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Name: Stephen
Status: student
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Question:
My Grade 8 Science class and I were wondering if an object would still be considered to have color in an environment without light. Is 'color' the light rays that are reflected off an object or the make up of a surface?



Replies:
In one sense, this is more a philosophical question than a science one.

'Color' is important to people because sight is so important to us. The nature of different materials causes us to see them as different colors. In one sense, color requires a human to be involved because it is not 'color' until we see it. Without people, it is just a wavelength-absorption property of materials -- it takes our eyes to pick out the specific frequencies that people can see and our brain to categorize them into 'color'.

In another sense, it is the nature of the material that causes it to interact with light in they way that it does -- its 'color' -- and that material exists whether there is someone to observe it or not. This is a chicken-egg problem in a way.

Since we do no think of 'color' in x-rays, or microwaves, which are just different kinds of radiation (that we cannot 'see'), I say human interaction is required for 'color' to exist.

Without light at all, the same argument applies. If there is no radiation to interact with the material and send off wavelengths can be observed, then we cannot know what color it is. Does it have a color, and we just will never know what it is? Again, this is more philosophical than scientific. If light didn't exist, then the concept of 'color' would be moot.

Also, there are distinctly different ways materials interact with light that cause us to see 'color'. As you noted, 'Color' is the light waves that get to your eye after hitting an object -- but it is not just reflection. They can be reflected, refracted, or transmitted. Think of the color of stained glass (transmitted), your desk (reflected), or butterfly wings or oil slicks (diffracted). (The rainbow colors you see in oil slicks or insect wings are due to refraction of light through very small features on the surface, either a thin oil layer, or tiny fibers or bumps on insect wings.) The physical traits of materials that cause them to interact with light the way they do exist irrespective of the observer (at least in classical physics).

As an aside, there is a branch of physics known as "quantum physics" -- well beyond the scope of grade 8 -- where the observer plays a critical role in the physics. This are different when you're watching them than they are when you are not watching them (yes, it sounds weird -- and it *is* weird). It turns out that light is one of those things that has weird quantum effects too. But I digress...

Hope this has helped,

Burr Zimmerman


Stephen -

This seems to be a bit philosophical. Similar to the proverbial question, "If a tree falls in the woods and no one is there to hear it, does it make a sound." The answer is determined by how you define sound. With your colored object... does it have color if no light falls on it? I think you could defend either answer depending on how you define color.

If it were my 8th grade class, I would explain that the object in the dark has the potential to absorb certain frequencies of light while reflecting others. The reflected frequencies would determine the perceived color. However, even though it has potential, that potential is not tapped until light is available.

I am not sure if that is an answer that will satisfy an 8th grade class...

Larry Krengel


You have raised a very semantically question (aka "meaning of word" question). Color is determined by a response in the brain from signals from the eye through the optic nerve. We know that different people perceive color differently -- 'color blindness', brain eye and optic nerve trauma, certain drugs, and so on. Substitute either the phrase "wavelengths of visible electromagnetic radiation" or the phrase "emit photons with energy in the visible range of frequencies" for the word "color" and you have a question cast in a more useful form. Some materials are fluorescent (or phosphorescent), so even in "total" darkness they emit photons even in "total darkness". Addressing you question "Is color the light rays reflected off an object or the make up of a surface?" The answer to both situation is "Yes". It sounds to me that you question is a variation of the "tree falling in the woods "riddle" --does it make a sound? With "color" you have even more subtleties: Is grass green on a moonless black night. All surfaces exhibit "metamerism" (a technical term you can search) the means that the "color" perceived depends upon the makeup of the incident light.

Vince Calder


Color as we know it is definitely a function of the light bouncing off a body. Think of a particular object that changes color depending upon the light source, say fluorescent versus "natural" light. Ever buy something in a store just to find it "changes color" when you get home? That is the effect of the different light sources at the store and home.

Having said that, any material with a temperature above absolute zero emits electromagnetic energy. This is the same kind of energy we see as light, but at frequencies we cannot detect directly. So, in a sense, a body in the dark does have a "color" that depends upon its temperature. Human eyes just cannot "see" it.

Bob Avakian
Oklahoma State University - Okmulgee



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