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Professor Sir Michael Berry

Professor Sir Michael Berry is a theoretical mathematical physicist at the University of Bristol.  He is perhaps best known for his work with the Berry Phase, a phase observed in optics and quantum mechanics.  He is a fellow of the Royal Society and was knighted in 2006 for his services to science.


When I come to work in the morning, I often don't know what I'm going to think about


On earliest memories of becoming interested in science

Like many people, I became interested in science through astronomy, and it's an interesting psychological question why that is. And I have a theory that in my case I had a rather unhappy childhood for reasons that aren't interesting now and, you know, thinking about realms pure and far from us somehow was comforting.  I don't know if that's correct because I'm not a psychoanalyst but, anyway, it was astronomy.  And then when I was at school, and then later on at university, I realised that astronomy is based on physics.  And I realised I liked that, and especially the sort of mathematical connections involved with that, so I became a theoretical physicist.


On science fiction as a gateway

That's a very good question. I loved science fiction, I was obsessed with science fiction. There was a chap down the road, an older…a grown-up who was a science fiction enthusiast and he bought magazines, subscribed to them, and he always gave them to me after he'd read them. So I devoured science fiction; whether that came before the interest in astronomy or after the interest in astronomy, I don't know, actually, I can't remember.


So it wasn't a decision [to go into science], it was a kind of migration, a sort of inertial migration, I think. I was good at science at school, I decided to do physics for the reason I told you at university.  And, you know, I did my degree in Exeter and I did a PhD in St Andrews and I came to Bristol and, you know, I was in my mid-30s before I had the confidence to actually say, ‘I have decided I am a physicist’. I always thought something would fail, it wouldn't work or something, and even when I had been moderately successful I didn't quite have the confidence to say it. So it wasn't really a decision, it was a sudden realisation that I am a physicist, later than most people.


On semiclassical physics

Right, in science we describe things on different levels. If you take a familiar example, you can talk about a rainstorm in terms of meteorology. If you look closely, you can think of it in terms of water droplets. You look more closely, you can think of it in terms of water molecules; you look more closely, you could be thinking in terms of atoms in the molecule, the nucleus of the...and so on. There are different levels at which you can speak about phenomena and it's an interesting and actually very contemporary, very modern activity, to try to unravel the relations between these different levels of describing things. 


One of these pairs of levels is the old mechanics of Newton and the more modern mechanics of quantum theory. Now, really, the world is quantum mechanical so...or really meaning, as far as we know now, I mean, it could be deeper still, but who knows? So the old classical physics is an approximation, but it's one that we use all the time. 


When you send a spacecraft to the moon we never use quantum mechanics, it's...a spaceship is a big heavy thing and it would be totally cumbersome to use quantum theory to describe that, although we know that fundamentally we could. Now, the question of the relations between these two ways of describing becomes important when you have things that aren't as big as spacecraft but they're not really so tiny. So a molecule, for example, for some purposes is like an object moving through space, it bounces around according to mechanics. But it also is a quantum thing, it has energy levels which quantum physicists…physical systems have, and there's a very subtle question, what's the relation between the two? And it's a...it's a very rich area, it's an area that I've studied for many years along with other areas of physics. 


So, for example, it's the same in mathematical terms as a different type of connection, with light. You can think of light as waves or you can think of it as rays. Rays is an approximation, but it's useful if you want to understand how a lens works or a telescope or a microscope, your camera. You just plot the ray paths through the object, through the lens, and you see they come to a focus and whatever. But that's an approximation, and it's a very subtle approximation and it's not always good enough. So this connection, rays to waves, is rather similar to the connection, classical to quantum. Indeed, the mathematical connections between different levels in physics have a lot of common features, and that's one of the themes that I study.


On working as a theoretical physicist

I once went to Chicago and I was the guest of a very distinguished physicist and I gave a series of lectures and after the lectures he said to me, ‘it was very good that you came here because it's very good for the students to see someone who has a very clearly defined research plan’. And I said to him, ‘I don't have a clear defined research plan, when I come to work in the morning I often don't know what I'm going to think about.’ Sometimes I do: when I'm hot on a problem it's in my mind all the time and I wake up thinking about it, but sometimes I don't, and don't know what I'm doing.


So I don't quite have a typical day, you know. Of course, there are things I do many days, like I think about a problem that I'm intensely involved with, or I have to write a referee report on a paper that somebody has sent, the ladies have sent me to make a decision on, or I recommend somebody for a job. People ask me often to do that kind of thing. Or I write a paper myself, which is of course…mostly that's our output as theorists: it's publish papers. So all those things, but in emphasis, that shift in balance from day to day and week to week.


On ‘thinking’ for a job

Well, there are two aspects to this. One is that very often the output of a theorist is a suggestion for an experimenter to go to the lab and measure something that you've predicted. And this happens very often, and if it...the more often it happens the happier you are, especially if the prediction comes out right. Or you want...an experimentalist has made some puzzling observation and they need a theorist to explain it. But there is another side to it which I want to emphasise, and it's a particular enthusiasm of mine. One of the glories of science, especially theoretical physics, is that you can explore realms that are very far from our direct experience. 


