Archive for September, 2009

Explaining the Arrow of Football

By Sean Carroll | September 28, 2009 8:44 am

Not sure which blogs the editors of the Onion have been reading, but I have to approve of their proposed model for explaining the low entropy at the beginning of a football game by recourse to an infinite series of downs before “first down.”

NEW YORK — Citing the extremely low level of entropy present before a normal set of football downs, scientists from the NFL’s quantum mechanics and cosmology laboratories spoke Monday of a theoretical proto-down before the first. “Ultimately, we believe there are an infinite number of proto-downs played before the first visible snap,” lead NFL scientist Dr. Oliver Claussen said during a press conference, adding that the very last yocto-down is a by-product of leftover fourth downs from this universe, as well as those from a theoretical universe running along an arrow of time concurrent to our own.

Probably some enthusiastic football coach is going to try to cash in by writing a book about the idea, while others fulminate on the sidelines about how such irresponsible speculation is destroying the game. (Thanks to Ahmet Toker and Tom Fishman.)


Open the (Virtual) Lab

By Sean Carroll | September 28, 2009 7:37 am

A quick reminder to submit your favorite blog posts to this year’s incarnation of Open Lab, the anthology of the best science blogging. (Printed on honest to goodness dead trees, suitable for placing on bookshelves.) You can also buy copies of the editions for 2006, 2007, and 2008. This year’s editor is Scicurious of the Neurotopia blog. There is already a formidable list of nominees, but they could always use more. Submission form is here; if you’re a blogger, feel free to submit your own best stuff, and if you’re a blog reader, make sure none of your favorite posts are being ignored.


Friday Ninja Cat Blogging

By Sean Carroll | September 25, 2009 7:57 am

I would not want to live in the same house as this cat. It’s a silent assassin. Via Cynical-C.


Atheism: Bringing the Sexy Back

By Sean Carroll | September 24, 2009 11:34 am

It would be amusing to just have a contest asking people to guess what the vertical axis on this chart is supposed to represent.


The answer is, “reply rate to first-contact messages on an online dating site, as a function of words appearing in the message.” In particular, the site OkCupid, which has a handy rundown of which words and phrases are most likely to garner a reply to an initial contact. (Via FlowingData.) The average response rate is 32%, so you can see how using some specific word increases or decreases your chances of success. Apparently mentioning “God” is a big turn-off, although calling Him by a proper name is slightly helpful. But nothing works at turning a stranger’s head quite like bringing up His complete lack of existence.

Other useful hints: real words good, fake internet words bad. Complimenting personality/intellect good, complimenting looks bad. Being specific is good, especially if it involves physics, heavy metal, vegetarianism, or zombies. Hey, I’m just the messenger here.


Abandoned Epigraphs

By Sean Carroll | September 24, 2009 8:36 am

The book ended up with a pretty fun collection of epigraphs for each chapter. But there are a lot more good quotes about time than chapters in the book. Here are some of the quotes I did not end up using. Further examples are hereby solicited — who knows when they might turn out to be useful?

“Everything happens to everybody sooner or later if there is time enough.” — George Bernard Shaw, Back to Methuselah

“Time is the longest distance between two places.” — Tennessee Williams, The Glass Menagerie

“The future’s not ours to see.” — Doris Day

“Time rushes toward us with its hospital tray of infinitely varied narcotics, even while it is preparing us for its inevitably fatal operation.” — Tennessee Williams, The Rose Tattoo

“Time, you old gypsy man,
Will you not stay,
Put up your caravan
Just for one day?”
— Ralph Hodgeson

“Time present and time past
Are both perhaps present in time future,
And time future contained in time past.
If all time is eternally present
All time is unredeemable.”
— T.S. Eliot, “Burnt Norton” (Four Quartets)

“Time is the substance from which I am made. Time is a river that carries me along, but I am the river; it is a tiger that devours me, but I am the tiger; it is a fire that consumes me, but I am the fire.” — Jorge Luis Borges, Labyrinths.

Apparently you have to be extremely careful when it comes to poetry; fair use doesn’t necessarily extend very far.


Walkout at the University of California

By John Conway | September 23, 2009 1:46 pm

Tomorrow, thousands of University of California faculty will walk out in protest of state budget cuts, furloughs, and increases to student fees. The action will happen across all ten UC campuses (can you name them all?) and is supported by simultaneous strikes by two unions (UTPE and CUE) representing clerical and technical employees of the university. Here at UC Davis, there is a large rally planned for the main quad in the morning to draw public attention to the issues.

