 Algebraic number field

An **algebraic number field** is a certain type of field in algebraic number theory. Specifically, an algebraic number field is a finite extension of the field of rational numbers, \(\mathbb{Q}\), that is generated by the roots of polynomial equations with coefficients in \(\mathbb{Q}\).

The set of all algebraic numbers forms a field.

This field contains all of the rational numbers, but it is a quadratically closed field.

Like the rationals, this field also has the same cardinality as the natural numbers, because we can specify and enumerate each of its members by a fixed number of integers from the polynomial equation that defines them. So it is a bit like the rationals, but we use potentially arbitrary numbers of integers to specify each number (polynomial coefficients + index of which root we are talking about) instead of just always two as for the rationals.

Each algebraic number also has a degree associated to it, i.e. the degree of the polynomial used to define it.