Nebular hypothesis | Geography for UPSC 2024 (Pre & Mains) PDF Download

 Page 1


 
 
       LECTURE – 1 
      TOPIC 
    ORIGIN OF THE UNIVERSE 
NEBULAR HYPOTHESIS 
BINARY THEORIES 
BIG BANG THEORY 
STEADY STATE THEORY 
 
NEBULAR HYPOTHESIS 
 
 
In essence, this theory states that the Sun, the planets, and all other objects in 
the Solar System formed from nebulous material billions of years ago 
Primordial matter existed in the form of a gaseous mass called ‘nebula’ Latin 
‘nebula’ means mist). 
Page 2


 
 
       LECTURE – 1 
      TOPIC 
    ORIGIN OF THE UNIVERSE 
NEBULAR HYPOTHESIS 
BINARY THEORIES 
BIG BANG THEORY 
STEADY STATE THEORY 
 
NEBULAR HYPOTHESIS 
 
 
In essence, this theory states that the Sun, the planets, and all other objects in 
the Solar System formed from nebulous material billions of years ago 
Primordial matter existed in the form of a gaseous mass called ‘nebula’ Latin 
‘nebula’ means mist). 
 
 
According to this theory, the Sun and all the planets of our Solar System began 
as a giant cloud of molecular gas and dust.  
Then, about 4.57 billion years ago, something happened that caused the cloud 
to collapse. 
From this collapse, pockets of dust and gas began to collect into denser 
regions.  
Most of the denser material ended up in a ball at the centre (gravitational pull) 
while the rest of the matter flattened out into ring (centrifugal force) that 
circled around it.  
While the ball at the center formed the Sun, the rest of the material would form 
into the RINGS eventually giving rise to planets. 
BINARY THEORIES 
As per these theories, the sun had a companion.  
In 1900, Chamberlain and Moulton considered that a wandering star 
approached the sun. As a result, a cigar-shaped extension of material was 
separated from the solar surface. 
As the passing star moved away, the material separated from the solar surface 
continued to revolve around the sun and it slowly condensed into planets. 
Sir James Jeans and later Sir Harold Jeffrey supported this argument. At a later 
date, the arguments considered of a companion to the sun to have been 
coexisting.  
These arguments are called binary theories.  
 
BIG BANG THEORY 
The most popular argument regarding the origin of the universe is the Big 
Bang Theory. It is also called expanding universe hypothesis.  
Edwin Hubble, in 1920, provided evidence that the universe is expanding. 
Page 3


 
 
       LECTURE – 1 
      TOPIC 
    ORIGIN OF THE UNIVERSE 
NEBULAR HYPOTHESIS 
BINARY THEORIES 
BIG BANG THEORY 
STEADY STATE THEORY 
 
NEBULAR HYPOTHESIS 
 
 
In essence, this theory states that the Sun, the planets, and all other objects in 
the Solar System formed from nebulous material billions of years ago 
Primordial matter existed in the form of a gaseous mass called ‘nebula’ Latin 
‘nebula’ means mist). 
 
 
According to this theory, the Sun and all the planets of our Solar System began 
as a giant cloud of molecular gas and dust.  
Then, about 4.57 billion years ago, something happened that caused the cloud 
to collapse. 
From this collapse, pockets of dust and gas began to collect into denser 
regions.  
Most of the denser material ended up in a ball at the centre (gravitational pull) 
while the rest of the matter flattened out into ring (centrifugal force) that 
circled around it.  
While the ball at the center formed the Sun, the rest of the material would form 
into the RINGS eventually giving rise to planets. 
BINARY THEORIES 
As per these theories, the sun had a companion.  
In 1900, Chamberlain and Moulton considered that a wandering star 
approached the sun. As a result, a cigar-shaped extension of material was 
separated from the solar surface. 
As the passing star moved away, the material separated from the solar surface 
continued to revolve around the sun and it slowly condensed into planets. 
Sir James Jeans and later Sir Harold Jeffrey supported this argument. At a later 
date, the arguments considered of a companion to the sun to have been 
coexisting.  
These arguments are called binary theories.  
 
BIG BANG THEORY 
The most popular argument regarding the origin of the universe is the Big 
Bang Theory. It is also called expanding universe hypothesis.  
Edwin Hubble, in 1920, provided evidence that the universe is expanding. 
 
 
As time passes, galaxies move further and further apart. The distance between 
the galaxies is also found to be increasing and thereby, the universe is 
considered to be expanding. 
The Big Bang Theory considers the following stages in the development of the 
universe. 
(i) In the beginning, all matter forming the universe existed in one place in 
the form of a “tiny ball” (singular atom) with an unimaginably small 
volume, infinite temperature and infinite density.  
 
