Sean cheekily comments in a recent post:

If you know that something exists, what’s the point in thinking about it?

My response to this is much the same as the post-I-meant-to-write-but-didn’t-get-around-to on Simon White’s smackdown warning against all astronomers turning into “dark energy experimentalists”.

Thus, here is sampling of astronomical facts that had to be learned before the high-z supernova teams could discover dark energy.

• That supernovae exist.
• That supernovae are exploding stars.
• That not all supernovae are the same.
• That variations in supernovae properties correlate with the properties of the progenitor star.
• That a significant subset of supernovae come from detonating white dwarfs (Type Ia SN).
• That Type Ia SN have a characteristic spectrum.
• That Type Ia SN have a typical luminosity of 10⁴³ ers/s, which we learned from figuring out how to measure distances to nearby galaxies that happened to host Type Ia Sn in the past, using a list of facts that is much longer than this one.
• That, in the absence of dust, the peak luminosity of Type Ia SN correlates with the color of the supernova and the rate at which it fades.
• That dust causes reddening and dimming of light, but in a usually predictable way which depends on wavelength.
• That the unreddened, undimmed color and luminosity of a distant, redshifted supernova can be estimated from the data alone.
• That the peak luminosities of Type Ia SN at different redshifts can be compared, even though observations measure different parts of the spectrum due to the cosmological redshift.

As long as this list is, it’s still highly incomplete, and takes for granted that we know even more basic things like “how do I calibrate how many ergs/s are coming from an astronomical object that I detect as a fuzzy blotch in my CCD detector?”. It represents decades of efforts by many hundreds of people (many of them theorists, but theorists working on Stuff That Exists), most of whom didn’t think twice about the existence of dark energy.

Given the above, one possible physics-biased reading of Simon’s article is that if you limit astronomers’ ability to go forth and characterize what the universe is actually like, no one will be laying the foundations for the next generation of crazy-physics-you-can-study-in-space. For astrophysics, the Universe is our LHC, and we’ve got to be free to characterize our widgets, even if they’re boring ole brown dwarfs rather than panels of supercooled silicon wafers.

Now, all of this diatribe is not meant to minimize the role of outside the box theory. You absolutely need that too. However, it’s not the only necessary thing, and it’s not for everyone. There’s an old chestnut that theorists are judged by their best paper and observers/experimentalists by their worst. In other words, once Alan Guth came up with inflation, he was rightly marked as a superstar, and he can safely spend the next three decades writing papers on Romulan cloaking devices if he chooses. However, if an experimentalist writes a paper saying they’ve detected Romulan cloaking devices, no one is going to believe them when they later say they’ve discovered the Higgs. Tempermentally, most people are probably more suited to one camp than the other. I know that I have a pragmatic streak a mile wide, and thus I’m better off in the “stuff that exists” camp. I can understand why that sounds terribly dull to Sean, but I’d bet he’s glad me and my ilk are doing so.

Dennis Overbye does us all a huge favor by coming clean about “the God Particle.” The phrase refers to the hypothetical Higgs boson, long-time target of particle physics experiments. It was coined by Leon Lederman as a shameless ploy to sell books, and ever since has managed to appear in every single mention of the Higgs in the popular media — for example, in the headline of Dennis’s article from a couple of weeks ago.

Physicists, regardless of their stance toward timeless theological questions, hate this phrase. For one thing, it puts this particular boson on a much higher pedestal than it deserves, without conveying anything helpful about what makes it important. But more importantly, it loads an interesting but thoroughly materialist idea with absolutely useless religious overtones. Even harmful overtones — as Lederman himself notes, his coinage came about just around the time when creationism began to (once again) become a big problem, and this confusion was the last thing that anyone needed.

Furthermore, everyone knows that “the God particle” is misleading — even all of the journalists and headline writers who keep trotting it out. It’s just too damn irresistible. Particle physics is fascinating, but it takes some effort to convey the real excitement felt by experts to people who are watching from the sidelines, and a hook is a hook, shameless or not. If my job were writing about particle physics for a general audience, I doubt I’d be able to resist the temptation.

