The Shape of Days

Took another sick day today. I stopped taking my temperature around noon. It was just depressing. I had so much tylenol in my body my pee was coming out as caplets, but I still couldn’t get that damn fever to break.

Feeling a little better now. My fever broke earlier. I got all hot and sweaty. Been standing out on the balcony in four inches of snow to cool off. Probably not the smartest move, but it made me feel a bit further from imminent death.

I napped for a little while earlier, and in my nap I dreamed. I dreamed about purple. You know what’s interesting about purple? It doesn’t exist. It’s an optical illusion.

Color is how the human eye perceives the energy of electromagnetic radiation. Electromagnetic radiation can have all sorts of different amounts of energy, but within a very narrow slice of that range, the radiation stimulates cells in our eyes and we perceive that stimulation as color.

There are lots of different ways to describe the energy of a single electromagnetic emission. As a measure of distance or wavelength, as a number of cycles per second or Hertz, as electron volts, whatever. They’re all valid, though in different contexts some are more useful than others.

Red light has a wavelength of about 700 nanometers. Unless you’re a particle physicist, that doesn’t really mean anything practically, but it’s how we define red.

Orange light has a shorter wavelength: about 620 nanometers. Yellow light clocks in at about 580 nanometers.

Between orange and yellow light, of course, there are shades of orangey-yellow and yellowy-orange. But not an infinite number of shades, because light can’t have just any amount of energy you want it to have. Light energy comes in discrete amounts called quanta. So there are a great many, but finite, number of color shades.

If you skip all the way down to the end of the visible spectrum, you end up at violet. Violet has a wavelength of about 420 nanometers. The eye perceives it as being, well, violet. There’s no other way to describe it, because that’s the name we’ve given to that color. If you had an object that emitted only light with a wavelength of 420 nanometers, you’d look at it and say “Yup. That’s violet all right.”

But there’s a color that’s not found anywhere in the visible spectrum. It’s just not there. You can start at the very limit of visibility of red and work your way down to the opposite limit of visibility of violet and you simply wouldn’t see it.

That color is purple.

Why doesn’t purple exist? And more importantly, if it doesn’t exist why the hell can we see it?

The answer has nothing to do with light and everything to do with the eye and the brain. If I shine a beam of light of just one wavelength into your eye, your brain will perceive the light as being of a pure color. Say the light is uniformly 530 nanometers. You’ll see that as green.

But if I shine a light of two colors into your eye, I can make you see a third color that’s not even present in the light at all. If I show you yellow light (580 nanometers) and blue light (470 nanometers) in the right proportions, you’ll see green light, even though there’s no actual green light present at all. Green is between yellow and blue, so the brain sort of averages it out.

Thus it is with purple. If I show you red light (700 nanometers, way down at one end of the spectrum) and blue light (470 nanometers, way down at the other end) you’ll see a color between red and blue: purple.

The fact that there is no “between red and blue,” since they’re at opposite ends of the spectrum, doesn’t bother the brain at all. It just keeps on going, inventing an entirely new and unnatural color. Long before we understood the relationship between color and light, we saw that artificial color and gave it a name. We called it purple.

So here we have a color spectrum defined by the various possible energies of light. And here we have a color spectrum defined by what our eyes see. Clearly the two are related, but just as clearly they don’t agree. They contradict each other. On one of them, there’s a color between red and blue that we call purple. On the other, red and blue are at opposite poles and purple doesn’t exist.

Which one’s right? Which one is true, and which is just an artifact of perception?

The answer, of course, is that the colors we see are just artifacts of perception. Red light isn’t objectively red in any meaningful sense. It just has a particular amount of energy. Our eyes perceive it as red because they do, because that’s how they work. And because our eyes work the way they do, and our brains work the way they do, we see combinations of colors as hues that never appear in the pure electromagnetic spectrum. That’s just how it is.

Color, by its very definition, is an optical illusion. The fact that some parts of it are more illusory than others shouldn’t surprise anyone.

After all, the only reason we even have color vision is so we can tell when the fruit is ripe. Or maybe fruit comes in colors only because it helps us see when it’s ripe. I get those mixed up. Either way, it’s an utterly pragmatic system, one that exists simply because it works, and any similarity between our perception and the real world should be seen as purely coincidental.

• Auspicious
• School
• A beautiful thing