Archive for May 30, 2011

Never Say Never …

Posted in Cricket with tags , , , , on May 30, 2011 by telescoper

It was tipping down with rain this morning so I wrote off the prospect of there being any result in the First Test between England and Sri Lanka at Cardiff which I’ve blogged about once already. However, the weather steadily improved and play eventually got started at about 3pm. England, resuming on 491 for 5, batted on for a couple of overs to allow Ian Bell to get his century then – perhaps surprisingly – declared on 496-5, with a lead of 96 on the first innings. An unusually adventurous decision by Strauss to declare so early, in fact. Nevertheless, a draw looked a virtual certainty to me (and most sports writers) so I wasn’t paying much attention to the cricket at first, deciding instead to get on with some other stuff at home.

When I checked the score around 4 o’clock I discovered Sri Lanka had lost a couple of early wickets and had gone in for tea at 33-2. It being free to get in for the last session and the weather now being very sunny, I finally decided to go and watch the final stages. A draw still seemed the likeliest outcome – Sri Lanka only had to bat out time for 35 overs or so. However, we don’t get much Test cricket in Cardiff and the last match here had an exciting finish, so I walked to the ground just after tea. There couldn’t have been more than a few hundred spectators in the ground, but what we saw turned out to be a demonstration of what Test cricket is all about.

I had hardly got to my seat when Tremlett produced a beauty that found the edge of M. Jayawardene’s bat and was caught at slip. Sri Lanka 33-3. A few minutes later Samaraweera played an inexplicable slash at spinner Graham Swann and dragged the ball onto his stumps; 36-4. Swann then disposed of Sangakkara and Maharoof, and Tremlett took the wicket of P. Jayawardene, all with the score on 43. Sri Lanka’s batting, so solid in the first innings was now in pieces on the floor. In came Herath with the air of a man wishing to commit suicide. Eventually he succeeded, playing an agricultural swipe at a delivery from Swann; he missed and the ball hit him on the back leg, plumb in front of the wicket. At 52-8 Sri Lanka looked doomed. Perera decided to take the attack to England. He played some good shots, as well as some lucky ones, and was fortunate to be dropped when two fielders ran into each other. Nevertheless, he and Mendis steadied the Sri Lankan ship for a while. I on the other hand was literally shaking with excitement and anticipation, hoping that I was about to witness a spectacular finale.

The score quickly moved onto 82 and it looked like Sri Lanka might at least have a chance of making England bat again. Then Broad replaced Tremlett, Perera tried to flick him away and Ian Bell took a superb reaction catch at short leg. 82-9. Last man Lakmal departed without troubling the scorers just three balls later, caught at 3rd slip by Alastair Cook. England had won by an innings and 14 runs. Amazing.

It had all been so exciting I hadn’t even had time to think about going for a beer. I think I’ll have one while I watch the highlights on TV.

There really is nothing like Test cricket, you know…

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Missing Mass Hysteria

Posted in Astrohype, The Universe and Stuff with tags , , , on May 30, 2011 by telescoper

It’s usually very satisfying to see science get covered in the popular media. Even if the story gets a little simplified or, more likely, garbled, press coverage often succeeds in getting at least a bit of the truth across. My own field of astrophysics has more popular appeal than many other branches of physics, but can nevertheless involve complex theoretical ideas and difficult observations that can be difficult to disseminate in a form suitable for public consumption. For the most part, the press do a good job for astronomy but occasionally news stories emerge that are simply ridiculous.

Take this one, for example, which begins:

A Monash student has made a breakthrough in the field of astrophysics, discovering what has until now been described as the Universe’s ‘missing mass’. Amelia Fraser-McKelvie, working within a team at the Monash School of Physics, conducted a targeted X-ray search for the matter and within just three months found it – or at least some of it.

What makes the discovery all the more noteworthy is the fact that Ms Fraser-McKelvie is not a career researcher, or even studying at a postgraduate level. She is a 22-year-old undergraduate Aerospace Engineering/Science student who pinpointed the missing mass during a summer scholarship, working with two astrophysicists at the School of Physics, Dr Kevin Pimbblet and Dr Jasmina Lazendic-Galloway.

On the face of it, this sounds an extremely interesting story not only because it apparently involves a major scientific breakthrough, but also because the result was achieved by an undergraduate student working on a summer programme. Unfortunately, however, a little digging reveals that there is much less to it than meets the eye. I know of many astronomers around the world who think the Press Office at Monash University is guilty of shameless exaggeration in the press release that initiated this bubble. This sort of deliberately misleading distortion is very bad for science, as it almost inevitably ends up splattered in unrecognisable form all over the media, especially the downmarket end.

