Paul Chiusano

Functional programming, UX, tech


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No you should not seriously consider whether we are living in a simulation

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I’m reading Superintelligence, a surprisingly dull book given its topic is, well, the possibility of a rampant superintelligent AI destroying civilization and what we might do to prevent that sort of thing. Along the way, the author speculates about how a caged hyperintelligent AI (not joking here) might incorporate reasoning about the the simulation hypothesis into its plans to escape confinement.

The answer to the question of “how do we know we aren’t living in a simulation” is similar to “how do you know the universe wasn’t snapped into existence 5000 years ago?”, “how do you know you aren’t dreaming right now?” or “how do you know you aren’t just a brain in a vat?” On some level, we can’t really know these things with certainty, but we don’t seriously consider these possibilities because we have simpler models that explain reality as well or better.

However, without any judgement, I report that some people take this idea of reality being a simulation pretty seriously. Elon Musk apparently believes we are likely living in a simulation and is rumored to have a team of people trying to figure out a way of breaking out of the simulation. I’ll admit: the first time I read that second article I had to double check that I was not reading The Onion.

Anyway, I want to spend the rest of this post picking apart the simulation hypothesis, but first, let’s hear the argument out! Enter Nick Bostrom:

Many works of science fiction as well as some forecasts by serious technologists and futurologists predict that enormous amounts of computing power will be available in the future. Let us suppose for a moment that these predictions are correct. One thing that later generations might do with their super-powerful computers is run detailed simulations of their forebears or of people like their forebears. Because their computers would be so powerful, they could run a great many such simulations. Suppose that these simulated people are conscious (as they would be if the simulations were sufficiently fine-grained and if a certain quite widely accepted position in the philosophy of mind is correct). Then it could be the case that the vast majority of minds like ours do not belong to the original race but rather to people simulated by the advanced descendants of an original race.

It is then possible to argue that, if this were the case, we would be rational to think that we are likely among the simulated minds rather than among the original biological ones.

Therefore, if we don’t think that we are currently living in a computer simulation, we are not entitled to believe that we will have descendants who will run lots of such simulations of their forebears.

Whoa there! First problem: one can’t just extrapolate from a few decades of computing trends (where computers have indeed become exponentially more efficient) arbitrarily far into the future, without considering that there are theoretical, physical, and practical limits to computing power, even for an advanced civilization. To put things in perspective, we cannot today build computers powerful enough to accurately simulate everything happening in a thimble full of blood; what makes us think we can simulate a planet, a solar system, or a universe?

Something underappreciated here is that the computation happening in the wild, including the computation done by our universe’s laws of physics, tends to be irreducible if we simulate it at sufficient fidelity. (And by all available evidence, our reality is “computed” at high fidelity down to quantum scales, not some vastly simplified approximation like what is done in video games.) It’s only when we consider much simpler idealizations of reality that we’re able to simulate or predict reality using more limited amounts of compute. Stephen Wolfram been beating this drum for a while, though I like to just view it as a consequence of Rice’s theorem or the halting problem: in general, you can’t fast forward the program to know what it does, you have to run it, and that requires energy, space, and time and eventually reaches physical limits. Though much is unknown, it is very possible that our universe cannot be simulated much more efficiently than by building an effectively universe-sized computer. This does not bode well for hypothetical future civilizations planning to simulate our current reality within our current universe.

A more fundamental issue with the simulation hypothesis is it requires speculating about an “outer universe” capable of simulating our current reality. Notice we can’t really speculate about this because nothing we can observe in our current reality places any constraints on such an outer universe. Is it similar size to our own? With similar computing power? Do its laws of physics work similarly? Anything goes here and is consistent with our observations of reality. So we can conjure up the idea that there is an outer reality but can’t actually investigate or test it.

A related objection is we have no idea what sort of activities civilizations in a hypothetical outer universe would engage in, so even if computers powerful enough to simulate our current universe are possible in some outer universe, will creating simulations of our currrent reality be something that is done?

Together, these points establish the simulation hypothesis as having roughly the same logical status as debating how many angels can fit on the head of a pin or what would happen if Superman and Cyclops fired their laser eyes at each other: it is speculation about the properties of things that can’t be disproven or shown to exist.

I find it odd that these presumed creators of the simulation we find ourselves in have left no trace that it is in fact a simulation and everything we observe seems indicative that reality is what it is. Give us a sign, dammit! The arguments one sometimes hears for this lack of evidence (“only when we reach a certain stage of technical advancement will we be able to detect the simulation”) remind me of other unfalsifiable explanations that conspiracy theorists invent: one can always make up reasons for why the thing you believe doesn’t have any observable evidence (or why observations contradict your belief).

But forget all that. We have no need to resort to outer universes simulating our current universe to explain reality, so why introduce that? Let’s all just stop there and get back to (what I sure hope is) reality.

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