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).
A quick pointer to Initiative for Cosmology (iCosmo). The website brings together a bunch of useful calculations for physical cosmology — relatively simple quantities like the relationship between redshift and distance, and also more complicated ones like the power spectrum of density perturbations (which tells us the distribution of galaxies on the largest scales in the Universe) and quantities derived from that like the distortions in the shapes of galaxies due to gravitational lensing, when the path of light from galaxies is perturbed by intervening mass in the Universe. Combined with good documentation and tutorials (and downloadable source), it makes a good companion to sites such as LAMBDA’s CMB toolbox, which provides similar services targeted specifically at Cosmic Microwave Background science. iCosmo looks like it will be useful for researchers in the field as well as students, so thanks and congratulations to its creators (I’d like to point directly at the page listing them, but that doesn’t seem to be possible… instead, there’s a discussion forum at CosmoCoffee.).
Dick Bond, a friend, mentor and longtime collaborator has won the 2008 Gruber Cosmology prize. Dick’s work has been instrumental at bringing us into this age of “precision cosmology”. He has always concentrated on that interface between theory and observation, making predictions for what we would see in the Cosmic Microwave Background, and how we might best extract that information. The present industry in Cosmological Data Analysis is in no small part down to his ongoing work in the field. To quote the Gruber citation itself:
Professor Bond’s work has provided the theoretical framework to interpret the observed inhomogeneities in the fossil radiation left over from the early stages of expansion of the Universe—the Big Bang. Professor Bond’s research has helped us understand the transition from the nearly featureless early Universe to the wonderfully structured world of galaxies, stars and planets today.
There’s a blog post about gender differences in scientific literacy over at The Intersection. And no doubt, it is a scary statement about our culture and educational system (in the US in this case, although I suspect the results would be similar elsewhere) that men uniformly score better than women. But (as other commenters have noted) one question stood out:
The universe began with a huge explosion. (True)
* that right folks, almost 3/4 of female respondents answered incorrectly
Despite calling it the Big Bang (originally a derisive term coined by Fred Hoyle), the Universe didn’t start in anything that could be described as a “huge explosion”. Yes, it’s been expanding for fourteen billion years from an incomparably dense initial state, but that expansion is happening everywhere, not exploding out from some single point. So maybe women actually knew too much to be tricked by the wording?
I spent the week before last in Portugal working with the team designing and building the GEM telescope: The Polarized Galactic Emission Mapping Project in Portugal. GEM (aka GEM-P or even P-GEM-P) aims to measure the emission of our Milky Way galaxy using light at a wavelength of 6 cm. Those frequencies are dominated by synchrotron emission, generated by electrons deflected by the magnetic field of the galaxy. These measurements will give us invaluable information about the structure of the galaxy. Moreover, this emission is an important contaminant for the cosmological maps that experiments like the Planck Surveyor and its successors like the BPol project that many of us have just proposed to the European Space Agency.
GEM-P is being built mostly by a small group at the Instituto de Telecomunicações and the Universidade de Aveiro. Here’s me with a large part of the Aveiro team:
That’s Rui Fonseca, Domingos Barbosa, me, Dinis Magalhães and Luis Cupido. This wasn’t taken at the GEM-P lab, by the way, but in Luis’s backyard, and that’s the 5.5 meter dish he keeps there to play with and do things like track NASA spacecraft in the outer reaches of the solar system!
Aveiro is a lovely town (even The New York Times agrees) experiencing a pretty remarkable building boom that manages to combine a high-tech University with an old-fashioned fishing village. For me, that meant the useful combination of pretty ubiquitous wifi and great seafood. (More pictures of Aveiro here).
(I also got to spend some time wandering around Porto, where I stayed right down the road from Rem Koolhaas’s new Casa de Musica, just shortlisted for the RIBA Stirling Prize. Photos of the older bits of Porto here.)
