Preposterous Universe

 
Testing general relativity

Some slightly-recycled content. (But it's new to you, right?) Science writer Amanda Gefter is working on an article for Sky and Telescope about testing general relativity. (See other articles by Amanda here and here.) She emailed me to ask some general questions about the state of GR and its experimental tests; here are the questions and my answers, just off the top of my head.

What are scalar-tensor theories of gravity? In these theories, where does the extra field come from (in other words, what is it, and why is it there?) How do these theories modify GR? If a scalar-tensor theory is found to explain experimental results, does that necessarily mean that there are extra dimensions? How viable do you think these theories are?

Scalar-tensor theories are simply generalizations of GR that add a new scalar field that interacts directly with gravity (i.e., couples directly to the curvature of spacetime). A scalar field is like the electromagnetic field, except that it only has a magnitude and not a direction; it simply takes on a single numerical value at each point in spacetime. The first scalar-tensor theories proposed that the gravitational constant, which fixes the strength of gravity, could have a variable strength that depended on some scalar field; but current theories are more general.

Scalar fields can arise in different ways. Often, they are simply put there. They can also arise from extra dimensions of spacetime, or from superstring theory. But if we find a scalar field, it certainly doesn't imply the existence of extra dimensions, as there are many other ways to get such scalars.

Scalar-tensor theories are simple and natural generalizations of GR, and it wouldn't be surprising if one of them were true. However, many theories that are studied in the literature assume that the scalar field is very light, and therefore leads to (potentially detectable) effects at large distances. It's much more likely that any such scalar has a significant mass, perhaps near the Planck scale, and so would remain undetectable in any conceivable experiment. However, we know little for sure, so it pays to keep an open mind.

Are there other alternatives to GR that are being explored? Any that you find particularly promising?

There are many alternatives being explored, too many to list or even catalogue. The most straightforward, and perhaps most promising, imagine that something like GR is true in extra dimensions, and lead to a modified theory at the level of our observed four-dimensional spacetime. The ways in which this theory can be modified will depend in the specific model of extra dimensions; it has been proposed that such theories can help explain the value of the cosmological constant, or explain the acceleration of the universe without any cosmological constant, or affect cosmology at very early times. It is also possible to modify GR directly in four dimensions to help do away with the need for dark energy.

Other models try to do away with the need for dark matter, by modifying gravity on the scale of galaxies. A famous example is MOND (Modification Of Newtonian Dynamics) by Milgrom, although that is more of an "idea" than a "theory" (although Bekenstein has recently tried to put it on a more sound footing). The biggest problem with such models is that they have a very hard time reproducing the many successes of the dark matter idea, for example in accounting for the perturbation spectrum of the cosmic microwave background.

Finally, there are models that don't try to explain some specific feature of astrophysical observations, but instead simply try to see how far we can go in modifying GR. For example, there are models which violate Lorentz invariance at a fundamental level. These are interesting to explore, if only to help us understand the extent to which GR can be trusted.

Why is it important for us to test GR? Has it become more imperative in recent years?

Gravity is an important force, and GR is our best theory of gravity, so it should be tested as well as we possibly can. More specifically, cosmological observations (dark matter, dark energy, and primordial perturbations) have revealed a universe that seems very surprising to us, and our interpretations of these observations rely on extrapolating ordinary GR to scales of time and distance that are far larger than where it has been directly tested. So any new tests can give us more confidence that we have the right to make such extrapolations.

Why is our understanding of gravity so important?

See above. On the large scales characteristic of cosmology, gravity is by far the most important force. In addition, it is the only force that has thus far evaded a quantum-mechanical understanding; reconciling GR with quantum mechanics is the greatest single quest in contemporary fundamental physics, and any information we have about gravity itself could be an invaluable clue along the way.

Up to this point, is GR a well-tested theory?

It is extremely well-tested in certain regimes, less so in others. Three regimes have been especially well-tested: the Solar System, where precision measurements have tightly constrained deviations from GR; the binary pulsar, whose orbit implies exactly the amount of gravitational radiation predicted by GR; and the early universe, where observations of light elements produced by nucleosynthesis and the anisotropies of the cosmic microwave background provide good evidence for the validity of GR when the universe was seconds old and hundreds of thousands of years old, respectively.

There is still a lot we don't know. For example, are the predictions of GR for gravitational lensing and dynamical measures of mass consistent with each other? Are there deviations at very strong curvatures, or for that matter very weak curvatures? Are there deviations at very small distances that may be probed in the laboratory? (Current best limits go down to about one tenth of a millimeter.) Are there long-range but subtle effects that still may show up in the Solar System?

As I understand it, GR has been inadequately tested in the strong field regime. Why is it important to test GR in such extreme circumstances? What kinds of tests will be helpful? In particular, how can we use black holes to test GR?

I wouldn't say "inadequately", but we can always do better. To be honest, I think that testing GR with black holes is interesting, but somewhat overrated. If GR is going to be modified, there are two likely ways it can happen: subtle long-range effects, and deviations that become important when the curvature of spacetime reaches a certain fixed value. In the first case, Solar System tests will usually do better than astrophysical tests, just because the precision is higher. In the second case, we would have to get extremely lucky indeed to notice any effects in black holes. The curvature outside astrophysical-sized black holes is actually not that great; the curvature radius would be measured in kilometers, while we would probably need to go to much smaller scales to observe any deviations from general relativity.

On the other hand, as already mentioned it's important to keep an open mind. Many of our tests of GR thus far have either been in cosmology or in the quasi-static, weak-field regime of the Solar System, with the binary pulsar being the notable exception. Even if our most respectable alternative theories wouldn't necessarily show up first in a dynamical, strong-field situation, we should certainly do as many tests in such regimes as we can, if only to make sure there are no surprises.

Is it strange to use black holes as testing grounds for GR when they them selves are consequences of the theory of GR? (in other words, if GR were wrong, would there even be black holes?)

Most respectable theories of gravity (all that I know of, to be honest) predict that there should be black holes, although their properties might be different in different models. So they are well worth investigating, keeping in mind the previous answer.

I understand you worked with Ed Guinan on DI Herculis -- what are your thoughts on that problem? Do you think it points to a gap in GR, or is it an experimental anomaly? Are physicists worried about it?

It's a very interesting system, and I don't know what is going on. I became skeptical that gravity is to blame when I worked out that the stars in DI Her are well within the weak-field regime where Solar System tests have already tightly constrained any possible deviations from GR; it seems very hard indeed to find a theory that could explain the motion of DI Her yet remain consistent with Solar-System tests. So I suspect that some astrophysical phenomenon is causing the discrepancy, but I'm by no means certain.

Have there been any other observations that seem to violate GR?

It's hard to say that any given observation violates GR, since there are always other assumptions that come into play. For example, the anomalous acceleration of the Pioneer spacecraft may be due to some extremely unexpected gravitational effect; more likely, however, there is some much more mundane explanation involving the spacecraft themselves. So far, there is certainly nothing we have observed that gives anything like a good reason to doubt GR.

