Archive for Durham University

The Durham YETI

Posted in Talks and Reviews, The Universe and Stuff with tags , , , , on January 9, 2015 by telescoper

On Wednesday afternoon, after an important meeting that took up most of the morning, I headed off my train to Durham. Unusually by the standards of my recent experiences of railways, the trip went smoothly and I arrived on time. The cathedral was looking rather spectral when I arrived:

Durham

The occasion of my vist was the Young Experimentalists and Theorists Institute (YETI for short), a gathering of early career particle physicists, mainly graduate students. I was scheduled to give a 90-minute lecture on Cosmic Microwave Background Theory to the 40-50 folks attending the workshop. It was nice to get the chance to get away from budgets and spreadsheets for a time and talk about cosmology, and it was an interesting audience different from the usual more specialist crowd I get to talk to at graduate workshops. It’s good, especially for beginning research students, to find out about subjects outside their immediate research topic and I’m glad the YETI organizers appreciate that. On the other hand, CMB theory is a huge topic so it was difficult to decide what to put in and what to leave out.

Incidentally, 2015 sees the 50th anniversary of the discovery of the Cosmic Microwave Background, and with yet more exciting results due out soon I’m sure the CMB will be in the news a lot this year.

I spent Wednesday night at Collingwood College, where the conference delegates were accommodated, and gave my 90-minute talk, starting at 9am yesterday morning, paused for quick cup of coffee and then legged it back to Durham station for the return journey back to Brighton. It’s a pity I didn’t get the chance to stay longer, especially because the second speaker of the morning, on CMB Observations, was Jo Dunkley of Oxford University who this afternoon is giving a talk at the Royal Astronomical Society because she has just been awarded the Society’s Fowler Prize. I can’t attend that meeting because of work commitments either. Sigh.

The train journey back to Brighton went smoothly and on time too. Wonders never cease!

Anyway, thanks to the organizers of YETI for inviting me. I hope the talk was reasonably comprehensible. Apologies to my other friends at Durham for not hanging around, but I really didn’t have time to stop for a natter or, more importantly, a beer or several.

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An Integral Appendix

Posted in Biographical, Cute Problems, The Universe and Stuff with tags , , , , , , on August 7, 2013 by telescoper

After the conference dinner at the Ripples in the Cosmos meeting in Durham I attended recently, a group of us adjourned to the Castle bar for a drink or several. I ended up chatting to one of the locals, Richard Bower, mainly on the subject of beards. I suppose you could call it a chinwag. Only later on did  we get onto the subject of a paper we had both worked on a while ago. It was with some alarm that I later realized that the paper concerned was actually published twenty years ago. Sigh. Where did all that time go?

Anyway, Richard and I both remembered having a great time working on that paper which turned out to be a nice one, although it didn’t exactly set the world on fire in terms of citations. This paper was written before the standard “concordance” (LCDM) cosmology was firmly established and theorists were groping around for ways of reconciling observations of the CMB from the COBE satellite with large-scale structure in the galaxy distribution as well as the properties of individual galaxies. The (then) standard model (CDM with no Lambda) struggled to satisfy the observational constraints, so in typical theorists fashion we tried to think of a way to rescue it. The idea we came up with was “cooperative galaxy formation”, as explained in the abstract:

We consider a model in which galaxy formation occurs at high peaks of the mass density field, as in the standard picture for biased galaxy formation, but is further enhanced by the presence of nearby galaxies. This modification is accomplished by assuming the threshold for galaxy formation to be modulated by large-scale density fluctuations rather than to be spatially invariant. We show that even a weak modulation can produce significant large-scale clustering. In a universe dominated by cold dark matter, a 2 percent – 3 percent modulation on a scale exceeding 10/h Mpc produces enough additional clustering to fit the angular correlation function of the APM galaxy survey. We discuss several astrophysical mechanisms for which there are observational indications that cooperative effects could occur on the scale required.

I have to say that Richard did most of the actual work on this paper, though all four authors did spend a lot of time discussing whether the idea was viable in principle and, if so, how we should implement it mathematically. In the end, my contribution was pretty much limited to the Appendix, which you can click to make it larger if you’re interested.

t2png

As is often the case in work of this kind, everything boiled down to evaluating numerically a rather nasty integral. Coincidentally, I’d come across a similar problem in a totally different context a few years previously when I was working on my thesis and therefore just happened to know the neat trick described in the paper.

Two things struck me looking back on this after being reminded of it over that beer. One is that a typical modern laptop is powerful enough to evaluate the original integral without undue difficulty, so if this paper had been written nowadays we wouldn’t have bothered trying anything clever; my Appendix would probably not have been written. The other thing is that I sometimes hear colleagues bemoaning physics students’ lack of mathematical “problem-solving” ability, claiming that if students haven’t seen the problem before they don’t know what to do. The problem with that complaint is that it ignores the fact that many problems are the same as things you’ve solved before, if only you look at them in the right way. Problem solving is never going to be entirely about “pattern-matching” – some imagination and/or initiative is going to required sometimes- but you’d be surprised how many apparently intractable problems can be teased into a form to which standard methods can be applied. Don’t take this advice too far, though. There’s an old saying that goes “To a man who’s only got a hammer, everything looks like a nail”. But the first rule for solving “unseen” problems has to be to check whether you might in fact already have seen them…

The Epoch of Galaxy Formation, Durham 1988.

Posted in Biographical, The Universe and Stuff with tags , , , on August 2, 2012 by telescoper

The previous old conference photograph I posted seemed to be quite popular, so I thought I’d try an even older vintage. This was also taken at Durham, but at a meeting entitled The Epoch of Galaxy Formation, which took place between July 18th and 22nd 1988. Appropriately enough, this one is in glorious monochrome. Spot any familiar faces?

A Blast from the Past

Posted in Biographical with tags , , , on September 5, 2011 by telescoper

I’ve just remembered that the annual STFC summer school for all new PhD Students in Astronomy finished last week. This year it was held in the fine city of Glasgow and I trust a fine time was had by all,  thanks both to the excellent astronomy staff there who organised the whole thing,  and to the eminent invited speakers who supplied specialist lectures.

When I was just about to start my PhD (or, more accurately, DPhil) in 1985 there was a summer school like this too only that was before STFC and even before its predecessor,  PPARC. The Science and Engineering Research Council (SERC)  summer school I went to was actually held at Durham University; we all stayed in St Mary’s College, just over the road from the Physics Department. I remember it well and indeed still have the notes I took during the lectures there.

Coincidentally, I recently unearthed this picture which has, unfortunately, been slightly damaged on the left  hand side. It might be interesting for all those who attended this year’s School to see how many of this group are still doing research 26 years later; the newbies may even be able to identify their PhD supervisors!

I’m in the middle with the Peter Beardsley haircut, and you can easily pick out a number of people who are still active in astronomy research, e.g. Melvin Hoare (Leeds), Moira Jardine (St Andrews), Alan Fitzsimmons (QUB), Steve Warren (Imperial), Alastair Edge (Durham), and Jon Loveday (Sussex), to name but a few. Anyone else see anyone they recognize? Or anyone else who was there happen to be reading this blog? Please do let me know through the comments box!

UPDATE: I’m grateful to Melvin for pointing out to me that Andy Norton has already posted a version of this picture elsewhere, with a much more complete list of identifications!