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My colleagues and I just submitted a paper about some of the technical issues associated with QUBIC, the new bolometric interferometer we’re trying to build for measuring the polarization of the microwave background.  In case you care, QUBIC stands for Q/U Bolometric Interferometer for Cosmology (and Q and U are the symbols for the two Stokes parameters that characterize linear polarization).  QUBIC is the merger of MBI (from the US)  and BRAIN (from Europe).  It’s what I’m here in Paris working on.

The paper addresses one concern that many people, both within the collaboration and outside, have worried about.  Traditionally, interferometers are narrow-band instruments — that is, they look at radiation within just a narrow range of wavelengths.  There’s a good reason for that: the whole idea of interferometry is to produce interference patterns out of the waves, and interference patterns get washed out when you have a wide range of wavelengths.  The instrument we’re proposing to build is a broadband interferometer, so there is naturally some worry about how or whether it’ll work.  We’ve made some general arguments before trying to quantify how much of a problem this’ll be.  This paper goes beyond those general arguments to lay out a detailed calculation showing that bandwidth issues don’t degrade the performance of the instrument too badly.

Even more than a lot of academic papers, this one is really aimed at specialists.  If you’re not interested in the details of CMB interferometry, it’s not for you.

then get an academic job in France.  They make you write and defend another thesis, after the Ph.D.  It’s called the habilitation à diriger des recherches (HDR), which I guess means “qualification to direct research.” As I understand it (i.e., not very well), you need to get it before you’re allowed to supervise Ph.D. students.  My colleague here in Paris just had his today.  He’s actually supervised Ph.D. students before, so it must be possible to get around that requirement, but I guess you need to get this certification to climb the academic ladder.

At first this sounded kind of cruel to me, but actually, I’d gladly have signed up to write another dissertation rather than go through the tenure process at U.R.

From time to time in the past, I’ve given my intro astronomy class the following assignment: Listen to Why Does the Sun Shine, by They Might Be Giants, and critique it for accuracy.  The answer is that it’s mostly very accurate, but there are a couple of things it gets wrong.

I’ll have to be careful assigning this in the future, though, because TMBG have written a followup song, Why Does the Sun Really Shine? (The Sun is a Miasma of Incandescent Plasma) that gives away part of the answer.

I learned about this via the radio show/podast Radio Lab.  One of their recent podcasts was all about TMBG and their new album of science songs for kids. (The part about the Sun starts at about 12:15, but it won’t kill you to listen to the whole thing.)

(In case any of my future astronomy students are reading this, the correction song reveals only one of the two things wrong with the original song; the Radio Lab interview reveals the other.)

My little piece on evolution and the second law of thermodynamics appeared in the most recent issue of the American Journal of Physics.  (Non-paywall version here.)  I wasn’t going to note that on the blog, since I’ve already written plenty about it before, but there’s one citation I wanted to include that didn’t make it in, so I figured I’d at least point it out here.

After the article had been accepted, Steven Morris pointed me to a piece he wrote back in 2005 for Reports of the National Center for Science Education that, like mine, quantitatively compares the entropy increase supplied by sunlight with the decrease required for evolution.  I was going to add a mention of this to my article when I got the proofs, but apparently AJP doesn’t do proofs for short notes like this, so I missed my chance. I figured I’d at least mention Morris’s piece here as a tiny mea culpa. 

To atone a bit further, I’m going to go send some money off to the NCSE.  This is an organization that fights for the teaching of evolution in US schools.  I used to give them money but haven’t for a while.  You should support them too.

I think that things like SETI (the search for extraterrestrial intelligence) are extremely unlikely to find a signal: even if intelligent life is out there, it’s not at all clear that such beings would spend much of their time communicating with each other by sending radio signals that leak off into space at detectable levels.  Even if they do that for a while, they’ll probably quickly learn ways of communicating that are less wasteful and harder to eavesdrop on.  In other words, whatever the other numbers in the Drake equation are like, L is probably quite small.

Still, I’ve generally had positive, warm fuzzy feelings about SETI.  Even if the odds are terrible, I figured, the payoff is huge, and the cost is low, so why not go ahead?  The first part is certainly true: if SETI saw a signal, it would be about the most important discovery ever made.  But my friend Allen Downey (CS professor at Olin College) recently gave me a convincing argument that the costs are higher than I’d realized, and I think I’ve changed my mind and become anti-SETI as a result.

Here’s my summary of Allen’s argument.

A key part of SETI  is combing through vast amounts of data from radio telescopes, looking for signals that look like those of extraterrestrial intelligence.  This is a big computational project, and the SETI people have adopted a clever way to achieve it: they farm it out to huge numbers of supporters, who run the computations on their own computers during times when those computers would otherwise be idle.

