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A brief history of time by Stephen Hawking chapter one summary

A brief history of time by Stephen Hawking chapter one summary


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
you guys enjoyed this video so give it a big thumbs up, subscribe to this channel for more
upcoming science videos and share this video till the length of universe. Till then bye
bye and see you guys in our next video.

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