Review: Beyond the Galaxy, by Ethan Siegel

Russ Allbery eagle at
Sat Apr 18 19:58:01 PDT 2020

Beyond the Galaxy
by Ethan Siegel

Publisher: World Scientific
Copyright: 2016
ISBN:      981-4667-16-1
Format:    Kindle
Pages:     370

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

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 astronomy 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


Russ Allbery (eagle at             <>

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