A Book Review of “Black Holes: The BBC Reith Lectures”
Stephen Hawking’s “Black Holes The Reith Lectures” is a book with write up about two broadcasts that happen on 26th January 2016 and 2nd February 2016 about the Black Holes.
I’ve just completed the book and it’s amazing as other books from Stephen Hawking.
1. Do Blank Holes Have No Hair?
In this chapter, the discussion begins with the origin of the theory regarding the gravity and collapse of an object due to gravity.
During the life of the star, the thermal pressure will support the star from collapsing under its own gravity for billions of years. Eventually, all the nuclear fuel will be exhausted. After that, the star will begin to contract. Subrahmanyan Chandrasekhar in 1930 showed that the maximum mass that the start can have before it starts collapsing in it’s own gravity is 1.44 times the mass of our sun. Up to this mass the star will become white dwarf. If the mass of the start goes beyond the above said limit it will become Neutron Star or a Black Hole. This limit is know as The Chandrasekhar limit.
In 1939 Robert Oppenheimer investigated the problem of countless stars with grater mass than a white dwarf or neutron star when they had exhausted their nuclear fuel. In his papers with George Volkoff and Hartland Snyder he showed that such stars could not be supported by the outward pressure. If we take pressure out of the calculation, a uniform spherically systematic symmetric star would contract to a single point of infinite density. This point is called a Singularity.
Albert Einstein in 1939 wrote a paper to show that the stars could not collapse under the gravity because matter could not be compressed beyond certain point. Most of the scientists at that time agreed to Einstein’s theory.
However, American scientist John Wheeler mentioned that many stars will eventually collapse in his work in the 1950’s and 1960’s. He also pointed out the problem this possibility posed to theoretical physics. He is in many ways the hero of the black hole story. In 1967 John Wheeler introduced the term Black Hole which replaced the earlier name Frozen Star
In 1972 Jacob Bekenstein suggested that when a black hole is created by the gravitational collapse, it rapidly settles down to a stationary state which is characterised by only three parameters, the mass, the angular momentum and the electric charge. Apart from this, the black hole does not preserve any other information about the object falling into it.
After that,The author talks about the entropy of the black hole. and the challenge it poses for Jacob’s theory, and end the chapter with the paradox of a black hole emitting radiation or heat.
2. Black Holes Ain’t As Black As They Are Painted
In this chapter, it talks about the paradox from the previous broadcast about the nature of black holes (The incredibly dense object created by the collapse of starts).
It talks about the problem of information, that is, the idea that every particle and every force in the universe contains an implicit answer to a yes-no question.
After that, the author talks about the black holes emitting particles at a steady rate. Initially, the author discard the possibility of anything emitting from black holes but eventually gave that idea a thought and provided a theory for the same. There are pairs of particles and antiparticles created and annihilated in the universe. If on the event horizon(A boundary around black hole beyond that even light can not escape the gravity of black hole) a pair is created and one of the particles fall into the black hole the other particle will go on as radiation. As this emission is suggested by Stephen Hawking it is known as Hawking Radiation.
It also talked about quantum mechanics and the law of uncertainty given by German scientist Werner Heisenberg. The law of uncertainty says, It is impossible to simultaneously know both the exact position and momentum (or velocity) of a particle with absolute certainty.
And at Last the book talks about the paper entitled Soft Hair on Black Holes.
Quotes
A scientific law is not a scientific law if it only holds when some supernatural being decides to let things run and not intervene.
Things can get out of a black hole both in this universe and possibly to another. So, if you feel you are in a black hole, don’t give up: there is a way out!