The Message That Is Sent

Rob Knop is blogging about the difficulties in getting tenure — his difficulties in particular, not the issue in some vague degree of abstraction. Very worth reading for a candid look at the kind of thing that goes on.

On a meta level, it’s interesting to contemplate how hiring and tenuring will ultimately be effected by blogs. Scott Aaronson is blogging at least some occasional facts about his job search. The proliferation of online rumor mills has already taken a lot of what used to be quasi-private information, shared among the old-boy network but invisible to outsiders, and put it out there for everyone to see. I can imagine a similar kind of effect if we ever get to the point that a critical mass of job- and tenure-seekers are blogging about their progress.

In the short term, I worry that the most obvious effect will be a deleterious one for the bloggers. For the most part, I don’t think that hiring/tenure committees care if you have a blog, occasional anonymous scare-mongering notwithstanding. (It might even help.) But blogging about the process might be the kind of thing that makes committees nervous. Personally, I would never blog about a major occupational transition while it was going on; when it’s all set up and the ink is drying, it makes sense to let people know, but in the middle of the process I would be (with good reason) worried about stepping on people’s toes. (Same thing with getting engaged.)

So, blogging about tenure and job searches: crazy or courageous? Or is there a difference? I guess we’ll see.

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Knowing How to Wear Clothes

I know everyone is eagerly awaiting the cinematic event of the summer: Ocean’s Thirteen, third in a series of the lighthearted adventures of a gang of elegant rogues who like to pull off elaborate capers centered on lavish casino heists. Admittedly, the Eurocentric Ocean’s Twelve was a somewhat rambling letdown, but the latest installment promises a return to Vegas and hopefully also to form.

George and Brad

Seeing buzz about the new movie reminded me of a review I read of Ocean’s Twelve. To paraphrase, it expressed the sentiment “This isn’t by any means a very good film, but man, these people sure know how to wear clothes.” This summer’s installment adds Ellen Barkin and Al Pacino to the cast, so the knowledge of clothes-wearing should only be enhanced. (Also Noureen DeWulf, although I’m not familiar with her work.)

Ellen, Al, and Noureen

So my question is, what does it mean to “know how to wear clothes”? We might at first guess that it refers to the ability of a person to choose clothes that are right for their style, their body type, and the occasion. But in a major motion picture, one presumes that there are professionals whose job it is to do the clothes-choosing, so (respecting the reviewer enough to imagine that they meant exactly what they said) that can’t be it. It could also mean “is wearing nice clothes” or simply “is pretty hot,” but neither of those talents would accurately be characterized as knowing how to wear clothes.

So is there a specific kind of knowledge that refers to the ability to wear clothes? Is it not just a matter of picking out a good outfit, but a particular method of wearing them, adapting one’s demeanor and bearing to the clothes one wears? Or are we just faced with a sloppy deployment of language in an attempt to convey “Boy, that George Clooney would look yummy in a burlap kilt” in an imaginative way? Help me out here, people.

(p.s. Apparently we don’t have a “fashion” category on this blog. Yet.)

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A Glimpse Into Boltzmann’s Actual Brain

You’ve heard the “Boltzmann’s Brain” argument (here and here, for example). It’s a simple idea, which is put forward as an argument against the notion that our universe is just a thermal fluctuation. If the universe is an ordinary thermodynamic system in equilibrium, there will be occasional fluctuations into low-entropy states. One of these might look like the Big Bang, and you might be tempted to conclude that such a process explains the arrow of time in our universe. But it doesn’t work, because you don’t need anything like such a huge fluctuation. There will be many smaller fluctuations that do just as well; the minimal one you might imagine would be a single brain-sized collection of particles that just has time to look around and go Aaaaaagggghhhhhhh before dissolving back into equilibrium. (These days a related argument is being thrown around in the context of eternal inflation — not exactly the same, because we’re not assuming the ensemble is in equilibrium, but similar in spirit.)

