The Colours Hiding in White Light

The story

Sunlight looks plain, doesn't it? White. Ordinary. The most everyday thing in the world. But sunlight is keeping a secret, and a young scientist named Isaac Newton caught it red-handed. And orange-handed. And yellow, green, blue and violet-handed too.

Here it is straight away: white light is not plain at all. Hiding inside every beam of ordinary daylight is a whole rainbow, all the colours riding along together, mixed so perfectly that they look white. Newton proved it with a piece of glass.

More than three hundred and fifty years ago, Newton was a young man in England with a burning curiosity. He darkened a room and made a small hole in the window covering, so a single thin beam of sunlight streamed in. Then he held up a prism, a solid bar of clear glass with triangle-shaped ends, right in the beam's path. The light dived into the glass, bent, and came out the other side transformed. On the wall stretched a glowing band of colours: red, orange, yellow, green, blue, violet. A rainbow, indoors, on demand.

Now, other people had seen prisms make colours before. But many people believed the glass somehow ADDED the colours, painting the plain white light as it passed through. Newton wondered if it was the other way around. What if the colours were in the sunlight all along, and the glass was simply sorting them out, spreading them apart like a hand fanning out playing cards?

So he designed one of the most famous experiments in science. From his indoor rainbow he blocked off every colour except one, letting just the green light, say, travel on. Then he put a SECOND prism in its path. If glass really painted light, this second prism should add new colours and change the green. It did not. The green light bent, and came out still purely green. Glass could not paint light. It could only unpack it. The colours belonged to the sunlight itself.

And once you know that, the sky starts explaining itself. A rainbow after rain is millions of raindrops doing Newton's experiment all at once, each tiny drop bending sunlight and fanning its hidden colours across the sky. The glitter of colours flashing from a diamond, or from the edge of a mirror, or from spray at a waterfall, is the same trick again: white light, unpacked.

Newton kept asking questions like this his whole life, about light, about gravity, about the moon, and he became one of the most celebrated scientists who ever lived.

So the next time you see a rainbow, remember what Isaac Newton found with his triangle of glass. You are not seeing colours being made. You are seeing what plain daylight was carrying all along, every moment of every day.