Nobel Prize-winner Professor Peter Higgs has died. While Higgs made many contributions to physics, his name will always be inextricably linked to the particle he predicted. His theoretical demonstration that such a particle could resolve many problems in physics sparked a search lasting almost 50 years. This became one of the major reasons for the construction of the Large Hadron Collider, one of the largest and most expensive pieces of scientific equipment in history. What then is the Higgs boson, and why did the world go to such lengths to find it?

By the mid-20^th century, it was becoming clear models of the universe, thought to be nearly complete 50 years earlier, couldn’t even explain why particles have mass – a fairly basic question, given how essential it is to everything.

Around the same time several scientists argued there must be a particle we had yet to find which was responsible for giving many other particles mass. This was particularly important for the W and Z bosons, which had recently been proposed to mediate the weak force, and were confirmed a decade later. Such a particle would be the last missing element in what became the Standard Model of Particle Physics.

Although Higgs was just one of those who reached this conclusion, his contribution was deemed to be sufficient that it was his name that was given to the missing particle, long before it had been found.

Mass seems such an intrinsic feature that non-physicists struggle to imagine why we need a particle to provide it. The Higgs boson has proven so hard to find because it collapses in less than a billion billionths of a second; the question extends to how such a short-lived particle could serve this purpose. 

However, models of the universe require particles such as quarks to have originally been massless, and for this to have changed within the first second after the Big Bang. Higgs proposed these particles must have gained their mass from interaction with a field, which later was also named after him. Just as other fields being discovered at the time required particles to carry them, the Higgs field needed a particle that would represent the field’s excited state. Higgs and others sketched out its properties, such as its lack of spin or electric charge, but its own mass could only be found experimentally. 

This set off the great search. At first, scientists wanted to confirm the Higgs boson’s existence, and therefore the field it carries. By the end, few doubted the field and particle were real. Instead, finding the Higgs boson was the only way to measure its properties precisely. The Higgs particle’s mass ripples through the universe, and determining it made possible the pinning down of a great many other aspects of the Standard Model, which until then had been hazy.

In 2012, it was found to be 125 billion electron volts/c², very much in line with predictions (mass being equivalent to energy divided by the speed of light squared under Einstein’s famous equations, particle masses are reported in units of energy).

The staggeringly short life of the Higgs boson means we never actually observe it directly. Instead, it decays into a bewildering variety of longer-lived particles, including two W and two Z bosons, which teams at the Large Hadron Collider did manage to observe, along with photons, a tau and bottom quark, and their respective antiparticles. Adding these together enabled a reconstruction of the Higgs mass.

By giving the W and Z bosons mass, the Higgs field limits their capacity to travel far, a vital step to making the Standard Model align with observations. The Higgs broadly does this, although there are hints of yet more particles lurking.

The Higgs boson, and therefore Higgs himself, achieved fame far beyond the physics community in part because of the nickname the “God particle”, leading to the impression of some sort of ruling status. However, while the Higgs is crucial for our understanding of the workings of the universe, many other elementary particles are equally essential. These, however, proved much easier to find. The Higgs’ elusiveness inspired the nickname the “goddamn particle”, which publishers opted to shorten. The new version was unpopular with physicists, but it did help spur public interest in the search for something whose significance was so hard to explain.

The fact that the Higgs field permeates the universe contributed to the public impression of an association with religion. The Standard Model relies on a great many other fields, but all the others have average values of zero, only obtaining a non-zero value at particular points, for example around a charged particle. The Higgs field, on the other hand, has an expectation of a non-zero value, with some strength at every point in space.

The Higgs’ boson’s fame has led to the impression among non-scientists that it is responsible for all the mass in the universe. This isn’t true. Even aside from the unsolved question of the nature of dark matter, most of the mass in a proton or neutron comes from the binding energy holding it together, rather than the quarks that get their mass from the Higgs.