The Little Book of Black Holes by Steven Gruber and Frans Pretorius

Source of book: Borrowed from the library

Occasionally, when I am at the library, I find a science related book to bring home for my 12 year old son. He is very much into science and technology, and finds these books fun, even when they aren’t exactly aimed at kids. In this case, this book was on the new books shelf and looked interesting. He read it first, and I thought it looked worth a read. Having read it, I am sure the math parts (and some of the science) were a bit over his head - but I have learned that he picks up a surprising amount from books like this. I am sure I will hear about it later.

In general, I am fascinated with astrophysics and astronomy, even if my limited math skills (I never did get to calculus) make some of the specifics hard to grasp. Previous selections include Phil Plait’s excellent and accessible Death From The Skies and David Weintraub’s more detailed How Old Is The Universe? In this connection, I should also mention The Hunt for Vulcan, about the way that an anomaly in Mercury’s orbit led to the discovery of relativity and a new theory of spacetime. In many ways, this book takes up the topic where the previous one left off.

This book is fairly short, and focused on one particular topic: Black holes.

One of the paradoxes of black holes are that they (by definition) cannot be “seen” in the traditional sense. Since light (electromagnetic radiation) cannot escape the event horizon, one cannot “see” the object at all. Instead, their existence is shown by two things: math, and their effect on objects we can see.

It was interesting that the math came first. One of the most amazing things about the universe is that it was written in the language of mathematics. Indeed, many discoveries have postdated the mathematics necessary to understand them. (Love and Math by Edward Frenkel is a fantastic book on this subject.) In this case, the existence of objects with the characteristics of black holes was mathematically predicted as early as the immediate aftermath of Einstein’s theories of relativity. Our technology, however, wasn’t yet able to provide the observational evidence.

Later, as our telescopes got better, and especially after we put them in space, we were able to observe the gravitational effects of black holes. Specifically, we were able to observe binary systems where the only explanation that worked was a black hole. (And later, the calculations of how galaxies like our own worked showed that a supermassive black hole was necessary at the center.)

More recently - and practically - evidence of gravitational waves and gravitational redshift (both predictions of general relativity) has been proven thoroughly. In fact, GPS has to take into account special and general relativity AND gravitational redshift in order to be accurate. A rather small force turns out to mean a lot even at short distances.

This book takes you through the theoretics, the observations, and some really, really crazy theoretical physics at the end. After all, despite the event horizon and all, black holes DO leak energy, and the way this works is pretty dang mind blowing.

The book is written by Steven Gruber and Frans Pretorius, both of whom are physics professors at Princeton. It is no surprise that they know their stuff. But they also write quite well, explaining tough concepts in an understandable way, without talking down to the reader. Gruber also wrote The Little Book of String Theory, which might have to go on my list.

Whether you start with this book really depends on your existing knowledge. If you glazed over at “event horizon,” this is probably not the place to start. Get a copy of Death From the Skies - or maybe a high school level astronomy textbook. If event horizons are okay, but you can’t remember what pulsars, quasars, and neutron stars are, you might want to read How Old is the Universe? to get a better overview of stellar objects in general. That book will also help with the math and physics of how we know there is an expanding universe, how we judge distances, and how we use math and observance to figure stuff out.

But, with a good background, this book is really quite fascinating. As some have pointed out (particularly in the wake of Stephen Hawking’s death), we haven’t ever “seen” a black hole, but we have strong evidence that they exist, and that they have specific characteristics and effects on the rest of the universe.