Lunar laser ranging

Greetings from Toronto, where I’m visiting UofT to talk about dark energy, the arrow of time, and other obsessions of mine. Which has prevented me from as yet writing the long-awaited second installment of “Unsolicited Advice,” the one that will tell you how to choose a graduate school. It is that time of year, after all.

Lunar Radar Ranging In the meantime, check out this nice post at Anthonares on Lunar laser ranging. The Apollo astronauts, during missions 11, 14, and 15, were sufficiently foresighted to bring along reflecting corner mirrors and leave them behind on the Moon’s surface. Why would they do that? So that, from down here on Earth, we can shoot lasers at the lunar surface and time how long it takes for them to come back. Using this data we can map the Moon’s orbit to ridiculous precision; right now we know where the Moon is to better than a centimeter. This experiment, called Lunar laser ranging, teaches us a lot about the Moon, but it also teaches us about gravity. The fact that we can pinpoint the location of the Earth’s biggest satellite and keep track of it over the course of years provides us with a uniquely precise test of Einstein’s general relativity.

You might think that general relativity is already pretty well tested, and it is, but clever folks are constantly inventing alternatives that haven’t yet been ruled out. One example is DGP gravity, invented by Gia Dvali, Gregory Gabadadze, and Massimo Porrati. This is a model in which the observable particles of the Standard Model are confined to a brane embedded in an infinitely large extra dimension of space. Unlike usual models with compact extra dimensions, the extra dimension of the DGP model is hidden because gravity is much stronger in the bulk; hence, the gravitational lines of force from an object on the brane like to stay on the brane for a while before eventually leaking out into the bulk.

The good news about the DGP model is that it makes the universe accelerate, even without dark energy! This is one of the things that I talked about at my colloquium yesterday, and I hope to post about in more detail some day. The better news is that it is potentially testable using Lunar laser ranging! The claim is that the DGP model predicts a tiny perturbation of the Moon’s orbit, too small to have yet been detected, but large enough to be within our reach if we improve the precision of existing laser ranging experiments. People are hot on the trail of doing just that, so we may hear results before too long.

Not to get too giddy, the bad news about DGP is that it may be a non-starter on purely theoretical grounds. There are claims that the model has ghosts (negative-energy particles), and also that it can’t be derived from any sensible high-energy theory (see Jacques’s post). I haven’t examined either of these issues very closely, although I hope to dig into them soon. Maybe if I could quite traveling and sit down and read some papers.

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An Interactive Day in Harlem

This famous 1958 photo by Art Kane, A Great Day in Harlem, brought together 57 jazz musicians for a group portrait. Luminaries range from Count Basie and Coleman Hawkins to Charles Mingus and Dizzie Gillespie and Sonny Rollins. Norbizness points to a helpful web page: harlem.org, which provides a clickable version of the photo! Point to any musician, and it will tell you who they are and provide a brief biography.
A Great Day in Harlem
Years ago I saw a documentary by Jean Bach about the making of the portrait, which included many interviews with the surviving musicians (now available on DVD). My favorite part was seeing Thelonious Monk get ready for the shoot. You see him strategizing about how to stand out among all the other luminaries. First he decides to wear black, to look cool. Then he figures that everyone else will be wearing black, so he’s going to wear white. (As it turns out, everyone else had the same thought, so there’s a lot of white jackets in the photo.) Finally he realizes that the best thing to do will be to grab a spot next to the ladies, where everyone will be looking first. And lo and behold there he is, next to fellow pianists Mary Lou Williams and Marian McPartland (still going strong as host of NPR’s Piano Jazz). Monk needn’t have worried; he didn’t have any trouble standing out.

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Rep. Miller takes on science abuse

Passed on by DarkSyde at Daily Kos — Rep. Brad Miller of North Carolina has posted a Daily Kos diary calling for Congressional hearings on the issue of the integrity of scientific research in the Bush Administration. He believes that Rep. Sherwood Boehlert, chair of the House Science Committee, may be amenable to such hearings.

