Blogs / Cosmic Variance

The internets have spoken, and it’s a good thing I listened. A few months ago I had the idea to organize a session at the upcoming meeting of the American Association for the Advancement of Science, in San Diego next February. It’s a giant cross-scientific-disciplinary meeting, offering a great chance for journalists and scientists in diverse fields to catch up on what’s happening in other areas.

But I couldn’t decide between two possible topics, both of which are close to my heart: “The Origin of the Universe” or “The Arrow of Time.” (My original book subtitle was “The Origin of the Universe and the Arrow of Time,” before that was squelched by the marketing department and replaced with “The Quest for the Ultimate Theory of Time.” Quests are big these days, apparently.) So I did the natural thing: I Tweeted the question. And the internet spoke with a fairly unambiguous voice: “Arrow of Time” sounded more interesting. So that’s what I proposed.

And now we’ve just been accepted, so it’s on for San Diego 2010. We have a fantastic line-up of speakers (and also me), spanning quite a range of topics:

• Me, setting the stage about the arrow of time and the Second Law, and drawing some connections to cosmology.
• Huw Price, director of the Centre for Time, Department of Philosophy, University of Sydney, and author of Time’s Arrow and Archimedes’ Point. Huw will be talking about the arrow of time in philosophy.
• Anthony Leggett, winner of the Nobel Prize in 2003 for his work on superfluidity. Tony will be talking about the arrow of time in quantum mechanics and condensed matter physics.
• Michael Lässig, University of Cologne. Michael specializes in statistical physics and quantitative biology, and will be speaking on the arrow of time in biology, in particular in evolution. He recently gave a talk on this topic at the KITP.
• Daniel Schacter, Harvard, author of The Seven Sins of Memory. Dan was the leader of the studies showing that the brain predicts the future in the same way that it remembers the past. He’ll be talking about the arrow of time in psychology.

That’s the fun part about this topic; it ranges naturally from the birth of the universe to the operation of your brain. Should be a good symposium.

I’m back from the World Science Festival, which was a rousing success, leaving thousands of smiling attendees chattering excitedly about the mysteries of the universe as they dispersed through the streets of Manhattan. So naturally I want to talk about how it could be improved. Writing about one’s travels can be one of the least compelling arrows in the blogger’s quiver, but it would be great if the science-festival idea caught on more widely, so perhaps there is something to be learned from the experience.

A science festival, one presumes, aims to bring science to a wide audience through a series of events concentrated in space and time. But there are a lot of different approaches we could imagine taking to achieve that goal. Kirsten Sanford insightfully compares the WSF to the San Diego Science Festival — two similar-sounding events that end up having a very different look and feel. The WSF appeals to the cultural and cool, while the SDSF aspires to be a noisy bring-the-family affair. Neither is right or wrong, and in these cases each is appropriate to the venue; but the choices of how to proceed should be made consciously.

Public events for science can be placed in a two-dimensional parameter space, where one axis ranges from “observational” to “participatory,” and the other ranges from “inspiring” to “informative.” Again, none of these reflects a normative judgment; inspiring and informing are both laudable goals, and sometimes the best way to achieve those goals is to have the audience observe a performance, while other times it’s better to have them participate more directly. The point is not to say what’s better or worse, it’s to figure out what is appropriate for the circumstances.

The parts of the WSF I experienced directly — the opening gala, the two events in which I participated, and two events where I sat in the audience — were roughly speaking more observational than participatory, and more inspiring than informative. For the three events I watched, I think that was exactly right, but for the two events I participated in, I think they could have been even better had the balance been shifted. (Which obviously raises the possibility of some sort of bias on my part, left for you to decide.) In other words, I think a slightly more diversified portfolio of approaches could be beneficial to future science festivals.

The opening gala, a science-and-art extravaganza that both set the stage for the festival and celebrated E.O. Wilson’s 80th birthday, was a great example of an event for which the inspiring/observational paradigm worked perfectly. It was a big production, at Lincoln Center, with a rapid-fire series of performances bridging the gap between art and science; it would have been crazy to try to invite audience participation. And inspiration is just what you need to kick off a big festival. Brian Greene, who along with Tracy Day (”the first couple of New York science“) founded the WSF, did a tag-team presentation with violinist Joshua Bell. Brian would talk a bit about string theory or various wonders of the cosmos, while videos from The Elegant Universe played in the background, and then Bell would play some music appropriate to the mood. Very little educational was going on — nobody came out of the performance considerably more knowledgeable about the secrets of string theory than they went in. But it was an artistic success, putting people in the frame of mind to excitedly tackle meatier fare over the next few days.

