The Cosmic Web: Mysterious Architecture of the Universe

  • J. Richard Gott
Princeton University Press: 2016. 9780691157269 | ISBN: 978-0-6911-5726-9

Over the past half-century, astrophysicists and cosmologists have revealed how structure formed in the Universe. This has vast importance: we exist only because tiny initial fluctuations in the density of matter grew through gravity to form galaxies, stars and planets. Key pieces of physics, astronomy and mathematics have only in recent decades been combined into a scientifically coherent and convincing origin story. In The Cosmic Web, astrophysicist Richard Gott, a compelling teller of cosmological stories, describes his part in this scientific quest.

Density fluctuations in the Universe (shown in a computer simulation) have a sponge-like topology. Credit: Illustris Simulation

He begins with a brisk primer on the early history of cosmology, starting with the discovery of the expansion of the Universe by US astronomer Edwin Hubble and others in the 1920s. The second half of the twentieth century, he shows, brought the detection by Arno Penzias and Robert Wilson of the cosmic microwave background radiation left over from the very early Universe (predicted by George Gamow and others), and the realization that fluctuations in this radiation would reveal the irregularities in density that seeded the growth of large-scale cosmic structure.

This is when Gott's work enters the picture. Beginning with his high-school obsession, topology — how geometric shapes can be connected — the book comes into focus. We start to follow Gott's fascinating path towards a better understanding of large-scale cosmic structure. Remarkably, his early discoveries led to a paper in American Mathematical Monthly when Gott was just 20, on a new class of regular 'pseudopolyhedrons' with sponge-like topology (J. R. Gott Am. Math. Mon. 74, 497–504; 1967). These polyhedrons are infinite, and their surfaces divide space into two identically shaped, interlocked regions. As in a sponge, each region (the 'sponge' and the 'holes' in it) is fully connected. If the Universe is separated into regions greater than and less than the mean density, it shows the same sponge-like topology, although with irregular patterns. Gott's enduring (and endearing) enthusiasm for this connection carries the reader through the more technical parts of the book.

The Cosmic Web is not a complete or representative intellectual history of twentieth- or twenty-first-century cosmology. Gott is rigorous in assigning credit for findings, but tells the history through the lens of his collaborations. This could leave a reader with the impression that a relatively small group of scientists is responsible for the discovery of dark matter, the development of structure-formation theory and progress on unravelling galaxy formation. Gott's major protagonists (including James Gunn, Jeremiah Ostriker and James Peebles) did make key discoveries, but in the context of a broader group than Gott describes. Gott also gives only a partial account of the creation and development of a key contemporary effort: work on large-scale structure and mapping of the cosmic web by the Sloan Digital Sky Survey (SDSS) — which uses the optical telescope at Apache Point Observatory, New Mexico — to create the most detailed 3D maps of the Universe yet, and continues to map further regions and earlier times.

Gott's is a personal view of cosmological developments, giving space and life to realities of research.

Gott's is a personal view of cosmological developments, giving space and life to realities of research. This evokes the best of physicist and science historian Abraham Pais's more comprehensive books, such as Inward Bound (Clarendon/Oxford Univ. Press, 1988). Unafraid of spending a page explaining an idea that turns out to be wrong, Gott engagingly describes the blind alleys along the way to current views. He presents figures and equations stripped to their fundamental forms, but avoids the common temptation to water them down unrecognizably.

His work shines with this approach. As 3D maps of the Universe emerged from the 1980s onwards, revealed by surveys such as the SDSS and its forerunners, and as the theoretical picture of cosmology developed, it became clear that the pattern of density fluctuations in the Universe is a cosmic, topologically sponge-like web. Gott's youthful work had primed him to grasp this, and gave him the mathematical tools to test it. This aspect of cosmology is now an essential facet of our knowledge, and our fullest understanding of the topology of large-scale structure is derived from techniques that Gott developed.

Gott's journey shows how scientists can be so motivated by their earliest obsessions that they persist in pursuing them — and how unique obsessions can let them bring something new to the crowded table of ideas. For working scientists, this book is a reminder of what drives us, the value of chasing down questions that only we would ask, and how circuitous that chase can be. The Cosmic Web is not just a well-told story about the frontiers of cosmological knowledge. It is also an inspiration to explore them further.