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Living in a vat

Ever since the accident, Brian had lived in a vat. His body was crushed, but quick work by the surgeons had managed to salvage his brain. This procedure was now carried out whenever possible, so that the brain could be put back into a body once a suitable donor had been found.

But because fewer brains than bodies terminally fail, the waiting list for new bodies had got intolerably long. To destroy the brains, however, was deemed ethically unacceptable. The solution came in the form of a remarkable supercomputer from China, Mai Trikks. Through electrodes attached to the brain, the computer could feed the brain stimuli which gave it the illusion that it was in a living body, inhabiting the real world.

In Brian's case, that meant he woke up one day in a hospital bed to be told about the accident and the successful body transplant. He then went on to live a normal life. All the time, however, he was really no more than his old brain, kept alive in a vat, wired up to a computer. Brian had no more or less reason to think he was living in the real world than you or I. How could he – or we – ever know differently?

The possibility that we are brains in vats provided the premise for the hit science fiction movie The Matrix. In that film, the hero, Neo, played by Keanu Reeves, was spared the indignity of having no body, but his situation was essentially the same as Brian's. He thought he was living in the real world when, in fact, his brain was simply being fed information to present that illusion. Really, he was in a pod, immersed in a kind of amniotic fluid. The sceptical doubt that we might be victims of such a whole-scale illusion is much older. The allegory of Plato's cave is an early precursor, as are the systematic doubts of Descartes, who wondered if we could be dreaming or deceived by a powerful demon.

What is neat about the brain-in-a-vat idea, however, is its plausibility. It certainly seems to be scientifically possible, which makes it more credible than a spooky demon deceiver.

Indeed, a recent argument has even suggested that it is over- whelmingly probable that we are living in a virtual reality environment, not perhaps as brains in vats, but as artificially created intelligences. The argument is that, given time, we or another civilisation will almost certainly be able to create artificial intelligences and virtual-reality environments for them to live in. Further, because these simulated worlds do not require the huge amount of natural resources to keep them going that biological organisms do, there is almost no limit to how many such environments could be created. There could be the equivalent of an entire planet Earth 'living' in one desktop computer of the future. If all this is possible, we have only to do the maths to see that it is probable we are in one such simulation. Let us say that over the whole course of human history, for every human being that ever lives, there are another nine that are the creation of computer simulations. Both the simulations and the humans would believe that they are biological organisms. But 90 per cent of them would be wrong. And since we cannot know if we are simulations or real beings, there is a 90 per cent chance that we are wrong to think we are the latter. In other words, it is much more probable that we are living in something like the Matrix than it is that we are walking the real Earth.

Most people sense something fishy about the argument. But maybe that is simply because its conclusion is too startling. The question we need to ask is not whether it sounds incredible, but whether there is anything wrong with its logic. And identifying its flaws is a very difficult, if not impossible, task.

from The Pig Who Wants to be Eaten by Juian Baggini (page 151)

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