S: I don’t know what sounds more suspicious, the word "flying saucer" or the phrase "project Mogul." The idea of a sound channel is pretty cool though.
M: Yes, you know this is the same physics we use to build fiber optics. You may have seen these little plastic tubes like in the picture on the right. You send a light ray through and the light ray will follow the trajectory of the tubes. This is because the tube is a light channel. (And, yes, you guessed it: light is a wave.) The tube is made of a particular plastic in which light travels slower.
M: Fiber optics are now super important for communication all around the world.
S: Wait! If light is a wave, what is the medium? What is waving for light?
M: Very good. Light was very confusing to physicists for centuries, and, as we will see, the behavior of light is the key to BOTH Relativity and Quantum Mechanics. So light is very important in this class and here we will just start scratching the surface.
M: Regarding the medium. Light travels through many materials and the speed varies depending on whether the material is water, glass etc... Interestingly, light can also travel in empty space and this is where light reaches its maximum speed of c = 299 792 458 m/s.
S: So what is it that is waving in empty space? You can’t have sound waves in empty space (even though movies do), but you can have light rays. Right?
M: That's correct. We will come back to that question later on, but we don’t need to know what is waving in order to know that light is a wave. In the lab this week, you will perform an experiment that proves without any doubt that light is a wave.