Andew said:
There is no such thing as "white" in the real physical world. "
This statement is hard to justify. The light we perceive as "white" light is real, there's real EM radiation there, the object reflecting that light is real, so the conclusion, "no such thing as 'white'" doesn't make much sense.
I think what the guy may be trying to explain is the concept of "qualia." But he's not doing a good job of it. The concept of qualia has to do with why we experience white (or any color, or any sensation)
the particular way we do. Given that there's an objective external phenomena that cause some things to appear white (as opposed to brown or blue or whatever)
why is it we have the exact experience of white we have? Why couldn't that same mix of light frequencies reflecting off that same object create the experience we think of as red, or some other experience completely unknown to us? Why does a certain frequency of light create the experience red, and not red? If you think about it, the only objective facts about the two colors is that there are two different frequency ranges and really, all you could expect is that the more energetic one should be a more intense experience of the other. The visual world really ought to be shades of grey only. In fact, though, we have this much more vivid and hard to explain experience of the differences.
Red doesn't come from the chemicals in the eye receptors, but from how the brain processes the information from those receptors. It takes info from the red receptors, processes it, and feeds it back to us as red.
Why couldn't the qualia, the subjective experience, of white and black be reversed, with surfaces receiving and reflecting more light appearing more dark and visa versa? There probably is no objective reason why not. We'd get used to it if that's the way it was from birth. The current subjective experience is simply the way it happened to play out, the way our brains evolved, and since it is useful, genes for that experience got passed on. The fact our brains make red look red, as opposed to red, is probably ultimately arbitrary, but it's quite wrong to conclude from that "there is no red." Red is real (light of a certain wavelength). There's just no single objective way it is constrained by physics to be subjectively experienced. The taste of salt might, in a different evolutionary train, have ended up being quite different than it is. In order for a sense to be of any use, it has to create some experience distinguishable from other sensory experiences. The actual subjective experience that gets created is most probably arbitrary, within limits, and many other subjective experiences might have served just as well. Of the choices mutations present, natural selection has left us with the ones that most contribute to survival (or are neutral).
Qualia started out as a philosophical concept ("How do I know my red is the same as another person's red?"), but the subjective experience of color is known to be created in the brain, since certain kinds of brain damage will alter or even remove the ability to see in color even while the eyes remain unharmed. Check out Oliver Sacks case study of such a patient (scroll down past bibliography):
https://people.rit.edu/wlrgsh/Sacks.pdf
Indeed, all subjective sensory experiences are given their particular qualities by the brain. The brain takes objective stimuli and creates a subjective, but useful, experience.