Boltzmann wasn’t the one to come up with the “brain” argument; I’m not sure who did, but I first heard it articulated clearly in a paper by Albrecht and Sorbo. It’s the maybe-our-universe-is-a-fluctuation idea that goes back to Boltzmann. Except it’s not actually his, as we can see by looking at Boltzmann’s original paper! (pdf) The reference is Nature 51, 413 (1895), as tracked down by Alex Vilenkin. Don Page copied it from a crumbling leather-bound volume in his local library, and the copy was scanned in by Andy Albrecht. The discussion is just a few paragraphs at the very end of a short paper.

I will conclude this paper with an idea of my old assistant, Dr. Schuetz.

We assume that the whole universe is, and rests for ever, in thermal equilibrium. The probability that one (only one) part of the universe is in a certain state, is the smaller the further this state is from thermal equilibrium; but this probability is greater, the greater is the universe itself. If we assume the universe great enough, we can make the probability of one relatively small part being in any given state (however far from the state of thermal equilibrium), as great as we please. We can also make the probability great that, though the whole universe is in thermal equilibrium, our world is in its present state. It may be said that the world is so far from thermal equilibrium that we cannot imagine the improbability of such a state. But can we imagine, on the other side, how small a part of the whole universe this world is? Assuming the universe great enough, the probability that such a small part of it as our world should be in its present state, is no longer small.

If this assumption were correct, our world would return more and more to thermal equilibrium; but because the whole universe is so great, it might be probable that at some future time some other world might deviate as far from thermal equilibrium as our world does at present. Then the afore-mentioned H-curve would form a representation of what takes place in the universe. The summits of the curve would represent the worlds where visible motion and life exist.

So even Boltzmann doesn’t want credit for the idea, which he attributes to his old assistant. Andy Albrecht points out that, in order to preserve the all-important alliteration, perhaps we should be calling them “Schuetz’s Schmartz.”

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Homework Solutions Online

Does everyone in the world but me know about Cramster.com? Basically it’s a website that includes as many answers to textbook homework problems as they can possibly put together. As far as I can tell it works on a Wiki system, where members submit the various solutions, although there are apparently also “expert” solutions. Odd-numbered solutions are available for free, but you have to pay to see the even numbers. Nothing there for my GR book, although there were some for Jackson’s E+M book, and plenty for Halliday/Resnick etc.

Not really sure what to think about sites like this. Part of me (a big part, actually) couldn’t care less about whether students do their homework, and for that matter thinks that grading is a complete waste of time. What matters is whether or not the students have learned the material, not how they perform on some formalized exercises. If they get perfect grades but don’t learn anything, ultimately they’re the ones who will suffer; even if they get into a better grad school thereby, they’ll just find that their fellow students are much better prepared than they are.

But then there is the whole “fairness” thing, which sadly does matter. There is a set of rewards — like good jobs and/or grad-school admissions — that we base on grades, and they should go to the most deserving students. So, unpleasant as it might be, we have to evaluate them somehow. But in this brave new world, it would probably be wise to make up original problems rather than using the ones from the back of the book.

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Coy Mistress

We’re just about to run out of poetry month! Here’s Annie Finch, to close things out until next year.

Sir, I am not a bird of prey:
a Lady does not seize the day.
I trust that brief Time will unfold
our youth, before he makes us old.
How could we two write lines of rhyme
were we not fond of numbered Time
and grateful to the vast and sweet
trials his days will make us meet?
The Grave’s not just the body’s curse;
no skeleton can pen a verse!
So while this numbered World we see,
let’s sweeten Time with poetry,
and Time, in turn, may sweeten Love
and give us time our love to prove.
You’ve praised my eyes, forehead, breast:
you’ve all our lives to praise the rest.

In response to Andrew Marvell, of course. Both poems are pretty good, so I’m reluctant to take sides. Except: Annie Finch has a blog! Does Andrew Marvell have a blog? Not to my knowledge, no. So Finch wins this round.

