The idea of probabilities has been in human beings at least as long as science. If you do not have complete knowledge – and you almost never have – then you have to resort to probabilities. Despite its age, there is surprisingly great disagreement over the status of the concept. How do you determine a probability, for example? Is it absolute and objective?
In physics, the problem has existed for many hundreds of years, and has literally demanded death victims – for example, Boltzman, who took his own life, was very depressed by the criticism of his probability interpretation of concepts such as temperature and entropy.
Out of the study of thermodynamics, one of the most universally used methods for determining probabilities was the principle of maximum entropy.
Quantum mechanics break with this principle and give another – and still very incomprehensible but workable – method of calculating probabilities.