Axiom 

Axioms are considered selfevident requiring neither proof nor justification.
Many areas of mathematics are based on axioms: set theory, geometry, number theory, probability, etc.
At the start of 20th Century Mathematicians showed great confidence in the development of the axiomatic foundations of Mathematics. However this confidence was shattered by the work of Kurt Godel.
One requirement of an axiomatic system is that it is consistent i.e. does not lead to contradictory theorems  thus creating a paradox (see Russell's Paradox).

In Euclidian Geometry the 5th (or parallel) postulate states:
However Nikolai Lobachevsky (1792  1856) and János Bolyai (1802  1860) considered this axiom was not selfevident. When they investigated the effect of substituting an alternative axiom such that lines do not meet, however far extended, found no resulting contradictions thus formulating the first nonEuclidian Geometry. This Geometry (called hyperbolic geometry) has many features different from Euclidean Geometry. For example, the sum of the angles of a triangle is less than 180 degrees and the greater the area of the triangle the smaller the sum. Poincare's Disc is a model of such a geometry.
Different axioms lead to different geometries. Mathematics thus supplies a number of competing descriptions of Space, the correct interpretation being found experimentally. The descriptions of Space by Albert Einstein and others requires Space to be nonEuclidean.