Book Review: Extreme Cosmos by Bryan Gaensler

The short version: read this book!

I’ve read quite a few astronomy books in my time, and this is one of the best. The problem with a lot of these books is that, once you’ve read one or two, they start covering the same ground. A novel example or illustration is nice, but you can read Fred Hoyle’s The Nature of the Universe from 1960 (review soon!) and get most of what we know about the lives of stars and the layout of the solar system. The most media-friendly breakthroughs have come in cosmology, which has gained more than its fair share of popular level books on dark energy, dark matter, multiverses and the like.

However, many of the major discoveries of the last few decades have been in fields like high-energy astrophysics, hypervelocity stars, supernovae, black holes, magnetars and the like. Bryan Gaensler gives an outstanding overview of these extreme objects.

A good example is his description of what it would be like to be inside a giant molecular cloud [pg 25]:

“Let’s imagine that one for these [molecular] clouds drifted through our part of the Milky Way, enveloping the Earth, Sun and the rest of the solar system. In the direction from which the cloud approached, there would be a growing inky dark patch, eventually blotting out all the starlight from half the sky. But looking in the other direction, out to free space, we wouldn’t notice any difference at all at first. The stars in that direction would seem just as bright as always.

After about 2000 years (by which point we would have penetrated around 20% of the way into the centre of the cloud), the half of the sky towards the cloud would remain totally black, but now the other half two would have started to fade. Over the centuries, the light from the various stars and constellations would have dimmed by about a factor of six – only about 150 stars would still be bright enough to be visible to the naked eye.

Wait another 2000 years, and the remaining half of the night sky would fade by a factor of 20, leaving only ten stars that we could see unaided. And if 2000 years passed once more (a total of 6000 years since our encounter with the cloud began), there would be no stars left at all visible with the unaided eye.”

This puts me in mind of a quote from Ralph Waldo Emerson:

“If the stars should appear one night in a thousand years, how would men believe and adore; and preserve for many generations the remembrance of the city of God which had been shown! But every night come out these envoys of beauty, and light the universe with their admonishing smile.”

As usual, I love a good illustration [Pg. 48]:

 To put this in perspective, let’s suppose that the Sun is 40 years old, rather than 4.6 billion. In this case, the Sun will live to be about 80, a solid, respectable life span. In comparison, Betelgeuse is then only a 4-week-old infant, but is already at the end of its life. And HE 1327 [the oldest known star] has just turned 100, but shows no signs of slowing down … a typical red dwarf would have a lifetime of 4000 years!

One quibble, and it’s a quibble I have with many astronomy books. Here’s Gaensler:

Until the end of the Middle Ages, people thought that the Earth was the centre of the Universe. Our modern picture is the opposite extreme: we live on a small planet, orbiting an ordinary star, hidden in the quiet suburbia of the Milky Way, which in itself is a typical galaxy located in an unremarkable part of the universe. Although there have been many discoveries that have gradually led us from the simple Earth-centred model of the cosmos to the complicated cosmology we study today, the story has been dominated by two seismic shifts in our understanding. the first was in 1543, when Nicolaus Copernicus … dramatically demoted the Earth, and moved the sun to the centre of all creation. But the second great moment was in 1918, when Shapley … demonstrated that even the sun was not especially important or central. [pg 33] …

Our entire Milky Way Galaxy is is unimportant, minute fleck on the celestial stage, an irrelevant region of bright light and dense gas, hidden amid the vast darkness and emptiness of the cosmic voids. On the other hand, what a triumph of pure thought it has been, that we mere humans, in the space of little more than a hundred years, have established how stars are born, live and die, how galaxies evolve, and how the whole structure of galaxies, galaxies and cosmic voids fits together. [Pg. 180]

Firstly, as I’ve noted before, moving the Earth away from the centre of the medieval universe was a promotion, not a demotion. In Aristotle’s universe, the element ‘earth’ falls to the centre of the universe because the crud settles to the bottom. We are the crud on the universe’s shoe, surrounded by perfection.

Secondly, modern cosmology is shockingly simple. The early universe can be summarised on a single sheet of paper. The stuff in the universe is complicated, but as a whole, the equation that describes the evolution of the universe is a doddle, solvable by a first year with paper and pencil in many cases, and much simpler than one might have expected given the vagaries of general relativity. (Granted, as a cosmologist, I might be a bit biased).

But most importantly, whence comes the charge of irrelevance? Relevance is not a physical property; there is no quantum mechanical importance operator; there is no pertinence-ometer. A feature of the universe can be dynamically negligible – take the Earth out of a model for the solar system, and our prediction for the position of Jupiter won’t change much. But when does a small change become an important change? When someone says so! Relevance is relevance to someone.

If you’re a materialist, then the only persons of which we have evidence are human persons.  This makes the Earth the most important planet in the universe because the only beings capable of bestowing importance are us. And if you think that there is a transcendent intelligence, then the Earth is only irrelevant if said agent scores importance solely on the basis of mass, size and dynamical influence on the universe as a whole. That would be a bit odd: my daughter contributes nothing to the structural integrity of this house, but in the event of a fire I’m not going back for the load-bearing beams. My considerable height and weight advantage over Martin Rees does not make me more important. This conflation of ‘size = importance’ makes no sense.

But, other than that, this book is highly recommended!