Consider the hypothesis that you are a disembodied brain floating in a vat of nutrient fluids. This brain is connected to a supercomputer whose program produces electrical impulses that stimulate the brain in just the way that normal brains are stimulated as a result of perceiving external objects in the normal way. (The movie ‘The Matrix’ depicts embodied brains which are so stimulated, while their bodies float in a vats.) If you are a brain in a vat, then you have experiences that are qualitatively indistinguishable from those of a normal perceiver. If you come to believe, on the basis of your computer-induced experiences, that you are looking at at tree, then you are sadly mistaken.I would argue that while this comparison immediately leaps to mind, the real problem raised by the Matrix is much deeper. The brain-in-a-vat Gedankenexperiment implicitly assumes both that there is a real world, and that the computer-generated illusion isn’t it. In the Matrix films, however, this isn’t quite so straightforward.
Most of the simulated worlds we’re familiar with mimic reality at a very high level of emergence. Physics engines used in video games, for instance, copy the effects of Newtonian physics with macroscopic objects treated as primitives. But in the real world, the behavior of macroscopic objects emerges as a consequence of the crowd behavior of microscopic objects. Since the physics engine does not simulate these, it must substitute other causes to reach the same effect.
Take, for instance, the fact that two solid objects which collide will bounce away from one another rather than pass through each other. In the real world, this will occur because the particles which make up the solids will electrically repel each other; in a physics engine, this effect must be created with explicit collision detection and response rules.
But what if our physics engines had a great deal more computing power at their disposal, and simulated physics at the microscale, allowing macroscopic effects to emerge? In such a situation, the artificiality of the physical effects is less clear. They are not explicitly created by the programmer, but rather appear as a result of the same processes by which they come about in real life. As artificial intelligence researcher Steve Grand writes in his book Creation:
A computer simulation of an atom is not really an atom.... But if you make some molecules by combining those simulated atoms, it is not the molecules’ fault that their substrate is a sham; I think they will, in a very real sense, actually be molecules. ... the molecules made from it are second-order simulations because they are made not by combining computer instructions but by combining simulated objects.Suppose we were to take this to its logical conclusion and posit a simulation based on the still-undiscovered Grand Unified Theory of physics, that is, a perfect physics engine from which even the behavior of the tiniest particles emerged from underlying rules rather than being directly simulated.
If we found ourselves in such a simulation, there is no way we could ever find it out; indeed, there is no way we can state with confidence that we are not. We don’t know anything about the nature of the ultimate substrate of this world. It could be a computer, the mind of God, or turtles all the way down. Yet this is the world which we refer to as “real.” I think we’re justified in referring to it as such, but in so doing we have to accept that being real does not necessarily exclude the possibility of being a computer simulation.
Although its portrayal is not entirely consistent, the fidelity of physical behaviors in the Matrix suggest that it’s just such a perfect simulation. The human occupants of the Matrix are shown to be aliens to that world. But it can never be entirely clear that the “real world” to which they escape is less of a simulation than the one they left, or that the natural inhabitants of the Matrix—the programs—aren’t less flesh-and-blood than their jacked-in counterparts. Indeed, both of these conclusions are hinted at in the second and third films.