The people who do this, of course, are paying a cost: they’re giving away free CPU cycles on their computers.  Aside from any other costs, this costs them money, because a computer that’s actually computing uses more power than one that’s idle.  I think that a decent estimate of that power difference is about 40 watts.  (You can find a bunch of estimates out there for this quantity.  There’s some variation, but this seems to be about right.)  Say a typical user has SETI@home running on one PC about 2/3 of the time for a month.  How much does it cost? To find out, multiply 40 watts times 20 days and convert the result into kilowatt-hours.  These days, 1 kWh costs about 12 cents, so multiply the result by $0.12.

If that’s starting to sound like work, it’s not.  Just ask Google.  (In case you didn’t know, Google’s also a calculator, and it knows a ton of unit conversions.)  The answer is that such a user is spending about $2.30 a month.

I’d bet that the typical SETI@home volunteer doesn’t know that it’s costing them that much, but that if they did they’d probably think it sounded like a reasonable cost.

So far, I probably haven’t convinced you that SETI costs too much.  But now let’s think globally.  In total, the project has used up 2 million years of computing time.  If you try the same calculation to get a total cost, you get  $84 million. I don’t know about you, but to me, that’s real money.  When you think about the things that could be done with $84 million, it’s hard to see that this incredible longshot is justified, in my opinion.

A few random notes:

1. Nobody’s actually paying this money directly, so it’s not noticeable. But just because the costs are hidden, that doesn’t mean they’re not real.
2. In fact, the cost is probably underestimated in a bunch of ways.  I was assuming that the computers would all be turned on anyway, and just considering the difference in power due to the extra computational load.  If people are leaving their computers on for SETI@home when they would otherwise be turning them off, then the cost is greater.  Also, the figure of 12 cents/kWh is the direct cost to the consumer, but there are externalities (greenhouse gas emissions, pollution, geopolitical problems due to resource competition) that that market price doesn’t include.
3. Instead of considering the cost savings, you could consider the other good things that people could be doing with all those CPU cycles.
4. Let’s come back for a minute to my original point about L in the Drake equation.  My reason for thinking it was small was simply that any communication method that sends radio power into space is wasteful.  A technologically advanced species will learn how to beam its communications directly to the intended recipient.  Allen pointed out a different reason, which I’d never thought of.  To prevent eavesdropping, you want to encrypt your communications.  The better a method of encryption is, the more the output looks just like noise.  If an advanced society is really good at encryption, we won’t notice its signals even if they’re out there, because they’ll look like noise.  I’m not sure I’m convinced by this, but it’s an interesting point.

I’ve linked to the webcomic xkcd.com in passing before, but it’s so full of science-geeky awesomeness that I thought I’d advertise it more explicitly, in case there’s anyone out there who would like it but doesn’t know about it.  Here are a couple of examples; if you like them, go there and waste an hour or two clicking “Random.”

Oh, and be sure to mouse over each comic.  There’s some extra text for each one, and often it’s the best part.  (The ones embedded in this post don’t have the extra bits; go to the web site to see them.)

And the geekiest for last:

The Augustine panel, the blue-ribbon (whatever that means) commission charged with assessing options for the future of human space exploration in the US, released the executive summary of its report today.  (The full report is coming soon.) So what did it say?  Here’s what the first two hits on Google News say.

First sentences of the Washington Post piece:

Don’t try to put astronauts on Mars yet — too hard, too costly. Go to the moon — maybe.

Headline of the Reuters piece:

NASA strategy proposal aims for Mars over moon.

So who’s right?  The Post is closer than Reuters. The summary lays out three possible strategies, which they call “Mars first,” “Moon first,” and “flexible path.”  The last one involves starting with “inner system locations such as lunar orbit, Lagrange points, near-Earth objects and the moons of Mars.” After describing all three options, “the Committee finds that both Moon First and Flexible Path are viable exploration strategies.” (I’ve argued before that the Flexible Path combines all the disadvantages of human spaceflight with none of the advantages.)

But the real takeaway from the summary, it seems to me, is not these three paths; it’s this:

Human exploration beyond low-Earth orbit is not viable onder the FY 2010 budget guideline.

That is, we either need to spend substantially more money or decide that human space exploration isn’t a priority at the moment.  This sounds right to me.

A few miscellaneous observations:

1. Early on, the summary says something that should be obvious but often seems not to be:

Planning for a human spaceflight program should begin with a choice about its goals — rather than a choice of possible destinations.

I’m really glad to hear them say this: I’m sick of people saying “we need to go to Mars” without saying why.  I don’t think that the rest of the summary always lives up to this laudable goal, but maybe I’m not being fair to the panel: the full report may do better.

2. The summary recommends keeping the international space station going for another five years (to 2020 instead of 2015 as currently scheduled).

It seems unwise to de-orbit the Station after 25 years of assembly and only five years of operational life.

This is true, if the Station is actually useful, a claim that has not been demonstrated to my satisfaction.  Otherwise, the 25 years is a sunk cost, and extending the operational life is throwing good money after bad.

