Archive for the Biographical Category

Phase Correlations and Cosmic Structure

Posted in Biographical, The Universe and Stuff with tags , , , on July 9, 2022 by telescoper

I’m indebted to a friend for tipping me off about a nice paper that appeared recently on the arXiv by Franco et al. with the title First measurement of projected phase correlations and large-scale structure constraints. The abstract is here:

Phase correlations are an efficient way to extract astrophysical information that is largely independent from the power spectrum. We develop an estimator for the line correlation function (LCF) of projected fields, given by the correlation between the harmonic-space phases at three equidistant points on a great circle. We make a first, 6.5σ measurement of phase correlations on data from the 2MPZ survey. Finally, we show that the LCF can significantly improve constraints on parameters describing the galaxy-halo connection that are typically degenerate using only two-point data.

 

I’ve worked on phase correlations myself (with a range of collaborators) – you can see a few of the papers here. Indeed I think it is fair to say I was one of the first people to explore ways of quantifying phase information in cosmology. Although I haven’t done anything on this recently (by which I mean in the last decade or so), other people have been developing very promising looking approaches (including the Line Correlation Function (LCF) explored in the above paper. In my view there is a lot of potential in this approach and as we await even more cosmological data and hopefully more people will look at this in future. In my opinion we still haven’t found the optimal way to exploit phase information statistically so there’s a lot of work to be done in this field.

Anyway, I thought I’d try to explain what phase correlations are and why they are important.

One of the challenges we cosmologists face is how to quantify the patterns we see in, for example, galaxy redshift surveys. In the relatively recent past the small size of the available data sets meant that only relatively crude descriptors could be used; anything sophisticated would be rendered useless by noise. For that reason, statistical analysis of galaxy clustering tended to be limited to the measurement of autocorrelation functions, usually constructed in Fourier space in the form of power spectra; you can find a nice review here.

Because it is so robust and contains a great deal of important information, the power spectrum has become ubiquitous in cosmology. But I think it’s important to realize its limitations.

Take a look at these two N-body computer simulations of large-scale structure:

The one on the left is a proper simulation of the “cosmic web” which is at least qualitatively realistic, in that in contains filaments, clusters and voids pretty much like what is observed in galaxy surveys.

To make the picture on the right I first  took the Fourier transform of the original  simulation. This approach follows the best advice I ever got from my thesis supervisor: “if you can’t think of anything else to do, try Fourier-transforming everything.”

Anyway each Fourier mode is complex and can therefore be characterized by an amplitude and a phase (the modulus and argument of the complex quantity). What I did next was to randomly reshuffle all the phases while leaving the amplitudes alone. I then performed the inverse Fourier transform to construct the image shown on the right.

What this procedure does is to produce a new image which has exactly the same power spectrum as the first. You might be surprised by how little the pattern on the right resembles that on the left, given that they share this property; the distribution on the right is much fuzzier. In fact, the sharply delineated features  are produced by mode-mode correlations and are therefore not well described by the power spectrum, which involves only the amplitude of each separate mode.

If you’re confused by this, consider the Fourier transforms of (a) white noise and (b) a Dirac delta-function. Both produce flat power-spectra, but they look very different in real space because in (b) all the Fourier modes are correlated in such away that they are in phase at the one location where the pattern is not zero; everywhere else they interfere destructively. In (a) the phases are distributed randomly.

The moral of this is that there is much more to the pattern of galaxy clustering than meets the power spectrum…

R.I.P. Jim Bardeen (1939-2022)

Posted in Biographical, The Universe and Stuff with tags , , , , , on July 4, 2022 by telescoper

I was saddened this morning to hear news of the death at the age of 83 of Jim Bardeen who passed away on June 20th 2022. Jim – the son of John Bardeen, who won two Nobel physics prizes – did important work in theoretical cosmology and general relativity. In my own field of cosmology he is probably best known for his work on perturbation theory where he clarified many longstanding issues about gauge-dependence and as the first author of the famous and heavily cited “BBKS” (Bardeen, Bond, Kaiser & Szalay) paper, published in 1986:

BBKS

I received this as a very hefty preprint when I started my graduate studies back in 1985 and it scared the hell out of me. I still have the photocopy of the published version I made when it came out (in the days when PhD meant Doctor of Photocopying). You can find the paper on the NASA/ADS system here.

I met Jim Bardeen only once, at an Aspen Summer Workshop back in the 90s. He was a very shy and modest man but very kindly and polite. I remember a couple of times out hiking with him, when a discussion about physics was going on he would keep quiet until he had figured out what he thought and when he did choose to speak it was usually brief and invariably very incisive. He didn’t write all that many papers either, but those he did publish were invariably excellent.

