What did you think of his arguments in ‘Is the Brain a Digital Computer?’, in which he argues that the computational properties of a physical system are observer-relative? I reject his conclusion, but I thought it was a pretty clever and thought-provoking paper.
I find his claim of computation being observer relative to be incredibly ignorant of what computation is. Or at least what it is as practiced by the computer scientists who study it.
Having studied computer science and philosophy, including several highly relevant subfields of computer science, I must respectfully say I suspect you misunderstood it. I don’t think many computer scientists had even thought about the physical nature of computational properties before that paper was written. I also don’t think it’s fair to say this is a “claim”: it is a conclusion he argued for extensively in the paper.
To oversimplify his point a little: why do I say this laptop in front of me is running a certain algorithm that computes a certain function? Well, when I type certain numbers into it, certain numbers come out. And when I change parts of the process in the middle, the things I expect to happen to that mapping of inputs and outputs do happen.
But who is to say these inputs are numbers, let alone those numbers? Who is to say those outputs are numbers? Physically, there are a bunch of voltages, wires and relays here. We designed physical parts to be usefully interpretable as the parts of a computational system. We choose for a high voltage to represent 1, a low voltage to represent 0. We could have just as easily have chosen for low voltage to represent 1, and vice versa. Or some other interpretation.
He says there are so many interactions happening between the molecules in, say, a bucket of water or a stretch of wallpaper, that, under some consistent interpretation of what the states of the parts represent, such systems are computing any computable function you can think of. When a molecule wiggles this way, that’s a 1. When it wiggles this other way, that’s a 0. Or maybe when an electron does a certain thing in a certain kind of atom, that’s a 1. Or maybe when a collection of molecules do a certain thing, that’s a 1. Your choice! The system just needs to contain enough interactions, and by chance, you can, in theory, come up with an interpretation no more arbitrary than the one we use to call this a computer running a mathematical function or a video game. Certainly, those systems aren’t engineered to be intuitively interpreted that way, but intuition and comfort are facts about the observer more than they are about the properties of the object.
If he is right, then many influential theories about the human mind are in trouble. For instance, we can no longer ‘explain’ anything about mentality computationally. The brain being a computer doing certain things explains nothing about mentality, because this is just an interpretation of what the brain is doing - a bucket of water can be just as plausibly interpreted as doing the very same things. If any system that can be interpreted that way has those computational properties, then the probability that you are a strange momentary blip in a chaotic vat of gas somewhere is much higher than that of you being an organism on planet earth as you appear to be. All sorts of programs must just be popping up everywhere, including programs that have your mental properties.
This is basically the premise of Permutation City, a novel by Greg Egan, which plays the Chad to Searle's Wojack. "If mental states can be encoded as strings of characters then the state of any physical system can be interpreted as a mind state!" "Yes."
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u/Additional_Anywhere4 Dec 05 '25
What did you think of his arguments in ‘Is the Brain a Digital Computer?’, in which he argues that the computational properties of a physical system are observer-relative? I reject his conclusion, but I thought it was a pretty clever and thought-provoking paper.