Andrew Jaffe: Leaves on the Line

The cosmology community has had a terrible few months.

I am saddened to report the passing of Andrew Lange, a physicist from CalTech and one of the world’s preeminent experimental cosmologists. Among many other accomplishments, Andrew was one of the leaders of the Boomerang experiment, which made the first large-scale map of the Cosmic Microwave Background radiation with a resolution of less than one degree, sufficient to see the opposing action of gravity and pressure in the gas of the early Universe, and to use that to measure the overall density of matter, among many other cosmological properties. He has since been an important leader in a number of other experiments, notably the Planck Surveyor satellite and the Spider balloon-borne telescope, currently being developed to become one of the most sensitive CMB experiments ever built.

I learned about this tragedy on the same day that people are gathering in Berkeley, California, to mourn the passing of another experimental cosmologist, Huan Tran of Berkeley. Huan was an excellent young scientist, most recently deeply involved in the development of PolarBear, another one of the current generation of ultra-sensitive CMB experiments. Huan lead the development of the PolarBear telescope itself, currently being tested in the mountains of California, but to be deployed for real science on the Atacama plane in Chile. We on the PolarBear team are proud to name the PolarBear telescope after Huan Tran, a token of our esteem for him, and a small tribute to his memory.

My thoughts go out to the friends and family of both Huan and Andrew. I, and many others, will miss them both.

One of my holiday treks this year was across town to visit Bunhill Fields, final resting place of two of my favorite Londoners: William Blake and Thomas Bayes.

Blake is of course one of the most famous poets in the English language, but most people know him only from short poems like The Tiger [sic] (“Tyger, Tyger burning bright/ In the forests of the night/ What immortal hand or eye/ Could frame thy fearful symmetry”) and Jerusalem, sung in Anglican churches each week. But most of Blake’s work is much too weird to make it into church. It is peopled by gods and monsters, illuminated by Blake’s own wonderful over-the-top illustrations. (For example, America: A Prophecy, his poetic interpretation of the American Revolutionary War, begins “The shadowy Daughter of Urthona stood before red Orc/When fourteen suns had faintly journey’d o’er his dark abode” — George Washington and Thomas Jefferson don’t make Blake’s version.)

Blake’s gravestone sits right on the pavement in the middle of Bunhill Fields, and as such unfortunately has been slightly damaged.

I don’t read Blake every day or even every week, but I probably do use Bayes’s famous theorem at least that often. As I and other bloggers have gone on and on about, Bayes’s theorem is the mathematical statement of how we ought to rigorously and consistently incorporate new information into our model of the world. Bayes himself wrote down only a version appropriate for a restricted version of this problem, and used words, rather than mathematica symbols. Nowadays, we usually write it mathematically, and in a completely general form, as

Which means, very roughly, that the so-called posterior probability, P(H|D) — the probability of some hypothesis, H, given data, D — is equal to P(H) — the prior probability of the hypothesis, H — times the likelihood, P(D|H) — the probability of observing the actual data that we obtained given that hypothesis; finally, all of this needs to be normalized by the quantity P(D). This seems pretty obscure, but it really is a model for learning: the prior represents our knowledge in the absence of the new data, and the theorem tells us how to update this in the face of new data. And it really is a theorem: a statement of mathematical fact. So this statement really is the foundation for the use of probability in reasoning about the world, which is the science of statistics (despite the internecine wars within the statistics community about exactly how one ought to make sense of the concept of “probability” itself), or more broadly, science itself. So Bayes is a man whose life is well worth celebrating by all of us interested in and affected by science.

Bayes is buried in his family tomb, now bearing the moss-covered Inscription: “Rev. Thomas Bayes, son of the said Joshua and Ann Bayes, 7 April 1761. In recognition of Thomas Bayes’s important work in probability this vault was restored in 1960 with contributions received from statisticians throughout the world.” (With restoration and upkeep since by Bayesian Efficient Strategic Trading of Hoboken, NJ, USA —across the Hudson River from New York City— and ISBA, the International Society for Bayesian Analysis.)

Luckily, not all the astrophysics news this week was so bad.

