The S-matrix, or scattering matrix, is a fundamental concept in quantum mechanics and quantum field theory that describes how the initial states of a physical system evolve into final states through scattering processes. It encapsulates the probabilities of transitioning from one set of quantum states to another due to interactions. In more detail: 1. **Definitions**: The S-matrix relates the "in" states (initial states of particles before interaction) to the "out" states (final states after interaction).
New to topics? Read the docs here!