Since my last post on this topic, when it appeared that there would be salary cuts announced, there indeed were. But, especially in the summer, things happen slowly at universities. The original proposal was to give everyone except graduate students a 5% pay cut. The faculty were asked for their input on whether they preferred a pay cut, a salary reduction, or a hybrid. Once it was established that the format would be furloughs, we were asked if furlough days should be on teaching days or not. Despite the overwhelming sentiment of the UC faculty that the students should feel some of the pain of the budget cuts (which they already do through increased fees this year and next) the UC Office of the President elected to mandate that furlough days not be on teaching days.

Many of us thought that it was completely crazy to make pay cuts apply to everyone. For example, on the federal grant on which I am principal investigator (meaning I manage the budget) we pay our postdocs 100% from federal funds, including their benefits and overhead, which is essentially a tax paid to the university. Cutting the salaries of our postdocs would have only a negative effect on the university budget, and would demoralize the most productive research workers at the institution. It would damage for years our ability to attract good people. These arguments won out, and so the furloughs apply only to faculty and staff. (The application to medical school personnel is even more complicated – we won’t go there.)

In the end, the faculty furloughs are on a graded scale according to pay, tooping out at 10% for those making over $240,000 per year. (You can see everyone’s salary in the whole UC system using the nice tool provided by the San Francisco Chronicle…it’s eye-opening.) But even faculty and staff earning less than $40,000 will get a 4% furlough, which, to many of us, seems cruel.

Anyway, things simmered along during the summer, with anger building steadily. The walkout was planned about a month ago, and has really caught fire now. But then, last week UC President Yudof, faced with the spectre of even deeper cuts next year (when federal stimulus money for the state of California runs out), and a continuation of the “fiscal emergency” he declared into the next academic year all but certain, he announced plans to dramatically increase student fees by 30%, to over $10,000 per year for the first time ever, in addition to the 9.3% increase pushed through in May to help close the budget gap.

Ultimately, we all realize that the budget problems we face stem from the poor economy coupled with the effects of Proposition 13, passed over 30 years ago. By requiring a 2/3 majority in the state legislature to pass budget actions, it has led to a tyranny of the minority, a minority of, yes, Republicans who simply will not accept any new tax no matter what it does to the future of the state. Prop 13 caps property taxes at 1% of assessed value of a home, and caps the rate at which that value can rise to 2% per year, unless the house is sold. Clearly in a housing market that saw huge increases past decades, with far faster increases than 2%, this has led to enormous inequities in tax rates. For example, though my neighbors across the street have a house worth about what ours is, they pay about a quarter of what we do in taxes. This has benefitted the elderly greatly, and was a strong motivation for Prop 13 originally, but it has hamstrung the ability of both the state and local governments to support education, both K-12 and higher education.

We, as a state, are eating our seed corn. The University of California and the California State University systems are a tremendous engine for both long and short term economic growth. From this great compilation of statistics about UC let me just point out a few:

  • More than 220,000 students are enrolled in the University of California.
  • For every dollar of state money, the university secures six dollars in federal research money.
  • UC researchers patent three new inventions per day.
  • UC has the highest proportion of low-income students among the country’s top research universities.

It’s just stupid to think that de-funding the university will not seriously damage the state in the long run.

When I am out on the quad tomorrow, it will be with the intention of motivating the leadership in this university to fight, fight like hell, to make the case to the public and the legislature that we MUST support a public option for higher education. So far I haven’t seen the passion. President Yudof, and the chancellors of the ten campuses should all be out there on radio talk shows, TV, and the print media making the case to the public that this situation is dire. They should join forces with other state institutions to over turn Prop 13.


I Hate Blackboards

By Julianne Dalcanton | September 23, 2009 11:44 am

I enjoy teaching.

But I really hate blackboards.

I’m not sure what the results of Chad’s latest poll will be, but I’m betting that I’m in the minority of scientists. The scientific community contains many former social outcasts who grew up flaunting the social rules, and yet have completely bought into the idea that using blackboards makes you look like a Real Scientist.

Well screw that. Students in the back can’t see what you write. You get dust all over your clothes. The chalk dries out your finger tips. The dust gets all over the floor, making a mess for your overburdened cleaning staff. For a community that prides itself on moving forward, why are we stuck with a 200+ year old technology that doesn’t work all that well?

