The Simulation Argument again

Nick Bostrom has argued that given some plausible assumptions, we should believe that we are not humans but rather conscious computer simulations of humans (Bostrom 2003). I will offer a new way of thinking about Bostrom's Simulation Argument. Bostrom envisages post-humans who create conscious minds on com puters. The post-humans use their vast computing power to implement programming that ensures that 'the computational processes of a human brain are structurally replicated in suitably fine-grained detail', in a way that 'would suffice for the generation of subjective experiences' (Bostrom 2003: 244). Brian Weatherson calls these non-human, computer-generated minds Sims (Weatherson 2003). Sims have experiences which represent the Sims to be normal, embodied humans living in a Sim-free 21st century world. The post-humans thus run ancestor simulations within the artifi cially created, computer-instantiated minds of the Sims. Here is how Weatherson sketches the Simulation Argument: since (1) 'the percentage of human-like agents that are Sims' (i.e. the number of Sims divided by the number of Sims plus humans) is 'far above 50 per cent', and since (2) 'we don't have any specific evidence that tells on whether we are a Sim or a human', we should believe that we are Sims, not humans (Weatherson 2003: 425). Says Bostrom: 'One's credence in the hypothesis that one is in a simulation should be close to unity', given the way in which the human like Sims vastly outnumber normal humans (Bostrom 2003: 249). It is worth noting that one reason why Bostrom thinks that the number of Sims will vastly outstrip the number of humans is that Sims 'will run their own ancestor-simulations on powerful computers they build in their simu lated universe' (Bostrom 2003: 253). The computers in question will be 'virtual machines' which can be 'stacked': 'it is possible to simulate one machine simulating another machine, and so on, in arbitrarily many steps of iteration' (Bostrom 2003: 253). However, since a Sim cannot really build a computer he merely seems to build one within his simulation it follows that he cannot really create another human-like Sim mind that is instanti ated in the programming of a real computer that he really builds. The Sims cannot really create other Sims. The idea that 'stacked virtual machines' can give rise to more and more conscious Sims seems to be just a confusion.1