Thursday, June 6, 2013

Scott Aaronson's "The Ghost in the Quantum Turing Machine"

Scott Aaronson recently uploaded a mind-boggling paper, full of challenging ideas regarding free-will, quantum mechanics and computing, philosophical big questions, neuroscience, and many other hot topics. The title is The Ghost in the Quantum Turing Machine, and will be a chapter in the book The Once and Future Turing, edited by S. Barry Cooper and Andrew Hodges, 2013.

His paper is like a storm of puzzle pieces, which fit together perfectly in an amazing tapestry, centered around his idea of Knightian freedom.

Here is the abstract
In honor of Alan Turing's hundredth birthday, I unwisely set out some thoughts about one of Turing's obsessions throughout his life, the question of physics and free will. I focus relatively narrowly on a notion that I call "Knightian freedom": a certain kind of in-principle physical unpredictability that goes beyond probabilistic unpredictability. Other, more metaphysical aspects of free will I regard as possibly outside the scope of science. I examine a viewpoint, suggested independently by Carl Hoefer, Cristi Stoica, and even Turing himself, that tries to find scope for "freedom" in the universe's boundary conditions rather than in the dynamical laws. Taking this viewpoint seriously leads to many interesting conceptual problems. I investigate how far one can go toward solving those problems, and along the way, encounter (among other things) the No-Cloning Theorem, the measurement problem, decoherence, chaos, the arrow of time, the holographic principle, Newcomb's paradox, Boltzmann brains, algorithmic information theory, and the Common Prior Assumption. I also compare the viewpoint explored here to the more radical speculations of Roger Penrose. The result of all this is an unusual perspective on time, quantum mechanics, and causation, of which I myself remain skeptical, but which has several appealing features. Among other things, it suggests interesting empirical questions in neuroscience, physics, and cosmology; and takes a millennia-old philosophical debate into some underexplored territory.

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