The World According to Physics w/ Jim Al-Khalili

Sep 4

EPISODE #23

Theoretical Physicist Jim Al-Khalili shares his thoughts on what physics can teach us about the nature of reality and the mysteries of our universe, the possibility of a theory of everything, and how to make scientific ideas accessible and captivating.

Jim Al-Khalili FRS is a quantum physicist, author and broadcaster and one of the best-known science communicators in Britain. He holds a Distinguished Chair in Physics at the University of Surrey where he teaches and conducts his research. He received a PhD in nuclear theory in 1989 and has since published widely on physics and the history of science. He has written twelve books, including his first novel, between them translated into over twenty-six languages. He is a regular presenter of TV and radio science documentaries and programs and is the recipient of numerous honours and prizes, including the inaugural Stephen Hawking Medal. His latest book, The World According to Physics, is published by Princeton University Press.

Find out more

YouTube

SoundCloud

Watch Live Replay

Transcript

Luke Robert Mason: You're listening to the FUTURES Podcast with me, Luke Robert Mason.

On this episode I speak to theoretical physicist, Jim Al-Khalili.

"But ultimately, there's a reality out there and for me, science - and physics in particular - is the best way of understanding the nature of that reality."
- Jim Al-Khalili, excerpt from interview.

Jim shared his thoughts on what theoretical physics can teach us about the nature of reality and the mysteries of our universe, the possibility of a theory of everything, and how to make scientific ideas accessible and captivating.

This episode is an edited version of a recent live stream event. You can view the full, unedited video of this conversation at FUTURES podcast dot net.

Luke Robert Mason: Now theoretical physics has become our most useful tool in understanding the origin of space and the meaning of time. It has been so effective that the late professor, Stephen Hawking, claimed that physics might soon provide us with a theory of everything. But new discoveries like quantum mechanics and dark energy, combined with a challenge of unifying all of these concepts are forcing physicists to confront captivating new unknowns. In his beautiful new book, The World According to Physics, Jim Al-Khalili explores just how far physics has gone in demystifying the world, and then outlines how far it still has to go in teaching us about the nature of reality and the weirdness of our universe.

So, Jim, there is so much that I want to ask you, but from reading the book it is abundantly clear that you have a - perhaps an appropriate - love affair with physics. I guess I want to know what it is about the world of physics that makes it such a captivating way to understand our reality?

Jim Al-Khalili: Well, you know, I sometimes am puzzled why everyone isn't completely in love with physics because it deals with the deepest questions. I remember when I was growing up as a kid wanting to know: Does space go on forever? What are stars made of? What do atoms look like? What is time? The big questions of reality that we ask. At some point - I must have been about 12, 13 or 14 - I realised that physics was the subject that tries to answer those questions, and that was it for me. So, okay, it helps that I'm good at maths. It helps that I like solving puzzles and solving mysteries, but physics was really, basically common sense about how the world works. It gave me the tools to ask some of these really deep questions and that's what I've done all my life, and I still keep asking those same questions

Mason: Now science and rational inquiry which underlies physics: it's done so much to demystify our world. Do you think that's necessarily a good thing or is some mystery actually quite useful?

Al-Khalili: I think it would be a boring world if we had all the answers. There's no doubt about that. It's a bit like the anticipation of opening your Christmas presents on Christmas morning. There's that excitement of not knowing what you've got as a kid. I mean, maybe not so much for me now. I know it's socks and aftershave. But once you've opened your presents, yes, you've got your new toys and whatever is there, but the mystery is gone. Somehow the magic has disappeared. I think it's the same with trying to understand the universe and our place in the universe. The mystery about it is wonderful.

I think a lot of people have this misconception that science is about - certainly demystifying, because mysteries are there to be solved - but somehow we want for there not to be mysteries. We want just for the world to be rationally explained away without any puzzles, without any magic, without any wonder. That's simply not the case. There are still so many mysteries out there, so many things we have yet to understand. Yes, physics demystifies, but it also shows us new mysteries that we have to tackle, and new challenges.

Mason: I mean, one thing that science and physics does really well is show us a version of reality. In some cases - in the case of physics - it shows us a singular objective reality that can be understood through science. Do you think there's such a thing as a singular objective reality? Do you think physical theories could really be able to be used to approximate the truth of physical reality?

Al-Khalili: I do, yes, but that's not to say that all physicists or philosophers of science agree with me on this. My view is that there's a world out there, there's a universe, a reality out there. It's been in existence long before humans came about and started asking questions about it. The role of science and the role of physics is, as you say, to approximate as closely as we can to that objective reality; the truth of the way things are.

There aren't different realities or different truths. It's not that you arrive at a different...there are different ways of explaining: different ideologies, religions, philosophies. But ultimately, there's a reality out there, and for me, science - and physics in particular - is the best way of understanding the nature of that reality.

Mason: Where have we seen examples of physics helping us to understand that physical reality? Physics theories helping us understand that physical reality?

Al-Khalili: The way physics has developed for many, many centuries. An example I use in the book is: If I were to drop a ball from a height of five metres, physics tells me that it will hit the ground in one second. There's a simple formula, actually developed by Galileo - even before Isaac Newton - that tells you: Drop it from five metres on Earth, the pull of Earth's gravity will mean it falls and hits the ground in one second. Not half a second, not two seconds. No ideology, no amount of meditation or prayer, no philosophy, nothing will tell you it'll hit the ground in one second, other than physics. The universe, described mathematically, which we now explain using physics. That's a fact, a truth about reality that physics tells us. It doesn't matter how far our theories develop. Einstein replaced Newton and someone else will replace Einstein, but that will always remain true.

Mason: When it comes to physics, it's often this thing that's done by, obviously, physicists. You say in the book that there are two types of physicist: Number one is the searchers and the dreamers; number two is those that play it safe by exploring the theories that can be attested with experimentation. Jim, what kind of physicist are you?

Al-Khalili: Somewhere in between, he says, boringly. Those two categories, I guess they apply more to theoretical physicists rather than experimental physicists. When you study physics at university, if you want to go on academically to do physics research, you have to make this choice: you either become a theorist or an experimentalist. The theorist does the maths, solves the equations, writes the computer code, develops the models and simulations. The experimentalist, in the lab, carries out experiments to test the way the world really is. But among theorists, yeah, there are these two types.

The example I use in the book is: If you walk along a quiet pavement late at night and you almost get home, but then you realise you've lost your keys through a hole in your pocket. You go back and retrace your steps, to look for your keys. If you look in the pools of light underneath the lampposts, that's where you're most likely to be able to see your keys, if they're there. But of course, they're more likely to be in the large areas of darkness, in between the lampposts. There's two types of physicists. There's the searchers in the dark who grope around in the dark. They don't know what they might find. They're less likely to find what they're looking for, but the rewards are bigger. Then, there are safer physicists who are in the pools of light. They're more likely to make advances, but they'll be incremental advances. They're not likely to create a revolution in physics. So yes, people working on cosmology or string theory - these are the searchers in the dark. They're the adventurers, but they could spend all their lives without coming up with a revolution in physics. If they do, there's your Nobel prize.

