The insoluble pancake

Two years of blog posts and not a single one about astrophysics! But today, once again, I was interviewed by a journalist who wanted to know about dark matter. Wouldn’t we all! Around a year ago the maps of dark matter made by my collaborators in the
COSMOS project made the front page of Nature and as I was a co-author on the paper I got quite a few questions from curious journalists. I have a particularly fond memory of the intensive questioning I was given by Raphael Hittier of E-tele on the roof of the IAP building in the middle of a particularly cold Paris winter with a Siberian wind blasting across the terrace whilst Raphael asked me: “Qu’est-ce-que la matiere noir”? Ahhh…brr….

What indeed? I remember being astonished whilst I was a postdoctoral student in Durham to find out about the current orthodoxy, the Cold Dark Matter model (CDM for the initiated). And to learn that people had spent millions of hours of computer time on the world’s fastest computers making model universes filled with a mysterious substance whose exact properties were known very well (it’s a cold, dark, collisionless fluid which doesn’t interact with ordinary matter) — but whose precise nature was and still is a complete mystery. Okay, so we know what this stuff does — but what is it, anyway?

People have speculated that dark matter exists since at least the 1930’s when Fritz Zwicky realised that the rotation curves of galaxies could only be explained if there was a lot of matter in those galaxies which was not luminous. And in recent years gravitational lensing has given us spooky cosmic x-ray vision showing us where exactly the mass is, thanks to the deflection of light near gravitational sources. So maybe this stuff is really there.

As a graduate student, under the shadow of the cathedral in Durham, the mystery deepened even further. A lunch-time talk, I think it was, that wonderful Anglo-Saxon tradition (no-one would ever countenance such a thing in Italy or France, can you imagine working whilst eating?), rustling brown paper bags, crisp packets, coca-cola, and a presentation with a graph showing distance to supernovae plotted against the speed they were moving away from us. The “Hubble diagram”, named after mr. Edwin Hubble, who presented some of the first observational evidence that the Universe was expanding (which some of the theorists of the time actually expected). Every Hubble diagram I’d seen until then had showed a neat, linear relation between distance and velocity; the universe, the fabric of space and time itself, was expanding, and as a consequence more distant objects were moving away more rapidly. Except that in this Hubble diagram, there was something not right: some of the most very distant supernovae were just off the simple linear relation. Their error bars grazed the arrow-straight line of constant slope. But only a few of them.

It was an error, right? There was some mistake with the observations? Nobody wanted to believe that those outliers were real. It would meant that not only the Universe was expanding but also- gasp – accelerating. The cosy preferred model of the Universe that theorists had built up (which admittedly was looking a bit frayed for other reasons) would have to be discarded, radically revised, and someone would have to explain what exactly was pushing distant objects faster and faster apart, almost like a negative gravity.

But the outliers were real, and the Universe really is accelerating. The universe it seems is filled with some kind of invisible, dark energy, the exact nature of which is still unknown. It is this, somehow, which is accelerating the expansion of the Universe. Most of the mega-projects planned for astronomy in the next ten or twenty years will be devoted to finding out more about dark matter and dark energy, projects like LSST or Pann-starrs, which will map thousands of square degrees of sky to incredibly faint limits, making the most detailed maps of the universe, and hopefully ruling out some of the wackier models of dark energy.

But you do wonder, don’t you? I think of Mr. Ptolemy and his planetary epicycles, a complicated model which was replaced by something simpler and more universal (newtonian gravitation). The current cosmological model works really well — add in dark matter, dark energy turn the handle, and you can reproduce incredibly well all of the current cosmological observations to exquisite precision (modeling the formation of galaxies is another story). But the fact that almost all of the Universe (70% dark energy, 25% dark matter) consists of material of which we know almost nothing is more than a little unsettling — there may well be a hidden truth lurking in there, waiting to be discovered. A sign change that changes everything? An extra ingredient added to the model that makes 70% of the Universe suddenly become something else? We will find out soon enough, I hope.

