Gell-Mann—Low Theorem

The Gell-Mann–Low theorem is a fundamental idea in quantum physics that helps connect the behavior of particles when they interact strongly to how they behave when they are almost free. It provides a rigorous way to relate the complex, interacting state of particles to simpler, non-interacting states by systematically accounting for interactions. This makes it easier for physicists to calculate and understand the properties of particles in quantum field theory, bridging the gap between complicated real-world interactions and the simpler models used in calculations.