Rest in peace, James Maxwell Bardeen (1939-2022)

A First Course in General Relativity

Posted in Biographical, Cardiff, Maynooth, The Universe and Stuff with tags , on June 30, 2022 by telescoper

This morning I received delivery of a brand new copy of the Third Edition (left) of A First Course in General Relativity by Bernard Schutz. I bought the First edition (right) way back in 1985 when I started out as a graduate student. Not surprisingly there is a lot of additional material in the 3rd edition about gravitational waves, which had not been discovered when the first edition was published. I notice also that Bernard has lost his “F”…

 In fact I have known Bernard for quite a long time, most recently as colleagues in the Data Innovation Research Institute in Cardiff. Before that he chaired the Panel that awarded me an SERC Advanced Fellowship in the days before STFC, and even before PPARC, way back in 1993. It just goes to show that even the most eminent scientists do occasionally make mistakes…

Anyway, the arrival of this book is a double coincidence because I’ve been thinking over the last couple of days about starting to organize teaching for next academic year. This isn’t easy as we still don’t know who is going to be available. We’re interviewing tomorrow for one of our vacant positions, actually. Yesterday also the University Bookshop sent out a request for textbooks to stock ahead of next academic year.

I was reflecting on the fact that I’ve been doing research in cosmology and theoretical astrophysics since 1985 and teaching undergraduate and postgraduate students since 1990 but I’ve never taught a course on general relativity. This may or may not change next year when teaching is allocated. There are many textbooks out there but, prompted by the arrival of Bernard’s new book, I was wondering if anyone reading this blog has any other recommendations, suitable for final-year undergraduate theoretical physics students, that might complement it on the reading list for my first course in general relativity, should I happen to give one?

Suggestions, please, through the comments box below!

The Queer Variable

Posted in Biographical, LGBT, Maynooth on June 29, 2022 by telescoper

As Pride Month comes to an end I thought I’d take this opportunity to advertise The Queer Variable which is a collection of 40 interviews with people who are studying or working in Science, Technology, Engineering, and Maths (STEM) and who are part of the LGBTQ+ community. You can find out more about the book and download it for free as a PDF or an e-book (whatever that is) here.

I am one of the people interviewed. My interview is actually the first in the book, which suggests I might have been the first person interviewed. Most of the interviews took place between 2020 and 2021, but I seem to remember doing the interview (over a rather choppy Zoom connection) back in late 2019 when I was a mere lad of 56 years old and before the Covid-19 pandemic. That all seems a very long time ago now!

Anyway, many thanks to Alfredo Carpineti and Shaun O’Boyle for compiling this collection and making it available. I hope people will find it useful.

Incidentally, one of the sponsors of this project is Science Foundation Ireland whose Director General, Prof. Philip Nolan (former President of Maynooth University) is quoted thusly:

SFI is delighted to support this important publication, which highlights the diverse spectrum of talent and experience among our LGBTQ+ research colleagues. STEM research must benefit all of our society and therefore STEM careers must also be welcoming and accessible to all members of our society. I thank all of the contributors for sharing their powerful personal stories and for providing insights into the challenges they have faced on their career journeys. By raising their voices, they are helping break down barriers for future generations.

Well said indeed.

A Second in Azed!

Posted in Biographical, Crosswords, Uncategorized with tags , on June 26, 2022 by telescoper

I was more than a little surprised this morning to find that I had won Second Prize in the latest Azed Crossword Competition in the Observer newspaper. This only the third time I’ve been among the medals (so to speak); I got a First Prize last year and a Third Prize exactly 11 years ago today.

As I’ve mentioned before, the monthly Azed Competition puzzle involves not only solving the Azed crossword but also supplying a cryptic clue for a word or phrase given only as a definition in the crossword. This competition is tough, partly because Azed is a stickler for syntactical soundness in submitted clues, and partly because many of the competitors are professional crossword setters. I’ve struggled recently to find the time and the energy to make a decent attempt at the Azed competition, but this competition puzzle was published on the last Bank Holiday Weekend so I had more time than usual to think about it. The target word was PEANUTS and my clue was

Source of allergic upset gripping one’s interior? Possibly!

Usually in a cryptic crossword clue one part of the clue provides a definition of the answer and the other a cryptic allusion to it; the solver has to identify each part. This clue is of a slightly different type called “&lit” which means that two different readings of the clue give you the definition and the cryptic allusion. The cryptic reading gives A (source of Allergic) in an anagram of UPSET containing N (oNe’s interior) indicated by the word “possibly”. UPSET is often used as a anagram indicator but not in this case. The surface reading of the clue also suggests PEANUTS.