In your opinion, what have been the most significant tests of GR?

Historically: precession of Mercury, deflection of light, gravitational redshift, and gravitational time delay. More recently: the binary pulsar and cosmological nucleosynthesis.

Any thoughts on the importance of Gravity Probe-B? Lunar laser ranging?

GPB is in a somewhat awkward position; it will either confirm the GR prediction for frame-dragging, or it will find a discrepancy and very few people will believe it. I'm not an expert, but my understanding is that the regime it is testing (in the "parameterized post-Newtonian" sense) has already been ruled out by other observations.

Lunar laser ranging is a very different story, well worth doing. There is an opportunity to greatly improve the precision of constraints on long-range deviations from GR, which is always interesting, even if there is no firm prediction from a specific model.

Will the detection of gravity waves be an important confirmation of GR?

Yes, absolutely. At this point, however, very few people doubt that gravitational waves exist, with essentially the properties predicted by GR, so they are more looking forward to learning about the astrophysical sources of the waves. If the observations are somehow inconsistent with GR, that would be an even more spectacular finding than anyone expects.

What makes general relativity such a beautiful theory?

It is extremely powerful (accounting for all gravitational phenomena ever observed), mathematically compelling (applying elegant results from differential geometry), and remarkably simple and robust (unlike, say, the Standard Model of particle physics). GR is simply the statement that "Gravitation is the curvature of spacetime", made precise and mathematical; few theories in science are simultaneously so simple, elegant, and comprehensive.

Finally, do you think that GR will ultimately prove to be wrong (or incomplete) at some level?

Yes. Everybody (in their right mind) does. GR is a classical theory, fundamentally inconsistent with the quantum world in which we live. At the very least we will have to find a quantum version of GR; more likely, we will have to find some more profound theory that is intrinsically quantum-mechanical and reduces to GR in the appropriate circumstances. If experiments reveal deviations from GR at even the classical level, so much the better.

~ posted by Sean Carroll at 7:43 AM ~ link ~ ~ ~

 
Cosmically Considered

The nice thing about jet lag after a long trip westward (say, from Austria to the U.S.) is that you wake up early enough to enjoy the morning, something I tend not normally to do. Which is why it's too bad I am not still in my beloved Chicago enjoying a cup of coffee while watching the sun rise over Lake Michigan, but instead sitting in a hotel room in Riverside, California, site (Riverside, not my hotel room) of the annual meeting of the Division of Particles and Fields of the American Physical Society. Tuesday afternoon I'll be giving a review talk on "Theoretical Cosmology," which sounds a bit too comprehensive to be coherent, but we'll give it a go. Since it's the last talk of the conference, likely nobody will be in the audience; if I remember I'll post a link to the slides (once, you know, they've been written).

In the meantime, I'll share this. Poet Richard O'Connell was kind enough to email me a copy of this poem he wrote in 1976:

To Beta, Cosmically Considered

If relic radiation bathes the spheres
Isotropically, as water is to fish,
To an observer here or on Andromeda,
Time has an arrow sharp as Cupid's kiss.

If all is that primeval fireball
Exploding yet beyond the verge of sight,
We're genesis and apocalypse ourselves
Galactic cousins, catastrophic flesh.

Let us junk tyrannical cyclopean clocks
Geared to the wormwork of industrious forebears
Who added pittance by the pendulum
Only to leave their wealth to wastrel heirs.

Let us accept that arrow in our hearts
Transfixing us, targets of joy and tears;
The stars may see how in our spendthrift love
We keep a better time by keeping theirs.

Maybe I can figure out some way to work it into the talk.

Also, read about a Big Bang in your bedroom. (No, it's not what you think.) I will explain later.

~ posted by Sean Carroll at 6:20 AM ~ link ~ ~ ~

 
USA Basketball

I remember, back in 1992 when the Dream Team of NBA stars first participated in the Olympics, someone telling me with a straight face that the US would never lose a basketball game in international competition again. Why not? Because basketball is a black person's sport, and the Europeans and South Americans just couldn't compete athletically.

Someone forgot to tell the Argentinians and Italians, as the former beat the latter for the gold medal yesterday. The US managed to squeak by a small former Soviet republic to claim the bronze. The team played hard, but was under-prepared and put together badly for this kind of competition, with a bunch of swingmen who can drive to the basket and a significant lack of big men and outside shooters.

Who comes out of the fiasco looking the best, from the US side? None other than poster boy for selfishness Allen Iverson.

To the Shaqs and Garnetts and T-Macs and Ray Allens who had better things to do than protect their homegrown game, Iverson said: "They have to understand that, first and foremost, it's an honor to be selected on this team. It's something that you should cherish for the rest of your life, and honestly, it's something I will cherish without winning the gold medal.

"I feel good about taking part in something like this. I feel like a special basketball player to be selected to a team like this."

To his former coach in Philly, Brown, who complained about the only-in-America rush job needed to field an Olympic team when he wasn't busy ripping his players and the USA Basketball selection committee that picked them, Iverson said: "I don't want to make (the rush job) an excuse. I think the time that we had, it was already known that that's how much time we were going to have. And we had to understand from the first day that that was the amount of time we had to prepare."

Like Lindsay, I don't really care that much about the Olympics. But it was sad to hear that the US team went from being worshipped a decade ago to being booed off the court this year. Of course, that might have something to do with issues other than basketball.

~ posted by Sean Carroll at 8:18 AM ~ link ~ ~ ~

 
From Europe to America

I'm back from the European Forum in Alpbach (where I was referred to as "herzig," which I think is good). Many thanks to Lindsay for keeping things active while I was away. Only after getting there did I understand what the Forum is about, partly because it is such a sprawling multi-dimensional thing that a focus can be hard to pinpoint. There are many events involving all sorts of discussions on politics, culture, and anything else (science is represented, but only as an amusing distraction). The seminar week, which is what I was there for, is almost a summer school; twelve seminars go on for a week of lectures, and about three hundred students (largely graduate and professional students) from throughout Europe come to listen and participate in the discussions. But the definition of "student" is pretty loose, and a good number were well past their student days.

What became clear only gradually was that, since most of the students are interested in public policy questions, many of the attendees are there largely to network amongst their fellow students, rather than to actually attend the seminars. And the seminars they did attend were those that related in some way to their careers; i.e. questions of European politics. So everyone was interested in our little cosmology discussion, but very few people actually came to it.

That's okay, since you can still learn interesting things by talking to the other attendees. Issues of the European Union were especially popular, for understandable reasons. Someone gave me an article to read by Stephen Breyer, my favorite Supreme Court Justice (although if Kathleen Sullivan is ever appointed, she will be granted this coveted honor), musing about the new European Constitution. It was fascinating reading, especially because Breyer was trying very hard to be polite but clearly has substantial worries about the new document.