And he’s asking a favor: Rep. Miller is looking for information about “instances of censoring, intimidating, blacklisting or whatever” concerning government scientists. Anyone fitting that description (not just random people with a gripe, but actual government scientists who feel that their integrity has been compromised for political reasons) should email Rep. Miller’s legislative assistant Heather Parsons, at heather.parsons [at] mail.house.gov, or Dan Pearson of the Democratic staff of the Science Committee at dan.pearson [at] mail.house.gov.

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We're creeping up on you

Melissa Fletcher Stoeltje takes an unflinching look at a small, quiet community that seems to be gaining in numbers in the unsuspecting coffee shops of San Antonio — atheists!

She wears stylish glasses, and her thick black hair is swept up in a ponytail; the only hint of a slightly rebellious streak is the tattoo that peeks from under her shirtsleeve. He is a slight, soft-spoken man with a laid-back demeanor and a full beard.

Melissa and Chanse are young atheists. They don’t believe in God. As such, they’re part of a small but substantial minority that swims against the overtly religious mainstream of America, a spiritual tenor that has grown more strident in recent times as issues of faith increasingly become entangled with politics and public policy.

Of course they are stylish! And only slightly rebellious, at least on the surface. In fact it’s a very nice article, the point of which is that atheists and agnostics, despite being a tiny minority (about 3 percent), constitute the fastest-growing category of religious “belief” in the United States.

This cheerful demographic fact ties into a discussion between Chris Mooney, PZ Myers and others a little while back, on how we should speak about science and evolution and religion in the public sphere. Chris suggested that, since we live in a very religious culture, it’s to our own benefit to emphasize the compatibility of religious belief with a scientific worldview. PZ replied that there is no reason to dilute our message just to win some temporary battles. And the truth is that, while there are some staunchly religious scientists who also believe in evolution, and there’s no reason not to have such people be fighting for the cause of science, most scientists are somewhat agnostic if not downright atheist, and there’s no reason to hide that fact. Chris’s response correctly identified the underlying disagreement, which is completely about tactics. (Be sure to read Chris at Mixing Memory on the use of “framing” in this context, and John Rennie at Scientific American on the Dover trial.)

If I may put words into their mouths, Chris is a strategist, looking for the most politically effective ways of fighting the battle currently before us, which is defending evolution in schools. PZ is playing the role of the intellectual, for whom strategy and tactics will always take a back seat to telling the truth. If it makes a few people uncomfortable, that’s their problem. This is why Richard Dawkins generates such emotional responses among people who are clearly on his side when it comes to the truth of evolution; intellectuals admire his fierce determination to call it as he sees it, while strategists cringe at his blatantly anti-religious rhetoric.

I am on the uncompromising-intellectual side of this debate (big surprise there), but I think that the truth-telling attitude has its strategic benefits as well. The fight over teaching evolution in public schools is a tiny skirmish in a much broader cultural conversation. (See? We don’t have to call it a “war.”) We do live in a religious society, remarkably so when we are compared to similar countries elsewhere in the world, and there are complicated reasons for that. But increasingly, a lot of folks are wondering whether their supernatural beliefs are really warranted by the evidence, or whether they’re not just going along because that’s what everyone does. To young people wondering about the meaning of it all, it can be extremely powerful to hear someone say that it’s okay not to believe in God. Everyone always says that you will never talk someone out of their religious beliefs by lecturing about the scientific method; that’s certainly true for a wide range of people who are very confident in their positions, but there are also a huge number of people who are legitimately questioning what to believe. In the long run, the way to squelch the political effectiveness of the intelligent-design movement, the anti-abortion movement, the anti-gay-marriage movement, and so on, is to relegate them to insignificant minority positions within the populace, and one good way to do that is to undermine their supernatural foundations. It’s an extremely long-term project, to say the least, but one worth keeping in mind.

