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 replicated, but rather that there was no necessity for replication. I will illustrate this with examples from the history of science. These will include Mendel’s experiments on pea plants that began modern genetics, 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 non-conservation of parity, or the violation of space-reflection symmetry, in the weak interactions.