Andrew Jaffe: Leaves on the Line

I spent a few hours last week with a bunch of science fiction writers, giving them a tutorial on modern cosmology as part of the (first) “Physics for Fiction” workshop organized by my Imperial Astrophysics Colleague Dave Clements. The participants were some very big names in modern Science Fiction, and some hot up-and-coming writers, including Stephen Baxter, Pat Cadogan, Jaine Fenn, Paul McAuley, Hannu Rajaniemi and Alastair Reynolds. There are some photos, including a couple of me in full-on lecturing mode, by photos by Simon Bradshaw on Flickr.

Science fiction writers are a tough crowd: many of them are technically literate (there were a few science PhDs among them) but it’s also clear that, for their writing at least, they don’t just want to know the facts, they want to know what’s cool, and what can be relevant on a human scale, and how they can pass that along to their readers. If it can be vaguely realistic, all the better. So there was perhaps more interest in planets and quantum cryptography than in the origin of the Universe (although that’s a subject that some of our participants who dabble in the grandest “space opera” could sometimes touch on.

The students in my cosmology course had their exam last week.

There’s no doubt that they found the course tough this year — it was my first time teaching it, and I departed pretty significantly from the previous syllabus. Classically, cosmology was the study of the overall “world model” — the few parameters that describe the overall contents and geometry of the Universe, and courses have usually just concentrated upon the enumeration of these different models. But over the last decade or two we’ve narrowed down to what is becoming a standard model, and we cosmologists have begun to concentrate upon the growth of structure: the galaxies and clusters of galaxies that make the Universe interesting, not least because we need them for our own existence. Moreover, that structure directly teaches us about those contents which make them up and the geometry in which they are embedded. I wanted to give the students a chance to learn about the physics behind this large-scale structure, not traditionally at the heart of undergraduate cosmology courses.

Unfortunately, this also meant that the traditional undergraduate textbooks didn’t cover this material at the depth I needed, and so the students were forced to rely on my lectures and the notes they took there (and eventually a scanned and difficult-to-read copy of my written notes).

I sensed a bit of worry in the increasing numbers of questions from students in the weeks before the exam, and heard rumors of worries. But the day of the exam rolled around, and indeed when I re-read the questions it didn’t seem too bad, although there were some grumbles evident in the examination room.

Later I learned that there was a “record-breaking” number of complaints about the exam. I gather it was perceived to be difficult and unfamiliar.

So marking the exams in the past week, I was happy to find that the students performed just fine: the right “bell-shaped curve”, the correct mean, etc. (Of course I should point out that all results are subject to final approval by the Physics Department Examiners Committee.) I admit some puzzlement, therefore, about the reaction to the exam. Were they worried because the questions were different from those they had seen before? That, I admit, was the point of the exam — to test if they have actually learned something. Which, I am happy to point out, it seems that they had!

There was one question that almost all students got wrong, however. I asked about the “Cosmological Constant Problem” and whether it could be solved by the theory of cosmic inflation. The Cosmological Constant is a number that appears in General Relativity, and, although we can’t predict it for certain, we are pretty sure that if it’s not strictly zero, in most theories we would estimate that it ought to have a value something like 10¹²⁰ (that is 1 followed by 120 zeros!) times greater than that observed in the Universe today. I suppose I didn’t write on the board the words “Cosmological Constant Problem” next to that extraordinarily large number. (In the end, I reapportioned the small number of marks associated with that problem.) Inflation involves something very much like the cosmological constant, but occurring in the very early Universe — so inflation can’t help us with the 120 zeroes, alas.

Next year, I’ll be sure to spell all of this out, but I’ll also show this movie of my old grad-school friend, collaborator, and colleague Lloyd Knox, now a professor at the University of California, Davis, singing this song about Dark Energy (of which the cosmological constant is a particular manifestation):

The scientifically-accurate lyrics are sung to the tune of Neutral Milk Hotel’s “In the Aeroplane over the Sea”.

Finally, I’d welcome comments on the course or the exam, anonymous or otherwise, from any students who may come across this post.

The Astrophysical Journal has recently shifted publishers from the University of Chicago Press to the Institute of Physics. There seems to have been very little fuss in the process, but I was amused to notice this Erratum for the article “A Search for Cosmic Microwave Background Anisotropies on Arcminute Scales With Bolocam”:

As a result of an error at the Publisher, the term “frequentist” was erroneously changed to “most frequent” throughout the article. IOP Publishing sincerely regrets this error.

Today is Ada Lovelace Day, “an international day of blogging to draw attention to women excelling in technology.” I — along with more than a thousand other people — have pledged to write about a female role model in technology.

