(mathematics) The branch of mathematics dealing with dynamical systems which can undergo abrupt irreversible qualitative changes due to a tiny change in parameters.

(mathematics) A branch of mathematics which deals with spaces and maps between them in abstraction, taking similar theorems from various disparate more concrete branches of mathematics and unifying them.

(physics) The theory that all gross matter is composed of atoms. / (physics) Any of several theories that explain the structure of the atom, and of subatomic particles.

(physics) The theories of special relativity and general relativity, two theories in physics developed mainly by Albert Einstein at the beginning of the 20th century from which several important results such as the equivalence of matter and energy and the Einstein field equations are derived.

(dated) atomic theory

(logic) Recursion theory. / (computer science) The branch of the theory of computation that studies which problems are computationally solvable using different models.

(algebra, field theory) The branch of mathematics dealing with Galois groups, Galois fields, and polynomial equations.

(mathematics) A branch of mathematics which deals with patterns that inevitably arise in sufficiently large sets (i.e., subsets of some structure).

(mathematics) A branch of mathematics concerned with dynamical systems which suffer sudden qualitative changes from an infinitesimal change in a parameter.

(logic) A branch of mathematical logic studying computable functions and Turing degrees, concerned with questions such as "What does it mean for a function on the natural numbers to be computable?" and "Can noncomputable functions be classified into a hierarchy based on their level of noncomputability?".