Mason: But which one is more fun? Is it the prediction game or is it the proof game? Much of physics that was theorised has now been proved, but the ones who did the predicting are the ones, as you just said, who win the Nobel prize. Which one do you think is more fun?

Al-Khalili: I think it depends on your personality as a scientist. There are physicists who are quite happy to spend their whole career developing a very esoteric, mathematical model of what happens, say, before the Big Bang. They almost know there's no way of testing that idea experimentally, but that's fine. They will come up with their elegant mathematical equations and for them, that's fulfilling enough. Then, there are the other physicists who don't feel a sense of achievement or fulfilment unless they can test their theory against data; against observation and experiments.

I've spent most of my research career actually developing theoretical models that can be tested against experiments and for me, that's a success. If my model prediction matches what people see in the lab, I say, "Okay, well my equation explains the way the world actually works." - and that's very, very satisfying, but it may not be so exciting.

Mason: Well you do such a good job in this book of making physics exciting, regardless of what sort of physics that it is. You do such a good job at summarising many of the key theories in physics. Everything from space and time, energy and matter, quantum mechanics, thermodynamics. I want to take it one step back and ask you: What was the impact of the telescope and the microscope on human perception? How were these two tools key to our understanding of the world, through something like physics?

Al-Khalili: More than any other instrument in human history - certainly in terms of understanding the world - the telescope and the microscope really revolutionised our view. Until then, all we could understand about the world is the world that we could see with our senses; with our naked eyes. Once you have a telescope, that brings the very far close to you, so we could study the stars and understand the cosmos. The microscope brings the very small, again, into view - and enlarges it - so we could delve into the microscopic world. Now of course, as you say, our two most important or powerful theories in the whole of physics are: General relativity - Einstein's theory of describing the very large, and quantum mechanics - describing the world of the very small. Without the telescope and the microscope, those worlds - the very far and the very small - wouldn't have been available to us. That happened in the 17th century, and suddenly that really kickstarted the scientific revolution.

Mason: That happened at that time, and also Galileo helped to mathematecise physics. Why was that so important to how we think about physics today?

Al-Khalili: It wasn't obvious that the universe spoke in the language of mathematics. Today we take it for granted, that it doesn't matter what part of the world you are as a scientist or what language you speak. You know you can write down an equation and it describes some aspect of the world which would be exactly the same equation for anyone else in the world, for any culture in any age. There's a universality about the mathematics of the physical universe. Galileo was trying to understand how objects fall. They accelerate in Earth's gravity, but to give a simple algebraic expression which allows us to make predictions and do calculations really meant that we could develop our theories because they could then mathematically make predictions that you could go and test against an experiment - rather than just qualitatively saying, "Well I suggest that the world looks like this. That the sun orbits the Earth." - or whatever the Ancient Greeks were thinking about. They were very good at philosophising but to pin the properties of reality mathematically allowed us to develop our theories much more effectively. Of course, there was no looking back after that.

Mason: In many ways it feels like physics is this process of picking the right model and picking the right mathematics, applying that to the right system. Is that a good way to summarise what physics actually is?

Al-Khalili: By and large, yes. The system, the phenomena that you want to study - you have to choose the right theory that applies there. It's a matter of scale, it's a matter of the sort of phenomena that you want to understand. If you want to fix your washing machine you don't need to know the standard model of particle physics, even though your washing machine is ultimately made of quarks and electrons. You don't need that. You need to understand the mechanics and electrical circuitry. Yes - whatever phenomenon or system you want to understand in the universe, you have to apply the appropriate theory that gives you the best way of learning.

Mason: Physics plays in two spaces, really. It feels like it plays in the big of space and time and in the very, very small. But what is so revealing about your book, as someone who knows absolutely nothing about physics, is that there seems to be some sort of relationship between the two. Could you explain that a little bit more?

Al-Khalili: Yeah. I mean these are the two most powerful theories in physics, certainly 20th century physics. Einstein developed his two theories of relativity at the beginning of the 20th century which we now know described space and time, and the cosmos and the universe at large. Essentially, how matter and energy have a gravitational field which shapes the structure of the universe. So that's on the very large scale, and it's a very beautiful, very accurate theory. But, it doesn't apply when you zoom down to the tiny, microscopic scales. Down there at the level of atoms, we need a completely different theory: quantum mechanics. Quantum mechanics, in its own domain, is also extremely powerful. With quantum mechanics, even though it only describes things we can never see with the naked eye - namely atoms and the particles that make them up - without it, we wouldn't be having this conversation. Without quantum mechanics, we wouldn't understand the nature of how material conducts electricity; how semiconductors work. We wouldn't have developed silicon chips, microchips and computers. Essentially all of modern electronics relies on our understanding of the quantum world. It's very powerful, but it doesn't apply, as far as we can deduce at the moment, to the very large - in the same way that general relativity, Einstein's view of the cosmos doesn't apply down at the subatomic scale. That's annoying.

You might think, well why? You've got the world out there, perfectly described by a theory, and the world down there at the very small, perfectly described by a very different theory. To live with it, that's the way it is. But there are instances and examples where both theories should apply. They're rather exotic examples. The first example is the Big Bang itself, or the singularity at the centre of a black hole. It seems that those two theories are very different and don't mesh together, and so the holy grail of physics - the ambition that so many theorists have - is to find a theory that somehow is an uber theory, from which emerge both quantum mechanics and general relativity. This is what we call a theory of everything.

Mason: It unifies everything, and that's really key to this book - or at least it feels like it's a key theme within this book: the idea that there will be a unification of physics. What is unification? What is this theory of everything? Why is it such a major aim for physics and physicists?

Al-Khalili: We've discovered ever since modern physics first developed by people like Galileo and Newton that seemingly two disparate and quite independent phenomena ultimately seem to have a connection between them. Newton started it off. He realised that the reason an apple falls to the ground - whether or not one actually fell on his head on his mother's farm, we don't know, he tells that story - but the reason the apple falls to the ground is due to the same force that keeps the moon in orbit around the Earth, and the Earth in orbit around the sun. The force of gravity - we learn about it at school now. Back in Newton's time, it wasn't obvious that the forces controlling Earthly objects need not have anything to do with those forces controlling the heavenly bodies. So there was that unification of forces due to gravity. James Clerk Maxwell, a Scottish physicist in the 19th century unified electricity and magnetism, and showed that they are part of the electromagnetic field, and light is a travelling electromagnetic wave. Again, people didn't realise there was a connection.

Throughout the 20th century we've seen this process of unification actually pick up pace. Quantum mechanics was developed. That was combined with Einstein's special theory of relativity. It was combined with Maxwell's theory of electromagnetism. The forces inside atomic nuclei were explained by quantum mechanics, and you get to a point where you have one all encompassing theory that describes all the forces down at the sub-atomic scale, and another all encompassing theory describing the universe at large. We sort of expect, or hope that there is that next step that brings these two theories together. We just haven't figured it out yet.

