Cosmological Principle
The Cosmological Principle and the Copernican Principle are philosophies which states that humans on the Earth or in the Solar System are not privileged observers of the universe. Astronomical observations must consequently be interpreted under the context of current astronomical theories, regardless of what reality might otherwise suggest. Read the following quote carefully:
“ ‘For instance, if the universe were finite and had a centre, and if the Milky Way were not near that centre, then the total brightness of all the rest of the matter in the universe should be slightly greater on one side of the earth than the other. But the night sky beyond the Milky Way is not noticeably brighter in one direction than the other; therefore astronomers are forced to conclude that the universe extends indefinitely far in all directions. The only other possibility is that the earth is the centre of everything – one planet serving as a focal point for thousands and millions of galaxies and millions of millions of other probable planets. This alternative is so preposterous that cosmologists have ruled it out from the beginning. In fact, they have made it a fundamental tenet of their creed that the Milky Way’s position in the universe is not peculiar or untypical in any way. From this idea they derive a basic axiom known as the cosmological principle: namely, that the universe must be the same on average everywhere and in all directions. ”
—‘Space, Time and the Universe,’ The Universe, Time-Life Books, 1962, p.170.
Below are miscellaneous quotes from astronomers and authors remarking that the universe is the same everywhere we look:
Cosmological Principle
“ A fundamental presupposition of modern cosmology is the Copernican Principle, that we are not in a central, or otherwise special region of the Universe. Studies of Type Ia supernovae, together with the Copernican principle, have led to the inference that the Universe is accelerating in its expansion. The usual explanation for this is that there must exist a ‘Dark Energy,’ to drive the acceleration. Alternatively, it could be the case that the Copernican Principle is invalid, and that the data has been interpreted within an inappropriate theoretical framework. If we were to live in a special place in the Universe, near the centre of a void where the local matter density is low, then the supernovae observations would be accounted for without the addition of dark energy. ”
—Timothy Clifton, Oxford Astrophysics Member, BSc, PhD. (T. Clifton, et al, “Living in a Void: Testing the Copernican Principle with Distant Supernovae,” Phys. Rev. Lett. 101 (13): 1302 (Sep 2008).
“ …the universe might look the same in every direction as seen from any other galaxy, too. This, as we have seen, was Friedmann’s second assumption. We have no scientific evidence for, or against, this assumption. We believe it only on grounds of modesty. ”
—Steven Hawking, A Brief History of Time, p. 42 (Bantam, 1988).
“ A widespread idea in cosmology is that the universe is homogeneous and isotropic above a certain scale. This hypothesis, usually called the cosmological principle, is thought to be a generalization of the Copernican principle that “the Earth is not in a central, specially favored position”. The assumption is that any observer at any place at the same epoch would see essentially the same picture of the large scale distribution of galaxies in the universe.
However, according to a Fourier analysis by Hartnett & Hirano, the galaxy number count N from redshift z data (N–z relation) indicates that galaxies have preferred periodic redshift spacings.........A natural interpretation is that concentric spherical shells of higher galaxy number densities surround us, with their individual centers situated at our location. ”
—Professor Shigeo Hirano, "Observational tests for oscillating expansion rate of the Universe" Physical Review D, 2010.
“ Often the simplest of observations will have the most profound consequences. It has long been a cornerstone of modern science, to say nothing of man’s cosmic outlook, that the Earth attends a modest star that shines in an undistinguished part of a run-of-the-mill galaxy. Life arose spontaneously and man evolved on this miscellaneous clump of matter and now directs his own destiny without outside help. This cosmic model is supported by the Big-Bang and Expanding Universe concepts, which in turn are buttressed by the simple observation that astronomers see redshifts wherever they look. These redshifts are due, of course, to matter flying away from us under the impetus of the Big Bang. But redshifts can also arise from the gravitational attraction of mass. If the Earth were at the center of the universe, the attraction of the surrounding mass of stars would also produce redshifts wherever we looked! The argument advanced by George Ellis in this article is more complex than this, but his basic thrust is to put man back into a favored position in the cosmos. His new theory seems quite consistent with our astronomical observations, even though it clashes with the thought that we are godless and making it on our own. ”
—Editor of Nature Magazine, Paul C. W. Davies.
Redshift
“ ...all this evidence that the universe looks the same whichever direction we look in might seem to suggest there is something special about our place in the universe. In particular, it might seem that if we observe all other galaxies to be moving away from us, then we must be at the center of the universe. ”
—Steven Hawking, A Brief History of Time
“ This assumption is made because it is believed to be unreasonable that we should be near the center of the Universe.” ”
—George F. R. Ellis, “Is the Universe Expanding?” General Relativity and Gravitation 9 (2): 92 (1978).
