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Expanding universe, conceptual image. The universe and its galaxies are shown on the surface of a balloon. As the balloon is inflated the galaxies recede from each other. The two-dimensional surface of the balloon is analogous to the three-dimensional fabric of space, showing that the motion of the galaxies is not through space, but is due to the expansion of space itself. In addition, there is no centre to this expansion as the universe will appear to be expanding uniformly from the point of view of any galaxy. This analogy was used by the British astronomer Arthur Eddington (1882-1944) in 'The Expanding Universe' (1933). (KEYSTONE/SCIENCE PHOTO LIBRARY/VICTOR DE SCHWANBERG)