Author: Sean Carroll

  • Gabriela Montero

    The bad news is that Rick Warren, author of The Purpose-Driven Life, will be giving the invocation at Obama’s inauguration. A terrible choice; reaching out to evangelicals is fine, but honoring bigoted homophobes is a bad strategy.

    The good news is that pianist Gabriela Montero will be performing at the inauguration! (Along with some other jokers: Aretha Franklin, Yo-Yo Ma, Itzhak Perlman, and Anthony McGill.) Hopefully this prestigious venue will bring an incredibly talented performer to much-deserved wider recognition.

    If you tend not to click on YouTube clips of musicians, you might want to make an exception this time. Here is Montero at a concert in Germany. She asks the audience to suggest a German song for her — “Mer losse de Dom in Kölle,” if commenters are to be believed — and gets them to sing it. She catches the tune (which apparently she’s never heard before), and starts improvising based on it. (There’s not nearly enough improvisation in modern classical music, in my jazz-inflected opinion.) It’s a throwaway, but quite joyous and beautiful. And most of all, fun.

  • Read the Scripts

    ‘Tis the season when various academies, all the way up to the Academy of Motion Picture Arts and Sciences, decide which movies were most deserving of our admiration this year. The studios know this, and make a big push to win awards, which can translate into box office. For example, this being the Age of the Internet, a number of screenplays are available for download online (including some for movies that haven’t quite been released yet). Some interesting choices:

    The Dark Knight

    Vicky Cristina Barcelona

    Frost/Nixon

    The Curious Case of Benjamin Button

    WALL•E

    You might not think that the script for WALL•E would be all that fascinating, since much of the movie was free of dialogue; but you’d be wrong.

    wall-e.jpg

    INT. ABANDONED BNL SUPERSTORE – NEXT DAY

    LOUIS ARMSTRONG’S “LA VIE EN ROSE” PLAYS

    Eve scans through the market.
    Wally follows from a safe distance.
    A stray puppy-dog.

    Eve glances over at him.
    Wally panics.
    Bumps into a RACK OF SHOPPING CARTS.
    Creates an avalanche.

    They chase him down a flight of stairs.
    Wally reaches the exit doors.
    Won’t open!
    Carts pig pile on top of him.

    It’s like a little poem. I laugh just thinking about that scene.

  • Dark Energy: No Longer a Surprise

    A bit of science news: Alexey Vikhlinin and collaborators have used observations from the Chandra X-ray satellite to uncover new evidence for dark energy. (More info here, and the paper is here.) In particular, they simply count the number of galaxy clusters with various masses at various redshifts, and compare with the predictions of models with and without dark energy. If there were no dark energy, matter would keep clustering on larger and larger scales as the universe expanded, making new clusters all the way. But if dark energy eventually takes over, the creation of new clusters begins to turn off, as the dark energy provides an extra push of expansion beneath the feet of the particles that would like to cluster together, preventing them from doing so.

    Just to guide the eye, here are plots of the number of clusters (vertical axis) as a function of their mass (horizontal axis) at two different redshift ranges — near is on top, far is at the bottom. The left plot, which fits the data, has an appreciable cosmological constant; the right one, which doesn’t, doesn’t. The graphs are a bit confusing, because dark energy affects not only the growth of structure, but also the relation ship between redshift and distance. But the point is that dark energy kills off cluster formation at late times.

    cluster-mass-functions.jpg

    You may ask the question: so? Didn’t we find dark energy ten years ago, and haven’t we confirmed its existence several times since? Yes, and yes. In a sense, this result doesn’t teach us anything we didn’t already know.

    But we should resist the temptation to become too blase about the whole thing. (Notwithstanding that I’ve been guilty myself.) On the one hand, this is a new manifestation of dark energy: a dynamical effect on the evolution of matter, rather than simply a background effect on the expansion of the universe. This is of great interest to astronomers, and should help to constrain alternatives to the now-standard picture. But on the other, more important hand, it remains astonishing that we have this preposterous model that keeps fitting the data. We shouldn’t lose our sense of wonder that we’re able to understand as much of the universe as we do, or that the reality of cosmology is so much more interesting than simple theoretical models of the past would have predicted.

    chandra-w-omegax.jpg Here is the graph from the paper showing limits on the equation-of-state parameter, w. Horizontal axis is the fraction of dark energy (about 75%, eventually I’ll have to stop using 70%), vertical axis is w (about -1, plus or minus 0.1). Looks pretty much like a cosmological constant (w=-1) from here, although there is obviously wriggle room.