Now, white boards have their problems too. They’re easier to see, but the markers are always dried out (and expensive to replace as well). They also are somewhat dusty (though not nearly as bad as chalk). Progress, but not perfect.

The solution, however, currently lies in your toddler’s grasp.

The Magna Doodle.

magna doodle
The Magna Doodle works by having small chambers filled with a thick liquid and magnetic filings. You drag a magnetic pen across the surface, and the metal filings jump to the surface, making the small chamber dark. To erase, you pull a lever that drags a magnet along the back surface, pulling the metal filings away from the front, making the chamber appear white again. No mess, no fuss, no need to replace any parts magna doodle close up

It also is substantially easier to write on than the Etch-a-sketch. At least for most of us.

etch-a-sketch obama


Philosophy and Cosmology: Day Three

By Sean Carroll | September 22, 2009 1:49 am

Back for the third and final day of the Philosophy and Cosmology conference in honor of George Ellis’s birthday. I’ll have great memories of my time in Oxford, almost all of which was spent inside this lecture hall. See previous reports of Day One, Day Two.

It’s become clear along the way that I am not as accurate when I’m trying to represent philosophers as opposed to physicists; the vocabularies and concerns are just slightly different and less familiar to me. So take things with an appropriate grain of salt.

Tuesday morning: The Case for Multiverses

9:00: Bernard Carr, one of the original champions of the anthropic principle, has been instructed to talk on “How we know multiverses exist.” Not necessarily the title he would have chosen. Of course we don’t observe a multiverse directly; but we might observe it indirectly, or infer it theoretically. We should be careful to define “multiverse,” not to mention “exist.”

There certainly has been a change, even just since 2001, in the attitude of the community toward the multiverse. Quotes Frank Wilczek, who tells a parable about how multiverse advocates have gone from voices in the wilderness to prophets. That doesn’t mean the idea is right, of course.

Carr is less interested in insisting that the multiverse does exist, and more interested in defending the proposition that it might exist, and that taking it seriously is perfectly respectable science. Remember history: August Comte in 1859 scoffed at the idea we would ever know what stars were made of. Observational breakthroughs can be hard to predict. Rutherford: “Don’t let me hear anyone use the word `Universe’ in my department!” Cosmology wasn’t respectable. For what it’s worth, the idea that what we currently see is the whole universe has repeatedly been wrong.

So how do we know a multiverse exists? Maybe we could hop in a wormhole or something, but let’s not be so optimistic. There are reasons to think that multiverses exist: for example, if we find ourselves near some anthropic cutoff for certain parameters. More interesting, there could be semi-direct observational evidence — bubble collisions, or perhaps giant voids. Discovering extra dimensions would be good evidence for the theories on which the multiverse is often based.

The only direct observations that currently exists that might bear directly on multiverses is the prediction of giant voids and dark flows by Laura Mersini-Houghton and collaborators.

Carr believes that the indirect evidence from finely-tuned coupling constants is actually stronger. Existence of planets requires a very specific relationship between strength of gravity and electromagnetism, which happens to exist in the real world. There is a similar gravity/weak tuning needed to make supernovae and heavy elements. Admittedly, many physicists dislike the multiverse and find it just as unpalatable as God. But ultimately, multiverse ideas will become normal science by linking up with observations; we just don’t know how long it will take.

9:45: George Ellis follows Carr’s talk with what we’ve been waiting for a while — a strong skeptical take on the multiverse idea.

There are lots of types of multiverses: many-worlds, separated by space or time, or completely disjoint. Anthropic arguments are what make the idea go. The project is to make the apparently improbable become probable.

The very nature of the scientific enterprise is at stake: multiverse proponents are proposing that we weaken the idea of scientific proof. Science is about two things: testability and explanatory power. Is it worth giving up the former to achieve the latter?

The abstract notion of a multiverse doesn’t get you anything; you need a specific model, with a distribution of probabilities. (Does Harry Potter exist somewhere in your multiverse?) But if there is some process that generates universes, how do you test that process? Domains beyond our particle horizon are unobservable. How far should we expect to be able to extrapolate? Into a region which, in principle, we will never be able to observe.

