Book review of David Deutsch

David Deutsch:
THE FABRIC OF REALITY (Penguin, 1997)

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In this book the Israeli physicist David Deutsch advances a theory that aims at unifying theory of evolution, theory of computation, theory of knowledge (epistemology), and theory of matter (quantum theory).
Deutsch starts out by attacking two dominant positions in philosophy of science: instrumentalism (that scientific theories do not explain reality, they are simply instruments for making predictions, and, as long as two theories both make valid predictions, neither can be considered better than the other, a theory simply predicts the outcome of observations, does not explain reality, the explanation is something that we attach to the theory in order to make it easier to remember) and positivism (only statements about predicting observations are meaninful).
Deutsch disagrees: scientific knowledge consists of explanations, not of facts or of predictions of facts. Deutsch believes that the explanation is as important as the predictions: experiments are the method that science uses to verify explanations, and predictions are what discriminates between theories. Predictions have a practical purpose, but they are not the reason we do science. Proof is that there is an infinite number of possible theories that we will never even test: they provide no explanation of reality and therefore we are not interested in testing whether they are true.
Then he attacks both reductionists (the explanation of a system is in terms of its components) and holists (the only legitimate explanation is in terms of the whole system). Again, Deutsch believes in explanations, higher-level explanations that can provide adequate answers to "why" questions: why is a specific atom of copper on the nose of the statue of Churchill? Not because the dynamic equations of the universe predict this and that, and not because of the story of that particle, but because Churchill was a famous person, and famous people are rewarded with statues, and statues are built of bronze, and bronze is made of copper. The reductionists believe that the rules governing elementary particles (the base of the reductionist hierarchy) explain everything but they do not provide the kind of answer that we would call "explanation".
Reductionists also believe that an explanation must explain how later events are caused from earlier events. This is also flowed: for example, we have theories of time, which, of course, can't possibly be based on "earlier events" of time.
Deutsch claims that we need four strands of science to undestand reality: quantum theory, theory of evolution, epistemology (theory of knowledge), and theory of computation. The combined theory is a theory of everything.
Deutsch views the technology of virtual reality as an expression of the most important power of computers: to simulate our world. He formulates the "Turing principle": it is possible to build a virtual-reality system that can simulate any environment which can exist in nature. Virtual reality is a "physical embodiment of theories about an environment". So defined, virtual reality is an important property of nature: it is life itself. Genes embody knowledge about their econological niche. An organism is merely the immediate environment which copies the replicators (the organism's genes). The genes, on the other hand, represent the survival of knowledge, knowledge about the environment. An organism is a virtual-reality rendering of the genes. Therefore, living processes and virtual-reality rendering are the same kind of process. Thus virtual reality is not only a property of computers buy a general property of nature, the very essence of life itself.
That said, Deutsch proposes a new type of computation. Classical computers conform to classical Physics. He proposes to build quantum computers that perform "quantum computation". Such computers would be able, through phenomena of quantum interference, to perform a new class of computations which are not possible with today's computers. "Classical" computation is actually an oxymoron, as computation has always been "quantisized" (computation works with bits and bytes, not with continuous values).
Based on the odd outcomes of quantum experiments, Deutsch decides that our universe cannot possibly constitute the whole of reality, it can only be part of a "multiverse" of parallel universes. Deutsch's multiverse is not a mere collection of parallel universes, with a single flow of time. He highlights the contradiction of assuming an external, superior time in which all spacetimes flow. This is still a classical view of the world. Deutsch's manyverse is instead a collection of moments. There is no such a thing as the "flow of time". Each "moment" is a universe of the manyverse. Each moment exists forever, it does not flow from a previous moment to a following one. Time does not flow because time is simply a collection of universes. We exist in multiple versions, in universes called "moments". Each version of us is indirectly aware of the others because the various universes are linked together by the same physical laws, and causality provides a convenient ordering. But causality is not deterministic in the classical way: it is more like predicting than like causing. If we analyze the pieces of a jigsaw puzzle, we can predict where some of the missing pieces fall. But it would be misleding to say that our analysis of the puzzle "caused" those pieces to be where they are, although it is true that they position is "determined" by the other pieces being where they are.
Deutsch's argument that, assuming the universe is run by deterministic regular "laws of nature", a mind that can understand those laws of nature can in principle understand everything, is persuasive. However, he doesn't talk about the one feature of this universe that no science has been able to express, describe and predict with mathematical laws: human consciousness; which also happens to be the one that i'm sure about, and the one i care most about. Colin McGinn has argued convincingly that the human mind might just not be capable of understanding it, no matter what (in this book). Deutsch provides a general framework in which the human mind can understand everything that can be expressed in mathematical laws, but the doubt remains that some things will never be expressed in a formal, mathematical form.

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