Ada Lovelace was Byron’s daughter and worked with computer pioneer Charles Babbage on his “Computing Engines” — and is widely thought of as the first computer programmer. A reconstruction of the “Difference Engine” is on view at the Science Museum around the corner from here, and if you’re reading this on 24 March, you can go and talk to Ada herself!

But I want to talk not about a programmer, but a computer. That is, a computer named Henrietta Swan Leavitt. In the early 20th Century, some (always male) astronomers had batteries of (almost always female) “computers” working for them, doing their calculations and other supposedly menial scientific work.

Leavitt — who had graduated from Radcliffe College — was employed by Harvard astronomer Charles Pickering to analyze photographic plates: she counted stars and measured their brightness. Pickering was particularly interested in “variable stars”, which changed their brightness over time. The most interesting variable stars changed in a regular pattern and Leavitt noticed that, for a certain class of these stars known as Cepheids, the brighter ones had longer periods. Eventually, in 1912, she made this more precise, and to this day the “Cepheid Period-Luminosity Relationship” remains one of the most important tools in the astronomers box.

It’s easy enough to measure the period of a Cepheid variable star: just keep taking data, make a graph, and see how long it takes to repeat itself. Then, from the Period-Luminosity relationship, we can determine its intrinsic luminosity. But we can also easily measure how bright it appears to us, and use this, along with the inverse-square relationship between intrinsic luminosity and apparent brightness, to get the distance to the star. That is, if we put the same star twice as far away, it’s four times dimmer; three times as far is nine times dimmer, etc.

This was just the technique that astronomy needed, and within a couple of decades it had led to a revolution in our understanding of the scale of the cosmos. First, it enabled astronomers to map out the Milky Way. But at this time, it wasn’t even clear whether the Milky Way was the only agglomeration of stars in the Universe, or one amongst many. Indeed, this was the subject of the so-called “great debate” in 1921 between American astronomers Harlow Shapley and Heber Curtis. Shapley argued that all of the nebuale (fuzzy patches) on the sky were just local collections of stars, or extended clouds of gas, while Curtis argued that some of them (in particular, Andromeda) were galaxies — “Island Universes” as they were called — like our own. By at least some accounts, Shapley won the debate at the time.

But very soon after, due to Leavitt’s work, Edwin Hubble determined that Curtis was correct: he saw the signature of Cepheid stars in (what turned out to be) the Andromeda galaxy and used them to measure the distance, which turned out to be much further away than the stars in the galaxy. A few years later, Hubble used Leavitt’s Period-Luminosity relationship to make an even more startling discovery: more distant galaxies were receding from us at a speed (measured using the galaxy’s redshift) proportional to their distance from us. This is the observational basis for the Big Bang theory of the Universe, tested and proven time and again in the eighty or so years since then.

Leavitt’s relationship remains crucial to astronomy and cosmology. The Hubble Space Telescope’s “Key Project” was to measure the brightness and period of Cepheid stars in galaxies as far away as possible, determining Hubble’s proportionality constant and set an overall scale for distances in the Universe.

The social situation of academic astronomy of her day strongly limited Leavitt’s options — women weren’t allowed to operate telescopes, and it was yet more difficult for her as she was deaf, as well. Although Leavitt was “only” employed as a computer, she was eventually nominated for a Nobel prize for her work — but she had already died. We can only hope that the continued use of her results and insight to this day is a small recompense and recognition of her life and work.

Just a quick apology for the lack of words appearing on the page here lately. In addition to planning for the upcoming launch of the Planck Satellite, I’ve been swamped with teaching my first-ever full-length undergraduate cosmology course. It’s lots of fun, but the biggest challenge is just systematizing this whole body of knowledge that I am supposed to already know so well. Like most scientists, I don’t quite want to take the information directly from someone else’s textbook (although there are quite a few good ones at the right level, notably Rowan-Robinson’s Cosmology and Liddle’s An Introduction to Modern Cosmology) so I am trying to put it all together in a way that fits my way of thinking about it (and, I hope, my students’). But probably, this is just my version of Blake’s “I must create a system or be enslaved by another man’s” (of course I am purposefully ignoring his next line from Jerusalem, the very wrongheaded miscomprehension of science, “I will not reason and compare: my business is to create”).

P.S. If you’re a student, feel free to comment here (anonymously, if you’d prefer) or on our favorite e-learning system at Imperial).

I’ve been busy the last few weeks, writing documents for the Planck SGS RR, grant proposals, getting ready for the exam season, and (I know I can’t complain), travelling to the Aegean.