But, as Dennis notes, this God-talk is part of a venerable tradition on the part of physicists. We use “God” all the time to refer the workings of Nature, without meaning anything religious by it. Or at least, we used to; the nefarious encroachment of Intelligent Design and the religious right on our national discourse has given some of us pause. In the past I could have given a talk and said “Either you need a dynamical origin for the primordial cosmological perturbations, or you just have to accept that this is how God made the universe,” without any worry whatsoever that the physicists in the audience would have been confused. They would have known perfectly well that I was just using a colorful metaphor for “that’s just how the universe is,” in a purely cold-hearted and materialistic fashion. Nowadays I find myself avoiding such language, or substituting “Stephen Hawking” for “God” in a desperate attempt to preserve some of the humor.

All of which is to say: religion is impoverishing our language. I want God back, dammit.

Now, I like dark matter and dark energy as much as the next person (ok, maybe not quite as much as Mark). Still, I simply don’t have the temperment to spend the majority of my mental energy on ideas that are so speculative that, while interesting, they’re probably wrong. I’m not trying to disrespect the theorists, but it takes a certain mindset to enjoy the type of process Sean described. If you read the three part series, nowhere will you see the evidence that Sean or his collaborators actually believe that inflation had a preferred direction. They just decided it would be cool to explore, and will shed no tears if inflation turns out to be a nice creamy vanilla of isotropy. Me, I’m enough of pragmatist that I’m happiest spending my time working on stuff that actually exists. So, no Nobel Prize for me, but I’m ok with that.

What this has been leading me to think about over these past few weeks is where the normal matter actually wound up. Astrophysicists usually refer to “normal matter” as “baryons” — stuff like neutrons and protons which carry most of the mass of the non-exotic universe — and astronomically speaking, there’s not that many places it can wind up. Most of the baryons in the Universe start out as hot ionized gas (i.e. a plasma of free electrons and positively charged nuclei), and as time goes on, some of this gas cools into colder phases (neutral atomic or molecular gas, which are fairly easy to detect), some of which further cools into dense stars (which then heat up again due to nuclear fusion in the core) or even into solids (dust or rocky planets). So, by the present day, normal matter is either in gas (of various temperatures, densities, and ionization states) or in stars, with a smattering of solids and a tiny pinch of liquids.

Although these cooling and transformation processes are a rich field of “gastrophysics” (as the term goes), the overall landscape of baryons is sculpted by the dark matter, to first order. Dark matter has more than 80% of the mass of the Universe, so it dominates the gravitational forces in more than 99% of the volume of the Universe. Only when the barons become extremely concentrated (like in stars, or in the centers of galaxies) does normal matter significantly shape where stuff winds up. In principle.

In reality, however, the baryons actually spend quite a bit of time bossing each other around, in spite of dark matter’s best attempts to impose the kind of order a theorist would prefer. Not only does gas cool through interactions with itself (i.e. particle A gets near particle B, and an energetic photon ensues, running off with some of the particles’ energy), it also heats back up, through supernovae, which spew superheated gas outwards which in turn shock-heats any cool gas unfortunate enough to get in its way, and possibly through jets emitted by accreting black holes in the centers of galaxies. (Astrophysical theorists are all a twitter about this last idea these days, but I haven’t bought into it yet.) In other words, the observable Universe contains a level of complexity that should make any theorist shudder.

Now, if you’re not predisposed to embracing such complexity, why might you care? Well, back when I was a grad student (you know, when dinosaurs roamed the earth and the iPhone did not yet exist), light emitted by galaxies traced mass. If you knew where the galaxies were, you knew where the dark matter was. Theorists stuck in a simple numerical constant (a “bias factor”) to allow some wiggle room, but mapping the observable Universe onto the dark sector was something we assumed we could do easily. Unfortunately, we’ve since come to appreciate how drastically baryonic process change where, when, and if stars form, and thus alter the numbers and properties of galaxies. These effects are worst in the smallest dark matter halos, where the gravitational binding energies approach the typical energies of baryonic heating by supernovae. Thus, when you count galaxies, you’re no longer counting dark matter halos in a simple one-to-one mapping.

