Instant Genius - Are We Living in a Simulation? How to Tell If Reality Is Fake

Episode Date: September 17, 2026

The possibility that we may be living in a simulation created by a more technologically advanced civilisation has occupied the minds of scientists, philosophers and fiction writers for decades. We may never be able to satisfactorily answer this question, but perhaps the best way of investigating its feasibility is by looking at how we might go about creating a simulation universe ourselves. In this episode we’re joined by Prof Catherine Heymans, Astronomer Royal for Scotland, who investigates this question in her new book, How to Design a Universe – The Science of Real and Virtual Worlds, the royalties of which will be given to the Royal Observatory Trust, which supports astronomy youth projects across Scotland. She tells us what our current knowledge tells us about the way that the universe operates, explains why we’d need an enormous amount of computing power to generate a simulation universe, and investigates the question of why we, or a more advanced civilisation, might attempt to do this in the first place. Take your curiosity further with a subscription to BBC Science Focus magazine. Every issue is packed with fascinating insights into the science behind everyday life, the latest breakthroughs and expert analysis, delivered straight to your door. Receive an extra £5 when you subscribe using the code SF5OFF, (minimum spend £20, see full terms and conditions on our website). https://www.ourmediashop.com/bbc-science-focus-magazine-pod30 Learn more about your ad choices. Visit podcastchoices.com/adchoices

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Hello and welcome to Instant Genius, a bite-tized master class in podcast form. Every Monday and Friday you'll hear world-leading scientists and experts talking about the most fascinating ideas in science and technology today. I'm Jason Goodyear, commissioning editor of BBC Science Focus. The possibility that we may be living in a simulation created by a more technologically advanced civilization has occupied the minds of scientists, philosophers and fiction writers for decades.

We may never be able to satisfactorily answer this question, but perhaps the best way of investigating its feasibility is by looking how we might go about creating a simulation universe ourselves. In this episode, we're joined by Professor Catherine Heyman's, Astronomer Royal for Scotland, who investigates this question in her new book, How to Design a Universe, the Science of Real and Virtual Worlds, the royalties of which will be given to the Royal Observatory Trust, which supports astronomy youth projects across Scotland.

She tells us what the current extent of our knowledge tells us about the way the universe operates, explains why we'd need an enormous amount of computing power to generate a simulation universe, and investigates the question of why us, or a more advanced civilization, might attempt to do this in the first place. So, welcome to the podcast. Thanks so much for joining us. I'm delighted to speak to you this morning. So today we're talking about your new book, How to Design a Universe, the Science of Real and Virtual Worlds. So you sort of kick off the whole kind of investigation of the book by looking at the possibility that we're living in a simulation.

And then from that you think, well, you know, maybe we are, maybe we're not, we'll talk about that later, but how would we go about building a universe? So in order to do so, we first have to know how the universe functions. So I think a good place, which is where you start, is with the fundamental forces. The clues in the name there, isn't it? The word fundamental. You know, first off, what are these? You know, how briefly, how do they work?

So, yeah, I should apologise to all the listeners for the existential crisis that we're about to drag you into with this big question of could we be living in a virtual reality. And I think, you know, it's a very difficult question to answer. Some would argue it's not even a scientific question to answer because, you know, How would you ever know if it was such a perfect reality? How would you ever be able to find out one way or another? But I think it is a very interesting question to ask, well, do we understand our reality well enough to be able to write a piece of computer code

that could create this reality? And I'm an astrophysicist, and we regularly run computer simulations of our universe. How does dark matter change and evolve over time? How do galaxies form and evolve over time? How do planets form? around stars. These are questions that we're always asking and using computer simulations to help answer. So it's a natural step for me to think, well, could we actually simulate everything? And if we did, what ingredients would we need? And the book starts with the four fundamentals.

The four fundamental forces, gravity, electromagnetism, the weak and the strong force, and how they impact your day-to-day reality. And this is, this is. This is a lot of the expert physicists who are potentially listening will be saying, oh, Catherine, you can merge three of those forces together in some great theory of everything, or the electro-week force. And yes, there are different theories of why we have these fundamental forces. But the bottom line is that when we look at our reality, we see on very large scales, we've got the gravitational force field that pulls us back down when we jump up in the air. Then we've got the electromagnetic force field.

