Is there any proof to Sir Isaac Newton's claim that color exists only in the mind? That there is nothing intrinsically blue about light with a short wavelength. To us it would look the same whether the cones in our retina detect color or whether they detect wavelength which our brains convert into color. Is there any definitive scientific evidence to prove or disprove his claim?
The human colour vision is bound to the cones. We have three types of cones with maximum of absorption in the wavelength domain respectively
The subjective impression of colour results from the neuronal processing by these types of cones by additive mixture of colours. The theory of Young, Helmholz and Maxwell from the 19th century explains this mechanism in our brain.
It is not the single wavelength which creates the colour impression. We do not have a continous range of receptors, each receptor restricted to one small range of wavelengths disjoint from the range of the next receptor.
Light is an electromagnetic wave like radiowaves. The only difference is their wavelength. We cannot detect any difference between radio waves in addition to their physical properties like wavelength, polarisation or intensity. Hence there is no evidence for colour as an intrinsic physical property.
One of the simplest proofs: Perceivable colors cannot be the same as specific wavelengths because there is a range of colors which do not correspond to a specific wavelength. These colors are called magenta, pink, fuchsia, and the like. They are all colors which are placed on the so called line of purples (the straight line on the CIE chromaticity diagram).
There are three types of cone cells (called S, M, and L) responsible for color vision in the human eye. Each type is sensitive to a range of wavelengths. If both the S and the L cones are stimulated, but not the M cones, the impression of the color magenta emerges. Because the main responsitivity ranges of the S and L cones do not overlap, one needs light of at least two wavelengths (a short "violet"/"blue" and long "red" wavelength) in order to stimulate both the S and the L cones, which in turn somehow trigger the phenomenal impression of the color magenta.
The "correct" interpretation of Newton's ideas and researches on light is a complex issue and Newton's theory for sure evolved during time.
But, having said this, here is an extract from :
- A Letter of Mr Isaac Newton, Mathematics Professor in the University of Cambridge, containing his new theory about light and colours received and published by The Royal Society in 1671:
So the true cause of [the phenomena experimented by Newton] found to be just this:
light consists of rays that are differently refractable.
I shall now tell you about another, more notable, unalikeness in light-rays, which is the source of differences of colour. I shall set out the doctrine first, and then describe one or two of the supporting experiments.
You will find the doctrine comprehended and illustrated in the following propositions.
(1) Just as the rays of light differ in degrees of refractability, so they also differ in what colours they are disposed to exhibit. Colours are not what they are generally believed to be, namely states that light gets into because of how it has been refracted or reflected by natural bodies. Rather, colours are basic properties of light, properties that come into existence when light does, and these properties are different in different rays. Some rays are disposed to exhibit a red colour and no other; some a yellow colour and no other, some a green colour and no other, and so on through the rest. [...]
(2) A given colour always has the same degree of refractability, and a given degree of refractability always goes with the same colour. [...]
(3) The kind of colour and degree of refractability that any particular sort of ray has can’t be changed by refraction, or by reflection from natural bodies, or by any other cause that I have so far found.
See also Newton's theory of colour.
Newton's theory is that colours are not properties of things; they are the way we "perceive" wave-lenght, which is an "intrinsic" property of light:
the colours of all natural bodies have no other origin than this, that they are variously qualified to reflect one sort of light in greater plenty than another. And this I have experimented in a dark room by illuminating those bodies with uncompounded light of diverse colours. For by that means any body may be made to appear of any colour. They have there no appropriate colour, but ever appear of the colour of the light cast upon them [...].
The word color has 3 different definitions, depending on context. When speaking about the color of an object, we're referring to a property of the object. Which wavelengths of light it absorbs or reflects. When we speak about the color of light, we're referring to it's wavelength or the combination of wavelengths from which it is comprised. When it comes to visual perception, we're referring to hue. So a red balloon (property) under blue light (wavelength) appears black (hue).
Light has no hue, but it does have different wavelengths, which result in the perception of corresponding hues.
Is there any proof of Newtons claim that colours appear in the mind? That there is nothing intrinsically blue about the light with a short wavelength.
