Joan asks her brother Luke, a physics nerd, to explain the elecromagnetic spectrum to her for an exam. He tells her that everything the eye can see is in the center; molecules, gravity, and things we can't see but can quantify based on their behavior are on the left; and on the right is everything we haven't figured out yet, such as time warps and ghosts. Wrong. There is no scientific scale divided into "things we know" and "things we don't". The electromagnetic spectrum is a range of wave frequencies. We define sound, ultraviolet light, infrared light, visible light, X-rays, and cosmic rays by this spectrum. Gravity is completely different, as are molecules and most of the things mentioned in the scene. Luke, as a physics geek, would absolutely know all this. He would never, ever describe the electromagnetic spectrum the way this scene had him doing. [It's a joke.]