The universe is made of (at least) stars and galaxies, dark matter and dark energy, cosmic rays and neutrinos. But cosmology is made of cosmologists. The index of Paul Halpern’s book Edge of the Universe bears this out, listing no fewer than 228 names of individuals and eponyms; even so, half a dozen names are missing just from the book’s discussion of dark matter. Of the 228, I know or knew 113, from Abell (George, who catalogued clusters of galaxies) and Abel (Tom, who makes computer simulations of them) to Zel’dovich (Yakov, who helped describe what passage through hot gas would do to microwave radiation left over from the very early universe) and Zwicky (Fritz, who saw what dark matter does to radiation trying to get away from its vicinity). And of the scientists mentioned, 17 are women, which is – believe it or not – a lot for this subject.

In his chapter titles, Halpern asks 15 challenging questions, from “How far out can we see?” to “What are the ultimate limits of our knowledge about the cosmos?” The answer to the first question is about 46.6 billion light-years, which is further than the 13.8 billion that light can travel in the age of the universe because the universe has been expanding while the light travelled. Not surprisingly, Halpern provides no answer to the last question, but the way it is worded (rather than “Are there ultimate limits to our knowledge?”) suggests he thinks such limits exist.

There are some very good approximations to explanations in the book of recent alternatives to the “chocolate” (in the sense of being everybody’s second-favourite flavour) inflationary standard cosmological model. These include models where 3D surfaces in higher-dimensional space bang into and bounce off each other to start new cycles of expansion, as well as assorted string theories in which both point material particles and particles that carry the forces of gravity (and so on) are replaced by loops and extended 1D strings.

On the observational side, 2013 data from the Planck satellite – the latest to observe the microwave background radiation – have, as the author anticipated, strengthened some results and weakened others. The winners include, especially, the now-standard model of a universe with 4–5% matter such as what we are made of, about 23% dark matter and about 73% cosmological constant or dark energy. On the other hand, the evidence for a preferred direction in the universe as a whole, and for patches in the microwave “sky” that possibly represent our cosmos colliding with other members of the multiverse in the distant past, is not looking as strong as it was.

The book’s light-hearted style will either become more appealing or more grating as you proceed through intermediate questions such as “What is dark energy”, “Do we live in a hologram?” and “Can we journey to parallel universes?” My own reaction is that some of Halpern’s puns are both delightful and telling, as when he uses the phrase “a tangled Webb” to describe the 20-year saga of the intended successor to the Hubble Space Telescope, while others are less so (“It is the best of times and the weirdest of times for cosmology”). Ditto for the analogies, which average about one per page. A memorable one concerns parallel universes: “It would be strange to be born in an alternative reality, but not paradoxical, if such parallel strands turn out to exist. It would be in some ways like being born in Yugoslavia or Czechoslovakia, countries that no longer exist, except that you would have much more explaining to do and couldn’t possibly recover your birth certificate unless you had brought it with you”. Another analogy, also memorable, but less happily, comes as part of a description of why our universe can harbour life, otherwise known as the fine-tuning problem: “Is ours a Goldilocks universe – uniquely suited for life – or is it just one of many, like the offspring in ‘The Old Woman who Lived in a Shoe’?”

Who are the intended readers of Edge of the Universe? Not modern cosmologists, whose teeth will be set on edge by repeated non-disambiguation between Doppler redshifts (caused by motion of light sources and receivers through space) and cosmological redshifts (caused by the expansion of space-time itself). And not us old-fashioned astronomers, who still hold to the 1922 decision of the International Astronomical Union that distances outside the solar system should be expressed in parsecs and multiples like kilo-, mega- and gigaparsecs, not in light-years.

Instead, the book is meant for the general public, and books that attempt to bring the universe to the people have become so many and so diverse in their viewpoints that e pluribus unum begins to seem a vain hope. If I were permitted to lay out a course of reading for this purpose, it would begin with Malcolm Longair’s The Cosmic Century (2006, Cambridge University Press), which takes the reader from stars to galaxies to the universe. It has a good many pictures, numerous graphs and even a few equations, along with more than 700 indexed people, including 33 women. Next might come Heart of Darkness by J P Ostriker and S Mitton (2013, Princeton University Press), which confines strings and such to the last few pages, has lots of pictures, a few graphs, no equations and nine women. Next, read in tandem this book (no pictures, graphs or equations) and Richard Panek’s The 4% Universe (2011, Oneworld Publications), which also has no pictures, graphs or equations, just six women, and fewer people in total than Edge, but much more human, detailed tales of some. You will then be ready for the more careful, equally charming history in Marcia Bartusiak’s The Day We Found the Universe (2009, Pantheon) and current events as they appear in the news columns of whatever publications you normally read.

Perhaps by then you will even join me in noticing that none of these books really mentions the best chance we have for observing the first stages of galaxy formation, which took place after protons and electrons combined to make (neut-ral) hydrogen atoms but before the first stars turned on to re-ionize the gas. The period in-between is often known as the Dark Ages, because although recombination freed the microwave background to stream toward us (carrying information about the very earliest stages of structure formation), it also made the universe opaque to visible light that would have come from stars, galaxies and clusters that were beginning to form around the low-amplitude density fluctuations revealed by the microwave background. The only wavelength of light emitted or absorbed in this period that can reach us is the 21 cm line from hydrogen, by now redshifted to very long radio wavelengths (2–200 m). This radiation will look a bit brighter in the directions of warmer and denser gas, and a bit fainter in the directions of cooler and more tenuous gas. Thus, by mapping the radiation across the sky as a function of received wavelength we can trace out the important initial stages of galaxy and cluster formation – where and when, how many, and how massive these first structures were. Several radio telescopes that should be able to study that dark era are currently under construction or planned, and I wish the book had mentioned them.

But the last word should go to Halpern and his example of Occam’s razor: “Thus if you walk outside and see puddles of water, Occam’s razor would suggest that you check if it had rained recently before jumping to the conclusion that a truck transporting piranhas to a nearby aquarium must have sprung a leak after a collision with an escaped rhinoceros.” If you can visualize this, you will like the book.