My answer to the question “What is Color?”

The Alan Alda Center for Communicating Science holds a contest each year to explain a complex scientific idea in under 300 words.  Those 300 words have to convey meaning (and here’s the hard part) to a 5th grader.  This year’s question was “What is Color?”  The finalists have been named and can be read and (in the case of the video entries) seen here.

My (non-finalist) entry is below.  I am posting it because I spent a fair bit of time writing it, so I both want it to see the light of day and receive feedback in the comments section or on twitter (@SGPrilliman).  So I hope you enjoy it and let me know what you think!  Make sure you check out the finalists at the link above.


What is color? That’s a really important question. When scientists say “That’s a really important question” it means “this isn’t going to be easy” so hang on!

Sometimes light behaves like a wave on the ocean. In this case color is the distance between the peaks of the waves. For red light, the distance from one peak to the next is 600 nanometers (one nanometer is one billionth of a meter). For blue light, the distance from one peak to the next is 400 nanometers. Light behaving as a wave explains why “Blu-ray” disks hold more video than DVD’s. The smaller the wavelength of the laser inside, the closer the grooves can be on the disk, the more data it holds.

That seems okay, right? But in the early part of the 20th Century it became clear that sometimes light was better described as a particle, not a wave. When light behaves like a particle, color is a measure of the energy of the particle. Red light particles have less energy than blue light particles. This is why cooler stars look red, hot stars look blue, and in-between temperature stars (like our sun) look yellow.

So which is it? Is color a measure of the distance between peaks in the waves, or is it a measure of the energy of light particles? The problem is, light is both a particle and a wave, so color is both the distance between waves and a measure of the energy of the particle.

Do you understand? Neither do I. Having two answers to one question is messy, but those are the best kind. Simple answers are boring. Messy answers lead scientists like me and future scientists like you to keep asking questions and developing a deeper understanding of our complex universe.