Emma Johnston: Welcome to The World According to Physics, where we're going to be hearing from the award winning science communicator and renowned scientist Jim Al-Khalili. I'm Professor Emma Johnston, the proud Dean of the Faculty of Science at UNSW, and your host this evening. This event is presented by the UNSW Centre for Ideas and supported by UNSW Science. Tonight is also part of the UNSW’s event series for National Science Week. Today, I join you from Bidjigal country, you will be joining us from a range of Indigenous land and sea countries from across this vast continent. I'd like to pay our respects to the people who are the custodians, the traditional custodians of those lands and seas, and to recognise their continuing connection to country and the deep knowledge that abides in those connections. I'd like to pay my respects to elders past and present and extend that respect to other Aboriginal and Torres Strait Islanders who are joining us today. Our speaker this evening is a physicist and author, a broadcaster, indeed someone with notable achievements in all of these fields. Professor Al-Khalili received his PhD in nuclear reaction theory in 1989 from the University of Surrey. He's published over 100 academic papers, mostly on nuclear physics. And he's currently co-director of the Leverhulme Doctoral Training Centre for quantum biology at Surrey, where he is still trying to make sense of quantum mechanics. Professor Al-Khalili or Jim is also one of the UK’s best known science communicators, for which he has received many awards including the inaugural Stephen Hawking Medal in 2016. Jim’s the author of 12 books translated into over 20 languages, and includes his first novel The science fiction thriller Sunfall, published this year. He's also a regular presenter of TV science documentaries, and is probably best known in Britain as the presenter of the long running weekly BBC Radio Four programme, The Life Scientific. Jim's going to be talking to us tonight about the world according to physics. His recent book, where he introduces the fundamental concepts of physics, and shows us what modern physics has discovered about the universe, and the nature of reality itself. It is a great pleasure to welcome him to speak albeit virtually at UNSW. Professor Jim Al-Khalili.

Jim Al-Khalili: Thank you very much, Emma, for that introduction. Hello, everyone. I'm just sorry I can't be with you at UNSW. Obviously, with the situation in the world today, I'm delivering this presentation from my study at home in Portsmouth on the south coast of England. So I want to talk to you a little bit about my book, why I wrote it, and what it's about. It's called The World According to Physics. When I showed it to a colleague of mine at the University of Surrey in the physics department, because I told him that really, this book is my, as I say, in the introduction, my ode to physics, my confession of a love affair with a subject that I have obsessed over for most of my life. And he said, well, you know, it's a bit polemical, so maybe if you put your thumb over the word physics, maybe this will be a better title, The World According to Jim Al-Khalili. I mean, I should say there are many popular science books that have been written over the years, many of them that have come out in recent years, very often, they tend to be these really sort of massive tomes, they cover the whole of the history of physics going back to the ancient Greeks. So not only saying what we know, but how we got to know what we know. I tend to think of our knowledge of the physical universe as an island, and these books are an exploration of that island, beyond it is this the ocean of the unknown, the yet to be understood, the yet to be discovered. And we don't know if it stretches on forever or this will come to an end, and one day we will discover it. But essentially, the island is growing in size, it’s expanding as we learn more. This book is an exploration of the shoreline. So where we are now, what do we understand about the nature of the universe, the nature of physical reality, put into language, I hope, which anyone can follow. And also looking beyond the shoreline, having a bit of a paddle in the water, and seeing what else there that we hope to understand soon, what are the known unknowns as it were? So this is a paper written about 40 years ago by Stephen Hawking, and he asked the question, is the end in sight for theoretical physics? So you see, this paper was published in 1981. And that first paragraph, let me just enlarge that a bit. He says the following. In this article, I want to discuss the possibility that the goal of theoretical physics might be achieved in the not too distant future, say by the end of the century – the 20th century – by this I mean that we might have a complete, consistent and unified theory of the physical interactions, which would describe all possible observations. What Stephen Hawking’s talking about here is a so-called Theory of Everything, a theory that brings together all the known laws of physics and known laws of the universe into one, an all encompassing idea, or theory, an equation that you could wear a t-shirt is very often the way people put it. Stephen Hawking thought we were getting close. Stephen Hawking was wrong, we're not close, there is still a long way to go. And there are still so many things out there that we don't understand. That's not to say that we haven't come a long way. We know so much about the building blocks of matter that make up everything, not just the atoms, but the particles that make up the atoms, the particles that make up those particles, the forces between them, the rules and laws that describe so many phenomena. But that's not the end of physics. Because the end of physics, as I will say in a moment, is really sort of a holy grail that physicists are hoping to one day reach. 

