Living With Gramps - The Rainbow

It had been a bit of a rainy day when I looked out of the second-floor window near sunset. There it was: the brightest, boldest rainbow I had ever seen. I immediately ran downstairs to tell gramps before going out in the drizzle to photograph it.

I had seen rainbows before, but not like this. In New Hampshire and Florida, trees, hills, and houses got in the way so I could never see where the rainbow touched ground. In Slocum, the sod farm was so expansive that I could clearly see stripes of color in front of the distant trees. I could see exactly where it hit Earth. Squinting, I almost thought I could see a leprechaun sitting on a pot of gold.

Although my grandfather’s vision was pretty bad by this point, he could still see this. He talked about it for days afterwards. It was kind of a big deal for him for some reason. “Do you know what the rainbow represents?” he asked.

I thought for a bit. First and foremost in my mind, a rainbow is a natural phenomenon. It is what happens when drops of water in atmospheric suspension refract sunlight at particular angles depending on wavelength. It represents the wonder and beauty of nature and the fact that even when the underlying principles of physics are known, there can still be surprises in how they manifest themselves under very precise conditions.

Of course, I was also familiar with the story in Genesis about the first rainbow as it appeared to Noah after the flood. It is symbolic of the promise God made to Noah and his descendants that he would never destroy the world by flood again.

To some people, the rainbow is also a symbol of magic – not scary witch magic or epic dragon battle magic, but the cute, whimsical magic of fairies. Lucky Charms cereal has rainbow-colored marshmallows.

The rainbow with all of its colors is also a symbol of diversity and inclusion – not only of ethnicity, but of religion, age, ability, sex, and especially sexual orientation. In recent decades, it has become a symbol of the gay rights movement.

While my brain tripped over the flood of data being recalled I’m not sure what was coming out of my mouth, but my grandfather was having none of it. “The rainbow represents God’s promise not to flood the whole world.” He wasn’t interested in anything else.

A few days later, he asked, “How many colors are there in the rainbow?”

“Well…uh…That’s a good question,” I babbled as my mind raced in circles. I had never thought of this before. The light is separated by its wavelength and light can have any wavelength at all, so the colors might be infinite.

Then again, there are minimum limits on wavelength such as the Plank length and without a theory of quantum gravity it’s hard to make any absolute statements.

Some wavelengths might be missing because absorbed by water, air, or dust in accordance with the energy levels of their electron orbitals.

In any case, any specific rainbow is finite in space and time and so only a finite number of photons will be involved. Each photon can only have one wavelength (when measured), so the answer at any given time for any one observer is finite.

What is color? Color is not wavelength. Human eyes use inputs from three retinal pigments to “triangulate” the wavelength, but cannot distinguish between truly green light and light that is a mixture of blue and yellow. We can also see imaginary colors like purple, which is what happens when red and blue mix without yellow, orange, or green being present. Several layers of processing in the retina and brain mean that no two people see color alike. Furthermore, birds and reptiles have four retinal pigments, most mammals have only two, and mantis shrimp have sixteen, so how many colors there are depends who’s looking.

Eyes aside, how many unique colors can be perceived by a typical human brain anyways? How many unique combinations of neural connections can stand for distinct, recognizable colors? With thirteen billion neurons, combinatorics predict a truly enormous number, but our symbol-using, conscious minds would likely break them down into just a few groups. Different cultures might define different numbers of colors or define the boundaries between them differently. Some hunter-gatherer groups only have two color words – one for “warm” colors and one for “cool” colors. Across the world, developing languages recognize “orange” last. In old Saxon, orange was known as yellow-red.

Color perception can also be influenced by surrounding backgrounds, making brown look orange or orange look brown. Optical illusions are everywhere.

I tried to explain all this, but my grandfather says I talk too much.