In the next few months, scientists at the Large Hadron Collider at Cern may detect one of the fundamental building blocks of the universe: the elusive Higgs boson. The collider, one of the most ambitious machines ever built—which sends two beams of subatomic particles around an underground circuit 27km in circumference, to crash into each other at close to the speed of light—may already have given them the crucial data.
The Swiss government asks Cern, the joint European research institution, to shut down the circuit in winter, to spare it the demand on the electricity grid; these cold months are used for analysing the torrent of data from the summer’s experiments. If scientists find the Higgs boson, then it will be one of the greatest advances ever in physics. The world’s attention—including that of the Nobel committee, will turn to, among others, Peter Higgs, 82, emeritus professor at the school of physics and astronomy at the University of Edinburgh.
But if they don’t find the particle, the consequences could be even more interesting—as Peter Higgs explains in this interview for Prospect. The particle that he has argued must exist “plays such a role” in the modern theory of the structure of the physical world “that if you tried to modify the theory to take it out, the whole thing becomes nonsense.”
Higgs takes the bus south through Edinburgh to the James Clerk Maxwell building of the science faculty, where a large portrait of him (above) looks out over the main staircase. When I accompany him to a talk given there by a Cern scientist, at one point, the lecturer jokes to the audience that he is attempting to make the discussion accessible to all, “even to you, Peter,” he says, gesturing towards Higgs. There is a communal intake of breath; students crane to look as they realise who is sitting in the front row. After, they crowd round asking to have their photos taken with Higgs, who obliges.
Higgs’s insights are central to the work at Cern. The experiments aim to answer some of the most profound questions, such as where the mass of fundamental particles comes from. For physicists, mass is an expression of a body’s resistance to changes in its velocity (its speed and direction). In everyday life, we are most aware of an object’s mass through its weight, a concept intuitively linked to our grasp of the physical world. But the individual bits that make up an atom, if weighed separately, would equal less than the mass of the complete atom. So where does that extra mass come from?
Higgs put forward the concept of the Higgs boson in the 1960s. Bosons, named after the Indian physicist Satyendra Nath Bose, are particles that carry force. Photons, the particles of light, are bosons, and convey the electromagnetic force. The others are called the Z and the W—these carry the weak force, which plays a part in radioactive decay—and also the gluon, which carries the strong nuclear force, which holds together the nuclei of atoms.
These bosons are a far cry from the Newtonian conception of particles as something like billiard balls, scaled down and down until they became microscopic points. Bosons—Higgs bosons included—are different. They are the result of goings on at the minuscule, quantum level. Quantum systems can undergo “excitations,” leading to the manifestation of particles, “the basic idea essentially being what was in one of Einstein’s famous 1905 papers—that the electromagnetic field has its energy delivered in a particle-like lump, which we now call photons.” The Higgs boson is, like the photon, a similar particle-like lump. If it exists, of course.
There are some who think that it does not. The British physicist Stephen Hawking, for example, has made it clear that he does not accept that the Higgs particle exists. Does Higgs ever consider that Hawking might be right—that there may be no Higgs boson? “I find it very difficult to imagine how the theory works without it,” he says. “So something has to have this sort of role in the theory, and have experimental consequences of some kind.”
Higgs accepts that the boson might be made up of other, even more minuscule particles. “I’m open-minded about what sort of structure, if any, this thing would have,” he says. “But according to this kind of theory, if you were to scatter ‘weak bosons’ off one another, which nobody has yet done, the theoretical account of this would be nonsense unless the Higgs particle existed.”
The sum total of particle physics is the Standard Model, a theory that sets out the particles that are known to make up the physical world. There are particles to carry force, particles to carry charges, particles to make up the nuclei of atoms and so on. Together they compose an interdependent whole of building blocks. Modern physics demands that there be a Higgs, or some Higgs-like particle to explain how these fundamental particles obtain their individual masses. If it does not exist then the model collapses. But though internally consistent, the Standard Model lacks more than just the Higgs boson. The most glaring omission is that of gravity—no force particle in the Standard Model yet accounts for this force.
In the early 1960s, physicists had started delving into the idea of symmetries that occur in nature, and incorporating them into their notion of the particles that make up atoms. The idea was that a sudden loss of symmetry in a system can cause particles to take on different properties.
