Archive for April, 2009

Leonid’s Shower

Posted in The Universe and Stuff with tags , , , , on April 18, 2009 by telescoper

Yesterday (17th April) was the last day of our Easter vacation – back to the grind on Monday – and it was also the occasion of a special meeting to mark the retirement of Professor Leonid Petrovich Grishchuk.

Leonid has been a Distinguished Research Professor here in Cardiff since 1995. You can read more of his scientific biography and wider achievements here, but it should suffice to say that he is a pioneer of many aspects of relativistic cosmology and particularly primordial gravitational waves. He’s also a larger-than-life character who is known with great affection around the world.

Among other things, he’s a big fan of football. He still plays, as a matter of fact, although he generally spends more time ordering his team-mates about than actually running around himself. One of his retirement presents was a Cardiff City football shirt with his name on the back.

My first experience of Leonid was many years ago at a scientific meeting at which I attempted to give a talk. Leonid was in the audience and he interrupted me,  rather aggressively. I didn’t really understand his question so he had another go at me in the questions afterwards. I don’t mind admitting that I was quite upset with his behaviour. I think a large fraction of working cosmologists have probably been Grischchucked at one time or another.

Later on, though, people from the meeting were congregating at a bar when he arrived and headed for me. I didn’t really want to talk to him as I felt he had been quite rude. However, there wasn’t really any way of escaping so I ended up talking to him over a beer. We finally resolved the question he had been trying to ask me and his demeanour changed completely. We spent the rest of the evening having dinner and talking about all sorts of things and have been friends ever since.

Over the years I’ve learned that this is very much a tradition amongst Russian scientists of the older school. They can seem very hostile – even brutal – when discussing science, but that was the way things were done in the environment where they learned their trade.  In many cases the rather severe exterior masks a kindly and generous nature, as it certainly does with Leonid.

I also remember a spell in the States as a visitor during which I heard two Russian cosmologists screaming at each other in the room next door. I really thought they were about to have a fist fight. A few minutes later, though, they both emerged, smiling as if nothing had happened…

Appropriately enough Leonid’s bash was held immediately after BritGrav 9, a meeting dedicated to bringing together the gravitational research community of the UK and beyond, and to provide a forum for the exchange of ideas. It aimed to cover all aspects of gravitational physics, both theoretical and experimental, including cosmology, mathematical general relativity, quantum gravity, gravitational astrophysics, gravitational wave data analysis, and instrumentation. I chaired a session during the meeting and found Leonid in characteristic form as a member of the audience, never shy with questions or comments, and quite difficult to keep under control.

I enjoyed the meeting because priority was given to students when allocating speaking slots. I think too many conferences have the same senior scientists giving  the same talk over and over again. Relativists are also quite different to cosmologists in the level of mathematical rigour to which they aspire.  You can bullshit at a cosmology conference, but wouldn’t get away with it in front of a GR audience.

On the evening of 16th April we had a public lecture in Cardiff by Kip Thorne on The Warped Side of the Universe: from the Big Bang to Black Holes and Gravitational Waves and Kip also gave a talk as part of the subsequent meeting on Friday in Leonid’s honour.


Kip and Leonid are shown together a few years ago in the photograph to the left here. The rest of the LPGFest meeting was interesting and eclectic, with talks from mathematical relativists as well as scientists in diverse fields who had come over from Russia specially to honour Leonid. We later adjourned to a “Welsh Banquet” at the 15th Century Undercroft of Cardiff Castle for dinner accompanied by something described as “entertainment” laid on by the hosts. That part was quite excruciating: like Butlins only not as classy. Heaven knows what our distinguished foreign visitors made of it, although Leonid seemed to think it was great fun, and that’s what matters.

Once the dinner was over it was time for Leonid to be showered with gifts from around the world and, by way of a finale, he was serenaded with a version of From Russian With Love, by Bernie and the Gravitones. Now at last I understand what the phrase “extraordinary rendition” means.

Ode to the Shipping Forecast

Posted in Uncategorized with tags , , , on April 16, 2009 by telescoper

It’s broadcast four times a day on BBC Radio 4 and is immensely popular even with those who know nothing about shipping and live miles from the sea. The Shipping Forecast is as deep a part of British culture as cricket and standing in queues, although it doesn’t take as long as either of those things. It’s like a kind of soothing ritual that tells you that the world is still functioning despite all the stresses of the day. It’s predictable, safe and very conventional, like a meteorological version of the Anglican liturgy, but the combination of the mystical names with numbers and obscure formulae gives it a peculiarly pagan dimension.

I have to admit I’m an addict.

The Shipping Forecast is based on the division of the seas around the British Isles into a series of 31 areas, shown on the map, all with wonderfully evocative names. I was born in the Northeast of England so the sequence Forth-Tyne-Dogger always has a particular resonance for me, although living now in Cardiff I now find Lundy-Fastnet-Irish Sea is growing on me. The only problem is it sometimes sounds like Fishnet rather than Fastnet.

The broadcast of the Shipping Forecast always follows a strict format. It always begins with the words “And now the Shipping Forecast, issued by the Met Office on behalf of the Maritime and Coastguard Agency at xx:xx GMT today.”, although some announcers may read out the actual date of issue as opposed to the word “today”.

