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This is an audio transcript of the Tech Tonic podcast: The quantum revolution: The way the world is

Madhumita Murgia By this point in our series on quantum technology, it should be pretty clear that when you travel into the realm of the very, very, very small, the subatomic level, things get pretty weird. Our common sense understanding of reality becomes warped and breaks down. Things are not as they seem, but weve kept one of the weirdest examples of quantum technology, the most mind-bending and confounding one to last. In this, our final episode in the series. So here goes.

It starts in Austria, early 2000s. Picture a bunch of seven or eight scientists at work in the dark on the shores of Viennas famous river.

Anton Zeilinger We were standing there on the banks of the river Danube during the night, and during the experiment that was kind of really fun, really nice.

Madhumita Murgia Thats the Austrian physicist, Anton Zeilinger, and I wanted to speak to him about this experiment because its really fascinating. Its an experiment that helped him win last years Nobel Prize in physics. An experiment in teleportation.

Anton Zeilinger You have a photon that you want to teleport, so you prepare it in a quantum state, and then you have a (inaudible) entangled state where one of them is kept by you, the sender, and the other one is sent across the river.

Madhumita Murgia Zeilinger was using the phenomenon known as quantum entanglement to transmit information from a particle on one side of the river to another particle on the other side of the river.

Anton Zeilinger The idea is that you transfer a quantum state of one photon or any other particle for that matter, or in principle, any distance using entanglement because the original loses its properties and the teleported one is completely identical with the original.

Madhumita Murgia When two quantum particles are entangled, they create a kind of spooky communication bridge between them. And using this bridge, Zeilinger was able to take the information about one particle, send it across the bridge, and construct a new particle carrying that information on the other side of the river. He was effectively teleporting the particle across the Danube, which makes it sound pretty dramatic, right? But this is actually one of many experiments that have demonstrated what is known as quantum teleportation. And you can do it over really large distances.

Anton Zeilinger The farthest we have teleported was between two islands, La Palma and Tenerife. Its a distance of 150 kilometres. Our Chinese friends have teleported quantum state from a ground station up to a satellite. So this is certainly farther than what we did.

Madhumita Murgia Bouncing information around between quantum particles like this is a perfect example of how our understanding of quantum physics is helping us develop new quantum technology. Because this kind of quantum teleportation is the basis for what could become a quantum internet.

Anton Zeilinger You could actually teleport the output of one quantum computer to the input of another quantum computer. And that is much better than just sending the normal information in bits and so on. Because you are not restricted by zero and one.

Madhumita Murgia A quantum internet could transmit information in quantum states rather than the zeroes and ones of classical computers. That could connect quantum computers together to create an ultra-secure, ultra-powerful communications system. But Zeilinger says the potential for this quantum teleportation doesnt stop at building a new internet. Things could get even stranger.

Do you ever see this happening on a larger scale, larger-scale object?

Anton Zeilinger For a large object, I suppose for molecules, et cetera, this can be done. If you ask about really big objects, amoeba for example or a virus, then this is a big challenge and I think it will happen someday. But nobody knows when.

Madhumita Murgia What Zeilinger is saying here that were on track to teleporting actual living organisms. Its kind of incredible. But no matter how counterintuitive all of this sounds, quantum technology like this is possible. Because at the fundamental level, this is how the universe really works.

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This is Tech Tonic from the Financial Times. Im Madhumita Murgia.

John Thornhill And Im John Thornhill. This season of the podcast is about the quantum revolution. Were asking if technology powered by quantum physics is going to change the world. Throughout this series, weve been looking at how quantum technology could have real-world applications, how quantum computers could help us do things we used to think were impossible and upend whole industries.

Madhumita Murgia But inevitably, weve also been thinking about the weirdness of quantum technology, how its based on a physics that no one fully understands and what it tells us about the world around us and the nature of reality.

Quantum technology holds a lot of promise. There are plans for quantum computers, quantum sensors and a quantum communications network. But some people think we should spend a bit less time thinking about the success of quantum technologies and a bit more time thinking about what quantum tech tells us about the true nature of our world. So I wanted to talk to someone whos asking the really tough questions, the ones that involve bold thinking and radical philosophical reflections.

