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Physics/colours of things


Dear Dr. Nelson,
I've no idea why colours are as we see. Are they the same for all of us or only we think that we see the same?

I'll apreciate your help and clarification.
Thanks a lot!

That's an excellent question.  Color vision and perception of vision are actually quite complex.  In general, people see the same colors because they have the same three types of cone structures in their retinas.  By reacting with different strengths to different wavelengths of light, we see colors.  Sometimes we see colors as they are, like if you saw light with a wavelength of 530 nanometers you would see green.  Sometimes we see something like yellow (about 580 nm) mixed with blue (about 470 nm) and because our cones react roughly the same as they do to green light (partial excitation of multiple types of cones) we perceive green light because our nerves in our retina are transmitting the signal for green... even if there's not actually any green light present at all.  Some animals, particularly the mantis shrimp (17 types of cones) have color vision we can only dream of.  Some humans have color blindness, where their cones are either missing or malfunctioning.  Again, color vision is somewhat complicated.  Some people actually have a fourth type of cone, allowing them to see colors differently than the rest of us (tetrachomacy), but the condition is supposed to be quite rare.  


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Dr. Stephen O. Nelson


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.


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.

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

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