June 2004

Back from sunny, cicada-ridden Baltimore and the conference mentioned previously. It was a small, fun conference; the idea was to keep it simple and informal, so that people could spend time talking to each other and perhaps even get some work done. My talk was scheduled at the very end, so I didn’t get any work done, but split my time between socializing and making an electronic version of the talk (which I had given previously, but only on the blackboard at seminars). In the end it was for naught, as I complained about having to make the electronic version and received a chorus of requests to just go ahead and give the blackboard talk, which I did. It went pretty well, so we’ll see what kind of reaction the paper gets.

The participants were all theorists working on particle physics, string theory, and cosmology — overlapping fields with a lot of activity and connections these days. Some of the memorable talks:

• Gia Dvali talked about modified gravity in cosmology (as I blogged about recently).
• Angela Olinto gave a nice review of ultra-high-energy cosmic rays and neutrino experiments.
• Shamit Kachru talked about compactifying extra dimensions in string theory and the string-theory “landscape” of possible vacua.
• Alex Szalay gave an interesting talk on the huge data sets appearing in modern astrophysics — we’re moving from terabytes to petabytes, leading to files that would take years just to search using ordinary methods.
• Ann Nelson and Neil Weiner both gave talks on interactions in the dark sector (undeterred by my skepticism).
• Eva Silverstein talked about inflation from nontrivial kinetic terms for string-theory moduli, including potentially observable signals (!) of non-Gaussianity in the cosmic microwave background.
• Jacob Bekenstein talked about modified gravity as a replacement for dark matter.
• Nima Arkani-Hamed talked about “ghost” fields as dark energy.
• Marc Kamionkowski talked about dark matter that is neutral, but couples to electromagnetism through a dipole moment.
• Hitoshi Murayama talked about the minimal possible model that is consistent with all of our current data.
• Even the summary talk, by Joe Lykken, was fantastic.

You get the idea, I hope: lots of interesting ideas, bumping up against new constraints from experiments, bringing together fields that weren’t talking to each other just a little while ago (e.g., when I was in grad school). It’s an exciting time.

I’ll be away for the next few days, attending this conference at Johns Hopkins. I’ve been trying to curtail my excessive traveling, but this workshop seems to have a lot of interesting speakers; I’ll report back if any startling new ideas emerge. I’ll be giving my soon-to-be-famous talk on how inflation explains the low entropy of the early universe. If only I could find time to write the actual paper, we could put Boltzmann’s ghost to rest.

We’re on a quarter system here at Chicago, which means we don’t start until October (good) but we keep going until the beginning of June (bad). Which is to say, I have just handed out the take-home final exam for my Spacetime and Black Holes class, an undergraduate introduction to general relativity. It has been a great class, full of curious and enthusiastic students (at least two of which, Maire and Colin, have blogs; feel free to let me know if anyone else does).

Let me see, I’ve been alive for thirty-seven years, thirty-two of which have involved spending much of my time in an educational institution of one sort or another, from nursery school to being a professor. And still, I have to admit, I love the rhythms of the school year, from the fresh fall days when the campus comes back to life with arriving students, to the slogging twilight of the winter quarter, to the cusp of summer when another year has been successfully negotiated. Why would anyone want to leave to go to the real world? But that, of course, is the downside: so many people at any school are there just temporarily, whether it’s students or postdocs or, when things don’t turn out as we hope, assistant professors. Some of the UofC students at Crescat Sententia are graduating seniors, and are grumbling wistfully (sounds impossible, but it’s true) about the impending end of their days here. It’s equally bittersweet to be on the other side, as students who you’ve seen working and growing in an impossibly short time prepare to take off for their next set of challenges.

So, congratulations to all the graduating seniors, not to mention graduate students about to get their Ph.D.’s and postdocs moving on to other jobs. For the students, be sure to enjoy the ceremony, which can seem anticlimactic if you don’t take time to reflect on what you’ve accomplished. It’s a big deal.

Looks like the idea of sending robots to repair Hubble is gaining some steam. They wouldn’t be able to do everything you could do with a servicing mission, but they could install new instruments and gyros to keep the telescope running for quite a while longer. (Or not — if it’s deemed unfeasible, they might use a robot just to prepare the satellite for re-entry into the atmosphere.) It will be up to the engineers to build robots that can reliably do the job, which isn’t easy; but my bet is that it can be done. This challenge has actually energized a lot of folks at NASA, and fixing the Space Telescope is a goal everyone can agree on.

Chicago is a fantastic city in many ways; at some point I should do a series of posts on why this is the greatest city in the world to live in. One reason, believe it or not, is geography. In some respects, it’s not good to live on a large plain in the middle of a large continent; there are no mountains nearby to go climbing, and with no nearby oceans the weather can get pretty dramatic. (I once read that there are only three metropolitan areas with greater than five million people in which the temperatures regularly reached over 100 degrees F in the summer and below zero in the winter: Beijing, Moscow, and Chicago.) But there is an important benefit as well: it’s much harder to sneak up on an inland city with a nuclear weapon than it would be if we were on one of the coasts.

To be sure, Chicago is only about the fourth-ranked U.S. target that one would choose for a dramatic blowing-up; New York, Los Angeles, and Washington D.C. have to be ahead of us on the list. That, coupled with the difficulty of smuggling a nuclear weapon all the way into the interior, makes it seem relatively safe here. If I lived in one of those three coastal cities, I wouldn’t be nearly as sanguine. It’s one of those things we don’t like to talk about, but the chances of a terrorist group cobbling together the technology and raw materials for making a bomb have to be appreciable, given the half-hearted efforts that have been made to quarantine both resources and know-how thus far. (Not only have we gone quite easy on people who are known to share nuclear secrets, but our violations of the test-ban treaty and plans to build “small” tactical nuclear weapons have created a climate in which other countries do not feel encouraged to give up their own nuclear programs. Not to mention the fact that successfully building a bomb would be excellent proof against getting invaded.)

Mutually Assured Destruction, shaky as it was as a defensive doctrine under the best of circumstances, is nearly useless against terrorist organizations. There’s no way of guaranteeing we would even be able to pinpoint the true culprits, nor to counterattack if we could. If terrorists somehow get the bomb, they’re very likely to use it.

So what are the chances of a nuclear bomb being detonated in a U.S. city sometime in the next fifty years? One percent? Ten percent? These seem like reasonable numbers to me. What to do about it, I’m less sure.

Of course, risk analysis is notoriously difficult, and people tend to do a terrible job even when it’s easy. How many people would evacuate L.A. if scientists could guarantee that there was a 20% chance of a devastating earthquake (millions dead, city in ruins) in the next twenty years? I suspect not many; when the danger is so diffuse, it’s hard to take the tangible steps necessary to avoid it.

It was good to hear that Kerry is putting nuclear proliferation high on his list of foreign-policy priorities. (Even if he did choose to wear an old Monday Night Football blazer while doing so. Doesn’t he have wardrobe consultants on staff?) I don’t know how effective we can be, but doing everything conceivable to prevent a nuclear weapon from exploding in one of our cities seems like an easy priority to agree on.