by kragen | 2025-05-11 08:17:27+00:00
One of the most peculiar facts about conscious beings is the way they invert causality. Normally we think, for example, of a fire under a teakettle as being a cause for the water in the kettle eventually boiling. But if I asked you, "Why is this stove burner on?" it would be entirely normal for you to answer, "I'm making tea." Mystically, the tea that does not yet exist, and will never exist if it turns out we're out of tea leaves, is purportedly causing the water to boil (in the future), which in turn is causing the fire to burn, all through the medium of your conscious intention to make tea. It's really a quite surprising ontological claim, and yet nothing could be more quotidian, at least for those of us in the tea-drinking parts of the world.

I walked to the electronics store yesterday morning and bought some opamps. I find it amusing to think of opamps as bringing intentionality to circuits: they invert causality in precisely the same way as you do when you are making tea. The non-inverting input voltage is the op-amp's intention, the inverting input voltage is its observation which it interprets as a model of the world, and its output current is the behavior it controls according to that model to bring the world into accordance with its intentions.

The op-amp's behavior is only effective if there is a "structural similarity" between the world as the op-amp imagines it and the world as it really is, namely, if spewing out more current on its output will raise its inverting input relative to its non-inverting input, and sucking in more or spewing out less will lower it; we normally call this the negative-feedback condition. An op-amp hooked up backwards so the feedback instead is positive and drives it into overload is, in this analogy, like an insane or otherwise irrational person who keeps taking actions that predictably achieve the opposite of their intention, like posting comments on HN in order to enjoy thoughtful conversation.

When we design analog circuits with op-amps, we do routinely use the same kind of inverted-causality reasoning we use with the tea. Suppose it succeeds at making its inputs equal; what then is the situation that must prevail in the circuit? Oh, Vo = V1 + V2 - V3 - V4. Or Vo = -5Vi. And so it is, at least if the op-amp's feedback is not frustrated, or so effective that it sends the circuit into oscillation.

Op-amps (and thermostats) are clearly doing something that shares important features with human goal-directed activity, to the point that it seems practically useful to ascribe intentions to it, saying "this op-amp wants these currents to be equal" in a way that it isn't useful to say "this weight wants to move downward".

So I wonder what it is like to be an LM324N op-amp. I imagine it to be a very simple sort of existence, if not always a happy one. I prefer to be a human, but, failing that, I'd rather be a bacterium than an op-amp.

So it's amusing to see that Chalmers had the same thought. I wonder if I got it from him through indirect memetic contagion. (Though as far as I can tell he doesn't discuss oscillation, positive feedback runaway, or this peculiar inversion of causality. But I really doubt those are original to me, either.)