History

Standard cosmological theory states that the Universe came into being at a definite moment, most astronomers are convinced that this was between 12 to 20 thousand million (or billion) years ago, on the basis that clusters of galaxies are moving away from one another causing the Universe to expand and from this it could be inferred, with the theory of relativity, that in the past these were closer together, and that far back enough everything came together at a certain point, known as a singularity, in an accelerated expansion known as the big bang.

The Universe

The Universe is the collection of all the celestial objects and the space between them. In cosmoslogy, the properties of model Universes are compared with observations of the real Universe to decide what type of Universe we live in. It is of imaginable size (10¹⁰ light years) and age (10¹⁰ years), leading to a high expectation, but no proof, that life exists elsewhere.