Mason: Why is there that hope, though? Why is it so necessary for physicists to find something that unifies all of these theories? Does it just satisfy some weird desire that physicists have for things to be mathematically perfect, and they just like theories when they're aesthetically pleasing? Or is there something deeper going on?

Al-Khalili: It's just so that we can fit an equation on our t-shirts.

Mason: A hundred percent.

Al-Khalili: No, it's more than vanity or just a sense of satisfaction. In unifying phenomena and ideas, and forces, we develop a deeper understanding. What we arrive at is a theory that gives us a better understanding of the universe than the previous two theories that were not connected. In unifying, we're not just simplifying for convenience and just for neatness, but because it helps us reach a deeper truth. That ultimate truth about the nature of reality that we spoke about at the beginning. We feel we're getting closer to it. We don't know how much further we have to go, of course. Almost sometimes, it feels like peeling back layers of the onion. Oh gosh, who ordered that? Dark matter? Come on. But, we do feel we are moving in the right direction.

One example of why as to why a theory of everything is there; why we want to unify Einstein's general theory of relativity and theory of gravity with quantum mechanics is that in quantum mechanics, there's this idea that a subatomic particle - say, an electron - can be in two places at once: what we call a superposition. Or, that it can actually have two energies at the same time - two quite separate energies. Just saying the words means it's absolutely meaningless. Quantum mechanics is counterintuitive. But, if an electron is in two places at once, we also know from relativity that matter causes spacetime to curve around it. That's a deep explanation of what the force of gravity is: the curvature of spacetime. If an electron is in two places at once, spacetime curvature has also been split. Spacetime is also in a quantum superposition. We know that ultimately, our theory of spacetime - general relativity - must somehow be combined, logically, with the theory of the quantum world. We know it's there, we just don't know whether we have to modify quantum mechanics, modify general relativity, or somehow scrap both and start from scratch.

Mason: You introduce us to two possible contenders for this theory of everything within the book. The first one is string theory and the second is loop quantum gravity, which sounds like something out of science fiction. What is the difference between the two, and do you think either of these could potentially become that theory of everything?

Al-Khalili: It's possible. They've both been going for some time now and they both have their proponents, their advocates and their cheerleaders. Physicists who have spent their careers thinking about them. They're both highly speculative, mathematical theories. String theory - developed first in the mid 80s and then underwent a second revolution in the mid 90s - suggests that ultimately, matter is made of tiny vibrating strings, not point particles. These are strings vibrating in higher dimensions. It's very esoteric and very abstract, but it gives us a way of unifying the force of gravity with the other three forces which are already contained within our quantum theories.

Loop quantum gravity, on the other hand, isn't about unifying the four forces - but rather: How do you quantise - this is the word you use when you make something behave quantum mechanically - how do you quantise space and time? Either of them could be right. I don't work in the field. I've got good friends and colleagues who work in both, and in fact I recently interviewed Brian Greene, an American string theorist who would argue that string theory is the theory of everything. We just haven't figured everything out about it yet, but it is the correct theory. Then Carlo Rovelli, for example - an Italian physicist who has written some wonderful, best-selling popular science books. He's a fan of loop quantum gravity and again, he would say, "Oh no, the string theorists - they've had their time. They've gotten nowhere. They've been thinking about this for decades. Loop quantum gravity is much more sensible." It's almost like different ideologies, different religions. Which camp are you in?

In the book, I try...because I don't work in either field, I can sort of step back and say, "Well you know, they've got their good points and they've got their good points." But what we need, of course, is to find a way of testing them. Ultimately, a scientific theory stands or falls based on whether it correctly describes the real, physical universe - which means we need to find some way of testing; carrying out an experiment; carrying out an observation that can tell us whether these theories are right or wrong. At the moment, we don't know how to test them.

You could almost ask whether they are proper scientific theories. Are they just metaphysics? Are they just philosophy with pretty maths? We don't know how we can check whether or not they're right.

Mason: Perhaps it's a good thing that we can't check if they're right yet. If we did achieve that unification, you talk about in the book achieving something else which is the end of physics. In other words, you can pack up and retire because physics will have achieved what it wanted: that unified theory. What is the end of physics, and could physics actually be in crisis in the 21st century if we find this unified theory?

Al-Khalili: I think many physicists would argue that if there is a crisis in physics, it's because the end that we thought was in sight, isn't. If you want more mysteries, if you're thinking about going to physics as a young budding scientist then great, because I think the end is further away than we thought. At the end of the 19th century, physicists thought that everything was done. We had Newtonian mechanics and his law of gravity; we had Maxwell's electromagnetism; we had thermodynamics; statistical mechanics - all branches of physics that are still good and proper today - but people thought that was all there was to know, and so the end was in sight. Then in the 1890s, we discovered the electron, we discovered x-rays - so called because 'x' for the unknown; we don't know what x-rays were - and we discovered radioactivity. Then, in the turn of the 20th century you have the quantum revolution, Einstein comes along and you realise: Whoa, you thought it was the end of physics. We're just starting.

We almost thought it was the same and we were getting to the end of physics at the end of the 20th century. Stephen Hawking even wrote a famous paper around about 1980 saying: is the end in sight for theoretical physics? We're getting close to the theory of everything. It looks like we aren't really very close to it at all, and other mysteries have popped up since then, anyway, that we have yet to try and understand.

Mason: Well if I can just be a cheerleader for the 21st century for a moment, we have actually discovered stuff in this century. In 2012 and 2016. Could you tell us about some of those discoveries?

Al-Khalili: Yes, of course. What's wonderful is that these are discoveries that have made it out into the wider world. It's not just physicists who will know about it. Everyone heard about the Higgs boson, discovered at the Large Hadron Collider in Geneva in 2012. Peter Higgs and others - the theorists who had predicted the existence of the Higgs boson, this elementary particle, this lump of energy - had predicted it half a century ago. Finally, the experiment confirmed that it really existed and they got their Nobel prizes.

Then of course in 2016, the discovery of gravitational waves. These were absolutely remarkable laboratories in America called LIGO - they're two twin laboratories on either side of the States, and they've picked up these very very tiny, delicate ripples in space itself, coming to us - from the collision of two black holes. It's like dropping a stone in a pond and then the ripples radially moving outwards. If the pond's very very large, you'll just see a tiny ripple at the shoreline and that's the evidence that a stone was dropped in the middle of the pond. So 2016: gravitational waves. But again, they were predicted by Einstein's theory a hundred years ago. Yes, these were absolutely incredible experimental results and got the world of science and beyond all very excited, but they were predicted already. We would have been much more surprised if we hadn't found the Higgs boson and if we hadn't found gravitational waves. Having discovered them, we've ticked the box. Good, yep okay, so Peter Higgs was right. Einstein was right. What now?

Al-Khalili: You almost reveal in the book - and you struggle to say it - but perhaps it would have been better for science if we hadn't found the Higgs boson, because it would have challenged the standard model of physics, and that could have actually been quite a positive thing.

