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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. Its meaning and scope have changed over the ages. 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 and the growing ability of astronomers to study very distant objects. 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? (see cosmological argument, cosmogony)

Religious cosmology

Many world religions have origins beliefs that explain the beginnings of the universe and life. Often these are dogmatic beliefs that arise in scriptures, but some theologians have tried go give philisophical argument for the existence of God.

• Both Christianity and Judaism accept creation according to Genesis. See also Biblical cosmology and Tzimtzum.
• Kalam cosmological argument in Islam's Kalam.

Eschatology is the religious description of the end of the universe. The study of the creation of the universe is also called cosmogony.

See also: Cosmology (band) for the jazz group.

• Cosmology