The only time I think the Stoeltje article stumbles is at the very end:

But what, exactly, do atheists believe in, if not in God?

In a nutshell, atheists believe in reason alone, in those things that can be arrived at through intellect and the scientific method. Concrete evidence for God, they argue, simply doesn’t exist. They don’t cotton to leaps of faith or anything that involves a supernatural being reaching into human lives. They believe you can live a happy, respectable life based on human ethics that were derived not from God handing down a tablet but from a code of rules that emerged naturally through an evolutionary process in which humans learned how to live together successfully.

The idea that atheists replace “religion” with “science” is an unfortunately common misunderstanding. Religion plays many roles — it tells a story about the workings of the universe, it suggest moral and ethical guidelines, and it provides social and cultural institutions and practices. Science does not play all those roles, nor should it pretend to; it talks about how the universe works, but is of no help with morality or culture. However, the moral and cultural roles of religion do not stand independently of its beliefs about the universe (existence of a caring supernatural being or what have you) — if that part of the story isn’t true, the other teachings of the religion (homosexuality is a sin, it is easier for a camel to pass through the eye of a needle than for a rich man to enter the kingdom of heaven) aren’t necessarily any better or worse than any other set of non-religious cultural practices, and should be evaluated on that basis. Science can’t tell us how we should treat other human beings. What it can do is to free us from the mistaken idea that the correct way to treat other human beings can be found in scripture or in church teachings or in the contemplation of God’s will; we human beings have to solve this hard problem all by ourselves.

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WMAP results — cosmology makes sense!

I’ll follow Mark’s suggestion and fill in a bit about the new WMAP results. The WMAP satellite has been measuring temperature anisotropies and polarization signals from the cosmic microwave background, and has finally finished analyzing the data collected in their second and third years of running. (For a brief explanation of what the microwave background is, see the cosmology primer.) I just got back from a nice discussion led by Hiranya Peiris, who is a member of the WMAP team, and I can quickly summarize the major points as I see them.

WMAP spectrum

  • Here is the power spectrum: amount of anisotropy as a function of angular scale (really multipole moment l), with large scales on the left and smaller scales on the right. The major difference between this and the first-year release is that several points that used to not really fit the theoretical curve are now, with more data and better analysis, in excellent agreement with the predictions of the conventional LambdaCDM model. That’s a universe that is spatially flat and made of baryons, cold dark matter, and dark energy.
  • In particular, the octupole moment (l=3) is now in much better agreement than it used to be. The quadrupole moment (l=2), which is the largest scale on which you can make an observation (since a dipole anisotropy is inextricably mixed up with the Doppler effect from our motion through space), is still anomalously low.
  • The best-fit universe has approximately 4% baryons, 22% dark matter, and 74% dark energy, once you combine WMAP with data from other sources. The matter density is a tiny bit low, although including other data from weak lensing surveys brings it up closer to 30% total. All in all, nice consistency with what we already thought.
  • Perhaps the most intriguing result is that the scalar spectral index n is 0.95 +- 0.02. This tells you the amplitude of fluctuations as a function of scale; if n=1, the amplitude is the same on all scales. Slightly less than one means that there is slightly less power on smaller scales. The reason why this is intriguing is that, according to inflation, it’s quite likely that n is not exactly 1. Although we don’t have any strong competitors to inflation as a theory of initial conditions, the successful predictions of inflation have to date been somewhat “vanilla” — a flat universe, a flat perturbation spectrum. This expected deviation from perfect scale-free behavior is exactly what you would expect if inflation were true. The statistical significance isn’t what it could be quite yet, but it’s an encouraging sign.
  • A bonus, as explained to me by Risa: lower power on small scales (as implied by n<1) helps explain some of the problems with galaxies on small scales. If the primordial power is less, you expect fewer satellites and lower concentrations, which is what we actually observe.
  • You need some dark energy to fit the data, unless you think that the Hubble constant is 30 km/sec/Mpc (it’s really 72 +- 4) and the matter density parameter is 1.3 (it’s really 0.3). Yet more proof that dark energy is really there.
  • The dark energy equation-of-state parameter w is a tiny bit greater than -1 with WMAP alone, but almost exactly -1 when other data are included. Still, the error bars are something like 0.1 at one sigma, so there is room for improvement there.
  • One interesting result from the 1st-year data is that reionization — in which hydrogen becomes ionized when the first stars in the universe light up — was early, and the corresponding optical depth was large. It looks like this effect has lessened in the new data, but I’m not really an expert.
  • A lot of work went into understanding the polarization signals, which are dominated by stuff in our galaxy. WMAP detects polarization from the CMB itself, but so far it’s the kind you would expect to see being induced by the perturbations in density. There is another kind of polarization (“B-mode” rather than “E-mode”) which would be induced by gravitational waves produced by inflation. This signal is not yet seen, but it’s not really a suprise; the B-mode polarization is expected to be very small, and a lot of effort is going into designing clever new experiments that may someday detect it. In the meantime, WMAP puts some limits on how big the B-modes can possibly be, which do provide some constraints on inflationary models.