If I think back to my own career in physics and my time studying physics, what are the big discoveries, what are the exciting new phenomena that we have understood? Well, I'll give you two examples here. One is the discovery of the Higgs boson in 2012. The Higgs boson is an elementary particle that was discovered at the Large Hadron Collider at CERN, by smashing subatomic particles together at very high energies, and they found this particle that Peter Higgs had predicted. The lower picture depicts the collision of two black holes. This is not to scale, so don't worry, these black holes weren't just outside of the orbit of the Earth, but in fact, over a billion light years away. What we discovered, what's so exciting, isn't the fact that we saw two black holes merge in this way – although that's very exciting in itself – but it's the confirmation of what are called gravitational waves. So this was a discovery made in 2016, at experimental facilities in the US. And gravitational waves had been predicted by Einstein himself, in his Theory of Relativity. And finally, we built instruments sensitive enough to pick up… So imagine dropping a stone in a pond and watching the ripples radiate outwards to the edge of the pond. Obviously, the further out they go, the less energy they have, they lose energy as they travel. And so it might be quite a big splash in the middle of the pond. But by the time it reaches the edges, it might be very tiny, faint ripples. This is what's happened here, black holes colliding creates enormous amounts of energy, which sends ripples through space itself. So the fabric of space itself stretches and eases as this energy passes through it. And a billion years later, we picked up those faint remnants as they washed through the earth, and we pick them up on our instruments. These two discoveries, of course, a lot of I mean, many of you, I'm sure will have heard about them, even if you're not physicists, if you don't understand the details. But what they tell us is that these are fundamental and exciting new discoveries in science. And yet, actually, they're not that exciting physicists, because the Higgs boson was confirmed half a century before it was discovered, gravitational waves were predicted a whole 100 years before they were discovered. So none of these discoveries were really a surprise, in a sense, there were box ticking exercises, we think the Higgs boson exists, yep, we found it. Gravitational waves should be out there, we just need to build the instruments that are sensitive enough, oh, there you go, here they are. 

And so, they weren't unexpected discoveries. If I think about what is probably the only really surprising discovery, certainly in my lifetime, it'll be the discovery of dark energy in 1998. This really no one saw coming. So astronomers were looking out into deep space, and measuring the rate of expansion of the universe. We've known for many years, since the late 1920s, that the universe is getting bigger. Expanding out from the Big Bang. So this is not matter moving through space. This is the space in between matter, that is stretching, at the scale of galaxy. So it's not the space, you know, here in the world that stretching, gravity holds everything together within our own galaxy even. But in the big gaps between galaxies, space is stretching and expanding. What was discovered in 1998, was the fact that this expansion was speeding up, it was getting faster and faster. And no one thought this was possible, because even though the universe is expanding, we all expected gravity to be putting the brakes on the expansion. Like it's like stretching a spring. And at some point, either you stretch it and it's then sort of pings back together, or you stretch it, and you know, a bit like blu tack, I don't know in Australia, whether it's called blu tack, as well, but you know, the stuff they stick papers to the wall, right? You stretch blu tak, and the more you stretch it, the easier it becomes to stretch, it just carries on stretching. But no one expected that expansion of space to actually get faster. So once we found this, the suggestion was, there must be some mysterious dark force, this is my depiction of it,  borrowed from Star Wars. We call it dark energy, for want of a better term, we don't still don't quite understand what it is. 

And there are other phenomena now that we also would like to understand more about. For example, the closely named, but not related, concept of dark matter. Dark matter we know is out there in the universe. We know it holds galaxies together, we know it has a gravitational pull on matter, but it's invisible. In fact, invisible matter would have been a much better name, really, in hindsight. So we know it's there, because we can see its influence. The universe wouldn't really exist the way it does now without the existence of dark matter inside it. But we don't know what dark matter is made of. So we're looking for some new type of part, that would be the constituent of dark matter. And we were looking for many years. And we're so confident that Dark Matter’s there. We're not going to give up looking until we find it. So dark energy and dark matter are still mysteries that need to be completely solved and understood. Similarly, there are questions, equally, similarly named, but also has nothing to do with the other two, antimatter. We know antimatter exists. We make antimatter, we use antimatter in experiments, we use antimatter even in medicine, would you believe. You may not know this, but a PET scanner, positron emission tomography, a scanner that scans for example, your brain in a hospital. It uses antimatter. Antimatter particles are created inside the parts of the body that you're imaging, and they meet normal matter. And that creates a little puff of energy that we pick up and we use that to create images of the inside of a body. So antimatter exists. That's not a mystery in itself. But the mystery is, why there isn't more of it? I mean, actually, it's good that there isn't more of it, because antimatter and matter would annihilate and we'd all disappear in a big puff of energy. But where did it all go? Because energy, certainly from the Big Bang should have created equal amounts of matter and antimatter. And yet most of the universe that we see around us is made of normal matter. Antimatter, you know, it appears and disappears very quickly down at the tiny quantum scale, that's another mystery. And there are other mysteries, and I’ll mention one or two at the end of the talk. Really just getting across the idea that, however wonderful and well understood the phenomena, the forces of nature and the building blocks of nature are, however wonderful the technologies have been that we've developed based on that understanding. I wouldn't be talking to you, using this technology, were it not for the development of modern electronics and computers, and they, in turn rely on our understanding of the nature of the subatomic world through the theory of quantum mechanics. So, we know a lot, we know it's right, because we develop technologies that rely on it. But that doesn't mean we've reached the end of the line. 

