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Question
Dear Dr. Stephen O. Nelson,
I would like to find out whether it is possible to create a rainbow with colors that are not those in the normal rainbow that is red, orange, yellow, green, blue, indigo and violet.And could you also explain why not if it is not possible?

Thanks,
Jennifer Yu

Answer
Well, those colors are human conventions for separating and naming colors.  In some languages, in some cultures, there are only two words for color.  Those words are apparently always for black and white.  In others, there are more, the third and fourth words being for red and green (blood and plants).  In others, there are many more.  So what you need to describe colors, in terms of physics, is their physical wavelength.  However, you can combine these colors to excite the cones of the human eye to see colors that aren't really there.  For example, if I shine a yellow flashlight and a blue flashlight at a white wall, I will see green.  Is there green light there?  No, just light that excites the short and medium cones of the eye in a way that I perceive as green.  If I shine green light there (of the actual green wavelength), I get the same effect on the cones of the eye.  Therefore, you can make colors out of different colors that are nearby, but you cannot make colors out of those outside of what the eye can see (infrared, ultraviolet, etc).

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Dr. Stephen O. Nelson

Expertise

I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

Experience

I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Education/Credentials
Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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