Is Simulation Possible?

In “the future”, when I upload my brain into a computer (whatever that means) and delete the physical original, have I transcended into immortal existence or did I just kill myself?

That question is too hard. Let’s start with an easier one: “is strong AI possible?” Here is an argument for why it should be possible:

We don’t understand how consciousness works, exactly, but however it works, it’s based on physical processes, because the brain is a physical object. (The notion of a soul existing in some astral plane separated from physical existence is absurd.) Even if we don’t have a good theory of how cognition works, we do have a good theory of how the universe works. Forget about cognition; it’s too hard. In two years when we have desktop running at ten thousand teraflops or whatever, let’s just simulate the brain at the sub-atomic level, lepton for lepton, leprechaun for leprechaun. Then you have machine sentience.

Implicit in this argument is that simulation is possible. Obviously, simulation is possible in the sense that you can simulate things (subject to computing power, which let’s assume is not an issue, because historical trends are good and the question here is whether simulation is possible in principle); what I mean by this is whether the simulated brain is just as “real” as an actual physical brain. Or, to be even more ambitious, let’s simulate a whole universe, with planets and meadows and people running through trees hunting dinosaurs, etc. Is this universe real? Are those people real?

It’s kind of a stupid question, because if it talks like a real person and acts like a real person, then… Also, you would argue that this universe is real enough to the people inside of it–they can feel the grass between their toes and be warmed by the sun and smell spring and all of that mushy stuff. They would have no idea that their existence is a simulation.

Nevertheless, accepting that the simulated universe is real is philosophically troublesome, because where does this universe exist? It emphatically does not exist in the wires in your fifty exoflop laptop, in its hard drives or transistors. Transistor/electrical is just one way to implement a turing machine; you could use billiard balls or even just do the computations by hand with pen and paper. You could simulate using one form of a turing machine up to some time T, output the simulated state onto some other medium, and resume the computation using another form of a turing machine! The simulated people would not know the difference.

If you accept that this simulated universe exists, you must also accept the following

1. The simulated universe exists in some platonic realm. There is a one-to-one correspondence with the numbers in your computation and the states of the objects in the simulated universe (variable x corresponds to some parametre of the wave function of this electron, etc.), sure, but the simulated universe does not exist “inside” of your universe.

2. All that is required for existence in this platonic realm is a representation, which means some descriptors (the numbers in the computation) and a model for interpreting that representation (this number maps to this thing in the simulated universe). As an aside, the descriptors themselves can be instrumented through representations! There are no bits in your computer, there are electrical signals that represent 1 or 0 based on voltage. There are no bits in your harddrive, there are physical pieces of medium that represent 1 or 0 based on magnetization. There are no bits when you write down a number, there are physical marks on paper that represent 1 or 0 based on what they look like. In other words, the bit already lives in the platonic realm.

Questions for next time

1. If all that’s required for existence is the representation, is it even necessary to run the simulation? Could you just say, here are the equations my simulation would have solved (here is the algorithm my turing machine would have run), here are the initial conditions, and now the simulated universe exists? If you’re in a deterministic universe, specifying the governing equations and initial conditions determines the state at every time point already–the solution exists, even if you don’t know what it is, so what extra value does doing the computation add? How does computing the solution (i.e., doing the simulation) make the simulated universe more real? Even if you’re in a non-deterministic universe, specifying the (probabilistic) governing equations and initial conditions determines every solution that is compatible with said equations and conditions (i.e., they determine every simulated outcome that could have taken place when you run the simulation), so what extra value does doing the computation add? You’re just moving from an implicit representation (the equations + initial conditions, or equivalently the algorithm + initial state) to an explicit one (the computed descriptors at each time step, as represented by bits as represented by whatever physical system your turing machine runs on).

2. What happens when you make an error in the computation, due to e.g. hardware glitch or human error if doing it by hand?

3. Glossed over is the fact that what we have are not exact governing laws of the universe (and we may never?), all we have are models to some varying degrees of accuracy, and additionally we may lose accuracy by choosing a coarse spatial or temporal resolution or poor numerical algorithm or not having enough sigfigs in our floating point arithmetic. Does that matter?