Tag Archives: science

Scientific Pilgrimages

One of the perks of being a scientist is that you end up travelling a hell of a lot, generally to places with universities and other sites of scientific interest (but not necessarily anything else of interest, as is sometimes the case…) This provides ample opportunity to do a bit of science sightseeing.

100" Hooker telescope, Mount Wilson Observatory

Over the past couple of months I’ve been in Pasadena, which is ripe for this sort of thing. I’ve been splitting my time between Caltech (the place of Feynman and Gell-Mann) and JPL (the place of rockets and twitchy security procedure); I can see Mount Wilson from my apartment; and there’s even the Cheesecake Factory, the (alleged) site of much of the action in the Big Bang Theory. A couple of highlights have been seeing the Hooker telescope — the very place where modern observational cosmology was founded — and visiting the Carnegie Observatories, or “Santa Barbara Street” as it was known back in the day when Hubble, and then Sandage, were knocking around. It’s even nice to just walk the same streets as Feynman.

Some of these visits feel like pilgrimages. Of the substantial number of places I’ve been able to visit over the past few years, a handful have inspired a genuine sense of awe, as if I were standing on hallowed ground. I think this comes from a feeling of being connected to the events and people that so significantly shaped our understanding of the Universe; to feel a small part of the momentous things I’ve been reading about in textbooks and popular articles for so long.  Standing on the spot where someone first split the atom, or first understood that the Universe had a beginning, separated from them by only a few decades — well, that’s as close as I can ever get.

I like the idea of being a part of a scientific tradition. Science is one of the more noble projects of humanity, and I feel pretty honoured to be able to participate in it — the same great adventure that occupied the Einsteins and Newtons of this world. Earning a place in said tradition isn’t easy, but at least I’m making some progress: my Erdos number is 5!


Numerical Cosmology titbits

I’m still at the Numerical Cosmology 2012 workshop in Cambridge (the last day is tomorrow). I’m pretty sleepy by now (9am start for talks makes Phil sad), but I figured I’d squeeze in a few stories before I retire to my bed.

Yesterday was one of those weird days that I seem have every so often which confirms to me that physics makes for an interesting life. After a full-ish programme of talks, we all watched Stephen Hawking unveil his new supercomputer, via video link, to an extremely chilly room just around the corner that we subsequently all piled into (along with grinning computer industry representatives and a TV crew) to prod the shiny new computer and gurn at the camera. Supercomputers are much smaller than they used to be. Later on, we had the conference dinner in Trinity Hall, where I sat opposite John Reid, one of the people involved in setting Fortran standards. Being the Python aficionado that I am (and also, having discovered earlier in the evening that Fortran 77 uses magic numbers for certain I/O tasks*), I solicited his thoughts on designing programming languages to encourage good programming style. Didn’t really get much out of him on that, but he did give an interesting talk on coarrays earlier in the day (coarrays are an extension to Fortran that are intended to make parallel computing a bit more transparent, and thus easier). Ho hum. I topped the evening off by introducing myself to Dick Bond as an emeritus professor. He didn’t seem convinced.

I also learned very, very much about High Performance Computing (HPC). By that, I don’t mean running your average MCMC code on the cluster in the basement – oh no, proper tens-of-thousands-of-cores stuff. It turns out that programming models and tools are beginning to look a little outdated in the face of modern HPC systems – technologies like OpenMP were apparently designed with a “many single-core nodes” architecture in mind, whereas we now have systems consisting of many nodes, each of which has many cores. Of course, it’s faster to transfer things between cores on a given node than it is to pass data between nodes, but OpenMP doesn’t make it easy to differentiate between the two situations. David Henty (Edinburgh) talked about the consequences of this for HPC – is guiding principle was to “keep data on the same device for as long as possible”. Transferring data and other communication between nodes is what kills performance on these massively parallel systems, since communication buses are intrinsically slower than working on-chip. Oh, and cache misses – if your parallel code isn’t scaling too well, or otherwise seems sluggish, the number one suspect has to be cache misses.

Another little performance-related tip comes courtesy of Hal Finkel (Argonne), who’s attempting trillion particle simulations (about 100x larger than the current state of the art) by using a whole host of clever computational tricks and optimisations. He mentioned that some architectures have specific instructions for providing rapid estimates of certain common floating point operations (e.g. square roots). If you can afford the reduced accuracy, using these prevents your code from having to branch and call sqrt() or whatever from a library. If this is happening in an inner loop – kerching! Easy instant speed-up.

And one final little note: Supercomputers break all of the time! The Mean Time Between Failures (MTBF) of a big computer system is typically a few days, so HPC codes have to store snapshots of their state (checkpoints) every few hours, and must support resuming from these checkpoints in order to be able to do anything useful.

* Why? Aaaaagh! Aaagh! (OK, it probably made slightly more sense at the time.)


I like to think that, 18 months (and three papers) into my PhD, I’ve learned a lot about how science works. The naive beliefs of my undergrad days have all but vanished, replaced with (presumably) slightly less naive ones. Science is messier than I thought, less “clean”. Things go wrong, mistakes are made, guesswork reigns, and absolute rigour is never attained. People, personalities and politics play a big role; egos and reputations are involved, and disagreements are common. Motivations are varied; not everyone is committed to some uniform ideal of “discovery” or “openness”. Science is a career like any other; success is not guaranteed, hard choices and sacrifices must be made, and some form of work/life balance attained. (By now, you might be thinking that I’ve been reading a little too much of PhD Comics, or that my supervisor has had the “getting a job” talk with me. Correcto.)

But while it’s easy to find expositions on the hidden flaws of academia all over the web, there have been plenty of pleasant aspects that I wasn’t expecting either. One thing that I’ve been getting a kick out of recently is exposure, or “recognition”, of my work. Although still decidedly a newcomer to the rarefied cosmological subfields in which I work, I’ve now put out enough papers and shown my face at enough conferences that some people know who I am and what I’ve been doing. So, when a scrap of evidence that someone cares about my work appears, it’s a great feeling. The novelty will wear off, I’m sure, and it’s hardly the reason I get up in the morning, but it is nice.

Some of the exposure that I’m talking about could be reasonably well expected, since my seniors in the department talk about it often enough. Citations? Check. Emails from other researchers? Yep. Cranks emailing me? Of course. But a couple of recent events were particularly pleasant, and wholly unexpected.

The first was having our kSZ+voids paper mentioned in Ellis, Maartens and MacCallum’s new textbook on relativistic cosmology (which looks excellent, by the way). Although I don’t believe that textbooks have any special claim to authority over other media, the fact that the paper is mentioned in one amplifies the feeling of having contributed something to the state of human knowledge, however minor. Maybe it’s my perception of books as being relatively permanent entities that does it? I should carve the damn thing in stone if that’s the case.

The second was being approached by a journalist and interviewed, by email, about some of my research. Some of this appears in a story about alternatives to dark energy on the PBS NOVA physics blog. That was an interesting experience too, and I like the idea that members of the general public will gain some insight into what I’m working on. Of course, I was exposed to some of the harsh realities of science/media interaction in the process – the story paints a very simplified picture of a complicated area of study, fails to credit lots of people who made important contributions, etc. (although for what it’s worth, I think the author, Charles, did a pretty good job). But it was still a good feeling to see my stuff mentioned in print (as it were).

I don’t anticipate changing my stance of “doing science because it’s interesting” and becoming a publicity whore off the back of these, but they put a smile on my face nevertheless.