Linear Response Theory

Linear Response Theory describes how a system reacts to small external influences. When a slight force or change is applied, the system responds in a way proportional to that input, similar to how a stretched spring exerts a restoring force proportional to how much it was pulled. This theory helps scientists predict the system’s behavior without solving complex equations for large disturbances. It’s widely used in physics, chemistry, and engineering to understand processes like electrical conductivity, material deformation, and temperature responses, under the assumption that the perturbations are small enough to keep the response linear.