First-Order Perturbation

First-order perturbation is a mathematical method used to estimate how a small change in a system's parameters affects its behavior or energy levels. Imagine a complex problem that's hard to solve exactly; instead, you start with a known, simpler version and then account for a tiny modification. This approach provides an approximate solution by considering only the immediate, or first, level of influence of the disturbance, making complex problems more manageable without requiring a full re-analysis of the entire system.