Unit 5 - Astronomy and Astrophysics - Cosmology

Astronomy and Astrophysics
Ms Dhivya R
Assistant Professor
Department of Physics
Sri Ramakrishna College of Arts and Science
Coimbatore - 641 006
Tamil Nadu, India
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Unit 5 – Cosmology
 Introduction
 Red shift and the expansion of the universe
 Matter density in the universe and the declaration
parameter
 The Cosmological Principle: The perfect cosmological
principle
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 Cosmology is “The scientific study of the large-scale
properties of the universe as a whole.“
 It is the scientific study of the origin, evolution, and
eventual fate of the universe. Physical cosmology is the
scientific study of the universe's origin, its large-scale
structures and dynamics, and Its ultimate fate, as well as
the laws of science that govern these areas
Cosmology
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 Astronomy is the study of everything in the universe.
 Astronomy includes determining the nature of things on
a small scale, such as the composition and evolution of
individual stars, planets and interstellar gas, building to
include the make up of galaxies and galaxy clusters, and
finally to understanding things on the largest scale.
 This is where cosmology comes in. Cosmology is a
subsection of astronomy and deals with the nature of the
universe itself: its beginnings in the Big Bang, its early
history, its current state, and its eventual end.
Difference between cosmology
and astronomy
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 Redshift and blueshift describe how light shifts toward
shorter or longer wavelengths as objects in space (such as
stars or galaxies) move closer or farther away from us.
 When an object moves away from us, the light is shifted to
the red end of the spectrum, as its wavelengths get longer.
 If an object moves closer, the light moves to the blue end of
the spectrum, as its wavelengths get shorter
 American astronomer Edwin Hubble (who the Hubble Space
Telescope is named after) was the first to describe the
redshift phenomenon and tie it to an expanding universe.
 His observations, revealed in 1929, showed that nearly all
galaxies he observed are moving away.
Redshift and Blueshift
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 This redshift appeared to be larger for faint, presumably
further, galaxies. Hence, the farther a galaxy, the faster it
is receding from Earth
 The galaxies are moving away from Earth because the
fabric of space itself is expanding.
 While galaxies themselves are on the move —
the Andromeda Galaxy and the Milky Way, for example,
are on a collision course — there is an overall
phenomenon of redshift happening as the universe gets
bigger.
 Redshift helps astronomers compare the distances of
faraway objects.
Red shift and Expansion of the
Universe
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 Two Observers at O & O’
 Galaxy at P
 Then
 Also and
 by Hubble’s Law.
 The universe looks same from all points
Red shift and Expansion of the
Universe
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Matter density in the universe
and declaration parameter
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9

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 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
Cosmological Principle
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 A cosmological model is a mathematical description of
the Universe that attempts to explain its current behavior
and evolution over time.
 Cosmological models are also rooted in two fundamental
assumptions:
 The Earth is not located at the center of the Universe nor
does it occupy a special place therefore the Cosmos looks
the same in all directions and from every location on a
grand scale.
 The same laws of physics which operate on Earth also
function throughout the Universe regardless of time.
Cosmological Models
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 STATIC MODEL OF EINSTEIN
 Universe is spherical, curvature parameter k=1, and constant
radius of curvature R
 THE DE-SITTER UNIVERSE
 Universe was expanding in an infinite flat space k=0 but he
visualized and empty universe
 THE LEMAITRE-EDDINGTON UNIVERSE
 Einstein’s universe was unstable
 Universe was expanding with ever-increasing speed (past in
Einstein’s and after disturbance)
 THE FRIEDMANN MODELS
 Oscillating model of universe
Current Theories
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 LEMAITRE UNIVERSE
 Based in general relativity
 Base foe big bang
 Beginning – superdense single mass(primeval atom) – explosion
– mater stated moving in all direction with high speed –
Einstein’s universe evolved – previous theory
 THE STEADY STATE UNIVERSE
 Universe if flat – characterised by decelerating parameter q=-1.
universe expands with an acceleration
 THE SCALAR – TENSOR MODEL
 Added a scalar field to the Einstein’s general relativity model
Current Theories
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Reference
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Unit 5 - Astronomy and Astrophysics - Cosmology

Unit 5 - Astronomy and Astrophysics - Cosmology

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