So how far have we come? And where do we want to get to? I'm going to encapsulate this in a slide, which I have to say, I'm very proud of. This is my unification of physics in one slide, slide. What we've discovered, over the centuries really, going back to the beginning of the scientific mission in this sort of 16th, 17th century, is that phenomena and ideas that we thought connected, have turned out to be related to each other in some way. And so, if we go back and start with, say, falling apples and orbits of planets, then Isaac Newton was the person who showed that they were related through the force of gravity, Newtonian gravity. You see until Isaac Newton. I mean, we sort of know this now. And it's obvious, and it's all taught in schools, you know, apple falls, why? Because the Earth's gravity pulls it down. Why do the planets orbit around the sun? Because the sun’s gravity holds them in place. But until Newton pointed this out, he said, they're part of the same phenomena, people thought that the phenomena down here on Earth, the falling apple, really had nothing to do with those laws of nature that govern the motions of out there. So that's a unifying idea that gives us Newtonian gravity. Ever since then, we've found other disconnected topics that are all phenomena, that you will realise are connected. So I'm going to jump around here, you can see why the fonts are small here. You know why, Jim, I can hardly read that. Why is it so small? I'm going to fill this up, don't worry. So electricity, and magnetism. They were shown, by people like Michael Faraday and James Clark Maxwell, to be part of one fundamental force of nature, electromagnetism. I jumped down to the bottom here, heat and energy. Is an idea that was developed…. the connection between heat and energy was a science that was developed in the 19th century. Together with another era called statistical mechanics, they were unified into what we now call thermodynamics. So I've put thermodynamics in bold, because that's one of these, the, what I call the three fundamental pillars of physics today. 

Okay, I'm going to jump up now, up there, space and time. Okay, no, no prizes for guessing who unified space and time, that was Albert Einstein. In 1905, who would have thought that space, the place where stuff happens, and time, this abstract concept that ticks by and counts the seconds, minutes, hours, years, everywhere in the universe, who would have thought they were somehow intertwined and connected when Einstein showed that they were. To talk about four dimensional space time, you can't talk about space and time separately in physics. So that… he came up with special relativity that unifies those concepts, special relativity, then unified with Newton's law of gravity, to give an even grander Theory of Relativity called general relativity. So he's now combined space time, matter, into general relativity. And that spawned a new field of science called cosmology, which really describes the nature, the age, the shape of the entire universe. So that's on the very largest scales. Meanwhile, the tiniest scales, you can see, I've just put here the word atoms. So atoms were proven to exist, proven mathematically at the beginning of the 20th century. We then within a decade, people like Ernest Rutherford, started looking inside the atom and down to its tiny atomic nucleus and discovered there were new forces inside the nucleus that were holding it together. At the same time, in the first decade or two of the 20th century, quantum theory was being used. This is a mathematical idea that describes the way the world of the very small behaves. By the mid 1920s, that had evolved into fully fledged quantum mechanics. Quantum mechanics is a famously confusing idea – cats in boxes that are dead alive at the same time – atoms in two places at once, and all the other, the other quantum business. It is a counterintuitive idea. And yet it is powerful. It is probably the most important theory in all of science, I would argue. A biologist would argue with me and say, no Darwinian evolution through natural selection is the most important theory in science. I reckon it's quantum mechanics. I've spent my whole career using quantum mechanics in my research and teaching it to students. It describes the building blocks of matter, how they fit together, the forces that exist between them, down at the microscopic scale, so not up at the scale of the Universe, cosmology. Quantum mechanics by the late 1920s, was combined with special relativity. So now we have something called quantum field theory. So I'm going to speed up now, because I'm just going to throw names of theories at you, but just have a look at the way these different phenomena are, sort of, gathering together and being unified. Quantum Field Theory and electromagnetism are then combined into something called quantum electrodynamics. The nuclear forces, we have two forces, the weak and strong nuclear, they were combined with quantum field theory to give quantum chromodynamics. So we have these two theories, quantum electrodynamics, and quantum chromodynamics. That describe three of the four forces of nature. The four forces of nature is gravity, which is up there at the top, that's the general relativity business, you have electromagnetism, electric and magnetic fields, the nature of light, then you have the two nuclear forces, electromagnetism and the two nuclear forces had been combined into these two quantum theories. Well, the strong nuclear force gives us quantum chromodynamics, the weak nuclear force was more recently combined with quantum electrodynamics, another theory, electroweak theory. These three forces and the theories that connect them together describe almost all phenomena down at the subatomic, microscopic scale. And that's what we call the standard model of particle physics. It's not a unified theory, it's a collection of everything we know about the world of the very small. Meanwhile, up at the top cosmology, gives us the standard model of cosmology. Standard model of the very large. Feeding into that, of course, will be things that we don't quite understand, dark matter, dark energy, but the holy grail is now to combine the Standard Model of cosmology, with a standard model of particle physics, into what we call quantum gravity. That's what we haven't achieved yet, the final unification. And my guess is that to unify that we have to bring in that third pillar, thermodynamics as well. So thermodynamics, particle physics, and cosmology have to come together to give us a theory of quantum gravity. And there may be other issues that are going to other areas of physics that may be able to help us quantum information, quantum computing, I'm just filling in the gaps now on this slide down the bottom right, nonlinear dynamics, complexity, non equilibrium thermodynamics. These are all very exotic sounding names. I don't, I'm not even going to try and explain them to you. But just to say, there's lots of question marks here. You know, we've come a long way in unifying physics, but there are still things we need to understand. Why are we obsessed with unification? Why should a theory of quantum gravity exist? Well, we've come this far and so far, it seems that phenomena are interconnected. And there are examples where you need to use quantum mechanics, the theory of the very small, and general relativity, the theory very large, to explain a single phenomenon. For example, the nature of the Big Bang itself, or the interior of black holes. So they may be, sort of, exotic things that are very far from our everyday world. You know, I don't need a theory of quantum gravity. to fix my washing machine, you know, horses for courses. But for a theoretical physicist like me, we feel there's some underlying, unified idea that describes physical reality. 