One of his worries is obvious: the new constitution is far too long (about eighty percent of it should be cut, in Breyer's estimation). In an effort to keep everybody happy, the framers have stuck all sorts of things into the constitution that should be ordinary law. One of the crucial features of a constitution is that it should be possible, but very hard and extremely rare, to amend it; so it should stick to enshrining absolutely bedrock principles rather than including every policy we might agree upon at the moment. (He also points out that the European court will have over twenty justices, speaking multiple languages, and can't resist mentioning the difficulty that he and his eight very capable colleagues sometimes have in reaching consensus, even in a common language.)

The more subtle of Breyer's points is the ease with which the constitution will allow centralization of power. From personal experience, he knows how ambiguous language in a constitution can be interpreted to funnel more authority to the federal government. He mentions the example of education, where the constitution innocently gives the European Commission power to pass rules to facilitate cooperation and compatibility between the educational systems of the member states. Who could object? Well, cooperation takes a lot of forms -- Breyer imagines that before too long the EC will be passing whatever regulations it likes on school systems throughout Europe, all in the name of increased cooperation. It will be interesting to see how the constitution actually fares in action (although they did manage to keep Christianity out of the preamble, despite heavy Papal lobbying).

So, while we're at it, do Europeans hate Americans? Well, the participants at Alpbach are traditionally conservative, establishment-oriented types, who generally are more pro-American than their lefty counterparts. But one over-simplified way to describe the current situation is that both left-wing and right-wing Europeans are horrified by our current administration. They don't hate Americans, but the disgust with the Bush regime is palpable. Of course, these are people who will willingly sit through hours of discussion and dialogue relating intricate philosophical questions to concrete issues of policy; something tells me Bush wouldn't like them, either.

~ posted by Sean Carroll at 9:13 AM ~ link ~ ~ ~

 
Fearless punditry

If there's one thing that you learn by being in academia, or by being a blogger for that matter, it's to speak with authority on things you know little about. On Sept. 1st I get to put my skills to some use, participating in a roundtable discussion hosted by the Remy Bumppo Theatre Company. Their upcoming season, entitled "Chaos Theory and Other Family Gatherings," features three plays with some connection to science: Delicate Balance by Edward Albee, Arcadia by Tom Stoppard, and Humble Boy by Charlotte Jones. Each play will be commented on by an expert of some sort or another, and then we will all join in with artistic director James Bohnen to discuss connections and so forth. I'm responsible for Humble Boy, and will also give some sort of lecture when the play opens in the spring (not that you can glean any info about it from the RBTC website).

I haven't actually read the play yet -- that's a project for the plane ride home -- but I've learned some of the basics about it. It's loosely inspired by Hamlet, and features as its central character an indecisive theoretical physicist who is struggling in his personal life when he's not busy trying to unify gravity and quantum mechanics. (Well, who isn't?) I'm crossing my fingers here -- the track record of authors using science as a source of metaphor and imagery is a mixed one, at best. I'll let you know how it goes.

And now I need to hop in a train and cross the Alps. You're in Lindsay's capable hands for the duration.

~ posted by Sean Carroll at 10:15 AM ~ link ~ ~ ~

 
John the Baptist and the Hermeneutics of Scientific Reporting

Being a science journalist has to be one of the most difficult jobs I can think of, requiring both common journalism skills as well as an ability to understand and judge the importance of claims in a wide variety of obscure specializations. Still -- a lot of it is very bad. Which is a shame, since so many people get most of their knowledge about contemporary science through the news.

Fortunately, there are certain strategies that can help you understand what is really going on when you read a piece of science journalism. As an example, let's consider the breaking news about the cave linked to John the Baptist that has just been found in Israel.

TZOVA, Israel (Reuters) - A British archeologist has dug up evidence linking John the Baptist to a cave used for bathing rituals in hills near Jerusalem in what he said could be one of the biggest recent finds for Christian history.

Shimon Gibson, who has been digging in the Holy Land for nearly three decades, told Reuters he believed the cave, hewn 24 yards deep into a rocky hillside, might also have been visited by Jesus as well as New Testament preacher John.

Okay. For a start, these claims seem pretty grandiose. I don't know anything about archeology, and precious little about Biblical history, so for all I know this guy could be completely accurate. But you do worry a little when scientists not only make absolutely fantastic claims, but seem willing to extrapolate far beyond what they have actually found evidence for (in this case, talking about Jesus). There is pressure to make your findings sound interesting to the public, and sometimes we get overly enthusiastic, but this is definitely a warning sign.

Discovered by Gibson in 1999, excavations at the cave since then have revealed a large bathing pool as well as objects used for anointing rituals that would be quite different from those used by most Jews there nearly 2,000 years ago.

Gibson, 45, said evidence of specific links to John at the site came from drawings made 400 to 500 years later, which portrayed him in a similar way to other Byzantine art. One of the pictures also showed John's severed head.

Perhaps this is just me, but that last paragraph makes no sense. Are the drawings at the site, or are there drawings elsewhere that link John to the site? Why do we care that he is portrayed in a similar way to other Byzantine art? How do we know that the drawings are of John the Baptist? Most of all, do the conclusions being reported here rely on the assumption that there are no distortions that might creep into an oral record over a period of 400 years?

"Nothing like this has been found elsewhere," Gibson said. "It is the first time we have finds from the early baptismal period ... It is an amazing discovery that happens to an archeologist once in a lifetime."

The discovery, 15 minutes drive into hills west of Jerusalem, is due to be announced officially Tuesday, ahead of the launch of a book by Gibson.

Ding ding ding! He's writing a book. Already has written one, in fact. So there might be some conflict of interest between appropriate scientific skepticism and the selling of the story. Also, why is the finding only being announced now? It must have taken some time to write the book -- presumably the archeological finding would have been published in a reputable journal some time back?

Any discovery of sites linked to the Bible is certain to stir controversy and its share of skepticism, but Gibson said he had carried out many tests to satisfy himself that his theory was sound. The Bible describes John performing baptisms -- including that of Jesus -- in the River Jordan, a good 25 miles east over the Judean desert.

But Gibson said the site at Tzova could be linked to early years "when John sought solitude 'in the wilderness."'

Okay, now we are told that there is actually a conflict between what we know about John and where the cave was found. And a flimsy explanation is offered. But we are supposed to be reassured, since Gibson himself has carried out many (unspecified) tests. Notice that there are no outside experts quoted in the article. Even when there are, you need to take what they say with a grain of salt, since they have typically not had a chance to review the claimed findings in any detail, and have to rely on their general expertise in the subject area. When they are completely absent, it's a bad sign.

"In addition to John the Baptist, there's a possibility that Jesus used this cave as well," said Gibson.

Yes. There is also the possibility that Alexander the Great slept there, and the Loch Ness monster has visited. There are lots of possibilities. If there were any actual evidence that Jesus had been there, do you think we'd spend so much time talking about John the Baptist?

