Brain in a vat and similar hypothesis

This essay will discuss the "brain in a vat" and similar hypothesis (such as computer simulations and the idea that we are dreaming), and discuss whether it is something that people should worry about. It will firstly explain what these hypotheses are, before exploring possible problems and advantages of such scenarios. It will then examine the plausibility of them (using Ockham's razor, and by examining the problem of reference) and the actual impact on ones life if any of them are actually true. The essay concludes that if we cannot tell the difference, and have no knowledge, then it does not matter whether we are in a simulated environment or not.

The basic conception of a "brain in a vat" is that an individual is no more than a mind that is being stimulated by an external force, and that the world, as the individual understands it, does not exist, except as stimulations in that individuals mind (or perhaps in a computer simulation). These ideas are skeptical hypothesis, the aim of which is to raise doubt about the existence of anything. If you do not know that you are not a brain in a vat, then you can not know anything about the external world.1 This conception of limited knowledge is not a new idea and traces back at least to Descartes.

Descartes imagined an evil demon that employ[ed] all his industry in misleading [him]2. This demon could not, however, mislead Descartes about the existence of himself. Which lead to Descartes to the conclusion that I think, therefore I am.3 He then went on to 'disprove' his own hypothesis (that a demon is misleading Descartes), based on proofs of the existence of God.4

Descartes came to his idea that an evil demon might be manipulating his world, from thoughts on dreaming and hallucinations.5 Other philosophers have considered the possibility that we are dreaming rather then living a real life. Chuang Tzu after a night in which he dreamed that he was a butterfly, asked, if he was in fact a butterfly dreaming that it was Chuang Tzu.6 Dreaming is different to other skeptical hypotheses as it does not include an external, potentially 'malevolent', actor. However, like other skeptical hypotheses it is not possible for (most) people to realize that they are dreaming.

A more modern variant on Descartes idea is that an individual is actually a brain in a vat that is being stimulated by electronic impulses from a giant supercomputer. This computer is able to create a 'virtual reality' based on impulses from the brain. If the brain attempts to move an arm, the computer sends back impulses that make it seem as if the arm has been moved.

However, there are other ideas that conceive of not just one individual being 'deceived', but rather everyone. These have come more into prominence since the creation of computers. Computer simulations have been used to simulate various things, from cities to weather to life itself.7 These have given rise to thoughts that perhaps people are not actually living in a real world, but rather living in a simulation. Variations on this include everyone being in vats connected up to the same computer.

Science fiction such as William Gibson's book Necromancer discusses the idea of computer simulations that are indistinguishable from real life. One variant has the body of a person still alive while it is simply their mind that is occupying the virtual reality, and another type where it is the mind alone that exists, inside the simulation, the body having died.8

Because there is so much thought given to such possibilities, it is not surprising that some philosophers have problems with living in such scenarios. Some philosophers feel that a simulated life is un-authentic, that real life is somehow 'better'.9 In his book Anarchy, State and Utopia, Robert Nozick mentions that "the experience machine" is not as 'real' as real life, that experiences in the machine are not connected with actual events or actions.10 He does not, however, give a reason for this beyond that a person in the machine is not actually doing what is going on in the machine (though that person is experiencing without knowledge that what they are experiencing is not real, and thus for the person they are doing that activity).

This and similar objections are merely these philosophers valuing an 'objective' experience beyond the subjective experience of the individual concerned. If an individual cannot have knowledge that they are not part of a simulation, then it does not matter to them what the 'objective' truth is, as it has no impact on them.

Just like there are potential problems with living in a 'fake' world, there are advantages in not living in the real world. These come down to the idea that the virtual world is potentially 'better' then the real one. Even if the experiences are not 'real' objectively; to the person experiencing them they are real and that is all that matters to that person. The only other advantage is that in certain scenarios (e.g. computer simulations), life might be longer then otherwise. However, in this world, it does not appear that this is the case. Though in most cases the person is unable to choice if anymore then anyone else if they are going to have a good life.

The plausibility of these scenarios, regardless of desirability or otherwise, is brought into question when one considers three arguments against them. The first is the use of Ockham's razor. While it is not apparently found in any of William of Ockham's writings it bears his name. The razor states that Entities are not to be multiplied without necessity.11 This means that given two equally valid hypotheses we should select the simplest one, the one that has the fewer assumptions.

