On 4 July scientists at CERN in Geneva declared that they had discovered a new particle 'consistent' with the long-sought Higgs boson, also known as the 'God particle.' Although further research is required to characterize the new particle fully, there can be no doubt that an important milestone in our understanding of the material world and of the evolution of the early universe has just been reached.
Exciting times! But why all the fuss? What is the Higgs boson and why does it matter so much? Was finding it really worth all the effort?
The answers to these questions can be found in the story of the so-called Standard Model of particle physics. As the name implies, this is the standard framework that physicists use to interpret the elementary constituents of all matter and the forces that bind matter together, or cause it to fall apart. It is a body of work built up over many decades of unstinting effort, which represents the physicists' best efforts to interpret the physical world around us.
The Standard Model is not yet a 'theory of everything.' It does not account for the force of gravity. In recent years you may have read about exotic new theories of physics which attempt to unify the fundamental forces, such superstring theory. Despite the efforts of hundreds of theorists engaged on these projects, these new theories remain speculative and have little or no supporting evidence from experiment. For the time being, and despite flaws that have been acknowledged since its inception in the late 1970s, the Standard Model is still where most of the real action is.
The Higgs boson is important in the Standard Model because it implies the existence of a Higgs field, an otherwise invisible force field which pervades the entire universe. Unlike other kinds of force field (such as an electromagnetic or gravitational field) the Higgs field points but it doesn't push or pull. It was invented in 1964 in attempts to explain how otherwise massless particles could acquire mass, by Belgian physicists Robert Brout and François Englert, English physicist Peter Higgs at Edinburgh University and Gerald Guralnik, Carl Hagen and Tom Kibble at Imperial College in London. The mechanism was applied three years later in the construction of a theory of electromagnetism and the weak nuclear force (responsible for a certain type of radioactivity) by American Steven Weinberg and Pakistan-born theorist Abdus Salam.
The mechanism works like this. Without the Higgs field, elementary particles such as quarks (the constituents of protons and neutrons) and electrons would flit past each other at the speed of light, like ghostly will o' the wisps. The elementary particles that make up you, me and the visible universe would consequently have no mass. Without the Higgs field mass could not be constructed and nothing could be.
What actually happens is that these elementary particles interact with the Higgs field and are slowed down by it, as though swimming in molasses. We interpret this 'slowing down' as inertia and, ever since Galileo, we have identified inertia as a property of things with mass.
Many of the predicted consequences of the Higgs field were borne out in particle collider experiments in the early 1980s. But inferring the field is not the same as detecting its tell-tale field particle.
The publication of Higgs: The Invention and Discovery of the 'God Particle' is timely, coming only six weeks after the discovery announcement. But I had the idea for a book about the discovery of the Higgs boson in March 2010, just as CERN's Large Hadron Collider (LHC) was setting a new world record for particle collision energy. I figured that there was a chance that this particle -- the last missing piece in the jigsaw of the Standard Model -- might be discovered soon. This is perhaps the first example of a book that has been largely written in anticipation of a discovery.
But the question was: How soon?
We saw tantalizing glimpses of the Higgs in summer 2011, and in August I met with Peter Higgs on a wet Thursday afternoon in Edinburgh. Higgs had retired in 1996 but had remained in Edinburgh close to the University department where he had first become a lecturer in mathematical physics in 1960. He was now a sprightly 82 years old.
Higgs had published the paper that was to bind him forever to the particle that bears his name in 1964, and had waited nearly fifty years for some kind of vindication. 'It's difficult for me now to connect with the person I was then [in 1964],' he explained, 'But I'm relieved it's coming to an end. It will be nice after all this time to be proved right.'
Alas. The tantalizing glimpses were a desert mirage. They faded as we got close enough to inspect them. But strong hints resurfaced in data reported in December. Expectations built in intensity. Right up to July 3 we had hypotheses and compelling theoretical structures. Finally, on the following day we began to gather hard scientific facts. Our understanding took a giant leap forward.
Simply declaring the discovery of a new particle pays little respect to the efforts of all involved in running the LHC, operating the two primary detectors -- ATLAS and CMS, setting the triggers, managing the pile-up of proton-proton collision events, calculating the background, managing the worldwide computer grid needed to analyze the results, performing the detailed analysis and not sleeping much. The discovery represents an enormous triumph for an experiment that was conceived nearly thirty years ago, on which construction began twelve years ago, and which has engaged worldwide collaborations of three thousand scientists working in competition on each detector facility.
Precisely what kind of boson has been discovered remains to be seen, and there's hope of more surprises yet to come.