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I spent most of last week back in Cleveland, at Case Western Reserve University, where I spent three delightful years working with Tanmay Vachaspati, Glenn Starkmann, and Lawrence Krauss (who recently left). The occasion was a workshop on Tests of Gravity and Gravitational Physics, organized by the Center for Education and Research in Cosmology and Astrophysics (CERCA).

An interesting mix of theoretical cosmologists, relativists, particle physicists, observers and experimentalists participated, and the aim was to pull and tug at the loose threads in various ideas of modifying gravity, while talking about how we might perform sensible tests of the theory in new regimes in the near future. Most of the program consisted of talks, both theoretical and experimental, which you can download from the main site. The theory talks ranged from Nima Arkani-Hamed’s talk on why general relativity (GR) is so remarkably robust, with the take-home message “Don’t modify gravity - understand it”, to Bill Unruh’s description of his “dumb Hole” analog models for black holes, and the discussion of the associated analogous phenomenon to Hawking radiation. On the experimental side, there were great talks covering tabletop tests of sub-millimeter gravity - like the one by Blayne Heckel - all the way up to tests of gravity on the scale of galaxies and above - like Stacy McGaugh’s talk on tests of MOND.

As well as taking part in the general discussions and chairing a session, my role in all this was to sit on a panel for a discussion of “Modified Gravity: What does it buy? and at What Price?”

Nima moderated the discussion, and the other panel members were Eanna Flanagan, Nemanja Kaloper, Glenn Starkman and Bob Wald. While everyone had their own particular take on this, a common theme was that the theoretical and observational constraints are such that we currently do not have any modifications to GR that are compelling, despite our attempts to find a way to address the cosmological constant problem, explain cosmic acceleration, and search for alternatives to the dark matter paradigm. This doesn’t mean it isn’t worth trying, of course, although Nima made a spirited argument that it is hard to maintain the important holographic (and hence nonlocal) features of general relativity in any modified theory that isn’t of the simple scalar-tensor type, and that this is an argument that we shouldn’t expect nontrivial modifications. Rather, he argued, we should search for a dual S-matrix description that applies in flat space (unlike AdS/CFT) and that may allow us a better understanding of, for example, the cosmological constant problem.

This was all heavy stuff, but it didn’t consume our entire time in Cleveland. Tuesday evening saw the workshop dinner and it turned out that our hosts had arranged some after dinner entertainment, in the form of an improvisational comedy team. These guys were big on audience participation, and I was one of the first people chosen to mildly (I hope) embarrass themselves. At first this seemed like a heavy price to pay for dinner. However, trust me, subsequently seeing Tanmay Vachaspati, Bill Unruh and George Pickett up there made me realize it was well worth every blush and squirm.

Update: Dmitry Podolsky has a couple of very nice posts over at NEQNET with quite a few details about the talks, including Nima’s.

Springtime in the Imperial Palace gardens, Tokyo:

Nikon D200.

It’s been a bit of a hectic week. Last Monday I took the train (can’t tell you how happy I am whenever I avoid flying these days) to Washington DC, for a couple of days of government work, finishing up quite late on Wednesday. The next morning I flew from DC to Vancouver (you can’t always avoid it), where on Friday I delivered the departmental colloquium at Simon Fraser University. My friend, and former postdoc, Levon Pogosian is a Professor there, and I spent a very stimulating couple of days discussing physics with him and his colleague Andrei Frolov. Everyone is always telling me how beautiful Vancouver is, but on my previous visits there has been nothing but rain and cloud, and I haven’t seen anything of the area’s natural assets. This time however, it was fifty degrees and sunny, without a cloud in the sky for the entire visit, and I was just blown away by the breathtaking scenery entirely surrounding the city. Completely gorgeous! I also managed to squeeze in a wonderful dinner with friend, UBC Professor and blogger, Moshe Rozali.

