In cosmology, the Copernican principle, named after Nicolaus Copernicus, states the Earth is not in a central, specially favoured position.^[1] More recently, the principle is generalised to the relativistic concept that humans are not privileged observers of the universe.^[2] In this sense, it is equivalent to the mediocrity principle, with significant implications in the philosophy of science. Cosmology, from the Greek: κοσμολογία (cosmologia, κόσμος (cosmos) order + λογια (logia) discourse) is the study of the Universe in its totality, and by extension, humanitys place in it. ... “Copernicus” redirects here. ... Two-dimensional analogy of space-time curvature described in General Relativity. ... This article needs additional references or sources for verification. ... Philosophy of science is the study of assumptions, foundations, and implications of science, especially in the natural sciences and social sciences. ...

Origin and implications

Michael Rowan-Robinson emphasizes the importance of the Copernican principle: "It is evident that in the post-Copernican era of human history, no well-informed and rational person can imagine that the Earth occupies a unique position in the universe."^[3] Astronomer. ...

Hermann Bondi named the principle after Copernicus in the mid-20th century, although the principle itself dates back to the 16th-17th century paradigm shift away from the Ptolemaic system, which placed Earth at the center of the Universe. Copernicus demonstrated the motion of the planets can be explained without the assumption that Earth is centrally located and stationary. He argued that the apparent retrograde motion of the planets is an illusion caused by Earth's movement around the Sun, which the Copernican model placed at the centre of the Universe. Copernicus himself was mainly motivated by technical dissatisfaction with the earlier system and not by support for any mediocrity principle.^[4] Professor Sir Hermann Bondi, KCB , FRS (1 November 1919–10 September 2005) was a British (formerly Austrian) mathematician and cosmologist. ... Paradigm shift is the term first used by Thomas Kuhn in his 1962 book The Structure of Scientific Revolutions to describe a change in basic assumptions within the ruling theory of science. ... Mediaeval drawing of the Ptolemaic system. ... This article is about Earth as a planet. ... For other uses, see Universe (disambiguation). ... This article is about retrograde motion. ... Standards Of Learning SOL stands for The Standards Of Learning. ... Split from main article Nicolaus Copernicus in order to concentrate on his work: // Much has been written about earlier heliocentric theories. ...

In cosmology, if one assumes the Copernican principle and observes that the universe appears isotropic from our vantage-point on Earth, then one can prove that the Universe is generally homogeneous (at any given time) and is also isotropic about any given point. These two conditions comprise the cosmological principle. Isotropic means independent of direction. Isotropic radiation has the same intensity regardless of the direction of measurement, and an isotropic field exerts the same action regardless of how the test particle is oriented. ... The Cosmological Principle is a principle invoked in cosmology that severely restricts the large variety of possible cosmological theories: On large scales, the Universe is homogeneous and isotropic. ...

In practice, astronomers observe that the Universe has heterogeneous structures up to the scale of galactic superclusters, filaments and great voids, but becomes more and more homogeneous and isotropic when observed on larger and larger scales, with little detectable structure on scales of more than about 200 million parsecs. However, on scales comparable to the radius of the observable universe, we see systematic changes with distance from the Earth. For instance, galaxies contain more young stars and are less clustered, and quasars appear more numerous. While this might suggest that the Earth is at the center of the Universe, the Copernican principle requires us to interpret it as evidence for the evolution of the Universe with time: this distant light has taken most of the age of the Universe to reach and shows us the Universe when it was young. The most distant light of all, cosmic microwave background radiation, is isotropic to at least one part in a thousand. Superclusters are large groups of smaller galaxy groups and clusters, and are among the largest structures of the cosmos. ... In astronomy, filaments are one of the largest known structures in the Universe, thread-like structures with a typical length of 70 to 150 megaparsec that form the boundaries between large voids in the universe. ... In astronomy, voids are the empty spaces between filaments, the largest-scale structures in the Universe that contain very few, or no, galaxies. ... A parsec is the distance from the Earth to an astronomical object which has a parallax angle of one arcsecond. ... This view, taken with infrared light, is a false-color image of a quasar-starburst tandem with the most luminous starburst ever seen in such a combination. ... “CMB” redirects here. ...

Modern mathematical cosmology is based on the assumption that the Cosmological principle is almost, but not exactly, true on the largest scales. The Copernican principle represents the irreducible philosophical assumption needed to justify this, when combined with the observations.

Bondi and Thomas Gold used the Copernican principle to argue for the perfect cosmological principle which maintains that the universe is also homogeneous in time, and is the basis for the steady-state cosmology. However, this strongly conflicts with the evidence for cosmological evolution mentioned earlier: the Universe has progressed from extremely different conditions at the Big Bang, and will continue to progress toward extremely different conditions, particularly under the rising influence of dark energy, apparently toward the Big Freeze or the Big Rip. Thomas Gold (May 22, 1920 – June 22, 2004) was an Austrian astrophysicist, a professor of astronomy at Cornell University, and a member of the US National Academy of Sciences. ... The Perfect Cosmological Principle is an extension of the Cosmological Principle stating that the Universe is not only homogeneous and isotropic in space, but also in time. ... In cosmology, the steady state theory (also known as the Infinite Universe Theory or continuous creation) is a model developed in 1948 by Fred Hoyle, Thomas Gold, Hermann Bondi and others as an alternative to the Big Bang theory (known, usually, as the standard cosmological model). ... For other uses, see Big Bang (disambiguation). ... In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe. ... scenario in which the universe becomes too cold to sustain life due to continued expansion and the decay of free energy due to the action of entropy. ... The Big Rip is a cosmological hypothesis about the Ultimate fate of the universe, in which the matter of the universe, from stars and galaxies to atoms and subatomic particles, are progressively torn apart by the expansion of the universe at a certain time in the future. ...

See also

• Anthropic principle
• Doomsday argument

In physics and cosmology, the anthropic principle is an umbrella term for various dissimilar attempts to explain the structure of the universe by way of coincidentally balanced features that are necessary and relevant to the existence of observers (usually assumed to be carbon-based life or even specifically human beings). ... The Doomsday argument (DA) is a probabilistic argument that claims to predict the future lifetime of the human race given only an estimate of the total number of humans born so far. ...

References

1. ^ H. Bondi (1952). Cosmology. Cambridge University Press, p. 13. 
2. ^ J. A. Peacock (1998). Cosmological Physics. Cambridge University Press. .
3. ^ M. Rowan-Robinson. Cosmology, 3rd ed., Clarendon Press, Oxford, p. 62. .
4. ^ Thomas Kuhn. The Copernican Revolution. Harvard University Press. .

Professor Sir Hermann Bondi, KCB , FRS (1 November 1919–10 September 2005) was a British (formerly Austrian) mathematician and cosmologist. ... Astronomer. ... Thomas Samuel Kuhn (July 18, 1922 – June 17, 1996) was an American intellectual who wrote extensively on the history of science and developed several important notions in the philosophy of science. ...

External links

• Spiked-online Article
• Slate: How will the Universe End?