Gibson said he was sure the cave could not have been put to other uses -- as a water store or a hideout for example -- or that it was used by any other group carrying out similar types of rituals around the same time as John.

"I don't believe in that kind of coincidence," said Gibson, who said he was not religious himself. "Pilgrims will be flocking to the cave."

What coincidence? That some non-famous person was using the cave for some good reason? Most of the people alive two thousand years ago were not celebrated figures from the Bible, and most archeological findings are not going to represent important events in the lives of famous people.

Again, I have no expertise in this actual area, and for all I know Gibson may turn out to be completely correct and his findings may go down in history as a major breakthrough. But we don't have evidence for that from this story. The journalist can always say that they are simply reporting what they have been told. But I don't really think that is the end of the journalist's job -- it's perfectly appropriate to exercise some judgement about the claims being made. Unfortunately, if you spend just a day talking to outside experts and verifying the credibility of the story, your rivals will get the story out before you, and that's the major criterion for success in the news business. So it's up to the readers to use their own judgement.

My personal experiences have been with stories about science. But something tells me that stories about politics are not that different.

~ posted by Sean Carroll at 7:46 AM ~ link ~ ~ ~

 
What do you call a drive-through liquor store?

Switzerland is a very cosmopolitan country (despite clinging to their own currency rather than bowing before the Euro), with no fewer than four official languages (German, French, Italian, and Romansh). On the Lufthansa flight from Frankfurt to Geneva, each announcement was first made in German and then repeated in both French and English. I don't know whether the English was simply a bow towards the universal language of the world, or whether the fact that the flight was officially a code-share with United had something to do with it.

The existence of multiple official languages must create occasional headaches. Of course, in the U.S. we don't have any official language, attempts by organizations like U.S. English notwithstanding (warning: cheesy patriotic music). And English doesn't have an official governing body, so we don't have to live through nonsense like the German spelling reform. Which I think is a good thing, since like Steven Pinker I fall firmly on the descriptivist side of the descriptivist/prescriptivist debate over the nature of language, believing that rules bubble up from the bottom rather than being imposed from the top. (Although I enjoy reading David Foster Wallace defending the opposition.)

Despite our lack of central authority, the usage of American English is probably more standardized than either French or German. But we do have charming regionalisms, which have been studied in the fascinating Dialect Survey. The Dialect Survey maps will tell you, for example, that "the devil is beating his wife" is simply Southern for "sunshower," while the important dibs/shotgun distinction has no strong geographical bias. I was interested to see that my linguistic upbringing was almost perfectly standard, in that I fall into the majority category of almost every regionalism. The one noticeable exception was that I grew up calling subs "hoagies," a distinct Philadelphia/New Jersey usage. And I am shocked to learn that nearly half of the country refers to sneakers as "tennis shoes." Takes all kinds, I guess.

Also, over seven percent of Americans have no word to describe the concept of ogling. How do they make it through the day?

~ posted by Sean Carroll at 4:35 AM ~ link ~ ~ ~

 
Jet-setty

Greetings from Frankfurt airport! I have nothing special to say, but it just feels especially modern and sophisticated to be able to sit in a European airport cafe and post to the same blog that I would from home. German was the language that I took in high school, but it appears to have completely fled my brain; when I try to talk to any of the airport staff, it comes out in French, and I don't even speak French. Fortunately they all speak English, as nobody is surprised to hear. Unfortunately, Germany seems to be one of those benighted countries in which the default mode for cappuccino is to have cinnamon on top.

No sleep on the flight over. All of my immediate neighbors were part of a single group, who seemed new to the concept of transatlantic travel, and thought it would be fun to chat the night away rather than grabbing a precious hour or two of sleep. What kind of group was it, you may ask? Well, they were going to Athens. For the Olympics. But not to actually watch the sporting events. No, they were going to be handing out tracts to passers-by, trying to persuade them to accept Jesus as their savior. (Chick tracts? I don't know, and feared to ask.) I alternated between reading the latest Harry Potter book (now out in paperback) and working on a paper on the Big Bang -- so I don't know if they didn't proselytize to me because they were saving their energies for Greece, or because they had given up on me without even trying.

Okay, so I did have something to say. I'm just too exhausted to say it in any sort of nuanced way.

~ posted by Sean Carroll at 1:15 AM ~ link ~ ~ ~

 
Jazz Ambassadors

The image of the United States in the world has, to be sure, taken a big hit over the last couple of years. Clearly drastic measures are called for. What better way to get people throughout the world to think better of us than to let them listen to some cool jazz? Something along those lines must have been going through the minds of the clever folks at the State Department and Lincoln Center, when they got together to start the Jazz Ambassadors program.

The idea is to assemble a few small groups of talented (and hopefully diplomatic) musicians, and send them on several-week tours of places that don't get much exposure to US culture. I know about it because Michael Raynor, a friend of mine who is Von Freeman's drummer, has just left for a tour with the Chicago Jazz Quartet, a group thrown together for just this purpose. They will be visiting Vietnam, Thailand, the Phillipines, Indonesia, Pakistan, and Bangladesh before returning to the City of the Broad Shoulders. Perhaps, through the wonder of swinging, improvised music, they can bring peace and prosperity to the far reaches of the earth. Or maybe they will merely entertain and stimulate some audiences of people who think of Rambo when anyone mentions the United States. Which would make the project more than worthwhile.

Meanwhile, I shall go hop on a plane, and when you next hear from me I should be in Geneva, land of international banking, accurate timepieces, and high-energy particle physics. Further reports as events warrant.

~ posted by Sean Carroll at 10:51 AM ~ link ~ ~ ~

 
Congratulations to Suz!

The National Science Foundation runs a Research Experience for Undergraduates (REU) program, which provides funds to universities that would like to sponsor undergrads to visit for the summer and engage in some real live research. This summer I've been advising Suz Tolwinski from Brown (see a tiny picture at my group web page), who gave a presentation this morning on what she's accomplished.

Undergraduate research experience is very valuable, but it's hard to do as a theorist, since there is so much background knowledge required before you can do original work. I've advised a few undergrads, both during the school year and during the summer, and usually ask them to learn enough general relativity and cosmology that they can at least begin to answer an original question. (Actually, I usually just say "no," but occasionally the stars align correctly and I agree to advise someone.) If all goes well, at least they will learn a lot of good physics. But teaching yourself GR over a summer, with time enough left over to work on a real problem, is undertaing a tremendous task. Suz did a great job, learning both GR and some bits of classical field theory from scratch, and then investigating whether Lorentz-violating vector fields would lead to an observable anisotropy (direction-dependent stretching) in the expansion of the universe. This is an extension of work I did with Eugene, except that Eugene's vector fields were pointing in a timelike direction, and Suz's were spacelike. Which is actually harder! So I was very impressed with the final project.

