Savan Kharel reviews Simulating the Cosmos: Why the Universe Looks the Way It Does by Romeel Davé
As I write this, I’m immersed in the excitement surrounding the upcoming solar eclipse in parts of North America. In Chicago, my home, we’re poised to experience 90% of the eclipse’s totality, a spectacle that has sparked enthusiasm among my undergraduate students, especially since we will be watching it during class.
We are not, however, the first to be drawn to these remarkable astronomical events, as Romeel Davé – a theoretical astrophysicist at the University of Edinburgh in the UK – explains in Simulating the Cosmos: Why the Universe Looks the Way It Does. In third-century China, eclipses were seen as important omens by the emperor, and astronomers developed remarkably precise methods to predict them.
The stakes were high for these early theorists – inaccuracies once resulted in the execution of two astronomers, turning the refinement of their predictive techniques into a quest for survival.
In his book, Davé traces a direct link between these ancient celestial predictions and modern cosmologists who use powerful supercomputers to model the universe. He explains how “numerical cosmology” can be used to compensate for our inability to experimentally manipulate the cosmos, and asks whether it will ever be possible to capture the entire universe in a simulation.
To recreate the cosmos on a computer, we first need to know what it’s made of. Davé sets the scene by clearly explaining the so-called “concordance model”, which tells us that the universe is 68% dark energy and 27% dark matter, with visible matter making up only 5%. In this framework, dark energy drives the accelerating expansion of the universe, while the gravitational pull of dark matter assembles galaxies and galaxy clusters into large-scale structures.
The book also offers theoretical insights into the Big Bang and the rapid expansion of the early universe, woven with engaging anecdotes. While explaining why those of us on Earth don’t notice the universe expanding, Davé recounts a memorable t-shirt worn by one of his professors during graduate school, featuring a whimsical question: “If the universe is expanding, why can’t I ever find a parking space?”
With the concordance model as our guide, Davé explains how, by inputting laws of physics and the conditions of the early universe into computer simulations, we can understand how and why the universe evolved to its current state.
Even with a simplified model that includes only gravitational effects, an accurate simulation of the entire universe would require far more computing power than exists on Earth. Astronomers must therefore accept some level of inaccuracy, and Davé dedicates considerable attention to the compromises and innovations that are made to optimize these simulations. He explains, for example, how astronomers have developed sophisticated algorithms to group nearby masses together, considerably simplifying the calculation of gravitational forces.
Davé does not shy away from technical explanations, but though the book includes equations, they’re presented in a way that shouldn’t be daunting to the general reader
Armed with this toolbox of simulation techniques, Davé then discusses in detail his main area of research – galaxy formation and its simulation. Pioneering theories of galaxy formation were developed in the 1970s and 1980s, but early simulations were beset by challenges – most notably the “overcooling problem” where the simulated universe cooled too quickly, and produced far more galaxies than are observed in real life.
But Davé believes that the field is now in a “golden age”. He explains how cosmologists developed corrections to the overcooling problem by including small-scale effects like black holes and supernovae. Once believed to be isolated entities floating through space, simulations suggest that galaxies form a vast, interconnected structure called the “cosmic web”. Towards the end of the book, Davé is optimistic about the future of cosmic simulations, predicting that the advent of machine learning and artificial intelligence will bring us even closer to building a working, evolving universe on a computer.
An ambitious journey through the cosmos that sometimes gets lost at sea
This book will be of particular pedagogical significance to students who are interested in numerical cosmology. Davé does not shy away from technical explanations, but although the book includes equations, they’re presented in a way that shouldn’t daunt the general reader. He also uses illustrations to guide the reader through this complex topic.
The final chapter is undoubtedly bold, but I found it somewhat disjointed and abrupt. The author’s discussion of the possibility that our world is a simulated reality feels forced, while the introduction of Stephen Wolfram’s speculative “theory of everything” is insufficiently tethered to the preceding chapters. Though speculative thinking has its place, I found myself wishing for a more solid motivation for the scientific groundwork laid out in the rest of the book.
Nevertheless, these criticisms are minor in the context of the book’s broader contributions. Today, our quest to simulate the universe is driven not by the immediate threat of an emperor’s wrath, but by a deep curiosity about our place in the cosmos. While many popular science books focus exclusively on early-universe phenomena like inflation and the Big Bang, there’s a noticeable gap in literature addressing computational physics and numerical cosmology, and this book fills a crucial void.
- 2023 Reaktion books 200pp £15.95/$22.50hb
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- Source: https://physicsworld.com/a/the-art-of-cosmic-simulations-can-we-build-a-universe-on-a-computer/