At the moment, we have candidates for potential theories of everything. I depict them here as an arm wrestle between two superpowers, two superheroes. On one side, you've got string theory. These are highly mathematical ideas, by the way, and not confirmed by experiment. One side, you have string theory. On the other side, you have what's called loop quantum gravity. There are physicists working in each area, and each group is optimistic that their theory of everything is the right one. They're developing the mathematics, these describe phenomena. The problem is that in science, a theory has to be held up to being confirmed by data, evidence and observation. We haven't yet devised an experiment that can adjudicate, that can tell us if either, indeed, of these two ideas is the correct Theory of Everything. Maybe we need to go back to the drawing board? Maybe we need to go back to basics. For example, ask the question, what is space? Now, thinkers, scientists, philosophers have asked this question for millennia. Some like Newton would argue that space is the place where stuff happens, right? So you need space before you can have phenomena and events and matter inside it. Other scientists, people like Aristotle, and indeed, Descartes believed that space only existed because it was the gap between matter, between stuff. So if there was no matter, there will be no space. It's just, it's just the emptiness. If you'd imagine an empty box, there's space inside the volume of this box. Let's say it's a vacuum inside, we have taken out all the matter, all the air, all the particles, all the subatomic particles. Does that space still exist, if you remove the walls of the box? Is it still there? Or was it only there because it was defined by the volume, by the cube that contained it? And what if that cube was then inside a larger volume? Now what if you remove the walls of the smaller box? Does that space now exist because it's part of the larger volume? These are simple philosophical questions, but there's a very deep and fundamental idea I'm trying to get across here. In fact, it was Albert Einstein, who showed that, in a sense, both ideas are right, Newton was right, and Aristotle was right. Einstein published a famous book called, Relativity: the special and the general theory, it was first published in 1916, in German, and then translated into other languages. And throughout his life – Einstein died in 1955 – throughout his life, he would continue not rewriting the book, adding appendices to the end. And in 1954, he wrote his most famous appendix number five, in which he defines what space is. He says, if we imagine the gravitational fields of gravity, remember, in general relativity, Einstein says gravity is due to matter and energy. But it's not an invisible force that pulls things together, the way Newton taught us. Gravity is simply the shape of space and time. And so without a gravitational field, there would be no space and time. So Einstein says, you need matter and energy, to give us a gravitational field, and that allows space and time to exist. Without matter and energy, there would be no space and time. Space time does not claim existence on its own, Einstein says, but only as a structural quality of the gravitational field. So Einstein says, space, forget time, for a moment. space exists, but it only exists because there's matter in it. But it's not imaginary, space is a thing, it's like a substance. It exists. It can be stretched, it can be squeezed, that's why we see gravitational waves. So it's a real thing.

We think Einstein was right. Is this the last word on the nature of space? Well, that we don't know. Particularly if you then ask the next question, what is time? This, more than anything else for me, tells us just how much more we have to understand about the nature of reality, because our three pillars of physics, general relativity, quantum mechanics, and thermodynamics, all give us a different definition, what time is. General relativity says, time is part of the physical fabric of the universe, Einstein, right? Is the four dimensional space. So, general relativity says, time is a dimension, a direction in four dimensional space time. It’s a dimension that can be stretched, it can be squeezed, it can be warped by gravity. Quantum mechanics on the other hand says something different, it says, no, time is not a dimension, time is just a number. It’s number you plug into your equation, your crank the handle, the mathematical handle, you can you know what a particle and electron is doing now, put in the time for now, you can work out what it's likely to be doing at some time in the future, you can crank the handle back, you can figure out what it may have been doing in the past. So it's a number. Time can run forwards and backwards in quantum mechanics. Then in thermodynamics, we have yet another definition that says it's not a dimension, it's not a number that you can put in to make it run forwards and backwards it’s an arrow that points from past to future. In thermodynamics, we know there's a past, we know there's a future, and time only points in one direction. So these are three definitions of the nature of time that I think we're going to have to sort of bring together if we're ever going to have hope of unifying the laws of physics. 

I want to end in the last minute or two by just saying a couple of other quick ideas of stuff that we're still hoping to understand. For example, people always ask what came before the Big Bang? You know, you say that you physicists are so sure that the universe starts in a big bang. Yeah, well, what happened for it? The old answer was that you can’t go to a time further back than the moment of the Big Bang. Because that's the earliest time possible. It's a bit like saying, walk down to Antarctica, we don't walk outside, okay, get a boat to Antarctica, wrap up warm, of course. Walk to this toll, and when you get to the South Pole, keep heading south. Meaningless, right? Because once you're at the South Pole, any direction you walk in, is taking you back north again. So, you can't go further than the South Pole sticking to the surface of the earth, and therefore you can't go to a time bang, because that defines the beginning of time. But even this is now being challenged, and there are ideas that suggest that maybe there was a time before the Big Bang. There's an idea called inflation, I don't want to go into it. But the notion was that the Big Bang happened and then the universe expanded for a brief moment very rapidly in a process called inflation, and then it slowed down to the rate we see it now. But of course, it's speeding up again. There's a new idea that says we're maybe inflation happened before the Big Bang, maybe there's a multiverse or bubble universes in which inflation is taking place eternally. And within it, there are individual universes with their own big bangs, creating them and expanding. So maybe before our big bang, there was still the inflationary universe, the multiverse, which is making lots of other universes. It starts to sound rather fantastical. But, these are the sorts of ideas that we're trying to understand now. We are now wading in the water outside of the island, just to show that there's still so much to understand. This is my last slide. I like this picture. Guess why? I wrote a book, a little ladybird book on gravity. And it's very illustrated. And so one of the illustrations is a depiction of the multiverse, bubble universe, and there's me blowing bubbles creating them. Do I believe the multiverse exists? Well, using the word believe isn't really very scientific, is it? I can believe, I can want a theory to be correct, I can believe that something is probably along the right lines, but in science, that's not enough. We need experimental confirmation. So I will end there. There's more I talk about in the book. But that's the basic idea. This is why I'm so in love with this subject. So thank you very much for your attention.