  • The Category Mistake at the Heart of College Football

    Too many things I would blog about, if only I could slip into an extra timelike dimension and experience several weeks in just a few of your Earth minutes. Between now and New Year’s I’m going to clean out my collection of blog-worthy things; if you’ve read enough of Cosmic Variance in the past, you should be able to extrapolate to a full post.

    Today: “Top Ten Stupidest Arguments in College Football,” which is itself so full of stupid arguments one suspects one is being punk’d. College football is the only major sport that decides who plays in the championship game on the basis of a vote, rather than by a playoff. One can debate the merits vis-a-vis excitement and revenues, but the whole operation is based on an epistemological blunder: the idea that there is something called the “best” team. The point of sports is not that there are better teams and worse teams, it’s that some teams win and some teams lose. Winning and losing is not some approximation to the true measure of excellence that we are forced to put up with; it’s what the games are all about. A sensible world would have a playoff, and let the teams play. (I’ve actually heard people argue that a playoff would be bad idea because the “best” team might not win.)

    (If I could just train myself to make posts that are that short all the time, I’d blog twice as often. Maybe five times as often. Are more/shorter posts better?)

  • If Aliens Decided to Destroy Humanity, Could We Blame Them?

    Friday was the opening of The Day the Earth Stood Still starring Keanu Reeves and Jennifer Connelly; it’s director Scott Derrickson’s remake of the 1951 Robert Wise classic. The previous Friday witnessed our panel discussion at Caltech about how science intersected with the film. Reviews thus far (of both the movie and the panel) have been mixed; personally, I thoroughly enjoyed the panel and thought the movie rose to the level of “pretty good.” (Lost amidst the excitement of aliens and CGI was the excellent acting in the film, including a great performance by Jaden Smith in the role of the petulant stepson.) But it could have been great.

    panel.jpg

    Derrickson refers to his own film as a “popcorn movie with interesting ideas,” and there is certainly nothing wrong with that. The original movie was extremely compelling because it managed to be gripping and suspenseful as a narrative, while also dealing with some very big ideas. In 1951 we had just entered the atomic age, the Cold War was starting, and the Space Race was about to begin (Sputnik was 1957). Moreover, radio astronomy was just taking off, and people were beginning to talk semi-seriously about the search for extraterrestrial intelligence; Fermi introduced his celebrated paradox (“Where are they?”) in 1950. The time was right to put everything together in a compelling movie.

    The threat of nuclear war hasn’t actually gone away — the chance of a nuclear weapon being used within the next decade is probably higher than it was in the 1970’s or 80’s (although perhaps not the 50’s or 60’s). But now we also have the danger of environmental catastrophe, which was alluded to in the movie. But the remake of The Day the Earth Stood Still basically sidestepped questions of international cooperation, which were crucial to the original version. The heady mix of ideas and drama that was waiting to be tapped in 1951 isn’t quite as obvious today.

    Gort
    A huge problem with a remake like this is that the 2008 movie-going audience comes with a very different set of expectations than the 1951 audience would have. We are very used to giant special-effects extravaganzas in which aliens want to destroy the earth, so the conceit itself is not sufficient to keep us interested. And there isn’t that much tension in the question of how the plot will be resolved; I hope I’m not giving away any spoilers by saying that humanity is not destroyed. We know that humanity is going to be saved (although it would be something if it weren’t), so we’re not on the edge of our seat wondering about that. There might be some tension in the particular method by which the saving is accomplished; the original did a great job on that score with the iconic robot Gort, and without giving away anything about the remake I’ll just say that I don’t think they managed to be quite as suspenseful this time.

    But there remains one form of suspense that I thought the film couldn’t have taken advantage of more than it actually did: the questions of why aliens might want to wipe us out, and whether humanity is worth saving in the first place. Judgmental aliens are a staple of science fiction, but how realistic are they?