3. The panel has good things to say about the idea of contracting out some of our space flight to the commercial sector:

As we move from the complex, reusable Shuttle back to a simpler, smaller capsule, it is an appropriate time to consider turning this transport service over to the commercial sector.

…

In the 1920s, the federal government awarded a series of guaranteed contracts for carrying airmail, stimulating the growth of the airline industry.  The Committee concludes that an architecture for exploration employing a similar policy of guaranteed contracts has the potential to stimulate a vigorous and competitive commercial space industry.

…

This would have the benefit of focusing NASA on a more challenging role, permitting it to concentrate its efforts where its inherent capability resides: for example, developing cutting-edge technologies and concepts, and defining programs and overseeing the development and operation of exploration systems, particularly those beyond low-Earth orbit.

I think this approach is well worth considering.

Well, maybe.  I learned via Sean Carroll about a study showing that physics and math majors get better LSAT scores than people who study any other subject.  The top 5 disciplines, with mean LSAT scores:

1. Physics/Math (160.0)
2. Economics (157.4)
3. Philosophy/Theology (157.4)
4. International Relations (156.5)
5. Engineering (156.2)

In some cases, disciplines with smaller numbers of students were lumped together, so Physics/Math were treated as one category.  Pre-law ranked 28th out of 29, with an average score of 148.3.

It’s tempting for us physicists to use this as propaganda to convince people that studying physics is good preparation for a variety of careers, including law.  Although I suspect that that proposition is true, this study probably doesn’t provide strong evidence for it, for the usual correlation-is-not-causation reasons.  Students may self-select into physics and math based on qualities that correlate with doing well on the LSAT, but that doesn’t mean that a given student would do better on the LSAT if she studied physics as opposed to something else.

Still, it’s always nice to have bragging rights over other disciplines.

The fact that pre-law ranks near the bottom sounds embarrassing, but I suspect there’s not too much significance to it.  Pre-law is a funny category: at many institutions (including, I think, every one I’ve ever taught at or attended), pre-law isn’t a major: a pre-law student majors in something else.  So I’ll speculate that the students counted as pre-law in this study are a non-representative sample: they come from a different (and plausibly biased in various ways) subset of universities than the others.

One last thing.  Sean observes

The obvious explanation: physics and math students get to be really good at taking tests like the LSAT. I don't imagine this correlates very strongly with "being a good lawyer." Then again, I don't think that good scores on the physics GRE correlate very strongly with "being a good physicist," over and above a certain useful aptitude at being quick-minded.

Regarding the physics GRE, I seem to recall some actual data showing that scores correlate extremely poorly with a variety of measures of success in and after graduate school, but I can’t seem to find it, so maybe I hallucinated it.  If anyone remembers what I’m thinking of and can point me to a citation, I’d appreciate it.

Let’s do it. Let’s practice Bayesian inference.

Knowing that I like this sort of thing, Malcolm Hill pointed me to a discussion group on Bayesian ecology.

It’s probably a mistake to wade into such a controversial topic, but anyway, here are some thoughts on Robert Wright’s Op-Ed in Sunday’s NY Times.  Wright’s clearly a thoughtful guy who knows about both science and theology.  I haven’t read his book, but I have read a number of reviews of it, heard interviews with him, and read his guest blog posts on Andrew Sullivan. He seems to be someone worth paying attention to. But …

The  headline of the piece is “A Grand Bargain Over Evolution.” The goal seems to be to lay out a stance that will turn down the heat in the evolution wars and help everyone to get along.  An excerpt:

The first step toward this more modern theology is for them [religious believers who have problems with Darwinian evolution] to bite the bullet and accept that God did his work remotely €” that his role in the creative process ended when he unleashed the algorithm of natural selection (whether by dropping it into the primordial ooze or writing its eventual emergence into the initial conditions of the universe or whatever).

Essentially, he’s proposing Deism, justified by a sort of God-of-the-gaps approach.  I’m sure he would say that’s an oversimplification.  Read his piece for yourself and see whether you think I’ve characterized it fairly.

I have two thoughts on this attitude (neither original, I’m sure, given the vast amount that’s been written on these subjects):

1. If presented with such a bargain, I would strongly urge my fellow scientists to accept it.  By this I mean not that you have to believe in it: go ahead and be a hard-core atheistic materialist if you want.  But don’t put any significant effort into convincing Deists that they’re wrong.  They’re not doing science any significant harm, and if you try to persuade people like this that believing in science means giving up all notions of religion, you’re going to do far more harm by hardening them against your point of view.
2. But this thought experiment is completely irrelevant to the battle as it’s being fought in the US.  The forces of good (i.e., science) in this battle are not confronting Deists.  If you think that the defendants in the Dover case, or the anti-evolution folks running for school boards around the country, are anywhere near being persuaded of Wright’s Deism, you just haven’t been paying attention. Try telling any of the anti-evolution activists that God’s “role in the creative process” of human development ended 14 billion years ago if you don’t believe me.