I was driving to work a couple of mornings ago and following a white car. It suddenly occurred to me that I wasn’t following a white car at all. Rather, I was following a car that reflected all the colors of the rainbow. If I could analyze each individual photon entering my eyes, I would discover not a single white photon in the bunch. Yet knowing this reality had no effect whatsoever on my perception of the car. No matter how hard I looked, all I saw was white.

That got me thinking about light and vision and how we see. Even when surrounded by white light, white isn’t really there. Instead we’re surrounded by individual photons, all different colors, none of them white. But of course “color” isn’t really there, either. There’s absolutely no difference between a red photon and a green photon except for a tiny difference in frequency (energy, wavelength, whatever you want to measure). The greenness or the redness doesn’t materialize until the photon enters your eye – and then it’s not a photon anymore!

And yet again, knowing that the greenness of a leaf or the redness of an apple doesn’t really exist until the light enters my eye doesn’t change the perception. Even more, just because an object like an apple looks red doesn’t mean it’s reflecting red light. It might be reflecting many colors which just add up to red, in the same way the white car is just a combination of colors that add up to white.

Trees grow red apples to make them more conspicuous to animals who eat fruit. This makes it more likely that the tree’s seeds will be spread. But apple trees have no eyes. Amazingly, they still produce the right chemicals to make the apple red. Pretty amazing. It’s like us being born with a dog whistle and knowing exactly how to use it.

Then the car turned and I went to work.