- The Big Bang theory proposes that approximately 13.8 billion years ago, the entire observable universe was concentrated into a very hot and dense single point, and then rapidly expanded over time. - As the universe expanded and cooled, particles formed which then clustered together under gravity to create the first stars and galaxies. Structures like stars and galaxies formed as early as 200 million years after the Big Bang. - Hubble's law, proposed by Georges Lemaître and later confirmed by Edwin Hubble, describes the observation that galaxies are moving away from Earth at speeds proportional to their distance from us, providing evidence that the universe is expanding.

1. B I G B A N G T H E O R Y
O F
U N I V E R S E ( G R O U P - 3 )
S O H I N I S U R
S H U B H A N G I D U T T A
S H R U T I
S M R U T I M A H A R A N A
S U B H A S M I T A
S O M S A R T H A K

2. A B B E G E O R G E S ( 1 8
9 4 - 1 9 6 6 )
• Belgian cosmologist .
• Professor of physics at the
catholic university of Leuven.
• He proposed the theory of
the expansion of the universe, widely
misattributed to Edwin Hubble.

3. According to the big bang theory:
• The universe originated approximately 13.8 billion
years ago from a singularity, an extremely hot and dense
point.
• At this moment, all the matter, energy, space, and time
in the universe were concentrated at a single point.
• Shortly after the initial moment of the Big Bang, the
universe began to rapidly expand.
• As it expanded, it cooled down, allowing particles and
elements to form.

4. B E G I N N I N G :
• The big bang theory is
prevailing cosmological model for the universe
from the earliest known periods through its
subsequent large-scale evolution.
• The universe began as a very hot , small, and
dense, with no stars, atoms, form,
or structure(called a " Singularity").
• The Big Bang is a scientific theory about how the
universe started, and then made the groups of stars
(called galaxies) we see today
This Photo by Unknown author is licensed under CC BY-SA.

5. F O R M A T I O N O F G A L A X I E S A N D S T A R S :
Over time, the force of gravity caused
matter to clump together, forming galaxies,
stars, and other celestial structures within
the expanding universe.
Matter coalesced when the universe cooled
and became “transparent” 380,000 years
after the Big Bang.
Structures like stars and galaxies formed as
early as 200 million years after the Big
Bang.
Atoms formed from tiny particles, and then
atoms grouped together to form stars and
galaxies.
Galaxies begin as small clouds of stars and
dust swirling through space.As other clouds
get close, gravity sends these objects
careening into one another and knits them
into larger spinning packs.
Stars develop inside a protogalaxy when
clouds of gas mix and collide. If the stars in
a protogalaxy form all at once, then the
mature galaxy essentially retains the
spherical shape of the protogalaxy and
becomes an elliptical galaxy. Spiral
galaxies occur when the stars inside the
protogalaxy arise at different intervals.

6. H U B B L E ' S L AW:
• Hubble's law, also known as the Hubble–
Lemaître law, is the observation in physical cosmology
that galaxies are moving away from Earth at speeds
proportional to their distance.
• In other words, the farther they are, the faster they are
moving away from Earth. The velocity of the galaxies
has been determined by their redshift, a shift of the light
they emit toward the red end of the visible spectrum.
• The motion of astronomical objects due solely to this
expansion is known as the Hubble flow. It is described
by the equation v = H0D, with H0 the constant of
proportionality—the Hubble constant.
• The Hubble constant is most frequently quoted in
(km/s)/MPC.
This Photo by Unknown author is licensed under CC BY.

7. B I B L I O G R A P H Y:
• Hubble's law - Wikipedia
• The big bang theory | PPT (slideshare.net)
• How Did Galaxies Form? | Astronomy.com

8. THANK YOU