Sean Carroll

Election day in Illinois is a week from now, March 16th. As usual we are too late to have any impact on the Presidential nomination process, but there’s an important Senate race. Republican Peter Fitzgerald is retiring, and chances are good that he’ll be replaced by a Democrat.

I’ll be voting for Barak Obama. (He seems to be leading the race at the moment, but my preferences are usually the kiss of death, so he’ll likely be issuing a press release declining my endorsement.) Not only was he president of the Harvard Law Review, he also has the grooviest campaign song of any of the candidates. (Via Crescat Sententia.)

I’ll be traveling for the next week — first the Perimeter Institute, then the University of North Carolina — so blogging may be spotty. Hang in there.

I promised earlier that I would talk about the Big Rip, but never got around to it, so here you go.

Since Edwin Hubble discovered in 1929 that the universe is expanding, cosmologists have suggested two possible ultimate fates for our currently-expanding universe: it could cease expanding and recollapse, eventually reaching zero size in a Big Crunch, or it could expand forever, but gradually more slowly (the Big Fizzle?). In a universe dominated by ordinary matter and radiation, these were really the only choices. Now we know that most of energy in the universe is some persistent dark energy that doesn’t diminish as the universe expands, and can continue to feed the expansion rate; therefore another possibility becomes likely, that the expansion will continue at a constant rate forever. Confusingly, a universe with constant expansion rate is said to be “accelerating,” because any individual galaxy appears to be accelerating away from us. That’s because Hubble’s Law says the recession velocity is the expansion rate times the distance (v = Hd), so a constant expansion rate H implies an increasing velocity v.

But there’s a lot we don’t know about dark energy, so it’s prudent to keep an open mind. The simplest dark energy model is an absolutely constant “vacuum energy,” but we can consider dynamical models in which the energy density is slowly decaying. Robert Caldwell and others have even suggested that the dark energy density (the amount of energy per cubic centimeter) might be increasing with time, a possibility he dubs phantom energy.

This opens the possibility of a Big Rip, in which the expansion rate increases without bound until it reaches infinity at some finite time in the future. This scenario was explored by Caldwell, Kamionkowski, and Weinberg. The consequences are dramatic: first galaxies, then stars and planets, then atoms and nuclei are ripped apart by the expansion of the underlying spacetime. The recent supernova results that were in the news indicate that the dark energy density is changing very slowly, if at all, so the Big Rip would have to be some time in the distant future (if, once again, at all).

It’s important to realize that the quoted numbers depend on an enormous extrapolation, one we have little reason to trust. Phantom energy density increases as the universe expands; but the above analyses made the simplifying assumption that the increase proceeded at a constant rate. In other words, imagine hopping in your car and accelerating to the speed limit, but then estimating your arrival time by guessing that your acceleration (rather than your speed) remains constant. You’d be able to get across the country awfully quickly if that were true; but it’s not a safe assumption.

The truth is, we can’t predict the future of the universe with any reliability at all until we understand much more about the underlying physics of the dark energy. If it is increasing, it might only do so temporarily, before leveling off to a constant value (see my paper with Hoffman and Trodden). If it’s currently a constant, it may decay completely away in the future. So, the choice between Crunch, Fizzle, and Rip is one we have no way to decide between right now. (But “Crunch, Fizzle, and Rip” is a great name for a band, or maybe a law firm.)

Here is why I could never be a politician. (Not that there are any movements afoot to draft me for major public office.)

A few weeks ago some friends and I went to the Lesbian Community Cancer Center Project Annual Ball (or the “Lesbian Prom” for short). True, I lack the traditional prerequisites for being a lesbian (female, homosexual), but it was a tolerant atmosphere, and my eccentricities didn’t seem to bother anyone.

The whole event was great fun. About a thousand people attended, festive, well-dressed (not as many outrageous costumes as Jerry Falwell would expect, but enough to be entertaining), and generally enjoying themselves in an easygoing and friendly atmosphere. It was a party, not a political event, and activism was in the background for the evening. It wasn’t until brief remarks associated with the presentation of some awards that anyone mentioned the same-sex marriage controversy. It only then struck me (I know, I’m slow) that all of these people around me, cheerfully having a good time, are systematically classified as second-class citizens in our country.

I doubt that anyone could get elected President today if they came out and said “This issue is completely ridiculous, of course same-sex couples should be allowed to marry.” But I wouldn’t be able to say anything else. We all know that progress in real-world politics sometimes relies on strategic compromise, and an ability to carefully prioritize efforts on controversial issues is absolutely necessary. But this one is simply not a close call. Furthermore, I don’t even think it’s especially interesting to talk about the arguments pro- and con-. It would be like debating whether apartheid was good or bad. (Racial discrimination is different than discrimination against gays, and drawing analogies between them isn’t generally useful, but one is just as obviously wrong as the other.)

