Expanding Universe Demo
If you participated in a general astronomy class at any point in the last 30 years, it’s likely you were shown a classic demonstration of how in our expanding universe, there is no central point from which everything else is receding. In fact, no matter where you are, on earth, or on a planet in a distant galaxy 10 billion light years from now, everything would appear to be getting farther away from you. Some find this a bit troubling, since normally if you were say standing in a crowded room and everyone took a step away from you, it would be pretty obvious that you are the center of the expansion. However, if you asked everyone to move 1 foot farther apart from everyone else, then there would be no ‘center of expansion’ in that case.
A classic demonstration involves making two copies of a ‘universe’ on transparency film. One is slightly larger than the other. When placed on top of each on the overhead projector, and aligned over a galaxy, it becomes obvious that everything would appear to be expanding away from the selected galaxy. Pick any galaxy, and you get the same results. I remember seeing it done a long time ago. It’s one of the demos that just stays with you after all these years.
Here is a modern version that just uses p5 and a Hubble deep field image to do the same thing. No transparency films necessary!