I finally had a chance to see The Fog of War, the Errol Morris documentary about Robert McNamara, Secretary of Defense during the Kennedy and (much of the) Johnson administrations. It was a great film, the kind you could talk about endlessly. I’ll try not to do that, but a few things are irresistible.

First, the obvious parallels with our current mess in Iraq. McNamara was Defense Secretary during the escalation of the Vietnam war, so the connections are inevitable (and have been commented to death already). One does wonder what Rumsfeld would make of the movie. The most unbelievable moment to me was the account of a 1995 meeting between McNamara and the former Vietnamese foreign minister, to discuss what lessons could be learned. The minister explained to McNamara that the conflict was a civil war, that they were historic enemies of the Chinese, and that the US could not have “won” because the Vietnamese were fighting against a colonial power and would never give up. Amazingly, McNamara claimed to be shocked by these revelations (in 1995!). Cluelessness about the culture we are interfering with must be one of the most common themes of US intervention. That’s the one very obvious connection to the Iraq adventure, which in many ways is a very different story.

Second, although Vietnam dominated the movie, the opening bit about the Cuban Missile Crisis was the most gripping. Given the insanity on all sides, it’s miraculous that the world escaped without a full-blown nuclear war. McNamara quotes Castro as saying that if the US had invaded, he would have launched all the nuclear weapons on the island, knowing full well that the consequence would have been complete annihilation of Cuba. He also quotes our very own Gen. Curtis LeMay, who thought we should quickly launch an all-out pre-emptive strike against the Soviet Union before they could catch up to our nuclear arsenal. As I said, miraculous.

Third, and perhaps the only point that hasn’t already been beaten to death, the movie rehearsed a tired critique of the concept of “rationality.” A common criticism of McNamara when he was Defense Secretary, which is trotted out essentially unmodified in the movie, is that he and his staff (the “best and the brightest”) were super-intelligent and supremely rational, yet continued to get us into all sorts of trouble. Clearly, we conclude, this rationality stuff isn’t all it’s cracked up to be. Well, rubbish. Rationality is never to blame for bad decisions, any more than arithmetic is to blame when you can’t pay your bills. Rationality can tell you how to achieve certain goals through certain actions. If the result turns out to be a mess, there are two possibilities: the goals weren’t the right ones, or your rationality was simply faulty. McNamara calls Castro “rational,” just before he relates the anecdote that Castro was willing to have Cuba be completely destroyed. Sorry, the mistake there is not an overzealous application of instrumental reason; it’s just being stupid. Rationality doesn’t tell you that preventing the fall of dominoes in Southeast Asia is worth any possible cost in human lives; your nonsensical value system is telling you that, and rationality simply allows you to implement this craziness efficiently.

I’m sure that, if the situation in the Middle East deteriorates (even further), pundits will point to Rumsfeld and his crew and accuse them of being too rational, not sensitive enough to human needs and foibles, as if those qualities were somehow in opposition. This history-repeating-itself thing grows tiresome awfully fast.

By popular demand, I am forced to reveal the recipe alluded to below for burnt caramel ice cream. I found this recipe on the web years ago, and had lost track of where it came from. But a quick googling led me to this page, which leads me to believe that the original source was a small book called Wild About Ice Cream by Sue Spitler. Which apparently costs $1.50, which is not as cheap as getting things for free on the web but is pretty good. Anyway:

BURNT CARAMEL ICE CREAM

=======================

(Yields: 1 Quart or 950 ml)

Ingredients:

————

1 C (190 g) granulated sugar

1 C (240 ml) hot water

4 eggs

1/2 C (40g) powdered sugar

2 C (450 ml) heavy cream

1 tsp vanilla extract

Instructions:

————-

Heat granulated sugar and 1/4 C (60 ml) of the water in a large skillet on medium high heat until the sugar melts and boils, stirring occasionally. (Water will essentially boil away.)

Boil until mixture is a dark brown; remove from heat. Gradually stir in remaining 3/4 C (180 ml) water.

Cool to room temperature and set aside.

Beat eggs in a medium bowl until thick and lemon colored; gradually beat in powdered sugar.

Stir in cream and vanilla; stir in the caramel mixture. Chill. Freeze in an ice cream machine according to manufacturers directions.

(Bonus tip from long experience: The secret to great home-made ice cream is to keep all the ingredients as cold as possible, at least just before you put them into the ice cream maker. That way the mixture will freeze quicker, preventing ice from crystallizing and giving you a smoother product. Not as rich as Toscannini’s, but surpassing anything outside the Boston area.)

