I used to have this fantasy about being able to predict the future by entering all the relevant data about the real world, down to the location of each atom, into a supercomputer and letting that supercomputer simply run a simulation of the world at a rate faster than actual time. My inner materialist loved the idea of every geological force, weather system, human brain and every therefore manifestation of the emergent property we call a “soul” being predicted (something about my needing to take the stuffing out of humanity as a teenager), and I believed that doing this with the power of computing was eminently plausible save for our lack of complete data. I now realize that it is impossible. No, not because I’ve stopped being a materialist.
Any computer used to run a complete simulation of the real world must be at least as big as the system that it will be used to simulate. That is, a complete simulation of an amoeba would require at least an amoeba-sized computer, a complete simulation of a human would require at least a human-sized computer, and a complete simulation of a planet would require a planet-sized computer, etc. This is for a reason that is a “bit” obvious once you come to see it, as I did sometime during my undergrad years (if my memory of conversations over AOL Instant Messenger serves). Data is instantiated in computer memory in chips as 1s and 0s, or bits, which have mathematical operations performed on them which in aggregate give rise to more complex operations, everything from blogging to Microsoft Flight Simulator. At the moment, each of those bits needs at minimum a single atom with a charge to represent its value (the details of the bleeding edge of computer memory are quite fuzzy to me; replace “atom” with “quantum particle” in this argument as you see fit). Any atom in a simulated universe would need great amounts of bits to represent its various properties (number of neutrons, location(s), plum pudding viscosity, etc.), and thus many atoms of real-world silicon would be a minimum to represent a single simulated atom. Because all matter is composed of particles that would need at least that number of particles of computing hardware to simulate them, hardware must always be at least as physically big as the physical system that it simulates. So much for running a predictive version of Grays Sports Almanac on my Windows computer.
But maybe not all that information is needed. Maybe not all aspects of the system need to be accurately represented in the simulation for the result to be close – the number of neutrinos flying through the Milky Way surely can’t have that much to do with whether Leicester beats Arsenal 2-1 or 2-0. But consider that that game takes place in a universe where neutrinos definitely exist and people know and talk about them. Some proportion of viewers, players, or advertisers are surely affected by the existence of scientific research being done in the city (Leicester and London are both home to renowned universities) where they live, even if indirectly – universities are huge employers with large real estate footprints. Seen in the broader picture, the existence of neutrinos seems like a variable actually capable of affecting the outcome of a soccer match. Even a single sporting event isn’t really a closed system – consider how directly they are affected by weather. And of course the types of simulated realities that are en vogue recently thanks to Black Mirror are earth-like or at least have environments capable of fooling complete human simulacra, which means that the humans in them need referents for the things that they talked about when they were still flesh and blood – can you imagine a physicist being confined in a San Junipero happily if the rules of atomic motion are not part of the virtual world? What would you do for fun when the 80s nostalgia wears off?
It’s an open question whether a simulated mind deserves moral consideration even if it has the subatomic workings of its nervous system simplified in order to make it run on a smartphone. The point I mean to make is just that it’s impossible to have a completely simulated anything without building a computer of at least that physical size in the real world.