First are the Gale warnings (winds of force 8 or more, on the Beaufort scale), if any (e.g. There are warnings of gales in Rockall, Malin, Hebrides, Bailey, and Fair Isle). This sometimes follows the opposite format (e.g. There are warnings of gales in all areas except Biscay, Trafalgar and FitzRoy).

The General Synopsis follows, giving the position, pressure (in millibars) and track of pressure areas (e.g. Low, Rockall, 987, deepening rapidly, expected Fair Isle 964 by 0700 tomorrow).

The forecast for each of the 31 shipping areas shown in the map is then read out. Several areas may be combined into a single forecast where the conditions are expected to be similar.

Wind direction is given first, then strength (on the Beaufort scale), followed by precipitation, if any, and (usually) lastly visibility. Change in wind direction is indicated by veering (clockwise change) or backing (anti-clockwise change). Winds of above force 8 are also described by name for emphasis, e.g. Gale 8, Severe Gale 9, Storm 10, Violent Storm 11 and Hurricane force 12. (See Beaufort scale). The word “force” is only officially used when announcing force 12 winds.

Visibility is given in the format: Good, meaning that the visibility is greater than 5 nautical miles; Moderate, where visibility is between 2 and 5 nautical miles; Poor, where visibility is between 1000 metres and 2 nautical miles and Fog, where visibility is less than 1000 metres. When severe winter cold combines with strong winds and a cold sea, icing can occur, normally only in sea area Southeast Iceland; if expected, icing warnings (light, moderate or severe) are given as the last item of each sea area forecast.

The extended shipping forecasts (0520 and 0048 GMT) also include weather reports from a list of additional coastal stations and automatic weather logging stations, which are known by their names, such as Channel Light Vessel Automatic. These are the Coastal Weather Stations, some of which are actually military bases. These add an additional movement to the Symphony of the Shipping Forecast. I’m a particular fan of Sandettie Light Vessel Automatic. It just sounds so good.

You can listen to an example here.

Deeply evocative, but with a perfect control of form and an economy of structure, the Shipping Forecast is ten minutes of pure poetry.

Perception, Piero and Pollock

Posted in Art, The Universe and Stuff with tags , , , , , on April 15, 2009 by telescoper

For some unknown reason I’ve just received an invitation to a private view at a small art gallery that’s about ten minutes’ walk from my house. Cocktails included. I shall definitely go and will blog about it next week. I’m looking forward to it already.

This invitation put me in an artistic frame of mind so, to follow up my post on randomness (and the corresponding parallel version on cosmic variance), I thought I’d develop some thoughts about the nature of perception and the perception of nature.

This famous painting is The Flagellation of Christ, by Piero della Francesca. I actually saw it many years ago on one of my many trips to Italy; it’s in an art gallery in Urbino. The first thing that strikes you when you see it is actually that the painting is surprisingly small (about 60cm by 80cm). However, that superficial reaction aside, the painting draws you into it in a way which few other works of art can. The composition is complicated and mathematically precise, but the use of linear perspective is sufficiently straightforward that your eye can quickly understand the geometry of the space depicted and locate the figures and actions within it. The Christ figure is clearly in the room to the left rear and the scene is then easily recognized as part of the story leading up to the crucifixion.

That’s what your eye always seems to do first when presented with a figurative representation: sort out what’s going on and fill in any details it can from memory and other knowledge.

But once you have made sense of the overall form, your brain immediately bombards you with questions. Who are the three characters in the right foreground? Why aren’t they paying attention to what’s going on indoors? Who is the figure with his back to us? Why is the principal subject so far in the background? Why does everyone look so detached? Why is the light coming from two different directions (from the left for the three men in the foreground but from the right for those in the interior)? Why is it all staged in such a peculiar way? And so on.

These unresolved questions lead you to question whether this is the straightforward depiction first sight led you to think it was. It’s clearly much more than that. Deeply symbolic, even cryptic, it’s effect on the viewer is eery and disconcerting. It has a dream-like quality. The individual elements of the painting add up to something, but the full meaning remains elusive. You feel there must be something you’re missing, but can’t find it.

This is such an enigmatic picture that it has sparked some extremely controversial interpretations, some of which are described in an article in the scientific journal Nature. I’m not going to pretend to know enough to comment on the theories, escept to say that some of them at least must be wrong. They are, however, natural consequences of our brain’s need to impose order on what it sees. The greatest artists know this, of course. Although it sometimes seems like they might be playing tricks on us just for fun, part of what makes art great is the way it gets inside the process of perception.

Here’s another example from quite a different artist.

This one is called Lavender Mist. It’s one of the “action paintings” made by the influential American artist Jackson Pollock. This, and many of the other paintings of its type, also get inside your head in quite a disconcerting way but it’s quite a different effect to that achieved by Piero della Francesca.

This is an abstract painting, but that doesn’t stop your eyes seeking within it some sort of point of reference to make geometrical sense of it. There’s no perspective to draw you into it so you look for clues to the depth in the layers of paint. Standing in front of one of these very large works – I find they don’t work at all in reduced form like on the screen in front of you now – you find your eyes constantly shifting around, following lines here and there, trying to find recognizable shapes and to understand what is there in terms of other things you have experienced either in the painting itself or elsewhere. Any order you can find, however, soon becomes lost. Small-scale patterns dissolve away into sea of apparent confusion. Your brain tries harder, but is doomed. One of the biggest problems is that your eyes keep focussing and unfocussing to look for depth and structure. It’s almost impossible to stop yourself doing it. You end up dizzy.