    To put things in perspective, the universe is 14 billion years old and the Solar System is about five billion years old. Let’s be conservative and imagine that life couldn’t arise around first-generation (Pop II or Pop III) stars, since the abundance of “metals” (to an astronomer, any element heavier than hydrogen or helium) was practically nil. You need at least a second-generation star, formed in a region seeded with the important heavier elements by prior supernova explosions. But nevertheless, it’s still easy to imagine that the aliens we might eventually come into contact with come from a planet that formed life a billion or two years earlier than life began on Earth. Now, a billion years ago, we were still struggling with the whole multi-celluarity thing. So we should imagine aliens that have evolved past our current situation by an amount analogous to which we have evolved past, say, red algae.

    It’s simply impossible for us to accurately conceive what such aliens might be like. (When Jennifer Connelly’s exobiologist asks Klaatu, the alien who has assumed the shape of Keanu Reeves, what his true form is like, he quite believably replies “It would only frighten you.”) It’s completely plausible to imagine that advanced civilizations routinely leave behind their biological forms to dwell within a computer simulation or some other form of artificial substrate for consciousness. As plausible as anything else, really.

    But if they did pay us a visit, is it plausible to imagine that they would want to wipe us out? Since we have no actual experience on which to base an answer, one option is to look at our own history, as the Kathy Bates’s Secretary of Defense does in The Day the Earth Stood Still. The lesson is not cheerful: more powerful civilizations tend to either subjugate less powerful ones, or wipe them out entirely. Okay, you say, but any civilization that is capable of traveling interstellar distances must have figured out how to live peacefully, right?

    Maybe. The problem is, it wouldn’t be a clash of civilizations; more likely, from the aliens’s perspective it would be like the clash of an annoyed homeowner dealing with mildew, or perhaps an infestation of cockroaches if we’re feeling generous. Turning again to experience, human beings are right now causing one of the great mass extinctions in the history of the planet. We could stop killing off other species, but we find that it would slightly cramp our lifestyle to do so, and we decide not to make that sacrifice. True, when we send spaceships to Mars and elsewhere, we are very careful to take steps to ensure that we don’t contaminate any traces of life that might be clinging to the other planet. But clearly, that’s not because we place great value on the continued existence of any one species. Rather, it’s because (to us) any kind of life on another planet would be incredibly unique and interesting. But there’s no reason to believe that we would be all that unique from the perspective of a galaxy-weary alien civilization. They may well have bumped into millions of worlds featuring all sorts of life. If we’re lucky, they might give us the respect that a human being would show an ant colony or a swarm of bees. If we’re lucky.

    This is an area in which science fiction, for all its vaunted imagination, is traditionally quite conservative. With some notable exceptions, we tend to assume that the forms life can take are neatly divided into “intelligent species” and “everyone else,” and we are snugly in the former category, and all intelligent species are roughly equally intelligent and it’s just a matter of time before we get our own seat in the Galactic Parliament. Although SF offers a unique opportunity to examine the way we live as humans in comparison to different ways we might live, the usual answer it gives is that the way we’re living now is pretty much the best we can imagine — alien lifestyles are much more often portrayed as profoundly lacking in some crucial feature of individuality or passion than they are as a real improvement over our current messy situation. We are special because we love our children, or because we are plucky and have so much room for improvement. We voted for Obama, after all. I bet there aren’t many alien civilizations that would have done that!

    So basically, I’m suggesting that this is a film that would have been improved by the addition of a few imaginative philosophical debates. You don’t want to be didactic or tiresome, but those are not necessary qualities of a discussion of deep ideas. If the ideas are interesting enough, they might even improve your box office.

  • Worst Predictions of the Year

    Foreign Policy has compiled a list of the Ten Worst Predictions for 2008. You’ll be happy to hear that physics has made the cut!