“ A widespread idea in cosmology is that the universe is homogeneous and isotropic above a certain scale. This hypothesis, usually called the cosmological principle, is thought to be a generalization of the Copernican principle that “the Earth is not in a central, specially favored position”. The assumption is that any observer at any place at the same epoch would see essentially the same picture of the large scale distribution of galaxies in the universe.
However, according to a Fourier analysis by Hartnett & Hirano, the galaxy number count N from redshift z data (N–z relation) indicates that galaxies have preferred periodic redshift spacings.........A natural interpretation is that concentric spherical shells of higher galaxy number densities surround us, with their individual centers situated at our location. ”
—Professor Shigeo Hirano, "Observational tests for oscillating expansion rate of the Universe" Physical Review D, 2010.
“ "It is shown that the cosmological interpretation of the red shift in the spectra of quasars leads to yet another paradoxical result: namely, that the Earth is the center of the Universe."
“The Earth is indeed the center of the Universe. The arrangement of quasars on certain spherical shells is only with respect to the Earth. These shells would disappear if viewed from another galaxy or quasar. This means that the cosmological principle will have to go. Also it implies that a coordinate system fixed to the Earth will be a preferred frame of reference in the Universe. Consequently, both the Special and General Theory of Relativity must be abandoned for cosmological purposes." ”
—Y. P. Varshni, “The Red Shift Hypothesis for Quasars: Is the Earth the Center of the Universe?” Astrophysics and Space Science 43 (1): 3 (1976).
“ If the redshifts are a Doppler shift...the observations as they stand lead to the anomaly of a closed universe, curiously small and dense, and, it may be added, suspiciously young. ”
—Edwin Hubble, Monthly Notices of the Royal Astronomical Society, 17, 506, 1937.
“ A 2.29 GHz VLBI all-sky survey of ultra-compact radio sources has formed the basis of a number of cosmological investigations, which examine the relationship between angular-size and redshift. Here I use a sample of 468 such sources with 0.5This is interpreted as meaning that the Universe is not spatially homogeneous on the largest scales, and is better represented at late times by a spherically symmetric model with a density enhancement at its centre. ”
—Ultra-compact radio sources and the isotropy and homogeneity of the Universe J. C. Jackson - https://arxiv.org/abs/1207.0697
Cosmic Microwave Background
“ In the Friedman universe, one possible interpretation of the coordinates is that the whole space is on the surface of an expanding balloon and has no center… [But] in such a universe, there is no cosmic microwave background (CMB) dipole, even in the presence of a peculiar velocity. In other words, the observation of a CMB dipole excludes such an interpretation of the coordinates for the Friedman universe. ”
—Y. Tomozawa, “The CMB Dipole and Existence of a Center for Expansion of the Universe,” Michigan Center for Theoretical Physics, University of Michigan, p. 2 (2 Feb 2008).
“ Additionally, we must take seriously the idea that the acceleration apparently indicated by supernova data could be due to large scale inhomogeneity with no dark energy. Observational tests of the latter possibility are as important as pursuing the dark energy (exotic physics) option in a homogeneous universe.
Theoretical prejudices as to the universe’s geometry, and our place in it, must bow to such observational tests. Precisely because of the foundational nature of the Copernican Principle for standard cosmology, we need to fully check this foundation. And one must emphasize here that standard CMB anisotropy studies do not prove the Copernican principle: they assume it at the start. ”
—George Ellis, “Inhomogeneity Effects in Cosmology,” arXiv:1103.2335v1 (Mar 2011).
“ Studies of the cosmic background radiation have confirmed the isotropy of the radiation, or its complete uniformity in all directions. If the universe possesses a center, we must be very close to it…otherwise, excessive observable anisotropy in the radiation intensity would be produced, and we would detect more radiation from one direction than from the opposite direction. ”
—Joseph Silk of the University of California, "The Big Bang: The Creation and Evolution of the Universe", p. 53 (W. H. Freeman, 1980).
Dark Energy
“ Although dark energy may seem a bit contrived to some, the Oxford theorists are proposing an even more outrageous alternative. They point out that it's possible that we simply live in a very special place in the universe - specifically, we're in a huge void where the density of matter is particularly low. The suggestion flies in the face of the Copernican Principle, which is one of the most useful and widely held tenets in physics.
