The Ghost in the Quantum Turing Machine

TL;DR

This paper explores the concept of 'Knightian freedom'—a form of physical unpredictability beyond probability—in the context of quantum mechanics, free will, and cosmology, proposing a novel perspective on causation and time.

Contribution

It introduces a new conceptual framework linking physical unpredictability with free will, examining boundary conditions and their implications for quantum mechanics and cosmology.

Findings

Identifies conceptual problems in linking free will to physical laws.

Connects ideas from quantum mechanics, cosmology, and philosophy to explore unpredictability.

Suggests empirical questions for neuroscience and physics related to free will.

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.