The Life Scientific: Hiranya Peiris

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1:08Last summer, filming began on a movie that promises to tell perhaps the greatest story of all time. But it's a movie with a difference. There's no director, no script, and it won't be on at your local cinema. This is the legacy survey of space and time. And it's one of the most ambitious projects in the world of astronomy, with a mission to create a decade-long time-lapse movie of the visible universe to answer fundamental questions about its origin, evolution and ultimately its fate. My guest today is playing a starring role. Hiranya Pieris is Professor of Astrophysics 1909, the prestigious chair at the Institute of Astronomy at Cambridge University.

1:49Over her career, she's been one of the pioneers of a revolution in astronomy, bridging fundamental physics with the observational data coming back from space to transform the field from the Wild West of physics to the modern era of precision cosmology. And ever keen to inspire women to take up careers in science, if this interview were a live show, she'd have reserved the front row for schoolgirls. Professor Hirania-Pierre is welcome to Life Scientific. Thank you so much, Jim. It's really nice to be here. Now, I mentioned that passion you have to inspire schoolgirls to take up science. Where does that come from?

2:24It comes from being a young girl myself and falling in love with science through, for example, books, where the people who were writing the books were very inspirational, but they did not look like me. And I want young girls to see role models that look like themselves doing the things that they can aspire to. And that's what drives my passion for having those young girls in the front row, not in the back row, and sometimes not even in the room. And for you as a young girl, you're developing this love for science, being part of the scientific enterprise. Why do you think that is? When I'm doing science, I feel that we are on a search for truth as humanity.

3:08And I really connect to that idea. For me, it is a safe place. It is a place where things make sense. When you state a fact, it is an objective truth about reality rather than something someone made up. I mentioned in the introduction that you are Professor of Astrophysics 1909. What's the 1909? This marks a time when astrophysics, as distinct from astronomy, became a subject of study. So astronomy can be thought of as mapping the universe, but astrophysics is turning the data or the observations we have made into understanding and connecting it to fundamental physics. And that started around the time of 1909.

3:55Well, Hiranya Pieris, you were born in Sri Lanka, in Colombo, in the mid-70s, to parents who are both civil engineers, I understand. That's right. So my mother was a bridge engineer. She designed bridges. She was one of Sri Lanka's first female civil engineers. And my father worked on big hydroelectric projects. And your mother in particular was your role model. Yeah, she's so good at so many different things, but she's very humble about it. And that is a quality that I really aspire to. I have a particular image in my mind of accompanying my mother when I was a small child to a building site where she was supervising a very large team of men constructing a bridge that she had designed.

4:37And she was very elegantly dressed in a sari. And she was very dignified. She was clearly in charge. But she wasn't shouting. She wasn't projecting dominance. It was a different kind of leadership. And I really connected with that image. And you'd have been about, I guess, seven years old when Carl Sagan's documentary series aired. And that sparked your interest in the cosmos itself, in the universe. That's right. I remember just being completely transfixed by these really vast horizons that he opened up, both space and time, how the universe connected to us as people. And that really was magical.

5:18And I believe your parents also nurtured your love of astronomy that was just beginning at this point. That's right. My father went on an international trip and he brought back a small telescope for me. And Sri Lanka had very, very dark skies. Just from my backyard, we could see, for example, Saturn's rings. It was the first time I saw Jupiter's moons. And I remember projecting solar flares and sunspots onto a sheet of white paper and looking at that. Yeah, it was a great time. Around this time, you were becoming increasingly curious about the universe, but it wasn't always easy to get hold of the books that you wanted to read.

6:02That's right. There was a kind of floating book ship which came to the harbour in Colombo. And my father took me and bought me a copy of A Brief History of Time. This is the first time that I actually encountered cosmology, which is my current field of study. It was very mind-expanding. That book by Stephen Hawking, most adults would say, I only read the first two chapters, then I stopped. You read it cover to cover. I read it cover to cover. I probably didn't understand everything, but I remember the diagrams from it to this day. Like right at the end of the book, it talks about two-dimensional creatures who are trying to visualise three dimensions and it's almost impossible.

6:46And I think the thing that really fascinated me was that the book took me to places that didn't exist in the real world, but I could imagine them in my mind. Hirani, you went to an all-girls school in Colombo throughout your childhood. Did you like it? I didn't really like school. I lived quite a lot in my mind. I remember one maths exam in particular where I didn't notice several pages of questions. I just stopped doing them and just sat there daydreaming. And so I nearly failed that test. But I do remember this wonderful teacher, Mrs. Mendes, and she had taught my mother before me. She really tolerated the why questions.

