As early as page 2, David Weintraub answers the title question of his book: The universe is now known to be 13.7 billion years old.

In answering the question so quickly, the author wants to show that the book is not about this precise value but rather about our long, successful quest to figure out the universe — its age, its size, its history and all the knowledge that comes from that pursuit.

Weintraub is a prominent astronomer — he has received the Chancellor's Award for Research in 2005 — a distinguished teacher — he has received an award for excellence in undergraduate teaching in 2003 — and an accomplished writer (his previous book was Is Pluto a Planet? A Historical Journey Through the Solar System).

All these talents can be seen in his new book, as Weintraub displays a complete mastery of the wide spectrum of science needed for the subject; he also shows good pedagogical skills in presenting advanced topics, with a special ability to find smart analogies — for example, the pattern of tiles in a kitchen — to explain complex ideas.

We may have gotten used to citing cosmic ages (of the planet, the solar system, the universe) in billions of years but even this is far from obvious today.

On the first day of my Astronomy course, I ask my students a number of "basic" questions, including the ages of the Earth, the Sun, the Moon and the universe. Very few of my students even give me answers in billions.

These long ages, along with the sizes of the solar system, the galaxy and the universe, have only become apparent to us in the past century or so. In fact, the very idea of an age for the universe, that it had a beginning, was debated for centuries.

Indeed, Weintraub begins with Aristotle, who proclaimed that the universe, and the Earth at its centre, are eternal and have always existed in their present perfect forms. Our author then jumps to the 17th century, skipping the whole Islamic civilisation, where such debates raged on philosophical and theological grounds (Al Gazzali against Al Farabi and Ibn Sina, Ibn Rushd against Al Gazzali), and discusses the "biblical chronology" method that was used by various Christian authors, who concluded that the world was created around 4,000BC.

We now know, of course, that the age of the universe cannot be determined by philosophy or theology and that the scriptures are not repositories of scientific knowledge.

The age of the universe is a purely astrophysical problem and once scientific methods were applied to it, progress was quickly made. Weintraub then shows that the different methods now neatly converge on that 13.7-billion-years figure, within half a billion or so.

Part 1 of the book is the shortest; it deals with the age of the Earth and the solar system, mainly using radioactive dating of rocks. Part 2 determines the age of our Milky Way galaxy from the ages of various stars. Part 3 seeks to determine the age of the universe, using either the rate of its expansion or the analysis of the "background" radiation that has filled it ever since atoms formed.

This is a very good book for those who want to understand how scientists tackle such big questions as the age of the universe. The pedagogy is excellent and one ends up not only understanding the subject but also learning large amounts of astronomy and cosmology in the process, from stars to dark matter and dark energy. It is a good investment of time for students and educated people.


Nidhal Guessoum is a professor of Physics and Astronomy at the American University of Sharjah.

How Old is the Universe?
By David A. Weintraub,
Princeton University Press,
370 pages, $29.95