Of Downward Causation and Hipsterism

I doubted that I would ever tell this little story in a serious academic context, until a version of it came tumbling out of me in my recent specialist exam. Now that I’ve already suffered the¬†embarrassment of having¬†my committee hear it, I may as well share it with the wider world.

As a bit of background, consider the question of downward causation. Some philosophers (Evan Thompson, R.C. Bishop, Alicia Juarrero) have been arguing that complex systems exhibit downward causation, where the system as a whole constrains or explains the behaviour of its parts. We can’t just look to the intrinsic properties of the parts to understand the overall dynamics, we have to also include their organization as a whole system.

The example I like best is Raleigh-Benard convection, this thing:

So imagine this is water (or some other fluid) and the bottom plate is heated. Above a certain temperature, the water will make these lovely little rolls that form hexagonal cells. That’s Raleigh-Benard convection.

And the argument is that before convection starts, the individual water molecules are just bopping around, doing their own thing. The relevant causes are just the low-level microphysics of the system. But once a convective regime takes hold, the story goes, we need to consider another kind of cause – the constraint put on elements of the system by the organization of the system as a whole. So because the whole system is spiralling, individual molecules can’t just bounce around in any old direction, their set of possibilities is constrained to just rolling action. And that’s downward causation – a kind of systemic constrain on the possibilities of the parts.

I’d like to propose that we look at that same story from a different perspective. Suppose we ask what it would be like to be one of those water molecules. I think that if you look at it from the water molecule’s point of view, it’s pretty clear that whatever these systemic constraints that convection introduces are, they aren’t ‘downward’. They may tell us something about the system as a whole, but they don’t really tell us anything about the parts of the system, and don’t constitute a real constraint on the behaviour of those parts.

To that end, I’m pleased to introduce to Walter the Water Molecule:

The life of a water molecule is a simple but satisfying one. The really nice thing is that, unlike people, water molecules always act perfectly authentically, according to their own Innate Physics. When bounced by something from the left, Walter zooms right..

When something bounces him from the right, Walter always reacts in exactly the way he pleases, bouncing away to the left.

And no matter what his circumstances, Walter would always remain true to his own Innate Physics.

But one particularly hot day, Walter noticed something funny. Despite his doing nothing different than what he always had, it seemed more and more that everyone else was doing exactly what he was doing. He had decided, on account of his Innate Physics, to do vertical loops that day, but for some reason everyone else was doing it as well!

Since he was doing what he had always done, and now everyone else was doing the same, there was only one conclusion that poor Walter could come to: they were all copying him! Walter therefore became an insufferable hipster.

The moral of the story is, don’t be like Walter. His confusion was to think that just because everyone is doing the same thing, they must be following the crowd somehow. He assumed that if the overall behaviour is orderly, that must mean that the individuals involved must somehow be constrained from following their own Innate Physics. But that’s just not true. Water molecules do their own thing, no more and no less, both before and after the onset of convection.

Of course, something does change when the system changes from being disorderly to the orderliness of convection. What I’m rhetorically gesturing at here is that what changes isn’t anything about the parts of the system – they keep on keeping on in exactly the same way no matter what. What changes is at the system level. So there isn’t any good sense in which this self-organized behaviour counts as ‘downward’ causation.