Emma Johnston: Thank you, Jim. You've given us a wonderful introduction to The World According to Physics, or a walk along the shell shoreline of the island of knowledge of physics, and us Australians being on the biggest island in the world, we appreciate that analogy. So, before we go back to this story and back, delving into some of the actual physics, I wanted to talk to you a little bit about your background and how you came to be a physicist. So I read in the book, ever since you were a teenager, you say you have been satisfied by physics. This is a little talked about bonus of being a scientist. Satisfaction. Can you describe how satisfaction arises? And from what is absolutely an ongoing quest for the truth?

Jim Al-Khalili: Yes, it's, I mean, satisfaction really began with frustration. As as a young boy, I, so I say my background is my father's from Iraq, my mother's English, but I grew up, I was born, I grew up in Baghdad, and over there, you know, the summers are so hot that you slip up on the roof in the summertime. So I remember as a boy, 10, 11 years old, gazing up from bed, through the mosquito net up at the night sky, and trying to understand you know, what’s a star? You know, does space go on forever, you know, the nature of space. And I mean, I had these vague questions bubbling around in my mind, but I had no way of finding answers. No one I could ask that could answer them for me. And so that frustration became a passion to try and learn myself. And you know, by the age of 13, 14, I had an inspirational teacher, which is always the case, right? You know you ask so many scientists, how did you get into science? Well, you know, I got hooked by a fantastic teacher. And by the age of 14, I still wanted to play football for my favourite team, Leeds United. I wanted to be a rock star, obviously. But gradually, I realised that physics is a subject that I had to study. And that was it, my mind was made up. And I've never lost that passion, that love for the subject, that curiosity about the world around me, I sometimes wonder why everyone isn't in love with physics.

Emma Johnston: I'm sure most of us are, we just don't have the opportunity to indulge. But that's a wonderful story of how your background has influenced your passion at the moment and potentially, the way you think. There are big questions for Western science and how we support and encourage diversity. I wonder if you could tell us a little bit about how potentially your background has influenced how you do your science, but also the science that you communicate? And I'm thinking in particular of the book you published in 2010, The House of Wisdom: How Arabic Science Saved Ancient Knowledge and Gave Us the Renaissance. What did you learn from these projects of writing the books and doing the TV shows?

Jim Al-Khalili: Yes, I mean, I got involved in science communication in parallel with my academic career. It was never, you know, my ambition to make TV documentaries, or broadcasting or popular science writing, I just found I enjoyed communicating these ideas in as simple a way as possible and having other people get a glimpse of why I love it so much. I enjoyed that as much as I did learning it for myself and doing research. I've made various TV documentaries. So I made a documentary called Science and Islam, which is about the development of science in the Islamic empire in the mediaeval world. So around, from the 8th century to the 13th century, in particular, the, what's called the golden age of Arabic science. Because in Europe, certainly, people aren't generally aware of that, you know, we think the era of the ancient Greeks were all over it, and then, you know, that finished the Roman Empire when it fell, Europe went into the dark ages, and nothing happened until Copernicus and Galileo and Newton came along. And of course,just because nothing was happening in Europe doesn't mean things weren't happening in the rest of the world. So I felt I wanted to tell the story about some of the advances in science, in mathematics, in physics and astronomy, in medicine, that took place under the umbrella of the Islamic world. So these are not just Muslims, could have been Muslims, Christians, Jews, people of no religion, different races. And I'd heard of some of the names of these great scientists at the centre of, Ibn-Sina, Ibn al-Haytham, people like that, from my school days in Iraq, but even there in Iraq, these guys are taught as figures in history rather than scientists. Whereas really they should be as well known as Galileo and Newton, so I wanted to get that story. So I think in that sense, the diversity, the fact that I grew up in a different culture, highlights to me the… first of all the universality of science, that science doesn't belong to any one culture or religion, it progresses and develops and it's like a baton handed on from one culture, one civilization to another, and each learns from the other. But also there are different ways of looking at the world, different ways of studying the world. And yet, we all come to the same conclusions, we all develop the same equations, that nature speaks the language of mathematics, and that crosses all borders of cultures, race, religion, creed, and so on.

Emma Johnston: So that's really interesting. That’s some big questions. Some people turn to religion to answer the big questions such as, where do we come from? Or, does the universe have a beginning? What is everything made of? You turn to physics. Can you explain why?