Al-Khalili: I think had it been confirmed not to exist, the standard model of particle physics - as it's known - would have had to have been...not ditched, but revised and rethought. It would have been back to the drawing boards. That's what we want. We want to prove theories wrong and replace them with new ones, because there's the excitement, there's the mystery, there's the Nobel prizes all around. You don't want to confirm that some guy a hundred years ago was right all along. Where's the fun in that?

Mason: I mean the one problem that that would have caused is the public perception of science. Especially publicly funding very expensive science would have been in real crisis if they'd turned the thing on and actually found nothing.

Al-Khalili: Absolutely, and we do really have to work hard - we're seeing this now during the coronavirus pandemic - need to work hard at explaining to wider public and wider society, how science works. That it's okay to make mistakes, or to be wrong, or to make a wrong prediction, because when you gather more evidence or carry out a new experiment, you learn something new and you can revise your picture of the world. To some extent, the Large Hadron Collider actually has been suffering from this point that you make about whether or not it was all worthwhile. For a lot of people, once the Higgs boson was discovered, they said, "Right, okay, you've found it. So you're just going to shut up shop now and go home?" and they say, "Oh no no. The Large Hadron Collider...we want to discover lots of other things. We want to discover if there is evidence of other new types of particles out there." - but that wasn't solved. The Higgs boson was the poster child of the Large Hadron Collider.

Of course what has happened is that we haven't discovered anything since then. Since 2012, eight years later, experiments have been running and we've not discovered any other new particles. There might be the accusation that it's a very, very expensive machine that has been built to confirm something that we thought probably existed all along. But then, you know, unless you're curious and unless you take the plunge and try to do what you can to unravel the secrets of the universe, that defines our humanity. It's there, like Mount Everest, and you have to climb it.

Mason: In many ways it's turned into just a very expensive cycle path. It looks fun when those people are cycling through that thing.

Al-Khalili: Maybe.

Mason: As I read the book and as I listen to you now, it feels like physics is like your email inbox. When I'm trying to empty my email inbox, the only way I can get to Inbox - 0 is to reply to all my emails, but when I reply to all my emails, that leads to more inbound emails. In the same way, the more answers that you get from physics, the more questions you seem to have. Why is that?

Al-Khalili: [laughter] Why even bother? You know, we think we're approaching that ultimate reality. We didn't understand the nature of matter. We discovered that normal matter is made of atoms, then we look inside atoms and realise they're made of atomic nuclei with electrons buzzing around the outside. Then the nucleus is made of protons and neutrons. Protons and neutrons are made of quarks and gluons. Are the quarks and gluons really vibrating strings? In a sense, you think well, are we going to keep going forever? But at the same time, I think there's good reason to believe that there should be an end in sight. We haven't discovered a fifth force, for example. We know there are four fundamental forces in the universe and we haven't discovered a fifth. There may be a fifth one, but we're getting closer to taming and understanding and unifying four forces of nature, so it may be that physics will come to an end one day. It may be that we'll get so close to understanding the ultimate nature of reality that there won't be many more revolutions or paradigm shifts, or big changes in our world view. I think we're a long way off from that, at the moment.

Mason: I mean when looking at the entire history of physics, what, personally, is more dazzling to you? Is it the success of fundamental physics to this day, or is it the questions we still have yet to answer?

Al-Khalili: That's an interesting question. I'm fascinated by the history of science and the history of physics and I love reading the biographies of some of the great heroes of mine - the big names. Niels Bohr, Richard Feynman, Einstein, Paul Dirac and so on. I get a tingle, a sense of following in their footsteps and how they came to understand what they did. For me, there is a romance about the journey that physics has taken thus far. In my day to day life, in my research, I've just spent several hours this afternoon talking to a couple of my PhD students and my collaborator Andrea Rocco, at Surrey, trying to figure out a way of solving certain equations, or trying to figure out a way of modelling a quantum phenomenon. We realise we just don't know which directions to go in. How do you solve that integral? What sort of approximation can we make there? There's an excitement in not knowing. Ultimately, that's what keeps me awake at night.

I swear, the other night, I woke up to go to the bathroom, came back to bed, was lying in bed and I started thinking about this equation that one of my students had sent me. I'm thinking...okay. I've got Greek symbols floating around in my head and calculus in my head, half asleep, and I figured something out! I didn't jump up and scribble it down in my notebook because my wife wouldn't have been pleased about that - putting the bedside light on - but the next morning I thought, oh yeah, I can do that. So for me, that's the wonder of what I do. It's the thing that I want to figure out lying in bed. It's the last thing I think before I go to sleep, and it's the first thing I think about in the morning. Not every day - I'm not that sad - but that excitement of the mysteries that get to be solved.

Mason: Well it's just as well you didn't solve a mystery in that moment, because it would have been a discovery that you'd have to publicly tell everybody you discovered just after taking a really good midnight urination. Ultimately, most people discover things in the bathroom. We can say that you were in the bathroom...similar sort of thing. But ultimately, where does that leave us? What do we know that we don't know? How do you know that we might eventually know what might seem unknowable? I don't know if that made sense.

Al-Khalili: The known knowns, the known unknowns, and the unknown...yeah. We know there are mysteries out there. There are phenomena that we need to somehow explain properly. The nature of dark matter - invisible stuff out there in the universe that's holding galaxies together. We know it's out there, we know it has a gravitational pull, but we don't know what it's made of. We know the universe is expanding evermore rapidly, so we know something called dark energy, but we don't quite understand its nature. We know that just after the Big Bang, matter and antimatter would have been created in equal amounts, but we don't know why there's no antimatter around now. Most of the universe, thankfully, is normal matter. We don't understand how to unify quantum mechanics and relativity.

There are other examples. We don't understand, for example, what is the correct explanation of quantum mechanics. How can a particle be in two places at worse? How can Schroadinger's cat be dead and alive at the same time inside the box? These are things we know that need to be resolved. Of course, we don't know what surprises there might be around the corner; new phenomena to be discovered. Dark energy, when it was discovered back in 1998, was an absolute shocking surprise that no one anticipated. We thought the universe was expanding but the expansion rate was slowing down, that gravity was putting the brakes on. All the matter and energy in the universe was stopping it from expanding so rapidly, slowing it down. We thought maybe one day, it'll re-collapse in on itself in a Big Crunch. No one anticipated there was something that was winning the battle against gravity and making the universe expand ever more quickly. That's part of the excitement: that we really don't know how much we don't know.

Mason: Despite the fact that we don't know some things, we can actually apply what we do know to the creation of new technologies. Our understanding of space and time, for example - that's led to so many technological innovations, hasn't it?