(ii)  At the Big Bang the “tiny ball” exploded violently. This led to a huge 
expansion. It is now generally accepted that the event of big bang took 
place 13.7 billion years before the present. The expansion continues even 
to the present day. As it grew, some energy was converted into matter. 
There was particularly rapid expansion within fractions of a second after 
the bang. Thereafter, the expansion has slowed down. Within first three 
minutes from the Big Bang event, the first atom began to form.  
 
 
(iii)  Within 300,000 years from the Big Bang, temperature dropped to 4,500 
K and gave rise to atomic matter. The universe became transparent. 
BIG CRUNCH  THEORY 
The Big Crunch is one of the theoretical scenarios for the ultimate fate of the 
universe, in which the metric expansion of space eventually reverses and the 
universe recollapses, ultimately causing the cosmic scale factor to reach zero 
or causing a reformation of the universe starting with another Big Bang 
STEADY STATE THEORY 
An alternative to this was Hoyle’s concept of steady state. 
 It considered the universe to be roughly the same at any point of time. 
Page 4


 
 
       LECTURE – 1 
      TOPIC 
    ORIGIN OF THE UNIVERSE 
NEBULAR HYPOTHESIS 
BINARY THEORIES 
BIG BANG THEORY 
STEADY STATE THEORY 
 
NEBULAR HYPOTHESIS 
 
 
In essence, this theory states that the Sun, the planets, and all other objects in 
the Solar System formed from nebulous material billions of years ago 
Primordial matter existed in the form of a gaseous mass called ‘nebula’ Latin 
‘nebula’ means mist). 
 
 
According to this theory, the Sun and all the planets of our Solar System began 
as a giant cloud of molecular gas and dust.  
Then, about 4.57 billion years ago, something happened that caused the cloud 
to collapse. 
From this collapse, pockets of dust and gas began to collect into denser 
regions.  
Most of the denser material ended up in a ball at the centre (gravitational pull) 
while the rest of the matter flattened out into ring (centrifugal force) that 
circled around it.  
While the ball at the center formed the Sun, the rest of the material would form 
into the RINGS eventually giving rise to planets. 
BINARY THEORIES 
As per these theories, the sun had a companion.  
In 1900, Chamberlain and Moulton considered that a wandering star 
approached the sun. As a result, a cigar-shaped extension of material was 
separated from the solar surface. 
As the passing star moved away, the material separated from the solar surface 
continued to revolve around the sun and it slowly condensed into planets. 
Sir James Jeans and later Sir Harold Jeffrey supported this argument. At a later 
date, the arguments considered of a companion to the sun to have been 
coexisting.  
These arguments are called binary theories.  
 
BIG BANG THEORY 
The most popular argument regarding the origin of the universe is the Big 
Bang Theory. It is also called expanding universe hypothesis.  
Edwin Hubble, in 1920, provided evidence that the universe is expanding. 
 
 
As time passes, galaxies move further and further apart. The distance between 
the galaxies is also found to be increasing and thereby, the universe is 
considered to be expanding. 
The Big Bang Theory considers the following stages in the development of the 
universe. 
(i) In the beginning, all matter forming the universe existed in one place in 
the form of a “tiny ball” (singular atom) with an unimaginably small 
volume, infinite temperature and infinite density.  
 
(ii)  At the Big Bang the “tiny ball” exploded violently. This led to a huge 
expansion. It is now generally accepted that the event of big bang took 
place 13.7 billion years before the present. The expansion continues even 
to the present day. As it grew, some energy was converted into matter. 
There was particularly rapid expansion within fractions of a second after 
the bang. Thereafter, the expansion has slowed down. Within first three 
minutes from the Big Bang event, the first atom began to form.  
 
 
(iii)  Within 300,000 years from the Big Bang, temperature dropped to 4,500 
K and gave rise to atomic matter. The universe became transparent. 
BIG CRUNCH  THEORY 
The Big Crunch is one of the theoretical scenarios for the ultimate fate of the 
universe, in which the metric expansion of space eventually reverses and the 
universe recollapses, ultimately causing the cosmic scale factor to reach zero 
or causing a reformation of the universe starting with another Big Bang 
STEADY STATE THEORY 
An alternative to this was Hoyle’s concept of steady state. 
 It considered the universe to be roughly the same at any point of time. 
 
 
In the steady state model, the density of matter in the expanding universe 
remains unchanged due to a continuous creation of matter, thus adhering to the 
perfect cosmological principle, a principle that asserts that the observable 
universe is basically the same at any time as well as at any place. 
ADDITIONAL INFO: 
COSMIC MICROWAVE BACKGROUND  
 Thermal radiation left over from early stage in development of Universe the 
“Big Bang”.