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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Copernican principle | 2/2 | https://en.wikipedia.org/wiki/Copernican_principle | reference | science, encyclopedia | 2026-05-05T12:42:26.378553+00:00 | kb-cron |
Before the term Copernican principle was even coined, past assumptions, such as geocentrism, heliocentrism, and galactocentrism, which state that Earth, the Solar System, or the Milky Way respectively were located at the center of the universe, were shown to be false. The Copernican Revolution dethroned Earth to just one of many planets orbiting the Sun. Proper motion was mentioned by Halley. William Herschel found that the Solar System is moving through space within our disk-shaped Milky Way galaxy. Edwin Hubble showed that the Milky Way galaxy is just one of many galaxies in the universe. Examination of the galaxy's position and motion in the universe led to the Big Bang theory and the whole of modern cosmology.
=== Modern tests === Recent and planned tests relevant to the cosmological and Copernican principles include:
time drift of cosmological redshifts; modelling the local gravitational potential using reflection of cosmic microwave background (CMB) photons; the redshift dependence of the luminosity of supernovae; the kinetic Sunyaev–Zeldovich effect in relation to dark energy; cosmic neutrino background; the integrated Sachs–Wolfe effect; testing the isotropy and homogeneity of the CMB; observation of the KBC Void – some authors claim it violates the cosmological principle and thus the Copernican principle, while others claim that it is consistent with them.
== Physics without the principle == The standard model of cosmology, the Lambda-CDM model, assumes the Copernican principle and the more general cosmological principle. Some cosmologists and theoretical physicists have created models without the cosmological or Copernican principles to constrain the values of observational results, to address specific known issues in the Lambda-CDM model, and to propose tests to distinguish between current models and other possible models. A prominent example in this context is inhomogeneous cosmology, to model the observed accelerating universe and cosmological constant. Instead of using the current accepted idea of dark energy, inhomogeneous-cosmology models propose that the universe is much more inhomogeneous than currently assumed — for example, that the Solar System is in an extremely large low-density void. To match observations the Solar System would have to be very close to the centre of this void, immediately contradicting the Copernican principle. While the Big Bang model in cosmology is sometimes said to derive from the Copernican principle in conjunction with redshift observations, the Big Bang model can still be assumed to be valid in absence of the Copernican principle, because the cosmic microwave background, primordial gas clouds, and the structure, evolution, and distribution of galaxies all provide evidence, independent of the Copernican principle, in favor of the Big Bang. However, the key tenets of the Big Bang model, such as the expansion of the universe, become assumptions themselves akin to the Copernican principle, rather than derived from the Copernican principle and observations.
== See also ==
== References ==