On Saturday morning I was up bright and early to fly back to Philadelphia, arriving late on Saturday, in time for a quick dinner and sleep before the firefighter and I had to drive up to Syracuse for some personal business that was going to take 25 minutes, but needed us to be there in person. We completed that this morning, and then I rented a car and drove immediately back to Philadelphia.

After a week like that, I’d normally think about taking a day off before driving back, but in this case that wasn’t an option because tomorrow is a big day for us here at Penn. You may recall me mentioning that the university was setting up a new Center for Particle Cosmology. Well, tomorrow is our launch event! The first part is a panel discussion, with program

The Center for Particle Cosmology presents Of Telescopes and Microscopes
A Panel Discussion and Q&A

Tuesday, February 24, 2009
4:30 – 5:30 p.m.
Bodek Lounge, Houston Hall
3417 Spruce Street

The study of the microscopically small and the unimaginably large are no longer distinct realms of inquiry. In the first of a series of events hosted by the Center for Particle Cosmology, leading experts will consider what insights modern observations might provide into phenomena such as dark matter, dark energy and the physics of the early universe.

Panelists Include:
Vijay Balasubramanian, Associate Professor of Physics and Astronomy
Bhuvnesh Jain, Associate Professor of Physics and Astronomy
Janna Levin, Assistant Professor of Physics and Astronomy (Barnard College of Columbia University) and author of A Madman Dreams of Turing Machines, winner of the 2007 PEN/Robert Bingham Fellowship for Writers
Mark Trodden, Professor of Physics and Astronomy

Moderated By:
Gino Segre, Emeritus Professor of Physics and Astronomy and author of Faust in Copenhagen: A Struggle for the Soul of Physics

Introduction By:
Tom Lubensky, Chair of the Department of Physics and Astronomy

Sponsored by the Center for Particle Cosmology and the School of Arts and Sciences.

This is then followed by:

Guests are invited to mingle with Center faculty who will be happy to answer questions and talk about their research. As part of the reception, attendees will also enjoy multimedia presentations by:

Mark Devlin, Professor of Physics and Astronomy and a principal investigator of BLAST (the “Balloon-borne Large-Aperture Submillimeter Telescope”)

Evelyn Thomson, Assistant Professor of Physics and Astronomy and a member of the ATLAS collaboration, a particle physics experiment at the Large Hadron Collider at CERN

Refreshments will be served.

which we expect to go on until around 7pm. Well, we’ll see about that “leading experts” stuff, but I’m hoping it’ll be a lot of fun. And with Gino and Janna involved, how could it not be? After all, if Janna can handle Stephen Colbert, and Gino can hold his own in the New York Times, they should be OK with us.

If you’re in the Philadelphia area you’re welcome to attend - you just need to register. This has taken up quite some time over the last two weeks, and so on Wednesday it’s back to work finishing a couple of papers that are begging for final edits.

I just got back from Pittsburgh, a city famous for honoring football players along with Fathers of our country. Apparently they recently won some sort of sporting contest, so the citizens were generally in good spirits.

I was visiting to Center for the Philosophy of Science at the University of Pittsburgh, to speak in their annual lecture series. The Center, along with the Department of History and Philosophy of Science, help make Pittsburgh one of the world’s leading institutions for studying philosophy of science.

The Center is also a remarkably friendly place, and I had a great time during my visit. The highlight, predictably, was lunch with some of the graduate students, where we got to let our hair down and talk about big ideas concerning time and causality and determinism. (Almost all professional academics start out fascinated by big ideas, but the interest is gradually beaten out of them along the way by the demands of professionalism and career advancement. Grad school is probably the peak combination of background knowledge and willingness to confront the hard problems.) I also got to chat with Adolf Grünbaum, whose declamations concerning the Primordial Existential Question had impressed me a year and a half ago. And I got to meet some fellow bloggers in the flesh — the formidable Cosma Shalizi, who helped me understand how to augment the principle of indifference with conditionalizing over the past hypothesis, and Bryan Roberts of Soul Physics, who was one of the aforementioned grad students.

But if I’m really honest, my favorite part of the trip was probably the building. The Center for the Philosophy of Science is housed in the Cathedral of Learning, a looming structure on the University’s campus — the second-tallest academic building in the world, after one at Moscow State University. Despite my lack of religious sympathies, I love cathedrals — the looming structures, swooping curves, open spaces, all designed to elicit a certain emotional response going far beyond their direct practical purpose. (Not that different from the best casinos in Vegas, really.) And I love learning! So the Cathedral of Learning is pretty much the perfect building.