7:29And I must have been a very annoying kid, constantly asking why this and why that. And some of them weren't so easy to answer. That's right. So I remember one particular occasion when the Buddhist monk came to the school assembly and there were several thousand girls there. And he was preaching to us from the Buddhist doctrines. And I put my hand up and asked a really impertinent question, which was, you know, in Buddhism, there's a concept called reincarnation. And I said, if there is a finite supply of souls that are being reincarnated, why is the population of the planet increasing? I don't remember his answer, but I remember the deathly silence afterwards.

8:11This reminds me a bit of what you took away from Stephen Hawking's book, A Brief History of Time. A realisation that you could go to places in your mind far beyond what you had imagined. Did you have dreams of going into space, becoming an astronaut? Absolutely. My life's ambition was to become an astronaut. It was only when I was about 16 when I became short-sighted. It was a devastating blow. I no longer could pilot the space shuttle. And so have you now ruled out any possibility of going into space or do you still have some ambitions? I want to go to space. I almost signed up for the Mars One to a one-way trip to Mars, but my partner said he wouldn't come.

8:53So I had to nix that idea. But then later I found out it was a scam anyway, but I still want to go. Well, fingers crossed for getting into space. But back in your teenage years, you did create your own journey through the solar system. That's right. I accompanied my mother to a course learning how to program in BASIC. It was a simple computer language, but you could do quite a lot with it. And for several weeks, I sat there coding a tour of the solar system, and I stored my programs on a five and a quarter inch floppy disk. And one day I came to class and found that the disk had been wiped. I still feel this devastating sense of loss.

9:35And ever since I've done like a zillion backups of everything I've worked on. You won't make that mistake again. Yeah, no, no, no. Hiranya, during your teens, the Sri Lankan civil war was escalating from simmering ethnic tensions to full-scale conflict. Your parents decided to bring you and your sister to the UK. What can you say about leaving Sri Lanka? You know, there was violence in everyday life. The universities were closed and my parents just didn't see any future for us there. And they decided to leave everything behind. You settled in Manchester. You had an uncle and aunt. who live there?

10:14So we arrived with very little. So my mother got a job in Manchester. We had to make do on my mother's salary, basically. So we watched the pennies. And, you know, I was 16 in a new country. I started in a new school, and I'd previously learned in my native language, Sinhalese. It was a mixed school. And for the first time in my life, I found that I was a minority in maths and science class. Oh, coming from an all-girls school in Colombo. That's right. And suddenly people just assumed girls couldn't do these subjects. I was 16 when I came over with my family from Iraq. I went to a school that had originally been a girls grammar school and then it became a mixed comprehensive.

10:56So I was one of only three boys in a year group of 120 girls. So doing A-level maths and physics, it never occurred to me that these were boy subjects rather than girl subjects. We were in the minority. That was fascinating. Did you enjoy your A-levels? I did, actually. The teachers were really good. There was a teacher called Dr Egan, and he was my further maths teacher. And he gave me, like, university-level textbooks, and he encouraged me to apply to Cambridge. What did you think about that? It felt like a really unattainable goal, but when he told me that I could do it, I didn't know anything about Cambridge, so I applied to a college.

11:33It's called New Hall at the time, now Murray Edwards. And there's a very iconic dome, which is suggestive of an observatory dome. And that's the reason I picked that college. Good enough reason as any. Now then, given where you've ended up in your career, you applied to study computer science. Why? We were not well off. And at that time, computer science was one of those subjects that was held to have very good career prospects. In fact, before you got to Cambridge, you had only lived in the UK for two years. And so you were still classed as an overseas student. So you had to wait another couple of years before you qualify for home fees.

12:11Cambridge kept that place open for you. What did you do in the meantime, though? I remember applying to so many different jobs and I accumulated the rejection letters in a binder. I still have that somewhere to remind me that rejection is okay. Eventually, I got into a scheme called the EAN Industry at Nuclear Electric, which ran the UK's nuclear reactors at the time. And I was placed in a team which was monitoring the turbo generator system for cracks. there was not a woman in sight and I was a young woman of colour but I was placed in this team which treated me no different. I was just told this is what you have to do and I taught myself to code in C++.

12:58I learned Unix. There's all these different computer languages. I always tell my students if you learn to code in one language basically what you're doing is learning to think the way a computer does. That's correct. And it's not so difficult to convert it to another. What helped me is this feeling that, and once you've done something hard once, you can do it innumerable other times. I could learn to do anything. Well, in 1994, Hirania, you started at Cambridge to study computer science. What was that like? Again, I didn't really connect to the way of learning in lectures and so on. It's a continuation of your school days experience.