That's governing most of your day-to-day reality, how you see. things, hear, things, touch, smell, taste, that's all the electromagnetic force. And then zooming down to the very, very small scales, what's happening on subatomic scales, you've got the strong and the weak force working there. And so depending on which scale you look in the universe, these different fundamental forces are guiding what changes and evolves over time. So let's start with, I think when most people, if you said to somebody, you know, what do people who study the universe actually study?

So their minds will go to galaxies, stars and planets, etc. Like the science are very big. And so here, gravity's king. We've got sort of Einstein's theories of relativity that we use, that we rely on really in many ways to explain the way these things are working. Can you just give us a sort of brief idea of what exactly that is? Yeah. So gravities are really interesting one out of these things.

for fundamental forces because it works very differently. So the forces that sort of govern our day to our day reality on the small scales, they take place in space and they evolve over time, whereas gravity is the curvature of space and time or space time, as we call it. So it's sort of very separate from the other forces. And that kind of motivates one of these questions that we have in physics is why do these fundamental forces sort of work differently? Is gravity even a, is it even a force? It's when we when we look at Einstein's, the way Einstein thinks about gravity, he thinks about the mass, any sort of stuff is curving space and time. So let's take a little step back. So Newton said that gravity was apple falls from tree on head. And that's because the gravity is,

pulling the apple down. Whereas what Einstein is saying is that the gravity of the earth has curved the space time. And so when the apple is moving through space and time, it's curved and rolled towards your head. And that's why it smashes into it when you're sitting under the tree. So they're very different ways of thinking about gravity. And Einstein's description works very well with our observations of the universe. We've just had that gorgeous total eclipse. back in August, which was an example of an observation that you can make that really, you know, all evidence points towards Einstein's theory of general relativity being right. So that's a wonderful example of where we have some mathematics that very clearly explains

how our reality works on the large scales. But is this also a red flag because it really doesn't mesh with our other fundamental forces, electromagnism weak and strong, that are sort of working on the much smaller scales. And so that's one of the questions I sort of explore during the book. Is this just because we don't have, we don't have all the information yet? Our blueprint of reality is not complete. Or is that an indication that our reality isn't as mathematical as we think it is that maybe there's more to it.

And if it's not mathematical, then we can breathe a sigh of relief because we're definitely real. It's that mathematical part of the universe is the key ingredient. If you want to create a virtual reality, if you want to be Neo in the Matrix, and discover you're in a virtual reality. The key ingredient to that is that everything around you is mathematical, something that a computer could code and replicate. So just sort of like you mentioned there that what most people think of gravity, it's what planes are resisting when they're flying the sky

or when we drop our phone on the floor or something, that's gravity. But it's also responsible for many things about the way that the universe looks, Like the way that galaxies are formed, the way that stars are formed, the way that planets are formed. You know, what can we say about that? Yeah, so when I'm not having an existential crisis and worrying about whether my reality is real or not, I am a dark matter researcher and a dark energy researcher. So I spend a lot of time working on some of the world's largest telescopes, taking these giant surveys of our night sky, looking for the gravitational.

effect of matter in our universe. And what we see when we look out into the universe is that there is a lot more gravity there than what would arise from just the stuff we can see. So a galaxy is a great example. You can look up at a galaxy and you can count how many stars are in that galaxy. We know roughly how much stars way. So we know how much stuff is there that we can actually see. And then we look at the gravitational pull of that galaxy. These galaxies are spinning around very quickly in order for those stars not to fly out into space. There has to be a lot of gravity keeping those stars contained in the galaxy. And there just isn't enough gravity there. And the work that I do, I look at the distribution of matter on incredibly large scales all the way

across our cosmos looking billions of years back in time. And all of the evidence points to there being extra stuff there, something that we call dark matter. We can talk about dark energy as well if you want, Jason, but we'll focus on the matter at the moment. Now, the answer to what is that stuff is either Einstein's theory of general relativity is wrong, our model of gravity is wrong, plausible. I've been trying my whole career to find some chinks in the armour of that wonderful theory and nothing is coming out. It honestly explains so many things absolutely exquisitely all of our observations. But, you know, eyes open, could be wrong, You never know with science and it's always worth testing.