    “There is a real possibility of creating destructive theoretical anomalies such as miniature black holes, strangelets and deSitter space transitions. These events have the potential to fundamentally alter matter and destroy our planet.” —Walter Wagner, LHCDefense.org

    Scientist Walter Wagner, the driving force behind Citizens Against the Large Hadron Collider (LHC), is making his bid to be the 21st century’s version of Chicken Little for his opposition to the world’s largest particle accelerator. Warning that the experiment might end humanity as we know it, he filed a lawsuit in Hawaii’s U.S. District Court against the European Organization for Nuclear Research (CERN), which built the LHC, demanding that researchers not turn the machine on until it was proved safe. The LHC was turned on in September, and it appears that we are still here.

    Admittedly, FP didn’t get it quite right — as loyal readers know, it’s something of an exaggeration to say that the LHC was “turned on in September.” Protons circulated around the ring, but there were no collisions, and there won’t be until later this year. Still, they were right about the wrongness. The LHC is perfectly safe.

    The other predictions were also amusing. Here’s my favorite:

    “If [Hillary Clinton] gets a race against John Edwards and Barack Obama, she’s going to be the nominee. Gore is the only threat to her, then. … Barack Obama is not going to beat Hillary Clinton in a single Democratic primary. I’ll predict that right now.” —William Kristol, Fox News Sunday, Dec. 17, 2006

    Weekly Standard editor and New York Times columnist William Kristol was hardly alone in thinking that the Democratic primary was Clinton’s to lose, but it takes a special kind of self-confidence to make a declaration this sweeping more than a year before the first Iowa caucus was held. After Iowa, Kristol lurched to the other extreme, declaring that Clinton would lose New Hampshire and that “There will be no Clinton Restoration.” It’s also worth pointing out that this second wildly premature prediction was made in a Times column titled, “President Mike Huckabee?” The Times is currently rumored to be looking for his replacement.

    Of course, asking Bill Kristol to predict the future is like asking Rod Blagojevich to head a good-government task force. Here’s my prediction: Kristol will continue to say dumb things, next year and far into the future. And get paid handsomely for doing so.

  • Steven Chu Nominated to be Secretary of Energy

    Steven Chu This is fantastic news. Steven Chu, director of the Lawrence Berkeley National Lab and 1997 Nobel Laureate in Physics for his work in laser cooling of atoms, has been nominated to be the next Secretary of Energy in the Obama administration. (Thanks to Elliot in comments.) This post is enormously important for science in general and physics in particular, as the DOE is responsible for much of the funding in physics and a lot of other R&D work. It’s also, needless to say, a crucial position for determining the country’s energy policy at a time when strong and imaginative leadership in this area is crucial.

    I can’t imagine a pick for the job that would make me happier. Obviously Chu is a Nobel-prize-winning physicist, which is not bad. Almost as obviously, he’s an incredibly smart and creative guy. For evidence, look no further than his group’s web page at LBL. You’ll see atomic physics, for which he won the Nobel, but there are also very serious efforts in biophysics and polymer science, just because he thinks those things are interesting. (Apparently he has not devoted much thought to advanced HTML design.) I got to talk with him at the launch event for the Science and Entertainment Exchange — he also cares about the public perception of science — and it’s clear that he has a wide-ranging, creative intellect, which is what we need to tackle the problems of energy production over the years to come. Chu has recently become intensely concerned about the challenge of global warming, and is serious about doing something to fix things. He and Craig Venter are teaming up to make microorganisms that turn carbon dioxide into strawberry ice cream, or something like that. I wouldn’t bet against them.

    Let’s be clear: just because Chu is an accomplished physicist, this doesn’t mean that researchers should expect a bonanza of new funds. The previous administration has left the budget and the economy in shambles, and nominating a Nobel Laureate to head DOE doesn’t magically bring new money into existence. But it means the hard choices that inevitably will be made will be made intelligently by people who understand the significance of what is going on. We can never ask for more than that.

    Here is Steven Chu talking about Science Debate 2008. Berkeley’s loss is Washington’s gain, but in this case the country will be better off for it.

  • Elevator Pitches: Time for Focus-Group Input

    If you spend a lot of time in the MGM Grand in Vegas (and who doesn’t?), you will have walked by Television City. It’s a fun place to get some free entertainment if the craps tables have been unkind (or if you had a great meal at Joel Robuchon), but it’s serious business for CBS/Viacom: this is where they show clips and pilots of prospective shows to average Americans, to gauge whether they should be picked up for seasons to come. Apparently it’s easier to find average Americans in Vegas than over here in LA.