To be fair, we’re not talking about what people should be allowed to do in the privacy of their bedrooms, but about whether society should extend a certain legal status to couples for whom the status was not originally intended. “Marriage” is an invented institution, originally intended to apply to male/female couples. There are undoubtedly all sorts of interesting historical/anthropological/sociological questions to be investigated about how the concept of marriage arose and what purposes it served in early societies. So what? In our actual world, marriage serves as a legal imprimatur to a romantic bond between two people in love. Some married couples have children, some don’t; some marriages last a long time, some don’t; some marriages are equal partnerships between two people, some are not. There is absolutely nothing about the contemporary idea of marriage which doesn’t make just as much sense when applied to same-sex couples as applied to opposite-sex couples. Convoluted rhetoric aside, the only possible ground of opposition to same-sex marriage is a conviction that homosexuality is wrong — a conviction which I don’t think deserves any respect.

Here is one example of an attempt at reasonable discussion of the issue, from Eugene Volokh:

[T]here’s an eminently legitimate argument that society would be better off if male-female couples were set up as the preferred, most legally and socially sanctioned mode. It is plausible to think that future generations would be better raised by male-female couples than by same-sex couples. And it is plausible to think that on the margins the laws related to marriage may subtly shift some people, either through incentive effects or through the law’s effects on social norms, towards male-female coupling and childrearing.

Now as it happens I’m not persuaded that these arguments are actually correct. I suspect that a same-sex couple that has gone through substantial effort to have a child will probably be at least as good parents as the average male-female couple, which might have had the child with much less forethought, work, and desire for a child.

I found this excerpt on Alas, a blog, who pointed out:

The problem with this analysis, as I see it, is that it fails to acknowledge that men and women are individuals, and should be given the opportunity to live their lives as individuals, not just as representatives of their sex.

Well, yeah. Do we really need this pointed out? I actually find it completely implausible that children raised by same-sex couples would necessarily (or even usually) be worse off than those raised by male-female couples. Does anyone in the world really believe that, given information about the psychological and socio-economic status of some selection of individuals chosen randomly off the street, they would be able to accurately judge which ones had been raised by single parents, which by divorced and remarried parents, which by same-sex parents, and which by traditional nuclear families? The argument might be logically coherent, but I can’t agree that it’s plausible. It would actually be more plausible to claim that children are better off if they are raised by wealthy parents than by poor ones; should we have minimum income requirements for prospective couples? Somehow I believe that the rights of the individual parents should be more important than some ham-handed social engineering.

Volokh continues:

But the arguments against same-sex marriage mentioned above are not ridiculous arguments, nor arguments that can only be justified by irrational hostility or contempt. These are arguments that sensibly cautious and methodologically conservative people can reasonably make against proposed changes in a fundamental social institution.

That’s precisely where I can’t agree. And I am convinced that, a few decades down the road, anyone who today is against same-sex marriages will be judged just as badly as everyone else throughout history who has fought to preserve discrimination of some minority on the basis of an irrational aversion on the part of the majority. (I don’t mean to single out Volokh, who is simply explicating the least-unreasonable arguments for the wrong side.)

Discussion of various aspects of the same-sex marriage controversy can be found at Andrew Sullivan, Angela Vierling, Dispatches from the Culture Wars, and Galois. There’s certainly a lot to say, from articulating defenses of basic rights to strategizing about the best balance between principle and politics. But I don’t personally have the patience to participate.

So that’s why I could never be a politician; on issues like this I find it impossible to be diplomatic. It’s possible to have reasonable disagreements about all sorts of things, from free trade to education reform to fiscal policy to foreign-policy strategies. I just don’t see how it’s possible to have reasonable disagreements about this one.

Besides, the idea of spending the winter months in Iowa, trudging between town meetings to declare my support for ethanol subsidies? No, thank you.

As advertised, I was on Science Friday this afternoon with Adam Riess and Richard Ellis. (Listen here; registration required.)

We talked mostly about dark energy, the mysterious stuff that is smoothly distributed through space, constant (or nearly so) as a function of time, and makes up 70% of the energy in the universe. It’s mysterious for several reasons. For one thing, the leading candidate for dark energy is vacuum energy, which is just a kind of energy that is perfectly constant throughout space and time; but our estimates of how big the vacuum energy should be are larger than the observed amount of dark energy by one hundred and twenty orders of magnitude (a one followed by 120 zeros). For another, the amount of dark energy is comparable to the amount of matter in the universe (the other 30%), even though they change dramatically with respect to each other as the universe expands.