P.S. I think the First Prize clue was very good indeed so congratulations to K. Bolton!

 

Bloomsday 2022

Posted in Biographical, Literature with tags , , , , on June 16, 2022 by telescoper

So it’s 16th June, a very special day in Ireland – and especially Dublin – because 16th June 1904 is the date on which the story takes place of Ulysses by James Joyce. Bloomsday – named after the character Leopold Bloom – is an annual celebration not only of all things Joycean but also of Ireland’s wider cultural and literary heritage. This year the Bloomsday Festival marks the centenary of the first publication of the complete Ulysses in Paris; it had been published in instalments before that but 2022 was when the full novel was published.

Here is a little video produced by the Irish Foreign Ministry spreading the impact of Bloomsday around the world:

This is also the first time for a few years that Bloomsday events have been held in person. I was toying with the idea of going into Dublin and wandering about some of the locations described in Ulysses, but I have too much work to do. One day I should try to write a paraody of Ulysses about a day in the life of a man who doesn’t go anywhere or do anything except spend the whole day on Microsoft Teams while real life passes him by.

If time permits, however, I will go out and buy the ingredients for a Gorgonzola and mustard sandwich, although unfortunately I shall have to forego the glass of Burgundy that Mr Bloom had with his.

Update: I tried the Gorgonzola and mustard sandwich. It’s an interesting (!) taste, but I don’t think I want to taste it again.

If you haven’t read Ulysses yet then you definitely should. It’s one of the great works of modern literature. And don’t let people put you off by telling you that it’s a difficult read. It really isn’t. It’s a long read that’s for sure -it’s over 900 pages – but the writing is full of colour and energy and it has a real sense of place. It’s a wonderful book.

(There’s also quite a lot of sex in it….)

Old School, Old Home

Posted in Biographical, History, Television with tags , , , , , on June 14, 2022 by telescoper

I’ve posted a few times posted about Benwell,  the part of Newcastle in which I grew up. For example I’ve posted about the little house where my first memories live here, and there’s an old photograph of it here:

The house itself (ours was the one on the left on this picture) was built of brick but to the left hand side you can just see a stone wall. The two cottages were demolished some time ago, along with Pendower School which was behind them as viewed from the picture.

I recently came across a picture of Pendower School taken sometime in the early 1990s when it was all boarded up and being sold for redevelopment.

The roof area with the fence around actually had a playground on it, used by Pendower Girls’ High school which occupied most of the building. The Infants and Junior schools which I attended were contained in the wing on the far right of the picture, the Infants downstairs and the Juniors upstairs. The school was built in 1929 and closed in 1992. It was used as a store for some time and then demolished.

The whole area including the school and the old cottages has now been covered with new houses, but for some reason they left the stone wall, part of which you can see to the left of the two cottages of the first picture. These were both taken from Ferguson’s Lane, which is immediately behind the stone wall to the left of the old photograph.

IMG-20121226-00026

IMG-20121226-00027

In the second picture you can see the filled in outlines of the door which led to our backyard (on the right) and (on the left) the holes through which the coalman used to deliver the coal that was the only form of heating in the house. There was no central heating and no heating at all upstairs, incidentally, so we had very cold bedrooms in winter!

Anyway, my excuse for reposting this trip down Ferguson’s Memory Lane is that I recently came across this fascinating picture taken from the West in 1897 of the old Benwell Village:

 

I had never seen this picture before but I am now quite sure from looking at street maps of the time that the houses you can see at the far left are in fact the cottages shown in the very first picture of this blog, including the one I lived in! I had never thought about it before, but notice how close the roofline is to the top of the first floor windows. Note also the wall separating them from the rest of the row as they were originally on a private estate.  In the background you can see Benwell Towers which, many years later, is where the TV series Byker Grove was filmed.

The row of houses you can see includes two pubs: The Hawthorn and The Green Tree. Both pubs survived in name though the newer premises were on opposite sides of the road when I lived there. These houses and pubs were all demolished long before I was born to make way for a road (Fox & Hounds Lane) which is basically continuation of Ferguson’s Lane but curving to the left.

A slightly better view from the early 1900s again shows the cottages on the far right. If you click to expand it you can see the drainpipe coming down the front of the house beside the first set of windows, exactly as in the first image on this blog.

Here’s a slightly different view of the same area, taken in 1920 and showing both sides of Ferguson’s Lane, again with Benwell Towers in the distance.

The lamppost is very useful for orienting these three images!