Okay, so let’s say you’re in Chicago. You’re taking the El (the elevated train; in Chicago the weather is always perfect, so there’s no reason to put public transportation underground as in climates that aren’t as blessed as we are). You get off at some stop, and the question hits you: What blogs are nearby? You can get the answers from Paul Goyette’s Chicago blog map, organized by El stop. There are 131 blogs as of this writing, although I’m sure there are many more to be dug up and linked to.

Now let’s imagine instead that you’re morbidly curious about the political-donation habits of important people (or unimportant ones). Just check out the fundrace.org neighbor search. For example, the President’s dad has donated to his pride and joy, just as you would expect. Less obviously, someone by the name of Howard Dean has donated to Bush as well. Or maybe that makes perfect sense.

Bill Gates has donated to Bush, but leading string theorist Ed Witten has donated to Clark and Edwards, and he’s smarter. Not at picking winners, obviously, but you know what I mean.

(Game inspired by Wonkette.)

The Supreme Court is hearing arguments about the Pledge of Allegiance. I think that the “under God” bit is an unconstitutional travesty, but honestly I don’t care too much; there are more important battles to fight. But this did amuse me:

Newdow, 50, held his own under a barrage of fast-paced questions. Chief Justice William Rehnquist threatened to clear the courtroom if spectators applauded Newdow a second time.

Rehnquist had asked what the vote was when the U.S. Congress in 1954 added “under God” to the pledge. The law was an effort to distinguish America’s religious values and heritage from those of communism, which is atheistic.

Newdow replied the vote was unanimous. Rehnquist said that did not sound divisive to him. “That’s only because no atheist can get elected to public office,” Newdow answered, triggering the applause, a rare event in the high court.

The applause must have been good to hear. I’m glad that someone takes this seriously enough to devote some real effort to demonstrating the obvious.

Update: Amanda Butler at Crescat Sententia was in the courtroom for the oral arguments, and gives a detailed account of the proceedings.

NASA reports that the Martian rover Opportunity is sitting on an ancient shoreline. The texture of ripples on the rocks indicates that they used to be under water; it must have been at least a couple of inches deep, in order to create the observed patterns. (Did you know that Opportunity has her own blog? Two of them, actually.)

Let’s indulge ourselves in thinking just about the scientific implications, instead of the icky politics. We instantly jump to speculations about life on Mars; the evidence is thin, but the temptation is irresistible.

I am by no means an expert on exobiology in general or Mars in particular, but it’s clear that sorting this out is going to be both complicated and fascinating. We don’t know all that much about the origin of life, to be honest. The famous Miller-Urey experiment showed that amino acids could be spontaneously generated inside a test tube filled with methane, ammonia, hydrogen, and water, if it was continuously zapped with electrical shocks (to simulate lightning). Amino acids are the building blocks of proteins, so this is certainly a step in the right direction.

But these days scientists think that the atmosphere of Earth long ago didn’t actually have the right compounds. Never fear, though; it seems as if the conditions for making amino acids happen naturally in outer space! Comets in particular seem to be thick with organic materials, and meteorites that have fallen to earth turn out to occasionally have actual amino acids in them. You might worry that the delicate organic materials would get destroyed when objects crashed into the Earth, but there’s some experimental evidence that they actually survive intact. In other words, it’s quite plausible that interplanetary chemistry played an important role in the first steps toward the development of life here on Earth.

I bring this up because 1) it’s intrinsically amazing, and 2) it’s going to make it very hard to sort out the life-on-Mars story. We might find all sorts of organic molecules on Mars, not because they developed there by themselves, but because they were brought by comets. We might even find evidence of Earth-like life, again not because it arose by itself, but because it was carried from Earth by our own spacecraft, or perhaps by rocks ejected from volcanoes.

None of this makes the effort to understand the status of life on Mars any less interesting; all of the possibilities are fascinating, for different reasons. But it will be a long time before we can say anything with confidence. Unless there is an entire civilization hiding underneath the Martian soil, waiting for the right moment to spring out and attack. Someone should make a movie about that.

I’m spending a few days in Cambridge, Mass, site of my old haunts from grad school and my first postdoc. One of the few places in the world where running into string theorists on the street (as I did today) is not too surprising.

And I enjoyed a treat I hadn’t had in years: Toscannini’s burnt caramel ice cream. I’ve always loved ice cream, but this is the flavor that made me a fanatic. After moving to California for my second postdoc, and making a desultory appraisal of the ice-cream situation, I was moved to buy my own ice-cream maker and churn out the burnt caramel myself. Some good comes out of every hardship.

Cambridge has an absolutely unique charm, although it’s not for everybody. I love the brick sidewalks, the scattered cafes and bookstores, the predominant scholarly aesthetic. I’ve only bought one book so far, but there are a couple of days left.