    So here’s your chance to chime in on our contest to choose a science-themed TV show. Recall that the idea behind the elevator pitch contest was that you had bumped into CBS bigwig Les Moonves, and taken the opportunity to quickly pitch a TV idea that made use of science in some way. While you might have thought that Mr. Moonves was just humoring you, in fact he took some of the ideas very seriously, and ultimately picked six of them to make pilots of each. Sadly, we don’t have clips from the actual pilots; something about intellectual property rights. But here are the original descriptions of the six finalists; note that CBS has tentatively assigned names to each show.

    Below the fold there is a poll, where you can vote on which show you like the best! Voting will be open for the next week. For the winner, a T-shirt, and who knows? Some people in high places read this blog.

    1. New Horizons (Jason Dick)

      Takes place about a century from now. Humanity has discovered planets around other stars harbor life. We send out a generation ship, where multiple generations of intrepid explorers will be born and die before it reaches its destination. This show follows their journey, where they are faced with mechanical failure, collisions with small dust grains that cause lots of damage, and people who crack under the stress of their situation. Mostly it’d be about a human drama of extremely driven people who are in a difficult situation, and whose children are forced to carry the torch of their parents.

    2. Three Geeks in Boston (Naveen)

      Three guys share an apartment in Boston: a freelance writer training for an ultramarathon, a chemistry student who wants to work in a Michelin star restaurant, and a disillusioned theoretical physicist in grad school. The runner views himself as a lab rat and writes about his experiments with the latest training gadgets and techniques. The chemist hopes that molecular gastronomy will be his path to a dream job with Heston Blumenthal or Grant Achatz. The theoretician realizes how his math can be applied to topics ranging from tracking flu epidemics to studying the sociology of Facebook.

    3. The Parameters (astromcnaught)

      An enormous laser experiment blows a hole in local space-time. Things start to behave strangely, and hilariously, the world over. Young Ruford with the assistance of a mysterious mechanics professor has to adjust the parameters of reality back to normal. Different parameter each week. E.g. speed of sound drops to 1 meter a minute. Something electromagnetical causes clothes to start becoming transparent. Gravity becomes stronger…the world starts spinning faster…the moon draws closer…air becomes thicker…ice sinks. The dog’s called Rhombus.

    4. The Scientific Inquisitor (Matt)

      A lapsed cardinal with a rigorous scientific background is called back into service by the Pope. When the vatican is under pressure to bestow sainthood on a politically inconvenient deceased priest, they dispatch the show’s hero. Our cardinal has secret instructions to debunk the would-be saint’s requisite “miracles”, thereby denying sainthood. He does so with scientific acumen and great aplomb. Each week, he struggles with being used by an organization he doesn’t respect, as well as his own emotional desire to believe in something beyond the cold materialism he practices. Both cynical and hopeful, the show illuminates the boundary between evidence and faith, in a (perhaps Sisyphean) struggle to find a balance between the two.

    5. Friends with Experiments (Peggy)

      Friends in a top university molecular biology lab. Three young men and three young women – a couple of postdocs, grad students, a Sigma sales rep and a departmental administrator – find love and laughs as they run gels, hang out in the departmental lounge, attend conferences, and interact with the other wacky lab denizens. Plenty of opportunity for sight gags, such as an unbalanced ultracentrifuge “walking” through a wall or the noob grad student accidentally setting her bench on fire. And lots of opportunities for romantic situations: all-night sample collecting in the cold room, working closely in the darkroom, or a mixup that puts our male and female postdoc in the same hotel room at the AAAS conference. And what holds them together is their love/hate relationship with their research.

    6. Apocalypse Tomorrow (Dr. Free-Ride)

      The economy has tanked and modern infrastructure (utilities, highways, food supplies, schools) is decaying – “pre-apocalypse”. We focus on a couple who left science a decade ago, moving to a small town for a new start. Their kids keep stumbling into sciencey situations, drawing their parents into them. Their town has a distinct anti-science vibe — science and technology didn’t hold off the decay gripping the community, and (we find out) the town is still scarred by tragic events due to mad scientists. Despite themselves, our family uses scientific reasoning and keen observation to rebuild the community and their own lives.