Your other option is that our understanding of our reality here on Earth is missing something big. It's missing this big component of dark matter. And, you know, when we look at how particle physicists explain our reality, when they go down to the quantum scale, they've got this standard model of physics. And that doesn't include any dark matter. So again, that tells us that our blueprint of reality is missing some key information. So certainly right now, we don't have all the information we need in order to be able to make a simulation of our reality as we know it. But that doesn't mean that in the future, some futuristic scientist won't be able to do that. Yeah, so you mentioned dark energy there and sort of, you know, again, going back to Einstein, we have this, the idea of kind of mass energy equivalents.

So where does dark energy fit into this picture? because I think if you combine them together, it's something like 90% of this stuff in the universe that is dark. I mean, that's wild. Yeah, 95% of our universe is dark. I mean, I've been working on this problem, Jason, for quarter of a decade now. And I'm not sure how many of the wise.

I wasn't when I started. And you may view that as an absolute major failure. of me as a scientist. But I prefer to see it as an opportunity for discovery. And the reason why so many of us are really driven by this question of what is out there in the universe, what is this apparent dark matter that's holding galaxies together? What is this apparent dark energy that when we look at how fast our universe is expanding, we see that that expansion is getting faster and faster each and every day. You know, what are these dark entities in our universe? The reason why we're so driven to answer that question is because the fact that we don't understand it

means that we don't understand our reality, our home, our place in the universe. And that's why we keep building bigger telescopes, getting more data, trying to get more information about all of it, because in order to understand why we're here, you need to resolve that question of why when we look out and the universe is it's so very different from our day-to-day reality here on Earth. New from Nespresso. Blend wellness into your coffee routine with the coffee plus range, infused with functional benefits. Choose the coffee you love with added B vitamins,

like coffee plus B12 to help support immune function, and coffee plus B6 to keep your day moving. Or go with the flow and choose ginseng delight. Our new double espresso with ginseng extract. Whatever lies ahead, Don't change your morning. Let your morning change you. Discover Coffee Plus on Nispresso.com. Where some see heroes and others see egos. Bloomberg sees the era of billionaire athletes. A fad to some, the future of money to others. We see crypto's trillion-dollar swings.

The end of jobs or the end of human struggle. We see the endless funds fueling the AI hype. While others follow the noise, we follow the money. Learn more at Bloomberg.com. Yeah, so that sort of feeds into a sort of wider idea about science in general, which you talk about, which is the scientific method. So as you said, some people who are like, well, blind me, you don't even know what 95% of the universe is. You know, what use is this? Obviously, an opinion I don't share. But, you know, it's sort of, we're gradually ticking things off, aren't we? Well, it's not that, it's not that, it's not that, it could be this.

It's a constant sort of process of evolution. Yeah. I mean, I know, you know, I said I've none the wiser than when I started this career journey, four of a decade ago, no, quarter of a century ago, 25 years ago. But I do know more about what dark matter is not. So, for example, the very first research project I did was asking the question, of is all the dark matter out there actually brown dwarfs failed stars you know stars that have never managed to to light up and start burning and so when we do those calculations to find out

to estimate how much stuff there isn't a galaxy to work at how much gravity it needs to be able to spin that fast you know maybe there's just a lot of brown dwarfs out there and we were using data from an infrared telescope because brown dwarfs do radiate light in the infrared to calculate how many brown dwarfs are out there no not nearly enough brown dwarfs to make up the missing matter. And you're right, the way we do the scientific method, we have our ideas about how, we have our question, we have our idea about what the answer might be, we design an experiment, we more often than not prove our idea wrong because the experiment doesn't agree with the idea

and we go back and we cycle around and around and we keep updating our ideas, updating the experiments. And this scientific method, you know, if there was one thing that, I could teach people about science. It wouldn't be a single fact or, you know, it wouldn't be a theory or anything. I would want to teach in the scientific method because I think it's a really important way to sort of structure the way you approach different questions. And I think it's very different from the way our politicians address questions. You know, they have their beliefs and they assert them very confidently. This is how it, this is, you know, this is, you know,

