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Cosmology, from the Greek: κοσμολογία (κόσμος world + λογια discourse) is the study of the universe in its totality. It describes disparate fields studied by physicists, philosophers and theologians.

Physical cosmology

Physical cosmology is the branch of physics and astrophysics, which deals with the study of the physical origins of the universe and of the universe on its very largest scales. In its earliest form it was what is now known as celestial mechanics the study of the heavens. The Greek philosophers Aristarchus, Aristotle and Ptolemy proposed different cosmological theories. In particular, the geocentric Ptolemaic system was the accepted theory to explain the motion of the heavens until Nicolaus Copernicus, and subsequently Tycho Brahe, Johannes Kepler and Galileo Galilei proposed a heliocentric system in the 16th century.

With Isaac Newton and the 1687 publication of Principia Mathematica, the problem of the motion of the heavens was finally solved. Newton provided a physical mechanism for Kepler's laws and his law of universal gravitation allowed the anomalies in previous systems, caused by gravitational interaction between the planets, to be resolved. A fundamental difference between Newton's cosmology and those preceding it was the Copernican principle that the bodies on earth obey the same physical laws as all the celestial bodies. This was a crucial philisophical advance in physical cosmology.

Modern scientific cosmology arose in 1915 with Albert Einstein's publication of his theory of general relativity. Prior to this, physicists' prejudices had led them to assume that the universe was static and unchanging. The general theory of relativity, however, was the first physical theory in which it was meaningful to address questions of the origins and age of the observable universe, and it was found that the theory was not amenable to a static universe. Thus the big bang theory was proposed by Georges Lemaître and confirmed by Edwin Hubble's discovery of the recession of distant galaxies and the discovery of the cosmic microwave background radiation by Arno Penzias and Robert Woodrow Wilson in 1964.

Cosmology (metaphysics)

Cosmology is also a branch of philosophy and metaphysics that deals with the world as the totality of space, time and all phenomena. It is the attempt to address the metaphysical question of the cause of the universe. No matter how successful a scientific theory, such as the big bang, is, explaining why matter exists in the first place is not a scientific question. Therefore, cosmology as a branch of metaphysics is an attempt to address three basic questions:

• What is the origin of the universe? What is its first cause? (see monism, pantheism and creationism)
• What are the ultimate material components of the universe? (see mechanism, hylomorphism, atomism)
• What is the ultimate reason for the existence of the universe? Do the cosmos have a purpose?

Religious cosmology

• Origin beliefs: Many religions have cosmological interpretations of the origin of the universe:
  • Cosmology in religion.
    • Cosmology in the Bible.
    • Cosmology (argument for the existence of God) in Christianity.
    • Cosmology in Islam's Kalam.
    • Eschatology is the religious description of the end of the universe.

See also: Cosmology for the jazz group.

• Cosmology