Green's function

Green's function is a way of showing what happens in two different places at the same time. Think of it like two mirrors that face each other - if you do something in one place, it will be reflected in the other mirror. Green's function lets us see this reflection between places. For example, if we have a spot on a wall in one place and make a sound, Green's function will show us what happens to that sound when it reaches the other place.