A simple example of this is that the Earth is the center of the universe, or it is not. For the Earth to be at the center of the universe, there is the requirement of very complex mathematics for the planets to orbit the Earth. For the alternative, that the Earth and other planets circles the Sun, the mathematics are much simpler (and it just happens to fit with observed facts). Similarly for aliens to have visited Earth requires many assumptions, such as they have very advanced technology (possibly enabling them to travel faster then the speed of light), are interested in Earth and so on. The alternative, that aliens do not visit Earth* can be explained by stating that some people have seen things that they simply think are aliens or that they are in an altered state of consciousness (e.g. drunk or under the influence of an hallucinogenic drug), or that people are simply lying. All these are much more plausible compared to the first set of assumptions.

As with God, fairies and aliens, there is no evidence that an individual or humans as a whole are being feed a simulated existence. This is due to the nature of the problem. So faced with two alternatives: one humans are part of a computer simulation (or an individual is a brain in a vat); or two, that they are not, the first requires an added assumption that the second does not, therefore the second should be preferred. There is no evidence that we are part of a simulation (due to the nature of the problem) and we should rationally choose the simpler of the two alternatives. That is, we are not living in a simulation and are not merely a brain in a vat.

Another argument is that of reference. In none of these scenarios is it possible to tell if you are in one of them, from the inside (which is the only reference point). Because this is the case, we cannot refer to objects or things outside the simulation. If I am a brain in a vat, then I cannot consider my self to be a brain in a vat, therefore I am not a brain in a vat (at least from my perspective). If you were living in a brain in a vat, nothing in your experience could possibly reveal that you were; for your experience is ex hypothesi identical with that of something which is not a brain in a vat.12

Ultimately it does not really matter if a person is a brain in a vat or not. It is not possible to tell from the individual who's brain is in the vat that it is the case, and in the more general case of everyone being part of a simulation there is no way for anyone to tell.

As such, while it is impossible to 'know' if you are doing something (such as reading this essay), and all your beliefs maybe false, it is impossible to 'not-know'. From your perspective anyway, you are reading the essay, and you cannot perceive yourself from another perspective.

It does not matter if we are being manipulated by an 'evil' demon or are living in a computer simulation. There is no way of knowing if we are or are not, and there is nothing we can do in either case. Worry in such cases is pointless, and discussion or thought about such matters does not directly produce anything of value.

Another argument for it not mattering is that for the universe to exist inside a supercomputer (either with humans inside it as well, or existing as 'brains in vats') requires a set of physical laws that do not exist in this universe. This is because it is not possible to simulate this universe inside it self. So even if we are living in a simulation, the laws of the universe in which the simulation exist (the 'real world') are radically different to this ('virtual') world. As such, it would not be desirable to live in the non-simulated world, even if we could.

The idea of a "brain in a vat" is not new, and while it is an interesting hypothesis, it is impossible for an individual to know if they are actually living in the 'real world' or if they are living in a simulated world. If they were living in a simulated world, they would have to treat it as the 'real world' as they would have no other reference point. While they may feel that it might not be real there is no way to show one way or the other, and nothing could be done in either case. It is also more simple, if humans are not living in a simulated world. For these reasons while it is an interesting idea to day dream about, discussion can ultimately do nothing in determining one way or the other if people are living in a 'real world' or not, and it is more likely that people are.


Dancy, Jonathan. Introduction to Contemporary Epistemology in 'Philosophy: Brains in Vats and The Evil Demon', (accessed 27/04/2006)

Gibson, William. Neuromancer. London: Grafton, 1986.

Hicke, Lance P. 'The “Brain in a Vat” Argument', The Internet Encyclopedia of Philosophy, (accessed 27/04/2006).

Nozick, Robert. Anarchy, State, And Utopia. Oxford: Basil Blackwell, 1974.

Russell, Bertrand. History of Western Philosophy. London: George Allen & Unwin Ltd, 1961.

Zipoli, Richard. 'Chuang Tzu’s Butterfly Dream', (accessed 26/04/2006)


*Ignoring whether they exist or not.

1Lance P. Hicke, 'The “Brain in a Vat” Argument', The Internet Encyclopedia of Philosophy, (accessed 27/04/2006).

2Bertrand Russell, History of Western Philosophy, (London: George Allen & Unwin Ltd, 1961), p 547


4Ibid. p 550

5Ibid. p 547

6Richard Zipoli, 'Chuang Tzu’s Butterfly Dream', (accessed 26/04/2006)

7here and there

8William Gibson, Neuromancer, (London: Grafton, 1986)

9here and there

10Robert Nozick, Anarchy, State, And Utopia, (Oxford: Basil Blackwell, 1974) pp43-45

11Russell p 462

12Jonathan Dancy, Introduction to Contemporary Epistemology p10 in 'Philosophy: Brains in Vats and The Evil Demon', (accessed 27/04/2006)

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