Statistical Mechanics
Statistical mechanics is a sub-branch of physics that attempts to explain the behavior of a macroscopic system based on the behavior and properties of that system's microscopic elements.
The number of these microscopic elements is usually very large, and it is impossible to accurately predict the behavior of each of these elements as they interact. However, the large number of interactions makes it theoretically possible for statistical mechanics to predict the behavior of the system as a whole.
Additional topics
Science EncyclopediaScience & Philosophy: Spectroscopy to Stoma (pl. stomata)