Actually, I was impressed with all of the REU presentations this morning, on topics from waves traveling through sand to numerical investigations of cellular automata. It was a tremendous joy to hear about the accomplishments of these students, especially when you remember that doing physics research is not how most undergraduates spend their summer vacations. Being an academic can be a stressful occupation, as discussed recently in posts at Pharyngula and Uncertain Principles (referencing several other academic blogs, including Making Contact, Steven Krause, Playing School, Irreverently, Just Tenured, Barely Tenured, and Bitch. Ph.D.). One of the things that Suz has been wondering about is how happy one actually is as a science professor, especially after talking to current graduate students and hearing stories of, shall we say, incomplete contentment. I'm not the most representative person to comment on the pros and cons of academia, since I've been passionately in love with the idea of being a professor ever since I understood what it meant. I mean, our job is to teach and do research; what could be better than that? There are certainly less-fun parts of the job (applying for grants, grading, committee meetings, etc), and it can undoubtedly be stressful and over-competitive. But it's too easy to get run down by these aspects and forget about the exhilarating ones. Listening to a collection of talented and enthusiastic students explain the research they've been doing over the summer is an excellent way of being reminded.

~ posted by Sean Carroll at 3:53 PM ~ link ~ ~ ~

 
Extinction of less-improved forms

Tangled Bank #9 is now online over at Pharyngula. The idea behind Tangled Bank is to collect together a weekly greatest hits of science/nature posts in the blogosphere and stick them in one place for easy consumption. The greatness of the posts themselves is decided upon by their authors; if only more things in life worked that way.

Most of the TB posts are oriented toward the biological sciences; I sneaked myself in only on the basis of my dinosaur reports. Maybe they should do more physical sciences?

~ posted by Sean Carroll at 1:07 PM ~ link ~ ~ ~

 
Guest-blogger Lindsay

On Friday I head off again for a couple of weeks, and blogging abilities might be spotty. I'm spending a few days visiting friends at CERN, the particle accelerator in Geneva where the World Wide Web was born, so presumably it won't be too hard to find an internet connection (although things might be hectic). After that it's off to the European Forum Alpbach, where Bob Wald and I will be giving a series of lectures on cosmology. Alpbach seems pretty far away from everything (not even a train station), and I'm guessing it's rather isolated.

So I'm very happy to introduce another guest-blogger to keep things cooking while I'm away: Lindsay Beyerstein will be piloting Preposterous while I'm galivanting around the Alps. Lindsay is the proprietess of Majikthise, one of the most stimulating and well-written blogs out there, as you will soon discover if you haven't already.

I am hoping that my willingness to choose guest-bloggers who are more entertaining than I am will be seen as an indication that I am self-confident enough to not fear being upstaged, much like John Kerry choosing John Edwards as his running mate.

~ posted by Sean Carroll at 8:40 AM ~ link ~ ~ ~

 
Daily dinosaur comics


Click the image for more. I had run across this some time ago, and was reminded of it in a post at Uncertain Principles. Consistently amusing, within even tighter self-imposed constraints than the original Law & Order series.

~ posted by Sean Carroll at 5:49 PM ~ link ~ ~ ~

 
Save yourselves! Move to the midwest!

Another reason why living by a Great Lake is better than living by the ocean: little danger of tidal waves.

A collapsing volcano could trigger a vast tidal wave capable of wiping New York, Washington and Miami off the map, warn geologists.

They also fear southern England could be hit.

Geologists are concerned that an unstable flank of the Cumbre Vieja volcano on the island of La Palma in the Canaries is in danger of sliding into the sea.

If shaken loose by a volcanic eruption, the huge slab of rock would send a tsunami more than 150 metres high racing across the Atlantic at the speed of a jumbo jet.

Within three hours, the wave would swamp the east coast of Africa, within five hours it would reach southern England and within 12 it would hit America's east coast.

New York, Washington, Boston and Miami would be hit by successive waves abound 20 metres high. Tens of millions of people could die.

Although the volcano could erupt any day - it has been dormant since 1971 but tends to erupt every 20 to 200 years - funding to British scientists investigating the threat has been stopped.

I like "They also fear southern England could be hit." And this is a British scientist, in a story reported by the London Telegraph.

But there's good news, as well: hysteria about being hit by an asteroid has somehow managed to decrease that risk from "microscopically small" to "really so miniscule that we can relax a little." Thank goodness about that.

~ posted by Sean Carroll at 11:30 AM ~ link ~ ~ ~

 
Hubble imaging spectrograph dies

As Jennifer mentions in the comments, one of the instruments on the Hubble Space Telescope has apparently broken down: the Imaging Spectrograph, used to (obviously) take images with simultaneous spectral information, for example of black-hole candidates. This is too bad but not a complete catastrophe (unless you had time on the instrument); it had already lived past its expected lifespan, and there are still three instruments working on HST. Sure would be nice to have a servicing mission, though.

~ posted by Sean Carroll at 8:30 PM ~ link ~ ~ ~

 
Western terminology

As far as I can tell, our track record of reaping long-term benefits from our support of repressive and authoritarian regimes is pretty dismal. Yet, we keep on doing it, mostly for short-sighted reasons. Saudi Arabia is the example that has been drawing increasing scrutiny.

The latest charming anecdote: three reformers (Ali al-Demaini, Matruk al-Faleh and Abd Allah al-Hamed) have been arrested for "calling for adopting a constitutional monarchy and using western terminology," among other heinous offences. These are not exactly anarchists we're talking about here -- their role model is Jordan.

I wonder what Western terminology they were using? "Radical, dude"?

~ posted by Sean Carroll at 2:54 PM ~ link ~ ~ ~

 
Millennium Park: Franks and Beans

This weekend I had a chance to visit Chicago's latest attraction, the somewhat-misnamed Millennium Park. This is a parcel of land just north of the Art Institute, adjacent to Grant Park, that had been languishing as a railroad yard, until the city powers decided to spruce it up as part of a celebration for the year 2000. Somewhat behind schedule and substantially over budget, the project has finally been completed, and has garnered rave reviews from visitors thus far.

Easily the most talked-about component of Millennium Park is the large reflective statue by Anish Kapoor, officially named "Cloud Gate" but universally dubbed "The Bean." (Click for full-sized version.)


Now, I had actually seen a model for the park a couple of years ago, and had no doubt that this abstract beast was going to be a complete disaster. Let me publicly state that I was completely wrong; the full-sized bean is strangely compelling and irresistible. Reflecting the skyline and the sky itself with a gentle distortion, this simple shape grabs your attention and holds it with an eerie fascination.


You can also walk underneath the bean, where Kapoor has manipulated the reflections to produce interesting multiple images. Viewers can happily alternate between looking for images of themselves in the interior of the bean, and wondering at the ease with which their fellow visitors are entertained.


Photos don't really do the bean justice, but you can't help but taking many pictures when you are in its presence; I predict with confidence that within a short time this sculpture will be recognized as the most-photographed object in the world. (Note that the sculpture is actually not complete; the visible seams are to be welded to form an unbroken smooth surface.)