In the good old days we accepted the Cosmological Principle, and assumed things continued uniformly forever beyond our observable horizon. Completely untestable, of course. If all the steps in the extrapolation are perfectly tenable, extrapolations are fine — but that’s not the case here. In particular, the physics of eternal inflation (gravity plus quantum field theory, Coleman-de Luccia tunneling) has never been tested. It’s unknown physics used to infer an unobservable realm. Inflation itself is not yet a well-defined theory, and not all versions of inflation are eternal. We haven’t even found a scalar field!

There is a claim that a multiverse is implied by the fine-tuning of the universe to allow life. At best a weak consistency test. Can never actually do statistical tests on the purported ensemble. Another claim is that the local universe, if it’s inside a bubble, should have a slight negative curvature — but that’s easily avoided by super-Hubble perturbations, so it’s not a strong prediction. We could, however, falsify eternal inflation by observing that we live in a “small” (topologically compact) universe. But if we don’t, it certainly doesn’t prove that eternal inflation is right. Finally, it’s true that we might someday see signatures of bubble collisions in the microwave background. But if we don’t, then what? Again, not a firm prediction.

Ultimately: explanation and testability are both important, but one shouldn’t overwhelm the other. “The multiverse theory can’t make any prediction because it can explain anything at all.” Beware! If we redefine science to accommodate the multiverse, all sorts of pseudo-science might sneak inside the tent.

There are also political/sociological issues. Orthodoxy is based on the beliefs held by elites. Consider the story of Peter Coles, who tried to claim back in the 1990’s that the matter density was only 30% of the critical density. He was threatened by a cosmological bigwig, who told him he’d be regarded as a crank if he kept it up. On a related note, we have to admit that even scientists base beliefs on philosophical agendas and rationalize after the fact. That’s often what’s going on when scientists invoke “beauty” as a criterion.

Multiverse theories invoke “a profligate excess of existential multiplicity” in order to explain a small number of features of the universe we actually see. It’s a possible explanation of fine tuning, but is not uniquely defined, is not scientifically testable, and in the end “simply postpones the ultimate metaphysical question.” Nevertheless — if we accumulated enough consistency tests, he’d be happy to eventually become convinced.

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Endgame for the Tevatron

By John Conway | September 21, 2009 12:27 pm

With little fanfare, last week the Tevatron at Fermilab, and the two experiments CDF and D0, emerged from an 11-week shutdown for what will likely be the final run of the collider, which is over 20 years old. In the past year, the machine has regularly set new records for luminosity (essentially the number of collisions per second) and delivered over 2 fb-1 (inverse femtobarns) of proton-antiproton collisions at a center of mass energy of 1.96 TeV to the experiments, still the highest in the world. The startup has gone very smoothly, and the Tevatron delivered a solid load of data to the experiments last week.


This funny unit, inverse femtobarns, allows us to calculate how many collision events of a certain type to expect. Take top quark pair production, for example. For protons colliding with antiprotons at Tevatron energies, we can calculate (or measure) what we call the production cross section. This cross-section is in fact expressed as an area, a very small area, since protons and antiprotons are so small. One “barn” is 10-28 m2, and the cross section for top pair production is about 7 x 10-12 barns, or 7 pb. By multiplying the cross-section times the integrated luminosity we can get the number of top quark pairs events produced. To get the number we actually observe in the detector, we need to take into account the efficiency for reconstructing them.

The plot here shows the history of what we call Run 2 at the Tevatron. After a very slow start in 2001, following a five-year shutdown to upgrade the whole complex, the collider set new luminosity records year after year, and has nearly delivered 7 fb-1. This final run is expected to last two years, until the end of 2011, by which point we hope to have recorded another 5 fb-1, nearly doubling the present sample.

This past year had been expected to be the year of the LHC at CERN. But the magnet quench incident of one year ago caused a delay of over a year in repairs and retrofits. It is still expected that the LHC will return to commissioning in November of this year, possibly colliding protons on protons before the end of the calendar year, albeit at low energies. When it does come online at higher energies, probably early next year, it is expected that the LHC will deliver no more than about 0.2 fb-1 at a collision energy of 10 TeV, five times that of the Tevatron. Even with such a small sample, there could be striking discoveries at the LHC which are out of reach for the Tevatron, simply because the LHC energy is so much larger.

