Scientific Thinking

House of Mirrors

When you see yourself in the mirror, the light bouncing off you is reflecting back to your eyes.

This is pretty straightforward, but things start to get more interesting when light is reflected more than once. If you've ever put two mirrors in the same room, you know that when the angle is just right, you can peer into an infinite abyss...

In this exploration we'll use puzzles to unpack some fascinating optical effects.

                 

House of Mirrors

Before we figure out optical puzzles with more than one mirror, we need to be clear about what happens to light at a single mirror.

You probably already know that a beam of light (like one from a laser) will always follow a straight line. That is, unless it encounters a mirror.

If a ray of light originates at this gem, where will the ray reflect to?

                 

House of Mirrors

Someone hands you an open box with a hole on one side and invites you to look inside.

Little do you know that the person who built the box laid a mirror on one of the walls. The rest of the walls don't reflect light.

How many jewels can you see when your eye is at the center of the hole?

                 

House of Mirrors

A different box has the same layout, but two mirrored walls.

How many jewels can you see in this one?

                 

House of Mirrors

With two mirrors, it is possible to see light from a single object (the jewel) coming from two different directions.

In the box with two mirrors, do the images of the jewel appear to be the same distance from you?

                 

House of Mirrors

The reflection of an object in a mirror is called an image. It doesn't matter where you look at the mirror from, the image of the gem appears to stay in the same place.

You can see it yourself by changing perspective with the slider below.

                 

House of Mirrors

Now you're handed a third box. This one also has two mirrors but is laid out a little differently.

Where is the image for the ray that makes one reflection on the left mirror and then exits the box?

                 

House of Mirrors

Rays of light from the gem reflected off of the mirrored walls can produce two images of the gem on either side of the real one.

Because the two mirrored walls face each other, rays from the jewel can reflect off of either mirror before exiting the box.

When you look into the sides of the box, how many gems do you see?

                 

House of Mirrors

If you peer into the box with opposite reflecting sides, you can see images of the jewel trailing into an infinite abyss. Of course, the box is not really infinite, but some of the light in the box takes a very long time to escape as it's reflected many times between the sides.

You'll find many more optical puzzles in the Light chapter, where you'll start from mirrors in a box and explore how to construct kaleidoscopic optical patterns with only a few mirrors and a single gem.

                 
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