deaths that can justify throwing away the high principles on which this country was founded.

And, ironically, it's most true where it has the least material impact-- in how we look at poems, songs, and stories, movies and tv shows, and all the trivial ephemera of pop culture. Snarky remarks about architecture in a Donald Westlake book spark flashes of speaking-ill-of-the-dead guilt, skyline views in a music video seem ghoulish, and an excellent song about a failed relationship becomes something altogether darker, for four lines at least.

Everything has changed. And I want it back the way it was, dammit.

Posted at 9:43 PM | link | follow-ups | 7 comments

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