David Deutsch No one should have to eat breakfast.

Madhumita Murgia I agree.

David Deutsch Sorry, Im currently eating biscuit. Im not speaking clearly now.

Madhumita Murgia Thats David Deutsch. Hes a professor at Oxford university, and hes a bit of a celebrity in this world of quantum research, known for his unusual work habits. I was reading the New Yorker profile of you, and it said that you eat your lunch at 8pm. So do you have a really long gap in the day?

David Deutsch Oh, well, unfortunately that was quite a while ago. Ive taken to getting up and going to bed at normal times. Much to my regret. (chuckles)

Madhumita Murgia Deutsch is regarded as the founding father of quantum computing. It started like this: in the 1980s, Deutsch decided to go over a famous paper written in 1936 by the English mathematician Alan Turing. In it, Turing outlined his idea of a universal machine, a hypothetical machine that could solve any mathematical problem. No one had built one. This was 1936, after all. But in that paper, Turing effectively invented the idea of the modern computer. Reading it again 50 years later, Deutsch pointed out that Turing had been working with classical physics without considering the new field of quantum physics. Deutsch is pretty nonchalant about his attempt to radically rethink computing as we know it.

David Deutsch I thought I would just update Turings paper, his 1936 paper, to take account of real physics rather than this imaginary restricted physics that he actually used. And more or less, the first thing I discovered was that a computer that operated on quantum physics would have a wider range of computations available to it.

Madhumita Murgia So Deutsch came up with the idea of the quantum computer, a hypothetical computer that operated according to the laws of quantum physics. And as a result, could do computations far beyond the capacities of classical computers. The paper that Deutsch wrote became a landmark. It opened up a completely new field and has inspired a generation of researchers in all sorts of disciplines to try and imagine what a quantum computer might be able to accomplish. And its set off this race to build a quantum computer among tech companies. But these days, Deutsch isnt too interested in the various efforts under way to build quantum computers or even what applications they might have for the world. What hes interested in today is what quantum computers tell us about the nature of the universe. And he says, they tell us something really strange. The thing about quantum computers is they seem to be able to perform calculations that according to the normal rules of computing, should be impossible.

David Deutsch With certain computational tasks, there exists a minimum number of Turing-type computational steps that would be required to get the answer, and this minimum number of steps could be enormous. It could be much, much bigger, say, than the number of atoms in the universe. And if you somehow made all the atoms in the universe into a computer, it wouldnt be able to scratch the surface of the number of parallel computations that even quite a small quantum computer could achieve.

Madhumita Murgia Take a really hard computational task, like factoring very large numbers. Thats the mathematical problem that underpins a lot of internet encryption. Its so hard that it would take a classical computer, even one as big as the whole universe, billions of years to do. But a quantum computer could, in theory, do it in minutes. And Deutsch says that theres no way to explain how thats possible within the limits of our known universe.

David Deutsch Supposing it works, supposing that you build a quantum computer and run that program and you get the answer and you know that nothing in the universe we see around us could possibly have discovered that, that means that theres more to reality, exponentially more to reality than just the states of the world that we see around us.

Madhumita Murgia Deutschs explanation is that quantum computers must be somehow accessing other realities in order to get the job done. Specifically, he argues, its accessing multiple parallel realities. The universe, he says, is in fact made up of multiple worlds, all existing simultaneously. This is known as the many-worlds interpretation. Its a bit out there. And its not just Deutchs explanation for how quantum computers work. Its also his explanation of how the world works.

David Deutsch Every physical object, not just quantum computers, not just electrons, but everything already exists in a range of universes. Most of the time, they dont affect each other. At least they dont affect each other in noticeable ways.