To be honest, the simplicity of the bean is also its limitation; it only provides perhaps fifteen minutes of contemplation before you are ready to move on to something else. Fortunately, the Art Institute is just to the south, so a pilgrimage need not be exclusively beanocentric.

The other new attractions in the park are also worth attention. An interesting, although less obviously successful, art installation is the computerized fountain designed by Barcelona artist Jaume Plensa. It consists of two rectangular towers that gently spray water in all directions, and project moving images of faces (apparently supposed to be representative citizens of Chicago). At occasional intervals the faces appear to spit water from their mouths, in a reference to more classical fountain designs.


While the fountains don't have the immediate and universal appeal of the bean, they are a big hit with kids, who can frolic around in the water to their heart's content. An obvious worry is the upkeep associated with the fountain systems -- these would be a complete disaster if they were allowed to fall into disrepair.

Before the bean captured everyone's heart, the centerpiece of the Millennium Park project was a new band shell designed by Frank Gehry. It brings to mind giant chocolate shavings on the top of an especially elaborately decorated cake (if chocolate shavings were made of stainless steel).


This photo isn't a very good view of the band shell itself, because I wanted to note a cute science fact about the trellis extending out from the shell and covering a wide section of park in which visitors can relax and listen to concerts. You will notice the speakers hanging from the trellis itself; often attempts to amplify outdoor musical performances result in acoustic nightmares. To prevent this from happening, the designers calculated the time it would take sound to reach from the stage to different points in the audience, and have built in an appropriate delay in the signal sent to the speakers so that the sound reaches the listener from both sources simultaneously. Now that is good planning.

~ posted by Sean Carroll at 9:59 AM ~ link ~ ~ ~

 
Finally, a choice

Longtime Preposterous readers know that some time ago I endorsed Barack Obama for our open Senate seat here in Illinois. At the time, I thought the alternative would be Republican Jack Ryan, who was most famous for having been previously married to an actress. But, as we all know, Ryan had to drop out after some messiness involving Paris sex clubs (always more trouble than they are worth, take my word for it). And now it looks like charismatic talk-show host Alan Keyes might be our new Republican nominee. Like everyone else, I always took Keyes for a complete nutcase. But perhaps I was wrong. According to his own website, Alan Keyes:

• Is widely considered the most formidable defender of America's founding principles in today's political arena.
  
  
• Is generally conceded to be the winner of the 2000 Republican Presidential Debates, due to his remarkable eloquence and persuasiveness.
  
  
• Has demonstrated exceptional ability to educate his fellow citizens about America's founding ideals, upon which we as a people must stand if we are to survive as a free nation.
  
  
• Is capable of leading our country to widespread moral and political renewal, once all of America has a chance to see and hear, first-hand, his self-evident brilliance.
  

Pretty impressive, you have to admit. By the way, "self-evident" means "evident, apparently, only to one's self," right?

~ posted by Sean Carroll at 6:10 PM ~ link ~ ~ ~

 
Violating Lorentz

When it comes to quantum gravity and fundamental physics more generally, there is a lot we don't know, and many different approaches to making progress. A top-down kind of approach attempts to figure out what the ultimate laws are, and then see what they might have to say about reality; string theory is the obvious example. But you could also take a bottom-up or phenomenological approach, in which you try to figure out what kinds of physical effects might arise due to quantum gravity and then go look for them, even if you haven't derived them from a more complete theory. Tests of Lorentz invariance provide a good example, and the subject of my recent paper. This is the paper I mentioned writing with my (former) student Eugene; he now has a follow-up paper extending our work.

Lorentz invariance is simply the idea that there is no preferred direction in spacetime. Not only do the laws of physics not care about the direction in which you are looking (invariance under spatial rotations), it also doesn't care about the speed at which you are moving relative to other stuff in the universe (invariance under "boosts," as physicists would say). The idea is a cornerstone of relativity, and got a big boost (pun unintended, but accepted) when the Michelson-Morley experiment showed that the speed of light seemed to be the same in all reference frames -- there was no evidence for a background "aether" with respect to which you could measure your velocity. But its roots actually go back to Galileo, who first proposed that all velocities were relative; to people on the sidewalk, the road is stationary and the cars are moving, but to people in the cars, they are stationary and the road is moving, and each perspective is perfectly valid.

Actually, this violating-Lorentz-invariance stuff is not new to me. Using cosmology to test Lorentz-violating theories was the subject of my first published paper. It was a collaboration with George Field (my Ph.D. advisor) and Roman Jackiw, both very accomplished theorists in astrophysics and field theory, respectively. My role as the meek young graduate student was largely to type in the data and make plots, but that's how you get started in this business.

The theory we considered had a fixed timelike vector field without any independent dynamics, but it was coupled to electromagnetism in a specific way that violated parity as well as Lorentz symmetry. We showed that the coupling would cause a "twist" in the polarization of light coming from distant galaxies, and George knew that for certain radio galaxies you could determine what the polarization should be without any Lorentz-violating effect, allowing us to put a very tight limit. The data I typed in came from different sources, and consisted of the polarization information plus the distance (actually, the redshift) of the different galaxies. Years later, much to our surprise, this same data appeared on the front page of the New York Times. Two researchers had used our dataset but analyzed it in a different way, trying to constrain a vector pointing in a spacelike direction rather than a timelike one. The big difference is that they claimed to actually find a nonzero effect, which they announced in a press release before they made the paper available to other experts. Unfortunately they were just mistaken, as I recount in great detail here. But it's still worth thinking about; indeed, some candidates for dark energy in the universe could lead to a very similar effect, so it's worth improving the present data to put much tighter constraints (or to discover dark energy!).

What Eugene and I have done is a little different. We imagine there is a vector field through spacetime that violates Lorentz invariance (since you could, in principle, measure your speed with respect to it in an absolute sense), but we worry about its gravitational effects rather than its interactions with ordinary matter and radiation. Interestingly, we find that the vector field has no effect if there is no matter lying around, but it works to alter the strength of the gravitational field caused by matter. In other words, it changes the effective value of G, Newton's constant of gravity. This would be an unobservable effect if it just changed Newton's constant once and for all, since we have no experimental knowledge of what the constant was before the vector field messed with it. Fortunately, it changes it in different ways in different circumstances: making the effective value of Newton's constant larger in the Solar System, but smaller when we consider the expansion of the entire universe.

Thus, we have an observational constraint: measure the value of G in the Solar System, use that to predict something about cosmology, and compare with the data. The most straightforward example is actually the primordial abundance of light elements such as Helium and Lithium. These were created at an early time after the Big Bang (between one second and a couple of minutes) as the universe expanded and cooled, and the precise amount of different elements you get depends sensitively on the expansion rate of the universe, and thus on Newton's constant. We find that our vector field must be less than ten percent of the Planck scale, the fundamental unit in physics where gravity and quantum mechanics come together. The Planck scale is pretty big, so it's not a great limit, but still an interesting one.

