Archive for Carlos Frenk

R.I.P. Richard Bower

Posted in Biographical, The Universe and Stuff with tags , , , , on January 10, 2023 by telescoper

I was shocked and saddened this weekend to hear of the death from cancer of Professor Richard Bower of Durham University. Richard was a leading light in the Institute for Computational Cosmology (ICC) at Durham, though his research interests spanned observational and theoretical studies of galaxy and cluster formation as well as numerical studies. 

I heard the sad news via social media and there have many tributes to and personal reminiscences of Richard have been circulated from friends, colleagues and former students, including this lovely one by Josh Borrow. I’m sure there will be official obituaries in due course that do justice to Richards personality and achievements in teaching and research; I’ll add links when I see them.

If I can add a personal note, I only worked on one project with Richard, about thirty years ago while I was still at Queen Mary & Westfield College in London. Doing the project was tremendous fun – so much so that the paper we ended up writing bears little relation to what we thought it would be like when we started. We were both young then – I think Richard was about a year younger than me – and both had a tendency to fly off at tangents, but fortunately we were working with two responsible adults (Carlos Frenk and Simon White) who kept us in order. I think the paper we wrote is a nice one, but the real point is that the whole experience was so enjoyable that it was not only formative experience for me from an intellectual point of view but also left me with very fond memories. Whenever we met subsequently, which happened fairly frequently and conferences and on panels and the like, we always talked about what a great time that was. It’s hard to accept we’ll never have that conversation again.

I send heartfelt condolences to Richard’s family, friends and colleagues, both past and present, and in Durham and elsewhere. was an irrepressible and irreplaceable character who will be greatly missed by the entire cosmological community.

Rest in peace, Richard Bower.

50 Years of the Astronomy Centre at the University of Sussex

Posted in Biographical, Education, The Universe and Stuff with tags , , , , , on October 18, 2016 by telescoper

On Saturday (15th October) I was back in Brighton for the first time since I left my job there at the end of July. The occasion was a very nice lunch party to celebrate 50 years of the Astronomy Centre at the University of Sussex, which started properly in 1966. It was a pleasant occasion, and great to have the chance to catch up with some people I haven’t seen for far too long. I had two stints in the Astronomy Centre: once as a student then postdoc from 1985 to 1990, and the other from 2013 to 2016 when I was Head of the School of which the Astronomy Centre is part. I had a lot more time to do research in the first incarnation than in the second!

Quite a few people present hadn’t realised I was no longer working at Sussex, which led to one or two slightly awkward conversations, but I was thankfully very far from being the centre of attention.

After the lunch itself we had short speeches from various alumni of the Astronomy Centre: esteemed science writer John Gribbbin (who was one of its first MSc students in 1966); Lord Martin Rees (who was briefly a Professor at Sussex, before he returned to Cambridge to take up the Plumian Professorship); John Barrow (who was my supervisor while I was there); Carlos Frenk (who was a postdoctoral researcher when I arrived in September 1985, but who left to take up a lectureship in Durham at the end of that year so we overlapped only for a short time); Andrew Liddle (who arrived near the end of my stay and was there for 22 years altogether, leaving at the end of 2012 to take up a post in Edinburgh); and Peter Thomas (current Director of the Astronomy Centre).

When I arrived in 1985 there were only four permanent faculty in the Astronomy Centre itself – Roger Tayler, Leon Mestel, John Barrow and Robert Smith – but research there was thriving and it was a great environment to work in. I count myself very lucky at having made such a good choice of a place to do my PhD DPhil. Leon and Robert both worked on stellar astrophysics, but after Leon’s retirement the centre increasingly focussed on cosmology and extragalactic astrophysics, which remains the case today. Roger Tayler sadly passed away in 1997, but Leon is still around: he is 89 years old and now lives in Cambridge.

Those present at the lunch were given a booklet featuring around 50 academic papers or other research “highlights”(e.g. the launch of Planck), approximately one for each year of the Astronomy Centre, chosen to be the “best” of that year. Each page was also shown as a slide during the lunch. I was thrilled to see that two of my papers (from 1987 and 1991 respectively) made it into the collection. The second one was published after I’d left Sussex, but I definitely did the work on it and submitted it while an employee of the Astronomy Centre. Andrew Liddle and John Barrow have the largest number of “greatest hits”, but the most famous paper is probably the classic “DEFW” which won Carlos Frenk and his collaborators the Gruber Prize about five years ago.

The book also contains various bits of interesting bibliometric information, such as this, which shows that the variation in the productivity of the Astronomy Centre over time.


Anyway, for those who are interested, the whole collection of slides can be viewed here:

Thanks to Seb Oliver and the rest of the Astronomy Centre for organizing this very enjoyable event – and for sending me the slides! Here’s to the next 50 years of Astronomy at the University of Sussex!


What’s the Matter?

Posted in The Universe and Stuff with tags , , , , , on September 19, 2011 by telescoper

I couldn’t resist a quick comment today on a news article to which my attention was drawn at the weekend. The piece concerns the nature of the dark matter that is thought to pervade the Universe. Most cosmologists believe that this is cold, which means that it is made of slow-moving particles (the temperature of  a gas being related to the speed of its constituent particles).  They also believe that it is not the sort of stuff that atoms are made of, i.e. protons, neutrons and electrons. In particular, it isn’t charged and therefore can’t interact with electromagnetic radiation, thus it is not only dark in the sense that it doesn’t shine but also transparent.

Cold Dark Matter (CDM) particles could be very massive, which would make them much more sluggish than lighter ones such as neutrinos (which would be hot dark matter), but there are other, more complicated, ways in which some exotic particles can end up in a slow-motion state without being massive.