Madhumita Murgia The many-worlds interpretation of quantum mechanics was first proposed in the 1950s. It paints a picture of multiple versions of reality being created by random events. So if you flip a coin, there are two new worlds created, one where the coin lands heads and a completely separate world where the coin lands tails. The people who support the many-worlds interpretation say that its a logical conclusion of quantum mechanics, and it not only explains how quantum computers can do impossible calculations, but it also helps explain some of the big mysteries of the quantum world. For example, it explains how we never see things in the state of superposition. Take the hypothetical experiment of Schrdingers cat, which we illustrated in episode three of the series. Theres a cat in a box that could be either alive or dead. (cat meowing) The many-worlds interpretation says that when you open the box to look, you create two separate realities that coexist. One where you see the cat alive and another way you see the cat dead. If you think thats a bit off the wall, youre not alone. Plenty of other physicists do, too. But Deutsch says the many-worlds theory has support, particularly among people working on quantum computers.

David Deutsch I should point out that a substantial minority of physicists find no problem with it, and this is especially true in certain fields of physics. Quantum computation is one of them. Because if you want to explain how a quantum computer works, or if you want to design a new algorithm or a new way of using a quantum computer, you have to engage in hideous circumlocutions if you want to avoid talking about multiple universes and in fact, you cant avoid it.

Madhumita Murgia He says that fundamentally, if you want to understand whats really going on inside a quantum computer, and by extension whats really going on in the quantum world, the many-worlds interpretation gives you the answer. But not everyone is convinced.

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David Deutsch is legendary in the world of quantum computing, and he is by no means alone in subscribing to the many-worlds interpretation of quantum mechanics. But its also true that the majority of people in physics arent on board with it. And John, you spoke to one of them?

John Thornhill Yes. Hes a physicist called Carlo Rovelli.

Carlo Rovelli Everything is quantum. In this cap I have in my hands, which looks so solid and well-defined, is actually a wavy thing that is constantly disappearing and appearing.

John Thornhill If anyone has popularised the big philosophical ideas behind quantum physics, its Carlo Rovelli. Hes written several bestselling books about the topic, and in the past he has called the many-worlds interpretation of quantum mechanics crazy. But he concedes that in the world of quantum mechanics, everything is a bit crazy.

Carlo Rovelli I dont take crazy in a negative connotation. I think that any attempt to make sense of quantum mechanics in that there is more than one, maybe the two or three taken more seriously by thinkers today, theyre all crazy. Whatever you do is crazy with quantum mechanics. Crazy because it challenges the usual understanding of the world in a very radical way.

John Thornhill Rovelli says you might not have to go as far as multiple realities to explain quantum mechanics, but the science does tell us that the world is very different to the one we experience in our everyday lives. And he says this was apparent from the early days of quantum mechanics nearly 100 years ago. Rovelli recently wrote a book called Helgoland. Its about Werner Heisenberg, a physicist who did some of the foundational work of quantum physics in the 1920s while he was living on a small, barren island called Helgoland out in the sea off the north coast of Germany.

Carlo Rovelli Werner Heisenberg was a 23-year-old young German physicist, a very young scientist. He was in this little island because he was suffering from hay fever. So for medical reasons, there is no pollen there. There are no trees, wind from the sea. So its perfect for somebody suffering allergies. And he wrote a paper. And this paper can be seen as the crucial stone on which quantum mechanics was built.

John Thornhill At the time, it had become clear to physicists like Heisenberg that Newtons classical physics didnt work when it came to the world on the scale of atoms. Some new physics was needed.

Carlo Rovelli People were trying new rules, new forces, new equations of motion, and nothing was working until this kid went to this island and alone there suffering hay fever came out with an idea.

John Thornhill Working deep into the nights on this barren rock in the North Sea, Heisenberg figured out that the only way to predict how atoms behaved was to change his approach. Instead of attempting to write equations describing what atoms did. He wrote equations that described what he could observe.

Carlo Rovelli Instead of writing how this electron move, Heisenberg said, forget what happens there. Lets only describe the way the atom affects me. What I see of the atom, the observable part of the atom. Remarkably, that was sufficient to write the mathematics is that suddenly everything went in place and he was getting the correct predictions of the behaviour of the atom.

