The Third Culture 



IT'S
A MUCH BIGGER THING THAN IT LOOKS
[11.20.00]
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. Introduction 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 handwaving 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. IT'S
A MUCH BIGGER THING THAN IT LOOKS 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. 