Some philosophers argue that some properties - such as colour - are bound up with human mental experience, and cannot be 'reduced' to physical properties. Where, then, does a property like 'redness' really reside? Redness appears to reside in the brilliant colour of a poppy. But physicists tell us that the colour red simply corresponds to a light wavelength of 7 x 10-7 metres. Is this part of the electromagnetic spectrum the residence of redness? Or is redness forever in the eye of the beholder - the subjective experience of a human (or non-human) observer?
Imagine somewhere deep in space a monochromatic planet: the local sun is a pale white star, shedding a moonbeam-like lustre on a dull metallic landscape. Everything is a shade of grey. The native alien life-form has evolved monochromatic eyes. If it arrives on Earth, it sees only in black and white. It regards a red poppy, and understands the wavelength of its colour is 7 x 10-7 metres, but its subjective experience is quite different from the human one - the poppy appears to the alien only as a rather fine shade of grey.
Or, at the other extreme, we can imagine an alien species equipped with senses that directly experience the whole electromagnetic spectrum (as we sense the visible portion directly through our eyes). This pan-electromagnetic-detecting alien is able to sense directly everything from gamma rays to radio waves, and can tune straight into TV transmissions from Earth (to start with, admittedly, rather quaint old TV shows in black and white). Its impression of the TV shows might be the same as if we were viewing them at home - though its interpretation of their meaning may only be guessed at.
But the fact that these experiences are subjectively different does not mean that they may not ultimately be reconcilable within a scientific framework. For now, physics may describe only a few narrow aspects of colour, such as wavelength or frequency. But we are on a long journey of human understanding. To be able to recognise and name different colours was a start. In a sense, this recognition allowed us to claim colour as a 'human' construct in the first place. Who is to say what advanced understanding might not achieve in the future? After all, to the ancients, it might have seemed like science fiction that something as sensual as 'redness' could be expressed using such hard, brain-bendingly small units of distance or time (i.e., wavelength and frequency).
Some might then wish to redefine redness as that bit of the colour that is experiential - that cannot be attributed simply to its wavelength. But who is to say that we could not also capture or synthesise this sense of redness, as experienced by human vision? After all, when we hear a voice on the telephone, we interpret it as a person talking, rather than a mechanical sound generated by a vibrating diaphragm. Similarly, without a thought we say we saw so-and-so on TV, when all we saw was a cathode-ray trace. If we can fire off the pleasure centres in our brains using electrodes, can we not recreate the sensation of redness in our minds? Surely it is not irredeemably beyond the scope of physics to synthesise the experience of seeing a red poppy - for humans or aliens of any visual capacity?
But some philosophers might still object that redness does not reside in anything to do with the physical experience of that colour of light hitting our retinas. They may forever wish to reserve redness for something that cannot be captured by any objective means. Then, however sophisticated our pinning down of redness as an objective property, there is a philosophical argument that insists that there will always be a remainder - some residual something - that must be reserved for the subjective, experiential world of what it is to be human - or alien.
In the face of a pan-galactic scientific convention for the definition of colours, we would be insisting that our redness is different from anyone else's. In the ensuing argument, even the human philosophers would start falling out with each other, as some insist they always experience everything uniquely anyway.
The dark recesses of individual conscious minds become the last refuges for the things we can't explain physically. As science expands our understanding of the composition of colour, light and matter, and human senses and mental processes, we surely 'reduce' the concept of redness in reserving it for the bits that yet remain beyond our ken. Is that really where redness resides?
by Stephen Marshall
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