In the last post we talked about inflationary cosmology, the density perturbations it predicts, and how these perturbations show up in the cosmic microwave background (not to mention in the large-scale structure of galaxies today).

If this story is true, properties of the universe during the inflationary era are reflected (albeit faintly) in properties of the perturbations. For example, the overall amount of perturbation A (which is one part in 100,000) is related to the energy density of the universe during inflation; unfortunately it’s also related to another number, the “slow-roll parameter” ε (epsilon), which describes how the rate of inflation gradually slows with time. (Have to be a bit technical here, sorry.) Roughly, the energy scale E_I of inflation (the number which, when raised to the fourth power, is the energy density during inflation) obeys

E_I = A^1/2 ε^1/4 E_P.

Here, E_P is the Planck scale, the magical energy at which quantum gravity is supposed to become important: E_P=10¹⁸ billion electron volts. (A billion electron volts is one GeV, “G” for “giga-“. The rest energy in a single proton, via E=mc², is about 1 GeV.) For comparison, the highest energy yet probed by particle accelerators here on Earth is about a trillion electron volts, smaller than the Planck scale by 10^-15. Accessible experiments are not going to tell us anything directly about energies as high as the Planck scale; cosmology might be our best hope for learning something empirical about quantum gravity. For more details about inflation and perturbations you can look at a technical introduction to inflation by Andrew Liddle.

Let’s plug in numbers. The perturbation amplitude A is 10^-5. The slow-roll parameter ε is supposed to be small, perhaps 10^-2; but we’re taking the fourth root, so we’ll end up with something of order unity. This means that the energy scale of inflation E_I appears to be of order 10¹⁵-10¹⁶ billion electron volts. This is intriguing, since this scale is right where we expect to have grand unification — the coming-together of the three major forces in the universe other than gravity (electromagnetism, the strong nuclear force, and the weak nuclear force).

Could this be a coincidence? Sure. We certainly haven’t been very precise, to say the least. But an optimist would see hints of a consistent picture forming, in which the physics of grand unification is somehow behind the phenomenon of inflation. It’s by no means a complete theory, but an encouraging tidbit that is worth pursuing. Theorists will look for specific models of inflation, while experimentalists will look for new ways to test its predictions. Unfortunately, there aren’t that many predictions. One is that the overall geometry of space is very close to flat; this has been spectacularly confirmed by observations of the microwave background and elsewhere. Another is that the fluctuations in density should be accompanied by independent fluctuations of the gravitational field (gravitational waves), which leave a distinctive signature on the polarization of the microwave background. Looking for such a signal is a big goal of cosmologists right now.

Meanwhile, the fact that the energy scale of inflation seems to be tantalizingly close to the Planck scale leads people to wonder whether we can’t see explicit effects of quantum gravity in the CMB. It’s hard to give a definitive answer to this question, just because we don’t really know what the explicit effects might be. They might, for example, cause the perturbations to deviate from perfectly uniform behavior on all scales, perhaps by imprinting a tiny oscillating variation. But right now there’s little consensus about this quantum gravity/inflation connection; we have a ways to go before making it into something concrete.

Peter Woit has some questions for cosmologists. Too many good ones to answer in a brief comment, or even a single post, but let’s tackle the first big one, which is fun to talk about in its own right.

The general question is “What can observations of the cosmic microwave background tell us about physics at very high energies?” Since there’s no reason why non-experts shouldn’t follow the discussion, I should explain briefly what the microwave background is and why “high energies” are interesting. It will take some time, but it’s not useless for me, since I’m supposed to be writing some public-education web pages for the Kavli Institute for Cosmological Physics (formerly “Center for Cosmological Physics”) here at Chicago, and I’ll use this as a rough draft.

The cosmic microwave background (CMB) is the leftover radiation from the Big Bang. When the universe was much smaller it was much hotter, emitting blackbody radiation just like anything else, and we can detect that radiation today. The very early universe was so hot that it was opaque, since the electrons were ripped off of individual atoms and photons kept bumping into them. At 370,000 years after the Big Bang, the temperature had dipped below about 3,500 Kelvin, cool enough for electrons to recombine with nuclei to make atoms, and the universe suddenly became transparent. The radiation subsequently cooled to about 2.7 Kelvin, which is what we see today; it provides a snapshot of what the universe looked like when it was 370,000 years old (it’s 13.7 billion years old right now, or about 100 billion dog years).

