If you can hear someone on the other side of a wall, then that someone can hear you as well. This is something to keep in mind when you’re snooping on your neighbour – but this straightforward statement also embodies a profound principle of physics called reciprocity.
What is reciprocity?
Simply put, the principle asserts that if a signal can be transmitted from Point A (the source) to Point B (the destination), the same signal can also be transmitted from Point B to Point A, simply by exchanging the positions of the source and the destination.