Jim Al-Khalili: Yes, I mean, I'm not religious, I think, it's probably inevitable. My mother was quite a devout Christian. My father was agnostic, Muslim. But you know, I grew up in a household where they believed in God, and God and Allah are just two names for the same creator. But at some point, partly because my parents both had different religions, partly because I had a fascination for science. I felt that I would seek answers through rational thinking using the scientific method. Yes, you can, you can look for answers using religion, using meditation, contemplation, other philosophising, you know, any other ideology. But for me, the scientific method is the reliable way of reaching what I would regard as some ultimate truth about the nature of reality. The universe is there, it exists, it has properties, regardless of whether humans ever would have evolved on Earth. And we want to understand those secrets of nature. And for me, science is the only reliable way to do that, because it relies on what we call the scientific method, checking and testing and looking for the scientific evidence.

Emma Johnston: You make a powerful argument for, I guess, a universal method. And you've also shone a wonderful light on work in the scientific fields that have been done in other cultures that can become invisible. A great contribution to our understanding of science, and the history of science. I did notice that while I was reading the book, there were no female physicists named in the book, and I wondered, did you have a perspective on gender diversity as well? Because physics is relatively well known for being male dominated.

Jim Al-Khalili: Absolutely. I mean, as an academic, I've spent my career involved with the UK Institute of Physics. I was a university admissions tutor for many years. So I'm well aware that there's an issue, and the issue particularly with physics, and certainly other subjects, like engineering, science, at school are perceived as boys' subjects. And that's a problem, there's certainly misogyny as there are in so many, sort of, lives still today. But it's a problem of our culture, that physics is seen as a boy subject. I don't know what it's like in Australia, but something like 20% of students at school who take A levels to go on to university are female, 20% of our undergraduate cohort and in the physics department is female. And we've not been able to lift that by much. And whereas I talked to some of my female colleagues who've made it to, who are professors of physics, very often they say it's because they went to an all girls school. And so physics is not, there's no such thing as a boy subject or a girl subject.  If you’re good at physics, you're good at physics. Your brain isn't wired up to be better at physics, depending on whether you're male or female. So it’s something in our culture. So certainly, to get back to your question, no, there aren't many women, or there are women in physics, but they are invisible. You know, there's a scientist here in the UK, Jess Wade, who's done a tremendous amount of work in raising the visibility of great women scientists and making Wikipedia pages for them. And when you look to see what they've achieved, you think we're not like we're scraping the pie to find a woman who's done something in science. These are people who have changed the world just as much as their male colleagues, and yet they've not been well known. You know, they, I have, you know, favourite scientists, there's a very good friend, colleague, of mine, Jocelyn Bell Burnell, the astrophysicist who discovered neutron stars, you know, who was famously passed up for a Nobel Prize because of misogyny. There are great women like Marie Curie and Lisa Meitner, in physics and chemistry, that are known, but maybe not as well known as their male colleagues. So I think we just have such a long way to go because diversity in science can only help when you have all ideas being promoted and developed and pushed by just one group, typically white males, then we're missing out on so many other different perspectives to give us fresh ideas and science.

Emma Johnston: And maybe that's why we haven't found those mysterious particles yet. We haven't had enough female Einsteins in the game.

Jim Al-Khalili: Absolutely. And look, you know, when half the population is out there, that's a big pool to look for female Einsteins in.

Emma Johnston: Exactly. So back to the physics for a moment, and also some questions from audience members. First of all, you did explain a little bit about the difference between dark matter and what I guess, light matter, which is what we're mostly dealing with. What makes Dark Matter invisible? Can you just explain it for the audience?

Jim Al-Khalili: Yeah, well, to see something, we need light, photons, particles of lights, or electromagnetic radiation, to enter our eyes. So it has to interact with whatever it is we're looking at, and then come into our eyes, or, if it's outer space, come through our telescope lenses. Dark Matter doesn't interact via the electromagnetic force, as far as we know. And so it's invisible to photons. Photons don't interact with it. And so it doesn't, we can't see it, because it's not sending light to us. Simply because it doesn't interact by the electromagnetic magnetic force. Electromagnetic force is what holds atoms together, it's what binds electrons to the atomic nucleus. And so, dark matter, which doesn't interact via electromagnetic force, doesn't see atoms, and it can pass through normal matter as though it weren't there. So, it really is quite literally invisible to us. But it still has mass, and it still has gravity. So that's why we know it's there. It's this invisible gravitational thing that we can't see.

Emma Johnston: That's fascinating. We know that the great advances in physics in particular, were aided by some inventions like the microscope and the telescope. Are you thinking that right now we're being held back by the technology? Or is it the theory that's holding us back?

Jim Al-Khalili: Well, at the moment, there are a number of suggestions, a number of theories to suggest what dark matter might be made of. But it's really now the time for experiments to adjudicate. So yes, I think it is the fact that we haven't developed the patents that are sensitive enough, in the same way that it took us 100 years to pick up gravitational waves, we're still trying to pick up big matter, particles don't interact, other than via the gravitational field. These are subatomic particles, they have very tiny mass. So individually, they have very, very little gravity. So really, the only way we can pick them up is if they have a head vision with a particle of normal matter. Matter, most of our bodies, for example is empty space, the chances of a head on collision with say an atomic nucleus is tiny. So we're developing these big chambers, experimental facilities that will be able to detect those very rare occasions when a particle of dark matter from space is captured. Likewise, we're trying to create particles of dark matter in colliders like the Large Hadron Collider. But again, since we don't know what we're looking for, we don't know where to look, we don't know what energy we should be smashing particles together to make. So it really is, keep going, developing our instruments, making them more and more sensitive, and no doubt one day we will find them.

