GHCL Digest-APRIL 2018

Book Review
A Brief History of Time: From the Big Bang to Black Holes- by Stephen W. Hawking
he book became a bestseller and sold more than
T10 million copies in 20 years. It was also on the
London Sunday Times bestseller list for more than
five years and was translated into 35 languages by 2001.
A Brief History of Time begins with a striking image and a
wonderful true story: An elderly lady a ended a public
lecture given by an astrophysicist on how the Earth goes
around the Sun and how the Sun circles about with
countless other stars in our galaxy the Milky Way. During
the ques on and answer session, the woman stood up
and told the dis nguished scien st that his lecture was
nonsense, that the Earth is a flat disk supported on the
back of an enormous tortoise.
. The scien st tried to outwit the lady by asking, "Well, my dear, what supports the tortoise?" To which she
replied, "You're a very clever young man, but not clever enough. Its turtles all the way down!”
Hawking uses the image of an infinite tower of tortoises to introduce contras ng views of the Universe.
Indeed, the first chapter con nues with an account of people's varying pictures of the cosmos over the last
few millennia. In the following chapters, Stephen Hawkins talks about - Space and Time, The Expanding
Universe, The Uncertainty Principle. He talks about me in Eins en's rela vity theory and uses the Doppler
Effect to explain how the universe is ge ng bigger. He also explains how light waves have crests and troughs.
The highest point of a wave is the crest, and the lowest part of the wave is a trough. Some mes more than one
of these waves can interfere with each other - the crests and the troughs line up. This is called light
interference. When light waves interfere with each other, this can make many colours. An example of this is
the colours in soap bubbles.
Chapter 5 is mostly about elementary Par cles and Forces of Nature. All par cles have something called spin.
The spin of a par cle shows us what a par cle looks like from different direc ons. Besides the force of gravity
and the electromagne c forces, there are weak and strong nuclear forces. Weak nuclear forces are the forces
that cause radioac vity, or when ma er emits energy.
The next chapter talks about Black holes. Black holes are stars that have collapsed into one very small point.
This small point is called a singularity. Black holes suck things into their centre because they have very strong
gravity. Some of the things it can suck in are light and stars. Only very large stars, called super-giants, are big
enough to become a black hole. The star must be one and a half mes the mass of the sun or larger to turn into
a black hole. This number is called the Chandrasekhar limit. If the mass of a star is less than the Chandrasekhar
limit, it will not turn into a black hole; instead, it will turn into a different, smaller type of star. The boundary of
the black hole is called the event horizon. If something is in the event horizon, it will never get out of the black
hole.
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