Bill Nye:Are we living in a video game? Are we actually part of a giant simulation?
Joscha Bach: The question of whether we are living in a simulation is more related to something more narrow, that is: Is this computer program that we're living in intentionally created or is it just a natural occurrence?
Bill Nye: It seems to me it's a hard question to resolve because it's easy to imagine a game designer, a simulation designer, making it so sophisticated that you can't tell.
Joscha Bach: There is this argument that, for instance, Elon Musk made that we can build game consoles that create virtual worlds that look a lot like simulations to us of this universe and they can be so realistic that we cannot really distinguish them. And this argument is to mean that every civilization that has sufficient technical capabilities is going to build many of these game consoles, so the probability that when you look around and you find yourself in a pretty realistic looking world that you're actually in a simulation is much higher than the probability that you are in base reality. But I think what this doesn't take into account is the level of detail that you can achieve in such a simulation.
Donald Hoffman: In the simulation hypothesis, there's some programmer at a lower level that has created the simulation that's us. But that programmer themselves could be a simulation by another programmer at a lower level and this keeps going. There could be a hierarchy of these different levels of simulation until you get to some bottom level.
Joscha Bach: It seems that our universe has an amazing amount of detail and to get this amount of detail in a subset of this computer is very hard because if you build a computer here on this planet it means you cannot simulate a big universe in it. You can only simulate a very, very, very small slow universe in it.
Donald Hoffman: And in the standard story of the simulation hypothesis, at the bottom level there's a physicalist spacetime world where there's a real programmer in space and time with a real physical computer that's programming the whole thing. So our spacetime might be virtual but at the bottom there is a real spacetime with a real physical world. And I'm denying that.
Joscha Bach: So every universe that you stack into another universe is going to have many orders of magnitude less detail. So I think if you find yourself in a very detailed universe that has many, many galaxies and much more detail than you need to have intelligent life and civilizations in it and so on, it's unlikely going to be a simulated universe created by a civilization. It's more likely that it's base reality.
Bill Nye: I think you can argue that whoever has written the simulation, whatever super entity has written the simulation, could make it so sophisticated that even your memories are a result of being programmed by the simulator or simulatrix. So the question is at some level irrelevant, but on another level I think we would have to agree it's unknowable. You can just presume any level of sophistication that makes it undetectable to us.
Joscha Bach: If the question is 'Could we be living inside of a computer program?' then my answer would be of course, yes. Because the only thing that we get with some certainty from the outside world is information. And the only thing that we find with certainty in this information is regularity and for a system to produce regularity and information, that is discernible differences that change in a way that is somewhat not random and somewhat predictable, for this it needs to compute. So it's necessary and sufficient for the universe, whatever else it does, that it computes. And we cannot really know what else this does. So in my view, by the way we define computers and computer science, it's necessary and sufficient that the universe is some kind of computer in a pretty literal sense.
Bill Nye: There have been a lot of science fiction stories where people discover that they're living in a dome or inside a hollow world or underground. And the metaphors for this are from our everyday experience. You hear about kids who have been kidnapped and kept in a room until they're 14 and they know nothing of the world outside. And the human mind apparently at some level is incapable of detecting that outside world unless something goes wrong.
Donald Hoffman: The idea that this is all a simulation, that we're not seeing reality as it is, is something that I'm saying as well. That this is, that spacetime itself is just a data structure. Physical objects are just a data structure. They're not objective reality.
Joscha Bach: It doesn't mean that we know what kind of computational class the system is in and there is, I think, a lot of contests and ideas in physics what kind of computational class the universe really is in. What capabilities it has. What it can compute and what it cannot compute. But still, it's computational in some sense. Of course we cannot really know this because no feature in the world clearly points at this thing being a simulation in that sense—I don't see anything that would convince me that we are in a simulation. But if it is one I don't think it's for our benefit. I don't think that all these galaxies and stars and all the intricate elementary particle structures that we can observe in some sense and that are not necessary for our experience as primates on the planetary surface would need to be painted on the telescopes and microscopes by the simulator. So I don't think that these are smokes and mirrors when we look into the sky and we see these bazillions of galaxies. I do think that if this is a simulation then they would be an important feature of the simulation which means the simulation is not there to create us. The simulation is probably there to explore some aspects of hypothetical physics and we are just a random side effect or an artifact of the fact that evolution is possible in this universe, so we could emerge in it.
Donald Hoffman: I agree with the simulation hypothesis that we're not seeing the truth. We're seeing something other than the truth.
Joscha Bach: I think it's very unlikely that we are in a simulation because if I would build a simulation of a universe I would make the computer that it runs on irreversible. What that means is that the operations that happen in that universe can delete bits. It means that a state that you observe in the universe can have multiple possible states that it comes from. And if you look at what we know empirically in physics this doesn't seem to be the case; our universe seems to be reversible and this means we cannot really delete bits. If we cannot delete bits it means that everything that we like is irreversible. You'd stabilize your body temperature. You forget yesterday's body temperature in your body. It means that you have to delete bits in some sense. All the things that we are interested in life, planets, stars, computers, organisms, minds are irreversible in some sense. They all need to delete bits to keep their structure stable against the onslaught of the substrate which has its different logic and its different direction that he wants to go into. So in some sense you get waste bits; you need to throw these bits out of your system and this is what we as observers perceive as increasing entropy, these waste bits. And if you would be living in a simulation like Minecraft—in Minecraft you can build perpetual mobilis. That's because you don't have entropies in Minecraft; Minecraft can delete bits, it can forget its previous state. This universe apparently cannot. So the reason why we cannot have nice things in this universe, why we cannot have perpetual mobilis, why entropy is always accumulating and is always going to get us in the end and we will always have to die as living beings. That's why life is always temporary—every self-stabilizing system, we only have a finite lifespan in this universe. That would not be a feature I would put into a simulation.
Donald Hoffman: I'm denying that at any point spacetime and physical objects correspond to an objective reality.
Bill Nye:For me as a philosopher to prove that we are living in a video game is an extraordinary level of effort. But if you can do it, bring it on.