Color Without Light
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?
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,
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...
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.
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.
Oklahoma State University - Okmulgee
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Update: June 2012