How many Lego bricks would it take to build a conscious, rational mind?
This may sound like an absurd question. Lego bricks don’t seem like the sort of thing that you could build a mind out of. (At least, I’m assuming that artificial intelligence researchers aren’t currently tinkering away in their state-of-the-art labs with a “Build Your Own Mind!” Lego set.) But the question shouldn’t, in principle, be absurd for a physicalist. There is a sense in which it should be a perfectly reasonable question to ask.
The Relevant Difference for Physicalism: Arrangement of Parts
The physicalist already believes that the mind is entirely made up of individually non-conscious, non-rational physical parts. (I am not counting panpsychism as a form of physicalism, so rest easy Galen Strawson.) Physicalism, as I am defining it here, requires that the most basic constituents of reality are non-conscious and non-rational—not to mention without teleology (goal directedness), without purpose, and without meaning (intentionality). Although Lego bricks and brain cells are made up of different elements on the periodic table, the different atoms that make up those respective elements are themselves made up of the same sub-atomic particles. So both Lego bricks and brain cells, at the most basic level, are made up of identical physical parts.
The only difference between the two, assuming physicalism is true, is the arrangement of the constituent particles.
What Is It about Arrangement that Explains Consciousness and Rationality?
Suppose we could create built-to-scale models of every sub-atomic particle using Lego bricks. An accurately scaled Lego model of a single atom might end up being the size of an entire planet, or even a solar system. Could we then arrange these Lego brick atoms to form a conscious, rational Lego brain (perhaps the size of the universe)? And if not, why not?
When we imagine arranging sub-atomic particles to form an actual brain (in parallel to arranging Lego bricks to form a Lego Brain), stacking them one-by-one until the overall structure is complete, what is it about the arrangement of individual parts that could possibly be responsible for consciousness and rationality? This question becomes more formidable when you consider that consciousness is an ON/OFF type thing—you either have it or you don’t. At some point in the assembly of a brain (or a complete body—or whatever collection of parts is taken to be conscious) out of individual, unconscious subatomic parts, consciousness would suddenly appear with the addition of a single sub-atomic particle.
If we cannot say what it is about the arrangement of particles in the actual brain that causes consciousness and rationality, we cannot say with any justification that it is impossible for a certain arrangement of Lego bricks to cause consciousness and rationality to arise. Although physicalists can point to plausible reasons for why it is unlikely than any Lego model would ever become conscious or rational, they cannot rule out the possibility until they point to what, precisely, it is about the arrangement of particles in the brain that generates consciousness and rationality.
A Difference in Kind, or a Difference of Degree?
The Lego Brain thought experiment draws out, for me, the central problem of any form of physicalism: pointing to the arrangement of physical parts doesn’t seem, in principle, to be able to explain consciousness or rationality. Consciousness and rationality (according the very common intuition that many people share) seem to consist of something fundamentally different than a particular arrangement of particles. The difference between conscious minds, for instance, and non-conscious physical objects appears to be a difference in kind, not just a difference in degree of the complexity of arrangement of particles.
The challenge to the physicalist, then, is to answer this question: What is it about the arrangement of individually non-conscious particles that causes consciousness and rationality? Without an answer to that question, physicalism would seem to offer no explanation at all.
Please let me know what you think in the comments below.