Al-Khalili: Oh, absolutely. What I don't want to give the impression of is that somehow, we're floundering and that we don't understand anything about the nature of the world. We pretty much understand all the phenomena and all the mechanisms, all the stuff that goes on around us in our world. When I talk about what we don't understand, that's at the far edge of existence, and doesn't really impact our daily lives. Einstein's theory of relativity that explained the nature of space and time tells us that gravity slows time down. Time itself runs slower, the stronger the force of gravity. Come on. Some guy with wild hair comes up with this thing. It's great for sci-fi movies but not in the real world. But then, that's how your smartphone works and that's how GPS works. GPS and your phone relies on signals coming from satellites in orbit around the Earth, that triangulate and pinpoint your position. Because those satellites are orbiting the Earth, they're feeling weaker gravity than we are on the surface of the Earth. Their time literally runs at a faster rate on a satellite than it does on Earth. We have to deliberately slow the clocks down on the computers on board the satellites, so that they match the rate of clocks ticking by on Earth in order to get GPS working. There's Einstein's theory of relativity about time slowing down which leads to time travel and all sorts of wonderful explanations, but without it, technology that we take for granted simply wouldn't work. We'd be lost.

Mason: We can go one step further now, because physics isn't just being applied to technologies that are purely based on physics theories. It's being used in interdisciplinary research. We're starting to see physics informing research in biology and things like chemistry. Could you give us some examples of that?

Al-Khalili: Yes. It's always been true that the boundaries between...although we learn physics, chemistry and biology as separate subjects at school, once you get into the cutting edge of research and developing technologies, it's always been true that you have this multidisciplinary approach. What we're seeing in the 21st century is the most exciting areas and developments in technology - whether it's genetic engineering, whether it's robotics and artificial intelligence, whether it's nanotechnology - they require input from lots of different fields.

One area in particular that I'm interested in, in my research is the application of quantum physics in molecular biology. This is this new area called quantum biology which is still speculative, and it's built around the idea that there are certain mechanisms and phenomena inside living cells which seem to only be explainable by appealing to the laws of quantum mechanics. In a very strange way that I think a lot of scientists still find...they're very sceptical about it - and it is speculative - but for me, it's wonderfully exciting to think that maybe the mechanisms of life itself rely on these counterintuitive ideas in the quantum world. Without quantum mechanics, life has had four billion years and during that time, evolution has reached down into the quantum world and plucked out some tricks that allow it to work more efficiently. That's still early days yet, but a very exciting new field.

Mason: So it could eventually be possible that quantum mechanics and quantum theories can explain the emergence of life itself?

Al-Khalili: It's very easy to appeal to quantum mechanics - to say that all mysteries we don't understand, "Well that's quantum mechanics." Quantum mechanics explains consciousness or explains, heaven forbid, nonsense things like homeopathy or whatever. Because quantum mechanics has this mysterious appeal to it, it's tempting to use it to explain other things we don't understand. I wouldn't go so far as to say quantum mechanics might explore the origin of life or the nature of life itself. But you know, who knows? It's exciting to think that quantum mechanics might play a role in an area where we were least expecting it: inside living cells.

Mason: It's so interesting what you say about that because people do get carried away by the idea of quantum. Suddenly, quantum can explain everything and we have things like quantum woo. If I think things then the universe will align itself to give me what I so desire. There's been such a misunderstanding in many ways of physics. You try and deal with some of that in the book by looking at this word, truth. In fact, the word truth features throughout the book and you really look closely at how science deals with this tricky issue of: What is truth? What is consensus? What is dogma? Why do we have to be so careful when we talk about truth?

Al-Khalili: We're seeing the importance of understanding how science works more than ever. When politicians say, "We are following the science. We're appealing to the scientific evidence. Science tells us this.", people really need to understand how science works: The idea of reaching consensus; the idea of coming up with a hypothesis that makes predictions that are repeatable, that can be tested experimentally. It really is very worrying when you see on social media the proliferation of conspiracy theories. People who promote them seem to think they are behaving and thinking scientifically, but they're not. In science, if you're faced with evidence contrary to your hypothesis or your theory, you have to revise your understanding in the light of that new evidence. In so many ways, when people appeal to science in a very loose way to develop whatever theory, or dogma, or ideology they want to promote, they're not following the scientific method properly. Yes, scientists have their own vested interests. I want to get my research grant. If I'm a string theorist, I want to believe that string theory is the correct theory of everything and I want people to give me research money and students so we can carry on doing that. But broadly, the scientific process itself does evolve by consensus. If I come up with an idea or carry out a measurement and discover something, someone else has to confirm it. It has to be reproduced.

There are lots of fail safes built into science but ultimately, I still think there is that single objective reality; that truth out there; the way the world actually is. The scientific method is the most reliable way of getting as close as we possibly can to that truth.

Mason: In this day and age, people seem to have their own truths about the way the world works, and you mention conspiracy theory there. How do we do better? How do we filter what is real science and what is pseudoscience - especially in an age of things like Twitter?

Al-Khalili: It is really hard when there is so much being bombarded left, right and centre by so many YouTube videos and views and opinions that go viral. There's all this confirmation bias and we live in these filter bubbles where we are fed the stuff that we want to believe in, and therefore we believe it. I'm not sure what the answer is. I could glibly say, "Well, not only should we communicate the scientific ideas - we talk about the Big Bang and quantum mechanics - we should also explain how science works." - but I think it's true. I think teaching kids at school the scientific method - what does it mean to have a theory? A scientific theory is not the same as, "I have a theory that aliens visited me last night." A scientific theory has to satisfy certain criteria and strict rules and regulations.

I do think explaining to people how the scientific process works and being open-minded. If you believe something to be true, don't believe it with certainty. Use doubts and self-criticism and think about whether or not that could be wrong. Listen to evidence from an opposing view and see if that makes sense. People think scientists are closed minded. No, no - quite the opposite, in the hope that we wouldn't discover the Higgs boson. We want to hammer and kill our theories. We want to replace them with better ones, if we can. We don't want to maintain the status quo. Be open minded, but not so open minded that your brain falls out - that's the only worry I have.

Mason: It was interesting to see in the book that you said that doubt, in not trusting your senses, and ignoring common sense can sometimes be the things that actually make good physicists, good physicists. In many ways, those sorts of things are key to the progression of science. Is that right?

Al-Khalili: Having doubts, yes. I said at the beginning, one of the reasons that I fell in love with physics was that I saw it as puzzle solving and common sense. The way the world works seems to make sense. It's explicable; it's understandable, and yet there's a danger in assuming that it's just common sense. Very often, if we don't apply the scientific method, we can be led to the wrong conclusions and science stops us from using what we think is common sense in coming to a conclusion about something, or the way something works, or an explanation. Sometimes the scientific method says, "No, what you expected to see, what you thought was logical, actually isn't the way the world is." So having doubts and having the willingness to revise your world view in the light of new evidence is the only way we'll make progress in science. We have to make mistakes, otherwise we'd never change our minds.

Mason: In a funny sort of way, do you think that post-truth is actually the key to the history of science? In other words, if it wasn't for the seekers and the searchers inventing new ideas and suggesting new truths, then perhaps we wouldn't have some of the physics theories that we have today. For example, some claim the existence of parallel universes just to make their science work today. It may be proven to be true and it may be proven to be not true, but we need people using the tools of post-truth to challenge the scientific dogma of today, for science to progress - don't you think?