Overall — our picture of the universe is hanging together. In 1998, when supernova studies first found evidence for the dark energy and the LambdaCDM model became the concordance cosmology, Science magazine declared it the “Breakthrough of the Year.” In 2003, when the first-year WMAP results verified that this model was on the right track, it was declared the breakthrough of the year again! Just because we hadn’t made a mistake the first time. I doubt that the third-year results will get this honor yet another time. But it’s nice to know that the overall paradigm is a comfortable fit to the universe we observe.

The reason why verifying a successful model is such a big deal is that the model itself — LambdaCDM with inflationary perturbations — is such an incredible extrapolation from everyday experience into the far reaches of space and time. When we’re talking about inflation, we’re dealing with the first 10-35 seconds in the history of the universe. When we speak about dark matter and dark energy, we’re dealing with substances that are completely outside the very successful Standard Model of particle physics. These are dramatic ideas that need to be tested over and over again, and we’re going to keep looking for chinks in their armor until we’re satisfied beyond any reasonable doubt that we’re on the right track.

The next steps will involve both observations and better theories. Is n really less than 1? Is there any variation of n as a function of scale? Are there non-Gaussian features in the CMB? Is the dark energy varying? Are there tensor perturbations from gravitational waves produced during inflation? What caused inflation, and what are the dark matter and dark energy?

Stay tuned!

More discussion by Steinn Sigurðsson (and here), Phil Plait, Jacques Distler, CosmoCoffee. In the New York Times, Dennis Overbye invokes the name of my previous blog. More pithy quotes at Nature online and Sky & Telescope.

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Chomsky, Krauss, and me

Science & Theology News was looking for some famous and charismatic scientists to respond to an interview with Noam Chomsky on various issues touching on science and religion. They were able to get Lawrence Krauss to agree, but then they ran out of ideas and ended up asking me. So you have some of the deepest questions we face about meaning and the universe, addressed by someone recently voted the world’s top intellectual, with responses by the author of The Physics of Star Trek and an assistant professor with a blog. What a great world!

You will notice that most of my answering comments are short and sweet. You can take this as evidence that I know how to pack a tremendous rhetorical punch into just a handful of words, or that I was in a hurry as the deadline was approaching. But sometimes I do go on a bit when a nerve is struck, such as this discussion on whether science and religion ever overlap in their respective spheres of interest.

