The Diagonal Argument Strikes Again: Why Physical Systems Can Never Be Sure

Chalmers has described the meta-problem of consciousness as the problem of understanding how and why we come to believe that we are conscious. Here we show that the meta-problem of consciousness is intimately related to another problem; the meta-problem of existence, or the problem of understanding how and why we come to believe that we exist. This problem is shown to lead to a version of Russell's paradox which makes it impossible for any physical system ever to be sure that it exists. The problem is illustrated by a thought experiment, the "sleepwalker paradox", which shows that no physical system can ever be sure that it is not in a dreamless sleep.