    Click to get to the poll and cast your vote… (more…)

  • Ripples in the Aether

    Prior to Einstein, physicists believed that light waves, like water waves, were ripples in a medium: instead of the ocean, they posited the existence of the luminiferious aether, some form of substance which supported the propagation of electromagnetic waves. If that idea had been true, one would imagine there would be a unique frame of reference in which the aether was at rest, while it was moving in other frames; consequently, the speed of light would depend on one’s motion through the aether. This idea was basically scotched by the Michelson-Morley experiment, which showed that the speed of light was unaffected by the motion of the Earth around the Sun. The idea was eventually superseded by special relativity, although (as with most interesting ideas) some adherents gave up only reluctantly. Indeed, if you had asked Hendrik Antoon Lorentz himself about the meaning of the famous Lorentz transformations he invented, he would not have said “they relate physical quantities measured in different inertial frames”; he would have said “they relate quantities as measured in some moving reference frame to their true values in the rest frame of the aether.”

    We know a lot more about field theory as well as about relativity these days, so we don’t need to invoke a concept like the aether to explain the propagation of light, and the idea that there is no special preferred frame of rest has been experimentally tested to exquisite precision. But precision, even when exquisite, is never absolute, and important discoveries are often lurking in the margins. So it’s interesting to contemplate the possibility that there really is some kind of field in the universe that defines an absolute standard of rest, within the modern context of low-energy effective field theories. Instead of a light-carrying medium, we are interested in the possibility of a Lorentz-violating vector field — some four-dimensional vector that has a fixed non-zero length and points in some direction at every event in spacetime. But the name “aether” is too good to abandon, so we’ve re-purposed it for modern use.

    A lot of work has gone into exploring the possible consequences and experimental constraints on the idea of an aether field pervading the universe (see reviews by Ted Jacobson or David Mattingly, or Alan Kostelecky’s web page). But the ideas are still relatively new, and there are still questions about whether such models are fundamentally well-defined. Tim Dulaney, Moira Gresham, Heywood Tam and I have been thinking about these issues for a while, and we’ve just come out with two papers presenting what we’ve worked out. Here is the first one:

    Instabilities in the Aether
    Authors: Sean M. Carroll, Timothy R. Dulaney, Moira I. Gresham, Heywood Tam

    Abstract: We investigate the stability of theories in which Lorentz invariance is spontaneously broken by fixed-norm vector “aether” fields. Models with generic kinetic terms are plagued either by ghosts or by tachyons, and are therefore physically unacceptable. There are precisely three kinetic terms that are not manifestly unstable: a sigma model $(partial_mu A_nu)^2$, the Maxwell Lagrangian $F_{munu}F^{munu}$, and a scalar Lagrangian $(partial_mu A^mu)^2$. The timelike sigma-model case is well-defined and stable when the vector norm is fixed by a constraint; however, when it is determined by minimizing a potential there is necessarily a tachyonic ghost, and therefore an instability. In the Maxwell and scalar cases, the Hamiltonian is unbounded below, but at the level of perturbation theory there are fewer degrees of freedom and the models are stable. However, in these two theories there are obstacles to smooth evolution for certain choices of initial data.

    As the title says, here we’re investigating whether aether theories are stable. That is, when you have the vector field in what you think should be the “vacuum” state, with all of the vectors aligned and nothing jiggling around, can a small perturbation lead to some sort of runaway growth, or would it just oscillate peacefully? If you do get runaway behavior, the theory is unstable, which is bad news for thinking of the theory as a sensible starting point for experimental tests. This is one of the first questions you should ask about any theory, and it’s been investigated quite a bit in the case of aether. But there is a subtlety: because you have violated Lorentz invariance, it’s not enough to check stability in the aether rest frame, you need to do it in every frame. (A perturbation caused by a source moving rapidly in a rocket ship is still a legitimate perturbation.) What we found was that almost all aether theories are unstable in some frame or another. There are just three exceptions, which we called the “sigma model” theory, the “Maxwell” theory, and the “scalar” theory.