Al-Khalili: Yes, but science only progresses when those ideas can be tested. It's true that postulating the existence of a multiverse and an infinite number of parallel universes is no different from theology or abstract philosophy, because you could say anything if you can't test it - I can come up with any idea. There's a difference though between some of these highly abstract esoteric ideas in fundamental physics, like string theory, like multiverse theory. There's a difference between them and other post-truth ideologies or woo-woo, as I say. They are built on a foundation of trying to explain the world that we know. Parallel universes do explain stuff. It will be great if it turns out that parallel universes really do exist, because that would explain why our universe is so special. How come all the dials for everything in our universe were tweaked for just the right to allow us humans to exist and have this conversation? Wanting something to be true because it's a neat idea isn't science. Science is only when that neat idea gets tested and verified and it makes predictions that turn out to be better than any other theory can predict.

Mason: So in other words, there's really a difference between scientific theories and scientific opinion?

Al-Khalili: Yes. I mean scientists are humans, so they will have opinions and ideologies and views and dogmas like anyone else. But a scientific theory that has been tested against experiments, against observation, is something that transcends human fallibility and opinion and views and ideologies, because it stands the test of the scientific method.

Mason: Listening to you, Jim, it sounds like I'm listening to a physicist, obviously, by training, but also there's so much in what you say that makes me feel like you have a little bit of a philosopher in you. Do you think there's a relationship between physics and philosophy? Do you think philosophers have added to the world of physics? Do you think philosophers and physicists can become uncomfortable bedfellows? Or are some physicists actually, deep down, secret philosophers?

Al-Khalili: Philosophy and physics, I think, have always been, actually, not too uncomfortable bedfellows. If you think back to some of those heroes of physics that I love reading about, certainly as a student - Einstein and Bohr and Feynman and others - they were steeped in philosophical thinking. They acknowledged the importance of philosophy in helping a science like physics move forward. I don't think science - and physics in particular - can advance without the clarity that's brought to new ideas from philosophers. People often talk about: "Philosophy is there to help ask the right questions and science then attempts to find the answers to those questions." I think that's true, and it frustrates me when colleagues would say, "Philosophy is dead. There's no room for philosophers. We don't need them anymore. Fundamental physics has taken over their role and we can do very well without them." I think we're getting to the point now where there are these mysteries about the universe that we don't understand. I think we do need the help of philosophers to sit down and talk to us and try and maybe give us a different angle. A different way of thinking about solving some of these problems.

Mason: Now we have one of our first questions from YouTube, and it's from Dave Weber who asks, "Will travelling in person beyond this solar system ever be physically possible?"

Al-Khalili: Since he's put the word 'ever' in, then absolutely. It won't be in our lifetime, but there's absolutely no reason why we couldn't imagine the technology. Nothing in the laws of physics would stop us doing it of course - it's just the technology. Having this technology, the propulsion system that'd allow us to travel that system is actually possible and science fiction - the very good science fiction - has really shown how that might be possible. You travel at a significant fraction of the speed of light and Einstein's relativity says that your time will slow down relative to the universe outside. What might, to us left on Earth, seem to be a journey that takes many, many decades, on board a spacecraft travelling at a fraction of the speed of light, it would be a lot shorter. You could actually get one from one side of the universe to the other in half an hour, providing you nudged close to the speed of light. Just don't bother trying to come back again and tell your family all about it, because a lot more time will have gone by on Earth.

Mason: You might accidentally end up behind your daughter's bookcase and that sort of thing might happen. Do you actually think that our physical human bodies will be able to travel to outer space or do you think it might just be our minds? In other words, if we can get information to travel at the speed of light, what we may do is send a robot in advance of us and sit here on planet Earth and control that robot as an avatar version of ourselves on another planet or on another spacecraft. Do you think it's more likely that our minds will travel to space rather than our bodies?

Al-Khalili: I think if we look into the far distant future then that's absolutely very likely, but of course the one thing we can't do is break the laws of physics and send any information faster than the speed of light. Even having that robot reaching Proxima Centauri - the closest star system to us, just four light years away - it takes four years for us to send our instructions through to the robot there. Four years for it to come back again. Whatever technology we develop, we still aren't, as far as we know, able to break that light speed barrier, despite that Star Trek might tell us.

Mason: Oh, if Star Trek was true. We have a question from Lisa on YouTube who asks, "Will an understanding of dark matter expand our understanding of gravity?"

Al-Khalili: I'm not sure that it would. The fact is dark matter behaves, gravitationally, like normal matter. It's stuff. It just happens to be made of particles that don't interact via the electromagnetic force, so that's why it seems invisible to us. The challenge is really not so much of understanding how dark matter behaves gravitationally, but what it's actually made of. But then, you know, with this idea of having doubts and never being certain about things, we don't know if dark matter behaves in the same gravitational way that normal matter does exactly the same way. If so, does it mean we have to revise Einstein's general theory of relativity: the way that matter curves spacetime. Does dark matter do something different? There are ideas that maybe dark matter doesn't even exist at all. That maybe we just have to revise our picture of what gravity is to explain away what we see as dark matter. The evidence for its real existence is too overwhelming at the moment. But yeah, who knows? It might revise our picture of gravity.

Mason: We spoke a little bit about some of the applications of some of the new physics like quantum mechanics. Ben Greenaway asks, "How far do you think we are from a home or personal quantum computer?" Of course, Google has achieved quantum supremacy - whatever that means. In terms of having one of these quantum computers in our homes, how far do you think we might be?

Al-Khalili: Probably closer than we thought we would be 10, 20 years ago. Last year I published my first novel, science fiction thriller, Sunfall, which is set 20 years from now, in 2041. In it, one of the protagonists, a young cyberhacker, uses a quantum computer; a home quantum computer, to hack into some highly encrypted, secret information which kick starts the whole adventure. I do think in maybe 20 years from now, we will have fully working quantum computers. As you say, companies like Google and IBM and others are working very rapidly. Quantum supremacy may not actually mean we've built a proper quantum computer, but it's a big step along the way and we're seeing success happening quite regularly now.

Mason: It seems like everyone wants you to make predictions, but I guess this is the FUTURES podcast. We have another question from YouTube from Suzy, who asks, "From your perspective on the current scene in physics, when do you think the next scientific revolution might arrive?"

Al-Khalili: My hunch...and what do I know? My hunch is that when we talk about wanting the next Einstein or the next Hawking to come along, I think the problem in really revolutionising fundamental physics is getting to be so complicated that it may well be in AI - an AI algorithm that's going to help us do that. A good friend of mine, a guy called Demis Hassabis, who is CEO of DeepMind, probably the world's leading AI research company - I agree with him. He says that maybe we've come as far as we can with our crude monkey brains, and we need an AI to really solve these deep problems. Finding the patterns in the mathematics that are far too complex for humans to see. The next revolution may well be 20, 30 years from now, but it may not be a human that actually takes us forward.

