Beyond the Zombie Argument

As a staunch physicalist I’ve spent a long time wondering how anyone could possibly find the zombie argument compelling. The intuition just doesn’t land for me. As Eliezer points out in his article here, a zombie duplicate of yourself would profess that it is conscious, when asked whether it had any conscious experience it would say “yes!” and when given tests designed to demonstrate its conscious experience it would pass. Zombies would also not be able to tell they’re not zombies – which leads to the disconcerting question – how do you know you’re not a zombie?

How could any rational person accept something so absurd?

To find out, I took to reading Chalmers’ 1996 book The Conscious Mind in an effort to understand exactly what Chalmers believes, and in engaging deeply with his arguments I think there is a much stronger intuition that can help us see what’s really driving the Hard Problem of consciousness and point towards a prospective solution.

Chalmers wants to establish that physical facts do not necessarily fix phenomenal facts. To grasp his intuition, instead of imagining a duplicate world where consciousness is absent (i.e. a zombie world) imagine a duplicate world where consciousness is different (i.e. a spectrum inverted world.)

Spectrum Inversion

Imagine an experiment where Bob is subject to two stimuli, let’s say a blue light on the left and a red light on the right. Now, imagine a duplicate world inhabited by twin-Bob. Twin-Bob is an atom-by-atom duplicate of Bob with identical physical properties. His world contains exactly the same physics as Bob’s where blue wavelength light is short and red wavelength light is long, and they interact with the same cones in twin-Bob’s retina and activate the same regions of his visual cortex in the exact same way. There is just one crucial difference. Where Bob experiences a blue light on the left, twin-Bob experiences a red light on the left. All the physical facts are fixed but the phenomena are inverted. Unlike zombie-Bob, twin-Bob is not confused about his consciousness – he genuinely experiences something, it’s just different to Bob’s experience. This avoids the absurdity of zombies pondering their own non-existent qualia but still leaves a challenge for physicalism.

Bob and twin-Bob seeing inverted spectra.

Is such a scenario conceivable? Or does a complete description of physics necessarily imply a resulting phenomenal experience?

The answer, I think, reveals something important about what physics actually describes and what is left out.

The Missing Piece in Physics: Russellian Monism

Spectrum inversion seems conceivable because physics only describes the structural and functional relationships between things. It doesn’t describe the intrinsic categorical properties which realise that structure. When we imagine spectrum inversion, we’re essentially holding the structure constant whilst varying the realiser of the structure.

Russellian monism offers a potential solution. On this view, there are intrinsic, categorical properties underlying physical structures and these properties are phenomenal (or necessarily give rise to phenomena.) So, returning to our thought experiment, spectrum inversion is actually impossible on Russellian Monism because the intrinsic categorical facts are also physical facts. If we truly hold all physical facts constant (including the intrinsic ones) then spectrum inversion is no longer possible.

Why this matters

Physical facts do fix phenomenal facts. It’s just that physics as currently construed doesn’t describe the intrinsic, categorical facts needed to fix phenomena.

The Hard Problem of consciousness is hard. But this spectrum inversion thought experiment, helps point towards a solution rather than a deeper mystery. It shows us exactly where our current physical picture is incomplete and what is needed to make it complete.