Worse still, it’s not even clear that most of the baryons wind up in galaxies at all. In the most massive gravitationally bound dark matter halos (i.e. those that surround clusters of galaxies), everything looks OK. If you add up the mass in stars and gas in the cluster, and compare it to the mass of the dark matter halo (which you’ve inferred from some combination of kinematics, gravitational lensing, or gas pressure gradients), you get about the ratio you expect from concordance cosmology. Basically, the cluster is massive enough that no matter what happened to the baryons, they got stuck in the gravitational potential well of the cluster, so they’re all still there when you count them. On the scale of galaxies like the Milky Way, however, our best accounting says that maybe 20% of the normal matter that exists actually winds up as stars or easily detectable cool gas. So, for typical galaxies, 80% of the normal matter just doesn’t seem to be around. It’s probably in some hot phase that we have a hard time detecting with current instrumentation, but its not clear if it came into the galaxy and then got shot back out, or just never made it in.

On the scale of the lowest mass galaxies (which are particularly interesting, because they give you the most leverage on the small scale power spectrum), we frankly don’t know what the f*@$ is up. Really. I’ve spent the past week or so working hard on this problem, and the lowest mass galaxies are just a huge freakin’ mess. We typically estimate the mass of the dark matter by using the motions of gas and stars and then assuming that if the whole mess isn’t flying apart, then there must be some amount of mass holding the galaxy together. However, these low mass guys are so puny and pathetic that (1) you can’t figure out if their motions are actually rotational or just localized gas physics pushing stuff around and (2) you can’t figure out what fraction of the galaxyies’ total motion is oriented along the line of sight. And don’t even get me started on interactions with larger galaxies. Thus, you measure a characterstic range of internal velocities for these guys, and it tells you squat about the characteristic velocities of the dark matter halo the galaxy lives in. It’s enough to make one go drink some beer.

Which I will now do.

Just a brief note to report that we have escaped from Yearly Kos unscathed. The science panel was a great success; Chris Mooney and Ed Brayton gave sparkling talks, Tara Smith moderated with aplomb, Lindsay Beyerstein snapped pictures, and the whole thing went smoothly due to the organizational skills of Stephen DarkSyde and Jennifer “Unstable Isotope” Thompson. The hot lights of CNN and C-SPAN glared down upon us, but we refused to wilt. Ed has a brief report here, and Chris describes the session in detail at the Huffington Post.

The conference highlight was the Democratic Presidential candidates’ forum, featuring all of the major candidates not from Delaware. (See reports on the forum here, here, here, and a convention overview by Ezra Klein here.) It was a sprightly debate, ably moderated by Matt Bai. Despite (or perhaps because of) the restriction to very brief answers, real distinctions between the candidates did shine through. Bill Richardson, for example, actually volunteered his support for a balanced-budget amendment, essentially removing himself from consideration as a serious candidate. John Edwards was slick and said good things, but that was in part because he ignored all of the questions. Hillary Clinton was, predictably, strong and well-informed, but this wasn’t her crowd. She bobbled a question about accepting donations from lobbyists, claiming that just because she took money doesn’t mean she would be influenced by the lobbying. My own biggest problem with Hillary is that she’s too willing to buy into a dramatically reductive view of how the world works, whether in all sincerity or just as a political stance. She dismissed the importance of anti-American sentiment in the world, claiming it was just anti-Bush sentiment, and claimed that we were now safer because we have to take our shoes off before passing through airport security.

I’m a longtime Barack Obama supporter, and the convention reinforced my feeling. His performance at the forum was careful and specific, not letting his charisma shine through, but he was enormously compelling in a breakout session afterward. Obama gets what it’s like to live in a complicated world, because he encapsulates a complicated world all by himself: American mother, Kenyan father, born in Hawaii, lived for four years in Indonesia as a child, educated at Harvard, trained as a street organizer in Chicago. He has an incremental but ambitious health care plan, and was anti-war from the start. Still, I’d be absolutely thrilled to support any of Obama/Clinton/Edwards against any of the embarrassments currently in contention for the Republican nomination. It’s an incredibly strong Democratic field, which is something I never thought I’d see.