This year’s Gruber Prize in Cosmology has been awarded to the two teams that used distant supernovae — exploding stars that are nearly “standard candles” — to be the first to conclusively determine that the expansion of the Universe is accelerating, likely due to something very much like Einstein’s “Cosmological Constant”. (Or, at least, among the first to observe the accelerated expansion, since Ostriker and Steinhardt had already dubbed the model “Cosmic Concordance” back in 1995, and even I managed to stake a claim, well before the Supernova data were in.)
One of the interesting things about the Gruber Prize is that the funds are given not only to the Principal Investigators, Brian Schmidt and Saul Perlmutter, but half of the funds are shared amongst the entire teams involved. So congratulations to everyone involved, and enjoy!
The Observer featured a lengthy article by Tim Adams bemoaning the generic scientific illiteracy of society today, tracing a line from CP Snow’s “Two Cultures” through Natalie Angier’s new book, The Canon:A Whirligig Tour of the Beautiful Basics of Science. It concentrates a bit too heavily on uber-agent John Brockman’s somewhat pretentious “Third Culture, a marriage of physics and philosophy, astronomy and art,” as exemplified by his website, The Edge, but it does finger a real and disturbing (but not really new) trend. But to me the real howler was the following quote:
George Smoot, the Nobel-winning astrophysicist who first identified the background radiation of the Big Bang and thereby invented cosmology.OK, first, George Smoot didn’t identify “the background radiation of the Big Bang”, he was the Principal Investigator of the DMR Instrument on the COBE satellite, which identified the fluctuations in the background radiation (aka the CMB), the seeds of structure that eventually grew into galaxies and cluster of galaxies in the Universe today. The CMB itself was first identified by Penzias and Wilson in the 1960s — for which they also won the Nobel Prize. That may give you a hint about the other problem here: George, although a pretty smart guy, certainly didn’t invent cosmology, which has been around as a legitimate scientific field at least since Einstein’s discovery of General Relativity, and as a human endeavor for thousands of years.
I haven’t had a chance to listen yet, but “Slacker Astronomy” is featuring a series of podcast interviews with cosmologists from the Kavli Center at the University of Chicago, where I got my PhD. There are interviews with my de facto PhD supervisor, Josh Frieman, my de jure supervisor (long story) Mike Turner, and even an interview in Second Life.
In other University of Chicago news, I’ll be on a panel discussing “Cosmic Frontiers” at The University of Chicago International Forum in London in September 28-29 (the big name on the marquee is “Freakonomics” economist Steven Levitt). So come along if you’re a Chicago alum (especially, presumably, if you feel like donating lots of money).
Yesterday evening I attended the launch party for Nature Network London, a new site run by Nature magazine, which hopes to be a web home for science and scientists in London. There are articles, blogs, discussion forums and calendars of scientific events.
Perhaps unsurprisingly, I ended up meeting lots of people from Imperial — whom of course I had never met here on campus. I also met the site’s editor, Matt Brown, as well as blogger Jennifer Rohn, who also runs the science/culture site LabLit.
It’s an ambitious idea, and anything that gets us out of our offices and talking with other scientists is welcome. The formal barriers to entry are quite low, but to get working scientists to spend their time blogging, posting in discussion forums, and just taking this newfangled social web 2.0 thing seriously may be a hard sell. We’ll have to hook ‘em young. However, “science” in London is dominated by Medicine and biology — we physical scientists are a distinct minority, and our interests, academic lives and ways of working are often very different indeed (for example, the biologists last night spent a lot of time trying to decide whether to approach someone like Paul Smith for a design of a fashionable lab coat — I’ve never worn a lab coat in my life!). Anyway, if you’re a London-based scientist of any stripe reading this, sign up and join in!
Tonight I’m off on a 24-hour jaunt to Rome to discuss our proposal for a new Satellite, BPol, to measure the CMB polarization (and thereby discover if inflation could be responsible for getting our Universe into the shape we find it today). Unfortunately, this satellite wouldn’t be launched until the late 2010s, which means that the data wouldn’t flow for a staggering decade and a half.
Luckily, cosmology will remain interesting while we’re waiting — as Tommaso Dorigo’s ongoing reports from our Outstanding questions for the standard cosmological model meeting continue to attest.