What it looked like was something extremely smooth; fluctuations in density from place to place were only about one part in 100,000. But we can detect these fluctuations; the image reproduced here is the famous map from the Wilkinson Microwave Anisotropy Probe satellite. Blue regions are slightly colder than average, red regions are slightly hotter. (The WMAP team actually knows physics much better than this color scheme would lead you to believe.)

There is a treasure trove of information contained in these fluctuations. In particular, statistical properties of the fluctuations depend on two things: the primordial perturbations from which they presumably arose, and the recipe of ingredients in our universe that controls the subsequent evolution of the perturbations between early times and now. Remarkably, an extremely simple specification of primordial perturbations works very well — simply imagining that the perturbations are (on average) of equal strength at all distance scales. From this guess, and the observed fluctuations in the CMB sky, we can derive very tight constraints on interesting cosmological parameters, such as the amount of ordinary matter and dark matter in the universe. See Wayne Hu’s tutorial for details.

But the simple guess for the form of the primordial perturbations is actually better than a guess — it’s a prediction of the inflationary universe scenario. Inflation is the idea that the extremely early universe underwent a period of accelerated expansion that stretched a tiny portion of space to the size of our entire observable universe. It was originally invented by Alan Guth and others to help explain precisely why the universe looks so smooth on large scales. See this intro by Ned Wright for more details.

Inflation came with an unexpected bonus. Try as it might, inflation can’t make the universe perfectly smooth, simply due to the strictures of quantum mechanics. Heisenberg’s uncertainty principle tells us that we can’t specify the state of a system with perfect precision; there is always an irreducible jiggliness when we look at, for example, the position of an electron. But the principle holds as true for the entire universe as it does for an electron. So inflation makes the universe as smooth as it can (imagine removing the wrinkles form a sheet by stretching it at the edges), but there is some amount of fluctuation left over — which, of course, precisely describes the universe we see. All of the stars, galaxies, and large-scale structure in our universe may have started as tiny quantum fluctuations in the primordial soup.

Okay, this has gone on a while already. Next time I’ll be more quantitative about the perturbations, and talk about how they might reveal something about physics at very high energies.

From Tbogg, a link to an article at Axis of Logic on the status of 9/11 as a political football, and in particular who is to “blame” for the incredible intelligence failure. This is a topic where it’s hard to find level-headed discussion, but this article is sufficiently well-documented as to be quite persuasive. Not to give you the wrong impression — it’s completely partisan, but defensibly so.

Astronauts who have risked their lives to explore space are joining the chorus to save Hubble. Let’s keep it up, hopeless though it may seem at the moment.

Peter Woit has a new blog. He’s a mathematician who argues that string theory (our attempt to derive a consistent quantum theory of gravity from a theory of extended objects, rather than ordinary point particles) is bad news for physics. I don’t agree, but it’s worth listening. I think string theory is fantastically promising and quite remarkable, but plenty of scientists (including particle physicists and gravitational physicists) disagree, which is an interesting state of affairs. Some time in the future our current generation of string theorists will either be viewed as visionary pioneers soldiering forward despite overwhelming odds, or misguided crazies who derailed progress in physics with their hopeless detachment from experiment. Maybe we’ll live to see which one.

Out here in the desert today we were worrying about dark energy. Seventy percent of the energy in the universe is some mysterious stuff whose density, as far as we can tell, remains constant as the universe expands. (In contrast to, say, ordinary matter, which dilutes away as a result of the expansion.)

The leading candidate for dark energy is vacuum energy, or the cosmological constant, which is exactly constant throughout space and time. But it’s not an especially attractive candidate, so we’re looking for alternatives anywhere we can — some persistent but nevertheless dynamical field, or even a modification of gravity on large scales.

To tell if the dark energy is vacuum energy, we try to see whether it’s changing or absolutely constant. The parameter we go out and measure is w; its value is -1 for pure vacuum energy. We know that w is pretty close to -1; if it’s a little bit greater (like -0.9) the dark energy is gradually diminishing, while if it’s less than -1 the density is actually increasing. (The amount of dark energy per cubic centimeter is going up everywhere in the universe.) That seems crazy, which was what my talk this morning was about. It is crazy, but it can’t be completely ruled out, so we should keep an open mind.

The first direct evidence for dark energy came from using supernovae as standard candles (objects whose intrinsic brightness is known, so their distance can be inferred from their aparent brightness). Many of the talks today were devoted to current and future supernova searches. There was much discussion between the observers, who wanted to know just what kind of deviation from w=-1 we should expect, and theorists (like myself) who kept admitting that we have no idea. I don’t think they believed us. Unfortunately it’s a question we have to keep asking, since it costs money to do these observations; money is tight, and we have to decide which experiments are most deserving of our efforts.