Heart of Darkness by Jeremiah P. Ostriker and Simon Mitton

Four distinguished cosmologists have contributed a bouquet garni of adjectives to the back cover of Jeremiah Ostriker and Simon Mitton’s book Heart of Darkness. These come in pairs: “penetrating and thorough”, “clear and fair”, “fresh and engaging” and “upbeat and inspiring”. Similarly paired nouns include “authority and style”, “precision and verve” and “vigor and enthusiasm”. This is a hard act to follow, and I can practically hear you sitting there expecting a remark about books and covers.

As it happens, your reviewer’s hearing is actually rather good for her advanced age (which is almost exactly the average of the ages of the two authors) and what I was listening hard for throughout the book, and never heard, was some explanation of the title. A canvassing of colleagues, friends and relations suggests that to older generations, Heart of Darkness means first and foremost the Joseph Conrad novella, and to younger folk perhaps the derived film Apocalypse Now, which moves the novella’s action from the Congo to Vietnam.

But the darkness our authors have in mind is physical, not spiritual: that is, dark matter and dark energy as the major components of our Universe today. Both refuse to interact with normal matter (meaning, of course, what we are made of) in any way, except, perhaps, weakly and gravitationally - no light emitted or absorbed, no radio waves or X-rays, and no nuclear reactions. Dark matter pulls stuff together and it was the winner for billions of years, allowing stars, galaxies and all to form, and providing at least one habitable planet. Dark energy is trying to push everything apart and is now winning, so that the expansion of the Universe is speeding up at present and is likely to continue until our remote descendants can see nothing but the Local Group of galaxies, probably merged into a single, lumpish ellipsoid of ancient stars.

The darkness our authors have in mind is physical, not ­spiritual: dark matter and dark energy as the major components of our Universe

The authors, their book’s four back-cover experts and I all agree about both the existence and the properties of dark matter and dark energy, the latter quite similar to Einstein’s old cosmological constant. And we agree, at least in broad outline, about how a small fraction of the astronomical community learned about these dark entities and the rest of us came to accept the findings. The story is definitely worth telling. Indeed, one of the cover experts recently wrote (in a different book) that anyone who has not heard about the great sweep of modern cosmology and the enormous explanatory power of biological evolution is culturally deprived. We also all concur that no one knows what either dark entity is, although one of several candidates for dark matter could advance from “promising” to “detected” even before you read this: they have names such as Wimps (weakly interacting massive particles), axions and lowest-mass supersymmetric partners. For dark energy, the candidates are more numerous, individually less well motivated by independent physical ideas, and even more strangely named.

Ostriker and Mitton begin with the ancient Greeks (Aristarchus), march forward with Galileo, Kepler, Newton and such to the arms of Einstein, some of the results of whose general theory of relativity can be closely approximated by simpler Newtonian calculations (although even these are relegated to an appendix here). Thus, in the course of the book, readers will be exposed to quite a lot of 19th-, 20th- and 21st-century physics and astronomy. The last few pages emphasise just how many things remain to be learned, and do not invoke the multiverse as a possible solution to some of the problems.

A full retelling of the dark story, as completely and accurately as existing sources allow, would require very many more than this book’s not- quite-300 pages of text, along with large numbers of end- or footnotes (none are provided), and hundreds of primary and secondary references (a bibliography of just 44 books appears here). Thus, my (free, pre-print) copy of Heart of Darkness has its margins defaced by my pencilled cries of “non!” (Fritz Zwicky did not write the words “dunkle Materie” in 1937; the paper in German in which it appeared was published in 1933); “oops!” (Einstein’s Nobel accomplishments included the explanations of the photoelectric effect, not its discovery) and “misleading” (the claim that you need metre sticks to do geometry, which in its pure form uses only compasses and straight edges). The total number of those marginal comments, along with “missing person”, “who?”, “not quite” and other expressions of reservation, is somewhere around 300. The authors have refrained from the “Uncle Tom Cobley and all” method of apportioning credit. That they do near-justice to Beatrice M. Tinsley (1941-81), the first person to show that the evolution of the colours and luminosities of galaxies was both calculable and important, goes far to making up for others who are given short shrift, including Morton S. Roberts, a major early radio mapper of the rotation of galaxies, and Peter Scheuer, who cheated Mother Nature out of a bit of extra data about the number of radio sources using Gaussian statistics.