An issue that arose during the discussion was whether dark energy worked against gravity. It’s important to understand that dark energy is not a new “force,” but a new kind of “stuff,” that creates its own gravitational field. The funny thing is that this gravitational field pushes things apart, rather than pulling them together. But the force communicating the push is just gravity as Einstein figured it out — a manifestation of the curvature of spacetime.

We also talked about crazy new ideas, which are certainly worth considering. (It was during the course of this discussion that I extemporaneously introduced the concept of “peppermint-flavored dark energy,” although I’m not sure that will catch on.) Crazy ideas range from some energy source that changes slowly, but is nevertheless dynamical, all the way to tossing out Einstein’s general relativity and invoking new behaviors for gravity. People have tried all sorts of things, and should definitely keep trying, but so far the vanilla-flavored dark energy remains the model to beat.

It’s good that the press isn’t letting Bush just get away with using images of the World Trade Center in campaign ads. Kerry cannot let Bush be the presumptive anti-terror candidate. Next time Kerry gets asked about those ads in an interview or debate, he should say something like this:

I think it reveals something about the President and his campaign. Personally, I don’t think it’s appropriate to use images of Ground Zero for political gain. Of course we should have a debate about how best to combat terror and preserve our national security, but our memories of the September 11th tragedies should be treated with respect. This president won’t spare more than one hour of his time to talk with the commission investigating what went wrong on 9/11; to me, that says he’s just not willing to do what it takes to make sure a tragedy like this never happens again.

I’m sure the Kerry campaign is overjoyed to get such insightful advice for free over the web. Here at Preposterous, we toil selflessly for the greater good.

Maybe my final exams are too hard, after all. At the University of Georgia, former assistant coach Jim Harrick Jr. (son of head coach Jim Harrick Sr.) taught a course in 2001 on Coaching Principles and Strategies of Basketball. There was only one exam, including questions along the lines of “How many halves are in a college basketball game?” and “In your opinion, who is the best Division I assistant coach in the country?” (Correct answer: C, Jim Harrick Jr.)

The test in its entirety is here. Everyone in the class got an A. Both coaches recently lost their jobs following an NCAA investigation of multiple rule violations.

I’m spending all day Thursday at DePauw University, as a guest of their Science Research Fellows program. It should be fun, although they’re keeping me busy: a lunchtime talk, two seminar class discussions, and a public lecture in the evening. The lunchtime talk will be a reprisal of one I gave at a conference on “God and Physical Cosmology” last year at Notre Dame. The conference consisted primarily of theologians and philosophers, but they invited a couple of cosmologists (Joel Primack and me) along to give some scientific perspective. I didn’t really want to give a standard gee-whiz cosmology talk, so they let me talk about Why (Almost All) Cosmologists are Atheists. As you can read, it’s just the standard argument about why scientific reasoning leads to a firm rejection of a supernatural being as an explanation for what we see in nature; the kind of thing you’ll find in Richard Dawkins or Steven Weinberg.

I went into the conference having no idea what the response would be; this was, after all, the only conference I had ever been to where there was a prayer to open the banquet. But as it turned out they loved my talk. I didn’t change anybody’s mind, nor did I expect to (although one participant did say that I had convinced him once and for all that the argument from design wasn’t one that theists should rely on). But they were very happy to get a completely different perspective, and I think they were pleased to really hear what a cold-blooded scientific materialist actually thinks, rather than just being humored. I certainly give everyone at the conference credit for being good sports (which academic theologians generally are, in my experience).

Meanwhile, on the drive down from Chicago, I found an evangelical radio program explaining in quite a bit of detail why “old-earth” theories of evolution had been convincingly disproved, and correct scientific analysis had demonstrated that most geological features originated in an hydraulic catastrophe (the Flood) four thousand years ago. (Ed Brayton has an interesting discussion of just this issue.) So the discussion continues, needless to say, on multiple levels.

Here is synergy for you. This Friday I’ll be a guest on NPR’s Science Friday, in the second hour (3:00-4:00 Eastern time). One of the things we’ll be talking about is dark energy, including some new data bearing on whether the universe will be torn apart in a Big Rip. (The Big Rip is a little overhyped, actually; hopefully I’ll say more about that later.)

But one of the reasons I was invited was that the producer, Annette Heist, noticed that I had a blog, and in particular that I had mentioned NPR. And now I can tell you about it using the blog. Dizzying.

Congratulations to Howard Dean for winning his first primary.

