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EspañolCOPERNICAN PRINCIPLE
(Redirected from Copernican Principle)
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 simple statement that humans are not privileged observers.[2] In this sense, it is equivalent to the mediocrity principle, with significant implications in the philosophy of science.
Rowan-Robinson emphasizes the importance of the Copernican priniciple:
The principle was named in the 20th century (by Hermann Bondi), although it refers to the 16th-17th century paradigm shift away from the Ptolemaic system, which placed Earth at the centre 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].
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 (at any given time) and is also isotropic about any given point; these two conditions comprise the Cosmological principle.
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 homogenous 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 comperable 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 centre 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.
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.
Some recent results from WMAP appear to run counter to Copernican expectations. The motion of the solar system, and the orientation of the plane of the ecliptic are aligned with features of the microwave sky which on conventional thinking are caused by structure at the edge of the observable universe[5][6]
Lawrence Krauss is quoted as follows in the referenced Edge.org article:[7]
It would be somewhat surprising if the WMAP alignments were a complete coincidence, but the anti-Copernican implications suggested by Krauss would be far more surprising, if true. Other possibilities are (i) that residual instrumental errors in WMAP cause the effect (ii) that unexpected microwave emission from within the solar system is contaminating the maps.[8]
★ Anthropic principle
★ Doomsday argument
1. Cosmology, H. Bondi, , , Cambridge University Press, 1952,
2. Cosmological Physics, J. A. Peacock, , , Cambridge University Press, 1998,
3. Cosmology, 3rd Ed., M. Rowan-Robinson, , , Clarendon Press, Oxford, ,
4. The Copernican Revolution, Thomas Kuhn, , , Harvard University Press, ,
5. CERN Courier "Does the motion of the solar system affect the microwave sky?"
6. On the large-angle anomalies of the microwave sky, C. J. Copi, D. Huterer, D. J. Schwarz, G. D. Starkman, , , Monthly Notices of the Royal Astronomical Society, 2006 preprint
7. "The Energy of Space That Isn't Zero."
8. Copi et al. ''op. cit.''
★ Spiked-online Article
★ Slate: How will the Universe End?
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 simple statement that humans are not privileged observers.[2] In this sense, it is equivalent to the mediocrity principle, with significant implications in the philosophy of science.
| Contents |
| Origin and Implications |
| Evidence against the Copernican principle |
| See also |
| References |
| External links |
Origin and Implications
Rowan-Robinson emphasizes the importance of the Copernican priniciple:
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]
The principle was named in the 20th century (by Hermann Bondi), although it refers to the 16th-17th century paradigm shift away from the Ptolemaic system, which placed Earth at the centre 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].
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 (at any given time) and is also isotropic about any given point; these two conditions comprise the Cosmological principle.
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 homogenous 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 comperable 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 centre 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.
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.
Evidence against the Copernican principle
Some recent results from WMAP appear to run counter to Copernican expectations. The motion of the solar system, and the orientation of the plane of the ecliptic are aligned with features of the microwave sky which on conventional thinking are caused by structure at the edge of the observable universe[5][6]
Lawrence Krauss is quoted as follows in the referenced Edge.org article:[7]
"But when you look at CMB map, you also see that the structure that is observed, is in fact, in a weird way, correlated with the plane of the earth around the sun. Is this Copernicus coming back to haunt us? That's crazy. We're looking out at the whole universe. There's no way there should be a correlation of structure with our motion of the earth around the sun — the plane of the earth around the sun — the ecliptic. That would say we are truly the center of the universe."
It would be somewhat surprising if the WMAP alignments were a complete coincidence, but the anti-Copernican implications suggested by Krauss would be far more surprising, if true. Other possibilities are (i) that residual instrumental errors in WMAP cause the effect (ii) that unexpected microwave emission from within the solar system is contaminating the maps.[8]
See also
★ Anthropic principle
★ Doomsday argument
References
1. Cosmology, H. Bondi, , , Cambridge University Press, 1952,
2. Cosmological Physics, J. A. Peacock, , , Cambridge University Press, 1998,
3. Cosmology, 3rd Ed., M. Rowan-Robinson, , , Clarendon Press, Oxford, ,
4. The Copernican Revolution, Thomas Kuhn, , , Harvard University Press, ,
5. CERN Courier "Does the motion of the solar system affect the microwave sky?"
6. On the large-angle anomalies of the microwave sky, C. J. Copi, D. Huterer, D. J. Schwarz, G. D. Starkman, , , Monthly Notices of the Royal Astronomical Society, 2006 preprint
7. "The Energy of Space That Isn't Zero."
8. Copi et al. ''op. cit.''
External links
★ Spiked-online Article
★ Slate: How will the Universe End?
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