Colors… one of the worst and most bizarre concepts you could ever attempt understanding, yet alone explaining using simple words.
Is this wall really green? How would you describe the color green to a blind person? How would you convince a person, born blind, that colors exist? Convince them that not all perceptions of colors are equal? And of course, convince them using hard physical evidence?
To answer all these questions, we must turn toward the biology of the eye. Inside the eye there are two types of neurons that can detect light, rods and cones. Rods are more adapted to low light situations, so we can rule them out for our purpose, and put our focus solely on cones instead.
There are three types of cones in the average human eye, one with a red pigment, one with a green pigment, and one with a blue pigment, but it’s not the types of pigments themselves that are the most interesting, it’s the range of wavelengths to which they respond. Compare the number of red, green and blue pigments, and you will see that Red creates a signal with a large range, Green a signal with a medium range, and Blue a signal with a short range. If your eyes possess only one type of cone, you will experience the world in shades of black and white.
Think about how the brain maps the different signals coming from the eye. As the cones receive many different beams of light of many different wavelengths, what is the characteristic difference between each signal? The intensity.
The brain can map each intensity of light to the strength of the signal it gets from the neurons detecting it. Under normal daylight condition, the flow of light through the eye is of a constant size, and so the intensity of the signal is dependent on how densely packed the cones are.
Even if the light is of a very different wavelength far away from the peak of the cone, there is still a good amount of activity going on, and the more packed the cones are the broader the range of wavelengths that can be detected. The curve becomes broader; the intensity decreases more slowly as you move away from the peak.
Conversely, if the cones are widely separated, the curve will become very narrow and the range of observable wavelengths will be much smaller, and the decrease of intensity much sharper. We can now begin to understand that the range of the visible spectrum of each color has something to do with the number of cones available to detect these colors, and how they are distributed within the eye. Each type of cone can be associated with a curve with not just a characteristic peak, but a characteristic width.
So with only one type of cone we cannot see the difference in wavelength, because different beams of light can have the same intensity yet different wavelengths. To the brain it’s all the same thing. The change in intensity is all that can be seen.
When analyzing colors, the brain doesn’t detect the actual wavelength of a photon, it only calculates the probability of it falling within a certain range of wavelengths. If you have multiple curves, the chance of a photon with a particular wavelength to fall within more than one spectrum is likely higher than zero. For example, purple correspond to a shorter wavelength but appears redder than blue. As the intensity of the blue peak drops, the chances of the photon falling in the long range goes up, and the color appears as a blend of red and blue. To the brain, a wave shorter than blue actually appears longer than it is, yet shorter than an actual longer wave.
So, we have three types of signals, three goldilocks spectrums of hot, cold and good enough; three types of cones distributed differently — with each serving as coordinates for the brain to map them as a unique value of wavelength. This mechanism is actually somewhat similar to how the brain detects temperature using a combination of hot and cold signals. To better understand how these signals combine together, let us examine several cases of color-blindness.
A person who is red-color blind has problems differentiating red from green, and experiences the world in terms of shades of blue and brown. Brown to a normal person is a blend of red and green, but with a disproportionate amount of red in it.
Without the long signal, green appears longer than it is, and red appears a bit shorter than it is. The chances of a wavelength within the range of the medium spectrum to be perceived as a mix of hot and cold signals are much lower, and the chances of it being in either extreme are much higher.
Similarly, a person who is green-color blind experiences the world in shades of blue and yellow. Without the medium signal, green appears longer than it is, but less so than in a red-color blind person. Everything appears more mellow, more in the middle. Without the middle signal, the chances of a longer wavelength of being perceived as a mix of hot and cold signals increases, while that of a shorter wavelength remains largely unchanged compared to a red-blind person.
(Because of the blue curve, those in the red are less differentiable from those in the green than those in the green are differentiable than those in the red. Confusing?)
The less a narrow signal overlaps with a larger signal, the more in the middle the wavelengths in the larger spectrum will appear to be. Conversely, the more two signals of similar size overlaps, the shorter the longer wavelengths will appear to be. A person who is blue-color blind has a harder time distinguishing green from blue. The longer wavelengths appear shorter than they are supposed to be. The chances of a longer wavelength of being shorter increases dramatically the shorter you go.
Look at the thresholds on each of the spectrums, each abrupt change of color corresponds to points where the different curves meet, the sharper the threshold the sharper the difference in color observed.
Our perception of color is not equal, a person who sees a green wall as yellow may be subjectively right, but is objectively less precise than a person who sees the wall as green. A wavelength of 550 is not equal to a wavelength of 650; they do not carry the same energy. A red-color blind person does not make the difference, and this fact can be easily proven by simply showing them a color with a longer wavelength, in which case they should prove themselves incapable of easily distinguishing the two.
Ultimately, colors are likely not an intrinsic property of the wavelength itself, but really a property of the energy being carried by the wave of light. For example, if it were the speed of the wave that was changing instead of the wavelength, the brain could still interpret this change in terms of colors, on the condition that the eyes would be equipped to detect the change in the speed instead of the wavelength.
That is to say, the brain can only create as many colors as how well it can detect the smallest difference in energy from the particles it comes in contact with. In this view, every quantum of energy would ultimately have its own objectively unique color, and subjectivity would really be a measure of how precisely we can experience this ‘absoluteness’ of color.
So yes this wall is yellow, yes this wall is green, but within the green we see there is still more wavelengths waiting to be discovered, and what we know is that these colors will be a combination of green and yellow, or green and teal.
Have you ever asked yourself, what would it feel like to see the world in 4-colors, or even 5-colors? And so finally… to answer the question how would you describe the color green to a blind person.
Well… imagine that your ears were little antennas that could rotate themselves all around towards any direction… And imagine that there was a giant tuning fork in the sky emitting a sound with a tone about in the mid-range of everything you can hear. Now this tone is bouncing everywhere, and depending on the composition of the material on which they bounce, they will bounce back at different wavelengths, or different tones. And now imagine that the most distinctive of sounds are those from tones bouncing back, and all the objects around you display not only very different tones from one another, but as your ears move the tone is perfectly even all over the surface matching the exact shape of the object your attention appears to be focused on, and stops abruptly when your ears go over the edge. The very sound all around you appears to be bending unto itself.
Focus your ears on a rectangular-shaped object. Imagine each point on the object as the source of a perfectly even tone, imagine all these sources as little balls of sound shrinking toward infinite nothingness. The object itself seems to be covered with an infinitely dense amount of infinitely small balls, each acting as a source for the sound entering your ears, and the little balls eventually get so small, so clumped up together that out of this world of curving sounds appears this big rectangle of darkness darker than empty space itself.
You try to listen in more closely, and you realize the surface is full of this ‘tone thing’ and then you realize, that the tone doesn’t just appear as sound anymore, but as a perfectly shaped object filled with something that you could only describe as being between incredibly cold and incredibly hot. It’s as if the rectangle itself had been set on fire by the giant tuning fork in the sky.
And as this realization dawns on you, you realize that sight and sound are not so different after all. It’s all energy. What really makes them different is the fact they are organized through space very differently, and the fact that they travel through space differently. What really makes them so different is that they are two worlds of wave each existing separately from the other inside the brain. In reality, these waves are all part of the same universe. Everything has a sound, everything has a color, everything has energy.
Religion, answers that must never be questioned. Philosophy, questions that may never be answered. Science, questions that one day will be more precisely answered.