I don’t know how Pollock came to understand exactly how to make his compositions maximally disorienting, but he seems to have done so. Perhaps he had a deep instinctive understanding of how the eye copes with the interaction of structures on different physical scales. I find you can see this to some extent even in the small version of the picture on this page. Deliberately blurring your vision makes different elements stand out and then retreat, particularly the large darkish streak that lies to the left of centre at a slight angle to the vertical.

This artist has also been the subject of interest by mathematicians and physicists because his work seems to display some of the characteristic properties of fractal sets. I remember going to a very interesting talk a few years ago by Richard Taylor of the University of Oregon who claimed that fractal dimensions could be used to authenticate (or otherwise) genuine works by Pollock as he seemed to have his own unique signature.

I suppose what I’m trying to suggest is that there’s a deeper connection than you might think between the appreciation of art and the quest for scientific understanding.

Spiritus Mundi

Posted in Poetry with tags , , on April 14, 2009 by telescoper

I found this poem by Simon Pomery a while ago in the Times Literary Supplement. Something made me cut it out of the paper and keep it. Part of the reason that it made an impression on me was probably that it is taken from a lengthy verse translation of one of Seneca‘s Moral Epistles called Divina Lux (a couple of other fragments of which you can find here) and this is a work I studied a bit in latin classes at School. You can also find prose translations of some of the 124 such Epistles Seneca wrote very near the end of his life here.

The soul of the world abides.
It doesn’t distinguish between
those born in town or country:
it makes its home in the wild sea,
the blur and seam of the horizon,
the cloud-racked firmament itself.
The space that separates the gods
from men unites them also, where stars,
like watchmen, sleep out in the open.

Seneca espoused a Stoic philosophy that was developed later by Marcus Aurelius, whose Meditations is one of my favourite books, although I’ve forgotten too much of my schoolboy Latin to read it in the original. I do, however, keep the paperback English translatlon with me when I go travelling. It is one the greatest works of classical philosophy, but it’s also a collection of very personal thoughts by someone who managed to be an uncompromisingly authoritarian Emperor of Rome at the same time as being a tender and introspective person.

Not that I’ve ever in practice managed to obey his exhortations to self-denial…

A funny thing happened on the way…

Posted in Columbo with tags , on April 13, 2009 by telescoper

Following yesterday’s emergency trip to the vet with Columbo, I took him back this morning. Although still very woozy from the tranquilizers he’s been having, he is much better this morning and the vet suggested no further action would be needed unless he had another episode. When the latest Diazepam wears off, hopefully he will return to some semblance of normality.

By the way, thanks for all the nice messages on here and on facebook. I really appreciate them.

While I was waiting in the reception area, a guy came in to make an appointment. When the receptionist asked what kind of animal he had, he said “Pet Sheep”. The animal concerned was waiting patiently in the back of his car.

It turns out the owner of this particularly sheep, David Palmer, is something of a celebrity and has even featured on Sky News. He found the sheep abandoned and brought it up as a pet. It lives in his house and is very tame, sitting quietly in the car while people chatted around him. It’s a substantial beast, though. Over 20 stones in fact -that’s 280lbs for any transatlantic readers.

I’ve never thought of sheep as pets. There are pet lambs on farms of course: when their mother has died or rejected them they are typically brought up by humans until they’re ready to go to market. But a full-grown sheep is a sizeable beast and, I would have thought, difficult to housetrain. Still, this one seemed quite affectionate. I asked Mr Palmer what he fed the sheep on. The answer was sprouts and carrots.

These days vets have to cope with all kinds of animals as well as the traditional cats and dogs. I’ve seen lizards, snakes, a monkey and vietnamese pig in various waiting rooms during various visits to various vets over the years.

The funniest thing I ever saw, though, wasn’t the sheep but a huge dog; a Great Dane no less. This enormous animal came  into the vet’s surgery with a little old lady in tow. She was like a character out of an old Ealing comedy and the dog was at least shoulder high to her. I thought she could probably ride around on it like a horse.

As they entered, a small dog barked and the Great Dane freaked out and started bounding around the room, knocking over a stand covered in pet treats and toys and generally causing a commotion. The old lady said “Brian! Calm down!”.

Brian. What a name for a Great Dane.

Arrows and Demons

Posted in The Universe and Stuff with tags , , , , , on April 12, 2009 by telescoper

My recent post about randomness and non-randomness spawned a lot of comments over on cosmic variance about the nature of entropy. I thought I’d add a bit about that topic here, mainly because I don’t really agree with most of what is written in textbooks on this subject.

The connection between thermodynamics (which deals with macroscopic quantities) and statistical mechanics (which explains these in terms of microscopic behaviour) is a fascinating but troublesome area.  James Clerk Maxwell (right) did much to establish the microscopic meaning of the first law of thermodynamics he never tried develop the second law from the same standpoint. Those that did were faced with a conundrum.  