Emma Johnston: We live in hope. Well, we certainly have found particles before that have been theorised many decades earlier. But this all sounds very far from everyday life. We've got this fabulous group of researchers at UNSW, who are quantum researchers working in particular, to develop quantum computing, and they're working on quantum computing in silicon. So there's a lot of members of our staff and our alumni who are really fascinated by the quantum world. The first question we had from one of our audience members, and this was a staff member.. Particularly, they're interested in, are there any quantum quirks that affect daily life? So bringing it back down to us. And if not, why not?

Jim Al-Khalili: There are lots of quantum phenomena that we know are there and and really… so in general, we tend to think that we don't see quantum effects, they get washed out, once you get trillions and trillions of atoms together to make stuff the size of us and our everyday objects. We don't tend to directly see quantum phenomena in action on the everyday scale. And yet we know they're there. I mean, some of the most famous examples, there’s something called Quantum tunnelling whereby a particle can move through an energy barrier, even though it doesn't have enough energy through it. Because particles can behave like waves, it can seep through an energy barrier, a bit like a ghost walking through a wall. Now, of course, you don't do that in everyday life, ghosts aren't real, by the way folk. You can't walk through a brick wall. And yet, sun shines, because particles, protons, are quantum tunnelling together. Two protons, the nuclear part, both have positive electric charge, and so they should repel each other. And yet, every now and again, they will get close enough that one of them can, in a sense, quantum tunnel through that energy force field, to the other side, and then they fuse together in a process that makes helium and hydrogen, which is what we call thermonuclear fusion, which is why the sun shines. So for me, that's the most important example of quantum mechanics that we see. The sun wouldn't shine if mechanics weren't true. And then, of course, the whole of modern electronics, as I mentioned in my talk, is developed on the basis of our understanding of the quantum world. Now, quantum computing, in a sense, that’s quantum 2.0, that's utilising some of the even more counterintuitive ideas of the quantum world, like particles being entangled, to separate particles, nevertheless, being somehow in instantaneous communication with each other, such that measuring one influences the other. Quantum computing, that again, is even more crazy. Even Einstein didn't like that idea. He called it spooky action at a distance, and yet, we need to understand it and utilise it if we're going to develop quantum computers.

Emma Johnston: And quantum baking, I’m thinking about, lying out in the sun, just quantum baking. That's a lovely thought. Maybe ghosts don't exist, but quantum information exists, and people are actually transferring quantum information over 1000s of kilometres. Can you explain how that works?

Jim Al-Khalili: Yeah, so this is linked to the idea of entangled particles. When two particles have been together at some point in the past, and you separate them, in a sense, their fates remain intertwined. It's not just that, if one was spinning one way, the other will be spinning the other way, in quantum mechanics, particles can spin both ways at once. What’s called quantum superposition. So you don't know which they're spinning until you measure one. But when you measure one of them and see it spinning, say clockwise, then the other one also decides and will spin, say, in the opposite direction, anti clockwise. Till then they were both spinning both ways. It's a very weird idea. But it means they're sharing information. They're part of what we call the same quantum state. And that's what's used to send information across vast distances. So these are ideas that are currently very much being developed around the world, which would allow us to send information securely as well, because there's there's another area called quantum cryptography, whereby we're making use of the fact that one can interfere, or find out this information without alerting the sender and receiver, because as soon as the measurements are made in quantum mechanics, that changes the nature of the system that you're looking at. So quantum information, quantum information transfer, quantum teleportation, quantum cryptography, these are all exotic ideas that are going to become the technology of the 21st century, in the same way that the microchip was the technology of the 20th century.

Emma Johnston: So if you're a primary school student, now, you will be using quantum technology very, very soon. We actually have a pre-recorded question now from a primary school student. Let's go to that question, now.

Pre-Recorded Question: Hello, I'm Fahad, and I go to Alexandria Park Community School. My question is for Mr Al-Khalili. Do you think that if black holes disrupt the buildup of space time, what happens to the matter the black hole congeals or swallows? Does it get compressed? Or does it or does the black hole lead somewhere else?

Jim Al-Khalili: Excellent question. So the question is, if the matter inside a black hole is so gravitationally strong, it curves spacetime around the black hole, that's why it closes the black hole off from the rest of the universe. And the question is what happens to this matter? That is swallowed by a black hole, because black holes can carry on sucking in matter from around them, and where does that go? The simplest type of black hole would have what's called, a singularity, a point in the middle where all the matter goes to. Where's the black hole that’s spinning, that singularity becomes like a ring. And there are ideas, in and in fact, developed by Einstein himself in the 1930s, that suggests that the interior of a black hole through this ring would lead us to another part of our universe or even, you know, if you enjoy science fiction, a parallel universe. So these are what then became known as wormholes. But in physics, we call them Einstein-Rosen bridges, Nathan Rosen and Albert Einstein being the two people who developed the idea. So what does happen to the matter when it falls into a black hole? Well, the one thing we do know is the stuff that the original star was made of, and all the other stuff that black hole sucks in, doesn't go anywhere, that's still there in whatever shape, point, or ring, it's still in the middle of black hole. How do we know this, because the black hole still has gravity, it can still pull stuff in. If the matter had disappeared into some other parts of the universe through a wormhole, then that black hole wouldn't have any gravitational pull. So the matter is there. But space itself might continue through the black hole somewhere else. We don't know yet. No one's, you know, we've seen black holes from afar. We've got a theory that describes them, but it breaks down once you get inside the black hole to singularity. So we still don't have an answer of whether there is really some other side to a black hole. But we know what created it should still be there in the middle.