“There’s a crude mechanical picture of this you can imagine,” says Higgs. “Suppose you have a bowl with a concave bottom and you allow a marble to roll about in it. With a normal sort of concave base, the state of lowest energy is when the marble sits in the middle—on the ‘symmetry axis.’ But now suppose that you have the same symmetry of the bowl, but it’s like the bottom of a wine bottle, where you have a peak in the middle and that makes the symmetry point unstable and if you put a marble in to that it rests in a trough. Oscillating around the trough is a very different proposition from oscillating up and down the curve of the trough.” This switching from one state to another is what physicists call a spontaneous breaking of symmetry.
In 1960, Higgs showed that the breaking of a symmetry in the earliest moments of the universe created a field that permeated all space. This field—the Higgs field—acted upon certain types of matter and, in doing so, gave them mass. Certain types of particle, such as the photon, were not affected and so remain massless. The agent of this field, he surmised, was the Higgs boson.
In 1964, two physicists working in Brussels, Robert Brout and François Englert made breakthroughs in understanding the implications and in 1967, two others, Steven Weinberg (below) and Abdus Salam took the idea further. “They took a theory formulated by [the American physicist Sheldon Lee] Glashow in 1960 and essentially bolted onto it what I had done in 1964 and solved the problem of how to generate masses for the carriers of the weak force in a rather neat way,” said Higgs. Weinberg, Salam and Glashow shared the 1979 Nobel prize in physics.
The Higgs mechanism, which explains how particles interact with the Higgs field and incur mass, is perhaps unfairly named after only one individual. Higgs himself notes that, chance has “confined mention of the other people to a footnote.” He regrets this, but points out that: “Of the various people who contributed to that piece of theory I was the only one who pointed to this particle as something that would be characteristic of that kind of theory and of interest for experimentalists.” Higgs felt all the more inclined to make noise about his theory, as the first version of a paper he wrote on the subject was turned down for publication by a science journal.
Much more than the use of his name, it is the excessive attention on the search for a single particle that has caused Higgs concern. “I’ve been worried over the years about the way that Cern handled its publicity,” he says. “Because I think they talked up the search for the Higgs boson too much—so much so that they were in danger of having their paymasters say, ‘oh well, you’ve found it now, you don’t need to run that expensive machine any more do you?’ And I think that it’s being realised that they need to devote more publicity to the other things they do there, which are equally important. From my point of view, finding this thing is just the end of a chapter.”
But perhaps discovering the Higgs would be something of a disappointment. It would close a line of enquiry that could then go no further. Not finding the Higgs—unearthing a surprising, more complex picture than that assumed hitherto would be even more exciting for science.
Where can experimental science go from here? Surely there could never be a larger collider—a bigger ring, more powerful magnets? “It has to be a design of a different kind of collider,” says Higgs. “People realise you can’t just go on building bigger and bigger circular machines; they’re extremely wasteful of energy.” Only a small fraction of the energy goes into accelerating the particles around a circle. “Most of it is generated as electromagnetic radiation and keeps the climate around Geneva warm—or warmer than it would be,” he says.
One answer may be to develop linear machines, which consume less energy, but which bring design problems. “In a circular collider, protons are propelled round in a circle using a magnetic field and given an added whack with an electric pulse every time they pass. In this way the speed of the particle beam can be built up to the rate required. “If you have a linear collider, you haven’t got the possibility of giving them the repeated whacks each time they come round.”
The worry is that technological constraints may check the advance of experimental science. “People are looking at theoretical systems which go far beyond what can be verified experimentally at the moment—superstring theories, all these things which seem to be necessary to include gravity in the unification with other fundamental forces,” says Higgs. “The problem to me seems to be that the difficulty of experimentally checking whether such theories are right is getting worse and worse.” He comments that with “superstring theory, we may end up just not knowing how to do the experimental checks other than analysing what we get coming in from outer space.”
For now, he stands by and waits for the word to come. “It’s agreed that I would be invited to—if the thing is confirmed—a seminar with various contributions at Cern and I will be one of the invited speakers. And I have to sort of stand by to go to Geneva at fairly possibly short notice, though I dare say that since the analysis is a continuing process there will be hints dropped that there’s something coming up.”
“It is obviously exciting for me,” he says “to have the prospect of this particle which has had my name attached to it being found in the next months. If not, then everybody has to think again,” he says, and laughs.
Listen to Part 1 and Part 2 of James Elwes's interview with Peter Higgs
More on the Higgs boson:
Mass, metaphor and Margaret ThatcherDavid Miller explains the boson in simple terms
The Higgs, and beyond Nobel prizewinning physicist Steven Weinberg looks past the Higgs boson to dark matter, technicolour forces and WIMPs