The behaviour of a system of interacting particles, such as the particles of a gas, can be expressed in terms of a Hamiltonian H which is constructed from the positions and momenta of its constituent particles. The resulting equations of motion are quite complicated because every particle, in principle, interacts with all the others. They do, however, possess an simple yet important property. Everything is reversible, in the sense that the equations of motion remain the same if one changes the direction of time and changes the direction of motion for all the particles. Consequently, one cannot tell whether a movie of atomic motions is being played forwards or backwards.

This means that the Gibbs entropy is actually a constant of the motion: it neither increases nor decreases during Hamiltonian evolution.

But what about the second law of thermodynamics? This tells us that the entropy of a system tends to increase. Our everyday experience tells us this too: we know that physical systems tend to evolve towards states of increased disorder. Heat never passes from a cold body to a hot one. Pour milk into coffee and everything rapidly mixes. How can this directionality in thermodynamics be reconciled with the completely reversible character of microscopic physics?

The answer to this puzzle is surprisingly simple, as long as you use a sensible interpretation of entropy that arises from the idea that its probabilistic nature represents not randomness (whatever that means) but incompleteness of information. I’m talking, of course, about the Bayesian view of probability.

 First you need to recognize that experimental measurements do not involve describing every individual atomic property (the “microstates” of the system), but large-scale average things like pressure and temperature (these are the “macrostates”). Appropriate macroscopic quantities are chosen by us as useful things to use because they allow us to describe the results of experiments and measurements in a  robust and repeatable way. By definition, however, they involve a substantial coarse-graining of our description of the system.

Suppose we perform an idealized experiment that starts from some initial macrostate. In general this will generally be consistent with a number – probably a very large number – of initial microstates. As the experiment continues the system evolves along a Hamiltonian path so that the initial microstate will evolve into a definite final microstate. This is perfectly symmetrical and reversible. But the point is that we can never have enough information to predict exactly where in the final phase space the system will end up because we haven’t specified all the details of which initial microstate we were in.  Determinism does not in itself allow predictability; you need information too.

If we choose macro-variables so that our experiments are reproducible it is inevitable that the set of microstates consistent with the final macrostate will usually be larger than the set of microstates consistent with the initial macrostate, at least  in any realistic system. Our lack of knowledge means that the probability distribution of the final state is smeared out over a larger phase space volume at the end than at the start. The entropy thus increases, not because of anything happening at the microscopic level but because our definition of macrovariables requires it.


This is illustrated in the Figure. Each individual microstate in the initial collection evolves into one state in the final collection: the narrow arrows represent Hamiltonian evolution.


However, given only a finite amount of information about the initial state these trajectories can’t be as well defined as this. This requires the set of final microstates has to acquire a  sort of “buffer zone” around the strictly Hamiltonian core;  this is the only way to ensure that measurements on such systems will be reproducible.

The “theoretical” Gibbs entropy remains exactly constant during this kind of evolution, and it is precisely this property that requires the experimental entropy to increase. There is no microscopic explanation of the second law. It arises from our attempt to shoe-horn microscopic behaviour into framework furnished by macroscopic experiments.

Another, perhaps even more compelling demonstration of the so-called subjective nature of probability (and hence entropy) is furnished by Maxwell’s demon. This little imp first made its appearance in 1867 or thereabouts and subsequently led a very colourful and influential life. The idea is extremely simple: imagine we have a box divided into two partitions, A and B. The wall dividing the two sections contains a tiny door which can be opened and closed by a “demon” – a microscopic being “whose faculties are so sharpened that he can follow every molecule in its course”. The demon wishes to play havoc with the second law of thermodynamics so he looks out for particularly fast moving molecules in partition A and opens the door to allow them (and only them) to pass into partition B. He does the opposite thing with partition B, looking out for particularly sluggish molecules and opening the door to let them into partition A when they approach.

The net result of the demon’s work is that the fast-moving particles from A are preferentially moved into B and the slower particles from B are gradually moved into A. The net result is that the average kinetic energy of A molecules steadily decreases while that of B molecules increases. In effect, heat is transferred from a cold body to a hot body, something that is forbidden by the second law.

All this talk of demons probably makes this sound rather frivolous, but it is a serious paradox that puzzled many great minds. Until it was resolved in 1929 by Leo Szilard. He showed that the second law of thermodynamics would not actually be violated if entropy of the entire system (i.e. box + demon) increased by an amount every time the demon measured the speed of a molecule so he could decide whether to let it out from one side of the box into the other. This amount of entropy is precisely enough to balance the apparent decrease in entropy caused by the gradual migration of fast molecules from A into B. This illustrates very clearly that there is a real connection between the demon’s state of knowledge and the physical entropy of the system.

By now it should be clear why there is some sense of the word subjective that does apply to entropy. It is not subjective in the sense that anyone can choose entropy to mean whatever they like, but it is subjective in the sense that it is something to do with the way we manage our knowledge about nature rather than about nature itself. I know from experience, however, that many physicists feel very uncomfortable about the idea that entropy might be subjective even in this sense.

On the other hand, I feel completely comfortable about the notion:. I even think it’s obvious. To see why, consider the example I gave above about pouring milk into coffee. We are all used to the idea that the nice swirly pattern you get when you first pour the milk in is a state of relatively low entropy. The parts of the phase space of the coffee + milk system that contain such nice separations of black and white are few and far between. It’s much more likely that the system will end up as a “mixed” state. But then how well mixed the coffee is depends on your ability to resolve the size of the milk droplets. An observer with good eyesight would see less mixing than one with poor eyesight. And an observer who couldn’t perceive the difference between milk and coffee would see perfect mixing. In this case entropy, like beauty, is definitely in the eye of the beholder.

