Subtle is the Lord

"The five books that I’ve given you are really books that have been important to me. They’re not books that I think are the best introduction to the Higgs, or the best guide to particle physics. They are books that have been personal. And this book is very personal. I picked it up after I graduated. I moved from Manchester to Oxford to study for a PhD. Again, you’re now drilling very deeply into a particular subject—in my case, chemical physics—and you become conscious that you’re almost putting the blinkers on and have become a little bit blind to other things that are interesting. I didn’t want that to happen. Einstein , of course, is a pivotal individual in 20th century physics. I must have spotted the book in the mid-eighties, not long after it was first published in 1982, and picked up a copy. I read it in some detail and I didn’t understand it all—not by any stretch of the imagination. It’s a scientific biography, not a biography necessarily about Einstein the person, although there’s a lot of personal stuff in it. It is about his work on the special and general theories of relativity, and quantum theory. I do. I learn something from it every time that I look at it. What I find quite extraordinary is that some of the bizarre stuff that we’re having to deal with now—stuff that makes us all a little bit uncomfortable, some of the madder aspects of quantum mechanics—was very much anticipated by Einstein. He had this famous debate with Niels Bohr. Although Einstein was instrumental in adopting the idea of the quantum, the truth was that he didn’t like what the theory was then saying about the nature of probability and causality in the physical world. You know—his famous ‘God does not play dice’ argument. It’s easily one of the best debates in the whole of the history of science, in my opinion. Again, from Abraham Pais’ biography, you get some sense of Einstein’s thinking. And it’s extraordinary how deeply he thought about some of these things. There’s a real strong element of philosophy in Einstein’s thinking, which is, to a certain extent, inevitable when you’re at that level—at the frontier of physics, talking about your understanding of space and time and matter and radiation. It is really a very good book. In some aspects, yes, but Einstein’s resistance to quantum ideas eventually meant that in his scientific career, certainly in the later years, towards the end of his life, he wasn’t part of the process driving physics forward. He was overtaken by events. There was the discovery of all sorts of weird particles that couldn’t really be understood. There was the development of something called ‘quantum field theory’ which he didn’t really participate in. And so he went off a little bit at a tangent and became a bit of a sorry figure, not really adding anything further. But I would argue that he’d already done more than any other individual in the history of physics to clear some of the mists of understanding. He wrote a series of five fundamentally important papers that were published in 1905. Out of those papers came the idea of the light quantum—the very beginnings of quantum theory, five years after Planck in 1900. There’s a paper on Brownian motion. You have to bear in mind that, in those days, people were very sceptical of the idea of atoms and molecules—of bits of matter. Many argued that matter was continuous and came all in one structure. You’ve got special relativity and you’ve got a paper with an equation related to the famous ‘E = mc2’ in it. “There’s a real strong element of philosophy in Einstein’s thinking, which is, to a certain extent, inevitable when you’re at that level” So, that’s in 1905 when he was a ‘technical expert, third-class.’ Then he had an insight, I think in 1907 or 1908, that would lead him, ultimately, some years later, to the general theory of relativity which explains how gravity works. By then, he had been promoted to ‘technical expert, second-class.’ I just love that."

