Reviewed document: Homogenous and Isotropic Cosmological Principle (Versha Rani) 17-5-2021.docx
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In 94 further documents exactly one sentence was found. (click to toggle view)
Homogenous and Isotropic Cosmological Principle
Versha Rani
ABSTRACT
The Cosmological Principle is a Copernican idea. It means we are not in special place. The Cosmological Principle allows the universe to change, or evolve throughout time. An extension of the cosmological principle called the perfect cosmological principle says that the universe also does not change with time, there is no evolution. We are interested in various aspects of models of the diffuse cosmological X-ray background, in particular its origin, spatial fluctuations, and what it can tell us about large scale structure. More recently, the emphasis is shifting toward the gamma-ray background.
KEYWORDS:-Homogeneous, Isotropic, Perfect Cosmological Principle
INTRODUCTION
In modern physical cosmology, the cosmological principle is the working assumption that observers on Earth do not occupy an unusual location within the universe as a whole, fudged as observers of the physical phenomena produced by uniform and universal laws of physics. An astronomer William keel explains.
The Cosmological Principle is usually stated formally as “viewed on a sufficiently large scale, the properties of the universe are the same for all observers.”This amounts to the strongly philosophical statement that the part of the universe which we can see is a fair sample and that the same physical laws apply throughout. In essence, this in a sense says that the Universe is knowledge and is playing fair with scientists.[1]
HOMOGENEITY AND ISOTROPY
The two testable structural consequences of the cosmological principle are homogeneity and isotropy. Homogeneity means that the same observational evidence is available to observers at different locations in the Universe.
Isotropy means that the same observational evidence is available by looking in any direction in the universe. The Principles are distinct but closely related, because a universe that appears isotropic from any two locations must also be homogeneous. The Cosmic microwave background is the same from all parts of the sky, yet in cosmological theory these must have originated in completely different parts of the early universe [2].
IMPLICATIONS
The cosmological principle represents both the principle on which cosmological theory and observation can proceed and a “null” hypothesis of uniformity that is an area of active research inquiry [3].Many important advances in astronomy and cosmology, and the formulation of new cosmological theories, have occurred through the resolution of apparent violations of the cosmological principle. In that sense, all spatial conditions in the Universe must appear to be homogeneous and isotropic to an observe at all times in the future and in the past [4].
Cosmologists agree that in accordance with observations of distant galaxies, a universe must be non-static if it follows the cosmological principle. In 1923, Alexander Friedman set out a variant of Einstein’s equations of general relativity that describe the dynamics of a homogeneous isotropic universe [5, 6].Independently, George Lemaitre derived in 1927 the equations of an expanding universe from the General Relativity equations [7].Thus a non-static, universe is also implied, independent of observation of distant galaxies, as the result of applying the cosmological principle to general relativity.
The idea of a uniform universe is called the cosmological principle. There are two aspects of the cosmological principle:
The universe is homogeneous. This means there is no preferred observing position in the universe.
The universe is also isotropic. This means you see no difference in the structure of the universe as you look in different directions.
Perfect Cosmological Principle
The Perfect Cosmological Principle states that the Universe is homogeneous and isotropic in space and time. In this view the universe looks the same everywhere, the same as it always has and always will. It is the principle underpinning steady state theory and emerging from Chaotic inflation theory [8,9,10].
The Perfect Cosmological Principle, which accepts that the universe changes its gross feature with time, but not across space.
RESEARCH IN COSMOLOGY:-
Cosmic High-Energy Radiation Background
We are interested in various aspects of models of the diffuse cosmological X-ray background, in particular its origin, spatial fluctuations, and what it can tell us about large scale structure. More recently, the emphasis is shifting toward the gamma-ray background.