And it really does work as a building. What everyone points to are the many Nationality Rooms scattered throughout the building — a series of 27 spaces decorated in the style of various different countries, often with the input (and financial assistance) of the respective governments, which work as display pieces but are also functioning classrooms. (I was told that prospective students are sometimes convinced to come to Pittsburgh by a visit to the room corresponding to their personal heritage.) But what I liked was the immense Commons Room (pictured), with impossibly high ceilings, which is just a place where people can sit down and read and talk and think. Such places are very precious, and the world should have a lot more of them.

If Wikipedia is to be believed, the Cathedral grew out of a vision of Chancellor John Gabbert Bowman in the 1920’s. He insisted that the Commons Room be built on the principles of true Gothic architecture, with self-supporting arches. When told that these things cost money, he replied:

“You cannot build a great University with fraud in it.”

I’m not sure if that’s strictly true, but it’s an honorable principle to strive towards.

As Daniel has already mentioned, I recently spent a week in Aspen, at a workshop on Understanding the Dark Sector: Dark Matter and Dark Energy, which I organized in collaboration with Rachel Bean, Carlo Contaldi, Marc Kamionkowski and Jochen Weller.

The Aspen Center for Physics is wonderful place. Unlike many physicists, I’m not a big skier, or a hiker, preferring to get my exercise through ball sports and in the gym, and so I don’t love Aspen in the way that many people do. But I do really like the Center, and I always have great physics conversations there, learn a lot, and am able to actually get work done. So I had been looking forward to our workshop for a while, and I wasn’t disappointed at all.

The conference spanned five days. We flew in on Sunday in time to register and have dinner, and then got started properly on the Monday morning. At many conferences, academic and otherwise, the day is full of sessions, and then the evenings are free. At Aspen, in the winter, this is modified somewhat, with the mornings, late afternoons and evenings full of sessions, and the middle part of the day free so that people can ski if they want to. We spend the same amount of time working as at a regular conference, but the time is just distributed differently. This last week, it was good that I don’t ski, since I had let a number of important deadlines slip to the point that I had to work each afternoon. I did have a great view while I was doing it though!

Our speakers covered a wide range of topics, experimental, observational and theoretical, covering dark matter and cosmic acceleration separately, as well as the possible interactions between them. I can’t possibly discuss all of the topic or talks here (but you can take a look at a slightly outdated program), but let me pick out one talk that particularly caught my attention, and one event.

The first morning we kicked off with a very nice talk by Doug Finkbeiner (Harvard), discussing his (and others’) recent work constructing a particle physics model of dark matter that is designed to account for the PAMELA and ATIC results. This was followed by later theoretical talks on related topics by Dan Hooper and Graham Kribs.The PAMELA results were a recurring theme at the workshop, and there were plenty of discussions in the free time and over dinner about the results themselves, their interpretation, and the models that a number of groups have constructed.

One talk that I particularly enjoyed was by Greg Tarle (Michigan), who gave an (originally unplanned) talk on the immense challenge of making the precise measurements that these quite beautiful experiments claim. From my perspective what was wonderful about Greg’s talk was that although he presented quite a few experimental details in the latter half, he constructed the first half in such a way as to get across some of the key things for theorists to keep in mind while they are rightfully getting excited by the data.

What I took away from it (although any mistakes here are naturally due to me, and not to Greg) is that, as we’ve discussed before, the big deal for PAMELA (and the earlier HEAT experiment) is an accurate measurement of the flux of cosmic ray positrons. The single largest challenge in measuring these is discriminating against the vast proton background, since protons have the same charge as positrons and are copious in cosmic rays. Ideally one needs to be able to reject the proton signal at the 10^-6 level. If this is done completely reliably and the dramatic rise of the spectrum at high energies persists, then we may indeed be seeing a signature of dark matter annihilation, or something more mundane, like nearby pulsars.

