The Shaw Prize in astrophysics has been awarded to Saul Perlmutter, Adam Riess, and Brian Schmidt, for discovering the acceleration of the universe by measuring the Hubble diagram using Type Ia supernovae. The Shaw Prize is relatively new, having first been given in 2004, and is awarded in three areas: Astronomy, Mathematical Sciences, and Life Sciences and Medicine. It comes with a total of US$1 million, split between the three recipients. Competitive with, although not quite as much as, the Nobel prize…

Brian was the leader of the High-Z Supernova Search Team and Adam was lead author on their paper; Saul was the leader of the Supernova Cosmology Project and also lead author on their paper. (Get some more inside scoop from Rob Knop.) To most of us, their finding was a complete surprise, as we were all quite familiar with the fine-tuning problems associated with the cosmological constant (the most straightforward explanation for the acceleration). But by 1998, it had become impossible to deny that something fishy was going on — the universe was not the simple matter-dominated flat Einstein-de Sitter cosmology of the standard Cold Dark Matter model. In late 1997 I was asked to give a review talk at a CMB conference in Santa Barbara, on the topic of “every way to measure the cosmological parameters other than the CMB.” In assembling the talk the overall message came through loud and clear, from considerations of the age of the universe, direct measures of the mass density, and properties of large-scale structure. There were plenty of ideas floating in the air, including an open universe (the most obvious choice), warm dark matter, a mix of hot and cold dark matter, or some dramatic features in the primordial power spectrum, as well as the old standby cosmological constant. But only the last of these solved all of the problems with one fell swoop. So when the two supernova groups announced in 1998 that they had direct evidence that there really was a cosmological constant, in the form of an accelerating universe, the community was primed to believe them, which they did fairly quickly. Soon thereafter, of course, improved measurements of the CMB anisotropies indicated that the universe was spatially flat, in perfect accord with the combined supernova and matter-density measurements. If you were to plot the inferred density of both matter and cosmological constant, the constraints from the three different techniques — supernovae, matter dynamics (clusters or large-scale structure) and the CMB — the allowed regions overlapped in perfect harmony.

A preposterous universe, maybe, but I like it.

A web page presenting a scale-model hydrogen atom (via Cynical-C):

And you thought there was a lot of empty space in the solar system. Well, there’s even more nothing inside an atom. A hydrogen atom is only about a ten millionth of a millimeter in diameter, but the proton in the middle is a hundred thousand times smaller, and the electron whizzing around the outside is a thousand times smaller than THAT. The rest of the atom is empty. I tried to picture it, and I couldn’t. So I put together this page – and I still can’t picture it.

The page is scaled so that the smallest thing on it, the electron, is one pixel. That makes the proton, this big ball right next to us, a thousand pixels across, and the distance between them is… yep, fifty million pixels (not a hundred million, because we’re only showing the radius of the atom. ie: from the middle to the edge). If your monitor displays 72 pixels to the inch, then that works out to eleven miles – making this possibly the biggest page you’ve ever seen.

Okay, we all know that, science-wise, this is utterly bogus. Mostly because the proton and electron are not little spheres of fixed size, as our classical intuitions inevitably imagine them to be — they should be represented by wavefunctions, and the electron’s wavefunction in particular should be spread throughout all eleven miles. Admittedly, an eleven-mile web page that accurately represented the ground-state wavefunction of the hydrogen atom would have been harder to construct (although, hmm, maybe not impossible). And I’m not sure where the “sizes” of the particles came from. The proton really does have a size, about 1.5 x 10^-15 m, since it’s a bound state of quarks. But the electron is a point particle, as far as we know. There are various distance scales you can associate to it, but the smallest of these is the classical electron radius, which is about twice the size of the proton diameter. John Baez explains. I don’t know how to get an electron to be one thousandth the size of a proton, unless you’re using masses rather than lengths, which is a big mistake because (in the wacky world of quantum mechanics) lengths get smaller when masses get bigger.

Still, it gives you some feeling for the instubstantiality of matter, as Geiger and Marsden long ago demonstrated. And it’s pretty cool.

In October 1984, it was announced that the Nobel Prize for Physics had been awarded to Carlo Rubbia and Simon van der Meer, for the discovery of the W and Z bosons at the UA1 experiment at CERN just the previous year. This was the capstone discovery in the establishment of the Standard Model of particle physics. The third generation of fermions had already been discovered (the tau lepton by Martin Perl in 1977, the bottom quark by Leon Lederman also in 1977), and the nature of the strong interactions had been elucidated by deep-inelastic scattering experiments at SLAC in the late 1960’s and early 1970’s. Unsuspected by many, particle physics was about to enter an extended period in which no truly surprising experimental results would emerge; subsequent particle experiments have only been able to confirm the Standard Model over and over again, including the eventual discovery of the top quark at Fermilab in 1995. (Astrophysics, of course, has provided substantial evidence for physics beyond the Standard Model, from neutrino oscillations to dark matter and dark energy.)

