The Science of Discworld II

commentary, interleaved between successive episodes of a Discworld story, will be to resolve that paradox: how did Mind (capital ‘M’ for ‘metaphysical’) come into being on this planet? How did a Mindless universe ‘make up its own Mind’? How can we reconcile human free will (or its semblance) with the inevitability of natural law? What is the relation between the ‘inner world’ of the mind and the allegedly objective ‘outer world’ of physical reality?
    The philosopher René Descartes argued that the mind must be built from some special kind of material – ‘mind-stuff’ that was differentfrom ordinary matter, indeed undetectable using ordinary matter. Mind was an invisible spiritual essence that animated otherwise unthinking matter. It was a nice idea, because it explained at a stroke why Mind is so strange, and for a long time it was the conventional view. Nevertheless, today this concept of ‘Cartesian duality’ has fallen out of favour. Nowadays only cosmologists and particle physicists are allowed to invent new kinds of matter when they want to explain why their theories totally fail to match observed reality. When cosmologists find that galaxies are rotating at the wrong speeds in the wrong places, they don’t throw away their theories of gravitation. They invent ‘cold dark matter’ to fill in the missing 90 per cent of the mass of the universe. If any other scientists did that kind of thing, people would throw up their hands in horror and condemn it as ‘theory saving’. But cosmologists seem to get away with it.
    One reason is that this idea has many advantages. Cold dark matter is cold, dark and material. Cold means that you can’t detect it by the heat radiation that it throws off, because it doesn’t. Dark means that you can’t detect it by the light that it emits, because it doesn’t. Matter means that it’s a perfectly ordinary material thing (not some silly invention like Descartes’ immaterial mind-stuff). Having said that, of course, cold dark matter is totally invisible, and it’s definitely not the same as conventional matter, which isn’t cold and isn’t dark …
    To their credit, the cosmologists are trying very hard to find a way to detect cold dark matter. So far, they’ve discovered that it does bend light, so you can ‘see’ lumps of cold dark matter by the effect they have on images of more distant galaxies. Cold dark matter creates mirage-like distortions in the light from distant galaxies, smearing them out into thin arcs, centred on the lump of missing mass. From those distortions, astronomers can re-create the distribution of that otherwise invisible cold dark matter. The first results are coming in now, and within a few years it will be possible to survey the universe and find out whether the missing 90 per cent of matter really is there, cold and dark as expected, or whether the whole idea is nonsense.
    Descartes’ similarly invisible, undetectable mind-stuff has had a very different history. At first, its existence seemed obvious: minds simply do not behave like the rest of the material world. Then, its existenceseemed obvious nonsense, because you can chop a brain into pieces, preferably after ensuring that its owner has previously departed this world, and look for its material constituents. And when you do, there’s nothing unusual there. There’s lots of complicated proteins, arranged in very elaborate ways, but you won’t find a single atom of mind-stuff. 2
    We can’t yet dissect a galaxy, so for now cosmologists can get away with their absurd invention of a face-saving new material. Neuroscientists, trying to explain the mind, have no such luxury. Brains are much easier to pull apart than galaxies.
    Despite the change in current conventional wisdom, there remain a few diehard dualists who still believe in special mind-stuff. But today, nearly all neuroscientists believe that the secret of Mind lies in the structure of the brain, and even more importantly, in the processes that the brain carries out. As you read these words, you experience a strong sense of Self. There is a You that is doing the reading, and thinking about the words and the ideas they express. No scientist has ever dissected out the bit of the brain that contains this impression of You. Most suspect that no such bit exists: instead, you feel like You