First, and most important, two of our Imperial College Astrophysics postgraduate students, Stuart Sale and Paniez Paykari, passed their PhD viva exams, and so are on their ways to officially being Doctors of Philosophy. Congratulations to both, especially (if I may say so) to Dr Paykari, who I had the pleasure and fortune to supervise and collaborate with. Both are on their way to continue their careers as postdocs in far-flung lands.

Second, the first major results from the Herschel Space Telescope, Planck’s sister satellite, were released. There are impressive pictures dwarf planets in the outer regions of our solar system, of star-forming regions in the Milky Way galaxy, of the vary massive Virgo Cluster of galaxies, and of the so-called “GOODS” (Great Observatory Origins Deep Survey) field, one of the most well-studied areas of sky. All of these open new windows into these areas of astrophysics, with Herschel’s amazing sensitivity.

Finally, tantalisingly, the Cryogenic Dark Matter Search (CDMS) released the results of its latest (and final) effort to search for the Dark Matter that seems to make up most of the matter in the Universe, but doesn’t seem to be the same stuff as the normal atoms that we’re made of. Under some theories, the dark matter would interact weakly with normal matter, and in such a way that it could possibly be distinguished from all the possible sources of background. These experiments are therefore done deep underground — to shield from cosmic rays which stream through us all the time — and with the cleanest and purest possible materials — to avoid contamination with both both naturally-occurring radioactivity and the man-made kind which has plagued us since the late 1940s.

With all of these precautions, CDMS expected to see a background rate of about 0.8 events during the time they were observing. And they saw (wait for it) two events! This is on the one hand more than a factor of two greater than the expected number, but on the other is only one extra count. To put this in perspective, I’ve made a couple of graphs where I try to approximate their results (for aficionados, these are just simple plots of the Poisson distribution). The first shows the expected number of counts from the background alone:

So even if there is no signal above the background, seeing two counts is not terribly unlikely. Now, here’s the likelihood function for the signal rate, given their background measurement:

It peaks away from zero, so the most likely interpretation of their experiment is that they see a signal, but it’s far from conclusive.

(I should point out a few caveats in my micro-analysis of their data. First, I don’t take into account the uncertainty in their background rate, which they say is really 0.8±0.1±0.2, where the first uncertainty, ±0.1 is “statistical”, because they only had a limited number of background measurements, and the second, ±0.2, is “systematic”, due to the way they collect and analyse their data. Eventually, one could take this into account via Bayesian marginalization, although ideally we’d need some more information about their experimental setup. Second, I’ve only plotted the likelihood above, but true Bayesians will want to apply a prior probability and plot the posterior distribution. The most sensible choice (the so-called Jeffreys prior) for this case would in fact make the probability peak at zero signal. Finally, one would really like to formally compare the no-signal model with a signal-greater-than-zero model, and the best way to do this would be using the tool of Bayesian model comparison.)

Nonetheless, in their paper they go on to interpret these results in the context of particle physics, which can eventually be used to put limits on the parameters of supersymmetric theories which may be tested further at the LHC accelerator over the next couple of years.

I should bring this back to the aforementioned bad news. The UK has its own dark matter direct detection experiments as well. In particular, Imperial leads the ZEPLIN-III experiment which has, at times, had the world’s best limits on dark matter, and is poised to possibly confirm this possible detection — this will be funded for the next couple of years. Unfortunately, STFC has decided that the next generation of dark matter experiments, EURECA and LUX-ZEPLIN, needed to make convincing statements about these results, weren’t possible to fund.

I presume that anyone reading this blog knows that today is the day when the great unwashed masses of UK Astronomers heard about our financial fate from the STFC, the small arm of the UK government responsible for Astrophysics, Particle Physics and Nuclear Physics.

For various reasons, some clear and others manifestly not, STFC is something like £70 million in the red. When all this started about two years ago, one of the main criticisms of the STFC management (beyond wondering how they could have got themselves — and us — into this predicament to begin with) was that they started to impose solutions that seemed to bear little resemblance to what the scientists themselves wanted. Trying to either genuinely ameliorate this, or at least give themselves good cover, they’ve spent much of the last year gathering input from various groups of physicists and astronomers, through a series of reports produced by scientist-led panels. These panels released their results this autumn, and STFC has supposedly used them to make decisions about the next five or so years of funding.