A month earlier, in September 1984, Michael Green and John Schwarz submitted a paper on anomaly cancellation in superstring theories. String theory had been around for a while, and it had been understood for ten years that it predicted gravity, and was a candidate “theory of everything.” But there were many such candidates, each of which had run into significant difficulties when taken seriously as a theory of quantum gravity. Most people who were paying attention had presumed that string theory would face the same fate, but the Green-Schwarz result convinced them otherwise. A brief article in Physics Today was entitled “Anomaly Cancellation Launches Superstring Bandwagon,” and theorists everywhere jumped to learn everything they could about the exciting new possibilities the theory offered.

So here we are, over twenty years later, still with no surprising new results from particle accelerators (although hopefully that will change soon), and still with strings dominating the landscape (if you will) of theoretical high-energy physics. And still, one hardly needs to mention, with no clear path to connecting string theory to low-energy phenomenology, nor indeed any likely experimental tests of any sort.

In the circumstances, it’s not surprising there would be something of a backlash against string theory. The latest manifestation of anti-stringy sentiment is in two new books aimed at popular audiences: Peter Woit‘s Not Even Wrong: The Failure of String Theory and the Continuing Challenge to Unify the Laws of Physics, and Lee Smolin’s The Trouble With Physics: The Rise of String Theory, The Fall of a Science, and What Comes Next. I haven’t read either book, so I won’t presume to review them, but I think we’ve heard the core arguments expressed on this blog and elsewhere. I’m a firm believer that it’s good to have such books out there; I’m happy to let the public in on our internecine squabbles, just as I’m happy to keep them updated on tentative experimental results and speculative theoretical ideas. It seems unduly patronizing to think that we can’t reveal anything to the wider world until everyone in the community agrees on it.

But I don’t actually agree with what the books are saying. Here is the main point I want to make with this post, trite though it may be: the reason why string theory is so popular in physics departments is because, in the considered judgment of a large number of smart people, it is the most promising route to quantizing gravity and moving physics beyond the Standard Model. I don’t necessarily want to rehash the reasons why people think string theory is promising — I’m not positing an objective measurement of the relative merits, but simply an empirical observation about people’s best judgments. Rather, I just want to emphasize that, when you get right down to it, people like string theory for intellectual reasons, not socio-psycho-political ones. It’s not a Vast String Theory Conspiracy, funded by shadowy billionaires who funnel money through Princeton and Santa Barbara to brainwash naive onlookers into believing the hype. It’s trained experts who think that this is the best way to go, based on the results they have seen thus far. And — here’s the punchline — such judgments could change, if new results (experimental or theoretical) came along to suggest that there were some better idea. The way to garner support for alternative approaches is not to complain about the dominance of string theory; it’s to make the substantive case that some specific alternative is more promising. (Which people are certainly trying to do, in addition to the socio-psycho-political commentating about which I am kvetching.)

That is, after all, the way string theory itself became popular. Green and Schwarz labored for years on a relatively lonely quest to understand the theory, before they were able to demonstrate anomaly cancellation. This one result got people psyched about the theory, and off it went. It’s not a matter of impressionable young physicists docilely obeying the dictates of their elders. Read Jacques Distler’s (absolutely typical) story about how he dived into string theory as a graduate student, despite the fact that his advisor Sidney Coleman wasn’t working on it. In a completely different field, listen to Nobel-winning economist Gary Becker on the response to his ideas (via Marginal Revolution):

“There was a sea change. I began to notice it in the 1970s and 1980s. A lot of the younger people coming out of Harvard, MIT and Stanford were very interested in what I was doing, even though their faculty were mainly – not entirely – opposed to the sort of stuff I was doing.”

This is just how academics act. They are stubborn and willful (even at a charmingly young age!), and ultimately more persuaded by ideas than by hectoring from their elders. And it’s not just the charmingly young — if good ideas come along, supported by exciting results, plenty of entrenched middle-aged fogeys like myself will be happy to join the party. If you build it, they will come.

There’s no question that academic fields are heavily influenced by fads and bandwagons, and physics is no exception. But there are also built-in mechanisms that work to protect a certain amount of diversity of ideas — tenure, of course, but also the basic decentralized nature of university hiring, in which different departments will be interested in varying degrees in hiring people in certain fields. Since the nature of science is that we don’t yet know the right answers to the questions we are currently asking, different people will have incompatible intuitions about what avenues are the most promising to pursue. Some people are impressed by finite scattering amplitudes, others like covariant-looking formulations, others don’t want to stray too far from the data. The thing is, these considered judgments are the best guide we have, even if they are not always right. Green and Schwarz were lonely, but they persevered. If you want to duplicate their success, find a surprising new result! You can’t ask a department to hire people in an area they don’t think is promising, just because it serves the greater goal of diversifying the field overall. Crypto-socialist pinko though I may be in the political arena, when it comes to intellectual life I’m a firm believer in the free market of ideas, and would tend to resist affirmative-action programs for underrepresented theories.

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