~ posted by Sean Carroll at 2:01 PM ~ link ~ ~ ~

 
Is that an expanding universe in your pocket, or are you just happy to see me?

Everyone was (justifiably) jealous sometime back when I revealed that I had received a WMAP beach ball in the mail. WMAP, the Wilkinson Microwave Anisotropy Probe, is a NASA satellite that has taken the most precise images yet of the leftover thermal radiation from the early universe. Who wouldn't want to have a beach ball with a snapshot of the whole universe on it?

Well, I can't help you with the beach ball, but here's something almost as good: a CafePress store selling all sorts of WMAP merchandise, including the boxer shorts shown at right. (Found linked from Licia Verde's home page.) There's something for everyone -- T-shirts, teddy bears, thongs, more than you would ever want, really.

Someday I will follow through on the idea of setting up a store for Preposterous Universe merchandise. (In the meantime, just go buy my book!) Maybe I'll stick with coffee cups, though.

~ posted by Sean Carroll at 11:02 AM ~ link ~ ~ ~

 
Dinosaur report II

Continuing the story from yesterday, let's say you're an enthusiastic amateur about to go out in the field (led by one of the world's experts) and dig up some dinosaur fossils. Your first question would of course be: what do I wear? You'll want good hiking boots, sturdy but not too heavy. It's beastly hot, so you'll be tempted to wear shorts, but don't; you'll be tromping through cactus and sagebrush, and then spending hours kneeling on rocks and dirt, so jeans are definitely called for. Hat and sunglasses are mandatory. Some of us wore lightweight long-sleeved shirts, although I did fine with T-shirts and heavy doses of sunscreen; despite the relentless Wyoming sun, I managed to keep my healthy pale complexion largely intact.

Besides clothes, the only necessary items we were personally responsible for were our water canteens. Bug spray is a good idea, and cameras or binoculars are useful, but not required. The serious equipment was provided for us by the Project Exploration folks: GPS units, walkie-talkies, brushes, awls, hammers, gloves, shovels, pickaxe, hardener, glue, tinfoil, burlap, plaster, measuring tape. Nothing very high-tech, other than the GPS. The physicist in me was sure that there must be some X-ray-like technique to probe into the soil to distinguish fossils from the surrounding rock; but nobody knows of any good way to do it, and I didn't have any useful ideas. (I'm a cosmologist, okay?)

Suitably equipped, we head out to the site. Let me just mention that none of the skills one develops by spending one's days doing theoretical physics and one's evenings at jazz clubs really come in handy out in the field. The work involves serious physical labor and tremendous patience; the good news is that, although it requires years of training and practice to be really good at it, essentially anyone can be productive after a short tutorial. It helps that Paul seems to have an endless (or at least substantial) supply of patience and confidence in his motley crew of city folks; in his shoes, I would be scared to death of what these klutzes were likely to do to my fossils, and would simply ask them to watch from a respectful distance while I did the work myself.

Our group was about fifteen people, of whom two (Paul and Bob Masek, a fossil preparator at the University of Chicago) really knew what they were doing. Of the rest of us, about half had been along the year before, and the newcomers would occasionally (in their naivete) look to us for guidance. We took two vans from the ranch where we were staying out to the site, or at least as close to the site as we could get in the vans. From there we have to lug the aforementioned equipment to the actual fossils, at which point the excitement starts.

The main fossil Paul and his students had found was a vertebra from the tail of what is likely to be a Camarasaurus, a large sauropod common in the Jurassic. (Yes I know the link says that Camarasaurus was "much smaller" than other sauropods, but when you're 60 feet long and weigh 20 tons, you're large in my book.) Sauropods are the hulking big four-legged herbivorous dinosaurs with long necks, like Brachiosaurus and Diplodocus; other major categories are the mostly-carnivorous theropods such as raptors and T. Rex, and ornithischians or bird-hipped dinosaurs, including most of the funky armor-plated species like Triceratops and Ankylosaurus. Just to add an element of confusion, actual birds evolved from the lizard-hipped theropods, not from the bird-hipped ornithischians.

What you typically find, of course, is a single bone sticking out of the rock. In this case, Paul had found a vertebra from the tail. The question then is, if you follow the trail into the rock, do you just find the tip of the tail, or most of the dinosaur? In other words, in which direction is the tail pointing? You just have to dig and find out.

This is where the patience and determination come in. You basically poke gingerly at the area around the fossil with an awl, then remove the dirt and stones with a brush. (Try not to use your fingers, or let the stones fall onto the fossil; a brush is gentlest.) The awl and brush are your most common tools. From the variations in texture and color, you should be able to tell the bone from the surrounding rock if you are careful, although sometimes it's tricky even for the experts. (The experts, by the way, refer to the rock in which the fossil is embedded as "matrix," thus adding to the science-fictiony feel of the whole enterprise.) At first you have to move extremely carefully and tentatively, as you don't know where the rest of the bones are. Every time you uncover a little bit of bone, you pour hardener over it to help protect it from being scratched or shattered. As often as not, the bones are not "articulated" -- arrayed in a nice dinosaur shape -- but rather are jumbled together. But after you make a little bit of progress, you can begin to get a feeling for the way in which the skeleton is arrayed in the rock. At that point, you might decide that the three feet of rock above your fossil can be removed more rapidly than awls and brushes allow; that's where the pickaxe and shovels come in, or even jackhammers or heavy machinery in extreme cases.


Here's a picture of Paul hugging the part of the tail we have uncovered. He's feeling protective because we had very good news: the fossil seems to be pretty much articulated, and even better the vertebrae are growing as we move into the rock! Which means there is an excellent chance of finding a substantial portion of Camarasaurus skeleton lying in there, undisturbed for the last 150 million years.

Our rate of progress wasn't nearly enough to imagine actually excavating the thing; the picture here basically shows the end result of a day and a half of work. Further trips will be required before the entire fossil can be shipped to Chicago. To protect what we have uncovered, we first cover the bones with tinfoil, then with strips of burlap dipped in plaster. The plaster will not only protect the bones once we cover them with dirt again, it also will make it much easier to eventually bring the fossil home. In fact you don't nearly dig away all the rock from the bone; you intentionally leave an inch or two of matrix surrounding the bottom half of bones, dig out from the bottom, and then plaster around the entire collection, which gets shipped back to the lab. (A ton or two of shipped materials is common.) There a real expert, working in decent conditions (presumably involving air-conditioning), can remove the rest of the matrix. Then you take appropriate pictures and measurements, and possibly think about mounting the specimen for display. If (as Paul often does) you went to Niger or Mongolia or Argentina to collect the fossils in the first place, the original country will typically want it back; you get the science out of it, and it ultimately returns home. For our Wyoming fossils, we hope to build up a collection at the University; the previous collection was short-sightedly given away.

