COSMOLOGY
PRESENTED BY
PADAM BAHADUR CHETTRI
MSc 4TH SEM
INTRODUCTION
Cosmology is the study of the origin, development, structure, history, and future of the entire universe.
ORIGIN OF THE COSMOLOGY
*Nicolas Copernicus in 1500s
*Isaac Newton in 1600s
*The door to modern physical cosmology opened early in the 20th century with Albert Einstein’s theory of relativity.
Cosmologists today believe that ordinary matter that we are known to is just a small part of the universe.
Most scientists agree that dark energy and dark matter make up a huge percentage of the universe.
This dark energy may be the force that overcomes gravity and allows the universe to expand in what is called cosmic acceleration. And the dark matter which is a hypothesized form of matter that interacts so weakly with normal matter and electromagnetic radiation that it is impossible so far for scientists to directly detect.
RED SHIFT AND THE EXPANSION OF UNIVERSE
Ever since 1929, when Edwin Hubble discovered that the Universe is expanding, we have known that most other galaxies are moving away from us. Light from these galaxies is shifted to longer wavelengths - in other words, it is 'red-shifted'.
The red shift of a distant galaxy is easily measured by comparing its spectrum with a reference laboratory spectrum. Atomic emission and absorption lines occur at well-known wavelengths. By measuring the location of these lines in astronomical spectra, astronomers can determine the red shift of the receding sources.
DENSITY PARAMETER OF THE UNIVERSE
The density parameter Ω is defined as the ratio of the actual (or observed) density ρ to the critical density ρc of the universe. The relation between the actual density and the critical density determines the overall geometry of the universe
Ω=ρ/ρc=8Gρ/3H^2
** When they are equal, the geometry of the universe is flat (Euclidean).
To date, the critical density is estimated to be approximately five atoms (of monatomic hydrogen) per cubic metre, whereas the average density of ordinary matter in the Universe is believed to be 0.2–0.25 atoms per cubic metre.
Case-I
If Ω is larger than unity, the space sections of the universe are closed; the universe will eventually stop expanding, then collapse.
Case-II
If Ω is less than unity, they are open; and the universe expands forever.
Case-III
If they are equal,and Ω is equal to unity than the geometry of the universe is flat (Euclidean).
COSMOLOGICAL PRINCIPLE
In modern physical cosmology, the cosmological principle is the notion that the spatial distribution of matter in the universe is homogeneous and isotropic when viewed on a large enough scale, since the forces are expected to act uniformly throughout the universe, and should, therefore, produce no observable irregularities in the large-scale structuring over the course of evolution of the matter.
PERFECT COSMOLOGICAL PRINCIPLE
The perfect cosmological principle is an extension of the cosmological principle, and states that the universe is homogeneous and isotropic in space and time. In this view the universe looks the same everywhere (on the large scale), the same as it always has and always will.
COSMOLOGICAL MODEL OF THE UNIVERSE
1.STATIC MODEL OF EINSTEIN:
also referred to as a stationary or infinite or static infinite universe, is a cosmological model in which the universe is both spatially and temporally infinite, and space is neither expanding nor contracting. Such a universe does not have spatial curvature; that is, to say that it is flat or Euclidean.
PERFECT COSMOLOGICAL PRINCIPLE
2. The de Sitter Universe
3. The Lemaitre-Eddington Universe
4. The Lemaitre Universe
5. The Friedmann Models
6. The Steady-State Universe
FRIEDMANN EQUATION
The Friedmann equations in physical cosmology is the equation that govern the expansion of space in homogeneous and isotropic models of the universe.
H=Hubble parameter
ρ=Volumetric mass density
a=Scale factor
k=Curvature Parameter
Case-I
If k = +1, then a is the radius of curvature of the universe.
Case-II
If k = 0, then a may be fixed to any arbitrary positive number at one particular time.
Case-III
If k = −1, then one can say that a gives some information about the dimension of curvature of the universe.
OBSERVATIONAL TESTS FOR COSMOLOGICAL MODELS
The most important conclusion is that several tests, among them the measurements of red shift and apparent magnitude, the counts of radio sources, the radio background at high frequency and the present He/H abundance ratio, all support a universe that was denser in the past.
Furthermore, recent tests suggest that the density of hydrogen in intergalactic space is below the mean density of luminous matter (galaxies) by several orders of magnitude. Thus the evidence is now extremely strong against the steady-state cosmology in its original simple form, while relativistic cosmology to the above extent finds support.
COSMIC MICROWAVE BACKGROUND RADIATION
The Cosmic Microwave Background (CMB) is the cooled remnant of the first light that could ever travel freely throughout the Universe. This 'fossil' radiation, the furthest that any telescope can see, was released soon after the 'Big Bang'. Scientists consider it as an echo or 'shockwave' of the Big Bang.
Sensitive Far Infra-red and Radio Telescope can easily detect the presence of these radiation.These radiation also supports the big bang phenomenon.
Cosmic Microwave Background Radiation
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