The Friedmann Lemaître Robertson Walker (FLRW) metric is an exact solution of Einstein's field equations of general relativity; it describes a simply connected, homogeneous, isotropic expanding or contracting universe. Depending on geographical or historical preferences, a subset of the four scientists Alexander Friedmann, Georges Lemaître, Howard Percy Robertson and Arthur Geoffrey Walker may be named (e.g., Friedmann Robertson Walker (FRW) or Robertson Walker (RW) or Friedmann Lemaître (FL) ). This model is sometimes called the Standard Model of modern cosmology.