ON STEVEN JAY GOULD AND “NON-OVERLAPPING MAGISTERIA”

CHOMSKY: Steve Gould [was] a friend. But I don’t quite agree with him [that science-and-religion are “Non-Overlapping Magisteria”]. Science and religion are just incommensurable. I mean, religion tells you, ‘Here’s what you ought to believe.’ Judaism’s a little different, because it’s not really a religion of belief, it’s a religion of practice. If I’d asked my grandfather, who was an ultra-orthodox Jew from Eastern Europe. ‘Do you believe in God?’ he would have looked at me with a blank stare, wouldn’t know what I’m talking about. And what you do is you carry out the practices. Of course, you say ‘I believe in this and that,’ but that’s not the core of the religion. The core of the religion is just the practices you carry out. And yes, there is a system of belief behind it somewhere, but it’s not intended to be a picture of the world. It’s just a framework in which you carry out practices that are supposed to be appropriate.

KRAUSS: Science and religion are incommensurate, and religion is largely about practice rather than explanation. But religion is different than theology, and as the Catholic Church has learned over the years, any sensible theology must be in accord with the results of science.

CARROLL: Non-overlapping magisteria might be the worst idea Stephen Jay Gould ever had. It’s certainly a surprising claim at first glance: religion has many different aspects to it, but one of them is indisputably a set of statements about how the universe works at a deep level, typically featuring the existence of a powerful supernatural Creator. “How the universe works” is something squarely in the domain of science. There is, therefore, quite a bit of overlap: science is quite capable of making judgments about whether our world follows a rigid set of laws or is occasionally influenced by supernatural forces. Gould’s idea only makes sense because what he really means by “religion” is “moral philosophy.” While that’s an important aspect of religion, it’s not the only one; I would argue that the warrant for religion’s ethical claims are based on its view of the universe, without which we wouldn’t recognize it as religion.

I was going to say that these guys might be famous, but do they have their own blogs? No! Except, of course, Lawrence was our very first guest-blogger, so that counts for something. And, I remembered, Noam Chomsky actually does have a blog. A funny one that consists of answers to occasional interview questions asked by someone from Z magazine, but I suppose it counts. Man, everybody has a blog these days.

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My conscious is worse than my unconscious

Michael Bérubé, International Professor of Danger, pimps out his upcoming collection Rhetorical Occasions by reproducing one of its essays as a blog post. The topic is well-known to any member of the professoriate: the academic anxiety dream. You show up to a class you are supposed to teach, but for some reason it’s not on the subject you thought it was going to be on, or you have completely neglected to prepare a lecture, or you have been reassigned to a classroom that looks like a castoff from the set of Brazil.

I was going to leave some smug comment to the effect that I never have such dreams, when it occured to me that I really shouldn’t, on the grounds that such a claim would not actually be “true.” Last quarter my travel schedule was even more hectic than usual; for an extended period I was flying out of Chicago at least once per week, sometimes twice. A couple of times I woke up early in a hotel room on the East Coast and zoomed to the airport, landing at O’Hare in time to make it to campus to teach my noon class. A couple of other times I went the other way, taking the red-eye from the West Coast. All in all quite hectic, and upon reflection I do remember one quite vivid anxiety dream during this period. The usual story: in the dream I kept thinking that I really should get around to the important task of actually preparing my lecture, but put it off, and suddenly there I was in front of the class. In fact, in the real world, it wouldn’t be such a big deal; at least once per term it’s a good idea to depart from the prepared text and have a free discussion about something related to the material but not formally part of the planned curriculum. Those are often the best classes.

However, I do have an unfortunate tendency to actually reproduce the conditions of the standard academic anxiety dream in real life. Not so much by being unprepared, but by sleeping right through some important event. (A habit which I take to be a sign of my innocence and inner peace.) It started as an undergraduate, when I woke up one day to find that I had completely slept through my E+M final. Fortunately, my professor was more worried about me than annoyed, and I made it up without incident. Then in grad school one of my apartment mates aroused me at noon one day after an all-nighter of general relativity and quantum field theory, to ask “Weren’t you supposed to be giving a lunchtime talk today?” Indeed I was, and I managed to run all the way to the department, showing up only twenty minutes late for my own seminar. I’m guessing that it was not the best talk I ever gave, but happily I have no actual recollection of what I said.