The refusal of many physicists to accept the subjective nature of entropy arises, as do so many misconceptions in physics, from the wrong view of probability.

Easter Emergency

Posted in Columbo on April 12, 2009 by telescoper

Well, this has to have been the most stressful Easter Sunday I’ve had in my whole life…

This morning, around 11.30 or so, my old cat Columbo (whose 15th birthday was on 31st March) suffered some kind of a seizure while I was sitting out in my garden reading the newspaper. It’s been warm and sunny over the holiday weekend so I’ve been trying to make the most of it, including having breakfast al fresco.

Columbo suddenly had a funny turn, cried out and then simultaneously evacuated bowels and bladder onto the garden path.  He staggered off into the house, alternately mewing and hissing, and proceeded to half-pace half-crawl around from room to room. Hoping he would settle down in due course, I just kept an eye on him and tried to let him find somewhere comfortable to recover from whatever bad thing had happened to him. He  didn’t seem to recognize me or the house he was in.

After about an hour of this, I gave up and called the emergency line and the vet. Such things always seem to happen during holidays when the vets are closed. Anyway, I managed to persuade the vet on the other end of the line that it was indeed an emergency, and rushed the sick moggy there in a taxi. The emergency vet arrived and opened up the clinic about ten minutes later.

Columbo hadn’t really improved in the meantime and he behaved very strangely in the vets, pacing around the examination table and sniffing everything repeatedly. The vet examined him thoroughly, including testing his eyes. It appeared that he had lost most of his vision, probably very suddenly, and although he wasn’t completely blind this could account for his disorientation and obvious discomfort and stress.

There could be a variety of causes of such a seizure for an old cat (stroke, toxic shock, neurological disease, etc) but the vet pronounced it unlikely to be directly connected to his diabetes as all the signs suggested a neurological problem. He had probably lost his faculties when whatever it was happened, and evidently lost control in  other ways too.

After lengthy consultations she (the vet) gave him a series of injections including antibiotics, an anti-inflammatory drug, and a sedative to try to calm him down a little.  She also gave me three diazepam tablets – which I initially thought were for me, as I was panicky too – in case he needed something later on to help him sleep. I was going to suggest that Mog-adon might be better but thought better of it.

It was clear that Columbo had experienced something that had completely deranged his mind, left him unable to see things properly, and put him into a state where he hadn’t the faintest idea where he was. The poor thing was obviously terribly frightened and confused. I think the vet knew that I knew how serious this could be and what I would have to do if the situation didn’t improve. I couldn’t allow him to suffer like that indefinitely.

But, the vet said, take him home, give him some rest, see if he’ll take food and bring him back tomorrow. We’ll see what state he’s in then.

So then I got him home. He carried on as before for about an hour and then either the sedative took effect or he was just knackered, so he climbed into his basket and went to sleep. I had some work to do so I left him on his own for a couple of hours, closing the kitchen door to give him some quiet. All the time I was thinking about soon having to make the decision to have him put down so I didn’t concentrate on my work at all well.

Eventually I went into the kitchen, where his basket is. I half-expected to find him dead. But as soon as I opened the door he climbed out of the basket and came directly to me. Clearly he was regaining some idea of where he was and could even see me. He purred when I reached down to stroke him. I went into the kitchen and he followed, still a bit groggy, but much better than before. I tried him with a bit of food and he wolfed it down quite happily before plodding off back to his basket. Not 100% by any means, but much better than the state he was in a few hours before.

So that’s where the story is so far. With  Columbo tucking in, I realized I hadn’t eaten a thing since breakfast so I’m warming something up now as I write this. I think I could do with a drink too.

For the time being, the emergency appears to be over, but we’ll see how he gets on at the vets tomorrow.

Easter Physics Quiz

Posted in Uncategorized with tags on April 10, 2009 by telescoper

Over the Easter holidays the newspapers seem to be full of quizzes and other distractions, so I thought I’d join in with a little quiz of my own.

So for a negligible prize can anyone point out the mathematical connection between these two pictures?








Answers via the comments box please.

Full Blast

Posted in Science Politics, The Universe and Stuff with tags , , , , , on April 9, 2009 by telescoper

Yesterday, Paolo Calisse and I were paid a visit by a reporter (Martin Shipton) and a photographer from Welsh newspaper The Western Mail who wanted to cover the sad story of Clover.

Paolo is heavily involved with Clover, but I was a bit hesitant about doing this because I’m not really part of the Clover team. Paolo suggested it might be an advantage that I wasn’t so directly involved as I might be able to give a more balanced view of the importance of the experiment than him. Anyway, the story came out today in the newspaper and is available online too.

DrThis is the picture they took of me and Paolo in the Clover lab, fiddling with the cryostat. I’ve already had my leg pulled enough about pretending to be an instrumentalist for the photograph so no jokes please…





In the same issue of the paper there is another feature about Cardiff’s astronomy research, concerning BLAST (Balloon-borne Large Aperture Submillimetre Telescope). This is a much happier story, as it marks the release of results from a highly successful science run from 2006. In the print version of the Western Mail the two stories were run on the same page, one above the other, making very effectively the point that cutting the funding of the Astronomy Instrumentation Group jeopardizes a great deal of world-leading research besides Clover itself. And when I say “world-leading” I mean it, whatever the RAE panel might have thought.

