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martedì, febbraio 27, 2018

The Little Book of Black Holes by Steven S.Gusber & Frans Pretorius


This book The Little Book of Black Holes by Steven S.Gusber & Frans Pretorius published by Princeton University Press is a new reality in grade of explaining clearly what the black holes are. The book ends with a letter dedicated to Albert Einstein by the two professors.
Written clearly also a profane reader can understands the most of it.

The book starts portraying scientist who studied the black holes  trying to define  them. a


What is a black hole first of all?
In every galaxy there is a black hole



A black hole is the "big eater" of the Universe, the one that egoistically eats with great appetite every kind of matter, light included. Nothing of what "falls" in a black hole will return to its surface. Where all this material goes it is still a mystery.

A black hole is a curved spacetime.

A black hole has a static part, an event horizon where for example light can be drunk and then the end of it.

Mr. Schwarzschild the discoverer of black holes in 1915 thought that at the end of this cosmic funnel "there is a terrible compressed kernel of matter lurking at its core."

Maybe it is true.

What scientists know for sure is that Einstein was right talking about cosmic waves. Three years ago the collisions of two black holes caused an important cosmic wave, the one Einstein talked about in his theory of general relativity. It was another victory for his general theory of relativity.

The authors don't want to start from Einstein but from special relativity born with Maxwell and electromagnetism. Electricity, although visible creates electromagnetism fields. We don't mind because we see it.
All the rest of the electromagnetism world is unseen, maybe perceived but because not visible not considered important or sensitive.

In the theory of general relativity gravity is not important. Not for a black hole.
Schwarzschild hypothesized that the matter of the Universe influences spacetime defining itself and for example giving to a black hole its curved spacetime.

Now, let's try to go close to a black hole or imagining to do that.

Time close to a black hole slow down and becomes 0 in the horizon the point where matter falls into the black hole.
We should also change modality of expression when referred to the horizon thinking at time commonly. Forget space, it is time and it goes infinitive. You can't see anything from there.
"Time says the authors, inside the black hole is altogether other than time outside time." It is "beyond infinite."

Another interesting part of the Universe are white holes. In this case anything inside is forced out without any chance of getting back in.
A white hole is a spacetime that begins its life. A black hole in general borns thanks to the departure of a big star in most cases.

Mr Kerr a mathematician during the 1960s elaborated another solution adding the rotation of black holes.
Let's imagine for example a ring or a circular place. It can be a pen where horses are kept.

Now: if you start to walk in a circular way from the beginning to the end of the perimeter of the pen at the end you are in the present/future. Your walk was part of your past.
With a timelike curve like the one of a black hole you turn back at the same space without any kind of time-consumption because at the same spacetime you started at.

Do you know what? Here we are in the time-machine theory!

Amazing. I leave you alone with this book  for reflecting about the universe, its paradoxes and the messages that everyday it sends us with its magic.

Why buying this book?
It's interesting, written with great competence. 




Anna Maria Polidori









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