What is light? If you’re like me, you’ve been trained to say “photons,” or, “electromagnetic radiation.” Well, there’s a guy who’s been working with the Exploratorium for several decades who can make you see light in a whole different way.
For a detailed “light walk,” you can go to the Light Walk on the Exploratorium website. That’s where the images in this blog post are from.
If you take two go outside on a sunny day and put a hole in a piece of cardboard, and let the dot of sunshine fall on a white screen, you’ll see an upside-down and backwards pinhole image of the sun. The image to the left was made with square holes in a board! You can do the same thing by making a mesh of your fingers — the bright spots on the ground where the sun gets through will be round images of the sun.
What did the hole do? What we did there was to block a bunch of light, and just let through a little bit of light. We let through one image of the sun.
What if we expanded the hole so it’s a slot? We’d see a slot projected on the screen — but with rounded edges. It’s a series of images of the sun, all stacked up together.
What if we took the paper away entirely? The screen looks bright white. That is infinitely many images of the sun.
So sunlight is a bunch of images of the sun, but so many that we can’t distinguish them. It’s too much information. By blocking most of the light, we make it possible to see just one of the images.
One way to convince yourself of this is with an anti-hole. Instead of a piece of paper with a hole in it, use a small scrap of paper (any shape) to block out a small bit of light. What do you see on the screen? A round black shadow. That’s a missing image of the sun. So shadows are missing images.
Definitely check out the link if you find this stuff interesting.