Beyond the Galaxy

In the preface of this book, Ethan Siegel recounts his experience as a new college professor in 2009, thrilled to learn that he would be teaching the college's introductory astronomy class. The only disappointment was that he could not find a textbook that described astronomy the way that he wanted to teach it. Siegel did not want to simply describe the current astronomical understanding. He wanted to start at the beginning and tell a story. What questions did we start with? How did we answer them? What new questions did those answers provoke?

I enjoyed Sabine Hossenfelder's Lost in Math, but I'm even happier that she included in it a recommendation of Beyond the Galaxy as a good introduction to modern astronomy. I am completely in agreement with Siegel: Astronomy is interesting however it is described, but the best presentation for the interested lay person who does not intend to become a professional astronomer is chronological. (I feel the same way about physics and mathematics.) The narrative structure of scientific discovery draws me in every time. It's so satisfying to see our knowledge growing, breakthrough by breakthrough, only to meet the next puzzling inconsistency. It also is a natural fit for bringing someone up to speed on a field, since the history of the field starts with simpler questions and problems, and the complications of later discoveries build on the gaps left by earlier theories.

Siegel tells that story well. Beyond the Galaxy starts with observations of seasonal changes in the path of the Sun through the sky and phases of the moon, quickly moves on to Eratosthenes's calculation of the circumference of the Earth, and continues at pace through early astronomy. The first chapter brings the reader up to the start of the 20th century, after which Siegel slows down and spends the remaining 10 chapters on the last 100 years: special and general relativity, the expansion of the universe, the Big Bang, dark matter, dark energy, the inflationary period, and more.

For me, this was perfect. The story of early astronomy and the fight over the heliocentric model of the universe is worth telling, but it's been told many times before and features prominently in history books outside of science classes. The weight of material in this book matched my interest: What new developments have there been after general relativity and the Big Bang theory? What inconsistencies are dark matter and dark energy explaining? What is the inflationary period and how did it modify the Big Bang theory? (My half-formed impression of this part of astronomy from news articles turned out to be almost entirely wrong.) And how do we know all of this?

The question of how we know as much as we do about the early origins of the universe turned out to be far more interesting than I had realized. It's one of those pieces of science where, when given only the conclusions, it's hard to imagine how our theories could be as complete as they are. Siegel is a bit repetitive in how he talks about theory development and occasionally skims over the details to avoid getting too deep into techniques and math, but he does a great job explaining the predictions of a theory, the design of experiments to prove or disprove those predictions, and the implications for the boundaries of what we know. This is the first time someone has explained the theorized origin of matter-antimatter asymmetry in sufficient detail that I was able to understand and internalize it.

Dark matter and dark energy are the current topics of astronomy that get the most press, and the coverage of both is very good here. I was particularly fascinated by the link between dark matter and the superstructures of the universe that we've discovered. Astronomy does scale in a way that no other science can manage, and the scale of structure we've discovered and been able to map has gone up considerably since the last time I refreshed my astronomical knowledge.

If you're looking for a math-light, comprehensive introduction to modern astronomy, I can wholeheartedly recommend this book. That goes double if you, like me, prefer a chronological view of scientific discovery so that you can understand what questions people were trying to answer and how our understanding changed over time.

One note on format: Astronomy being what it is, this book is very heavy on pictures. It is not at all suitable for a dedicated ebook reader. The Kindle tries, but the combination of a small screen and black and white e-ink fail miserably. I switched to reading on a tablet, and that was a far better experience. The Kindle app still struggles to put the figures next to the text that discusses them, but that's a typesetting problem that I often have with physical books as well. If you don't have a tablet and you aren't willing to read on a computer screen, you probably want a physical copy of this one (which, sadly, means academic textbook pricing).

Rating: 8 out of 10

Reviewed: 2020-04-18