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Simulating the Cosmos – Romeel Davé ****

There’s never been any shortage of popular science books about cosmology. But these books tend to focus on the two ‘ends’ of the subject: raw observations, such as the cosmic microwave background and Hubble’s deep field images on the one hand, and theoretical inferences ranging from cosmic inflation to dark energy on the other. There’s a whole ‘excluded middle’ between them that explains how the observational data leads to those theoretical conclusions, yet it’s rarely discussed in any depth at a popular level. It’s this omission that Romeel Davé seeks to remedy in this engrossing and entertaining book.

The ‘missing link’ I’m talking about is computer simulation, and the basic idea is simple enough. As Davé explains: ‘We put the relevant laws of physics into a computer, set up some initial conditions at an early cosmic epoch, add in all the ingredients we know of... and let it all churn in the world’s most powerful supercomputers until we produce a simulated universe.’ He goes on to say that, if the resulting ‘universe’ matches the observational data, then the simulation provides a very good pointer to its past history. If it doesn’t match, on the other hand, then there must be something wrong in all those assumptions – the ones about initial conditions, basic ingredients and so on – and we just have to keep revisiting them until the simulation comes out right.

This is a subject that’s close to my heart, since much of my career was spent developing and running simulations, both in astronomical and other contexts. Even so, I’m not sure I’d want to write a popular-level book about it, because I could easily get bogged down in technical minutiae of little interest to the general public. That’s why I’m so impressed by Davé’s book. He manages to convey a great sense of how cosmological simulations work, what they’re used for, and why the results are so important - all with very little technical detail or jargon – certainly no more than any other popular account of cosmology or extragalactic astronomy that I’ve read.

There was a time, not very long ago, when academic scientists really weren’t very good at doing popular science books. It wasn’t that they were poor writers, but they seemed to assume the general public’s level of education in their subject was roughly the same as one of their own undergraduate students, which meant they constantly used concepts and jargon that would alienate most people. Fortunately this ‘ivory tower’ attitude seems to be on the way out, and the younger generation of academics often make excellent science communicators. Romeel Davé, a professor of astronomy at the University of Edinburgh, is a case in point. I enjoyed his laid-back style so much I can’t help quoting a few bits:

On the state of cosmology in the 1990s: ‘Bizarre notions that sounded more like Isaac Asimov than Isaac Newton were wafting through the cosmological community.’ On the unpredictability of computer simulations: ‘Anything that is not explicitly forbidden will eventually happen, and even things that are explicitly forbidden will happen, only less frequently.’ On the physics of radiative cooling: ‘Electrons, like English bulldog puppies, are lazy; they would rather live at the lowest energy state possible.’

Despite this highly accessible writing style, and the book’s lack of unnecessary technicalities, I still think its audience is limited. That’s simply because it addresses a question – ‘how do astronomers use computer simulations to get from raw observational data to theories about the universe?’ – that I don’t think is going to appeal to everyone. Personally I loved it (Davé even devotes three pages to an obscure technique, called ‘N-body particle-mesh simulation’, that was the subject of my PhD thesis), and I’ve happily given it a five-star rating on Goodreads. Getting closer to what I suspect is the book’s core audience, the same might well be true of any space-mad teenager who spends their spare time coding video games. But I do recognise that not everyone in the world is a computer geek, so I’ve gone with four stars as far as general readers are concerned.

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