This week is the big “Outstanding questions for the standard cosmological model” meeting here at Imperial. I am too busy finishing up my topology talk to blog about it (and recovering from running 13.1 miles yesterday), but luckily Tommaso Dorigo has been on the ball (and has also taken some good photos which I’m sure will be posted soon).
If you are up tomorrow morning (i.e., Tuesday, 27 March), listen for a cosmological discussion on the BBC’s Today show, probably between conference organizer Carlo Contaldi and Michael Rowan-Robinson, president of the Royal Astronomical Society (and both from Imperial Physics).
I’m just back from a couple of days up in Edinburgh, one of my favorite cities in the UK. London is bigger, more intense, but Edinburgh is more beautiful, dominated by its landscape—London is New York to Edinburgh’s San Francisco.
I was up there to give the Edinburgh University Physics “General Interest Seminar”. Mostly, I talked about the physical theory behind and observations of the Cosmic Microwave Background, but I was also encouraged to make some philosophical excursions. Needless to say, I talked about Bayesian Probability, and this in turn gave me an excuse to talk about David Hume, my favorite philosopher, and son of Edinburgh. Hume was the first to pose the “problem of induction”: how can we justify our prediction of the future based on past events? How can we logically justify our idea that there is a set of principles that govern the workings of the Universe? The canonical version of this asks: how can we be sure that the sun will rise tomorrow? Yes, it’s done so every day up until now, but tomorrow’s sunrise doesn’t logically follow from that. One possible argument is that induction has always worked up until now, so we can expect it to work again in this case. But this seems to be a vicious circle (rather than a virtuous spiral). As I discussed a few weeks ago, I think this whole problem just grows out of a category error: one cannot make logical proofs of physical theories.
I also went down the dangerous road of discussing anthropic arguments in cosmology, to some extent rehashing the discussion in my review of Paul Davies’ “Goldilocks Enigma”.
But in between I talked about the current state of CMB data, our own efforts to constrain the topology of the Universe, and the satellites, balloons and telescopes that we hope will improve our knowledge even further over the coming few years.
Next up, a more general talk on the topology of the Universe at next week’s Outstanding questions for the standard cosmological model meeting, and then a more general review of the CMB at the Institute of Physics Nuclear and Particle Physics Divisional Conference.
In his comment on last week’s post, fellow physicist blogger Tommaso lets me know that he’ll be attending a meeting that we’re hosting here at Imperial College next week, Outstanding questions for the standard cosmological model. We’ll be casting a critical eye over current cosmological models and data, but I expect most of us will come to the conclusion that the whole structure is surprisingly weather-sturdy.
In fact if you’re any sort of astrophysicist, particle physicist or cosmologist, Imperial Physics is likely to have a meeting for you in London over the next few months. In addition to “Outstanding Questions”, we’ll have
- A meeting making plans for XEUS, April 2-4. XEUS is the X-Ray Evolving Universe Spectroscopy mission, an X-Ray telescope satellite under consideration by the European Space Agency;
- PASCOS (Particles, Strings and Cosmology) 07, July 2-7, the latest in a series of meetings examining the interface between theoretical particle physics and cosmology; and
- From IRAS to Herschel-Planck, July 9-7. This is a special meeting, in honor of Professor Michael Rowan-Robinson on his 65th Birthday. Michael is currently the head of our Astrophysics group, and is one of the founders of the field of sub-millimeter and infrared astronomy, using long-wavelength photons to observe those parts of the Universe often hidden behind clouds of dust — veiled stellar nurseries where indeed a significant fraction of the stars were formed in the universe’s first few billions of years. IRAS was the first large-scale infrared satellite, and Herschel (along with its sister spacecraft, Planck, about which you’ve heard plenty here) will be the next ambitious project to observe the whole sub-millimeter sky.
There was a pretty good turnout a last night’s Café Scientifique in London. Thanks to any and all who showed up to hear my spiel about the cosmos (and, crucially, to talk back). We talked about matter & antimatter, the Cosmic Microwave Background, and even more esoteric topics like the origins of time (about which I had nothing more interesting to say than many members of the audience).
