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Do androids dream of electric sheep? Colin Tudge in London examines definitions of consciousness and artificial intelligence.
Is the brain simply a computer, and is consciousness merely the feeling we get when we think? Or is consciousness a primary component of the universe, which the brain can latch on to, like a radio receiver?
A definitive answer will always be elusive, but scientists are making intriguing forays into the subject, and if they are not explaining consciousness, they are certainly telling us a great deal about the nature of science.
There are three points of view. The first, which can be traced back to the founder of modern computing, Alan Turing, and is embraced by the Oxford physiologist Colin Blakemore, is pragmatic. Turing pointed out that it is impossible to know whether other human beings are conscious. Because we feel conscious, we assume other people must be like us. But this can only be an inference.
But suppose we made a computer - a robot - that could make whimsical jokes and pass the sandwiches without being asked and generally behave, spontaneously, like a person. It would appear conscious - and since, in judging the consciousness of others, appearances are all we have to go on, why not assume it is conscious?
Is it reasonable to ascribe consciousness to a droll and well-mannered aunt, yet deny it in a robot that behaves like one? This dilemma prompted Brian Aldiss's Supertoys Last All Summer Long, which became Steven Spielberg's film, Artificial Intelligence: AI.
But this reasoning has the feel of the old adage: "If it looks like a duck and quacks like a duck, then it is a duck." If all you want to do is shoot ducks, then a rough-and-ready appr-aisal serves well enough. But if you seek to understand ducks and how they evolved, then you ought to know the difference between a duck and a grebe.
Turing showed that a machine's ability to compute does not depend on what it is made of. All that matters is that the parts should be arranged appropriately. Many assume that the same principle must apply to brains.
Brains are made of flesh - but, the argument goes, would function just as well if they were made of silicon chips. By the same token, consciousness is perceived simply to be an "emergent property".
If a computer was sufficiently complex, then it, too, would assume consciousness - or at least would appear to do so, which (so Turing said) is the only way to judge whether it is.
Disciples of the idea commonly invite us to indulge in a thought experiment. Suppose we replace a single neurone in the brain with a silicon chip that precisely imitates that neurone; that is, is "functionally equivalent". Would the brain still be conscious?
The answer is surely "yes". Suppose we replace 100 neurones with chips, then several billion, and so on. Can we define a point at which consciousness is lost? If not, then we would have produced an all-silicon brain that retained the consciousness of the original.
Thus we seem to have proved Turing's point: that the material of which the brain is made is irrelevant. It's the organisation that counts.
But there is a huge snag in this reasoning, one that springs from the philosophy of science. For we cannot replace a single neurone with a "functionally equivalent" microchip unless we understand the function of the original neurone. Yet complete understanding is impossible because, as the great British zoologist Sir Peter Medawar commented, science in the end is merely "the art of the soluble".
Science answers only those questions that scientists ask, and which they are technically able to investigate. But it is impossible to know which questions are worth asking unless you are already omniscient. So we can never know everything that might be relevant about a neurone or about anything else.
Thus the thought experiment falls at the first hurdle. It is impossible in theory as well as in practice to replace all the neurones of the brain with "functionally equivalent" chips, since we cannot know whether the replacement chips were functionally equivalent or not.
This leads to a line of reasoning totally at variance with Turing. Perhaps, some suggest, consciousness is not just a matter of computational complexity. Perhaps the material of which the brain is made matters very much. Perhaps only entities made of flesh (or at least of organic materials such as proteins and fats) are truly capable of consciousness.
In this vein, Oxford mathematician Roger Penrose suggested in his book, The Emperor's New Mind, that consciousness partakes of physical principles not yet understood. Certainly, there's a great deal in physics that is not understood.
Perhaps the flesh-and-blood brain has the chemistry required to invoke and partake of the novel physics required to produce consciousness, while silicon chips lack this ability?
The notion I like best, however, is even more radical. It is that the nature of consciousness and of the universe have been misconstrued.
For, until now, three main views have prevailed. One is the "dualism" of Rene Descartes, which says the universe has two components - matter and mind. The second is the modern orthodox idea - that only matter "exists", and that mind (including consciousness) is just an "epiphenomenon"; something that seems to emerge when matter is suitably organised. The third is reflected most starkly in the idealist philosophy of Bishop Berkeley; that only thought is real, and matter is an illusion. But the emerging modern view says that matter and consciousness are not separate entities, as Descartes supposed, but complementary aspects of the universe. Both exist, but neither is primary. Each is the obverse of the other, like two sides of a coin.
There is a rough analogy between this idea and Einstein's theory of relativity, which envisages space and time not as independent entities, but as aspects of the more fundamental space-time.
The ultra-modern view of consciousness is plausible, and if it is right - and there is much in quantum physics to suggest it might be - then it turns science upside down. It also re-opens channels between science and theology that might have seemed forever closed.
Colin Tudge's The Variety of Life: A survey and a celebration of all the creatures that have ever lived, is published by Oxford University Press.
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