A deluge of articles about BLAST appeared on the arXiv today, one of which is now published in Nature. I thought I’d put up the abstracts here in order to draw attention to these results. The author lists contain many Cardiff authors and, as you’ll see, the results are both fascinating and wide-ranging. I’ve put links to the arXiv after each abstract:

Title: BLAST: Correlations in the Cosmic Far-Infrared Background at 250, 350, and 500 microns Reveal Clustering of Star-Forming Galaxies

Authors: Marco P. Viero, Peter A. R. Ade, James J. Bock, Edward L. Chapin, Mark J. Devlin, Matthew Griffin, Joshua O. Gundersen, Mark Halpern, Peter C. Hargrave, David H. Hughes, Jeff Klein, Carrie J. MacTavish, Gaelen Marsden, Peter G. Martin, Philip Mauskopf, Lorenzo Moncelsi, Mattia Negrello, Calvin B. Netterfield, Luca Olmi, Enzo Pascale, Guillaume Patanchon, Marie Rex, Douglas Scott, Christopher Semisch, Nicholas Thomas, Matthew D. P. Truch, Carole Tucker, Gregory S. Tucker, Donald V. Wiebe

We detect correlations in the cosmic far-infrared background due to the clustering of star-forming galaxies, in observations made with the Balloon-borne Large Aperture Submillimeter Telescope (BLAST), at 250, 350, and 500 microns. Since the star-forming galaxies which make up the far-infrared background are expected to trace the underlying dark matter in a biased way, measuring clustering in the far infrared background provides a way to relate star formation directly to structure formation. We test the plausibility of the result by fitting a simple halo model to the data. We derive an effective bias b_eff = 2.2 +/- 0.2, effective mass log(M_eff/M_sun) = 13.2 (+0.3/-0.8), and minimum mass log(M_min/M_sun) = 9.9 (+1.5/-1.7). This is the first robust clustering measurement at submillimeter wavelengths.

Title: Over half of the far-infrared background light comes from galaxies at z >= 1.2

Authors: Mark J. Devlin, Peter A. R. Ade, Itziar Aretxaga, James J. Bock, Edward L. Chapin, Matthew Griffin, Joshua O. Gundersen, Mark Halpern, Peter C. Hargrave, David H. Hughes, Jeff Klein, Gaelen Marsden, Peter G. Martin, Philip Mauskopf, Lorenzo Moncelsi, Calvin B. Netterfield, Henry Ngo, Luca Olmi, Enzo Pascale, Guillaume Patanchon, Marie Rex, Douglas Scott, Christopher Semisch, Nicholas Thomas, Matthew D. P. Truch, Carole Tucker, Gregory S. Tucker, Marco P. Viero, Donald V. Wiebe

Journal-ref: Nature, vol. 458, 737-739 (2009) DOI: 10.1038/nature07918

Submillimetre surveys during the past decade have discovered a population of luminous, high-redshift, dusty starburst galaxies. In the redshift range 1 <= z <= 4, these massive submillimetre galaxies go through a phase characterized by optically obscured star formation at rates several hundred times that in the local Universe. Half of the starlight from this highly energetic process is absorbed and thermally re-radiated by clouds of dust at temperatures near 30 K with spectral energy distributions peaking at 100 microns in the rest frame. At 1 <= z <= 4, the peak is redshifted to wavelengths between 200 and 500 microns. The cumulative effect of these galaxies is to yield extragalactic optical and far-infrared backgrounds with approximately equal energy densities. Since the initial detection of the far-infrared background (FIRB), higher-resolution experiments have sought to decompose this integrated radiation into the contributions from individual galaxies. Here we report the results of an extragalactic survey at 250, 350 and 500 microns. Combining our results at 500 microns with those at 24 microns, we determine that all of the FIRB comes from individual galaxies, with galaxies at z >= 1.2 accounting for 70 per cent of it. As expected, at the longest wavelengths the signal is dominated by ultraluminous galaxies at z > 1.

Title: The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) 2006:
Calibration and Flight Performance

Authors: Matthew D. P. Truch, Peter A. R. Ade, James J. Bock, Edward L. Chapin, Mark J. Devlin, Simon R. Dicker, Matthew Griffin, Joshua O. Gundersen, Mark Halpern, Peter C. Hargrave, David H. Hughes, Jeff Klein, Gaelen Marsden, Peter G. Martin, Philip Mauskopf, Lorenzo Moncelsi, Calvin B. Netterfield, Luca Olmi, Enzo Pascale, Guillaume Patanchon, Marie Rex, Douglas Scott, Christopher Semisch, Nicholas E. Thomas, Carole Tucker, Gregory S. Tucker, Marco P. Viero, Donald V. Wiebe

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) operated successfully during a 250-hour flight over Antarctica in December 2006 (BLAST06). As part of the calibration and pointing procedures, the red hypergiant star VY CMa was observed and used as the primary calibrator. Details of the overall BLAST06 calibration procedure are discussed. The 1-sigma absolute calibration is accurate to 10, 12, and 13% at the 250, 350, and 500 micron bands, respectively. The errors are highly correlated between bands
resulting in much lower error for the derived shape of the 250-500 micron continuum. The overall pointing error is <5″ rms for the 36, 42, and 60″ beams. The performance of the optics and pointing systems is discussed.

