Wiener–Khinchin theorem

The Wiener–Khinchin theorem is a math statement that explains how energy and power are related in a system. In simpler terms, it is a way to measure the total amount of energy in a system based on how much power it creates. To understand this better, imagine a system like a string of Christmas lights. The more lights that are on, the more power the system has and the more energy the system contains. So, the Wiener–Khinchin theorem explains that the total amount of energy in a system can be determined by how much power it creates.