Once Can Be Enough: Decisive Experiments

There have been recent suggestions that replication is the “gold standard” for validating an experimental result. In this talk I will argue that a single experiment, well-performed and in an appropriate context, can serve to establish the existence of a physical phenomenon, an elementary particle, or a law of physics. This is not to say that the experiment was not replicate3d, but rather that there was no necessity for replication. I will illustrate this with examples from the history of physics. These will include the Ellis-Wooster experiment that established the continuous energy spectrum of electrons emitted in β decay, and the experiment of Wu and her collaborators that showed the nonconservation of parity, or the violation of space-reflection symmetry, in the weak interactions. In these two episodes there were earlier experiments that showed the same phenomena, but which were not accepted by the physics community. The reasons for this will be discussed.