Miscellany

I tend to travel a lot for work purposes, spreading the word about the accelerating universe to rapt audiences across the country. And I like the travel, and enjoy giving the talks, especially to people who are still skeptical about this whole dark-energy thing and appreciate a balanced telling of the story. But it does take time, and I am not an efficient traveler; on flights I am more likely to curl up with a good novel than to pull out the laptop and work on a paper or a referee report. So I promised myself that I would do no more than two trips per month from now on. As it turns out, in the next five weeks I will be visiting Boston (Brandeis), Tucson (University of Arizona), Urbana-Champaign, Philadelphia (University of Pennsylvania), Baltimore (Johns Hopkins), Pasadena (Caltech), and San Diego (UCSD). So you can judge for yourself how successful I’ve been at keeping my own promise.

It’s a shame in a way, because this is my favorite time of year to be on campus. For one thing, September is a little oasis of calm in Chicago’s playfully rambunctious weather patterns, and the lake and the sky are glowing magnificently. But at any university, it is always a thrill to see the campus come alive with the students returning (or arriving for the first time) after the summer exodus. We start late at Chicago because we’re on a quarter system, with one quarter before New Year’s and two after, so this week is actually the first week of school. I’m teaching Physics 300, “The Teaching and Learning of Physics,” a required course for first-year graduate students in which we help them learn how to be good teachers. It’s great for the students, if only because it conveys the impression that the department cares about the quality of teaching. (Sadly, we cannot force the faculty to take the course.) And it’s great for me, as I get to meet all of the new graduate students. They are full of enthusiasm spiced with trepidation, and contemplating hard questions like whether they should refer to professors by their first names. (Answer: yes, but with exceptions, and the rules concerning exceptions can only be learned from experience.)

Speaking of traveling: a common prediction of technological triumphalists is that easy access to computers and comprehensive connectivity will eventually do away with the notion of a “conference” at which people physically assemble. From the evidence of the recent DPF meeting I attended, the reality is precisely the inverse. Conferences will continue as scheduled, but members of the assembled audience will each sit with their laptops open, connected through their wireless links to the internet, ignoring the speaker as they always have. The flaw in the triumphalists’ prediction is the assumption that people don’t like to travel, they just want the content you get from the conference talks. It’s just the opposite: people do like to travel, and especially to shmooze at the coffee breaks, but they hate to be stuck in talks. Now that technology has liberated us from that onerous requirement, conferences will become more popular than ever. At the end of each talk, of course, some member of the audience will still ask a question that is really more of a comment.

An interesting contrast comes to light by jumping around the blogosphere (kind of like playing your CD’s on “shuffle”).

• From Anomalous Data, via Pandagon and Pharyngula: If you strip the candidates of personality and presentation, leaving only issues, you get overwhelming support for Kerry.
• From Stanley Fish (writing in the New York Times) via Karl Fornes: If you completely ignore substance and look only at the clarity with which ideas are being articulated, you get overwhelming support for Bush.

The target audiences were upper-class 11-year-old schoolchildren in the first case, and University of Illinois at Chicago undergraduates in the second case, but that hardly seems to matter.

The good news is: Kerry’s problem would seem to be more easily correctible than Bush’s (we hope).

By Adrienne Rich:

Thinking of Caroline Herschel (1750-1848), astronomer, sister of William; and others.

A woman in the shape of a monster

a monster in the shape of a woman

the skies are full of them

a woman         ‘in the snow

among the Clocks and instruments

or measuring the ground with poles’

in her 98 years to discover

8 comets

She whom the moon ruled

like us

levitating into the night sky

riding the polished lenses

Galaxies of women, there

doing penance for impetuousness

ribs chilled

in those spaces         of the mind

An eye,

        ‘virile, precise and absolutely certain’

        from the mad webs of Uranusborg

                      encountering the NOVA

every impulse of light exploding

from the core

as life flies out of us

        Tycho whispering at last

        ‘Let me not seem to have lived in vain’

What we see, we see

and seeing is changing

the light that shrivels a mountain

and leaves a man alive

Heartbeat of the pulsar

heart sweating through my body

The radio impulse

pouring in from Taurus

        I am bombarded yet         I stand

I have been standing all my life in the

direct path of a battery of signals

the most accurately transmitted most

untranslatable language in the universe

I am a galactic cloud so deep         so invo-

luted that a light wave could take 15

years to travel through me         And has

taken         I am an instrument in the shape

of a woman trying to translate pulsations

into images         for the relief of the body

and the reconstruction of the mind.

