The Brain in a Vat – Your brain could be attached to a supercomputer so that your everyday experiences are perfectly simulated—even though “you” are just a brain attached to a computer. How do you know reality is not like this? You don’t. Four hundred years ago Rene Descartes explored similar themes—that an evil demon might be deceiving us about everything we see and think. Can we offer any evidence against such a scenario? Before considering this question let us consider another unusual possibility.
Subjective Idealism – When you “see” a tree what you experience are sense-data (colors, patterns, sounds, etc.). But why assume there is a tree, external to you, that provides this sense-data? Why not just assume there are only ideas or experiences within your mind, and no physical phenomenon at all. This conclusion was embraced by the philosopher George Berkeley: “reality is constituted entirely of minds and their ideas.” The basic objection to idealism is that our experience suggests there is an external world. Berkeley assumed that his god was always perceiving the universe thereby making it real.
Do We Live in the Matrix? – There could be evidence for this view. For example, we might wake up in a hospital and see a white-tinged background. But even if we had this experience we might conclude we’ve gone crazy. And we have no evidence that we live in a simulated realities or that subjective idealism is true. (There are good arguments that we live in a simulation.) But are there any reasons to reject the view that we live in a matrix?
To answer this question let us return to Descartes who argued:
- An evil demon might be deceiving me about empirical and mathematical knowledge. But if I am being deceived, I must exist, since I must be to be deceived.
- If I have experiences I must exist. Hence “I think, therefore I am.”
- The idea of a god stands out, the idea of a perfect being which must be.
- Since we exist and god exists and god isn’t a deceiver, then the external world exists.
- Thus, our senses and reason are reliable.
Problems – Even if there are gods and they gave us senses and reason to understand the world, why do they sometimes deceive us? Descartes says it is our fault when our faculties deceive us, because we often employ them carelessly, or others try to deceive us. But this isn’t very convincing. Furthermore, Descartes’ argument is circular: reasoning is trustworthy because god made it that way, and we know that god exists because its reasonable. So he hasn’t satisfactorily demonstrated that we can know anything with certainty. For all we know we may still live in a simulated reality.
Direct Realism – We still haven’t explained why a belief in a physical world is more reasonable than belief in the matrix-like scenario. But maybe this isn’t a problem. Consider how sense perception works. We look at something, have an experience, and then make an inference about the external world. But maybe this is all wrong—maybe we don’t infer trees, we see trees! Thus common sense answers the problem of how we know the world—we perceive it, rather than perceiving some data and then making an inference. This view is known as direct realism.
Problems – 1) Direct realism is consistent with idealism, brain in vat, evil demon, etc.; 2) direct realism doesn’t fit with what we know about the complicated ways brains process information and sense-data; 3)modern science confirms that sense experience is not a passive process, but an active one involving the brain; and 4) we assume a physical world primarily because we have inherited the ways of processing information that contributed to the survival of our ancestors. So while our perceptual system is useful, it is also full of gaps, and with different brains we would see things differently.
Natural theory – We could say that we see trees and then have an experience which causes the belief in an independently existing tree. This is sometimes called the natural theory or indirect realism. It says that we don’t directly experience a tree, and it assumes both the existence of an external world and senses that give reliable knowledge about the world. But while we might believe the natural theory, we haven’t shown that any of the other possibilities are mistaken. For all we know we do live in a computer simulation.
The Simulation Argument – In fact we may already be living in a computer simulation. The Oxford philosopher and futurist Nick Bostrom argues that advanced civilizations may have created computer simulations containing individuals with artificial intelligence and we might unknowingly be in such a simulation. Bostrom concludes that one of the following must be the case: civilizations never have the technology to run simulations; they have the technology but decided not to use it; or we almost certainly live in a simulation.
Conclusion – In the end I am agnostic about whether or not we live in a simulation.