Given the current rate of progress, it is probably only a matter of time before human technology reaches a level of sophistication such that it can create incredibly sophisticated computer simulations of human minds and of worlds for those minds to inhabit. Maintaining such simulated worlds will require relatively tiny computer resources – a single laptop of the future could be home to thousands or millions of simulated minds – so in all probability simulated minds will vastly outnumber biological ones. The quality of the simulation will be so high that the experiences of biological and simulated minds will be indistinguishable, so the latter will be totally unaware that they are simulated. But they will be wrong. We, of course, know that we are not computer-simulated minds living in a simulated world …
Or do we? That is certainly what we would think, but how could we possibly tell? How do we know that such computer expertise has not already been attained and such minds already simulated? Indeed, given the logic of the scenario outlined above, it is in fact much more likely than not that we are already living in just such a simulated world.
Of vats and virtual worlds Serious food for thought, prepared according to a recipe devised in 2003 by the Swedish philosopher Nick Bostrom. Bostrom’s simulation argument (simplified here) is not the first argument to raise the possibility that what we believe about ourselves and our world is grossly mistaken. In 1981 the US philosopher Hilary Putnam told a celebrated story of an evil scientist who removes a person’s brain and places it in a vat of nutrients, where it is connected to a super-powerful computer that gives the person – or is that the brain? – the impression that everything is perfectly normal. It sounds like a nightmare, the stuff of science fiction, but of course that is exactly what you would say if you were a brain in a vat. The point is that it is hard to see how you could know for certain that you are not, and if you cannot rule out the possibility, all the things you think you know will turn out to be false. And if that’s possible – just possible – you don’t really know anything at all, do you?
‘Every passion is mortified by it [sceptical philosophy], except the love of truth; and that passion never is, nor can be, carried to too high a degree.’
David Hume, 1748
Scenarios of the kind envisaged by Putnam and Bostrom have always been powerful weapons in the arsenal of the philosophical sceptic. As a philosophical position, scepticism sets out to challenge our claims to knowledge. We think that we know all sorts of things, but how and on what grounds can we defend those claims? Our supposed knowledge of the world is based on perceptions gained through our senses, but are not such perceptions always prone to error? Can we ever be sure that we are not hallucinating or dreaming, or that our memory is not playing tricks? If the experience of dreaming is indistinguishable from our waking experience, we can never be certain, in any particular case, that something we think to be the case is in fact the case – that what we take to be true is in fact true. There is always, it seems, the possibility that we are brains bobbing about in vats or virtual avatars in a computer-simulated reality.
The Greek sceptics Since its origins in ancient Greece, scepticism has typically developed as a strategy against forms of dogmatism that claim, in a particular area or in general, to have established a definitive view of how things stand in the world and/or in heaven. Anticipating concerns that were to re-emerge 2000 years later, Greek scepticism was motivated primarily by the seemingly unbridgeable gulf between appearance and reality – by the fact that our means of engaging with the world always leave us at one remove from truth and that it is always possible in principle to present counterexamples against any claim to knowledge. Though far from sceptical himself, Plato’s Socrates employs a probing dialectical method that seems capable of undermining any dogmatic claim made by his contemporaries, and the scepticism that could be inferred from his claim that wisdom lies in awareness of one’s own ignorance left a deep impression on his successors. The most influential sceptic, known to us only through the writings of others, was Pyrrho of Elis, who was active around 300BC. His response to the essentially provisional nature of truth-claims – to the fact that questions of knowledge could never be finally decided – was to counsel suspension of belief whence came a tranquillity that would be proof against the disappointment inevitable in the frustrated search for certainty.
From doubt to certainty? Scepticism resurfaced with particular vigour in the 15th and 16th centuries, when the first stirrings of the scientific revolution led people to question the proper basis of knowledge and the validity of theological truth. In a deep historical irony, the man who stepped forward to dispel sceptical doubts once and for all succeeded only in pushing scepticism to the centre of the stage and ensuring that its defeat would remain one of the central tasks of subsequent philosophy.
The Frenchman René Descartes was himself at the vanguard of the new science sweeping through Europe in the 17th century, and it was his ambitious plan to cast aside the tired dogmas of the medieval world and to ‘establish the sciences’ on the firmest of foundations. To this end his plan was to turn scepticism against the sceptics by adopting the most rigorous ‘method of doubt’. Not content to pick out the odd rotten apple (to use his own metaphor), he empties the barrel of beliefs completely, discarding any that are open to the slightest degree of doubt. In a final twist, he imagines an evil demon (the clear ancestor of Putnam’s brain in a vat) whose sole object is to deceive him, and so ensures that even the apparently self-evident truths of geometry and mathematics are no longer certain.
Stripped of every belief that could conceivably be doubted, Descartes desperately casts about for some foothold, some firm ground on which to rebuild the edifice of human knowledge:
‘I noticed that while I was trying to think everything false, it was necessary that I, who was thinking this, was something. And observing that this truth, ‘I am thinking, therefore I exist’ [cogito ergo sum], was so firm and sure that all the most extravagant suppositions of the sceptics were incapable of shaking it, I decided that I could accept it without scruple as the first principle of the philosophy I was seeking.’
After he has dug down to bedrock, the rebuilding phase of Descartes’s enterprise proves to be remarkably straightforward. Founded on belief in a non-deceiving God who will guarantee the veracity of our senses, the world is swiftly restored and the task of reconstructing our knowledge on a sound and sceptic-proof basis can begin. The force of Descartes’s famous cogito has been continuously debated ever since, but most of his critics, contemporary and modern, have been unconvinced by his attempt to climb out of the sceptical hole that he had so adroitly dug for himself. He had summoned up the spectre of scepticism in order to exorcize it, but he signally failed to put it to rest and left later philosophers in thrall to its spell.
the condensed idea
The scourge of dogma