This is fun, I may just turn this into a poetry blog.

Something I didn’t get around to in last week’s discussion of dark energy and its equation of state parameter was the question of priors — i.e., what do we expect the parameter to be? Physically, this is equivalent to asking how we expect the dark energy to evolve with time, if at all.

We have to admit that there is one special value that the equation of state parameter w might have: namely, w=-1, corresponding to a dark energy density that is strictly constant (equivalent to vacuum energy or Einstein’s cosmological constant). In that case, the dark energy is simply a constant amount of energy that is inherent in each cubic centimeter of spacetime. Any other possibility means that the dark energy density is dynamical, and is presumably obeying some equations of motion. In the comments, Serenus was hoping that I would encourage people to be completely open-minded, and not favor w=-1 over any other value; rather, just collect the data and take the results at face value. In other words, he wants a uniform prior, in which the a priori probability of w=-1 is the same as w=-0.99 or w=-1.01.

Although I hate to disappoint anyone, I can’t agree. The reason is pretty straightforward; I think it was Tolstoy who said, “Cosmological constants are all alike; every model of dynamical dark energy is dynamical in its own way.” Tautological enough, but it points to an important feature of dynamical dark energy candidates — because they have more features than simply their energy density, there are more ways they could be detected and thus more parameters you need to fine-tune to explain why we haven’t noticed them yet.

The simplest example of dynamical dark energy (although by no means the only interesting one) is quintessence, a light scalar field gradually rolling down a potential. Since the field is rolling slowly, the kinetic energy is extremely small and the potential is nearly constant, giving us a nearly-constant energy density, which is just what you want for dark energy. But as soon as you allow for dynamics in this way, there are things you need to explain. For any dark-energy candidate, you need to explain why the energy density is small. But for quintessence, you also need to tell me why it is rolling so slowly; this translates into the fact that the potential must be very shallow, which then translates into the fact that the mass is very small. (The mass is a measure of the curvature of the potential; this is not exactly the same as the slope, but they should be related unless you want to do even more fine-tunings.) In particle physics, masses of scalar fields tend to be very large. The Higgs boson purportedly has a mass of order 10¹¹ electron volts, and a big problem (the “hierarchy problem”) is why this number is so much smaller than the Planck scale, 10²⁷ electron volts.

The quintessence field, meanwhile, would have to have a mass of order the present Hubble constant, about 10^-33 electron volts. So if 10¹¹ electron volts is very small, how do we hope to explain 10^-33 electron volts?

Once you know the mass is so small, you realize that low-mass particles tend to give rise to observable long-range forces. The two forces we know from our macroscopic experiences are gravitation and electromagnetism, mediated by two zero-mass particles (the graviton and the photon); the nuclear forces are less manifest because they are such short-range. So the quintessence field should give rise to an observable, long-range “fifth force.” The typical way out of this conundrum is to simply declare by hand that the new quintessence field doesn’t interact with ordinary matter, so we can’t feel the force. But this is a cheat; we know that quintessence interacts with gravity, and gravity interacts with ordinary matter, and the miracle of quantum field theory tells us that if A and B both interact with C, then A and B will interact with each other. We can even estimate the strength of this interaction, imagining that it is suppressed by the Planck scale. Then we go look for it, for example in the delicate torsion-balance experiments at the University of Washington. The idea is that the strength of the quintessence force will necessarily be different for objects of different compositions; it’s a rule that only gravity can couple to objects in a way that is completely indifferent to what they are made of. So by looking for tiny anomalous accelerations of, say, Aluminum and Copper in the direction of the Sun, we can put limits on the strength of any purported new long-range forces.

The answer is that we don’t see any such forces, at least not yet. From the upper limits we currently have, the forces must be about 10^-5 times less than what you might have expected. That’s pretty small, although not so small (especially given the roughness of the theoretical estimate) that there’s no reason to keep looking.

What’s more, there is another way to constrain the direct interactions of quintessence. If you have a scalar field that is slowly evolving as the universe expands, all of the “constants of nature” tend to change along with it. That’s because what we think of as constants of nature, like the mass of the up quark or Newton’s constant of gravitation, are actually parameters that depend on the quantum state of the universe (just as the speed of sound depends on properties of the medium through which it is traveling). This is interesting, because there are claims that the fine-structure constant, which determines the strength of the electromagnetic interaction, has actually been experimentally observed to be varying with time. Now, to be honest, these measurements are very hard to do, and people have obtained conflicting results, and the most likely situation is that the experiments are simply in error. So there is some possibility that we have actually already detected the signature of quintessence in a time-variation of the fine structure constant, but it’s somewhat safer to simply imagine that we’ve put a good upper limit on any such variation.

