Gerard Gilmore

When was the last time you checked up on the state of the galaxy we live in? I’m thinking about how out-dated my charity shop-bought copy of Carl Sagan’s Cosmos is and how our earth is practically in mint condition compared to the stars on the edges of galaxy by the time their light has got to us. “When we look at the most distant bits of the Milky Way, we see them as they were 100,000 years ago,” Professor Gerry Gilmore tells me. “Exactly as they were. So we’re not like people studying fossils, we’re not looking at the consequences or the debris, the ashes from the past, we’re actually looking at the past.”

Gilmore is a Fellow of the Royal Society, professor of Experimental Philosophy (a title which we’ll come to later), a researcher at the university’s Institute of Astronomy and chief UK Investigator for the European Space Agency’s international space mission Gaia, a satellite on which he has worked since the 1990s. It’s essentially a giant camera; several metres across, it recently celebrated its first year in orbit and is set to define this era of astronomy.

“It is an absolute revolution. It’s the biggest precision camera ever built and by far bigger than anything put into orbit before. The accuracy and quality of the images from Gaia are such that we can very accurately measure the positions and brightnesses of every star that Gaia sees – which is about one and a half billion stars and galaxies that are repeatedly observed as Gaia scans the sky.”

The mechanism of measurement uses a parallax angle from two different points in the satellite’s orbit to calculate the apparent change of position of each galactic object, indicating their distance from earth (the smaller the apparent change, the further it is from earth), adding this to measurements of speed in order to create a comprehensive 3D map of our Milky Way. “Gaia does this to ridiculous precision. The accuracy of each measurement is the same as determining the distance between the left side and the right side of a human hair seen from a thousand kilometres away.”

Indeed, it would be difficult to overstate the scale, accuracy and universal importance of the data Gaia will be sending to the 400-odd data scientists around Europe over the next four years. Cambridge’s Institute of Astronomy is one of the centres – and it’s far from backyard telescope business. “Here you have the computers, you have the people and you have the ideas. It’s exactly the same as any other research department in any other subject: it’s just that we don’t have machines in the basement generating the data, we have machines in the sky.”

I can’t help but mention how cool that sounds. “It is pretty cool, actually,” he admits. The amount of data from the unprecedentedly accurate billion pixel camera surveying over a billion bright objects, will add up to over a petabyte – that’s a thousand terabytes – by the mission’s end. Gilmore is naturally grateful for his lenghty involvement in such a massive overturn in astronomy.

From what he tells me, there seems to be no end to the number of fundamental findings this immense amount of precise data may bring to our understanding of – well – probably everything, if we give it enough time. First, there’s the actual knowledge of where our closest stars are and how fast they’re moving. Then there’s identifying the clusters that are joining our galaxy falling in on it “a bit like a comet tail without the comet”, something we haven’t been able to distinguish before now. There’s also knowledge of the stars’ chemical composition that will tell us how old they are and help understand how our galaxy formed. “In a very technical sense it’s actually 12 dimensions that we’re working in,” he explains.

“In practice, this explosion in volume and quality of data that we’re getting out of Gaia is something that’s completely unprecedented, and so one of our biggest challenges is to learn how to visualise it and how to think about it in 12 dimensions. There are a lot of people working on it and it’s going to be one of the big interfaces between big data and everyday computing.”

Gaia’s data is also set to elucidate one of my favourite fundamental physical questions: What is dark matter? “The famous, mysterious stuff,” he says. “Gaia will give the first reliable 3D map of how dark matter is distributed. This is totally fundamental because dark matter has created every structure that we see in the universe, and we’ve got no idea what the stuff is.”

Hoping to allay some of my wild speculations as to its nature, I had to ask what he thinks dark matter is, and what we will discover. “It’s quite likely dark matter is particles that are associated with the answer to some really fundamental questions. Questions like: ‘Why does the universe exist? Why is the universe made of matter and not-matter? Why does time go only in one direction?’

“The fact that there is so much dark matter out there is a suggestion based on history that those questions have answers. So if we can learn something about dark matter, then we can actually learn something about the answer – and then hopefully work out which question it is the answer to.”

When working in this field, it’s difficult to escape the big questions and this explains Gilmore’s capacity as Professor of Experimental Philosophy. “Astronomy is uniquely the science that does ask really fundamental things like ‘Where do we come from? Where do I fit in? Am I important, yes or no?’ Part of it is just thinking about it for yourself. […] Every culture has created some sort of a story to explain the sky. So it’s clearly a question of universal significance.” It really is amazing stuff, and he is contributing to a large step in humanity’s empirical explanation of the sky.

“Gaia is creating knowledge for the first time, so it’s well named. In classical mythology, Gaia brought the ability to understand and also brought the earth and the sky into existence. Our Gaia is bringing understanding of that same earth and sky.”

See, science can do poetry, too.

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