Thanks especially to Daniel Glaser and Ashish Ranpura for running the Café Sci series, and to all the people at the Photographers’ Gallery.
And now a deomographic question: was anyone reading this in the audience? If so, did you read about it here on the blog, or via Café Sci? Please leave a comment and let me know.
I’ll be speaking at 7pm Tuesday, 16 January, at London’s Cafe Scientifique, held at the Photographers’ Gallery near Leicester Square. I’ll expound on “Why the Universe isn’t Boring” for about 20 minutes, followed by about an hour of questions and, apparently, free beer. I’ll be talking about why there is matter rather than an even mix of matter and antimatter, why the Universe is lumpy rather than smooth — some of the things that make it an interesting place to live, or indeed possible to live at all.
By the way, the posted title, “A Hitchhiker’s Guide to the Universe” wasn’t my idea, I promise.
Starting tomorrow, you’ll be able to sign up with MI5 to receive an email notice when the “Threat Level” changes. Right now it’s “severe”, but they have the fine-grained menu of “low”, “moderate”, “substantial”, “severe” and “critical” to choose from — we certainly need that much more detail compared to the meagre green/yellow/red of the US system that everyone checks each and every morning. In a grotesque act of fearmongering, MI5 use a picture from the September 11 wreckage of the World Trade Center on their page outlining “The Threats”.
But maybe we need a new level for “smelly”, like New York?
[Yes, I know there has been big cosmology news today, but in this twenty-four-science-blogging culture everyone else, like Sean, Clifford and Steinn, has already posted the lovely pictures, and fine explanations, of the dark matter distribution.]
The work that I’ve been doing with my student is featured on the cover of this week’s New Scientist. Unfortunately, a subscription is necessary to read the full article online, but if you do manage to find it on the web or the newsstand, you’ll find a much better explanation of the physics than I can manage here, as well as my koan-like utterances such as “if you look over here, you’re also looking over there”. There are more illuminating quotes from my friends and colleagues Glenn Starkman, Janna Levin and Dick Bond (all of whom I worked with at CITA in the 90s, coincidentally).
We’re exploring the overall topology of space, separate from its geometry. Geometry is described by the local curvature of space: what happens to straight lines like rays of light — do parallel rays intersect, do triangles have 180 degrees? But topology describes the way different parts of that geometry are connected to one another. Could I keep going in one direction and end up back where I started — even if space is flat, or much sooner than I would have thought by calculating the circumference of a sphere? The only way this can happen is if space has four-or-more-dimensional “handles” or “holes” (like a coffee mug or a donut). We can only picture this sort of topology by actually curving those surfaces, but mathematically we can describe topology and geometry completely independently, and there’s no reason to assume that the Universe shouldn’t allow both of them to be complicated and interesting. My student, Anastasia Niarchou, and I have made predictions about the patterns that might show up in the Cosmic Microwave Background in these weird “multi-connected” universes. This figure shows the kinds of patterns that you might see in the sky:
The first four are examples of these multi-connected universes, the final one is the standard, simply-connected case. We’ve then carefully compared these predictions with data from the WMAP satellite, using the Bayesian methodology that I never shut up about. Unfortunately, we have determined that the Universe doesn’t have one of a small set of particularly interesting topologies — but there are still plenty more to explore.
Update: From the comment below, it seems I wasn’t clear about what I meant by asking if I could “keep going in one direction and end up back where I started”. In a so-called “closed” universe (with k=-1, as noted in the comment) shaped like a sphere sitting in four dimensions, one can indeed go straight on and end up back where you started. This sort of Universe is, however, still simply-connected, and wasn’t what I was talking about. Even in a Universe that is locally curved like a sphere, it’s possible to have multiply-connected topology, so that you end up back again much sooner, or from a different direction, than you would have thought (from measuring the apparent circumference of the sphere). You can picture this in a three-dimensional cartoon by picturing a globe and trying to “tile” it with identical curved pieces. Except for making them all long and then (like peeling an orange along lines of longitude), this is actually a hard problem, and indeed it can only be done in a small number of ways. Each of those ways corresponds to the whole universe: when you leave one edge of the tile, you re-enter another one. In our three-dimensional space, this corresponds to leaving one face of a polyhedron and re-entering somewhere else. Very hard to picture, even for those of us who play with it every day. I fear this discussion may have confused the issue even further. If so, go read the article in New Scientist!