This is the problem and this is the solution because that's their societal belief. But the scientist will always attack a question with an open mind. And yeah, they've got their ideas about what the answer might be. But if, you know, if their experiment proves their idea wrong, that's absolutely fine. That I have learned something. That failure is a huge success. And then you can go forward and you can learn more. And actually, I think that scientific method is the,

reason why in the future, scientists will attempt to build a virtual reality that we might be living in Jason, probably not. But I think that's scientific method. There are lots of scientific questions that we have that we can't build an experiment for here in the laboratory. And astrophysicists are really good at this. So we can't bring a galaxy into the laboratory with us to do an experiment on it. It's just too big. It doesn't fit into my back pocket. The galaxy is too big. The timeframes are too long. The temperatures are too hot. The density is too vast. And when you look out into the universe, it's just too much to do any sort of laboratory experiment on. So, you know, for decades, astronomers have been applying the

scientific method to their questions using computer simulations. So we say, well, let's pick a question. How would, if our universe was filled with dark matter, how would it look when the galaxy is lit up? And so then you birth the universe with dark matter in it and you let the laws of physics that you know work very well here on Earth. You let them run and evolve and you see how your universe responds. And we see in our computer simulations that you get this giant cosmic web of dark matter. And it's that cosmic web that dictates where and when the galaxies form and when they light up. And we tweak our numbers and how does the dark matter behave? How hot or cold is it? Does it interact with itself? Does it not? And that allows us to build up this picture

of what our universe looks like if we could see dark matter. And that scientific method just goes round, around, we keep iterating, changing our simulations and going around. And now we have amazing simulations of our universe that look very similar to the actual universe that we can see out there with our telescopes. And that's just because of this iterative approach, failing, trying again, failing, trying again. And so looking forward to the few, What does a future scientist want to know? Well, one of the biggest questions that we have is to understand consciousness. We don't understand consciousness. Why are we conscious? Why do we experience our reality? What is it in our brains that creates this conscious experience? You know, this is what philosophers have been talking about for hundreds and hundreds of years. But you could never design an experiment to test human consciousness. This is, you know, known as the hard problem of consciousness. It's impossible to find out if anyone else is conscious but you. So therefore it's very hard to build experiments to test consciousness. But with this computational scientific method, that I can see as a route that a future

neuroscientist might want to take to explore consciousness by building a virtual reality, trying to build a virtual human who becomes conscious to really explore that scientific question of consciousness. Ethics Committee, morals and ethics, big question. there. Should the scientists actually do that? Probably not. Lots of questions there, but that's that scientific method and my experience of being a scientist using computer simulations just makes me think if we were living in a virtual reality. It's most likely being one created by a scientist who is trying to answer a scientific question. Yeah, yeah, I think that's a really fascinating point. So if we're doing that, then presumably we're going to need a pretty impressive amount of

computing power if we're going to create a simulation universe. So, I mean, could we just use a kind of super powerful version of the computers that we currently have? Or would we likely need something sort of more exotic and technologically advanced? So if the scientific question that some futuristic neuroscientist was trying to answer is let's say they're building this simulation because they want to address scientific questions about consciousness. I think there are lots of different theories about consciousness and where it arises from and I'm not a neuroscientist, but I did enjoy researching this part of the book. But my takeaway from looking at all of the different research was that consciousness is something that is created through your experience and your learning.

You know, as you develop, your brain develops, it learns. And so you would have to create your virtual human in an environment where they could learn and develop. And I think you would have to simulate them from the quark level up, or at least that's where certainly I would start if I was designing this experiment. So you would want to simulate absolutely everything. And gosh, if you really want to get into a discussion about whether AI is conscious, we can. Bottom line, I don't think it is and I don't think it will be because I think consciousness is something that comes from experience, learning and experience. Anyway, that's a side question. If you were simulating everything sort of from the quark level up, then you would need a lot, a lot of energy.

So I looked at a calculation. There are different ways you can calculate this. But if you wanted to simulate absolutely everything in the universe, from the big bang to the present day, all of the galaxies in our observable universe, everything sort of from the quart, from the subatomic level, sort of all the way up. You would need an inordinate amount of energy. So at least as much energy as the total mass in a galaxy. So if you could somehow convert all of the mass in a typical galaxy into energy through sort of the E equals MC squared, you would need all of that energy to conduct that universe.

