I’ve been traveling this past week (in Israel and the French Riviera), heavily distracted by real life from my blogging career. But by popular request, let me now provide a link to my very first post-tenure publication: The Ghost in the Quantum Turing Machine.
Here’s 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.
See here (and also here) for interesting discussions over on Less Wrong. I welcome further discussion in the comments section of this post, and
will jump in myself after a few days to address questions (update: eh, already have). There are three reasons for the self-imposed delay: first, general busyness. Second, inspired by the McGeoch affair, I’m trying out a new experiment, in which I strive not to be on such an emotional hair-trigger about the comments people leave on my blog. And third, based on past experience, I anticipate comments like the following:
“Hey Scott, I didn’t have time to read this 85-page essay that you labored over for two years. So, can you please just summarize your argument in the space of a blog comment? Also, based on the other comments here, I have an objection that I’m sure never occurred to you. Oh, wait, just now scanning the table of contents…”
So, I decided to leave some time for people to RTFM (Read The Free-Will Manuscript) before I entered the fray.
For now, just one remark: some people might wonder whether this essay marks a new “research direction” for me. While it’s difficult to predict the future (even probabilistically 🙂 ), I can say that my own motivations were exactly the opposite: I wanted to set out my thoughts about various mammoth philosophical issues once and for all, so that then I could get back to complexity, quantum computing, and just general complaining about the state of the world.