"Subtle is the Lord is a biography of Einstein . It’s a thick book, it’s not just a breezy, gentle read. It contains mathematics in it as well. The author is a physicist and he tries to get across Einstein’s thinking when he was developing his relativity theories. I read it in my final year as an undergraduate and, at the time, I didn’t follow all of the maths, but I surprised myself by wading through it. So it’s not the easiest of reads, but it’s one of the books that made me fall in love with physics. It’s one of the books that persuaded me that I wanted to spend the rest of my life dedicated to thinking about some of these ideas. “I’m not expecting a person to read my book and say, ‘OK. I now understand the subtleties of quantum gravity or the nature of space and time.’ That takes a lifetime of effort and dedication.” Biographies are wonderful for making science come to life. This book was the first time I had a really good look behind the iconic Einstein, the Einstein as an old man sticking his tongue out, holding his trousers up with a piece of cord. That’s the Einstein everyone knows. But the really great Einstein was the man in his twenties who did all this great work, a man with all this time on his hands to think deep thoughts. He was almost an amateur at the time, in comparison with the big names based at the top universities. He was an amateur who figured out what no one else had done before. That’s not what he won the prize for. There were a few months in 1905 when he published four earth-shattering papers. One of them was on Brownian motion. When you put specks of particles of pollen seed in water you can see them jiggling about. What, he wondered, is the life force inside water that makes them do that? He proved that it was the thermal vibrations of water molecules. This was the first mathematical proof that atoms exist. If that was all he’d ever done in his career he could have retired famous. No. He won the prize for the photoelectric effect. If you shine ultra-violet light at a metal surface the light can knock out electrons from the surface of the metal. So the light has an oomph to it. At the time people thought light was a wave and if they sent brighter light then electrons would be knocked out with greater energy. But it didn’t happen. Einstein understood that light isn’t exactly a wave. It’s made of particles, what we call photons. The only way you can knock off electrons more energetically is to change the wavelength. He won it for this because to win the Nobel Prize your theory has to be backed up by experimental evidence. Relativity was, at the time, just a theory. Well, there are two. When he came up with the special theory of relativity in 1905 people had almost got there before him. Again, this was to do with the nature of light. Sound waves need air, water waves need water. What is the medium you need to carry light waves? What is the oscillating thing that light travels through? It must be invisible to us and must pervade all space or the light from the sun and stars would not reach us. At the time scientists called it the ‘ether’. But when they did experiments it seemed not to exist. No one could understand how, but Einstein proved it doesn’t exist – light travels through empty space and doesn’t need a medium. I should say that I teach this to undergraduates and this one concept takes me all term to explain so it’s hard to do it in a few sentences. Light will travel at the same speed according to all observers no matter how fast they are moving in relation to each other. So, if you stay still but I head off chasing a beam of light in a space rocket that travels at three quarters of the speed of light then you would expect that when I looked out of the window it would appear to be going more slowly than it would to you on the ground. But, actually, we both see it moving away from us at the same speed. Because in my space rocket my time is running more slowly than yours. This is where all the stuff about time as the fourth dimension comes from, the space-time continuum. And the fourth paper, the E=mc² one, was an afterthought. When I ask people what they know about the theories of relativity this equation is what they come up with, but it was a consequence of the more important first paper about the way time slows down and space stretches. Yes, the easiest way to explain why this happens is to think speed is distance over time. So, if speed (of light) is constant and time changes then distance has to change too. If you are travelling very fast, close to light speed, then your clocks will appear to outside observers to be running slower and you will look squashed up and flatter. This is not an optical illusion. Well, it seems like an optical illusion because you don’t feel any different. You don’t feel yourself becoming squashed up but the point is that everyone’s point of view is equally valid. The popular way of describing this would be to say: ‘Everything’s relative.’ No. Einstein says there is no absolute constant for length or time. If something that is 1m long is moving very fast it looks shorter. There is no frame of reference because nobody can say that they are truly stationary. It is democratic – you can’t say my clock is fast and yours is slow. Yes, because we don’t move anywhere near the speed of light so these effects are tiny enough for us to ignore in ordinary life. But in things like GPS systems, satellites, these effects have to be taken into account – a satellite is moving round the earth so they only work if we do take into account the fact that the clocks on the satellites slow down. This all follows from the weird nature of light. And that’s just the special theory of relativity. There’s also the general theory of relativity. We all know about Newton’s law of gravity. The apple falls on his head because of this invisible force of attraction. It turns out that this is actually a very crude explanation for what happens. What Einstein said was that actually anything with mass, which therefore has a gravitational pull, actually curves space around it. When the earth orbits around the sun it is just following the curved path in space-time. Einstein’s general theory even explained black holes and how the universe began with the Big Bang. When a massive star runs out of nuclear fuel, has no more hydrogen to change into helium (this is thermonuclear fusion), it stops shining and there is nothing to stop it collapsing under its own weight. It has been inflated by heat and energy but then it collapses. If a star is massive enough it collapses under its own weight so violently, getting denser and denser and curving space around it until it literally punches a hole in the universe. Yes, and it could be curved but finite. We don’t know. It could be infinite but it is impossible to imagine because we can’t visualise higher dimensions. So we can simplify it a little: a sheet of paper could be infinite but you could still punch a hole in it. You could even imagine this hole leading to another sheet underneath it, which would be a parallel universe. Einstein suggested that there could be a parallel universe at the other end of a black hole. Black holes could be like tunnels leading back out of another black hole via what is called a wormhole. Like Alice in Through The Looking Glass , they become gateways to somewhere else. It’s mathematically possible but can’t be proved yet. Einstein’s theory of relativity works because it’s been tested many times, so if it predicts this other more exotic stuff that we can’t test we still have to take it seriously."