Perhaps the central argument for thinking that the mind, consciousness included, must be a part of the physical world comes from the causal efficacy of mental states. Epiphenomenalism may be logically possible but we would need very powerful reasons for accepting it and many find that there are more powerful reasons for thinking that consciousness must play a causal role in the physical world. This has led many people to think that physicalism has the upper hand. Recently this status quo has been challenged by some philosophers who think that consciousness must be a fundamental irreducible component of the world.

One prominent defender of this view is David Chalmers who splits his credence between panpsychism and interactive dualism. On either of these views consciousness is a fundamental feature of the world that is posited in addition to the physical properties and yet it allows, or at least aspires to allow, that consciousness has a causal role to play in the physical world. Though I am optimistic about the prospects for physicalism, the kind of dualism I am most sympathetic to is the kind of Quantum Interactive Dualism as presented by Chalmers (and even more nice would be a physicalist version of that theory).

The basic idea is to define an m-property as one which acts as if it performs a measurement. M-properties will then have the effect of collapsing the wave function. Though there are many candidates for these kinds of properties consciousness seems to be a natural candidate. On this view we postulate a fundamental law that says that consciousness cannot be in superpositions and one that connects the physical correlates of consciousness to conscious experiences. This, argues Chalmers, gives us a way to make sense of a kind of interactive dualism. He does not endorse it, but it is worth exploring.

How does this give us interaction? He says,

what I think is going to actually happen here, if you think about it, is that consciousness most directly interacts with the neural correlates of consciousness, collapsing those out of superposition. So when you have an experience of red as opposed to green that may collapse a superposition of neural correlates of consciousness, say in inferiotemporal cortex, into the neural correlates of seeing red as opposed to the neural correlates of seeing green. That will then have an effect downstream. (at minute 56:33 in above linked video)

I like this kind of view and have floated something like it in an episode of spacetimemind (though, again, I would prefer it in a physicalist version). I figured I would jot down a few thoughts in hopes of eliciting some discussion to help me think through the various ideas.

First one might wonder why it is that consciousness cannot be in a superposition? Why can’t there be a state that is a superposition of consciously seeing red and consciously seeing green? One thing we might say is that phenomenal consciousness essentially involves awareness, so if I am consciously experiencing red this is essentially bound up with an awareness of myself as seeing red. This may provide some grounds for arguing that conscious experiences cannot be in superpositions.

Another major issue with this approach is the Quantum Zeno Effect. The rough idea here is that if you have a particle that will typically decay at some rate you can stop it from doing so by measuring it. This threatens to make it impossible for consciousness to show up in our world or to change. One possible way to use the above noted kind of awareness as a solution. If we suppose that we have the an unconscious representation of red, and that to make that unconscious representation conscious (in the phenomenal sense) we need to have a (possibly special kind) of awareness of that state (which in effect is the measurement by the outside observer) it will collapse into the (full) neural correlate of consciously seeing red. That will keep that state from evolving, and so will continue to be a conscious experience of phenomenal red. But since the relevant kind of awareness is external to the content (i.e red), the content of the awareness can change, thereby allowing conscious experience to change. This is, in effect, to combine a realist representationalism with a higher-order view.

One thing that seems to be in the background of Chalmers’ talk is the idea that when we get an interference pattern we have evidence that there was superposition, and conversely when we do not have an interference pattern we have wave function collapse (see minute 34-37 of his talk). But the Delayed Choice Quantum Erasers (which I have talked about previously) experiments put pressure on this kind of view.

There have been several recent experiments that build on this basic idea (see this recent paper in PNAS, or this recent paper in Science, or this one is Physical review Letters). I take these experiments to suggest that the existence of which-path information is enough to destroy the interference pattern.

So in these kinds of cases we make a measurement but since the measurement results in the loss of which-path information we still end up an interference pattern and so we seem to have an m-property (i.e. my conscious perception of the click produced by some detector) but we don’t have collapse (as indicated by the presence of an interference pattern).

Thus if we are to take the consciousness-as-m-property to be compatible with delayed choice quantum erasures we need to say that the system is in a superposition until there is a conscious experience and that even in the cases where there is an interference pattern there is still collapse. The system has collapsed from the superposition of interference pattern + no interference pattern into one or the other.