In quantum field theory, and especially asymptotically free quantum field theories, an observable is infrared safe if it does not depend on the low energy/long distance physics of the theory. Such observables can therefore be calculated reliably using perturbative methods and then compared to experiment.[1] [2] An example of an observable which is infrared safe is the total scattering cross-section for the collision of an electron and a positron to produce hadrons.[3]