All of the above gives some reason to think that a constant vacuum energy is preferable to dynamical dark energy, simply because it makes more sense that we haven’t yet detected any direct interactions (because constant vacuum energy doesn’t have any). This is not really the same thing as just using Occam’s Razor, which is an important principle but usually only reliable when everyone already agrees on what the correct answer is.

Of course, the idea that dynamical dark energy is a simple scalar field is a nice one, but not unique; there are other possibilities. An especially exciting possibility is that the dark energy does have non-trivial interactions, but only with hard-to-detect particles like dark matter or neutrinos. But the moral of the story remains: once you admit the possibility of dynamics, the models generally allow for all sorts of ways to detect them in principle, and you have to do more fine-tunings to explain why the dark energy hasn’t been seen directly. The idea of an absolutely constant vacuum energy (w=-1) is the simplest and most robust; it’s therefore perfectly permissible to imagine that it’s a little more likely than the other possibilities. Personally, I give about a 10% chance that the dark energy is dynamical. But it’s a testable hypothesis, and if you find some variation then you get in line for the Nobel Prize. So even if it’s something of a long shot, it’s well worth looking for.

The latest Tangled Bank is now up at Lean Left. TB is a collection of the (self-nominated) best science writing in the blogosphere over the previous couple of weeks. This edition is especially strong on bugs, in various senses of the word.

The next Tangled Bank will be hosted right here at Preposterous Universe on October 6th. All you have to do is email me (carroll@theory.uchicago.edu) with a pointer to an interesting science-oriented post you have recently written, and our world-class panel of experts will make an impartial determination of your worthiness as a scientist, a blogger, and a human being (not necessarily in that order). If you are fortunate enough to pass through this rigorous screening process, you just may be included in the upcoming edition. (Sure, if you read the ground rules, you might get the impression that it’s pretty easy to get accepted into the lofty company of Tangled Bank authors. Don’t get complacent, that’s all I’m saying.)

The Tangled Bank idea was originated by the redoubtable PZ Myers, and there was a natural slant towards things biological in the early days. (More recently it has been hosted by ornery liberals, a phenomenon still imperfectly explained.) But participation is wide open to those of us in the less squishy sciences, and I want you physicists out there to represent. If you don’t volunteer I may have to hunt you down. Let’s show the world that we can be lucid and enthusiastic explainers of recondite ideas, not merely the flamboyant show-offs that unfair stereotypes so often paint us to be.

Also, I’m thinking of instituting a dress code.

I thought I would try to draw some traffic by having a provocative title for folks out there using RSS readers and whatnot. But it’s true, I have proof:

• Among men nationwide, 51% say they would vote for Bush and 42% say they would vote for Kerry.
• Among women nationwide, 42% say they would vote for Bush and 50% say they would vote for Kerry.

Okay, got that out of my system. Science forthcoming.

Daniel Drezner looks at Russia and Pakistan and wonders whether the Bush administration isn’t really committed to democracy-promotion after all.

Notwithstanding my political leanings and well-documented opinions about the President, I really do try (like John Rawls with his philosophical predecessors) to give people the benefit of the doubt, imagining that their hearts are in the right place even if perhaps we differ on certain particulars of strategy. And I make a good-faith effort to steer away from the far fringes of cynicism and paranoia. (Readers are welcome to comment on my success.)

But the following thought experiment occurred to me: Imagine that we were governed by an administration that was truly driven by absolutely nothing other than a desire to increase the wealth of the very wealthiest Americans. They don’t care about democracy, terrorism, other countries, any of that. Perhaps they give lip service to such goals as a way of promoting their central agenda, but only for reasons of practical politics. Just imagine how they would act.

Now that you’ve finished imagining — is there way in which the actions of such an administration would be incompatible with the acts of the actual administration currently in power? Any way at all? (I’m open to the possibility that there are, let me know if there’s something obvious that I’m missing.)

For extra credit, discuss the conclusions that would be drawn from this thought experiment by a Comtean positivist, a Machiavellian realist, a Deweyan pragmatist, and a Popperian natural scientist.