But this afternoon I took a few hours off and attended the Imperial College postgraduate degree ceremony. In and amongst the several hundred students received their degrees were all three of my first students (I celebrated their successful PhD vivas here, here and here). There were a couple of short speeches, and a few honorary degrees awarded (the morning ceremony gave one to F1 head and infamous labour donor Bernie Ecclestone), but most of the time was taken up by the students marching up one at a time and shaking the hand of an Imperial luminary. In addition to my students, their were a few other astrophysics PhDs awarded, including to Dr Brian May, who got (by far) the biggest cheer of the day. Me, I got the rare honor of sitting on the stage of the Royal Albert Hall, in my academic regalia (American PhDs robes are heavier than those from the UK, for reasons that escape me, not ideal for a couple of hours under stage lights — and it now appears that my hood wasn’t even the proper maroon and black combo that my Chicago degree apparently calls for).

I admit I was inordinately proud of my students, in my meagre supervisory role as Doktorvater (to use the excellent Germanic term for supervisor): they’ve all done fantastic theses, important science, and most importantly by the end I was able to just get out of the way while they did the hard work. Congratulations again to each of them.

Congratulations to Joe Zuntz, recipient of Imperial Astrophysics’ latest Doctorate for successfully defending his entertainingly-titled Ph.D. Thesis, “Cosmic Microwave Background Power Spectrum Estimation and Prediction with Curious Methods and Theories”. Joe had been my student since 2004, working on topics from hard-core data analysis with the MAXIPOL team to exploring the repercussions of exotic theories such as the Causal Set idea for unifying quantum mechanics with relativity (which, alas, he has shown is unlikely to be able to match our current observations). Joe has already moved over to a postdoctoral fellowship at Oxford where he is sure to (continue to) prosper. Congratulations, Dr. Z!

I gave the last lecture in my Fourier class today. I think the course started alright, but I seemed to be losing the students for the last few lectures (not helped by the fact that three of the ten hours of the course were 5-6pm on Fridays, but a good workman doesn’t blame his tools…). Trying to get some immediate feedback (although still too late to do this year’s cohort any good) I handed out sheets of paper and asked them to write down, anonymously, something they understood, something they didn’t understand (a request greeted with an uncomfortably loud giggle) and any other comments. Although I only got about a dozen responses, there were some commonalities: indeed the first half of the course (Fourier Series) seemed well-understood, and the second half (Fourier Transforms) much less so; I should try to include more examples of the use of the methods (which will require changing the syllabus a bit), and more explanation of what the mathematics mean.

But one remark stood out: “Your handwriting is really bad. And you smell. Sorry.” Further comments — perhaps from readers who might have some knowledge of the subject — welcome.

Too busy for much blogging for the next few weeks. In the meantime:

First, my grad students: Goodbye to one just finishing, hello to my new one, congratulations to the one who just transferred to official PhD-student status, and, finally, to the one staying on as a postdoc! I’m excited that I’m able to still work with all of them on various projects, all concentrating on understanding the state of the Universe at its very earliest moments.

Second, to the undergrads: I hope that my teaching is going better than last year.

Third, the new record from my homestate boy, Bruce Springsteen, is better than you might expect from a still-left-wing pro-Union old-fashioned rock’n’roller. And “Girls in Their Summer Clothes” sounds like it could have been written and performed by Stephen Merritt and his Magnetic Fields (this is intended as a huge compliment!).

Next time, an update on the odd combination of Philip Glass’s versions of Leonard Cohen’s poems. And maybe that 16-solar-mass Black Hole (technical paper here). Conversely, I am unlikely to usefully comment on race relations as seen through the eyes James Watson or Sasha Frere-Jones. But the rest of the blogosphere has those well in hand.

Well, Summer break is over, the days are surprisingly short already, the sky is rarely clear, and the students are back.

Warm-weather highlights ranged from the intellectual pleasures of my visits to Portugal and Chicago, to the rather more visceral ones of Sonic Youth’s Daydream Nation at the Roundhouse, The Hold Steady at Shepherds Bush, and the diminutive Prince somehow filling up the massive O2 arena formerly known as The Dome. I also let my PhD Alma Mater pimp me to promote themselves, but I got lunch with the writer of Freakonomics out of it, and a surprisingly wonderful cocktail party at the residence of the used-car-salesman-cum-American Ambassador in London.

But now, back to real work. I’ve spent the day in front of my computer, more even than usual, dealing with the repercussions of our having decided to give the returning second-year students a test to get them to flex their mathematical muscles in preparation for the year — during which they’re liable to see lots of new mathematical and physical concepts for the very first time. We’ve decided to run the test through our online learning system, and, unfortunately, new technology almost always has its quirks: we had some fires to quench in the early hours of the day, but things seem to be running smoothly now. My proverbial and actual fingers are all crossed.

I’ll be covering quite a few of those new concepts in my second attempt at teaching our course on Fourier Methods; it didn’t go very well, last time, I must admit, and I’m hoping that the changes I’ve made in both the form and the content of the course — and the test they’re taking now — will make it better for the students. Feedback, positive, negative, or even ranting, is appreciated, from any present or past students.