Copernicus was among the first scientists to argue that we're not in a special place in the universe, and that any theory that suggests that we're special is most likely wrong. The principle led directly to the replacement of the Earth-centered concept of the solar system with the more elegant sun-centered model.
Dark energy may seem like a stretch, but it's consistent with the venerable Copernican Principle. The proposal that we live in a special place in the universe, on the other hand, is likely to shock many scientists. ”
—Dark Energy: Is It Merely An Illusion? ScienceDaily (Sep. 26, 2008) - http://www.sciencedaily.com/releases/2008/09/080926184749.htm
Nebulae
“ The departures from uniformity are positive; the numbers of nebulae increase faster than the volume of space through which they are scattered. Thus the density of the nebulae distribution increases outwards, symmetrically in all directions, leaving the observer in a unique position. Such a favoured position, of course, is intolerable; moreover, it represents a discrepancy with the theory, because the theory postulates homogeneity. Therefore, in order to restore homogeneity, and to escape the horror of a unique position, the departures from uniformity, which are introduced by the recession factors, must be compensated by the second term representing effects of spatial curvature. ”
—E. Hubble The Observational Approach to Cosmology, 1937, p.58
Gamma Ray Burst
“ The uniform distribution of burst arrival directions tells us that the distribution of gamma-ray-burst sources in space is a sphere or spherical shell, with us at the center (some other extremely contrived and implausible distributions are also possible). But Copernicus taught us that we are not in a special preferred position in the universe; Earth is not at the center of the solar system, the Sun is not at the center of the galaxy, and so forth. There is no reason to believe we are at the center of the distribution of gamma-ray bursts. If our instruments are sensitive enough to detect bursts at the edge of the spatial distribution, then they should not be isotropic on the sky, contrary to observation; if our instruments are less sensitive, then the N ∝ S-3/2 law should hold, also contrary to observation. That is the Copernican dilemma. To this day, after the detection of several thousand bursts, and despite earnest efforts to show the contrary, no deviation from a uniform random distribution (isotropy) in the directions of gamma-ray bursts on the sky has ever been convincingly demonstrated. ”
—Jonathan I. Katz, The Biggest Bangs: The Mystery of Gamma-Ray Bursts, The Most Violent Explosions in the Universe, pp. 84, 90-91 (Oxford University Press, 2002).
Copernican Principle
“ The Copernican principle states that humans are not privileged observers of the universe and provides our philosophical basis for assuming that on the largest scales the universe is spatially homogeneous. While it is one of the foundational aspects of modern cosmology, this assumption remains untested outside of the standard paradigm. Though it may seem pedantic to test something so obvious, the standard paradigm itself is built on shaky foundations, relying on an unexplained, gravitationally repulsive, dark-energy component for observations to fit the model. The implications of this cannot be overstated. Assuming that the laws of physics do apply equally everywhere in the universe, the only non- copernican configuration possible is one in which we live in a place that originates from special initial conditions. ”
—'Testing the Copernican principle by constraining spatial homogeneity' : Wessel Valkenburg,1, 2 Valerio Marra,2 and Chris Clarkson3 1Instituut-Lorentz for Theoretical Physics, Universiteit Leiden Postbus 9506, 2333 CA Leiden, The Netherlands. - http://arxiv.org/pdf/1209.4078v1.pdf
“ Astronomers will find it hard to settle that troubling sensation in the pit of their stomachs. The truth is that when it comes to swallowing uncomfortable ideas, dark energy may turn out to be a sugar-coated doughnut compared to a rejection of the Copernican principle. ”
—Dark Energy and the Bitterest Pill,” July 14, 2008 at the Physics arXiv blog.
“ Dark Energy is problematic. No one really knows what it is. We can make an educated guess, and use quantum theory to estimate how much of it there might be, but then we overshoot by an astounding factor of 10120. That is grounds enough, says George Ellis…to take a hard look at our assumptions about the universe and our place in it. “If we analyse the supernova data by assuming the Copernican principle is correct and get out something unphysical, I think we should start questioning the Copernican principle…. Whatever our theoretical predilections, they will in the end have to give way to the observational evidence.”
So what would it mean if…the outcome were that the Copernican principle is wrong? It would certainly require a seismic reassessment of what we know about the universe….If the Copernican Principle fails, all that goes [with] that goes out the window too….Cosmology would be back at the drawing board. If we are in a void, answering how we came to be in such a privileged spot in the universe would be even trickier. ”
—Marcus Chown, “Is the Earth at the Heart of a Giant Cosmic Void? New Scientist, Nov. 12, 2008, pp. 32‐35.