Titans of Science: Martin Rees
PodcastsThe Naked ScientistsTitans of Science: Martin ReesCambridge University's Astronomer Royal shares his insights. . . 16 January 2024Titans of Science returns with another out-of-this-world guest:. . .
PodcastsThe Naked ScientistsTitans of Science: Martin ReesCambridge University's Astronomer Royal shares his insights. . . 16 January 2024Titans of Science returns with another out-of-this-world guest: astronomer, astrophysicist and science populariser, Lord Martin Rees. Martin Rees: Early lifeMartin ReesChris Smith met up with Martin Rees at his Cambridge home to hear about his life's work. . . Martin - Well, I was very lucky because I grew up in this village in the South Shropshire Hills - beautiful natural world. My parents were teachers and I was sent away to boarding school (which wasn't quite so happy) when I was 13. But I was very well taught and I did get into Cambridge and I read mathematics. I wish actually I'd done a broader curriculum at university because, when I got to university, I realised I wasn't quite the same as other geeky people doing mathematics in that I like to think in a more synthetic or synoptic way. I became a research student in 1964, and that's when quasars had just been discovered, the evidence for the Big Bang from the radiation, the so-called afterglow of creation and lots of other exciting things and theoretical work by Hawking and Penrose on Black Holes was being done. Advice I would still give to any young person starting is, if you pick a subject, pick something where new things are happening and then the experience of the old guys is at a heavy discount and you can immediately make an impact. Don't go into some sterile subject because then you'll be trying to do the problems the old guys got stuck on. Chris - Do you think then you got lucky with the subject? Did you have some foresight? Because you've said to me, go and pick something that's an exciting, emerging, evolving area. That is current. Don't get stuck on the old stuff. Did it find you or did you already have that view and therefore you were seeking out that kind of thing and you were able to say - well, I'm good at maths. I've got the kind of mind that would suit this, that's where I'm headed. Martin - It was really just luck rather than careful planning. I had decided I didn't really want to pursue mathematics as a career. I liked the idea of something academic. I thought quite seriously about economics because I had some good friends who had defected from maths to economics and did very well as economists. I might have tried to follow that route and I might have been happy if I'd done that too, but I was very lucky to get a place as a graduate student in Dennis Sciama's group. And it was luck because some other person who'd got the job in preference to me dropped out, and so I just managed to get my position as a graduate student. Chris - What was going on in Dennis Sciama's domain that really drew you in and what did you think were the areas that were going to be the exciting ones to pursue?Martin - Well, I realised that I liked a style of thinking where you try to make sense of something from limited information rather than doing complicated deductive reasoning like in mathematics - a bit like engineering where you try to make something that works from given specifications. We had these objects that are very bright, flashing away, which we now think are massive black holes in the centre of galaxies, which are called quasars, and I wrote some papers trying to understand that sort of thing and also to understand the expanding universe where the idea of an evolving universe was a fairly new one. I think it was a style of thinking that I quite enjoyed. I mentioned Dennis Sciama. He was very plugged into what was going on in all these fields, and he'd come in excitedly every day with some new preprint for the new paper he'd been sent and circulated. He had students like Stephen Hawking, who was two years ahead of me, and he told those students to go and listen to Roger Penrose in London who had exciting new ideas. They duly did and followed them up spectacularly. He was someone who exemplified that you can be a great coach without being a great player. He didn't do any amazing science himself, but he was an enthusiast and he inspired us all, a whole group in Cambridge, and then he moved to Oxford in the 1970s where, again, he had an equally strong stable of students there. Martin Rees: Our changing view of black holesMartin ReesChris Smith asked Martin Rees to explain how the complexity of black holes was tamed by scientists. . . Chris - Can you give us a flavour for how the space science domain has evolved over the course of the time when you finished your PhD to where we are today. What have been the really big changes and what have been the waves that you've most enjoyed surfing?Martin - Well, of course, space science only really got started in the 1960s, looking at x-rays from cosmic objects. X-rays come from especially energetic objects and so they were able to highlight in our view of the sky the objects which are especially exciting. It started off with sounding rockets being sent, so they got a few minutes' observation before they came crashing down again, but then the first satellites were launched in about 1970 to study the sky in x-rays, and they found the first evidence for black holes orbiting stars. I had a lot of contact with Ken Pounds, who was then a young lecturer at Leicester, who managed through his energy and initiative to make Leicester a major international centre for space science. His group were important in x-ray astronomy. That was something that I was very interested in. Chris - At that time, were black holes something that people had thought about but they hadn't got any demonstrable evidence for? They were a theory, but you actually have now seen over your career them manifest for real. Martin - That's right. The theory was worked out - some bits were done very early on. Some bits incidentally were done by Oppenheimer in 1939 before he was otherwise distracted. A lot was done in the 1960s under the inspiration of Roger Penrose bringing new mathematics into it. But on the observational side, I think when these objects appeared in surveys of the sky, which couldn't be ordinary stars, they were too bright, varying too rapidly, etc. , I think, from the mid to late sixties, everyone speculated that they could be black holes, but the evidence was rather indirect. Some of my early work was in trying to work out how gas swirling down into a black hole could produce x-rays and things varying rapidly and this could explain some of these things. But it wasn't until the late 70s, 10-15 years later, that there was a general agreement that what was causing the big energy output from the centre of some galaxies was flowing around a black hole. It gradually emerged. While I've got one of the foremost experts on this sitting next to me, can you explain to me the differences between the massive black holes we see at the centres of galaxies and the little ones we see doing collisions that we can pick up with our gravitational wave detectors and so on. What's the difference between them apart from size? And what's their origin?One feature of black holes is that they are scalable. In fact, a black hole of a few times the mass of the sun and a black hole a few million times the mass of the sun, like the ones in some galaxies, are exactly the same in their properties - it's just a simple scaling factor. Of course some stars, in their lives collapsing and leaving black holes behind, those are the ones which we see in binary star systems in our galaxy. And incidentally, those are the ones that give rise to the gravitational waves that have been detected to black holes weighing between 10 and 50 times as much of the sun crashing together. But there is a separate category of supermassive black holes which form somehow by an agglomeration of mass in the centre of a galaxy. It's still debated whether the mass accumulates by just gas falling in or do lots of stars collide and fall together. All those things play some part. All we know is that there are, in the sense of galaxies, black holes where the biggest ones are several billion times the mass of the sun. In our galaxy's centre, there's one which is about 4 million times the mass of the sun. That's small by the standards of these massive black holes, but of course much bigger than any star. And in fact, Don Lyndon Bell, who was my senior colleague in Cambridge, and I wrote a paper back in 1971 first arguing that there could be a massive black hole in our galactic centre, and that of course has been firmed up gradually over the years.