On the other hand, it is possible that the signal is due to protons leaking in. Obviously, the key to figuring this out is particle identification. One point of caution Greg pointed out is that on PAMELA, the particle ID is solely dependent on calorimetry. Greg certainly wasn’t saying that he believes that the PAMELA signal is contaminated, but he did want to point out how a possible contamination might lead to an erroneous result. In his talk, to demonstrate this, he showed how to reproduce the observed effect (at high energies) with a model of proton contamination at the 3×10^-4 level. Note though, that PAMELA claims proton rejection at the 10^-5 level, but one can at least get a simple idea of what a small error might yield. Again, I as a theorist can’t comment on this at all, and my understanding is that the PAMELA experiment is an excellent one. Still, it is nice to have a feeling for the possible issues involved. All should be settled by FERMI (GLAST) hopefully.

On the Tuesday evening we had a couple of public events as part of the workshop. In the first, Dan Hooper, particle phenomenologist, dark matter expert and author extraordinaire, teamed up with me to conduct a Physics Cafe in the mezzanine of the Wheeler Opera House. I’m awful at estimating numbers, but I’d say somewhere between fifty and a hundred people, members of the public who either live in or were visiting Aspen, turned up to ask us any kinds of questions they liked about particle physics and cosmology. This was terrific fun, and we got some wonderful questions, my personal favorite of which was “What does entropy have to do with gravity?” Not something to which one can give a full answer (in public or professionally), but a great chance to talk about the general issues that gravity raises for thermodynamics.

I participate in a lot of events like these, and one thing that never ceases to surprise me is the general perception that scientists treat theories like general relativity as received wisdom, about which one should not ask questions. Dan and I had to go out of our way to explain that science is, in fact, about challenging ideas, and forcing them to stand up to evidence and scrutiny. This is not the fault of the audience, of course, but reflects the way in which I think science is often taught and portrayed.

Directly after this, also at the Wheeler Opera House, my new colleague Bhuvnesh Jain gave a wonderful public lecture on Einstein Rings and Giant Arcs: Mapping Dark Matter with Gravitational Lensing to a large and lively audience. Bhuv has some great animations and movies, plus some fun props - optical lenses that are machined to reproduce the effects of gravitational lenses - and he did an admirable job of the lecture.

My own talk at the workshop was as part of a trio of talks, the other two of which were delivered by my collaborator Rachel Bean and her student Istvan Laszlo. I spoke about work with Rachel and Eanna Flanagan on adiabatic instabilities in coupled dark matter-dark energy models, and Istvan and Rachel covered different parts of a longer paper the three of us co-authored with Flanagan a few months ago, mapping out general constraints on such couplings.

Speaking of which, I have a seminar at Penn State to give on this topic on Wednesday, and I should probably get to finishing that!

Yesterday, during our meeting’s afternoon break, I finally hustled up to Aspen Highlands Bowl. This involved taking two lifts, and then a snowcat, and then a 45 minute hike along the ridge, ending at over 12,000 feet elevation. The bowl is steep. Very, very steep. Up to 48 degrees steep (measured down from horizontal). For some perspective, if you were to point your snowboard straight down the mountain for 3 seconds, you’d find yourself going 50 miles per hour [exercise for the reader]. Well, at least that would be true if the mountain was covered in a sheet of (perfectly frictionless) ice. Fortunately, it wasn’t.
When you’re at the top, you need to peer over the edge to see the terrain. For the record, I’m afraid of heights. Standing on a ridge in the freezing cold, with a brisk wind blowing, with a thousand foot steep vertical drop on both sides, should not be a pleasant experience. The whole Freudian death wish thing should kick in pretty hard. But something about all that fluffy powder magically transforms imminent death into the perfect playground. Dropping into the bowl was heavenly. The whole place was virtually deserted. Waist-deep powder in places. With a wonderful runout through the trees.

Two hours later I was back in the conference room, learning more about the latest results on dark matter detection. A good day.

NOTE: Aaron Sheldon brings up a good point in the comments. I’m a big fan of helmets on the slopes. For me it’s a no-brainer, as it were. Plus, helmets keep your ears toasty warm. Also, especially if you’re going out-of-bounds, pack appropriate avalanche gear (a beacon, a probe, a shovel, etc.). It’s dangerous out there.

One of the great things about being a physicist, it turns out, is the travel. I’ve had the opportunity to travel all over the world, including to some destinations that I might not otherwise have put on the must-see list. In fact I am at one right now, along with Robin and our five month old, Ian.