The cottages on the right no longer existed by the time I lived in Benwell: the new Hawthorn Inn stood at their location. At the far end of that row of houses was the old Smithy part of which became a dodgy garage called HQ Motors, which when I lived in the area was guarded by a very scary dog called Patch.

I never really knew what the old Benwell Village looked like. Now I have a much better idea, despite the fact the School the cottages and the pubs have now all vanished!

R.I.P. Phil Bennett (1948-2022)

Posted in Biographical, Rugby with tags , , , on June 13, 2022 by telescoper

With the passing of Phil Bennett at the age of 73, one of the true greats of Rugby Union has left us. Known to many as “Benny”, Phil Bennett was one of the best players ever to play at fly half for any team at any time. While the role of outside half in the modern game involves a much greater emphasis on kicking ability, Bennett just loved to run with the ball and had an amazing box of tricks with which to bamboozle the opposition, including but not limited to his famous sidestep.

Watch him here in the classic Barbarians versus New Zealand match in Cardiff 1973. The coach of a mere mortal would tear his hair out seeing a player what Bennett did under the shadow of his own posts, but he didn’t just get away with it – he started the move that created a part of Rugby history.

Phil Bennett took over as outside half for Wales from Barry John, who retired early from Rugby, and soon established himself as a permanent member of the phenomenal Welsh team of the early 1970s, joining the ranks of such legends as JPR Williams, Gerald Davies, and Gareth Edwards.

I was born in England but had family connections to Scotland, Wales and Ireland too. Partly because the English team of that period was not strong we always cheered for Wales when we watched the Five Nations games at home. Years later I managed to meet a few of the players of that time. I was flabbergasted to bump into JPR Williams once just outside my house; met Gerald Davies at an event in Cardiff Bay; and encountered Phil Bennett in a bookshop in Cardiff city centre. On all occasions I was completely tongue-tied, struck by the awe of being in the company of such people. All of them were modest and gracious. Remember that Rugby Union in those days was an amateur sport and none of these extraordinary men became rich like modern players do.

Anyway, here is another sensational try featuring Phil Bennett who both starts and finishes the move – with a fantastic contribution from Gerald Davies in between. In the words of the great Bill McLaren “That was absolute magic, and the whole crowd here knows it”.

Rest in Peace, Phil Bennett (1948-2022)

Concerning Covid Immunity

Posted in Biographical, Covid-19, Maynooth with tags , , , on June 10, 2022 by telescoper

Over the past few weeks I’ve attended a number of events at which most people were not wearing face coverings, including a recent Open Day at which I took my mask off in order to be heard in a very crowded space. Although I still wear a mask on public transport and in shops, most people now do not.

The first thing I’d note is that that there has been a clear upturn in reported Covid-19 cases, with figures now running at about 700 per day:

(Official figures for Ireland are only issued weekly these days…)

It’s not an alarming increase but hospitalizations and testing positivity are also increasing, though the mortality rate remains low because of the protection afforded by vaccines. Incidentally, it was a year ago on Wednesday (8th June) that I received my second Pfizer dose. One wonders how long vaccine protection will last, though, until further boosters are needed. If cases continue to rise I wonder if any measures will be put in place before the start of next academic year?

A number of my colleagues at home and abroad have attended scientific conferences recently, a number of which have led to mini-outbreaks and some instances of quite serious illness. Although most people seem to think Covid has gone away, it clearly hasn’t. A resurgence is all we need right now.

Anyway, one of my colleagues at work expressed surprise that I didn’t catch Covid during the largely unmasked Open Day at the end of April. Of course I might have done but I certainly didn’t display any symptoms. I’ve actually been quite surprised that I have never shown any sign of SARS-Cov2 at all during the entire period of the pandemic, while many of my colleagues and students in the Department have come down with it.

Coincidentally, a comment appeared yesterday on a blog post I wrote a while ago in which I revealed that I have the  CCR5-Δ32 genetic mutation which confers protection against HIV infection. As a matter of fact I have it twice (i.e. homozygotic). For one thing the commenter pointed out that this mutation may have protected against smallpox, which means some evolutionary selection may have been involved in its propagation. The commenter also drew attention to the evidence – by no means conclusive at this stage – that this mutation may also protect against Covid-19. If you’re interested here are links to some papers:

The last of these is a preprint but the other two are peer-reviewed publications.

Could it be that I’ve yet again been a jammy bastard and inherited immunity to Covid-19 too?