Newton may, surprisingly enough, demur; in part Book 2 of his opticks, he wrote:
Proposition 4: the transparent parts of bodies, according to their several sizes, reflect rays of one colour, and transmit those of another, on the same grounds that thin plates or bubbles do reflect or transmit those rays. And this I take to be the ground of their colours.
Newton appears to take rays to be coloured.
In a later chapter, he does claim though that vision is:
Qu.23: is not vision performed by the excitation of this medium, excited at the bottom of the eye by the Rays of Light, and propagated through the pellucid, uniform cappilimenta of the Optick Nerves into the Place of Sensation?
There's no mention of Mind, though; perhaps you've confused Newton with Hume, or perhaps Saussure; or both.
To follow up on the very good answer already offered by Max, we can observe that all the things in our natural environment that would have mattered to our survival as a species don't come in pure wavelengths. From this, we have to assume that our vision system has evolved and has been selected for by evolution not to be able to "measure" each of the possible pure wavelength but to be able to identify any particular mix of them.
It is therefore clear that having only three different types of cone cells in our eyes, each working on a specific range of wavelengths, is a very economical, and probably optimal, organisation if you keep in mind the cost for our metabolism of producing and maintaining the neurobiological "infrastruture" of our vision system. With such a low-cost "design", with only three types of cells, our vision system can identify a very large range of all the mixtures of wavelengths that occur in our environment.
You could still salvage your suggestion by insisting that colours really exist outside our minds or brains as mixtures of pure wavelengths rather than as pure wavelengths, but that possibility is really far too implausible to take seriously.
There is another reason. Light has one objective property which is its wavelength. It is an objective property because we can make experimental setups, for example the "double-slit interference", that produce observations that are best explained by assuming that light has a wavelength. If light had another, different, property, colour, we would expect to be able to observe some objective consequences. Yet, assuming wavelengths is all we need to comprehensively explain the objective behaviour of light. Colour doesn't explain anything that wouldn't be explained, and more gracefully, by wavelength.
The only thing we cannot fully explain with wavelengths is our subjective experience of the colours themselves, but, precisely, we experience colours as a subjective property, something that as far as we know only occurs within the confine of our mind or brain, whereas wavelengths explain elegantly everything that happens objectively outside our minds.
So, no proof definitive, but we won't have any such anyway for anything objective. Rather, we use common sense to opt for the more sensible option. Scientists say wavelengths and I agree with them. Still, you're the only one who can decide which option seems more sensible to you.
EDIT: Light has several other objective properties, such as intensity, speed and direction. All these other properties can be evidenced by well-known experimental setups.
Intensity is measured as a "macroscopic" property of light. It is the power transferred per unit area when light falls on a material. It depends on both the energy of each of the individual particles of light involved, the photons, and the quantity of these photons per unit area and per unit of time.
Intensity is the main objective factor affecting the subjective sensation we have of the brightness of light, whereas our subjective sensation of colour is mainly affected by the mix of wavelengths received by cone cells.
Light has also objective wave-like properties and particle-like properties, which can both be evidenced by experimental setups.
Intensity as a property of light is a function of the other properties of light that are its particle-like property, the energy of its particles, and its speed.
The direction of light is one of the objective factors affecting our subjective sensation of brightness.
Please note that all the elements used in this explanation are very basic and can be found in all science textbooks and from well-known and publicly available websites such as Wikipedia.
If colour was intrinsic to light, then colour blindness should not exist, but it does therefore colour is not intrinsic to light. Red-green colour blind people detect light, but because of defects in their eyes cannot differentiate between the two colours i.e different wavelengths of light semingly have the same wavelength.
Color may be only in the mind, but remember that we associate colors with everything around us, and that is what gives them meaning. For example, the sky appears blue, the trees green and the sun yellow-orange. The universe is made up of colors or in other words differences which emerge from the oneness (of love) To truly understand why colors are so magnificent, you need to back to the creation and stare in wonderment of who we are. You might be interested to know that some species can differentiate more color than humans, as they have more than three types of receptors. Look up mantis shrimp for more information.