Max Hodak Writings

We are probably not living in a simulation

May 2020

One of my long-running interests is thinking about how to build a virtual world to go with our future neural interfaces. It’s not just a software engineering challenge: there are real physics problems hidden in it.

Separately, some of my friends are enamored with the simulation hypothesis — briefly, that we are living in, and our entire universe is, a computer simulation — and so I’ve ended up spending a fair amount of time thinking about that, and specifically whether it’s possible to say anything concrete about the probability that it is actually true.

A little while ago I realized that if you turn the build-a-virtual-world problem inside-out, you can start making fairly interesting statements about the simulation hypothesis in the form of constraints that must be imposed on any “containing” universe. Importantly, these arguments have nothing to do with the amount of available compute power, which felt like a significant advance. (It avoids the handwavery that comes from believing you can approximate any otherwise intractable problem reasonably fast if you have a sufficiently powerful machine, which seems to be an oft-used escape hatch.)

These arguments do require making a couple assumptions, but in my opinion they end up being pretty mild. The two critical assumptions are that we have to believe that any universe must be internally consistent to exist, or at least talk about describing; and that the creators of a simulation have to end up with some way of interacting with it. If you could build a virtual world full of simulated organisms, but to you it would look like a black hole, why would you bother, much less let it consume your resources?

Long story short, we can pretty much rule out the conclusion that we are living in a simulation and that the external universe at all resembles our own. Simply put, we can bound that only one of these can be relativistic, and since we know that ours is, the outside universe cannot be. At this point I think the simplest thing to do is to discard the simulation hypothesis, but it is true that an alternative is to just take this constraint and run with it in terms of imagining what the outside universe might be like. It would be very different from anything we’re capable of imagining, completely lacking a space-time connection, and that’s probably only scratching the surface of this line of reasoning.

Full article: Constraints on an external reality under the simulation hypothesis, pdf