And that's a minimum, a minimum number. Actually, you probably need far, far, far, far, far more than that. So I don't think any futuristic computational overlord is going to be simulating absolutely everything. And if they are, they're not going to be siming a lot of them. But if you just wanted to simulate just one person, if your scientific experiment was trying to understand consciousness, and you just wanted to simulate a single person, put them in an environment where they could learn, where that conscious experience could evolve and grow, that you could do with a reasonable amount of energy. So yes, we're going to need advances in quantum computing because everything,

Everything that's happening inside your body, inside your brain is a quantum process, so you would want a quantum computer to be able to calculate all of that. That I could imagine would be plausible in the future if you're just focused on simulating a single sort of centrepiece for your simulation and then creating a more energy efficient environment for them to live in. So you mentioned there's sort of quarks and quantum physics a few times. So this is the sort of the physics, the science, of the incredibly small.

So we've been talking about gravity, like the science of the big. So, of course, if we're going to make a simulation of the universe, if we're going to build a universe, even if we're going to build anything pretty much from absolute scratch first principles, we have to know all about atoms and about the quantum world, which gets really, really counterintuitive.

So, you know, there's still, there's a lot of unanswered questions, you know, residing it in pretty much everything that we see in front of us. Yeah. So when I was writing the, I call it the quantum verse, so the universe on a very small scale, going down to the quantum verse. When I was researching that section of the book, Jason, I was out for walk with my long-suffering partner and I was explaining how and this and he just stopped.

He was like, Catherine, can you just stop talking about this? Because it just doesn't make any sense. Yeah, you're right. Because when you zoom into the quantum verse, you have to throw away common sense because things on a very small scale just don't work as you anticipate them to work. But the flip side of that is that my particle physics cousins have come up with the standard model of particle physics. It is a single equation, a very, very long-winded equation with us. But, you know, they, and that equation, that mathematical prescription of reality on small scales, works incredibly well, you know, they predicted the existence of the Higgs boson, then built themselves a really massive piece of kit,

you know, CERN, 27 kilometre ring underneath the Swiss-French border, smashing protons together at 99.9, probably some other nines, after their percent speed of light to see what falls out. And all of their predictions came true, you know, that we understand. understand the mathematics of the particles that we're made up of incredibly well. Now, there are some weird things that happen with those particles. So listeners have may have heard of wave particle duality depending on whether you are looking at the particle or not. It behaves like a wave or not. And people will have heard of the story of the quantum cat. Is the quantum cat alive or dead? You don't know until you look into the box. There are all of these sort of stories that we tell

about quantum physics. But those are us trying to put our human perception of reality onto the mathematics. If you're happy to just accept the mathematics, I call this the shut up and calculate approach to quantum physics. I'm not the only one. Lots of other people call it that as well. The shut up and calculate approach to quantum physics. You can calculate very accurately what should happen next at each stage. And the problem only comes in when you start really thinking about, well, what does this mathematics mean for our reality? And unfortunately, the best, if you really want to delve into it, if you don't want to just just shut up and calculate, which is the standard approach that we take. We don't worry about what this actually means. If you really want to dig into it and really want to understand what happens when these quantum interactions occur, then unfortunately your best answer is that each time there's a quantum reaction. So we call it quantum entanglement, but basically any sort of interaction that co-locates quantum particles in the same place at the same time.

Every time that happens, the entire universe branches creating a multiverse of different versions of the universe. And unfortunately, if you're a science fiction fan, you can't jump. between those different versions of reality because you don't exist in the other versions. And, you know, there are so many of them because these branches happen every time a quantum interaction takes place. But it's that sort of prescription, that view of the quantumverse comes about from looking at the mathematics that we know works really well to explain our day-to-day reality. But it really does make your brain hurt. And I quite understand why my

partner on this walk just said, just stop talking, Catherine, just stop. And my apologies if the listeners are reaching for the stop button right now. Oh, I doubt that. We've talked about an awful lot there, and you kind of touched on this earlier. And we talk about, you know, theories and theoretical physicists and experimental physicists and, you know, the different work that they do. So do you think it's ever really possible to know if we are living in a simulation? Could it be so good that there's just absolutely no way that we'd know?

