All experiments have uncertain or random aspects, and quantifying randomness is what probability is all about. The mathematical axioms of probability provide rules for manipulating the numbers, and yet pinning down exactly what a probability means can be difficult. Attempts at clarification have resulted in two main schools of statistical inference, frequentist and Bayesian, and years of raging debate.
For frequentists, a probability is something associated with the outcome of an observation that is at least in principle repeatable, such as the number of nuclei that decay in a certain time. After many repetitions of a measurement under the same conditions, the fraction of times one sees a certain outcome—for example, 5 decays in a minute—tends toward a fixed value.
The idea of probability as a limiting frequency is perhaps the most widely used interpretation encountered in a physics lab, but it is not really what people mean when they...