I was selfishly relieved to see that our work with the Planck Surveyor Satellite is rated “alpha 5”, and that our other local grants don’t appear directly affected (i.e., we weren’t drastically cut). However, STFC has “requested” (not sure what that means in this context) that even these projects reduce their costs by 15%. Other programs were not even this lucky — a not-quite-complete list of the cuts is on the STFC site. The cuts (a.k.a. “managed withdrawal”) include the UKIRT telescope, the LOFAR array, future work at the low-background facility at the Boulby mine, and future science exploitation of the XMM and Cassini missions (among many others). Alongside this, there will be a 25% cut in studentships and fellowships, although the details of this have not been revealed.

In his independent response, the Science Minister, Lord Drayson, says “we are investing record amounts into scientific research, but it is absolutely right that it is the scientists themselves, through the Research Councils, that decide how best to spend this money.” Of course we scientists don’t necessarily feel that our voices have been heard. The prioritized list of projects is available from STFC, and although it generally correlates with both the inputs from the various sub-panels and the financial outcome (in particular, many of us were pleased and relieved to see the much-criticised MoonLITE project at the bottom of the heap), there are some striking differences from at least my understanding of the panel recommendations, such as the “alpha 4” grade given to the Aurora human spaceflight program.

However, Drayson does seem to understand some of the issues: “…there are real tensions in having international science projects, large scientific facilities and UK grant giving roles within a single Research Council. It leads to grants being squeezed by increases in costs of the large international projects which are not solely within their control. I will work urgently with Professor Sterling, the STFC and the wider research community to find a better solution by the end of February 2010.” Not sure what this means, but even if we are grasping at straws, it’s the only promising news of the day.

I’ve got 11 browser tabs open just to get myself up-to-date. Here are some of them:

• An excellent summary of the situation before the announcement is at To the Left of Centre.
• Paul Crowther’s page has become the canonical clearing-house for information on the astronomy side of the “STFC Funding Crisis”.
• Blogs from Andy Lawrence and Peter Coles are both well-wrought and likely feature commentary from the opinionated luminaries of UK astronomy.
• The Institute of Physics and the Royal Astronomical Society respond.
• The BBC talks about the cuts with Lord Drayson.
• Physics World summarizes the situation as “savage cuts”.
• Our US counterparts get in on the commentary at Science magazine.
• There’s a web campaign to help save astronomy in the UK.

FInally, the #stfc twitter hashtag has been a great source of commentary, rage, and information, trending high today.

When I’m traveling I try to read the New Yorker — a transatlantic flight usually gets me through most of an issue. I was even more interested than usual when I picked up the issue at Heathrow and found the front-cover blurb, “Physics vs Poetry: New fiction by Ian McEwan”. McEwan is thought of as a “science-friendly” writer and has often populated his fiction with scientists and scientific ideas (usually doctors and medicine, as in Enduring Love and Saturday). His new story is called “The Use of Poetry”, but doesn’t quite manage to escape stereotyping his protagonist, the made-up physics Nobelist Michael Beard. McEwan’s Beard doesn’t really get poetry for its own sake; for him, “The Use of Poetry” is mostly for seducing his wife-to-be. At least McEwan is smart enough, and a good enough writer, that his stereotype isn’t quite so simple: his Beard is so smart that he can fake his way into smart opinions about Milton. He doesn’t really get it, it seems, but he can mouth the words at least as well as the supposed literary scholars (who, needless to say, neither try nor succeed at understanding his physics).

And — I’m not sure if this is to McEwan’s credit or otherwise — he stereotypes Beard’s counterpart, his future wife Maisie Farmer, studying English at Oxford when Beard is doing Physics, even more. After University, she becomes a hackneyed post-sixties feminist figure, attending “a group run by a collective Californian women…. Her consciousness was raised.”

McEwan, I think, prefers rationalists to literary types, but draws the divide too sharply. As Peter Coles has been talking about lately, that stereotypical distinction is just wrong. Most of my physicist friends love art, novels, poetry, music — and quite a few of them make it themselves, usually quite proudly if with varying degrees of emotional and aesthetic success.

