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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