Mason: What you're doing here is such a wonderful example of the public communication of science. Why do you think it's so important that we make this sort of work accessible to as many people as possible? Why is science communication so important to you, Jim?

Al-Khalili: For a number of reasons. One is that I've always, ever since I started communicating science; talking to the public; writing articles; talking to journalists - I mean this goes back over 25 years ago now when I first ventured out of my ivory tower of academia. I'd always felt that I wanted science to be part of popular culture. That we would talk about black holes and dark matter and quarks and whatever, down the pub, in restaurants, among friends in the same way that we talk about music, and sport, and politics. So for it to be just part of the conversation. I think to a large extent, that has happened. People know about the Higgs boson. They know about the discovery of exoplanets and they know about gravitational waves and so on. In the same way that we appreciate art and music, there's no reason why we couldn't appreciate - even though we don't have a deep mathematical understanding - we can't appreciate some of these concepts in science. That's one reason.

Another, of course, is to inspire the next generation. That's always going to be true. We need more scientists and engineers in an increasingly technological world.

The third reason is one we're now seeing unfold today. People are faced and bombarded with conflicting evidence about the coronavirus: about how it's spreading; whether we should wear face masks; whether we should social distance. Do I go back to work? Is it coming down? Is there going to be another spike? There are so many questions we want to know and everyone is told all the time that the decisions governments are making are based on scientific evidence. It's vitally important that people understand how science works. That it is not always about having all the answers to begin with. We have to be honest and transparent and say, "Well, to the best of our understanding, this is what we think is happening. Maybe next week, we'll find some more out, and we'll realise that we weren't quite right." It's not a failure. It's not like, "Sack them all, sack all the scientists. What do they know? They were wrong. They said something last week and they said something different this week. They know nothing." - that's why we have to communicate science and how it works, and the scientific method itself.

Mason: Sometimes, do you think there's actually a danger that comes from increased public interest in science? For example, the Schrodinger cat experiment, originally, was supposed to make people think the whole thing couldn't be correct, but it entered the public consciousness. With things like quantum, we now have quantum woo and, "Our thoughts can affect the universe.", and all of these ideas that get misconstrued because the public thinks they understand something about the science but in actual fact, it's the way in which science is being communicated which is the issue, really.

Al-Khalili: There's certainly a danger that people know a little bit of science and they assume that that means that they are experts. My view is as valid as yours. I've regularly get very sweet emails and Tweets from people saying, "I know nothing about science. I'm not educated in physics at all, however I've figured out what dark matter and dark energy are. It explains the Higgs boson and it explains this and that."and you think: yes, but I've spent my whole life thinking, working hard trying to understand this stuff, and you just say, "I've got no background but I've just come up with this idea." I think it is dangerous for people to know a little bit based on popular accounts of science and then to just completely get the wrong end of the stick. On the other hand, it's great that people are curious. It's great that people are thinking about this stuff. When the LHC was first switched on, people were worried that it was going to create a black hole that was going to swallow up the whole Earth. Of course that was nonsense, but it got people talking about particle physics and quarks and so on. Part of the conversation is fine, providing it doesn't infect and create conspiracy theories and people going around burning 5G masks and saying, "5G is creating viruses." There is some danger in people having a little bit of scientific knowledge and extrapolating it into crazyville.

Mason: We have another question from YouTube, this time from Ingrid who asks, "Are there parallel or other ways to explain phenomena of reality besides mathematical language?" for example, analogies or metaphors, or diagrams or drawings. Could these actually be cleaner and better than mathematical language in many ways, or is maths always going to be the paragon through which we describe physics?

Al-Khalili: Ultimately, the universe speaks the language of mathematics, so ultimately that is the way we have to understand reality. But in other ways, I think she's right. Metaphors and imagery can be very powerful. A lovely example is the great American physicist, Richard Feynman, who developed what are called Feynman diagrams, which are ways of explaining how subatomic particles interact and create new particles, and e = mc squared. It wasn't rigorous mathematically, but it was a very powerful way that gave new insights. There are lots of ways that allow us to maybe understand the mathematics better or give us a picture of reality that allows us to move forward. All of those tools should be available to us.

Mason: We have another question from Andre who asks, "What do you think the confirmation of Bell's theorem through experiments tell us about the nature of the universe?"

Al-Khalili: John Bell was an Irish physicist who essentially helped bring to a head a long running debate in physics. Very often in popular accounts, it boils down to an argument between the two biggest names in physics - certainly in the first half of the 20th century - Albert Einstein and Niehls Bohr, the Danish father of quantum mechanics. Each of them had a different view of what quantum mechanics meant, and what John Bell did was come up with a theory that said, "You can't both be right. If this condition is satisfied, he's right. If this condition is satisfied, he's right." Bell's theory, also known as Bell's inequality, was then tested experimentally. It gave us a way of really probing the mystery of the quantum world. It's not the end of the story, through. It hasn't resolved things yet. We still argue about whether Einstein was right or whether Bohr was right. What is the ultimately correct description of quantum mechanics? We still don't know. That's one of the outstanding mysteries. It's probably the thing that I will most want to have resolved in my lifetime. John Bell is certainly a big hero of mine - I've met him a couple of times. If he says something, I sit up and listen because I think he's one of the great, unsung geniuses of physics.

Mason: You mention, briefly, your work in science fiction. Science fiction is so important for how we perceive the world of science. I guess this is more of a personal question that I have for you, but where have you seen physics principles best represented in science fiction? Also, where have you seen some of the worst case examples of physics represented in science fiction?

Al-Khalili: I give a regular schools talk to teenagers on time travel and separating science fact from science fiction. When it comes to good science fiction with time travel, that's a really nice example. Probably the best movies on time travel are Interstellar - despite Matthew McConaughey floating behind the bookcase in his daughter's bedroom bit towards the end, which gets a bit trippy at the end of the film - but Interstellar, however weird or wacky you think it is, is built on solid physics. There's nothing in Interstellar that violates the laws of physics, and that's thanks to Kip Thorne, one of the Nobel prize winning, American physicists who was one of the producers on the film. He made sure the science was right.

At the other end of the scale, I don't know. Hot Tub Time Machine? A pretty awful example of time travel. Yes. There's a whole range. There's science fiction that is really well made in movies, or well told - particularly if scientists are involved. The better science fiction is probably from people like Arthur C. Clarke or Isaac Asimov. Why? Because they were scientists themselves. The worst science fiction is the fantasy which is not really meant to follow the rigours of science - but that's fun in its own way. I love watching the Marvel movies. I don't storm out of the cinema because Spiderman's broken the laws of physics. I just enjoy it.

Mason: Another part of that question is, what made you and inspired you to write science fiction? Why did you suddenly realise: You know what? Instead of writing these non-fiction tomes explaining science, perhaps the best way to do it is through the use of science fiction.

