universe

The red shift causes lines in the spectra of galaxies to be shifted towards the red end of the spectrum. More distant galaxies have greater red shifts than closer galaxies. The red shift indicates that distant galaxies are moving apart rapidly, as the universe expands.

All of space and its contents, the study of which is called cosmology. The universe is thought to be between 10 billion and 20 billion years old, and is mostly empty space, dotted with galaxies for as far as telescopes can see. These galaxies are moving further apart as the universe expands. Current theories that attempt to explain how the universe came into being and evolved are all versions of the Big Bang theory of an expanding universe originating in a single explosive event creating hydrogen and helium gases.

The most distant detected galaxies and quasars lie 10 billion light years or more from Earth. Apart from those galaxies within the Local Group, all the galaxies we see display red shifts in their spectra, indicating that they are moving away from us. The further we look into space, the greater are the observed red shifts, which implies that the more distant galaxies are receding at ever greater speeds.

This observation led to the theory of an expanding universe, first proposed in 1929 by US astronomer Edwin Hubble, and to Hubble's law, which states that the speed with which one galaxy moves away from another is proportional to its distance from it. Current data suggest that the galaxies are moving apart at a rate of 65–75 kps/40–47 mps for every million parsecs of distance (one parsec equals 3.26 light years, or 3.08 × 10¹³ km). Recent discoveries suggest that the speed of recession is accelerating rather than slowing.

Recent advances In 2003 astronomers revealed the most detailed map ever produced of the known universe. The three-dimensional map, covering 6% of the sky, contained over 200,000 galaxies and was constructed using wide-angle images taken by the telescope at Apache Point Observatory, New Mexico. Data from the telescope's fibre-optic system was used to calculate the distance and position of each galaxy on the 3-D map. Astronomers analysed the positioning of the galaxies to provide further evidence for the existence of ‘dark matter’.

The deepest images ever taken of the universe were reported by astronomers in 2004. The visible and infrared images of 10,000 galaxies were obtained from the Ultra Deep Field instrument of the Hubble Space Telescope.

The galaxies are thought to have formed 700–900 million years after the Big Bang, a period considered crucial to understanding the formation of the early universe.