• The discovery of the expansion of the universe 

      Grøn, Øyvind (Galaxies;Volume 6, Issue 4, Journal article; Journal article; Peer reviewed, 2018-12-03)
      Alexander Friedmann, Carl Wilhelm Wirtz, Vesto Slipher, Knut E. Lundmark, Willem de Sitter, Georges H. Lemaître, and Edwin Hubble all contributed to the discovery of the expansion of the universe. If only two persons are ...