A panoramic shot of my bathroom.
The picture above is a photo of my house’s main bathroom. Exciting, right? It may not seem so exciting at first glance, but once you realize that there are two plane mirrors in the room, things start to get pretty crazy. What could be so exciting about two plane mirrors placed across from each other? Won’t you just see the image of the other mirror? Not quite. In fact, it gets much more complicated than that and the image calculations almost become impossible to perform.
A photo taken of the main plane mirror that allows me to see the oval-shaped mirror.
There are two mirrors in my bathroom: the large plane mirror on the main wall and the small oval-shaped plane mirror above the toilet. While brushing my teeth tonight thinking about what I should write for my physics blog about optics, I realized something strange about the two mirrors. As I was looking into the main plane mirror, I noticed that the oval-shaped mirror in the back seemed to show me a reflection of my back. That observation was intuitive, but what really intrigued me was the fact that there seemed to be an infinite series of mirrors in which I could see a small portion of my bathroom. The picture to the left shows a photo that I took of the main plane mirror. The photo of the main plane mirror allows me to see the oval-shaped mirror and an infinite series of oval-shaped mirrors inside of it.
How and why does this series of infinite mirrors appear? The reason lies behind arguably the most basic fact about plane mirrors: plane mirrors produce virtual images that seem to appear “behind” the mirror. Because the oval-shaped mirror and the large plane mirror are located across from each other, they keep making images of each other. Let’s follow the light path for a few steps so we understand how this happens. Light from in front of the main plane mirror travels to the plane mirror and produces a virtual image that appears “behind” the plane mirror. At the same time, light in front of the oval-shaped mirror (which is coming from the image of the main plane mirror) travels to the oval-
A photo taken of the oval-shaped mirror.
shaped mirror and produces a virtual image that appears “behind” the oval-shaped mirror. Essentially, the two mirrors in this situation and producing images of images. Inside those images are two mirrors, the main plane mirror and the oval-shaped mirror. This sequences of events happens over and over again, forming an infinite amount of mirror images. That is, the mirrors are making images of images, and the images that the mirrors form go on to make further images of the formed images! Phew, that was a mouthful.
Infinity mirrors are an interesting application of optics. Although infinity mirrors are not extremely useful for us in our day-to-day lives, they can produce stunning designs. Check out the image below of an artificially made infinity mirror placed above a bathroom sink. Without physics, bathrooms would be extremely boring.
Infinity mirror in a bathroom.
A Day in the Life of Physics 