We’re in Taipei, Taiwan, at a joint UC Davis - Taiwan workshop somewhat grandly titled “From the LHC to the Universe”. The participants are just from UC Davis and Taiwan universities including National Taiwan University, Academia Sinica, and National Tsing Hua University. The workshop grew out of the fact that there are strong ties between the Davis faculty and that of NTU, especially in the area of particle theory. Our present dean, Winston Ko, a particle experimentalist, is from Taiwan, as is one of our recently retired but still very active particle theorists, Ling-Lie Chau. A number of the former postdocs and students of our theory group leader Jack Gunion are now at NTU, as is one of his close collaborators George Hou. And so the idea for this workshop was born, to further strengthen the ties between the particle phyiscs and cosmology groups at the two institutions, hopefully leading to more collaboration.

Perhaps the most striking thing I’ve found about Taiwan is the absolutely amazing friendliness, generosity, and hospitality of the people. Our NTU hosts have set the bar very high in terms of the organization of the meeting, our local accomodations, and events like the fantastic 10-course banquet we had last night atop Taipei 101, presently the tallest building in the world.

Wherever we travel, we love to eat, and the food here in Taiwan is superb. On Saturday we ate at the unpretentious but world-famous dumpling restaurant, Din Tai Fung. The service was amazing - for example, when I went to change little Ian’s diaper they set up a special changing station for me and stood there to assist me! For a battle-hardened parent of a five month old, this was incredible,
but it happened at the next restaurant at which we ate too!

Later in the day Saturday we ate on the street at the Shilin Night Market. It was a tough choice, and very inexpensive. We found a stall where you take a basket, and put into it lots of different food items on skewers, which they subsequently grill for you with a delicious garlicky sauce. Just grab a couple of what we call “walking around beers” and you are set.

Wherever we go, the sight of little Ian in the front pack inevitably brings smiles to people’s faces, who, with little hesitation, come straight over to coo at him and elicit smiles (and mostly he obliges). Clearly the sight of a western baby is a novelty here, and, of course, he’s pretty cute anyway.

Traveling with a five-month-old is a challenge: probably most of you reading this think we’re nuts to take him half way around the world…and you are probably right. But we’ve gotten along fairly well, hiring a baby sitter here who watches him in a back room of the physics department library. He’s gotten pretty fussy a lot of the time, partly due to jet lag, but he does that at home too!

Taiwan has a rich and turbulent history, right up to the present day. In fact, the day we arrived, the first non-Kuomintang president of the country, Chen Shui-bian (elected in 2000 and re-elected by a slim margin in 2004), was indicted for embezzling millions of dollars. A few days later, for the first time in decades, direct flights and shipments began between Taiwan and the mainland. The economic crisis is taking its toll on industry here, with people debating the relative merits of reducing pay or reducing hours (furloughs).

Our only regret is that we don’t have more time to see all there is to see on this beautiful island! We return home tomorrow, but hope to be back here some day.

The first things we noticed, as we climbed into the back seat of the taxi, were the books. A tiny six-volume library, tucked between the driver’s and passenger’s front seats — just a bit of reading material offered to customers who would rather read through a silent journey than chit-chat with the driver. Interesting books, too: I noticed Natalie Angier’s Woman: An Intimate Geography, as well as Ambrose Bierce’s The Devil’s Dictionary. None of the American taxis I had ever been in had sported anything more literary than glossy magazines packed with ads.

We had just landed in Ireland, and despite the literary offerings, the taxi driver had no intention of letting the ride pass in silence. He inquired what had brought us on the long trip from Los Angeles, and I explained that I was participating in a debate at the Literary and Historical Society of University College, Dublin. That was a mistake, as I should have seen the next question coming: What was the debate about? Well, it was going to be about the existence of God; the L&HS revisits the topic every year, and I was one of a handful of visitors they were bringing in this time to defend either side of the question. And which side was I on? Trapped, I confessed that I was on the “does not exist” side. It’s not a discussion I like to force on people, but he did ask.

Our taxi driver took a moment to reflect on this information. Then he came back with: Well, you know Ireland has traditionally been one of the most religious countries in Europe, with an extremely strong Catholic tradition — but in the last couple of decades it had become increasingly secular. I hadn’t actually been familiar with the situation; despite my name (which I was politely informed should really be spelled “Seán”), I don’t have much connection with Ireland.