The media love this sort of race, and have portrayed it as a race to discover the particle the media has heard the most about – the Higgs boson. With 12 fb-1, even combining all the search modes and channels, and combining the data from both experiments, a standard model Higgs boson might be seen at the three standard deviation level, but almost certainly not the five standard deviation level, which is the gold standard in the field. The LHC won’t be able to see a standard model Higgs boson with the initial sample either. It will take a year or two at higher luminosity, probably starting in 2012, to get there.

To my mind, if there is a race, it is a race for the unknown. What I worry about, what I literally lie awake thinking about, is whether we are looking at the Tevatron data exactly the right way. People have searched for many different new physics signals at the Tevatron, but there has been no unambiguous observation of anything beyond the standard model. To get a five sigma discovery with the remainder of the Tevatron data, it would have to be the case that there is already about a three sigma excess in the data we have. But have we looked at everything?

Nevertheless, a hard-core of dedicated, talented, and very new-physics-hungry physicists will continue to operate the detectors and analyze the data to come, myself among them. Like many, I am playing both sides: when LHC data come we’ll analyze that, too.


Philosophy and Cosmology: Day Two

By Sean Carroll | September 21, 2009 1:42 am

The previous post on the Philosophy and Cosmology conference in Oxford was growing to unseemly length, so I’ll give each of the three days its separate post.

Monday morning: The Case for Multiverses

9:00: We start today as we ended yesterday: with a talk by Martin Rees, who has done quite a bit to popularize the idea of a multiverse. He wants to argue that thinking about the multiverse doesn’t represent any sort of departure from the usual way we do science.

The Big Bang model, from 1 second to today, is as uncontroversial as anything a geologist does. Easily falsifiable, but it passes all tests. How far does the domain of physical cosmology extend? We only see the universe out to the microwave background, but nothing happens out there — it seems pretty uniform, suggesting that conditions inside extend pretty far outside. Could be very far, but hard to say for sure.

Some people want to talk only about the observable universe. Those folks need aversion therapy. After all, whether a particular distant galaxy eventually becomes observable depends on details of cosmic history. There’s no sharp epistemological distinction between the observable and unobservable parts of the universe. We need to ask whether quantities characterizing our observable part of the universe are truly universal, or merely local.

So: what values of these parameters are consistent with some kind of complexity? (No need to explicitly invoke the “A-word.”) Need gravity, and the weaker the better. Need at least one very large number; in our universe it’s the ratio of gravity to electromagnetic forces between elementary particles. Also need departure from thermodynamic equilibrium. Also: matter/antimatter symmetry, and some kind of non-trivial chemistry. (Tuning between electromagnetic and nuclear forces?) At least one star, arguably a second-generation star so that we have heavy elements. We also need a tuned cosmic expansion rate, to let the universe last long enough without being completely emptied out, and some non-zero fluctuations in density from place to place.

If the amplitude of density perturbations were much smaller, the universe would be anemic: you would have fewer first-generation stars, and perhaps no second-generation stars. If the amplitude were much larger, we would form huge black holes very early, and again we might not get stars. But ten times the observed amplitude would actually be kind of interesting. Given an amplitude of density perturbations, there’s an upper limit on the cosmological constant, so that structure can form. Again, larger perturbations would allow for a significantly larger cosmological constant — why don’t we live in such a universe? Similar arguments can be made about the ratio of dark matter to ordinary matter.

Having said all that, we need a fundamental theory to get anywhere. It should either determine all constants of nature uniquely, in which case anthropic reasoning has no role, or it allows ranges of parameters within the physical universe, in which case anthropics are unavoidable.

10:00: Next up, Philip Candelas to talk about probabilities in the landscape. The title he actually puts on the screen is: “Calabi-Yau Manifolds with Small Hodge Numbers, or A Des Res in the Landscape.”

A Calabi-Yau is the kind of manifold you need in string theory to compactly ten dimensions down to four, picked out among all possible manifolds by the requirement that we preserve supersymmetry. There are many examples, and you can characterize them by topological invariants as well as by continuous parameters. But there is a special corner in the space of Calabi-Yau’s where certain topological invariants (Hodge numbers) are relatively small; these seem like promising places to think about phenomenology — e.g. there are three generations of elementary particles.

Different embeddings lead to different gauge groups in four dimensions: E6, SO(10), or SU(5). Various models with three generations can be found. Putting flux on the Calabi-Yau can break the gauge group down to the Standard Model, sometimes with additional U(1)’s.

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