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How Did the Universe Start?

I’m on record as predicting that we’ll understand what happened at the Big Bang within fifty years. Not just the “Big Bang model” — the paradigm of a nearly-homogeneous universe expanding from an early hot, dense, state, which has been established beyond reasonable doubt — but the Bang itself, that moment at the very beginning. So now is as good a time as any to contemplate what we already think we do and do not understand. (Also, I’ll be talking about it Saturday night on Coast to Coast AM, so it’s good practice.)

There is something of a paradox in the way that cosmologists traditionally talk about the Big Bang. They will go to great effort to explain how the Bang was the beginning of space and time, that there is no “before” or “outside,” and that the universe was (conceivably) infinitely big the very moment it came into existence, so that the pasts of distant points in our current universe are strictly non-overlapping. All of which, of course, is pure moonshine. When they choose to be more careful, these cosmologists might say “Of course we don’t know for sure, but…” Which is true, but it’s stronger than that: the truth is, we have no good reasons to believe that those statements are actually true, and some pretty good reasons to doubt them.

I’m not saying anything avant-garde here. Just pointing out that all of these traditional statements about the Big Bang are made within the framework of classical general relativity, and we know that this framework isn’t right. Classical GR convincingly predicts the existence of singularities, and our universe seems to satisfy the appropriate conditions to imply that there is a singularity in our past. But singularities are just signs that the theory is breaking down, and has to be replaced by something better. The obvious choice for “something better” is a sensible theory of quantum gravity; but even if novel classical effects kick in to get rid of the purported singularity, we know that something must be going on other than the straightforward GR story.

There are two tacks you can take here. You can be specific, by offering a particular model of what might replace the purported singularity. Or you can be general, trying to reason via broad principles to argue about what kinds of scenarios might ultimately make sense.

Many scenarios have been put forward among the “specific” category. We have of course the “quantum cosmology” program, that tries to write down a wavefunction of the universe; the classic example is the paper by Hartle and Hawking. There have been many others, including recent investigations within loop quantum gravity. Although this program has led to some intriguing results, the silent majority or physicists seems to believe that there are too many unanswered questions about quantum gravity to take seriously any sort of head-on assault on this problem. There are conceptual puzzles: at what point does spacetime make the transition from quantum to classical? And there are technical issues: do we really think we can accurately model the universe with only a handful of degrees of freedom, crossing our fingers and hoping that unknown ultraviolet effects don’t completely change the picture? It’s certainly worth pursuing, but very few people (who are not zero-gravity tourists) think that we already understand the basic features of the wavefunction of the universe.

At a slightly less ambitious level (although still pretty darn ambitious, as things go), we have attempts to “smooth out” the singularity in some semi-classical way. Aguirre and Gratton have presented a proof by construction that such a universe is conceivable; essentially, they demonstrate how to take an inflating spacetime, cut it near the beginning, and glue it to an identical spacetime that is expanding the opposite direction of time. This can either be thought of as a universe in which the arrow of time reverses at some special midpoint, or (by identifying events on opposite sides of the cut) as a one-way spacetime with no beginning boundary. In a similar spirit, Gott and Li suggest that the universe could “create itself,” springing to life out of an endless loop of closed timelike curves. More colorfully, “an inflationary universe gives rise to baby universes, one of which turns out to be itself.”

And of course, you know that there are going to be ideas based on string theory. For a long time Veneziano and collaborators have been studying what they dub the pre-Big-Bang scenario. This takes advantage of the scale-factor duality of the stringy cosmological field equations: for every cosmological solution with a certain scale factor, there is another one with the inverse scale factor, where certain fields are evolving in the opposite direction. Taken literally, this means that very early times, when the scale factor is nominally small, are equivalent to very late times, when the scale factor is large! I’m skeptical that this duality survives to low-energy physics, but the early universe is at high energy, so maybe that’s irrelevant. A related set of ideas have been advanced by Steinhardt, Turok, and collaborators, first as the ekpyrotic scenario and later as the cyclic universe scenario. Both take advantage of branes and extra dimensions to try to follow cosmological evolution right through the purported Big Bang singularity; in the ekpyrotic case, there is a unique turnaround point, whereas in the cyclic case there are an infinite number of bounces stretching endlessly into the past and the future.

