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Books

The Beginning of Infinity by David Deutsch

Alistair MacFarlane finds himself in the foothills of infinity.

Everyone who is interested in the relationships between science and philosophy should read this book. Its central claim is that all progress, theoretical and practical, scientific, philosophical and cultural, results from a single human activity: a quest for good explanations.

In making such a comprehensive claim, the book necessarily covers a huge range of topics. There are three main threads. First is a coherent and comprehensive exposition of Karl Popper’s philosophy, that knowledge (ie, successful explanation) arises only from a process of conjecture and refutation. The scope here is wide-ranging and the presentation lucid, but the alternative views of most other philosophers receives very short shrift indeed. The second thread is a realist explanation of quantum theory, positing the existence of the multiverse. Deutsch is well known for his own work at Oxford on the development of quantum computers, which is seen as offering computational technology of such power and scope that it will transform our future development in hitherto unimaginable ways. From this follows the third thread, and the reason for the title of the book – the contention that the reach of good explanations is unbounded, and so our future development will be subject only to those limits imposed by scientific laws, and is otherwise potentially infinite.

Realistic Expectations

Philosophically, a realist is someone who holds that our theories are descriptions of how the world really is. Yet realist explanations of the behaviour of elementary particles face a fundamental challenge. Although electrons, for example, would seem to be simple entities – they have no internal structure – a satisfactory description of their behaviour in classical Newtonian terms, as if they were little balls, proved impossible. Theorists therefore turned to building mathematical models which could predict electron behaviour rather than explain electrons in realist terms. Instrumentalism is this view that theories are useful for explaining and predicting phenomena, rather than that they necessarly describe the world. Yet the mathematical apparatus underpinning such instrumentalism, such as Dirac’s use of infinite-dimensional Hilbert [abstract mathematical] spaces, and Feynman’s sums-over-all-possible-histories, are so powerful, and so beautiful, that the lack of a convincing realist alternative has so far not proved to be a significant handicap in the development of quantum physics and its technological applications. In fact, quantum theory in its instrumental form has provided the most successful explanation of all time, by being the most powerful of all scientific theories. But Deutsch wants a realist quantum theory.

Any realist explanation of the physical world at the submolecular, quantum scale, must involve some physical manifestation of infinity. Deutsch tackles this need head on by using the concept of a real multiverse. According to him we live in one out of an unfathomable number of parallel universes, which interact at the quantum level. In this multiverse, the idea of individual photon and electron interactions are replaced by an infinite number of interacting instances which collectively can account for all possible forms of behaviour. What many will find very hard to accept is that this idea of an infinite number of alternatives for any given quantum event may provide both the simplest explanation of quantum phenomena, and a first glimpse of a new vision of reality.

Most attempts to make quantum ideas accessible seek ways of making unrealistic instrumental approaches graspable by using exotic metaphors. There is none of that here – no zillions of little clocks whizzing about, or ghostly superpositions of alive and dead cats – just simple, clear arguments demanding a philosophical consideration, and a philosophical response.

Computing Infinity

In quantum computation, the key concept is parallelism – the simultaneous execution on one device of many different computations using the alternative possible states of quanta which quantum mechanics relies upon. If achieved as a reliable technology, this would mean that extremely complex computations which currently take an impractically long time on conventional computers could be executed in a vastly shorter time. The philosophical implications are as far-reaching as the technological. With quantum computing, quantum theory’s many current instrumentalist interpretations, such as the popular Copenhagen interpretation, could come to be seen as what Deutsch calls bad explanations. So if quantum computing becomes an everyday event, the multiverse concept may become widely accepted as a realist explanation. What could be more exciting than that?

When Deutsch hits his stride in contemplating our infinite future development, conjectures proliferate but refutations fade away. There is much of great philosophical interest in this part of the book, and very much that is arguable. For example, many would question whether it is conceivable, or desirable, for our physical bodies to be replaced by computer simulations which would make ‘us’ immortal. Some have conjectured that what makes us what we are are the facts of our physical embodiment and our mortality. Scientists should be reminded that knowledge is not wisdom, and the more we have of one, the greater our need for the other. The more science develops, the more we will need a humanistic ethical philosophy to complement it. However our world may be transformed, we will have to learn how best to live there.

Sir Alistair MacFarlane is a former Vice-President of the Royal Society and a retired university Vice-Chancellor. He gives a Brief Life of Bertrand Russell in this issue.

• The Beginning of Infinity: Explanations That Transform the World, David Deutsch, Allan Lane, 2012, 496 pages, £10.99 pb, ISBN 978-0140278163.

The Beginning of Infinity

A psychedelic reflection on The Beginning of Infinity.