But the really interesting news (to me) at the conference was that Bill Foster is running for Congress. Bill’s name might not be familiar to you unless you’re a particle physicist — he’s played a major role in a number of particle-physics experiments, including Fermilab’s antiproton Recycler Ring. Before becoming a physicist, he became independently wealthy when he and his brother founded a company (while at college) that has become the world’s leading provider of lighting systems for theaters. He’s running in Dennis Hastert’s district, although it’s not yet clear whether Hastert himself will be standing for re-election. It’s a Republican district, but not so much so that we couldn’t imagine taking it in a year when Republicans are as unpopular as they’ve been in recent memory. You can donate here to Bill’s campaign.

Wearing the little blue tag that identified me as a speaker at Yearly Kos, I was warned on multiple occasions to be on the lookout for Fox News and other nefarious media outlets, who were said to be lying in wait to ambush the innocent Kossacks, hoping to record them saying outrageous things for later broadcast. I was really looking forward to being thus ambushed, but it never happened. I spent hours lurking in the public areas, doing my best to look vulnerable and yet potentially outrageous, but no luck. My inevitable on-air showdown with Bill O’Reilly will have to wait for some other day.

p.s. It’s true, we did have non-YK fun while in Chicago. I’ll report later on our restaurant exploits, but I’d be remiss not to mention the trouncing at poker that was administered by Jeff Harvey on Friday night, thus falsifying (or at least offering one data point against) my conjecture about string theorists. Jeff had been dominating the local game since I left for California, and he proved on Friday that his success was no fluke. Or maybe it has been a fluke, but it’s a consistent one. Until next time, anyway.

In a few hours Future Spouse and I will be hopping on a plane for Chicago. All sorts of fun things are planned, but the nominal excuse for the trip is to attend the second annual YearlyKos convention, where perhaps we’ll score some party invitations. On Friday afternoon at 2:30 I’ll be speaking on the science panel, along with fellow bloggers Chris Mooney and Ed Brayton. The moderator will be Tara Smith of Aetiology, and we’ve even corralled Lindsay Beyerstein to be the official photographer; Stephen Darksyde, who put it together, unfortunately won’t be able to make it, but we hope to do him proud. Unconfirmed rumors suggest that the panel will be taped by C-SPAN for later broadcast, so don’t be shocked if you tune in hoping for some hot congressional-subcommittee action and catch science bloggers instead. It’s also supposed to be broadcast in Second Life, although I don’t know that means. Tara will also be moderating a science bloggers caucus on Thursday afternoon. Any CV readers who are at YK should certainly drop by and say hi.

Politics is a funny thing. Like last year, I anticipate being moved by the sincere passion for effecting political change in evidence among the participants, and also being a little creeped out by the attitudes of the less reasonable among them. Among the latter we are currently faced with the spectacle of Mike Stark, who decided it was a good idea to harass Bill O’Reilly at his house, putting up signs and stuffing reports of O’Reilly’s sexual-harassment lawsuit into his neighbors’ mailboxes (via Balloon Juice). This was Stark’s idea of a clever response to O’Reilly’s ludicrous attempts to smear Kos as a “hate site” by trolling thousands of diaries and millions of comments for outrageous remarks. Now, reasonable people can all agree that Bill O’Reilly is an obnoxious twit. But even twits shouldn’t be bothered at their homes, and that’s even true if they themselves have engaged in the tactic. “Two wrongs…” and all that. So it was depressing to read so many of the comments at Kos coming out in defense of Stark (although there were also many that took him to task).

Nevertheless, I have not given up my ambitions to someday be a big-shot A-list left-wing blogger. From my close readings of The Poor Man Institute and other sites, I gather that the accepted strategy is to post YouTube videos of progressive rock bands. All I can say is, if that’s the game you want to play, then don’t mess around.

Don’t. Mess. Around.