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Welcome to In-Orbit, the fortnightly podcast exploring how technology from space is empowering a better world.
[00:00:00] Dallas Campbell: Ahoy and welcome to Outer Orbit. In these short bonus episodes we're going to be continuing the conversation from our main episodes, but focusing in on a particular topic or a point of view. In today's episode Daniel Oi, who's a reader at the Department of Physics at the University of Strathclyde, is giving us a crash course in quantum physics, from interpreting quantum theory to the possibility of a multiverse. Fasten your seatbelts.
One of the problems with doing podcasts with interesting people is you go down these rabbit holes of really interesting conversations about all different things, which are slightly off topic. Today's a really good example, I'm with Daniel Oi from the University of Strathclyde. We were talking about quantum physics and computers and sort of applications in space thereof and I just thought, well, why don't we just take a little moment, just you and I, just gently, you can tell us a little bit about what quantum mechanics, quantum physics is the uninitiated, one because it's those subjects everyone's like, Oh, yes, I don't understand. Well, there's the old joke at the Richard Feynman joke of if you think you understand quantum mechanics, you don't understand quantum mechanics. Do you understand quantum mechanics I suppose is my question.
[00:01:23] Daniel Oi: I think there are two parts to understanding quantum mechanics. One is you know, can we do the calculations and actually get the right predictions to experiments? And yes, we do understand quantum mechanics, if that is what we mean. Do we understand it in terms of the philosophical implications and what it actually means? I don't think anyone has the right idea.
[00:01:44] Dallas Campbell: Okay, so let's just, let's pause there. Normal physics, the everyday physics, I drop my phone and gravity pulls it down the Earth you know, the kind of, the Newtonian physics, the physics of Isaac Newton, I suppose, classical physics, is that what we call it?
[00:01:57] Daniel Oi: Yes. Classical physics.
[00:01:58] Dallas Campbell: We had physics summed up and then suddenly in the 20th century, someone, some people thought, hang on, it goes a bit deeper than this.
[00:02:05] Daniel Oi: Yes.
[00:02:06] Dallas Campbell: We're talking about the physics of the very small, so not how everyday objects behave, but the particles that make up everyday objects, I suppose, atoms and subatomic particles, and they tend to behave in slightly odd, magical ways.
[00:02:21] Daniel Oi: Yeah, well, that was how it was first discovered when, we couldn't understand radiation, how, heat, blackbody radiation, how hot things radiate and the classical physics of the day would predict that objects would basically glow xinfinitely hot. There'd be so much energy radiated out of, you know, classical objects at any finite temperature and this led Planck to discover that, in fact, electromagnetic radiation is quantized.
[00:02:49] Dallas Campbell: This is Max Planck.
[00:02:50] Daniel Oi: This. Is Max Planck and you know, that was, you know, the very dawn of the 20th century and then Einstein actually, a couple of years later explained the behavior of how light interacts with atoms and he came up with the photoelectric effect, which actually won him the Nobel Prize, not special relativity. So it's amazing that Einstein wasn't just the father of relativity, but also was one of the originators of quantum theory and it really began with the study of these small objects or how matter and energy behave at the small scales. But quantum mechanics, as far as we understand it at the moment, it is a universal theory in that underlies the behavior of reality at the very fundamental level. But we don't understand why we don't see quantum effects at the everyday scale.
[00:03:43] Dallas Campbell: That's my question. Is there a point where, you know, when we talk about quantum theory, we talk about atoms being in the same place at once and all this kind of crazy mixed up Alice in Wonderland world, is there a point where it suddenly goes and stops being that, and it's like, Oh, back to normal now, back to Isaac Newton. Is there a kind of like a line?
[00:04:00] Daniel Oi: Well, we wish we could draw a very clear line where that transition happens. But experiments have been very you know, industrious over the years, trying to bring that line to ever larger scales. People once thought that, you know, maybe that, you know, once you got above a certain size of particle, that it couldn't behave in a quantum way, but at the moment we've been able to get large biomolecules, you know, hundreds of thousands of atoms to behave in a quantum way. There have been attempts to try to get living things like, well, arguably virus to behave in a quantum way.
[00:04:40] Dallas Campbell: Okay, when you say quantum way, give me an example of quantum way, of like quantum weirdness. What are we talking? So I mentioned atoms being at two places at once, that sounds ridiculous and how can something be in two places at once?
[00:04:54] Daniel Oi: You know, we all heard of Schrodinger's cat. Schrodinger's cat, which is simultaneously dead and alive and so it's this idea that something can be simultaneously in two contradictory states of being at once and a particle being in two places at once is in a sense like a Schrodinger's cat. Though Schrodinger was trying to make the point that surely it's ridiculous to think of large objects behaving in this quantum way.