This is the second year I've gone on one of these trips with PE. The first year was great fun but I was exhausted by the end; this year I wanted to stay out there and keep digging. It's an exhilarating experience, and utterly different from being a theoretical physicist. On the other hand, dinosaurs and cosmology are two topics that readily engage the public imagination, and the folks at PE hope to extend their reach into other areas of science, so I hope I can be some help. At the end of a long day in the field I gave an informal lecture on black holes -- amazingly, despite myriad other distractions and every reason to be tired (the lecture began at 9:30 p.m.), everyone on the expedition attended and asked great questions about the curvature of spacetime. Just one more reminder, as if any were needed, that most people are intrinsically fascinated by science, and it's our duty to do a better job of sharing the excitement that professional scientists get to feel all the time.

~ posted by Sean Carroll at 11:06 AM ~ link ~ ~ ~

 
Loyalty oaths

Found over at Talking Points Memo, this amazing story from Associated Press:

Some Democrats seeking Cheney tickets had to sign oath

By RICHARD BENKE
Associated Press Writer

RIO RANCHO, N.M. (AP) -- Some Democrats who signed up to hear Vice President Dick Cheney speak here Saturday were refused tickets unless they signed a pledge to endorse President Bush.

The measure was a security step designed to avoid a disruption, which Bush campaign spokesman Dan Foley alleged Democrats were planning. Democratic Party officials denied it.

Several Democrats, at least, encountered the screening measures Thursday after calling from a line that self-identified as ACT, America Coming Together, an activist group that supports Kerry, Foley said. Others attempted to give false names and were denied tickets, he said.

Two men who had sought tickets reported they were required to give name, address, phone number, e-mail address and driver's license number, then were presented the pledge of endorsement when they arrived to pick up the tickets Thursday.

The purported explanation is that a speech by the Vice-President is a "reward" for loyal supporters, and consequently need not be open to ordinary non-supporting Americans.

Outrage fatigue. That's the only way they can get away with this stuff.

~ posted by Sean Carroll at 8:23 PM ~ link ~ ~ ~

 
Dinosaur report I

Having returned from dinosaur hunting basically intact, I'd like to explain a little of the process that is actually involved. Also very interesting, of course, would be to talk about the dinosaurs themselves, and what we hope to learn by studying them. But that's another huge subject, which I am fairly unqualified to talk about, so you'd do better to hunt about on the web (or visit a museum). What I can try to do is give you an idea of what it is like to actually go out there and dig up some bones.

In particular, there are two questions I've always had about the nuts and bolts of paleontology: how do you actually find the fossils in the first place, and how to you dig them out once found? Answer in both cases: a little bit of know-how, and a huge amount of effort.

This is the second year I've gone to Wyoming with Project Exploration; last year I did manage to find a fossil myself, but this year we focused more on digging than on prospecting for new specimens. The prospecting was done ahead of time by Paul Sereno and some of his students. (Paul is the paleontologist half of the husband-and-wife team who founded PE; Gabrielle Lyon is the educator half.) The relevant know-how, as best I can make out, involves a combination of geological background and word of mouth. In fact, it seems from my outsiders perspective that there isn't much of a bright line separating the disciplines of geology and paleontology; each relies heavily on knowledge from the other field, and experts in one are typically well-versed in the other. For dinosaur-hunting purposes, the geology comes in once you realize that your prospecting efficiency is greatly enhanced if you spend your time peering at rocks that actually date from the Mesozoic (the dinosaur era, between 248 and 65 million years ago), rather than before or after. Not only that, but you would especially like to have a layer that has been uplifted by geological activity, so that exposed rock faces (out of which might be sticking dinosaur fossils) are plentiful. Formations of this sort are common in certain areas of the Rocky Mountains, which is one reason why this region has produced so many significant dinosaur finds. We were working in the Morrison Formation, a limestone bed dating from the Jurrasic. (The Mesozoic is divided into three periods: the Triassic [248-108 Mya], the Jurassic [208-146Mya], and the Cretaceous [146-65 Mya].) The Morrison has long been a prolific source of dinosaur fossils. Here is a picture of the layered topography through which we were poking around; click for a bigger view.


Word of mouth comes in for the simple reason that, once you find a dinosaur somewhere, the surrounding regions are (sensibly) thought to be more likely to contain fossils than other randomly-chosen regions of the countryside. Not only that, but much of the land in this region of Wyoming is owned by ranchers who know the terrain like the back of their hand, and have become adept at spotting fossils. So sometimes it's as simple as being told by a local rancher that there are some interesting-looking fossils at a certain site, or at least that a certain region seems promising.

In this particular case, Paul and some of his students had visited some formations around Shell, Wyoming (pop. approx. 50) a few weeks before we went for our expedition. They found some interesting fossils the old-fashioned way: waking up early in the morning and spending their days walking for miles, paying close attention to every rock that was part of the relevant geological layer. Fossils, of course, are bones (or other parts of an organism) that have been preserved in rock, and the process of fossilization typically involves much of the original organic material actually being replaced by rock. Which is to say, the fossils look awfully rock-like. So you have to know what you are doing, and long practice is at least as important as being told ahead of time what to look for. (Most common sentence heard at these digs, spoken by we amateurs to one of the people who knew what they were doing: "Is this a bone?") Once you've seen some examples, you begin to recognize the striations characteristic of fossilized bone marrow, in contrast with the relative smoothness or unstructured graininess of rock. Still, wandering through long stretches of hillside, you need to have an eagle eye to be effective at prospecting.

In addition to a few dinosaur fossils, they found the trunk of a tree from the Jurassic that was over five feet wide; if it continues into the rock in which it is embedded, it may very well be over forty feet long. Paul calculated that two semi trucks should be able to haul the thing back to Chicago, where it could be used as part of an exhibition for PE of dinosaurs in their native habitat. At the same time, by looking at the interior we could learn something about the climatological conditions at the time the tree was alive (over perhaps a century or two). Personally, I'm happy to spend my time doing the delicate work of digging out dinosaur bones, and not having to be responsible for a several-ton fossilized tree.

The areas in which one finds these specimens are what most of us would describe as the middle of nowhere. Once you've found an interesting site, you mark its location in the handheld GPS unit that you remembered to bring with you while prospecting, so that you can actually find the thing when you come back. (Don't ask me what they did before GPS.) There is also the worry that someone else comes along and digs up the fossil that you have found (expeditions like ours take place largely on government land, maintained by the Bureau of Land Management, so in principle anyone can come and dig them up, so long as they get a government permit to dig). So after finding a fossil and perhaps doing some preliminary digging to verify that it's worth a follow-up visit, you then take a shovel and cover it back up with dirt so that it's not obvious to future visitors. It's not even obvious to you when you come back some time later, so a certain amount of time is spent re-finding the sites that were found on a previous visit.

Tomorrow: we go out and actually dig up some bones.

~ posted by Sean Carroll at 9:53 AM ~ link ~ ~ ~