Principles of Physical Cosmology

by P.J.E. Peebles

This overview of contemporary physical cosmology explains how observation has combined with theoretical elements to establish the subject as a mature science. The author describes notable recent attempts to understand the origins and structure of the universe.

Genres: Physics, Science, Astronomy, Textbooks, Reference

Hardcover

First published April 1, 1993

About the author

also Phillip James Edwin Peebles, P. James E. Peebles

Phillip James Edwin Peebles was born in Winnipeg, Canada, Province of Manitoba, on April 25, 1935. Living in the tiny town of St. Vital and graduating in a high school class of 12, his interests in science were not tapped until his college days. Although planning to study engineering at the University of Manitoba, he encountered four inspirational physics professors who sparked a career in physics. He received his BS degree from the University in 1958 and moved next to Princeton University, intending to study particle physics.

Instead he became the only student of his influential mentor, Robert Dicke, to enter into theoretical physics. Under Dicke's influence Peebles gradually moved from studies of gravity to astronomy and from astronomy to cosmology. Dicke also planted the original seed that inspired Peebles to look for the presence of background radiation in the universe. In 1965, as a result of Peebles' post doctoral research, he and Dicke boldly predicted the existence of cosmic background radiation. In 1966 he began work on the theoretical calculations that would make cosmological studies an important topic for physicists. His book Physical Cosmology (1971) established the framework for a series of challenging new theoretical proposals that helped shape the field of cosmological studies. In 1984 Peebles was named Albert Einstein Professor of Science at Princeton University.

Peebles has written many influential and provocative articles in addition to his important books. His contributions have been recognized with honorary degrees from the University of Toronto, University of Chicago, McMaster University, University of Manitoba, University of Newcastle-upon-Tyne, and the Université Catholique de Louvain. He has also received important awards, including the Eddington Medal of the Royal Astronomical Society (1981) and the Gold Medal of the Royal Astronomical Society (1998).

Prof. Peebles and his wife, Alison, live in Princeton, New Jersey, where they share an interest in gardening and in exploring nature. Although he plans to retire from his faculty position at Princeton in the near future, he does not plan to discontinue his life long pursuit of understanding the nature of the

Reviews

[Manny · Rating 5 out of 5]

In this magnificent book, James Peebles, in 1993 perhaps the world's most distinguished cosmologist, sets out to present a detailed overview of the subject. It is an absolute model of how to do this kind of thing: the scope is suitably encyclopedic, the treatment is scrupulously balanced and the writing is excellent. My only complaint is that I don't know enough physics to follow all of it; he assumes a decent graduate-level acquaintance with the subject, which is more than I can claim.

The book is divided into three parts. The first summarizes the global observational picture, what we knew empirically about the universe at the time the book was written. There are many interesting charts showing our cosmic neighborhood, going out to distances of a few tens of thousands of light years. It becomes clear that galaxies, at least on this scale, do not appear to be randomly distributed. Many of them collect together in vast sheet-like structures, introducing a theme which will play an important role throughout the book. There is data about the Cosmic Background Radiation (the light left over from the Big Bang) and evidence for the likely presence of dark matter, inferred from anomalous movements of stars within galaxies and galaxies within galactic clusters. Reading this section left me feeling much more confident about my grasp of cosmic geography. If I have to take a citizenship exam for the Virgo Supercluster Federation, there is now a reasonable chance that I'd pass.

The second part presents a concise but rigorous treatment of general relativity. Everyone who reads pop science books knows the basic ideas, but the curvature of space is here treated almost as a branch of engineering. Peebles is interested in calculating specific things he will need in the later chapters, and it is impressive how he manipulates the equations to get his results; you see him estimating values for the components of the metric tensor as matter-of-factly as a garage mechanic checks the oil in a customer's truck. He is most occupied with gravitational lensing, and also spends quite a lot of time discussing cosmic strings, hypothetical ultra-dense wires which could have formed at an early stage in the universe's history and now stretch for billions of light years through the cosmos. If cosmic strings exist, this book gives a good description of how they would affect the space around them. It is conceivable, though not likely, that they are responsible for creating those gigantic sheets of galaxies as they sweep majestically though space.

The third section uses all the machinery introduced in the first half of the book to discuss a variety of more or less controversial topics in cosmology. In his usual balanced way, Peebles describes the idea of "inflation", then a little more than a decade old. Maybe this is how the universe got started, as a brief exponential expansion driven by the "inflaton field". He lays out the advantages and disadvantages of the idea. There is no clear idea of what the inflaton field actually is, and it is hard to test the theory empirically. On the other hand, it explains several otherwise baffling things, in particular the flatness and homogeneity of the universe, and no one can come up with anything that makes more sense. He goes on to discuss possible candidates for what dark matter could be, and looks at various techniques for probing the structure of the early universe. One in particular, the so-called Gunn-Peterson test, caught my imagination; astronomers look at the light from quasars, emitted when the universe was less than a quarter of its current age, and from the spectral structure infer things about what kinds of objects that light has passed through on its way to us. It is almost like a cosmic version of Plato's Allegory of the Cave. There is a great deal about galaxy formation, a subject where Peebles is an acknowledged expert. I had not realized that galaxies started to coalesce so early: at the beginning, they were almost touching each other. Another thing I had not understood is that galactic clusters seem to be created bottom-up, not top-down. The great clusters and superclusters we see are comparatively recent, and are indeed still forming.

At the end, when I was feeling quite dizzy from the variety of remarkable things I'd been shown, Peebles fits the pieces together. What does all this tell us about the large-scale structure of the cosmos? I had the advantage of reading his summing-up in 2014, so I was able to evaluate the reasoning; I knew that, only half a dozen years later, people would find clear evidence for the existence of dark energy accounting for about 70% of the universe's mass density. But although Peebles has nearly everything he requires to conclude that the dark energy must be there, he can't quite believe it. He knows very well that it's a possibility; he presents convincing arguments to show that space should be flat, which requires a certain critical density of mass-energy; he ingeniously interprets the evidence to show that, on most reasonable models, visible matter and dark matter aren't enough to reach that critical density. He's almost got the answer. But he thinks dark energy is an inelegant solution, and dismisses the idea after brief consideration.

I was disappointed that Peebles didn't find the buried treasure; but he'd done such an excellent job of mapping the terrain that other researchers were soon able to pick up where he'd left off. I'd wondered why everyone was so willing to accept the 1998 dark energy results, which to me seemed to report a staggering leap into the unknown. Now I see that it was anything but unexpected. It had to be there, it was just the last piece of the jigsaw.

It's fascinating to see how science works.

[MJ · Rating 4 out of 5]

Heavy with formulas and equations but good overview of different topics in cosmologies that are still relevant to modern science with emphasis on dark matter (hot & cold), galaxies formations and large mass distributions. Good build up to General Relativity and Cosmology section.

[Phil Lawless · Rating 3 out of 5]

This is an ambitious book that covers most of the physics in the field of cosmology. It is dense with equations and sparing of discussion. It required several months (not all at once) to get through it. The book seems unlikely to be used as a reference.

[Richard]

Equations, equations, equations. If you want to read this, you'll have to have a math background.