Al-Khalili: I'll be honest with you, it wasn't altruistic in that sense at all. I'd just published a book and it was at the launch party - actually, a book on quantum biology, this new area that I talked about earlier - the publishers wanted to know what my next book was. I said, "Well, I've got everything off my chest that I wanted to write about. I've written about relativity, quantum mechanics, and so on. Maybe I'll write a novel." I just said it as a joke and they said, "Ooh, really? What would it be about?"..."Probably science fiction. I enjoy sci-fi, Michael Crichton. It'll probably be a thriller because I love Stephen King books." Before I knew it, they'd set me up with a science fiction commissioning editor and I had to come up with an idea. Of course, once that seed was planted in my head: Jim, maybe you should write a novel - that was it. That was what I was thinking about last thing at night, and first thing in the morning. It was a steep learning curve, but an absolutely fantastic experience.

Mason: How does the process change from writing something like the book that we have here to something that's a science fiction book? Does it change the way you have to write? Does it change the way you have to think?

Al-Khalili: Very much so. It was very liberating in a way, but also I know how to write non-fiction. I know how to explain - that's what I spend half my life doing: I explain. In fiction, I have to invent a whole universe. I have to invent a world and invent people who didn't exist before my brain thought them up, and suddenly they have to be people that you can believe in. They have to be three dimensional and have personalities. I couldn't come home from work or be in my office and think, Ah I've got an hour before my next meeting, I might get another chapter done. I had to shut myself away - actually in this study, here where I'm recording this evening. I'd block off days on end - I wouldn't stay in the study for days on end - but I'd block off days on end and I wouldn't check email, I wouldn't deal with any other work. I'd just immerse myself in building this imaginary world. It was very, very different from writing non-fiction. Apart from all of the creative writing techniques that you have to learn: Show don't tell; mind your point of view; all the stuff that hadn't occurred to me.

I remember starting one paragraph in my novel with 'nevertheless', and my editor came back to me and she scratched it out and said, "Don't use the word 'nevertheless' in any novel you ever write. That word is barred from fiction." Ah, okay. No one told me that.

Mason: I was surprised by so much in the book and you're so matter of fact about the way in which physics has evolved and changed throughout history. I was personally surprised, but it made me wonder: Is there anything that still surprises Jim? It feels like he knows it all, so perhaps there's no new surprises for you. Is there anything recently that's made you go, "Oh wow! I didn't even think about that."?

Al-Khalili: Yes, I think it happens regularly. That's what makes physics research so exciting. I'm constantly appreciating how little I know. I think when you're doing research - and particularly when you move into a field, maybe, that you haven't worked in before, as I've been doing for the last two or three years - an area called open quantum systems - the nature of how a quantum object interacts with its surroundings. Concepts that are bandied about now in popular science: decoherence, quantum entanglement. You realise there are people who have been working in this field for years and years and years and they know so much more than you, that I'm constantly surprised when I learn something new and think, ah, I really have to remember that. Of course, now I'm getting to the age where I don't remember stuff, so I read it again a month later and I'm surprised all over again, because I'd forgotten it from the first time.

Mason: We have one last question, I guess, from YouTube, which is: "Do you think that there's a limitation to what we can understand because of our human consciousness?" In other words, do you think there's some fundamental limit to what we can understand with mathematics and metaphors, purely because we have this wetware human brain?

Al-Khalili: It may be the case that our brains are not complex enough to unravel the deepest level of reality; the truth of objective reality - which is why I said it'll maybe take an AI to help us achieve that. You know, we've come this far and we haven't reached any limit yet. Our brains are three dimensional, and yet we can imagine four, five, an infinite number of dimensions - because we have tricks, and because we have mathematics. Developing mathematical tools allows us to go beyond the confines of the images that we can create in our brains. We haven't reached that limit yet. That's not to say that however long the journey is to uncover the deepest secrets of the universe, our brains are capable of doing it. It may be that we will start to reach a stumbling block where we think: No, that's it. I can't get my head around this any more, this is as far as we can understand. But, we haven't got there yet, so I remain optimistic.

Mason: I mean, you've teased it a couple of times now but you say in the book, many times, that physics is waiting for the next Einstein to come along. Perhaps the next Einstein will be an artificial intelligence. Perhaps an AI-stein - if that makes sense. Suzy goes one step further and says, "To understand that AI, will we have to actually augment not just our understanding of physics, but augment ourselves?" How will we be able to realise if an AI made some revolutionary scientific discovery if again, we have this limitation of our own consciousness and our own understanding?

Al-Khalili: I think in that case, we're going to have to rely on the AI to explain to us - as we would explain to a toddler - we are not going to be able to appreciate what the AI is doing or how the AI has come to the conclusions it has. We're already seeing this. Famously, these AI algorithms developed by DeepMind like AlphaGo and AlphaZero. These are algorithms that learn how to play chess or the Chinese game of Go, just by being given the rules of the game. Then, they play against themselves a thousand times and they can beat any human on the planet. How they do it is almost a mystery, because it's gone beyond what we can figure out. That's the whole point of these ideas of machine learning; that it's learning itself. We're not programming the computer and saying, "Right, if this, do that. I'm giving you the instructions, therefore I know, as the coder, how you're going to behave." True AI, when it comes, is going to be soaring off, solving problems without us ever understanding how it does it. It's going to have to be quite gentle in explaining in simple language to us mere mortals, exactly how it's done what it does.

Mason: I love the idea that we have to to have to train our AI to become good science communicators before they're good scientists. That thing about scientific discovery and curiosity: on reading your work and listening to you, it feels like that is really at the heart of what it means to be human. Do you think there's a relationship between our desire for discovery and our desire to know these massive questions? Do you think that just goes back to the very heart of what it means to be human, our own humanity?

Al-Khalili: Absolutely. No, absolutely. I think that's what defines our...we talk about what it is to be human, to know our place in the universe. There are traits that we have to do with empathy and compassion and kindness, that I think are wonderful ways that we behave towards each other, but also we've always had this curiosity about the world. It's built into our DNA. It was probably even an evolutionary trait. You want to know what's behind the next hill. You want to know if there's a sabre-tooth tiger hiding behind that tree. Trying to understand the heavens and therefore the seasons to make our lives more comfortable. We've always wanted to know our place in the universe so I think we'll never stop asking those questions. We are born curious. All children are, by their nature, curious. Why is this? Why is that? But why? But why? But why? Most people grow up and stop asking, "Why?" A scientist is just a child who's never grown up and has never stopped being curious.

Mason: So on that note, Jim Al-Khalili, thank you for joining us today.

Al-Khalili: My pleasure. It's been fantastic.

Mason: Thank you to Jim for sharing his insights into the fascinating field of theoretical physics.

You can find out more by purchasing Jim's new book, 'The World According to Physics' - available now.

Don't forget, you can watch the full, unedited video of this conversation at FUTURES Podcast dot net, where you can also find out about all of our upcoming live stream events.

If you like what you've heard, then you can subscribe for our latest episode. Or follow us on Twitter, Facebook, or Instagram: @FUTURESPodcast.

More episodes, transcripts and show notes can be found at FUTURES Podcast dot net.

Thank you for listening to the FUTURES Podcast.