Yeah. So that's the problem. So if we are living in a virtual simulation right now, Jason, it has to be perfect in every way because if it wasn't, we would already know. You know, science fiction fans will say, well, we need to look for the glitch, you know, the black cat that crosses our path and then it crosses our path again in exactly the same way, exactly the same mannerisms. If those glitches existed, we'd already know about it. So I think, you know, our reality, whether it's virtual real, it's perfect in every way. you could imagine an experiment, you know, so there are different ways that you could search for it that I talk about sort of looking for computational artefacts. So, for example, when we look at a

digital image that you take on your camera, if you want to, you can zoom into it on your phone, keep zooming, keep zooming, eventually you'll reveal the pixelization in that image. And that pixelization is maps onto the detectors, the sensors in your, in your camera. It's actually the same with your eye. So our vision is also digitized. because you have a limited number of cells in your retina, and each one of those rodent cone cells that are detecting the light, they are basically pixels. So you already have a gridded vision of your reality.

You just don't perceive it because you can't zoom into your own vision as you can on your digital camera. But your vision is pixelized just like a digital camera is. But you could imagine designing some experiment to zoom down and down, down and scale to see if there is any pixelization there. And there's something that we call the plank scale, which is sort of like a fundamental scale limit in our reality. But could that be the grid that we're built upon?

Or is that just the mathematical scale of our universe? And there's other examples of potential computational artifacts. So, for example, Einstein's theory of gen relativity tells us, well, actually it was a special relativity, told us that light travels at a fixed speed. So the speed of light is the maximum speed limit in our universe. universe. And actually, everything is moving through space time at this maximum speed. It's just light uses that speed to travel through space, doesn't travel through time. And we're pretty

stationary. The earth is spinning. We're moving around the sun. In the grand scheme of things, we're not moving very fast. So we use all of our motion through space time to move through time. But we have a fixed speed. There's a fixed speed that we can move. There's a fixed limit to how information can travel across our reality. So, for example, when you see a thunderstorm, you see the light before you hear the sound, that's because there's a fixed speed that that information can travel to us across time. And that could be a computational artifact. You know, if your computer was processing, was creating your reality, was building your reality, it would have a fixed speed. You know, it needs time to crunch the numbers to run the calculation.

So those are examples of computational artefacts that you could say that these are things we observe in our own reality. And you could say, okay, those are computational artefacts. Or you can say, no, that's just the mathematical structure of our reality. That's what the fundamental force of gravity. That's what Einstein's theory tells us. We have that fixed limit. We don't know why. But that's the nature of our reality.

So it's a long, I said we might rumble a bit tonight. start. But your question was, will we ever know if it is a perfect reality that you can never, that's so perfect you would never be able to distinguish it from the real world, then yeah, no, of course we're never going to be able to know one way or another. And all of my research over the last few years, you know, I've come to the conclusion that our reality does appear to be incredibly mathematical. And if it is mathematical, that means a computer could code it up. So I can't rule out. I can't disprove the hypothesis that we're in a virtual reality. But I think it's highly unlikely. For all of the reasons we've talked about so far, the

inordinate amount of energy that you'd need, the fact that I think is most likely that it would be developed for a scientific reason. Scientists don't, you know, we just build the simulations that we need to answer our question. We don't build like trillions of them. So I think it's unlikely that we're living in a virtual reality. But there's no. Nothing I've found that says we can rule it out, which is the approach that we take with the scientific method. We only ever disprove things we can never prove them. Thank you for listening to this episode of Instant Genius, brought to you from the team behind BBC Science Focus. That was Professor Catherine Heyman's. To discover more about the topics we've

just discussed, check out her book, How to Design a Universe, the Science of Real and Virtual Worlds. If you liked what you just heard, then please do consider subscribing to Instant Genius on your preferred podcast platform. If you'd like to see our guests and hosts and person, then why not check out our YouTube channel at ScienceFocus. If you've enjoyed this podcast, why not take your curiosity a step further with BBC Science Focus magazine?

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