13:37Yeah, so I used to fall asleep. But in my second year, I was accepted into a summer research internship at the Jet Propulsion Laboratory in California. And that was a real turning point in my life. you found it so inspiring, you decided to switch degrees from computer science to physics, which you knew would then open the door to astrophysics, the bridge between physics and astronomy. And during your third year, you met one of your childhood heroes, Stephen Hawking. That was a wonderful occasion. So Stephen and Roger Penrose had contrasting ideas about the physics of the very early universe, and they were debating each other.

14:20And I was transfixed by this lecture. And then afterwards, I built up my courage. I was a very, very shy young girl. But I went up to Stephen and asked for his thumbprint. And lo and behold, they actually had an ink pad, because other people probably do also ask for his thumbprint. And so I actually still have that somewhere. Well, after completing your degree, you embarked on a PhD at Princeton University in the US in their Department of Astrophysical Sciences. What led you there? I visited there to see whether that's where I wanted to go. And a young professor called David Spurgle came late in the evening to pick me up from the train station and take me to a very welcoming group of graduate students.

15:09And again, it was this feeling of belonging. It felt like I had come to another family. And David later was my PhD advisor as well. But I had this gut reaction that that was the place where I belonged. Well, you started your PhD at Princeton in 1998. NASA already had plans in place to launch a satellite mission called the Wilkinson Microwave an isotropy probe. Now, the idea was to take detailed measurements of the faint radiation that permeates the entire universe, which would help us understand something about the universe's origin and its evolution. So your supervisor asked you to lead on the analysis.

15:49Maybe you can first briefly say something about this radiation, the cosmic microwave background, and what it tells us about the early universe. One of the crucial points that makes my field possible is that light has a speed limit, which means that when you look into the distant universe, you see things as they were in the past. Because it's taken a long time to get to it. That's absolutely right. So the oldest light we can see in the universe is the cosmic microwave background. And the probe was picking up the faint patterns of this ancient light. You were part of the team that analysed the data.

16:25What did that involve? So the analysis involved comparing the patterns of the very early light that we can see in the cosmic microwave background with theoretical models. And different cosmological models make different predictions for the pattern. It's like a fingerprint. It identifies the theory. and my job was to build a sort of statistical bridge between the data that we had measured from the sky and the theoretical fingerprints that we needed to compare them to. So these theoretical fingerprints are basically stories of how the universe came to be and how it evolved and you want to see which story is the correct one, which one matches the data.

17:11That's absolutely right. Okay, so let's talk about what you discovered. Maybe we can start with the age of the universe and then maybe how far back in its existence we can measure. The age of the universe, we were able to put a number to that, 13.8 billion years old. And we could also measure when this early light came from. It comes from a time when the universe was about 380 ,000 years old. So this is like a baby picture of the universe. So the 380 ,000 years, that's how many years after the Big Bang itself? That's correct. We can therefore tell a story about the evolution of the universe, at least from that early age till now.

17:55Now back to what you found then. Your observations confirmed a simple model for the origin and evolution of the universe. Yeah, it's a simple model, but it's a really bizarre one. It is described by just six numbers. So we need two numbers to describe the origin of cosmic structure. Where did everything come from? Then we have three numbers to describe how it's evolving. So that's the amount of ordinary matter in the universe. Everything our world is made of, what we are made of, that's ordinary matter. It's only 5%. And then there is dark matter and dark energy, which are very mysterious components of the universe.

18:33And yet they make up 95%. 95%. We can see that they are there, but it's not like anything we know. And then the geometry of the universe, which tells you something about its fate. And then we also need to know when the first stars formed in order to describe the universe. One of the ideas that you've been working on is what happened to the universe very, very soon after the Big Bang itself, long before even this cosmic microwave background was set free. This is what's called inflation. Now, inflation theory says the earlier universe dramatically expanded right after the Big Bang. That's right.

19:09In a tiny fraction of the second, so like a trillionth of a trillionth of a trillionth of second, the universe expanded by a factor of about 10 to the power 30. Let's see. Now, that's a million, trillion, trillion, right? That's right. I mean, it's just incredible because, you know, here we are talking about the universe being 13.8 billion years. now we're talking about something that seems to have happened within such a tiny, tiny fraction of a second. It sounds like science fiction, but it gets even more science fiction-y than that. Not only it is thought that the universe expanded that rapidly, but also little quantum fluctuations literally in the structure of space have caused all of the structure in the universe to form in those tiny instants and then be stretched out to the size of the whole universe.

