Dear Colleagues,Science & Ultimate Reality
In a famous lecture titled 'There's plenty of room at the bottom,' delivered
at the Massachusetts Institute of Technology in 1981, Richard Feynman
outlined a vision of harnessing quantum processes to compute. It fell to
David Deutsch of Oxford University to flesh out Feynman's ideas and place
them on a rigorous footing. Ten years later, the race to build a functioning
quantum computer was engaging the attention of some of the world's finest
physicists, and attracting significant sums of public money. Though the
technological challenges to realizing this practical goal remain
considerable, quantum information processing has now blossomed into a
subject in its own right.
Deutsch himself was primarily concerned about the conceptual foundations of
quantum computation. His trailblazing paper addressed the issue of whether a
quantum Turing machine made computational sense, and explored the
ramifications for the nature of reality in a world that at rock bottom obeys
quantum laws. Indeed, he even applied his investigation of the nature of
reality that flows from these ideas to the subject of time travel.
It is certainly fitting that Deutsch's paper revisits these deep conceptual
issues in a meeting devoted to John Wheeler. A summary appears below.
Paul Davies
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Title: It from Qubit
Author: David Deutsch
Summary:
Of John Wheeler's 'Really Big Questions', the one on which most progress has
been made is it from bit? - does information play a significant role at the
foundations of physics? It is perhaps less ambitious than some of the other
Questions, such as how come existence?, because it does not inherently
require a metaphysical answer. It does not even require the discovery of new
laws of nature - unlike, say, why the quantum? There is room for hope that
it might be at least partly answered through a better understanding of the
laws as we currently know them, particularly those of quantum physics. And
indeed, this is what has happened: the better understanding is called the
quantum theory of computation.
In this article I shall explore how quantum theory might have been conceived
if it from bit had been a motivation from the outset. No one will ever
derive it (the nature of the quantum world) purely from bit (the idea that
information plays a significant role at the foundations of physics). But we
can do the next best thing: we can start from the qubit.
It then turns out that the quantum theory of computation isn't just the key
to a new technology, nor even just a new branch of quantum physics. Thanks
to the Turing Principle (of the universality of computation), it is quantum
physics. It is a simpler and more general way of formulating quantum theory,
which has the potential to revolutionise the teaching of the subject as well
as providing powerful theoretical tools for research and philosophical
understanding.
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