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Why do Small Objects have No Color?
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Question:
Why do objects such as quarks,
which are smaller than the wavelength
of visible light, have no color? If the
color of an object is simply the color
of the light that is reflected off it,
then why cannot extremely small objects
reflect wavelengths of light that are
larger than themselves? On the macro-
scopic scale, small objects can "reflect"
larger ones. For example, if one had very
good aim, one could theoretically bounce
a tennis ball off a pinhead.
Why is the same thing not possible on
the microscopic scale?
Replies:
In some sense micorscopic things DO have color! Take the
example of a single atom. When light falls on an atom,
it scatters, which can be considered a reflection. This
scattering depends on the wavelength of the light, with
some wavelengths scattered very strongly and others not
at all, just like you would say the color of a macroscopic
object is determined by which wavelengths are reflected.
(This selectiveness is due to the energy level structure
and quantum mechanics.) This is also true for other
microscopic things such as nuclie, subatomic particles,
but the smaller the object, the harder to "hit".
The reason we do not really say an atom has a "color"
is that color is a bulk property just like roughness,
for example. But by the strict definition of which wavelengths
are reflected, small things are colored. Another
"law" you may be thinking of is that light cannot
image details smaller than a wavelength. This IS
true, although some current research is trying to
find ways around this law. But that is another story!
timo p grayson
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Update: June 2012
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