News flash: John Mather and George Smoot, two of the scientists behind the COBE Satellite, have won the 2006 Nobel Prize in Physics for their measurements of the average temperature of the CMB and the fluctuations about that average. (Here’s one self-aggrandizing reason why I find this particularly exciting.)
The average, measured by the FIRAS instrument, proves that the CMB is a “black body” to an accuracy actually better than the instrument was capable of measuring, which in turn proves that the Universe started out in a hot, dense state and has been expanding ever since — the hot Big Bang.
The DMR instrument measured tiny — one part in 100,000 — fluctuations on top of that average. These hot and cold spots trace the tiny initial lumps and voids that eventually grew into the so-called large-scale structure of galaxies and clusters of galaxies that we see today.
Of course these measurements open up some very big questions: why is the Universe so very nearly homogeneous (i.e., why is the temperature the same in every direction?)? What caused those tiny inhomogeneities that became everything that we can see in the Universe today? Unfortunately I’ve got lectures to prepare, so I can’t tell you about cosmological inflation, currently our best idea for solving both of these problems in one swoop….
(Images courtesy Lambda and the COBE Team.)
Physics-watchers will have found it hard to miss the recent flood [?] of public criticisms of String Theory, the currently favored candidate for a ‘theory of everything’ unifying particle physics and gravity (and therefore providing a fundamental theory of cosmology). The two most prominent have been Peter Woit from Columbia, who has spun off his blog, Not Even Wrong into a book of the same name, and Lee Smolin of the Perimeter Institute, who has written one of his own, The Trouble With Physics (whose publishers have been kind enough to send me a copy, so you can look forward to my commentary at some point when it gets to the top of my bedside table book pile).
Woit, in particular, continues to comment on the situation on his blog. And he’s got some suggestions for improving things, starting at the graduate level:
Although Woit specifically aims these comments at theoretical particle physics, just substitute “cosmology” into each of these ideas, and they stand up just as well. We’ve got too few senior jobs and too many people jumping on the latest bandwagon. But maybe I’m just getting curmudgeonly — although I’m not sure that I’m with the doomsayers like Woit and Smolin that this bespeaks a general crisis in physics, rather than just a period of consolidation, especially as cosmology in particular adjusts to its transition from a data-starved discipline to a data-driven one.
- Giving people directly out of graduate school longer term postdocs (e.g. 5-6 years), so they have more than 1-2 years in which to come up with something for their next job.
- Graduate student birth control, bringing the ratio of Ph.Ds to jobs to something reasonable, so that the job market is not so insanely competitive and people are more likely to feel that they can have a future in the field even if they don’t work on the latest, hottest topic.
- Senior theorists need to stop putting students to work on the latest, trendiest string theory topic, encourage their students to work on a wider variety of things. At the same time they need to change their standards for hiring postdocs and junior faculty, making it clear to applicants that they want to see original ideas, not the same thing everyone else is doing.
- The NSF/DOE should explicitly admit that particle theory research is in trouble, give guidance to people reviewing proposals that copycat proposals on the latest string theory topic will not be funded, and emphasize that priority will be given to diversity, that proposing to do something different will be a lot more likely to get you funded. This applies to grants for workshops/conferences, as well as grants to individuals and theory groups.
Anyone reading this blog has doubtless heard about the results announced a few weeks ago, observations of the “bullet cluster” claimed (in the title of the paper) to be “A direct empirical proof of the existence of dark matter.” (The basic idea is recounted better, and with prettier pictures, than I can do here by Sean in Cosmic Variance, and in their own press release.)