Tony Auth:

Tom Toles:

Ben Sargent:

In honor of Ye Olde Phart, who is going on vacation (hopefully temporarily).

Fafblog! has another hard-hitting political interview, this time with that wacky duo, God and Satan.

FB: What can we do to make sure that American politics is Godly politics?
GOD: Vote for Godly Republicans, like Tom Coburn and Alan Keyes! You will know them by Mine mark: they will be alight with the Holy Spirit, and shall speak in strange tongues – equating the estate tax with slavery, and calling for the death penalty for doctors who perform abortions on rape victims!
SATAN: No, Fafnir, listen to me, and be seduced to the Dark Side by my vile policies of nuclear non-proliferation, equality of all citizens, and fiscal discipline! BLAAARRRRHHH!

(Is it me, or does Satan sound like Howard Dean?)

But the best part was the link to the always-zany Presidential Prayer Team. With the power of prayer on their side, the visionaries at the PPT are never afraid to confront the difficult questions that bedevil those of us of lesser virtue. Consider for example today’s PPT Poll Question: “Have you, personally, grown spiritually stronger since September 11, 2001?” Happily, we click on the link to discover … Yes! Most of us have grown stronger! Only a tiny fraction have declined, or merely maintained their previous level of spiritual strength (no distinction between these two possibilities was made in the poll). And perhaps they clicked the wrong choice by accident (for example, if they were from Florida).

We fear, naturally, the creeping menace of sample bias — perhaps only PPT visitors have grown spiritually stronger? What if the rest of the country has weakened in the face of adversity? Pray harder!

Leave it to Umberto Eco to draw together the recurring themes of the humble blog before you. From Arts and Letters Daily, a link to a rumination by Eco on Stephen Hawking’s recantation of his previous stance that black hole evaporation destroys information. Eco uses the occasion of Hawking’s flip-flop to draw a distinction between science and idealistic philosophy. (Thanks to Norman Graf for the last link.)

It’s a distinction well worth drawing. One of the reasons why it’s hard to define “science” is that the nature of scientific theories keeps changing, with concurrent debates about what really counts as scientific (e.g., whether entities we can never in principle observe should be part of a respectable scientific theory). But the distinguishing feature of science is not the theories it produces, but the methodology it uses for getting there. Eco labels the crucial feature of this methodology “provando e riprovando,” Italian for “try and try again.” That is to say, we propose all sorts of ideas, not because we have convinced ourselves that they are right, but because we don’t know what is right and we’re searching through all of the possibilities. Ultimately, agreement with the data will be the deciding factor, and often we can be very surprised at what kinds of theories come out on top (quantum mechanics being the most notable example.)

This strategy is something that non-scientists have trouble really believing in, even those who rub up against science every day. For example, I have been heavily involved in studying models of dark energy, or more broadly why the universe is accelerating. One idea that received some attention is the possibility that Einstein was wrong, and we have to modify gravity on cosmological scales. In talking to journalists, they would often ask me to explain why my theory was better than the alternatives. I had to explain that I didn’t think it was better than the alternatives — it was interesting and provocative, and it had a chance of being correct, but I didn’t necessarily believe that it had a better chance than anything else. We don’t only propose ideas we are convinced are right; we propose lots of things and let the chips fall where they may.

Even scientists and other academics don’t always quite get the idea. I recall a talk given by an evolutionary psychologist, about the new center he was trying to found. The point of this center, according to his conception, was to demonstrate how important behaviors can find their explanations in the evolution of adaptive strategies. This is a terribly depressing mistake; the point of science is never to “demonstrate” anything, it’s to sift through the interesting alternatives and decide which works the best, keeping an open mind at all times. (There is some art, to be sure, in deciding which alternatives are even worth our attention, and at what point a question can be considered to be satisfactorily settled.) If the “physics envy” felt in other disciplines were directed toward this kind of open-minded methodology, rather than to the impressively quantitative final products of physics, the world would be a better place.

It’s not a coincidence, of course, that Eco also wrote the article on fascism that I commented about a sort while back. Nor is it a coincidence that scientists are especially riled up by the transgressions of the Bush administration (much more so than their general liberal tilt can explain). The distrust of indecision and ambiguity that is a hallmark of our current administration is an especially anti-scientific attitude. So you see, the science and politics posts here at Preposterous do share deep connections. Still no explanation for the posts about poker.