Calder's Theorem

Calder’s Theorem, in the context of quantum field theory, shows that complex interactions between particles—like the creation and destruction of particles or their changing energy states—can be modeled mathematically using linear operations called "unitary transformations." Essentially, it guarantees that the evolution of a quantum system can be described consistently and predictably through these transformations, maintaining probabilities and the fundamental structure of quantum mechanics. This provides a rigorous foundation for understanding and calculating how particles behave and interact in quantum fields over time.