THE MYSTERIES OF THE UNIVERSE
Cosmology is the scientific inquiry into what the universe is like. By making
assumptions that are not contradicted by the behaviour of the observable universe,
scientists build models, or theories, that attempt to describe the universe as a whole,
including its origin and its future. They use each model until something is found that
contradicts it. Then the model must be modified or discarded. Cosmologists usually
assume that the universe, except for small irregularities, has an identical appearance
to all observers - identical to the laws of physics - irrespective of where in the
universe the observers are located. This unproven concept is called the
cosmological principle. One consequence of the cosmological principle is that the
universe cannot have an edge, for, otherwise, an observer near the edge would
have a different view from that of someone near the centre. Thus, space must be
infinite and evenly filled with matter, or, alternatively, the geometry of space must be
such that all observers see themselves as at the centre. Also, astronomers believe
that the only motion that can occur, except for small irregularities, is a uniform
expansion or contraction of the universe.
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