Writing, Publishing and Blogging

Posted in Biographical, Maynooth on June 8, 2022 by telescoper

This morning I saw this bit of guidance about writing a blog produced by a colleague from Maynooth:

I’m not sure how well I’ve followed this guidance over the last 14 years or so but was struck by the assertion that “a blogpost is a publication”. It reminded me of a webinar I did a while ago about Open Access publication which led to a discussion of whether or not a preprint is a publication. Taking the definition of “publish” to be “to issue to the public”, I think it is. In the digital era methods of publication are much simpler and more diverse than in the days when everything was circulated on paper and although I haven’t thought much about it before, I agree on this basis that a blog post is indeed a publication.

That means I have 5942 publications! Or actually 5943 after I’ve published this one. Not counting a couple of hundred “proper” ones, of course…

Anyway I have never really seen a good reason why this blog should be entirely about my professional life. It is true that the most popular posts have proved to be about my research interests but people seem to read the other stuff too so I see no reason to be restrictive.

A dozen years ago I wrote a post about how and why I started blogging, and what follows is an edited version of that.

Lots of people have asked me over the years why I have a blog and why I apparently spend so much time writing it. Well, for me, there are two answers. The first is just that I enjoy writing. I think because of that I’ve always been able to write stuff fairly quickly and developed a little bit of a knack for it. I also sometimes find it easiest to figure out what I actually think about something by trying to write about it. Publishing a post written for this reason is almost irrelevant and there have been a few occasions when I’ve regretted posting items in which I’ve been “thinking out loud” in this way. Sometimes it’s good to remember that people may actually read what you write…

When I started blogging I realized that it gave me the chance to write about things quite different from the usual themes I had previously tackled in publications. I’d written scientific papers, textbooks, lecture notes, popular books and newspaper articles before but most had  been quite strictly controlled by editors and were always related to my scientific work.

It was only after I’d been blogging quite a while that I started doing music and poetry items, entirely for my own amusement, like keeping a scrapbook, but if people actually enjoy things that I’ve put up that they’d never seen before then all the better. I know a lot of people think I’m a pretentious twat for posting about poetry or Opera or modern jazz – some have said as much to my face, in fact – but that’s what I like. There’s enough blogs about pop music, TV celebrities and computer games already, not that I’d be able to write about them. I’m flattered too by the fact that some of my music and other posts have been linked to Wikipedia articles – and, no, I didn’t put them there!

The other reason I had for starting to blog is much more personal. I moved job from Nottingham to Cardiff in 2007, but I got caught up in the credit crunch and was unable to sell my old house for quite a while. I spent far too much time commuting from Nottingham to Cardiff and back for the weekends and got thoroughly depressed, a state of mind not helped by some other issues which I won’t go into. In the middle of this my father died. Though not entirely unexpected, I did have to take some time out to deal with it. He hadn’t left a will, and I had to sort out the legal side of things as well as dispose of his belongings and arrange the funeral. In the aftermath of all that I had pangs of nostalgia for my childhood in Newcastle and an urge to connect with all that through writing down some thoughts and memories. Many of my early posts on here were quite morbidly introspective and probably not much fun for anyone to read, but I found writing them quite cathartic, as indeed I’ve found other posts for different reasons.

Anyway, knowing my tendency to write bits and bobs and then forget about them, quite a few people had encouraged me to start writing a blog but I hadn’t done it because I didn’t know how to go about setting one up. Fortunately, after a public talk I’d given, Phil Brown of the British Association for the Advancement of Science gave me a few pointers to getting started writing a blog. After finally managing to sell off the Nottingham house and after relocating fully to Cardiff, I started blogging in 2008.

So there you are.  That’s some of why and most of how I came to start writing this blog. I wish I could say I had a mission to change the world, but it’s really just partly a big exercise in self-indulgence and partly a piece of occupational therapy.

I would add two things in my defence. One is that I think that among all the other stuff, I do a bit of public service on here. Any bits of news about funding, exciting or controversial science results and things I think my colleagues might find interesting tend to go on here and I do think that’s a useful thing to do. People in my own Department sometimes find things first from reading here, which I think adds a healthy bit of transparency to the otherwise closed world of academic life. The other thing to say is that, contrary to popular opinion, I don’t actually spend a huge amount of time writing the blog. Much of it is recycled and the rest thrown together quite quickly. I know it’s rubbish, but at least its fast…

Some time ago I came across the idea of a “commonplace book“. To paraphrase Wikipedia

Such books came into use in the middle ages and were essentially scrapbooks, filled with items of every kind: medical recipes, quotes, letters, poems, tables of weights and measures, proverbs, prayers, legal formulas. Commonplaces were used by readers, writers, students, and humanists as aids for remembering or developing useful concepts ideas or facts they had learned. Each commonplace book was unique to its creator’s particular interests.

Dare I say, just like a blog?