Life's Great Mysteries - When you turn off the lights, where does the light go?

I’m being serious here. Think about it… light is pretty persistent. After all, you can see stars that are many light years away. That means the light from those stars has traveled for years—even thousands of years—to get to your eyeball, and over all that distance and all that time the light has persisted. So, it seems logical to me that, in an enclosed room with no windows, the light from a flashlight should stay in the room even after you turn off the flashlight. After all, light is an electromagnetic wave that goes on forever…

But only if nothing absorbs it. Let’s say you’re in a room with no windows. You turn on a light bulb to light up the room, but the room gets dark again as soon as you turn off the bulb. Why? Because the light is quickly absorbed by the walls (and even by the air particles in the room). It happens so fast your eyes can’t detect it. It occurs to me that if the light wasn’t being absorbed, the room would get brighter and brighter the longer you left the light bulb on because the light would just continue bouncing off the walls, and the “old” light would remain in the room even as new light is being added. That’s a strange thought, but strange thoughts are the way I roll.

Okay, let's take this a step further… what if the walls of the room are mirrors? Wouldn’t the reflected light just keep bouncing around in the room for a long time? Nope. The light still disappears in an instant, due to the fact that typical mirrors do not reflect 100% of the light hitting them. Okay, then what if we had really, really good mirrors? Like, perfect mirrors that reflect 100% of the light. Well, as it turns out, the mirrors with the highest reflectivity, made for reflecting a laser beam, have a reflectivity of about 99.999%. Therefore, the light in the room of mirrors would still disappear in an instant. You have to consider how fast light travels. If you have a little cubical room that is 10 cm wide on each side, a beam of light will bounce off the walls about three billion times in one second! So, even if the walls were made of the best mirrors in the world, with 99.999% reflection, the light would be gone in a tiny fraction of a second.

So much for my idea of making a container to hold some light for when I might need it later.

Photo Credits:
- Hands holding light - DepositPhotos