Personally, I think that the looming flaw in all of these ideas is that they take the homogeneity and isotropy of our universe too seriously. Our observable patch of space is pretty uniform on large scales, it’s true. But to simply extrapolate that smoothness infinitely far beyond what we can observe is completely unwarranted by the data. It might be true, but it might equally well be hopelessly parochial. We should certainly entertain the possibility that our observable patch is dramatically unrepresentative of the entire universe, and see where that leads us.

Landscape

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Cheap, Crappy Calories

You know what’s a really big problem? The Farm Bill. The quintennial piece of legislation that steers billions of dollars into subsidies for farmers who mass-produce the raw materials of which junk food is made. Yeah, I know, not exactly a hot topic, nor our normal fare. But Michael Pollan in the Times lays out a devastating indictment of the current system, which encourages our economy to overproduce food that is incredibly bad for us, while busting the federal budget, ruining the environment, and hurting small farmers and developing countries to boot. (Via Marginal Revolution.)

Here is the basic econo-physics of the situation:

As a rule, processed foods are more “energy dense” than fresh foods: they contain less water and fiber but more added fat and sugar, which makes them both less filling and more fattening. These particular calories also happen to be the least healthful ones in the marketplace, which is why we call the foods that contain them “junk.” Drewnowski concluded that the rules of the food game in America are organized in such a way that if you are eating on a budget, the most rational economic strategy is to eat badly — and get fat.

This perverse state of affairs is not, as you might think, the inevitable result of the free market. Compared with a bunch of carrots, a package of Twinkies, to take one iconic processed foodlike substance as an example, is a highly complicated, high-tech piece of manufacture, involving no fewer than 39 ingredients, many themselves elaborately manufactured, as well as the packaging and a hefty marketing budget. So how can the supermarket possibly sell a pair of these synthetic cream-filled pseudocakes for less than a bunch of roots?

For the answer, you need look no farther than the farm bill. This resolutely unglamorous and head-hurtingly complicated piece of legislation, which comes around roughly every five years and is about to do so again, sets the rules for the American food system — indeed, to a considerable extent, for the world’s food system. Among other things, it determines which crops will be subsidized and which will not, and in the case of the carrot and the Twinkie, the farm bill as currently written offers a lot more support to the cake than to the root. Like most processed foods, the Twinkie is basically a clever arrangement of carbohydrates and fats teased out of corn, soybeans and wheat — three of the five commodity crops that the farm bill supports, to the tune of some $25 billion a year. (Rice and cotton are the others.) For the last several decades — indeed, for about as long as the American waistline has been ballooning — U.S. agricultural policy has been designed in such a way as to promote the overproduction of these five commodities, especially corn and soy.

I remember the moment it first dawned on me that Coke was significantly less expensive than orange juice. But making soda is a complicated chemical process, while oranges literally grow on trees! Of course, once you master that process, mass-producing the chemicals is fairly straightforward, while growing oranges requires a certain amount of patience. At the time I didn’t really appreciate the other aspect of the puzzle: we pay people to grow corn, which is turned into high-fructose corn syrup, which sweetens all of the processed food we find on our supermarket shelves.

Now, there does seem to be an obvious point missing in the article: the popularity of Twinkies over carrots cannot be put down solely to the greater density of calories per dollar. A lot of people like how Twinkies taste, deep-fried or not. But that doesn’t mean we should be actively subsidizing their production.