20:01This was the first evidence-based standard model of cosmology, as we now call it, the origin evolution of the early universe. And it's now pretty much accepted, I guess, but it's not a done deal. You know, there are still those who argue that inflation, is it necessary? Do you think that it's well understood enough now that it's confirmed? Inflation is by no means confirmed yet, but the data is discriminating enough to be able to say something about the trillionth of a trillionth of a second. But there's still quite a lot of work to do. Which is what makes it all so fascinating, right? What was it like for you working on this?

20:37What I remember about this time is the feeling of working within this amazing team of people. It felt like our brains were connected like a neural network. We basically worked around the clock to turn the data into numbers. It was such an amazing experience that I've not had before in my career or after. Stephen Hawking called that, certainly the evidence for inflation that you and others had provided, the most exciting development in physics during his career. I think Stephen is being quite modest in making this statement because he should be proud of his work in giving us the predictions to test.

21:16You know, science is like a tapestry and he wove a very big piece of that tapestry with his work. And what we did was to pick up those threads and weave further. Well, I'm certainly old enough to remember that cosmology, the field concerned with the origin and evolution of the universe, was very much the Wild West of physics. Your work ushered in what has become known as precision cosmology. We're no longer relying on speculation. We're relying on hard data. We should also, I guess, remember here that all of this work that you were doing was still part of your PhD. Well, where do you go from there?

21:55You stayed working on this project before you then moved to the University of Chicago. But you were soon tempted back to Cambridge to analyse data coming from another space mission. This was the European Space Agency's Planck Observatory, which was also mapping the cosmic microwave background, but even with greater precision than ever before. I gather you are particularly interested to learn more about inflation, this super fast expansion of space. So what did you find? I can give a musical analogy, OK? So according to inflation, if you represented the universe as a symphony, it should have more bass notes than treble notes.

22:34And a simple idea of the origin of structure tells you that there should be equal amounts of bass note and treble notes. but the inflationary prediction was tested and found to be correct by Planck. In 2009, Haranya, you took up a lectureship at University College London. You later became professor of astrophysics there and during this time you got interested in dark matter. Now, we know dark matter is out there. We still don't know what it's made of but you've been trying to detect dark matter particles. Yeah, so this is kind of a side project but my favourite dark matter candidate is called the axion.

23:10Axion particles, if they exist, are very light. So they behave less like particles and more like a radio wave permeating the universe. And so you can kind of do a tabletop experiment in a university lab to try to detect this radio wave. The experiment is like a radio receiver. We have to tune it and find the right frequency, but we don't know what the frequency is. It's in a range. Yes. So we need to tune into it. Well, in 2023, you returned to Cambridge as Professor of Astrophysics 1909. While for much of your career you'd focused on the early universe, more recently you've turned your sights to the more recent universe.

23:49This is a hugely exciting project. It's known as the Legacy Survey of Space and Time, carried out at a new astronomical observatory based in Chile called the Vera Rubin Observatory. This is named after the woman who first explained how dark matter holds galaxies together, that it had to be out there. The project is going to generate this time-lapse movie of the visible universe. This is the biggest digital camera ever built. Each image is 3.2 billion pixels. And what do you see in these images? The first images are just astonishing. So not only are they super high resolution, but the depth is very great so that you can see much, much further into the universe.

24:35So when you look at pictures of galaxies, for example, they look super crisp, but you can also see the faint outskirts of these galaxies where gas is accumulating, which is going to feed into future generations of stars that we couldn't see before. And also because it is a time lapse, you can see exploding stars in the universe. I've had a look at some of these moving images online and it really is mind-blowing. But in terms of the science, how does this enhance what you can learn about the universe? We are going to use these images to map dark matter across half the sky and about halfway into the lifetime of the universe.

25:16We can't see dark matter, but the presence of dark matter bends light when they encounter concentrations of matter. So this causes tiny, tiny distortions in the shapes of galaxies. which we can map. So if you have billions of galaxies, you can back out the intrinsic shapes of the galaxies and extract the very, very faint dark matter signal and use that to map out how structure is evolving over the course of the universe's history. So that's what we plan to do. What is your role then on the project? So I'm one of the people who is going to turn those pictures into conclusions about dark matter and dark energy.

26:00So it's another statistical bridge, but because the volume and complexity of the data is so great, the statistics now has to be augmented by machine learning and very advanced AI technique. The statistical bridge that you create that enables you to compare the data coming in with the fundamental physical theories. It reminds me of your mother, your role model, who as an engineer spent her career building bridges. Absolutely. It is a really nice way to think about it. And thank you for making this connection. One of the things that the survey is hoping to look at is asteroids. Yes, that's right.