Here is the abstract of the actual paper which this story is supposed to be about:

Most of the baryons in the Universe are thought to be contained within filaments of galaxies, but as yet, no single study has published the observed properties of a large sample of known filaments to determine typical physical characteristics such as temperature and electron density. This paper presents a comprehensive large-scale search conducted for X-ray emission from a population of 41 bona fide filaments of galaxies to determine their X-ray flux and electron density. The sample is generated from Pimbblet et al.’s (2004) filament catalogue, which is in turn sourced from the 2 degree Field Galaxy Redshift Survey (2dFGRS). Since the filaments are expected to be very faint and of very low density, we used stacked ROSAT All-Sky Survey data. We detect a net surface brightness from our sample of filaments of (1.6 +/- 0.1) x 10^{-14} erg cm^{-2} s^{-1} arcmin^{-2} in the 0.9-1.3 keV energy band for 1 keV plasma, which implies an electron density of n_{e} = (4.7 +/- 0.2) x 10^{-4} h_{100}^{1/2} cm^{-3}. Finally, we examine if a filament’s membership to a supercluster leads to an enhanced electron density as reported by Kull & Bohringer (1999). We suggest it remains unclear if supercluster membership causes such an enhancement.

You won’t find anything in there about finding the “missing mass” of the Universe, nor will you find it anywhere else in the paper, because they haven’t. The “targeted X-ray search” involved stacking old ROSAT observations of filaments that were discovered and catalogued in previous papers; this study merely matched them to existing X-ray data. ROSAT ceased operations in 1999. The results do give some evidence for a higher electron density than previously thought in some of the filaments, so it’s a fairly interesting “incremental” paper, not by any stretch of the imagination revolutionary.

I’ve got nothing against Amelia Fraser-McKelvie, who seems to have done some solid scientific work during her summer internship, and who may not have played any role in spinnng the shameless press release that led to this story getting into the world’s media. However, the more senior scientists involved in this work should not have let the story come out in this form.

Guest Post – Bayesian Book Review

Posted in Bad Statistics, Books, Talks and Reviews with tags , , , on May 30, 2011 by telescoper

My regular commenter Anton circulated this book review by email yesterday and it stimulated quite a lot of reaction. I haven’t read the book myself, but I thought it would be fun to post his review on here to see whether it provokes similar responses. You can find the book on Amazon here (UK) or here ( USA). If you’re not completely au fait with Bayesian probability and the controversy around it, you might try reading one of my earlier posts about it, e.g. this one. I hope I can persuade some of the email commenters to upload their contributions through the box below!

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The Theory That Would Not Die: How Bayes’ Rule Cracked the Enigma Code, Hunted Down Russian Submarines, and Emerged Triumphant from Two Centuries of Controversy

by Sharon Bertsch Mcgrayne

I found reading this book, which is a history of Bayes’ theorem written for the layman, to be deeply frustrating. The author does not really understand what probability IS – which is the key to all cogent writing on the subject. She never mentions the sum and product rules, or that Bayes’ theorem is an easy consequence of them. She notes, correctly, that Bayesian methods or something equivalent to them have been rediscovered advantageously again and again in an amazing variety of practical applications, and says that this is because they are pragmatically better than frequentist sampling theory – ie, she never asks the question: Why do they work better and what deeper rationale explains this? RT Cox is not mentioned. Ed Jaynes is mentioned only in passing as someone whose Bayesian fervour supposedly put people off.

The author is correct that computer applications have catalysed the Bayesian revolution, but in the pages on image processing and other general inverse problems (p218-21) she manages to miss the key work through the 1980s of Steve Gull and John Skilling, and you will not find “Maximum entropy” in the index. She does get the key role of Markov Chain Monte Carlo methods in computer implementation of Bayesian methods, however. But I can’t find Dave Mackay either, who deserves to be in the relevant section about modern applications.

On the other hand, as a historian of Bayesianism from Bayes himself to about 1960, she is full of superb anecdotes and information about
people who are to us merely names on the top of papers, or whose personalities are mentioned tantalisingly briefly in Jaynes’ writing.
For this material alone I recommend the book to Bayesians of our sort and am glad that I bought it.