The bullet cluster is actually a pair of galaxy clusters that have recently slammed into one another. We call them “galaxy clusters” but in fact the galaxies themselves are a relatively small fraction of their mass. The rest is hot gas — shining in the x-rays — and, we think, dark matter. When the two clusters plowed into each other, the galaxies themselves, and the dark matter, just passed through, interacting only through gravity, but the gas actually collides, heating up in what is called a shock front. So we can easily observe that the galaxies, observed with optical telescopes, aren’t quite aligned with the gas, observed with the Chandra X-Ray satellite. Over the last decade it’s become possible to observe the mass distribution of clusters directly, using the technique of weak lensing. And it seems that the mass is aligned with the galaxies, not with the gas — much more mass, and more smoothly distributed, than the galaxies themselves. The argument rests on the idea that alternatives to dark matter, such as Modified Newtonian Gravity (MOND) would have the mass exactly tracing the light, specifically the x-ray-emitting gas. So: it must be dark matter. Case closed.
Well, sort of.
The simplest versions of MOND were always known to be too simple to apply to the largest scales such as clusters and the Universe as a whole (i.e., cosmology). But more recently, Bekenstein has created a “relativistic” version of the theory which, Skordis and collaborators have shown, reproduces at least some cosmological observations. This theory, known as TeVeS (for Tensor, Vector, Scalar gravity) is hardly simpler than a theory with Dark Matter; as the name implies to physicists, it requires a vector and a scalar field in addition to the metric tensor that characterizes Einstein’s relativity. These fields don’t weigh much — they’re not the dark matter — but the forces that they implicitly exert mimic its effects.
The vector field, in particular, can have unexpected repercussions beyond this, however: it’s a vector, an arrow, which means it has a direction. It breaks the symmetry of the situation, and could, in specific circumstances displace some gravitational effects from others (the lensing from the light, for example, perhaps in exactly the same way as dark matter — a distinction without a difference?). No one has performed the required calculations yet, but other groups have argued that other possibilities, such as Moffat’s MOG and massive neutrinos combined with these MOND-like theories could in principle explain offsets between lensing and light. Indeed, they point out that MOND-like theories have already had a problem with explaining observations of clusters in which the details of the mass distribution had rarely lined up with the light. (See this Cosmocoffee discussion for more, from the authors of these papers themselves.)
These responses point to the real worry here: any single observation can be refuted. (Worse, of course, is the simple fact that lots of observations are wrong, and it’s impossible to know at the time which ones.) Moreover, such an argument from a single case is the same tactic used by those offering weak evidence against the current paradigms (not to mention the real crackpots). Despite claims to the contrary, science does not progress by simple falsification, by the single case that brings down the old paradigm. Extraordinary claims require extraordinary evidence. Back when it was first suggested by Zwicky in the 1930s, the existence of dark matter was an extraordinary claim. Now, dark matter, especially the weakly interactive massive particles that seem to be a natural corollary to supersymmetric theories in particle physics, is a much more parsimonious explanation of the various observations of galaxies, clusters and the cosmos as a whole than these baroque theories. Refuting its existence would certainly be extraordinary — but so would declaring the issue completely finished, at least until its definitive non-gravitational detection.
The Balzan prize, worth 1,000,000 Swiss Francs, was just awarded to Andrew Lange and Paolo de Bernardis for their work as the original Principal Investigators of Boomerang, which, in 2000, produced the first high-resolution maps of the Cosmic Microwave Background and allowed a definitive measurement of the curvature of the Universe, in the sense of Einstein’s General Relativity. In fact, Boomerang showed that the Universe is flat: parallel lines don’t ever cross, and triangles have 180 degrees. I am lucky enough to be part of the Boomerang team, and I remember being interviewed on Irish radio at the time of our first results, and explaining to a puzzled newscaster that, no, we didn’t contradict Einstein: a flat Universe was just one of the particular kinds of curvature allowed by Relativity. Since then, Boomerang has refined its measurements of the cosmological parameters and, most recently, measured the CMB’s polarization (as I discussed about a year ago, and are summarized in this week’s Science).
Congratulations to Andrew and Paolo and the rest of the team.