You know, no one has seen an atom, nobody has directly felt a gravitational wave, as this wonderful experiment, observation that was recently made. And it's a wonderful thing that theorists and our apparatus work, but pointing out how the explanations involve very abstract objects, abstract ideas. I call it the arcane in the mundane. OK, so for example - and this is also an example of these connections between theories - if you look at a rainbow you see a curve in the sky, the colours are explained by Newton but it's more fundamental to ask why you see a curve at all, OK? And that's a particular kind of ray focussing that comes from sunlight, coming into a raindrop and coming out again. This was Descartes, 1638, understood that in a rather modern way we would think…you read his paper now, it resonates with us. 


But that's ray theory, you take the rays of light. But if you look closely at a rainbow you can sometimes see - and this is especially if the raindrops are nearly all the same size, it depends on the meteorology - you can see inside the rainbow a couple of additional little rainbows very close to it. I don't mean the second rainbow far away, that's a different thing, within the main rainbow. These are interference fringes which reveal the fact that light is really a wave. So with your own eyes, you can see magnified in the sky this transition between waves and rays. 


And when Thomas Young taught us that light is really a wave phenomenon unlike what Newton thought, which was [that] it was rays, he used these additional little rainbows, they're called supernumerary. Supernumerary means surplus to requirements, unwanted. Because they were seen before they were explained, you really couldn't see where they came from. So you see with your own eyes in the sky this kind of transition between one level and another level, the ray level and the wave level. So explaining, I would say, the arcane in the mundane is a theme of what I do.


On the beauty in scientific understanding

Oh, it's the exact opposite, you see something beautiful and you want to explain it and explaining does a different thing. It does..first of all, it in no way diminishes one’s astonishment at seeing a rainbow in the sky. My heart leaps up when I behold a rainbow in the sky, I can't remember who wrote it, it's still true. But when you understand it and you think about it, you're unifying that observation that you make with a whole other area of human culture. You are unifying it with mathematics, you're unifying with other physics, you're unifying it with what I’ve said, the relation of one level to another. So it enormously widens your cultural experience if you understand it. 


So I've never been able to understand, certainly not sympathise with, this view that you don't need...you don't need to explain anything, well of course you don't, but we're a species, we’re…what is it? We're apes with curiosity, that's what we are, so in a way we deny our essence if we deny the impetus to understand things. There's no way...understanding is beautiful.


On asking questions that may be unanswerable

We do it because we can do it, because science is a communal, a collective cultural enterprise. This is a discovery we've made in the last few hundred years. There were great scientists before that, for example in the Islamic world, in India, in the Greek world, but they were rather isolated individuals. We've learned the trick now, and it's this kind of magical thing somehow, of collaborating. Even when we think we're competing we really all depend on each other’s work. We make little tiny steps, we're very proud of them, we think, oh, I did this, and so on, you didn't understand it, I did. But really these are little steps in developing what is already a known...Einstein, I mean, they knew the literature and so it's not so brave as if you would start out like the ancients did and starting from nothing, try to understand the world. We work in...we have a background of people like us who have thought about these things, it's a happy accident that humanity has discovered this working together. It's the nearest thing to what science fiction people used to call a group mind, and these sciences are a collective cultural enterprise.


On ganging the public with complex science

I don't need to now, I used to say this 20 years ago, or 30, you know, but now you look on the television almost every night there's really good science, it's a great age of science. Books, there are more wonderful popular science books than there ever were, people buy them and read them, very successful. So when...of course there are people that aren't interested in science, well, fine, they're more interested in football than, you know, me for example. Fine, nobody has to be interested. But in fact it's not a problem now, I give a lot of public lectures and people come, they're enthusiastic and ask intelligent questions and make interesting remarks, so I don't see it as a problem.


On the current ‘golden age’ of physics

Yes, I think science generally, biology as well, it's not just physics, yes, it is, it's a great era. I worry that it might not last and there is historical precedence for enthusiasm for science not lasting, for example in the medieval Islamic world, many discoveries were made which are still important now. A lot of things I do started in Baghdad in the 11th and 12th centuries, Alhazen Ibn al-Haytham, other people. But that disappeared, it disappeared because religious fundamentalists somehow inhibited the free exercise of curiosity in favour of formulaic adherence to particular precepts and dogmas and rituals. And if it happened then it could happen again, you know, we hope it doesn’t. 


If you look at America, it's easier to see from the outside, if you look at America for example, it's surely the worlds leading scientific country. But it's also the world leader in denial of science, but these are different people of course. 


So, you know, they're the people who deny different aspects of science, they still want their mobile phones which are based on quantum mechanics and so on. But still it isn't obvious that it will continue, of course we hope it will, but you know, I...and the only way to really try to ensure that it does is to do science and to talk about it enthusiastically but, you know, nothing is guaranteed.


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