Pollan strikes an optimistic note at the end of his piece, suggesting that the importance of the Farm Bill may finally be percolating up to the national consciousness. (At least until the next time that a celebrity with fake boobs dies of a drug overdose.) It’s long been considered political suicide to even suggest messing with farm subsidies, especially with the Iowa caucuses playing such a large role in Presidential primaries. We’ll see if next year is any different.

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The Spirits of Those Who Have Been Destroyed By Love

It’s going to be Poetry Month all month long! But really, aren’t all months Poetry Month? Especially when time for substantive blogging is hard to come by?

Today we dip back a few millenia, to offer an excerpt from Virgil’s Aeneid, in the Robert Fagles translation. The backstory is that Aeneas has fled from the fall of Troy, charged by Jupiter with traveling to Italy and founding a new city (Rome). Along the way his party is diverted to Carthage by winds whipped up by the wind god Aeolus. (Who was in turn urged on by Juno, Jupiter’s wife, who was piqued at Aeneas because his mother, Venus, was judged to be better-looking than Juno by Aeneas’s countryman Paris. Gods have rarely risen above the standards of their humans.)

So anyway, in Carthage Aeneas is smitten by the widowed queen Dido, and they become lovers. Eventually Jupiter becomes impatient with this lollygagging, and urges Aeneas on his way. Dido, heartbroken, kills herself in her grief. Once in Italy, Aeneas does what any great epic hero would do, and takes a detour to the Underworld. There he comes across the shade of Dido, and appeals to her.

      “Tragic Dido,
so, was the story true that came my way?
I heard that you were dead. . .
you took the final measure with a sword.
Oh, dear god, was it I who caused your death?
I swear by the stars, by the Powers on high, whatever
faith one swears by here in the depths of earth,
I left your shores, my Queen, against my will. Yes,
the will of the gods, that drives me through the shadows now,
these moldering places so forlorn, this deep unfathomed night–
their decrees have forced me on. Nor did I ever dream
my leaving could have brought you so much grief.
Stay a moment. Don’t withdraw from my sight.
Running away — from whom? This is the last word
that Fate allows me to say to you. The last.”

Aeneas, with such appeals, with welling tears,
tried to soothe her rage, her wild fiery glance.
But she, her eyes fixed on the ground, turned away,
her features no more moved by his pleas as he walked on
than if she were sent in stony flint or Parian marble rock.

A great article in the New York Review (subscription required) by Hayden Pelliccia unpacks the layers of meaning behind the simple line “I left your shores, my Queen, against my will.” Although to us the scene is poignant, the emotional center of the entire poem, that particular line is an echo of a comic line in a poem of Catullus that would have been well known to Virgil — “I left your head, my Queen, against my will,” spoken by a shorn lock of the hair of Queen Berenice, cousin of the Egyptian king Ptolemy. So is the scene tragic, or secretly facetious? The answer is ambiguous, but involves an intricate digression into Roman politics and the loves of Cleopatra. That’s why every month is Poetry Month.

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How Nice Should We Be to Students?

At Crooked Timber, Ingrid Robeyns passes along an email she received from an undergraduate student she doesn’t know. It’s a list of seven essay-type questions about the work and impact of economist Amartya Sen, along the lines of “How has Sen’s thought changed traditional development?” (Tyler Cowen, playing the straight man, actually answers the questions.)

A long discussion follows: What is the duty of professors, when it comes to answering questions from students? Heated arguments from different sides, largely for good reasons, and largely talking past each other. Students are complaining that they come to school to wrestle with great and challenging ideas, work hard and become passionate about what they’re being exposed to, only to find that professors are too busy to talk to them outside of class. Professors are shaking their heads in sympathy with the original post, amazed that a student who wasn’t even in a class with someone would feel justified in essentially asking them to do their homework for them.