[00:05:17] Dallas Campbell: The cat's clearly dead. Even if you're not looking at the cat, the poison is there and the cats, isn't it? It's okay. This is the bit that does my head in. It's this idea of like, somehow, if I look at the cat, it's suddenly, or if I look at the particle, it's a particle rather than a wave. Like, how does the particle know I'm looking at it? Or how does the cat know, this is what I don't like...
[00:05:39] Daniel Oi: That is one of the fundamental questions in quantum theory. What does it constitute to look at something or to measure something? So the measurement paradoxes, you know, as some people call it in quantum theory is what really constitutes, you know, something actually measuring the quantum wave function and then some people would call that a collapse of the wave function but in the theory itself, there's nothing mathematically to really define that clearly, what that means.
[00:06:09] Dallas Campbell: So it's a maths problem rather than an actual real word. So, for example, you talked about wave functions. I'm very old. I did my maths O level in I can't remember when, 1988, okay, and I never got the result. It's in an envelope and I've never opened it. If I open the envelope and look at my maths result, I'll either have a maths O level or not have a maths O level. So by opening the envelope, I'm collapsing the wave function, is that right? So is my O level in a quantum state at the moment where I both have and don't have a maths O level?
[00:06:42] Daniel Oi: So...
[00:06:42] Dallas Campbell: Or is that being...
[00:06:43] Daniel Oi: I mean,
[00:06:43] Dallas Campbell: I know that's ridiculous.
[00:06:45] Daniel Oi: I mean, that's what some people try to interpret this collapse, or the wave function to be and that was a position that Einstein had. Einstein had this idea that the wave function really wasn't a true description of reality, but there was an actually underlying, more complete description of reality and he came up with his famous, what's called the EPR paradox to try to, you know, try to prove that quantum mechanics was incomplete.
[00:07:12] Dallas Campbell: What was the EPR paradox?
[00:07:13] Daniel Oi: So it's named after Einstein, Podolsky and Rosen, which were the three authors on this paper and it's really about saying that, you know, if we've got two entangled particles, we know that entangled particles, in a sense, the fate of one particle is linked with the fate of the other. So if you sort of discover and measure one particle, then the other particle could be very far apart and in a sense, you know, one may think that instantaneously the properties of one particle instantly defined by the measurement of the other particle and in fact, you know, the 2022 Nobel Prize in physics was given to people who actually showed that Einstein's idea of local realism was violated. That quantum physics and reality does not obey this idea that Einstein had, that universe is both local, both in think in the sense that things can't travel, the fast and speed of light, as well as being real, that things actually have properties without you actually looking at them.
[00:08:11] Dallas Campbell: Crikey! Okay, I'm going to ask you some questions because I'm getting lost. Is there a separate universe for every possible thing? This is, because that seems to me what you guys are saying, and that's ridiculous.
[00:08:25] Daniel Oi: That's one interpretation, right? So if you believe in the no collapse model, right? That, in fact, there's no actual collapse of the wave function. That, you know, measurement really is just discovering which branch of the universe you are living in.
[00:08:39] Dallas Campbell: There's a universe where I have an O Level and there's a universe where I don't have an O level.
[00:08:42] Daniel Oi: Well, you know, it's...
[00:08:44] Dallas Campbell: Seems like an awful waste of universes. I mean...
[00:08:48] Daniel Oi: You know, some people would say that, you know, that is actually more elegant because we don't invoke this mysterious collapse process, which we haven't yet been able to define in a very clean, unambiguous way. There are other problems with the multiverse or interpretation, or the many worlds interpretation and people are still arguing over, you know, how do we interpret quantum theory?
[00:09:11] Dallas Campbell: So the quantum world, the world of the very small, as talked about by, you mentioned Max Planck, Heisenberg and who's the other one?
[00:09:21] Daniel Oi: Schrodinger.
[00:09:21] Dallas Campbell: And etc, and then there's the sort of physics of the sort of general relativity, which is the sort of physics of the very big galaxies and planets and iPhones and that kind of thing. In terms of what you do as a physicist and the applications of space, what is our knowledge of quantum mechanics going to give us that's good? I suppose. Sorry to phrase it badly, but why are we so excited about things like, oh quantum
computers and quantum keys and...
[00:09:49] Daniel Oi: Well, so, one of the original killer applications of quantum computers was to factorise large composite numbers into their prime factors and this just happens to be a problem which allows you to break RSA, which is the encryption method, which underlies a lot of the, you know, modern day communications, including the internet.
[00:10:10] Dallas Campbell: So basically hacking.
