The Black Hole War: My Battle with Stephen Hawking to Make the World Safe for Quantum Mechanics Reviews
May 7, 2011 by Actaphysica
Filed under Mathematical Physics Book Reviews
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![The Dark Matter & Dark Energy [1/5]](http://i.ytimg.com/vi/rLmcbjLVPKc/default.jpg)
A popularisation that mostly works,
Susskind describes the decades-long battle between the quantum mechanics community and the general relativists as to whether information is lost when objects pass through the event horizon of a black hole and the hole eventually evaporates. According to Prof. Hawking and the GR community, as nothing can ever reappear from inside an event horizon, the information is indeed totally lost.
Susskind and Gerard ‘t Hooft begged to differ. Loss of information would violate the basic time-reversibility of QM: Hawking’s ideas would lead to universe-destroying phenomena (p. 23). Somehow, the information locked the wrong side of the event horizon must leak out via Hawking radiation. But how?
The resolution of this dilemma took many years of conjectures and refutations. Susskind takes us on a tour of entropy, holographic principles and physics at the Planck scale. And the adversarial plot keeps the reader turning the pages.
I am normally very dubious about popularisations. They proceed by raking up endless analogies which never quite fit together, so that by the end of the book, your mind is like that jig-saw puzzle you bought and could never fit together.
This book was never going to be the exception – the mathematics of quantum field theory, general relativity and string theory are just too arcane for popular culture concepts to cohere around. However, there are wonderful insights all the way through this book and we do end up learning something about the large scale map of the territory. Apparently even the experts find it hard to get the whole thing into one focus.
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Black Holes,
The book discusses a problem. According to Hawking, when an object falls down a black hole (BH), all information is lost. The problem is that this violates a principle of physics that information is never lost. The future cannot lose track of the past, for then the past would cease to exist, as the only meaning to the past is present observations and records. Susskind proposes a solution that took him a decade to resolve, and he discusses this in the book. The solution is the Holographic Principle, which is that all the information inside the 3-dimensional sphere of the BH resides on the 2-dimensional surface. An object falling down a BH never crosses the surface, and so the information is not lost. There is a “dual description” that does not refer to the inside.
Susskind makes heavy use of String Theory to establish the theory. Actually, one can arrive at the same conclusion without the use of String Theory or quantum mechanics, by simply focusing on basic principles of physics and general relativity (GR). According to GR, it takes an object forever to reach the BH, and so it never gets inside. We therefore cannot speak about the inside. Everything falling down a BH is eternally falling, and so the information is not lost. We cannot speak about the inside of the BH. This then is exactly Susskind’s Holographic Principle, where all information is outside the BH.
Science, and in particular physics, is a collection of theories. A theory is a mathematical system along with observational and experimental agreement. If it is impossible in principle to perform an observation, the theory cannot speak about that situation. Science also includes guesses, research proposals, and hypotheses, not all of which are theories.
The confusion arises from the formal existence of a solution of GR that from the viewpoint of the falling object, the object crosses the event horizon in finite time. However, since it is impossible in principle to observe an object “entering” the BH, this formal solution does not exist in reality.
If we accept the argument that something that a falling observer (someone who cannot return nor communicate with the rest of the world) can observe is considered as a valid scientific observation, we then lose our ability to criticize people for believing that the dead go to Heaven. The dead person (one who cannot return nor communicate with the rest of the world) observes Heaven. We scientists must be very careful about our scientific reasoning, and not give others the opportunity to twist it to make it sound as if we support religion, as is, unfortunately, often the case.
In summary, the principle of objective observation implies that no object can enter a BH.
Another point is that the formal solution of GR from the viewpoint of the falling observer is not a valid solution of GR. This is due to the proven existence of a singularity at the center. Since the object reaches the singularity in finite time, this solution is not valid. If we insist on accepting this formal solution, we get into paradoxes, as is usually the case when one accepts formal invalid solutions.
According to the Holographic Principle, no future theory can discuss the inside of a BH.
I gave four stars. The book makes excellent reading. It helps clarify some aspects of String Theory. For this, I give it three stars. His points about information residing outside the BH give it another star. I do not give it five stars, as his main point about where the information is can be proven by understanding and applying basic principles of science. We scientists and teachers must never lose sight of basic principles.
Susskind makes the common error of defining a BH as a place where light cannot escape, implying that the idea of an inside of a BH is a meaningful concept, contradicting his own Holographic Principle. A correct definition of a BH is a mass so large that objects falling towards it are time-dilated and red-shifted out of existence.
Another error in the book is mentioning “the 3-dimensional space inside the BH”. The geometry is very much non-Euclidean. Approaching a BH is geometrically similar to moving eternally outwards to the “end” of the universe. Speaking about the inside of a BH is geometrically similar to speaking about space outside the universe, i.e., not meaningful.
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Liked it, didn’t love it,
I find the material covered by Leonard Susskind in The Black Hole War intrinsically interesting, and Mr. Susskind does a creditable job of laying it out. The problem with this book is not the subject matter, but rather the writing and, even more so, the editing. The editor should have reigned in Mr. Susskind’s penchant for rambling, tangential explanations. Covering this material without mathematics is a daunting task, and Mr. Susskind gives it a reasonable shot. But I was often left with the feeling that I should have had a better understanding than I did. For instance, his treatment of “horizon atoms” left me scratching my head.
One other aspect bothered me, and that was the overly blunt assessment of Stephen Hawking’s current cognitive abilities. It was speculative and not particularly nice. A scientist search for truth needs to be bounded by a respect for the personal (as opposed to professional) privacy of living fellow scientists.
Finally, the whole premise of a “war” is really labored. Scientific theories change over time as new facts arrive. War is something else. The Catholic Church went to war against Galileo. Mr. Susskind participated in a, at-best, spirited debate.
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