Title: A Bright Submillimeter Source in the Bullet Cluster (1E0657–56) Field Detected with BLAST

Authors: Marie Rex, Peter A. R. Ade, Itziar Aretxaga, James J. Bock, Edward L. Chapin, Mark J. Devlin, Simon R. Dicker, Matthew Griffin, Joshua O. Gundersen, Mark Halpern, Peter C. Hargrave, David H. Hughes, Jeff Klein, Gaelen Marsden, Peter G. Martin, Philip Mauskopf, Calvin B. Netterfield, Luca Olmi, Enzo Pascale, Guillaume Patanchon, Douglas Scott, Christopher Semisch, Nicholas Thomas, Matthew D. P. Truch, Carole Tucker, Gregory S. Tucker, Marco P. Viero, Donald V. Wiebe

We present the 250, 350, and 500 micron detection of bright submillimeter emission in the direction of the Bullet Cluster measured by the Balloon-borne Large-Aperture Submillimeter Telescope (BLAST). The 500 micron centroid is coincident with an AzTEC 1.1 millimeter detection at a position close to the peak lensing magnification produced by the cluster. However, the 250 micron and 350 micron emission is resolved and elongated, with centroid positions shifted toward the south of the AzTEC source and a differential shift between bands that cannot be explained by pointing uncertainties. We therefore conclude that the BLAST detection is contaminated by emission from foreground galaxies associated with the Bullet Cluster. The submillimeter redshift estimate based on 250-1100 micron photometry at the position of the AzTEC source is z_phot = 2.9 (+0.6/-0.3), consistent with the infrared color redshift estimation of the most likely Spitzer IRAC counterpart. These flux densities indicate an apparent far-infrared luminosity of L_FIR = 2E13 L_sun. When the amplification due to the gravitational lensing of the cluster is removed, the intrinsic far-infrared luminosity of the source is found to be L_FIR <= 1E12 L_sun, consistent with typical luminous infrared galaxies.

Title: Radio and mid-infrared identification of BLAST source counterparts in the Chandra Deep Field South

Authors: Simon Dye, Peter A. R. Ade, James J. Bock, Edward L. Chapin, Mark J. Devlin, James S. Dunlop, Stephen A. Eales, Matthew Griffin, Joshua O. Gundersen, Mark Halpern, Peter C. Hargrave, David H. Hughes, Jeff Klein, Gaelen Marsden, Philip Mauskopf, Lorenzo Moncelsi, Calvin B. Netterfield, Luca Olmi, Enzo Pascale, Guillaume Patanchon, Marie Rex, Douglas Scott, Christopher Semisch, Nicholas Thomas, Matthew D. P. Truch, Carole Tucker, Gregory S. Tucker, Marco P. Viero, Donald V. Wiebe

We have identified radio and/or mid-infrared counterparts to 198 out of 351 sources detected at >= 5 sigma over ~ 9 sq. degrees centered on the Chandra Deep Field South (CDFS) by the Balloon-borne Large Aperture Submillimeter Telescope (BLAST) at 250, 350, and 500 microns. We have matched 92 of these counterparts to optical sources with previously derived photometric redshifts and fitted SEDs to the BLAST fluxes and fluxes at 70 and 160 microns acquired with the Spitzer Space Telescope. In this way, we have constrained dust temperatures, total far-infrared/submillimeter luminosities and star formation rates for each source. Our findings show that the BLAST sources lie at significantly lower redshifts and have significantly lower rest-frame dust temperatures compared to submm sources detected in surveys conducted at 850 microns. We demonstrate that an apparent increase in dust temperature with redshift in our sample arises as a result of selection effects. This paper
constitutes the public release of the multi-wavelength catalog of >= 5 sigma BLAST sources contained within the full ~ 9 sq. degree survey area.

Title: BLAST: Resolving the Cosmic Submillimeter Background

Authors: Gaelen Marsden, Peter A. R. Ade, James J. Bock, Edward L. Chapin, Mark J. Devlin, Simon R. Dicker, Matthew Griffin, Joshua O. Gundersen, Mark Halpern, Peter C. Hargrave, David H. Hughes, Jeff Klein, Philip Mauskopf, Benjamin Magnelli, Lorenzo Moncelsi, Calvin B. Netterfield, Henry Ngo, Luca Olmi, Enzo Pascale, Guillaume Patanchon, Marie Rex, Douglas Scott, Christopher Semisch, Nicholas Thomas, Matthew D. P. Truch, Carole Tucker, Gregory S. Tucker, Marco P. Viero, Donald V. Wiebe