[00:10:11] Daniel Oi: Hacking things, yes, as well as other public key crypto systems, which are being used at the moment. So, this obviously had quite a lot of interest from certain three letter acronym agencies around the world and governments. So, a lot of the primary impetus to, fund the quantum computing research was for this kind of application.
[00:10:33] Dallas Campbell: bit of an arms race? It's like, we're going to build a quantum computer. We're going to be able to hack your quantum computer. Is it a kind of...
[00:10:38] Daniel Oi: Well, so the quantum computer, you know, could be used to, you know, decrypt some communications. We can use quantum communication to actually close off that, possibility through, something called quantum key distribution, which allows you to communicate securely, which is not vulnerable to a quantum computer.
[00:10:56] Dallas Campbell: Okay. Just finally, what are the applications to do with space? Like why do we're going to send it into orbit. Like, why do we want to do that?
[00:11:05] Daniel Oi: So I mentioned quantum key distribution, which is one way that we can have communications, which is secure against a quantum computer. So one problem is that the way that we usually communicate these days over long distances with optical fibers is that there's exponential losses and that you can't really send a single photon, a single quantum photon, very long distances down an optical fiber. Actually going through the vacuum of space, that's actually much more efficient and also the losses are much lower, we can go from one side of the earth to the other side of the earth, you know, missing, you know, all the earth in between just going through space. The particular application I'm very interested, going into the future is how can we test fundamental physics in space? How can we use quantum mechanics, quantum technology to probe, for instance, how does gravity and quantum mechanics interact?
[00:11:57] Dallas Campbell: Could we build, like, a big collider in space, for example? Or that kind of, you know, to sort of really drill down into physics.
[00:12:04] Daniel Oi: Well, people have proposed, you know, solar system sized colliders, trying to get energies that wouldn't be possible on Earth. But I'm interested in how to probe, for instance, the behavior of quantum mechanics over long distances. How does quantum mechanics and gravity interact? So it's really only going to space and being able to access these regimes where, you know, a very fast, relative motion of different gravitational potentials over long distances, that we may be able to find, you know, the discrepancies between what we currently know about how quantum theory behaves and how it may interact with gravity and find the first hints of what might be a unified theory might look like.
[00:12:44] Dallas Campbell: Well, Unified Theory, this idea, are we going to get to a point where we'll have physics? A bit like they thought at the end of the 19th century, that's physics done, are we going to get that? Are we going to, like, what is the, when you talk about the unification of quantum mechanics and general relativity, what does that actually mean to...
[00:13:01] Daniel Oi: Well, I mean, so traditionally, people have been, you know, have various approaches, right? So, at the moment we've got, you know, unification of three forces, the electromagnetism, the weak nuclear force and the strong nuclear force and the standard model which basically encompasses that has been very successful and really, it's been a victim of its own success in that, you know, there's very little it can't predict. Now, there are a few things which are just these anomalies, which show that everything isn't all right, right? There's the dark energy problem, there's the dark matter problem and so these are indications that, you know, our current understanding... yes. Now there's also a very fundamental discrepancy between the mathematical formulation of general relativity and quantum theory and so therefore, you know, we have to overcome this fundamental incompatibility in how we describe the universe, how describe reality at this very mathematical, fundamental level and without any good experimental evidence as to how do we do this? What does a unified theory look like? You know, we have had various attempts over the past string theory, you know, quantum gravity, you know, loop quantum gravity, you know, lots of different approaches, but nothing so far has satisfactorily answered all of the challenges and how to unify these two things.
[00:14:25] Dallas Campbell: String theory was the kind of only game in town a few years ago and I wonder, with kind of better computers, quantum computers with AI doing crazy things, are we, is that going to sort of solve some of the big physics mysteries you think? In my lifetime, because I'm like, I'm getting old and I want to know, I want to know the answer.
[00:14:44] Daniel Oi: You know, there's some proponents of AI would love to be able to, you know, show that, you know, their approach has comes up with unique novel solutions, you know, generating knowledge and you know, trying to find new physical theories obviously would be a tremendous advance. I'm quite neutral as to whether, you know, AI can really come up with a good synthesis of existing knowledge and to really develop new approaches. I think that's what we need, we need new approaches to how to tackle this problem and fundamentally, we really need empirical evidence as to which direction do we go.
[00:15:18] Dallas Campbell: Thank you so much for staying and giving us a little bit of a refresher course in quantum mechanics. God, it's complicated and also a little bit about what you do and what the future holds. It's been absolutely fascinating. Thank you so much.
[00:15:28] Daniel Oi: My pleasure.
[00:15:29] Dallas Campbell: To hear future episodes, be sure to subscribe on your favourite podcast app and to find out a bit more about how space is empowering industries between episodes, why not visit the Catapult website, or join them or me on social media.