Dark matters under discussion at Trinity College

In the throes of a recession, pondering the fabric of the cosmos is more important than ever, says physicist Gerry Gilmore who was at TCD last night, writes ARMINTA WALLACE.

TEN YEARS ago, nobody except physics buffs had even heard of dark matter. Now, everyone seems to be singing about it. Earlier this year the Dublin band Dark Room Notes released an album called We Love You Dark Matter, while a delightful ditty by the singer-songwriter Jonny Berliner poses the question to which the entire world of contemporary cosmology would like an answer. "So what does it feel like and how does it smell," runs the chorus of Berliner's song Dark Matter. "If you had some in a bucket, well how would you tell?"

One man who knows his galaxy clusters from his neutrino nuggets is Prof Gerry Gilmore from the Institute of Astronomy at Cambridge University, who gave a public lecture on dark matter at Trinity College, Dublin last night.

"Over the last two or three years we've been making dramatic progress in discovering what the universe is really made of and, in particular, what our Milky Way galaxy is made of," he told The Irish Times. "It has become clear that the universe out there is something very different to what we thought it was, and very different to what we can actually see ... People have become captivated by that idea."

A genial New Zealander who has spent much of his time gazing through the Hubble telescope in order to generate a 3D map of the universe, Prof Gilmore brought his Irish audience up to speed on the latest goings-on in his field. What dark matter might be made of is still a matter of considerable speculation, although Gilmore’s money is on an as-yet-unidentified elementary particle, “some mysterious new type of matter that’s not like anything we’ve ever touched”.

Essentially, however, dark matter is the glue that holds us all together. “Our sun is moving so fast that it should fly off into outer space. The whole Milky Way should fall apart, actually, because all the stars are moving way too fast to stay where they are. So there must be an awful lot of weight pulling on those stars, and on our sun, to hold them in place.”

On a bigger scale, the opposite is happening: we appear to live in a runaway universe, with galaxies flying away from each other at an ever-faster rate. This is caused by dark matter’s even more mysterious opposite, dark energy – which, according to Prof Gilmore, is “a much flakier business than dark matter. We really have no idea what’s going on there.”

In a world dominated by recession and climate change, do we have time for such outré concerns as the fabric of the cosmos? Besides being an astronomer, Gilmore is a lecturer in experimental philosophy who believes that humankind’s approach to practical matters should be informed by our most up-to-date thinking on the big questions of existence. If we’re to make real intellectual progress, we may need to start singing from a new, revised hymn-sheet, he suggests. And he insists that dark matter has a great deal to teach us, not just about our insignificance in the greater scheme of things, but also about the nature of human imagination. “People often think that science is just technology, and that the universe is just like your back garden, only a bit bigger. But it isn’t.”

The universe explained, sort of

What is dark matter?An invisible, undetectable substance that makes up some 25 per cent of the critical density of the universe. By contrast, everything we can actually see – from enormous galaxies to Michael Jackson CDs – makes up just five per cent.

What is it made of?Nobody knows. All kinds of exotic particles have been mooted, from axions to zinos. According to one suggestion, it may be reverse-time matter from the future.

Where is it?Everywhere. According to some estimates, billions of dark matter particles are shooting through your body every second.

Why doesn't it leave a Harry Potter-style dark mark?Contrary to its name, according to Prof Gerry Gilmore, dark matter is actually transparent.

A DVD of Prof Gerry Gilmore’s lecture can be ordered from Astronomy Ireland at www.astronomy.ie