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) has made one square-degree, deep, confusion-limited maps at three different bands, centered on the Great Observatories Origins Deep Survey South field. By calculating the covariance of these maps with catalogs of 24 micron sources from the Far-Infrared Deep Extragalactic Legacy Survey (FIDEL), we have determined that the total submillimeter intensities are 8.60 +/- 0.59, 4.93 +/- 0.34, and 2.27 +/- 0.20 nW m^-2 sr^-1 at 250, 350, and 500 microns, respectively. These numbers are more precise than previous estimates of the cosmic infrared background (CIB) and are consistent with 24 micron-selected galaxies generating the full intensity of the CIB. We find that more than half of the CIB originates from sources at z >= 1.2. At all BLAST wavelengths, the relative intensity of high-z sources is higher for 24 micron-faint sources than it is for 24 micron-bright sources. Galaxies identified very broadly as AGN by their Spitzer Infrared Array Camera (IRAC) colors contribute 32-48% of the CIB, although X-ray-selected AGN contribute only 7%. BzK-selected galaxies are found to be brighter than typical 24 micron-selected galaxies in the BLAST bands, and contribute 32-42% of the CIB. These data provide high-precision constraints for models of the evolution of the number density and intensity of star-forming galaxies at high redshift.

Title: BLAST: A Far-Infrared Measurement of the History of Star Formation

Authors: Enzo Pascale, Peter A. R. Ade, James J. Bock, Edward L. Chapin, Mark J. Devlin, Simon Dye, Steve A. Eales, Matthew Griffin, Joshua O. Gundersen, Mark Halpern, Peter C. Hargrave, David H. Hughes, Jeff Klein, Gaelen Marsden, Philip Mauskopf, Lorenzo Moncelsi, Calvin B. Netterfield, Luca Olmi, Guillaume Patanchon, Marie Rex, Douglas Scott, Christopher Semisch, Nicholas Thomas, Matthew D. P. Truch, Carole Tucker, Gregory S. Tucker, Marco P. Viero, Donald V. Wiebe

We use measurements from the Balloon-borne Large Aperture Sub-millimeter Telescope (BLAST) at wavelengths spanning 250 to 500 microns, combined with data from the Spitzer Infrared telescope and ground-based optical surveys in GOODS-S, to determine the average star formation rate of the galaxies that comprise the cosmic infrared background (CIB) radiation from 70 to 500 microns, at redshifts 0 < z < 3. We find that different redshifts are preferentially probed at different wavelengths within this range, with most of the 70 micron background generated at z < ~1 and the 500 micron background generated at z >~1. The spectral coverage of BLAST and Spitzer in the region of the peak of the background at ~200 microns allows us to directly estimate the mean physical properties (temperature, bolometric luminosity and mass) of the dust in the galaxies responsible for contributing more than 80% of the CIB. By utilizing available redshift information we directly measure the evolution of the far infrared luminosity density and therefore the optically obscured star formation history up to redshift z ~3.

Title: BLAST: The Mass Function, Lifetimes, and Properties of Intermediate Mass Cores from a 50 Square Degree Submillimeter Galactic Survey in Vela (l = ~265)

Authors: Calvin. B. Netterfield, Peter A. R. Ade, James J. Bock, Edward L. Chapin, Mark J. Devlin, Matthew Griffin, Joshua O. Gundersen, Mark Halpern, Peter C. Hargrave, David H. Hughes, Jeff Klein, Gaelen Marsden, Peter G. Martin, Phillip Mauskopf, Luca Olmi, Enzo Pascale, Guillaume Patanchon, Marie Rex, Arabindo Roy, Douglas Scott, Christopher Semisch, Nicholas Thomas, Matthew D. P. Truch, Carole Tucker, Gregory S. Tucker, Marco P. Viero, Donald V. Wiebe

We present first results from an unbiased, 50 square degree submillimeter Galactic survey at 250, 350, and 500 microns from the 2006 flight of the Balloon-borne Large Aperture Submillimeter Telescope (BLAST). The map has resolution ranging from 36″ to 60″ in the three submillimeter bands spanning the thermal emission peak of cold starless cores. We determine the temperature, luminosity, and mass of more than a thousand compact sources in a range of evolutionary stages and an unbiased statistical characterization of the population. From comparison with C^18 O data, we find the dust opacity per gas mass, kappa/R = 0.16 cm^2/g at 250 microns, for cold clumps. We find that 2% of the mass of the molecular gas over this diverse region is in cores colder than 14 K, and that the mass function for these cold cores is consistent with a power law with index alpha = -3.22 +/- 0.14 over the mass range 14 M_sun < M < 80 M_sun, steeper than the Salpeter alpha = -2.35 initial massfunction for stars. Additionally, we infer a mass dependent cold core lifetime of tau(M) = 4E6 (M/20 M_sun)^-0.9 years — longer than what has been found in previous surveys of either low or high mass cores, and significantly longer than free fall or turbulent decay time scales. This implies some form of non-thermal support for cold cores during this early stage of star formation.

You can find a lot more detailed information on the dedicated BLAST website.

Tommy Flanagan

Posted in Jazz with tags , on April 8, 2009 by telescoper

I’ve only got time for a quick post today so I thought I’d put up a clip of someone I think is one of the most consistently enjoyable but underrated Jazz pianists of all time. He was probably best known as the long-time accompanist of Ella Fitzgerald but he also played on a number of really important Jazz albums with Sonny Rollins and John Coltrane, to name just two. He also loved to play within the classic Jazz trio format of piano, bass and drums as represented here.

This is the marvellous Tommy Flanagan playing yet another tune by the great Billy Strayhorn; this one’s called Raincheck.