    You might ask, what is this talk about “theories”? Why is there more than one theory? For a vector field, it turns out that there are a number of different quantities you can define (three, to be precise) that might play the role of a “kinetic energy.” So we study a three-dimensional parameter space of theories, corresponding to any possible mixture of those three quantities. The three theories we pick out as stable are simply three specific mixtures of the different kinds of kinetic energy. The Maxwell theory is very similar to ordinary electromagnetism, while the scalar theory more closely resembles a scalar field than a vector field.

    The other theory is actually our favorite, as both the Maxwell and scalar cases seem to have potential lurking pathologies that we can’t completely get rid of (although the situation is a bit murky). So we wrote a shorter paper examining the empirical behavior and constraints on that model:

    Sigma-Model Aether
    Authors: Sean M. Carroll, Timothy R. Dulaney, Moira I. Gresham, Heywood Tam

    Abstract: Theories of low-energy Lorentz violation by a fixed-norm “aether” vector field with two-derivative kinetic terms have a globally bounded Hamiltonian and are perturbatively stable only if the vector is timelike and the kinetic term in the action takes the form of a sigma model. Here we investigate the phenomenological properties of this theory. We first consider the propagation of modes in the presence of gravity, and show that there is a unique choice of curvature coupling that leads to a theory without superluminal modes. Experimental constraints on this theory come from a number of sources, and we examine bounds in a two-dimensional parameter space. We then consider the cosmological evolution of the aether, arguing that the vector will naturally evolve to be orthogonal to constant-density hypersurfaces in a Friedmann-Robertson-Walker cosmology. Finally, we examine cosmological evolution in the presence of an extra compact dimension of space, concluding that a vector can maintain a constant projection along the extra dimension in an expanding universe only when the expansion is exponential.

    Even this theory, as interesting as it is, is plagued by a problem. In the spirit of low-energy phenomenology, we basically fix the length of the vector field by hand. But we recognize that in a more complete description, there is probably some potential energy that gets minimized when the vector takes on that value. But if you allow for any variation whatsoever in the length of the vector, you are immediately confronted with a dramatic instability once more.

    So, to be honest, there are no aether theories that we can guarantee are perfectly well-behaved, even as low-energy effective theories. (All the problems we identify exist at arbitrarily low energies, and don’t rely on the short-distance behavior of the models.) The three theories to which we gave names are problematic but not manifestly unstable, so it will be worth further investigation to see if they can be patched up and made respectable.

  • Science and Culture at the White House

    It’s going to feel so good to have a real grown-up as President.

    “Part of what we want to do is to open up the White House and remind people this is the people’s house,” Obama told NBC’s Tom Brokaw during a “Meet the Press” interview taped Saturday in Chicago…

    The president-elect said his administration is interested in “elevating science once again, and having lectures in the White House where people are talking about traveling to the stars or breaking down atoms, inspiring our youth to get a sense of what discovery is all about.”

    “Thinking about the diversity of our culture and inviting jazz musicians and classical musicians and poetry readings in the White House so that once again we appreciate this incredible tapestry that’s America,” he said.

    “Historically, what has always brought us through hard times is that national character, that sense of optimism, that willingness to look forward, that sense that better days are ahead,” Obama said. “I think that our art and our culture, our science–you know, that’s the essence of what makes America special, and we want to project that as much as possible in the White House.”

    I’m looking forward to having new results from the LHC explained at the White House and broadcast on C-SPAN.

    Relatedly, Dreams from My Father is an impressive book, well worth reading if you haven’t already. Impressive not only for its content and candor, but because the guy can flat-out write — he turns a phrase masterfully, but also has a talent for finding the illuminating perspective or a telling anecdote. And he has a writer’s appreciation for ambiguity. Not always a good feature in a politician.

    Obama was something unusual in a politician: genuinely self-aware. In late May 2007, he had stumbled through a couple of early debates and was feeling uncertain about what he called his “uneven” performance. “Part of it is psychological,” he told his aides. “I’m still wrapping my head around doing this in a way that I think the other candidates just aren’t. There’s a certain ambivalence in my character that I like about myself. It’s part of what makes me a good writer, you know? It’s not necessarily useful in a presidential campaign.”

    After eight years of unshakable certainty, I’ll take it.