So where is the line exactly to be drawn? I don’t know, but it’s a really good question, to which we give very little systematic attention, preferring instead to let every professor work things out according to their own preferences. Professors hold a privileged role in our culture; in return for years of hard work and devotion to an esoteric academic pursuit, society gives them jobs with lifetime tenure (ultimately, one hopes) and no heavy lifting, thinking about ideas at the edge of our understanding. In return, they are asked to assist in the production and dissemination of knowledge — doing original research, teaching students, and talking to the wider public. But what is an appropriate portfolio of these very different activities?

At the extremes, it’s not so hard. If a professor is teaching a class, there should be some time set aside for real-time interaction with the students outside of class. Traditionally these are “office hours” (a concept which, in my experience, undergraduates love and then completely forget about when they go to grad school). And at the other end, professors shouldn’t be expected to do students’ work for them. (I once got an email from a colleague, who was forwarding an inquiry from a student that he thought I’d know the answer to. Indeed I did know the answer, because I had just given that problem on a take-home exam that the student was supposed to be doing. More or less the definition of “busted.”)

But in between the extremes it’s harder, and there are few firm guidelines. And the invention of email has lowered a great deal of barriers, for better and for worse. What emails should we answer, and in how much detail? You don’t want to be a jerk, but you do want to get work done.

Crucially important is the relationship between the emailer and the recipient. In the original example, the fact that it was an unknown student was extremely relevant; if the student had been taking a class with the professor in which they were talking about Amartya Sen, there would have been some context to evaluate whether a straightforward answer should be given, or simply some pointers about where to look. But equally important is the form of the questions. In this case, they were so vague and essay-like that there was almost no simple answer that could have been of any use; the temptation to respond with a map to the library or instructions on how to use the internet must have been overwhelming. A good rule of thumb is: the less time it would take to respond, the more likely it is that a response will be forthcoming. And if it’s pretty clear that the original emailer has done next to no work themselves, they shouldn’t get their hopes up.

I get a lot of email, as well as occasional phone calls and regular mail. And I’m happy to admit, I don’t answer all of them. If they are technical questions about general relativity (about which I’ve written a book, don’t forget), I generally do not answer, but rather point to some promising resource — exactly because I’ve written that book, and if I answered all the questions about GR that I get I would do nothing else. If they are inquiries from students or sincerely interested people on the street about the state of physics or cosmology or whatever, I try to respond with short but substantive answers. If, as is often the case, they are from crackpots who say “I dare you to refute my theory!”, I generally don’t take the dare. (An exception is a letter I recently received from a state prison in New York. The writer is not a crackpot himself, but is stuck in prison with another guy who is convinced that special relativity is internally inconsistent, and he would like to know how to respond. In that case, I’ll definitely answer.)

The answering-email issue is just part of the much larger question of how much time professors should devote to students. The paradox is that what often draws students to a university — the place’s academic reputation, which rests on the research accomplishments of the faculty — can be an obstacle to fruitful interactions once they get there. Imagine how many physics students came to Caltech because of Richard Feynman. Undoubtedly they could have had some interesting interactions with him while they were here. But undergraduates would have found that he taught graduate seminars almost exclusively, while graduates would have found that he almost never took on any Ph.D. students. Too much worry and responsibility — he wouldn’t feel right giving a student a problem that he hadn’t already solved himself. While to me this seems like a scandalous abdication of duty (where would he have been if John Wheeler and others at Princeton had felt the same way?), the motivation is perfectly understandable.

What this calculation leaves out, of course, is that it can be extremely rewarding to advise students, or more generally to help people to understand things. But that sometimes gets lost amidst the feelings of being burdened and distracted from what we’re “really” here for.

Advising graduate students is a terrifying prospect, if you take it seriously; you’re wielding an extraordinary amount of influence over a young person’s life. Answering questions by email is a much smaller burden. But multiplied by dozens or hundreds of examples, and you can quickly get swamped. I suspect that most of us try to be reasonable, but walking the line between having individual chats with every interested person in the world and actually producing the research that made us experts in the first place is a delicate operation.

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