Emma Johnston: Wonderful explanation. So let's move to the final chapter of The World According To Physics, you make some important points in that chapter about how physics and how science more generally, work. And you give an example of where you were filming a story about one of the scientific ideas, you made a mistake, instead of editing it out, you actually filmed more material to explain what went wrong. What kind of point are you making here?

Jim Al-Khalili: This was very interesting, I was talking about how gravity affects the nature of time itself. The stronger gravity, the stronger the gravitational field you're in, the slower time runs. Sounds like science fiction, but in fact, it's the way GPS works. Satellites send the data to your smartphone, time ticks py on the satellite slightly more quickly than it does on Earth. Because they're further away from the centre of Earth, they feel weaker gravity. And so we have to deliberately slow down the clocks on board the satellites so that they measure the same time as the clock. So that we can very accurately determine the distance from the satellites to your smartphone, and therefore where you are. So I was getting across this idea that, you know, timelines are at different rates. And I realised, together talking with my producer, that I had made a mistake about two thirds of the way through, making this documentary, ready to be… it had been edited, I was going to be recording the voiceover, and it was going to be aired on the BBC, a few days… a few weeks later. I realised that what I had said was actually wrong. And I panicked. And I contacted a few colleagues and said, of course, yes, you're right, you're wrong, has to be corrected. At the BBC, the commissioning editor said, well, look, can't you just reshoot the bits where you made a mistake, and, you know, no one will be the wiser. But I saw this as a wonderful opportunity of getting across the fact that in science, it’s ok to make mistakes. And it's okay to admit that you've made a mistake. Making mistakes or how you learn. So we actually filmed me saying in the documentary, unfortunately, at this point, things went a bit pear shaped because I realised I'd got it wrong. And then I'll go on to explain why I got it wrong. And people asked me, said, oh, you're very, very brave, Jim, to admit your mistake, which seems weird to a scientist that, you know, that you don't like to admit mistakes. That's how we work in science. A bad scientist is one who never admits their mistakes, you wouldn't get very far, if only politicians would learn from science. And I think it's a lesson in the way we do science, that we can maybe export to wider public life, admitting your mistakes is not something to be ashamed of.

Emma Johnston: I was going to ask you about that, too. Do you think we're actually seeing those lessons play out during the COVID crisis? Is there a silver lining in the way that science and learning and continuous improvement is playing out in the way we manage this crisis?

Jim Al-Khalili: Yeah, I think absolutely, during this pandemic, you know, for the wrong reasons. You know, scientists are really under the spotlight and have never been under such intense scrutiny. Suddenly, you know, the public realise that, you know, and politicians realise that, you know, they need the scientific advice they need to act on the best scientific evidence. And so sometimes when a scientist says, well, I'm not sure, I'm uncertain, or I have doubts about this, people get worried. Well hang on a minute, if you're not sure, you know, how can we believe anything or trust anything you say. So I think it's vitally important to get across the idea of the scientific method, how science works, that being unsure, to be uncertain, to have doubts. Like, being prepared to admit your mistakes, is a good thing, is part of the power of the scientific method. That we need to check, never be sure, to always be prepared to change your mind in the light of new evidence. And that's what we're seeing with the COVID pandemic, we're learning more about this virus that we didn't know before. So if the advice sometimes that comes from scientists, or – excuse me, kicked my microphone – if the advice that comes from scientists or politicians may sometimes be changing. Well, that's not because we can't decide or make up our minds. It's because we've learned more, and we've had to adapt to new evidence and new data coming in.

Emma Johnston: Well, that is a wonderful take home message for us celebrating National Science Week in Australia. Thank you. I hope you're writing a book about this, Jim.

Jim Al-Khalili: Oh, thank you for asking Emma. Actually, yes. Not that we're not the way that you primed you to ask me that question at all. I am writing a book called Towards a Rational Life. Lessons on how to think more scientifically to navigate through the world. And so it's, it's really, you know, because we see around us today, you know, polarisation of opinions. Everything is in black and white. No one's prepared to give an inch. You look on social media, and everyone's shouting at each other. It's so far removed from the way we do science, which is about collaboration, which is about saying, oh, okay, no, I was wrong. Your evidence suggests that what I thought before has to be changed. If only we could…. not teach, I mean, that sounds a bit condescending. But there are lessons from the way we do science that I think would be good if we could bring them into everyday life. So I'm hoping this, in my next book which should be out next year, people can see the way science works and get a sense of trusting that a scientific view of the world is one that… it's powerful, because we'll we're confident that we know we can we're always checking it, we are testing it, we prepare to change our minds. And in doing so we advance our knowledge, we expand that island that tells us about the nature of reality.

Emma Johnston: Well, I'm not your editor, Jim, but I think you should hurry up and get that book finished. Get it out on the shelves. Thank you everybody for tuning in to The World According to Physics. I'd like to thank Professor Jim Al-Khalili for joining us from the UK. To hear about more events please subscribe to the UNSW Centre for Ideas newsletter. Thank you.