Physics Science

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.

Rating: 4 / 5

The Black Hole War: My Battle with Stephen Hawking to Make the World Safe for Quantum Mechanics is really several books in one. On the surface, this book tells the human story behind a debate that divided the physics community for decades: what happens to the information in the matter that is absorbed by a black hole, and can that information be retrieved or is it lost forever?

Yet in attempting to explain the various interconnections between general relativity, quantum field theory and string theory, Susskind has also provided us with a second book: a great general physics primer. Thirdly, by effectively telling the history behind some science’s greatest discoveries, Susskind has penned a very nice book for those interested in the history of science. Finally Susskind has made all three of those books more accessible and enjoyable by infusing his off-color personality.

This book covers a lot of ground, and at times it seems to lose a sense of flow as it delves into many different areas of physics, at each stop providing a primer of the basics. Yet by Chapter 5 the book really starts to heat up. Even though it is only five pages, they are five really good pages. This is where Susskind best makes the connection, calling a black hole horizon “the most concentrated form of information that the laws of nature allow.” As he guides us through the potential implications of information loss, he simplifies many complicated subjects without watering them down. We have wonderful treatments of the holographic and equivalence principles, entropy and the laws of thermodynamics. We also are treated to great historical accounts of the many conferences and papers that put faces and personalities behind the unraveling of the debate surrounding information loss and black holes.

There are times when he seems to use footnotes to his own peril, such as his explanation of how to calculate entropy versus bits of information in Chapter 7. At first he indicates that they are calculated in the same way, but in his footnote he clarifies that they differ by a mathematical factor. I would have appreciated it more had he made his points accurately in the text instead of having to explain them in poorly structured footnotes.

At least one other aspect of this book might, unfortunately, alienate some from what is an excellent read. Susskind is unapologetically irreverent regarding religion. In Chapter 17, while recounting his frustration with the information-loss debate, he discusses time he spent at Trinity College in Cambridge and how it gave him “Cathedralitis.” He outlines his disdain for the idea of intelligent design. There is also an inexplicably long section on Mormon history that seems totally irrelevant. These sections added little. His efforts to breathe life and personality into an abstract subject do give readers a sense of his personality. I simply think he should have steered clear of controversial topics.

The only other warning I can give people regarding this book is to set aside sufficient time in order to truly digest it. While, in theory, one could read this book in a week, to think through and understand all the examples takes some time. This book took me a long time to digest, and the books I have waiting to be read have multiplied during that time.

CONCLUSION

Initially I suppose I was somewhat put-off by the self-serving aspect of Susskind writing a book that starts off sounding like “I am right and Hawking is wrong.” You have to read between the lines for it, but it’s unclear if Hawking saw Susskind as a key player in the original debate about black hole information loss. I personally suspect that what was a “war” to Susskind was less than that to Hawking. In the end, some think this debate may not be over.

Where Susskind succeeds is in making an interesting story out of the debate. That makes readers want to understand some complex areas of physics, even if only from a 20,000 foot view. The way Susskind covers string theory and how it relates to other disciplines is particularly well done. For that alone, this book is worth the price of admission.

This is a great book that is well worth your time. I plan to seek out Susskind’s other books soon.

Enjoy.

Rating: 4 / 5