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Dark matter and dark energy -

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Robyn Williams: In fact 2012 saw our leading astronomer Ken Freeman from the ANU win the Prime Minister's Science Prize for his work on dark matter, which makes up much more of the universe than ordinary stuff. Here's Ken Freeman with Nobel laureate Brian Schmidt in conversation on the night with Adam Spencer.

Adam Spencer: How significant were Ken's 1970 observations and derivations, Brian?

Brian Schmidt: Well, they are foundation, they were the first thing I was taught when I went to graduate school, so that's pretty basic. So it's right there at the pinnacle. And to be clear, every graduate student takes a class on galaxies, and of course galaxies are the building blocks of everything we see in the universe. I mean, stars are maybe slightly more fundamental. They're going to learn this stuff, they're going to learn about something called Freeman's Law which is from that 1970 paper, and they are going to be learning about galactic archaeology of course, which he's done in the last 10 years.

Adam Spencer: Can I ask, Ken, is it actually pretty cool to have a law named after you? Come on, there must be moments when you look at yourself in the mirror and go, 'That's the Freeman of Freeman's Law I'm looking at.'

Kenneth Freeman: I think that's really a question for Julia Gillard, not for me.

Adam Spencer: Now, it's not dark matter that's making things expand at an increasing rate, it's dark energy.

Brian Schmidt: Dark energy. So you'll notice that we use the word 'dark' in astronomy as a euphemism, meaning we don't really understand it or we can't see it, and so dark matter, dark energy.

Adam Spencer: Ken, they've both got the word 'dark' in common. Is that the only similarity between dark matter and dark energy? Are they in some subtle way related? Are they two completely different beasts? Do we know?

Kenneth Freeman: At the moment we would think that they are two completely different beasts. We could be proven wrong on that one.

Adam Spencer: You'd agree with that, Brian?

Brian Schmidt: Yes, I mean, I would love for them to be the same thing, and indeed there are many theorists trying to link them to be the same thing. But the evidence right now, the model we use that explains every cosmological observation we've been able to make perfectly well is that they are two separate entities, two different things.

Adam Spencer: Since 1970, Ken, what do we know about dark matter?

Kenneth Freeman: Well, we know a few things that dark matter is not. During the 1990s people thought that dark matter could possibly be dead stars, and we did an experiment at Mt Stromlo, a big collaborative experiment with American colleagues that took a whole decade, and it turned out that that idea was wrong, so we can quite safely say that whatever dark matter is, it's not dead stars. And so that really leaves the likelihood that it's some kind of sub-atomic particle left over from the very early days of the universe, as various different kinds of particles just fell out of the universe as it expanded. But at this point we really don't know much more than that.

Adam Spencer: Dark energy, how far along the path are we to having any real idea, to making it not so dark anymore?

Brian Schmidt: So the difference between dark matter and dark energy is I could give you five or ten plausible particles that would explain dark matter. For dark energy I really don't even have a plausible explanation. So dark energy we are pretty sure is energy that is part somehow of the fabric of space. Why is it there? That's the big question. No one has come up with I think a sensible answer.

Adam Spencer: How much of the universe is made up of stuff that I can see and touch and feel, and how much of it is 'dark'?

Brian Schmidt: 4.5% are the atoms that we are made out of that make up galaxies that you see, 22.5% is the dark matter, the stuff that Ken first detected, and then the other bit, 73% seems to be this dark energy that is part of space itself. So we are literally the frosting on a very large cake.

Adam Spencer: When you look back on a career of achievement, Brian, and someone who has both made those observations about dark matter in 1970 and established the field of galactic archaeology, as an outsider I would presume doing either of those would be impressive in a career, to have those two and other achievements of that magnitude, is that one of the things that's...I don't want to embarrass you, Ken, but you're up here in front of 600 people and you've won a major award, let's be honest, you're a gun. That's one of the things that strikes me as amazing about Ken's career, not just incredible distinction in one field but achievements in various areas that have redefined the thinking.

Brian Schmidt: Yes, so Ken said he came to Australia in 1967, that was the year I was born, that was when he had his big first discovery. He has been continually doing discoveries every year since. Ken is now someone who still has the heart of a 25-year-old. So one of the reasons that we like to have people retire is because they don't do as good a work as they did when they were younger, they're not as useful, they not as vigorous. Ken takes every day and every problem like it was his first day at graduate school, and he's out there thinking 25, 30 years in advance, and he's talking, you know, 'In 30 years we're going to be able to do this with this telescope.' And I'm, like, 'Ken, you're going to be 102 then,' 'I don't care, this is what we've got to do.' So that's just the way he approaches the problem. So yes, incredibly vigorous research throughout his career, even to this day, he hasn't slowed down a bit.

Adam Spencer: And one of these things you're so excited about at the moment is the Pathfinder project we saw the images of. What's so exciting about Pathfinder for you, Ken?

Kenneth Freeman: It opens up all sorts of possibilities for doing that kind of work that's very relevant to dark matter, for example. It's a brilliant instrument for measuring rotation of a lot of galaxies, because we measure the rotation from gas and that's the kind of thing the Pathfinder can do really well. Another thing that it's going to be really quite spectacular for I think is looking to see what's between the galaxies. The space between galaxies isn't actually empty, it's got gas in it, and we'd really like to detect that gas and see how that gas has been changing as we go back into the early history of the universe, because some pretty major changes are going to happen to the way that gas is, and it's a great instrument for doing this sort of work.

Robyn Williams: 2012, the year that the Prime Minister recognised the colossal contributions of Professor Ken Freeman from the Mt Stromlo Observatory in Canberra, as he was awarded the PM's Science Prize. And there you heard Adam Spencer with Professor Freeman and Dr Brian Schmidt, also of the ANU.