The Third Culture

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A Talk with David Deutsch

However useful the theory [of quantum computation] as such is today and however spectacular the practical applications may be in the distant future, the really important thing is the philosophical implications — epistemological and metaphysical — and the implications for theoretical physics itself. One of the most important implications from my point of view is one that we get before we even build the first qubit [quantum bit]. The very structure of the theory already forces upon us a view of physical reality as a multiverse. Whether you call this the multiverse or 'parallel universes' or 'parallel histories', or 'many histories', or 'many minds' — there are now half a dozen or more variants of this idea — what the theory of quantum computation does is force us to revise our explanatory theories of the world, to recognize that it is a much bigger thing than it looks. I'm trying to say this in a way that is independent of 'interpretation': it's a much bigger thing than it looks.

EdgeVideo David Deutsch (5 min.)
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In 1998 Oxford physicist David Deutsch was awarded the Paul Dirac Prize "For pioneering work in quantum computation leading to the concept of a quantum computer and for contributing to the understanding of how such devices might be constructed from quantum logic gates in quantum networks."

"Quantum computing," Deutsch says, "is information processing that depends for its action on some inherently quantum property, especially superposition. Typically we would superpose a vast number of different computations potentially more than there are atoms in the universe and then bring them together by quantum interference to get a result. Other quantum computations, notably quantum cryptography, couldn't be done by classical computers even in theory."

Deutsch's work on quantum computation has led him into two important areas of research concerning (a) "the structure of the multiverse making precise what we mean by such previously hand-waving terms as 'parallel', 'universes' and 'consists of'. It turns out that the structure of the multiverse is largely determined by the flow of quantum information within it, and I am applying the techniques we used in that paper to analyse that information flow"; and (b) "a generalization of the quantum theory of computation, to allow it to describe exotic types of information flow such as we expect to exist in black holes and at the quantum gravity level. This is all in the context of my growing conviction that the quantum theory of computation is quantum theory."

According to Deutsch, one spinoff from the quantum theory of computation is that "it provides the clearest and simplest language, and mathematical formalism, for setting out quantum theory itself."

– JB

DAVID DEUTSCH'S research in quantum physics has been influential and highly acclaimed. His papers on quantum computation laid the foundations for that field, breaking new ground in the theory of computation as well as physics, and have triggered an explosion of research efforts worldwide. His work has revealed the importance of quantum effects in the physics of time travel, and he is an authority on the theory of parallel universes.

Born in Haifa, Israel, David Deutsch was educated at Cambridge and Oxford universities. After several years at the University of Texas at Austin, he returned to Oxford, where he now lives and works. He is a member of the Centre for Quantum Computation at the Clarendon Laboratory, Oxford University. He is the author of The Fabric Of Reality.

See David Deutsch's Edge Bio Page

A Talk with David Deutsch

EDGE: In what direction are you asking the most questions at the moment?

DEUTSCH: The direction of even deeper connections between physics and the theory of computation. We've got the quantum theory of computation — which, by the way, is THE theory of computation. As I always say, we have to regard the Turing theory (the traditional theory of computation) as being just the classical approximation to the real, quantum theory of computation. We already know of a few issues in theoretical physics (like the Maxwell Demon question, and the relationship of thermodynamics with statistics) which it is useful to regard as computational questions — questions about how information can or cannot be processed. What I am aiming for now is a new kind of theory, quantum constructor theory, which is the theory of what can be built, or more generally, the theory of what can be done, physically.