What makes McEwan’s portrayal of Beard so unappealing is the backhandedness of the compliment behind it: yes, he’s smarter than everyone around him. But somehow even he doesn’t quite get the poetry, even if that’s almost a distinction that doesn’t make much of a difference.

The perfect stocking-stuffer for that would-be Bayesian cosmologist you’ve been shopping for:

As readers here will know, the Bayesian view of probability is just that probabilities are statements about our knowledge of the world, and thus eminently suited to use in scientific inquiry (indeed, this is really the only consistent way to make probabilistic statements of any sort!). Over the last couple of decades, cosmologists have turned to Bayesian ideas and methods as tools to understand our data. This book is a collection of specially-commissioned articles, intended as both a primer for astrophysicists new to this sort of data analysis and as a resource for advanced topics throughout the field.

Our back-cover blurb:

In recent years cosmologists have advanced from largely qualitative models of the Universe to precision modelling using Bayesian methods, in order to determine the properties of the Universe to high accuracy. This timely book is the only comprehensive introduction to the use of Bayesian methods in cosmological studies, and is an essential reference for graduate students and researchers in cosmology, astrophysics and applied statistics.

The first part of the book focuses on methodology, setting the basic foundations and giving a detailed description of techniques. It covers topics including the estimation of parameters, Bayesian model comparison, and separation of signals. The second part explores a diverse range of applications, from the detection of astronomical sources (including through gravitational waves), to cosmic microwave background analysis and the quantification and classification of galaxy properties. Contributions from 24 highly regarded cosmologists and statisticians make this an authoritative guide to the subject.

You can order it now from Amazon UK or Amazon USA.

The Institute of Physics is weighing in on the issue of climate change, so I thought I would take the opportunity to try to dumb things down as much as possible. The basic science behind climate change is well-understood:

1. The mean temperature is increasing, with significant variation superposed from place to place and year to year.
2. This is caused largely by the anthropogenic increase in carbon dioxide and other greenhouse gases in the atmosphere, due to the very well-understood and uncontroversial physics of the carbon-dioxide molecule.
3. Significant further increase would be societally bad for many people.
4. Lowering our greenhouse-gas emissions can slow or halt the increasing temperatures.

At this coarse level, both the data and the theory underlying these conclusions are almost incontrovertible and ought to be uncontroversial, although each of these has been questioned by the politically-motivated or ignorant deniers sceptics. Significant questions remain at a more detailed level, of course: what is the precise correlation between greenhouse-gas emissions and temperature? How much of the increase is due to emissions, and how much to other effects (e.g., solar irradiance variations)? Most importantly, what will the temperature increase be in the future, for various amounts of future carbon emission. These are important details, but the main point — the earth is warming due to our activities — is settled.

(Scientific American has an excellent rebuttal of the main points raised by the so-called sceptics.)

What I’ve never quite understood is the politics of climate change. It is an observational fact that climate change deniers tend to be from the (mainstream and libertarian) right. I can certainly understand political differences regarding the solution to climate change — a true free-marketeer wouldn’t want a carbon tax or even a cap-and-trade system (although, of course, either of these attempt to estimate the true cost of future emissions, rather than their purely short-term economic benefit). But why do politics trace our opinion of the science? The only explanation for this I can come up with is the right’s longstanding association with big business — in particular the oil business — which, even today, retains a vested interest in denying the simple truth of climate change.

I was saddened to hear this morning that Lev Kofman, a friend and fellow-cosmologist, died yesterday. Lev has been at CITA in Toronto for a decade, and has had a huge impact on the field, scientifically and personally. He will be missed. He is already.

I’m sure there will be more remembrances to come, but here is just the first, from his family and colleagues in Toronto. Our thoughts are with them.

Lev Kofman: June 17, 1957 - November 12, 2009

We are deeply saddened to inform you that the fabulous Lev Kofman, husband of Anna, father of Sergei 13 and Maria 15, brother of Svetlana, and our great friend, died in the early morning of November 12 from cancer. Many of you were able to commune with Lev as the situation deteriorated over the past weeks, by visits, phone calls, and emails read to him. We are deeply grateful for that: and it provided some solace for Lev to know the tremendous impact he has had on the lives of so many of you.