John Thornhill These equations helped lay the foundations of quantum physics and totally changed the way we understand the physical world. But the quantum mechanical theories that came out of Heisenbergs work suggest something quite odd. It seems like particles only really existed when being observed. When they arent being observed, they just arent there until they pop back into existence when you next look at them. Particles or anything else for that matter, dont really exist in their own right.

Carlo Rovelli If I want to think of a particle like an electron, I cannot say the electron is there. Its a little stone in a position. Thats wrong. Its there with respect to me. But if its maybe somewhere else with respect to something else, its a relational object, its something that has properties only, as referring to something else.

John Thornhill And Rovelli says, this is true of everything in the world. Nothing exists on its own. And reality isnt really made up of things, but the relationships between things.

Carlo Rovelli So quantum mechanics tell us that we make a mistake if we think that a piece of nature or a particle or any object in nature, or a galaxy or a stone have a position, have properties by themselves. They dont have properties by themselves because when theyre not affecting something else, they dont have properties. So properties are ways in which one piece of nature affects other piece of nature, which means that we cannot describe nature in terms of isolated objects. Its properties, we have to describe nature by bringing the various pieces together and always something in relation to something else.

John Thornhill So what it suggests is something like there is no objective reality. The world out there isnt made of objects that hang around with independent physical attributes or properties. The world isnt made up of things at all. Its made up of relations between things. Is this more or less crazy than the idea that the universe is made of many worlds? Perhaps its a matter of taste. Theres no agreement among physicists.

Madhumita Murgia You might be asking why we even need to think about these things. Why we should spend our time worrying about the nature of reality. After all, whether or not were in some kind of multiverse, or whether the world is made up of objects or relationships between objects, none of it really changes our experience of everyday life. But if you really want to understand how quantum technology works and why it works, these are the questions you need to ask. Heres David Deutsch again, a pioneer of quantum computing.

David Deutsch Some people say that we cant and shouldnt try to understand. We need only predict. You simply apply the equations of quantum mechanics. Turn the handle. Dont ask what happens inside the computer. Just ask what the outcome is. But I think for most people and most people who work on this, that is unsatisfactory because they want to understand what to do to make the quantum computer do new things that we havent thought of before.

Madhumita Murgia For Deutsch, answering the big questions is important, and it could help us build better technology. What I find so interesting is that the recent advances in quantum technology are, in turn, shining a light on these fundamental questions of reality. Anton Zeilinger, the Nobel Prize-winning physicist you heard from at the beginning of the show, is pushing the envelope of quantum technology. But for him, the technology itself is somewhat beside the point.

Anton Zeilinger I am mostly excited by the fundamental questions. What does all this tell us about the nature of the universe? And what does it tell us about our role in the universe? I hope some young chip finds out what is really going on in quantum mechanics. What is the basic fundamental reason why we do have this theory, which is beautiful, extremely beautiful mathematically, extremely precise, but in a way, doesnt make sense. And I am sure there is a fundamental explanation, and that will be found someday, and I hope within my lifetime.

Madhumita Murgia In the series, weve been asking if and when quantum technology is going to change the world. Quantum computers could end up being revolutionary, ushering in a new quantum age where extraordinary computing power lets us do things that just werent possible before. But in the meantime, what makes this technology exciting is that it explains the nature of the universe in a way that nothing else can. Quantum computers often seem radical and out of this world, but the world is a quantum world, and quantum computers are just reflections of it.

John Thornhill Youve been listening to Tech Tonic from the Financial Times. This is the last episode in our season on quantum technology. You can listen to the previous episodes wherever you get your podcasts and make sure you subscribe for the next season due out in the summer. Tech Tonic was presented by me, John Thornhill.

Madhumita Murgia And me, Madhumita Murgia. Our senior producer is Edwin Lane, and our producer is Josh Gabert-Doyon. Our executive producer is Manuela Saragosa. Sound design by Samantha Giovinco and Breen Turner. Original music by Metaphor Music. The FTs global head of audio is Cheryl Brumley.

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The quantum revolution: The way the world is - Financial Times