Hey guys ! I am Abhijeet Anand and you are
watching our channel All n one. So guys if
you want to start reading science books and
you have keen interest in cosmology, galaxies,
milky way, stars, planets, nebulas, many many
manyyy more space interesting stuffs, then
it is recommended that you have to start with
the book the brief history of time. It is
also believed that if you want to start Stephen
hawking books then this should be started
first as it covers all the things in brief
and it can be read by person without science
background. So today I am discussing the summary
of chapter one of this book the brief history
of time. So let’s begin. A scientist (Bertrand
Russel) was giving lectures that earth revolves
around sun, sun revolves around galaxy. An
old lady got up and said there is towers of
tortoise and our flat-round earth is situated
at top of tortoise’s shell. Well, now it
seems it ridiculous to us but at that time,
many people believed this theory. We have
many questions now-a-days too like the beginning
of universe of universe, what was there before
the beginning of universe, time travel , can
we change the past through time travel etc.
in future these questions will have answers
and all other theories regarding this will
be ridiculous. Aristotle in his book “On
the heavens” gave two arguments which prove
earth is spherical not a flat round plate.
His first argument was on lunar eclipse as
the shadow of earth on moon is always round
not elongated or elliptical. Second, on the
position of North Star seen in north and south
as the distance of star from north seems larger
than south. One more argument was on the ship
that we see the sail of the ship first and
then the hull coming from horizon. All this
is possible from earth as a sphere. Aristotle
thought the earth is situated at the center
and moon, stars and other planets revolve
around it. Ptolemy gave further explanation
to this idea with his cosmological model.
In his model, the earth is at center and other
eight objects rotate in their respective spheres
around the earth. The fixed stars are stationary
and are below. What is beyond the sphere was
unknown to mankind. This model was not accepted
universally but Christian church accepted
as it resembles in the bible and there were
lot of space available beyond the sphere for
heaven and hell. A simpler model was given
in 1514 by a priest Nicholas Copernicus but
due to fear of church, he circulated his model
anonymously. In this model, the sun was at
center and other eight planets revolve around
it. Almost after a century, two astronomers
Kepler and Galileo Galilei supported it publicly.
In 1609, Ptolemic theory was blowed away.
Galileo observed Jupiter through a telescope
that several moons orbit Jupiter. At the same
time, Kepler modified Copernicus theory and
suggested that the planets does not revolve
in circular path rather they obey elliptical
path. This hypothesis was merely ad hoc and
repugnant as ellipse is less perfect than
circle. He failed to explain the cause of
elliptical path. In 1687, sir Isaac newton
published a book Philosophiae Naturalis Principia
Mathematica in which he explained space time
and complex mathematics needed for explaining
motion. He also gave universal law of gravitation.
The story that an apple fell to his head which
gave idea of gravity is almost false. He was
just thinking why apple falls down always.
Newton showed that due gravity, the planets
revolve in elliptical path instead of circular.
Before 20th century, no one had suggested
that universe is expanding or contracting.
It was accepted either universe is existed
as today forever or it was created in the
past more or less same as today it is. According
to early cosmologist and Jewish/Christian/muslim
tradition the universe started at finite,
not very distant time in the past. St. Augustine
in his book “the city of gods” he pointed
that man and also universe could not have
been around all that long. He proposed a date
of about 5000 B.C. for the creation of universe.
Interesting, this date is around the end of
last ice age, about 10000 B.C. which is believed
to be the beginning of civilization. Aristotle
and other Greek philosophers didn’t accept
the idea of creation as it intervene their
divine beliefs. According to them natural
disasters occur time to time so that civilization
will be forever same. Immanuel Kant in his
book “critique of pure reason” in 1781,
supported both arguments. If the universe
did not have the beginning, the time would
existed till infinity in past and if there
is beginning, the time before the beginning
would gone past till infinity. St. Augustine
said that universe is created by god, and
time is the property of god. It didn’t exist
before the beginning of universe. In 1929,
Edwin Hubble said that galaxies are moving
far away from us and universe is expanding.
This means that there was a point of time
when all the objects would have been closer
together. About 10 or 20 million years ago,
all existed at the same place. Hubble’s
observation suggested that there was a point
of time called big bang where the universe
was infinitely small an infinitely dense.
All laws of science break down there. Time
also started from big bang. There was no existence
of time before that. The goal of science is
to provide a single theory that describes
the whole universe. Today, scientists describe
the universe in terms of two basic partial
theories –
1. The general theory of relativity
2. Quantum mechanics
The general theory of relativity gives force
of gravity and large scale structure of universe.
Quantum mechanics deals with the phenomenon
of extremely small scale. But at the same
time both theories cannot be correct. One
contradicts with the other. We need a theory
that unifies all the partial theories available
now. Till date we don’t know such theories
but advancement in science can lead us to
that. So, basically in this chapter, we came
to know about early beliefs, early cosmological
models, some traditional and divine thinking
and beliefs and what should be done to full
fill our curiosity about universe. I hope
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till the length of universe. Till then bye
bye and see you guys in our next video.