But I did have a remarkable cab driver, who was willing to fill us in. His theory of Irish religious consciousness began with the very early Church, which had co-opted many of the existing pagan traditions. Druidical rites, women priests, celebrants running around naked, that kind of thing. The turning point, he explained, was the Synod of Whitby in 664. (Whitby Abbey is actually in Northumbria, northern England, but apparently the repercussions of this event spread through Celtic society.) The ostensible focus of the synod was fairly narrow: how do we calculate the date of Easter? The choices were between the algorithm favored by the indigenous church, and that advocated by the catholic hierarchy in Rome. So it wasn’t really a controversy over the Easter Bunny’s work schedule; it was a power struggle between the locals and the establishment. Needless to say, the establishment won; the synod agreed to calculate the date of Easter using Roman methods.

Thus began (our loquacious driver continued) centuries of Catholic dominance over Irish religious life. And he pinpointed the peak of that dominance quite precisely: the 1979 visit of Pope John Paul II to Ireland. The Pope was treated like a rock star, speaking to audiences of hundreds of thousands of cheering supporters. But it was the beginning of the decline. The years to come would witness a dramatic collapse of religious devotion in Ireland generally, and in the influence of the Catholic church in particular.

What happened? Our cabbie had a theory, and it had nothing to do with the implications of natural selection or the logical status of the ontological proof for the existence of God. It was simple: Loss of moral authority of the Church. (Back home and consulting the Google, I find that Kieran Healy agrees.) And the loss of moral authority could be traced to a constellation of issues centering on … sex. On the one hand, the Church in Ireland took its usual predilection for sexual repression to extremes — while Americans debated over the right to have an abortion, in Ireland it was illegal to use any form of contraception as late as 1978. On the other hand, it was increasingly clear that clergymen weren’t always the best examples of sexual morality. Cases of priests fathering babies with their housekeepers or abusing young children (and then being protected by the Church hierarchy) were rampant. And so, while most Irish continued to symbolically profess the Roman Catholic faith, the populace converted gradually from fervent believers to modern secularists.

It’s very chagrining for we believers in logic and rationality to be confronted with the real reasons why people often change their minds about things. Belief in God isn’t something about which most people start with a completely open mind, sit down and carefully weigh the options, and reach a conclusion based on reasoning and evidence. More often, they believe in God because it serves a purpose in their lives, offering purpose and meaning and structure and guidance that is otherwise hard to come by.

When Shadi Bartsch and I taught a course on the history of atheism at the University of Chicago, we certainly had no plans to proselytize, but we had some concerns that a vigorous to-and-fro concerning the existence of God might strike an emotional chord for some of the students. That was a naive worry; students could be intellectually engaged and rigorous when talking about philosophical arguments for or against atheism, no matter what their personal beliefs happened to be. But we covered one topic that some people weren’t comfortable hearing about: how the Bible was written. Sure, they may be willing to accept that the Pentateuch wasn’t really penned by Moses himself. But when you start digging into the details of the documentary hypothesis, demonstrating that the Bible is just like any other collection of essays, culled from disparate sources with incompatible agendas and stitched together by more or less conscientious editors — human, all too human, in other words — it really hits home. For most believers, their belief is not a logical conclusion, it’s a mode of living. And the erosion of that belief will typically not, for better or for worse, be accomplished by the presentation and examination of evidence; it will be through telling a better story than the one told by religion. One that helps make sense of the world, provides a template for a fulfilling life, explains the difference between right and wrong, and brings meaning to people’s experiences.

That was the most erudite and educational cab ride I’ve ever had. The next evening we had the actual debate, which was more amusing than enlightening; the visitors such as myself trotted out various shopworn arguments, while the student speakers showed flashes of genius, skewering our stolid positions with wit and verve and only marginal attention to which side they were supposed to be upholding. A vote was taken, and reliable eyewitnesses will uniformly testify that the “God does not exist” side came out handily ahead, although the result was recorded in the record of the Society as the other way. Divine intervention, I suppose.

And then we repaired to a pub across the street, to drink Guinness (a miracle forged of human hands) and tell jokes and swap stories and share small slices our varied experiences. Living life.