These days I am much better; I only sleep through events that are important for other people, like their thesis defenses (sorry about that, Tanya). On the other hand, as Michael says, why shouldn’t we be anxious about getting up in front of a bunch of smart people (youthful and inexperienced or otherwise) and attempting to teach them something? My very first assignment at the UofC was a graduate course on particle physics — something I know a bit about, but am certainly not the world’s expert. This was a useful experience, as I hit on a helpful philosophy right from the start: it’s not the professor explaining the material to the students, it’s the professor and the students engaging with the material together. In that case, it was “us against the particles,” and I think we acquitted ourselves just fine. And never once did I show up for class in my pajamas.

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It's good to hope

From Rate Your Students, via Ernie’s 3D Pancakes:

My classes are large, so I mostly use multiple-choice tests. One day, being one question short of a nice round number, I used this question: “The answer to this question is D. Be sure to mark D on your answer sheet.” The offered choices were: (A) This is the wrong answer. (B) This is the wrong answer. (C) This is the wrong answer. (D) This is the correct answer. Be sure to mark it on your answer sheet. (E) This is the wrong answer.

About 20% of the students got it wrong. One possibility is that they couldn’t read any English. Another is that they didn’t care. But one student had the courage to admit that he always marked B for every answer (true, that’s what he did) in hopes that all the answers were B.

One wonders how these students would have performed on Jim Harrick Jr.’s basketball exam?

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Message discipline

You may have heard that 72% of U.S. troops in Iraq think that the U.S. should leave the country before the end of the year. Presumably that’s because they can see for themselves that it’s a bit of a sticky wicket over there. On the other hand, they don’t seem to be getting very accurate reports from the outside world, since 90% think that the war is retaliation for Saddam’s role in the 9/11 attacks.

Hmm, I wonder why their information would be so faulty? Wonkette reported recently on an email from a soldier stationed in Iraq, reporting that their site was blocked by the censors at the USMC Network Operations Center in Quantico. Perhaps the military doesn’t want to distract the troops with salacious stories of Washington sexcapades? In a more recent followup (via firedoglake), the same soldier reports on just which sites are blocked, and which our troops are allowed to spend time surfing.

  • Wonkette – “Forbidden, this page (http://www.wonkette.com/) is categorized as: Forum/Bulletin Boards, Politics/Opinion.”
  • Bill O’Reilly (www.billoreilly.com) – OK
  • Air America (www.airamericaradio.com) – “Forbidden, this page (http://www.airamericaradio.com/) is categorized as: Internet Radio/TV, Politics/Opinion.”
  • Rush Limbaugh (www.rushlimbaugh.com) – OK
  • ABC News “The Note” – OK
  • Website of the Al Franken Show (www.alfrankenshow.com) – “Forbidden, this page (http://www.airamericaradio.com/) is categorized as: Internet Radio/TV, Politics/Opinion.”
  • G. Gordon Liddy Show (www.liddyshow.us) – OK

Interesting. I wonder if there is any pattern there? I suspect that there is, but somehow I just can’t put my finger on it. Probably just being paranoid.

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Primary season opens

First-round voting for the 2005 Koufax Awards has now begun over at Wampum. Here are the categories:

Best Blog (non-professional)

Best Blog — Sponsored or Professional

Best Blog Community

Best Writing

Best New Blog

Most Deserving of Wider Recognition

Best Single Issue Blog

Best Post

Best Series

Best Expert Blog

Best Group Blog

Most Humorous Blog

Most Humorous Post

Best State or Local Blog

Best Commenter

Cosmic Variance is nominated under Best Expert Blog, Best New Blog, and Best Group Blog. (Does the name “Harold Stassen” mean anything to you?) You are welcome to go vote for anyone you like, but keep in mind that it will go into your permanent record. Discover some new blogs and have fun.

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