It's that particle again
Jun 20, 2013 6 comments
The Particle at the End of the Universe: How the Hunt for the Higgs Boson Leads us to the Edge of a New World
2012 Dutton/Oneworld $27.95/£16.99hb 352pp
The quest by particle physicists to understand nature at its most fundamental level has necessitated the construction of ever larger "atom smashers" to probe ever shorter distances. The Large Hadron Collider (LHC) at CERN is the latest in a long line of these machines. From late 2010 until early 2013, the LHC was colliding protons together at the unprecedented energy of 7–8 TeV, collecting enormous amounts of data in the process – data that led, among other things, to the announcement on 4 July 2012 that a new particle with a mass of 125 GeV/c2 had been observed. When the collider restarts in 2015 after a period of scheduled maintenance, it is expected to collect even more data at almost twice the energy.
Complementing this successful experimental programme has been an equally successful theoretical effort. One of the great achievements of modern science has been the uncovering of the rules that govern subnuclear processes. These rules, which are unimaginatively called the Standard Model (SM), predict the existence of various particles and interactions. The principle of symmetry played a central role in their development. The laws governing the physics at these very short distances display a huge amount of symmetry – so much so that, naively, one might think that the SM should be a theory of only massless particles, since the electroweak symmetry forbids the equations governing the SM from having masses in them. However, even if the interactions are symmetric, it is possible for the lowest-energy state of the system to break this symmetry in so-called spontaneous symmetry-breaking.
How this symmetry is broken and how the fundamental particles acquire a mass has been, for many years, the outstanding question within the SM. There are various competing proposals for how this occurs, but in the SM, the symmetry-breaking is carried out by something called the Higgs mechanism. Associated with this mechanism is a new particle – a fundamental scalar boson – called the Higgs boson. This mechanism, the particle, the developments in science that led to its prediction and the decades-long experimental effort to find it are the focus of Sean Carroll's book The Particle at the End of the Universe.
There are many popular-science books about particle physics and the search for the fundamental laws of nature. Two things set Carroll's apart: its rather singular focus on the Higgs, and the timeliness of its release. As Physics World readers are no doubt aware, the last year or so has seen the LHC's search for the Higgs take centre stage and receive much media attention. While CERN officials were understandably cagey when they announced their discovery of a "new boson" back in July 2012, subsequent data releases later in 2012 and early 2013 mean that even if the new particle may not yet be said to quack exactly like an SM Higgs, it certainly looks like an aquatic bird. Carroll's book – which came out in late 2012, before some of the new results – proceeds under the hypothesis that this new particle is a Higgs boson, and that 4 July 2012 was the day we learned that Nature chose the Higgs mechanism over the alternatives as the way to break the symmetries of the SM.
Books about particle physics often follow a standard format. After describing the history of the field and the developments that led to where we are now, they devote a couple of chapters to open questions in the field and then conclude with an outline of some of the more exotic possibilities that could be found at future experiments. Carroll's book, in contrast, provides a more dynamic perspective on how science proceeds. It presents the field as it currently is: slightly giddy and in a state of great flux. His writing style is light, lively and often humorous, and he does a good job of capturing the excitement in the field. Carroll is a cosmologist, and as a working scientist he has seen the developments in the field that have led us to this point and knows the personal investments that people have made to make the discovery possible. His position also affords him closer access to the main players than a science journalist might be able to get. As a result, the book is littered with anecdotes and inside stories that don't often see the light of day. His discussion of bets that physicists make among themselves is particularly amusing, but perhaps makes it into the book because both of his own bets – made with the unlucky Brian Schmidt on the subject of measuring the density of matter and energy in the universe, and whether the Higgs would be discovered at the LHC – were ultimately decided in his favour.
This attention to the human side of the field does not come at the expense of the science, which is presented with a deft touch. Nor does Carroll's focus on the Higgs sector of the SM mean that he ignores what else might be in store for the LHC. In one of the later chapters, he describes some of the more exotic suggestions for what lies beyond the SM, and there are also frequent discussions of dark matter and other cosmological discoveries. Throughout, Carroll seems well aware that he is writing for dual audiences of lay readers and professionals, and he does a good job of keeping both on board as the book progresses. He is, for example, careful with the science and clear about where his analogies break down, and the book is littered with comments to the cognoscenti. On the other hand, he serves his less-expert readers by relegating certain technical details to appendices, allowing the story to flow and maintain the excitement. The fact that they are included at all should insulate him to some degree from colleagues' complaints; however, this colleague would still have preferred it if Carroll's detailed but accessible description of the Standard Model and its interactions – especially those of the Higgs, which are central parts of much of the story – had appeared in the main text.
This book is an enjoyable and informative read and does an excellent job of explaining "how science is done" and in particular how the Higgs boson was found. It accurately reflects the scientific and emotional state of the field at this momentous time while also putting it in a historical context. Towards the end of the book, Carroll finds time to discuss what new discoveries may lie ahead, and one can only hope that when these discoveries are made – whether at the LHC or elsewhere – he is around to chronicle them.
About the author
Patrick Fox is a theoretical physicist at the Fermi National Accelerator Laboratory in Illinois, US