Here is an example of text that Annette wrote for a display at the Berkeley Lab open house:
Soapy Science: The Color Machine
What causes the colors and patterns in a soap film and why do they change?
Sunlight contains all the colors of the rainbow, and bubbles separate the colors so that we can see them. (Instruments in the ALS use a similar method to separate out certain types of ALS light.)
What's Happening?
When light waves hit a thin soap film, some waves reflect off its outer surface and some travel through to bounce off its inner surface. When the two bunches of reflected waves meet, they interfere with each other. That is, the waves either reinforce each other, cancel each other out, or partly cancel each other out. We call this phenomenon "interference."
How Does This Make Color?
Sunlight includes light waves of many different wavelengths, each of which appears as a different color when viewed alone. You can think of sunlight as a mixture of red, blue, and green light. Together they look white, but when one color is missing, we see the colors that remain. For any particular thickness of soap, light of one color will have the right wavelength to get canceled out by interference, so we see just the remaining colors. For example, if red waves cancel out, we see white light minus red light, which appears blue-green to our eyes.
A Cool Fact
Why do the patterns of color change? As the soapy water in the very thin bubble flows and shifts around, the bubble's thickness is changing too--just a little--only millionths of an inch! That is about the difference in the wavelengths of light that we see as different colors. It's pretty cool to realize that when you look at a soap bubble and see different colors, your eyes are measuring millionths of inches.