So Kerry is the nominee. From Fark.com (somewhat indirectly, since they mangled the link) comes the news that he wants to be our second black president:

Speaking to the American Urban Radio Network, Kerry said Monday that he hoped to emulate former President Clinton in the eyes of blacks, the party’s most loyal constituency and a solid source of support during his stretch of primary wins.

“President Clinton was often known as the first black president,” Kerry said. “I wouldn’t be upset if I could earn the right to be the second.”

Now we can look forward to a stream of articles speculating about the veep slot, followed by a compensating stream telling us it doesn’t matter because the vice-presidential candidate can rarely even help win their home state. (Of course, Gore couldn’t win his home state in 2000, so maybe the presidential candidate doesn’t matter either.)

Nobody’s really excited about Kerry, are they? He seems like Gore with a different accent. Aloof, drifting, only predictable in his willingness to back down on questions of principle when an opportunity to pander presents itself. But we should give him a chance, and see how he does under the spotlight of the general-election campaign.

So it looks like there used to be a lot of water on Mars.

This is a great discovery. There’s so much we don’t know about the origin and evolution of planets and their chemistry, any little bit of information helps. The evidence seems to be somewhat indirect (sulfate concentrations, shapes of rocks), but I’m willing to believe that it paints a compelling picture.

Still, I have profoundly mixed feelings about this. Of course, the result is immediately spun as evidence for the possibility of life, with some intentional ambiguity about how strong the possibility is, when the life might have died out, or what form it took. More than one of the scientists comes right out and says that this part of Mars would have been an hospitable environment for life to exist. Really? Just because there was water? Wouldn’t we need to know a little more than that to make such a sweeping statement?

Discovering solid evidence for life native to Mars (as opposed to some organic material that was splashed there from Earth, as we now know can happen after comets or meteors impact us) would be a truly wonderful event. But it’s not very likely. For one thing, it’s just hard; I can imagine a long series of experiments reaching inconclusive results. For another, the a priori chances that life evolved separately on Mars seem incredibly small. There seem to be a lot of planets in our galaxy (one hundred billion, maybe?), but yet the galaxy is not teeming with the electromagnetic buzz of numerous advanced civilizations (the Fermi paradox). Either civilizations destroy themselves with extremely high probability, or life comes into existence with extremely low probability. Choose for yourself which seems more reasonable.

But still, it would be well worth chasing after this remote possibility if it didn’t cost anything. (Warning: curmudgeonly realism ahead.) But this finding will certainly be used as justification for funneling yet more money away from other NASA science programs and into the Mars program, especially into the manned mission which Bush recently proposed. Which is just silly.

The space shuttle and the space station were part of a NASA strategy to make travel to Earth orbit cheap and routine, which is certainly a laudable and achievable goal. The problem is, it’s been an abject failure. Shuttle missions are infrequent, unsafe, and fantastically expensive; the space station is even worse on all counts. So the new strategy is to build a base on the Moon and then visit Mars? This is like a kid who can’t quite get the hang of riding a bike without any training wheels, who decides that everything would improve if he enters the Tour de France. Not that it’s not a worthwhile goal (either the Moon or the Tour de France), but it’s not necessarily right under any circumstances. And we’re just not there yet.

Meanwhile, the rest of NASA’s science budget is being strangled. I gave a colloquium at the Space Telescope Science Institute on January 14th this year; the starting time had to be delayed so that everyone could listen to the President’s announcement of the new initiative, which had been (coincidentally, one assumes) scheduled for the same time. The sense of dread in the room was palpable; here were dozens of dedicated scientists, who were devoted to using this fantastic instrument to discover new things about the universe, who could see it being undermined before their eyes. And indeed, soon thereafter the planned servicing mission (to install $200 million of new equipment, which has already been built) was canceled. Safety was certainly a major concern in the decision, but money was a crucial factor.

And Hubble is not the only thing to go. I was recently on a NASA “roadmap team” to sketch out a future plan of missions in cosmology and astrophysics. We came up with the Beyond Einstein program, an ambitious but practical set of missions to learn about black holes, dark matter, dark energy, and the early universe. In the President’s new budget, all of the new missions were pushed back several years; of course they can continually be pushed back until they never happen. I have a vested interest in this kind of science, it’s true; but by any objective measure the most successful science missions that NASA has done have been unmanned satellites, not sending people around the solar system. Our scientific decisions are being increasingly driven by spectacle and political calculation, which is a shame when there are such exciting results potentially within reach.

It’s terrible that I can’t simply enjoy a wonderful scientific result for what it is, but automatically start fretting about the wider political consequences. Must be a grownup or something.