A lump of uranium left to itself will gradually decay, one nucleus at a time.
The rate of decay is measured by how
long it would take for half of a given bunch of uranium atoms to decay
The decay of an individual uranium nucleus is completely unpredictable, but we can accurately
predict the way a large lump of uranium will decay.
It is upsetting to think that chance can
rule physical properties. In response to this theory
Einstein proclaimed "God doesn't play dice!" (Einstein was wrong.)