So why do so many of us think the dark matter is cold? The answer to that is threefold. First, this is by far the simplest hypothesis to work on. In other words, good old Occam’s Razor. It’s simple because if the dark matter is cold there is no relevant physical scale associated with the speed of the particles. Everything is just dominated by the gravity, which means there are fewer equations to solve. Not that it’s exactly easy even in this case: huge supercomputers are needed to crunch the numbers.

The second reason is that particle physics has suggested a number of plausible candidates for non-baryonic candidates which could be cold dark matter particles. A favourite theoretical idea is supersymmetry, which predicts that standard model particles have counterparts that could be interesting from a cosmological point of view, such as the fermionic counterparts of standard model bosons. Some of these candidates could even be produced experimentally by the Large Hadron Collider.

The final reason is that CDM seems to work, at least on large scales. The pattern of galaxy clustering on large scales as measured by galaxy redshift surveys seems to fit very well with predictions of the theory, as do the observed properties of the cosmic microwave background.

However, one place where CDM is known to have a problem is on small scales. By small of course I mean in cosmological terms; we’re still talking about many thousands of light-years! There’s been a niggling worry for some time that the internal structure of galaxies, especially in their central regions,  isn’t quite what we expect on the basis of the CDM theory. Neither do the properties of the small satellite galaxies (“dwarfs”) seen orbiting the Milky Way seem to match what what we’d expect theoretically.

The above picture is taken from the BBC website. I’ve included it partly for a bit of decoration, but also to point out that the pictures are both computer simulations, not actual astronomical observations.

Anyway, the mismatch between the properties of dwarf galaxies and the predictions of CDM theory, while not being exactly new, is certainly a potential Achilles’ Heel for the otherwise successful model. Calculating the matter distribution on small scales however is a fearsome computational challenge requiring enormously high resolution. The disagreement may therefore be simply because the simulations are not good enough; “sub-grid” physics may be confusing us.

On the other hand, one should certainly not dismiss the possibility that CDM might actually be wrong. If the dark matter were not cold, but warm (or perhaps merely tepid), then it would produce less small-scale structure whilst not messing up the good fit to large-scale structure that we get with CDM.

So is the Dark Matter Cold or Warm or something else altogether? The correct answer is that we don’t know for sure, and as a matter of fact I think CDM is still favourite. But if the LHC rules out supersymmetric CDM candidates and the astronomical measurements continue to defy the theoretical predictions then the case for cold dark matter would be very much weakened. That might annoy some of its advocates in the cosmological community, such as Carlos Frenk (who is extensively quoted in the article), but it would at least mean that the hunt for the true nature of dark matter would be getting warmer.


Posted in The Universe and Stuff with tags , , , , , , , on June 2, 2011 by telescoper

Just a quickie this fine summer morning to pass on the news – for those of you who haven’t heard yet – that this year’s Gruber Prize for Cosmology has been awarded to Marc Davis (Berkeley, USA), George Efstathiou (Cambridge, UK), Carlos Frenk (Durham, UK) and Simon White (Garching, Germany). This prestigious award is given for their pioneering work on the Cold Dark Matter model of structure formation, which included some of the first large-scale N-body computer simulations. The “Gang of Four” produced a number of papers during the 1980s that established the idea that galaxies form by hierarchical clustering from small initial fluctuations in a matter distribution dominated by massive collisionless non-baryonic particles, the most famous of their papers being pretty universally referred to as DEFW.

In fact, if you’ll forgive me going on a trip down memory lane, that paper, published in 1985, was one of the first papers I read when I started my research degree the same year at Sussex. It was back in the days when everyone seemed to use a VAX for big computing jobs and the simulations presented in that paper involved a mere 323 = 32768 particles. You could probably run that kind of simulation on a mobile phone these days!

This early work on Cold Dark Matter wasn’t the final word, of course. Subsequent observational evidence for an accelerating Universe resulting in our standard cosmological model being modifiel to include an additional (large) component of dark energy in addition to dark matter. Nevertheless, the core ideas presented by DEFW established the basic foundations of structure formation upon which the current standard model is built.

Incidentally, you can read an interesting account of the discovery of the accelerating universe here; a cosmologist by the name of “George F. Stathew” plays a prominent role in that piece and it’s curious I’ve never heard of him before now.

Each of the four winners gets a share of the $500000 Gruber Prize, i.e. in “normalized” terms, they get $125000 each. Why is it so controversial to suggest dividing citation counts the same way? The DEFW paper has about 1500 citations according to ADS, so I think it’s quite reasonable to award the authors 370-odd each towards their respective h-indices. That’s still a pretty good result by any bibliometric standard!

The four also get a Gold Medal each to wear at parties, although by my previous logic they should have to share one between them. Perhaps George might consider donating his to Arsenal Football Club, as their trophy cabinet is looking rather empty these days?

None of the winners are Australian undergraduates, so this award probably won’t be considered newsworthy by the mass media. Believe it or not, however, the Gruber Prize is held in even higher regard by cosmologists than the Templeton Prize, so I’d like to take this opportunity to congratulate them myself for their thoroughly well-deserved honour!

Astronomy Look-alikes, No. 33

Posted in Astronomy Lookalikes with tags , on July 2, 2010 by telescoper

Last week’s epic first-round singles match at Wimbledon between John Isner and Nicholas Mahut will have reminded many people of the classic 1969 contest between Pancho Gonzales and Charlie Pasarell. What isn’t so well known is that after retiring from the professional tennis circuit, Pancho Gonzales took up a new identity as cosmologist Carlos Frenk. Makes a change from serving up balls for a living. Oh no, wait, hang on…

Pancho Gonzales

Carlos Frenk