He bravely kept the physics going strong throughout his illness, characteristic of Lev. His scientific outpourings and influence will transcend this passage. As you know, he made fundamental contributions to Lambda cosmology and dark energy, structure in the cosmic web, inflationary theory, its Gaussian and non-Gaussian aspects, and gravitational waves. He initiated and developed the theory of preheating, showing how all matter could arise from a coherent vacuum energy at the end of inflation, his cosmic baby. And much more besides. He was the quintessential leader, for CITA and CIFAR as a whole, and for the vibrant early universe group he established, providing inspirational guidance to a generation of young researchers.

He felt the physics to his very core. Beyond this, it is the indomitable, fun-loving, deeply philosophical spirit, a gourmand of life in all its manifestations, that we will miss so much.

With our best wishes in these sad times,

Anna Chandarina (Kofman)
Svetlana Kofman
Dick Bond
Andrei Linde
Renata Kallosh

In one of my earliest memories, I’m about four years old, at nursery school, sitting on the floor looking up at what must have been a small black and white television sitting on a table. The teachers were all terribly excited, and we little kids were always happy to watch television. But this wasn’t Sesame Street. This was a rocket launch, a rocket to the moon. (I suspect it was Apollo 14.)

I was hooked immediately, and although I wasn’t well-suited to becoming an astronaut, I’ve managed to channel that impulse into science (and of course I finally got to see a rocket launch up close).

So without human spaceflight I probably wouldn’t be who I am, doing what I do.

But does space travel help us answer any of the “Big Questions”? Whither humanity in the long run? Will we stick to our crowded but beautiful planet or eventually spread our metaphorical wings and move on up?

Unfortunately spaceflight nowadays isn’t about the long-term future of humanity, but aerospace contracts, cool pictures, and good PR (except, of course, when something goes wrong). As I’ve said, that PR is certainly important, but it is very hard to know what exactly we’re getting for that considerable investment.

If you’d like to hear — or say — more about this, that’s exactly the question being asked at the latest instalment of Imperial’s “Big Questions” debates — Human Spaceflight: Science or Spectacle? Please come over to Imperial on Thursday night (but register in advance).

This week I was in the truly wonderful city of Bologna, home of possibly the oldest university in Europe. Nowadays, Bologna is also the home of IASF-BO, the Italian Istituto di Astrofisica Spaziale e Fisica Cosmica, and was hosting this year’s Planck Satellite Consortium meeting.

Of course I can’t talk about anything that was actually presented at the meeting — as I’ve mentioned before, there are strong restrictions on what is allowed to be discussed before the data become public in about three years. Indeed, that communication policy was itself the topic of considerable discussion — it turns out that at least a couple of Planck’s “highest ranking” scientists had recently been deemed to be in “non-compliance” with the policy (which may be different from actually violating the policy, but no one is quite sure…).

Luckily, there was plenty to talk about amongst ourselves between the political discussions. I reported on our efforts in London to recover Planck’s “pointing solution” — that is, to figure out where, exactly, each of Planck’s fifty or so detectors are actually looking on the sky at any given moment. This is obviously crucial to getting good science out of Planck — indeed, even though the instrument smears the sky with a resolution of about four arcminutes (about 1/15 of a degree), we want to know the pointing to roughly 10 arcseconds (about 1/360 of a degree)! But there were several hundred scientists at the meeting, so plenty to discuss, besides, over the course of the week, from Planck’s electronics to the eventual scientific results on the earliest instants of the Universe. The first hints of this science, but not much more, are present in the pictures we showed from Planck’s first-light survey. And I should point out that, despite at least one attempt — which I hesitate to even link to — there is really no science to be had in any analysis of what we’ve presented. We’re not taking three years to analyze the data just to be selfish — at least not entirely. It will take that long before we can understand the instrument well enough to interpret the data that comes out of it.

Luckily, Bologna is also known for its food, and aside from the excellent conference snacks and lunches (and a blow-out dinner at a local Palazzo from which I mostly recall the giant parmigiana wheel and the copious grappa), it was pretty easy to find excellent food at pretty much any local Trattoria (like La Montanara and the strangely-named Serghei). So now I am back, fat, happy, and with plenty of Planck work to do in the next few weeks, months and years.