In a series of papers, P.M. and collaborators (A. Meszaros, Z. Bagoly, H. Bi) investigated the effects of the very large scale structure on the spatial fluctuations of the cosmic X-ray background (CXB)[11,12]. This can be modeled as a redshift dependence of the mass contrast inside and outside structures, which varies as the structures form and become bound, and assuming a relationship between this and the birth of X-ray emitting objects which contribute to the CXB. The main effect is given by the distance fluctuations of the large structures, with the varying density contrast adding a small correction. We concluded that, independently of whether one uses a hot or cold dark matter prescription, the discrete sources contributing to the CXB in constant commoving density structures may have present separations of order 30 Mpc, but structures larger than about 60 Mpc may only be one-dimensional, and any great attractors may only be present at low redshifts below 0.5, otherwise they would have considerably exceeded the fluctuation upper limits of HEAO-1.
Rudak and Meszaros considered the effects upon the X-ray background of the scattering by dust in intervening young galaxies, assuming the X-rays arise in discrete sources. This effect has been previously observed to produce X-ray halos around the image of distant point sources, but its effect upon the background had not been explored. The effective angle of scattering is 1-10 arc minutes at 1-3 KeV, over which scale it can give a significant reduction of the background spatial fluctuations. As a result, the number of sources needed to explain the smoothness observed with the IPC can be reduced to values of about 1000/sq.deg. The effect may be much stronger in the direction of distant clusters, or for dustier disk galaxies [13]. This has implications also for the increasing scarcity of optical QSO at very high redshifts, and may be used for putting limits on a possible IR background.
Ricker and Meszaros investigated the contribution of starburst galaxies and reflection-dominated AGN to the diffuse X-ray background [14]. The contribution of the former cannot be larger than about 30% at energies below about 15 KeV, and do not affect the diffuse spectrum at higher energies. Reflection-dominated AGN were modeled with a detailed code including scattering and metallic absorption lines, as well as a varying covering factor. The conclusion is that, in their simple form, such models do not satisfy a statistical chi-squared fit with sufficient significance, in the context of relativistic cosmological models, and additional ingredients to the model are necessary to model the phenomenon.
CONCLUSION:-
The universe is homogeneous. This means there is no preferred observing position in the universe. The universe is isotropic. This means you see no difference in the structure of the universe. The rotation of the Earth produces a unique orientation, but the universe appears the same from any position. Observations to date support the idea that the Universe is both isotropic and homogeneous. Both facts are linked to what is called the Cosmological Principle. The conclusion is that, in their simple form, such models do not satisfy a statistical chi-square fit with sufficient significance, in the context of relativistic cosmological models, and additional ingredients to the model are necessary to model the phenomenon.
REFERENCES:-
1. William C.Keel (2007).The Road to Galaxy Formation (2nd ed.)Springer Praxis.
2. George Ellis & Mauro Carfora (2000).Flat and Curved Space times.
3. GFR Ellis (1975).”Cosmology and Verifiability Royal. Astronomical Society, Quarterly Journal.”
4. Klaus Mainzer and J Eisinger (2002).The Little Book of Time.
5. Alexander Friedman (1923).Die Weltals Raum and Zeit. (The world as space and time.)
6. Eduard Abramovich Tropp, Viktor Ya. Frenkel, Arthur Davidovich Chernin (1993).
7. Lemaitre Georges (1927), UN Universe homogenate de masse content et derayon croissant rendant compete de lavitesse radial des nebuleuses extra galactiques.
8. Aguirre, Anthony and Gratton, Stevenn (2003).Inflexion without a beginning. A null boundary proposal.
9. Aguirre, Anthony and Gratton, Steven (2002).”Steady –State Eternal inflation”.
10. Gribbin, John “Inflation and Beginners.”
11. Meszaros A and Meszaros P.”Large scale structure of the Universe: constraints from the X-ray Background AP.J, 327, 25-33(1988)
12. Bagoly, Z, Meszaros, A and Meszaros, P,”Cosmological Constraints on the Clustering of X-ray Background Sources”AP.J, 333, 54-63(1988).
13. Rudak, B.and Meszaros,P.,”Dust from Early Galaxies and the X-ray Background Radiation”,AP. J.,371,29(1991).
14. Ricker, P.M. and Mesz, P,”Starburst and Reflection Dominated AGN contribution to the Cosmic X-ray Background”, AP J., 418, 49(1993).