Technorati Tags: Dark Energy, Dark Matter, cosmology

I have some amount of catching up to do. I realise that more than two months have elapsed between the last post and the one before that. It’s not as if I haven’t read anything or been anywhere: I just lacked a little bit of motivation, milord. So here goes again, this with E. M. Gombrich’s “History of art”:

It must have taken almost a year for me to read this book, but then I started it at the same time as Pynchon’s 1000-page “Against the day” and both of them are weighty tomes. The Gombrich was actually written in English, but I read the French translation, all five hundred pages of it. Another no mean feat in itself.

Gombrich’s book comes in many editions. There is the heavy coffee-table version, with colour reproductions of famous artworks interleaved with the text. I had bought the “edition de poche” which I carried with me during many months. In this edition, the plates are all at the back, and there are two bookmarks so one can find one’s way easily from the text to the illustrations. The green paper cover on my copy is now pretty worn, but all the pages are still there. The illustrations are a judicious selection of works of art spanning thousands of years of human civilization, from the caves in Lascaux to David Hockney. Deep underneath Paris, wedged between three other people in the tiny narrow seats of the line four metro, I felt more than a bit relieved to gaze at reproductions of Vermeer, Carvaggio, El Greco, Piero della Francesca, or to stare at pictures of famous buildings from Rome or Naples. I’m kind of disappointed to have finished the book, to no longer have those images with me wherever I go.

Gombrich is “old school”: he believes, unfashionably for today I suppose, that there is such a thing as art, that there are absolute standards of excellence which can be divined by any intelligent person and which endure over the centuries. Every plate is discussed and placed into context. I learned more than a little about each painter and architect but what was most interesting was the historical context. You see, at the start, thousands of years ago, there was not even the notion of “the artist”: there were artisans, who created objects on commission. Monuments for tombs, sculptures for public buildings. The renaissance in Italy, in Rome, in Florence: frescos for altars, paintings for churches. The best artists, like Caravaggio (I’ve just read a recent biography of him, maybe I will find time to write about it) could became very wealthy from their work. The next century, however, everything had changed. The commissions dried up; the reform in Northern Europe meant that displaying images in churches was proscribed. Artists could paint whatever they liked, but they lived a poverty-stricken existence; the best might be able to make a living from drawing portraits.

Fast-foward to the early 20th century. The impressionists: Paris is the world centre of art and culture. What I didn’t really appreciate was how much the impressionists were completely rejected by the critical press of the time before being accepted, famous and even rich. All this in the space of a few short years. It’s interesting to note that the term “impressionist” was derisory in intent — as was “gothic”, “baroque”, and “mannerist”. (As was Fred Hoyle’s “Big Bang”, too.)

In the last chapter, Gombrich makes some interesting comments about art and creation today. In our time, he says, it may be too early to distinguish between fashion and real movements in art which will still be talked about in a hundred years. But the initial rejection of the impressionists by the critics of their epoch has led to a gross overcorrection. Today, the most important aspect of any work of art is if it’s new; the search for novelty has become the most important aspect of creation. The public suffers from the same malady: the tradition of the new has rendered irrelevant all other traditions. This, added to the fact that artists today have an incredible freedom which has never existed in any time in history has led to some very strange effects indeed. Everyone is a revolutionary these days.

I’m not sure I completely agree with this. After all I spend more time at Beaubourg than I do at the Louvre; perhaps I am a sufferer as well. But it’s interesting to realise to what extent attitudes have changed over the centuries. I think after reading Gombrich’s book I do have a better appreciation of what constitutes a work of art, although it is not easy to put into words; the excellence with which the work has been executed perhaps, or the purity of the form, whatever that means. In the end it is perhaps better to look at the plates. Especially whilst making journeys through subterranean Paris, staring out the window from time to time at the utter blackness.