The Higgs universe

Peter Higgs is used to delays. The Nobel Prize-winning physicist waited for sight of the eponymous “Higgs boson”—the “God particle” of media headlines—for 48 years. Then, on 4th July last year, scientists at the Large Hadron Collider in Cern, Geneva, announced the proof of this fundamental entity, but for which our material universe could not exist. But, the waiting was far from over for Higgs who had to endure another year of speculation of a different sort, before his achievement was finally capped on 8th October this year by the joint award of the Nobel Prize to himself and François Englert of the Université Libre de Bruxelles. In a final nail-biting twist, the announcement of his long-awaited victory was delayed by an hour as the committee struggled to reach the famously reclusive scientist. Unlike Samuel Becket’s Vladimir and Estragon, who waited for Godot in vain, Higgs has been successful.

I was watching on the Internet as the Nobel Committee explained that it had given the prize for the: “theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles…”. As tweets flooded my inbox it seemed that the whole of the physics world was watching too. All, but one it seems. Peter Higgs had gone on holiday to avoid the media storm. Without a phone. In a prepared statement released by the University of Edinburgh, Higgs expressed his humble thanks and said: “I hope this recognition of fundamental science will help raise awareness of the value of blue-sky research."

Everyone has heard of his boson, even if they don’t know what it is or why physicists give it such huge importance. For most of the last half century, Higgs has had a quiet life, away from the spotlight. Now, in the space of a few years, he has become a celebrity and public property.

How does he feel to have seen his theory proved correct after waiting so long? Did he ever doubt his theory, or worry that he was wrong as thousands of scientists and engineers devoted their professional careers to pursuit of the boson? Now that the eponymous particle is found, how does he react: with relief, or trepidation that his life will be irrevocably changed? What does he foresee as the future of physics? These are the questions that I have been discussing with him during the last four years, as he lived through the dramatic days that have moved a theory from speculation to lore, establishing for all time some of the most profound implications about the nature of the universe.

In 1964 Higgs, and five others independent of him (François Englert and Robert Brout in Belgium; Tom Kibble, Gerald Guralnik and Carl Hagen at Imperial College), produced a theory about the nature of matter and the fundamental forces of nature, with remarkable consequences. The theory assumes that the universe is filled with some weird stuff, which has become known as the Higgs field. We have been immersed in this essence forever, and been unaware of it. The idea that there is a ghostly presence everywhere, seemingly invisible, but which can be made manifest only when some clever people smash pieces of atoms into one another at almost the speed of light, sounds dangerously like the tale of a gullible public being told that their king, who was in reality naked, was clothed in wonderful raiment visible only to the highly intelligent. Even some renowned physicists had their doubts.

Nonetheless, the theory had some remarkable successes. It explains why the sun barely stays alight, the force converting its hydrogen fuel into helium and liberating energy being so feeble that the sun, instead of expiring almost immediately, has survived billions of years—long enough for evolution to have worked its magic, producing sentient humans, collections of atoms capable of knowing the universe. These ideas also explain how the basic particles of matter, such as electrons and quarks, can form molecules and atoms rather than flying around at the speed of light in some form of cosmic goo. In summary: they explained how the universe that erupted in a Big Bang some 13.8bn years ago is today full of shapes and forms, rather than being a bland morass.

“It is easier to be Shakespeare or Beethoven than a theoretical physicist,” is how I introduced Higgs to the audience at the Borders Book Festival in Melrose during June 2012. Being in Scotland, I suggested that changing a few words in Macbeth, or a few notes in Mendelssohn’s Hebrides Overture, would still leave wonderful works of art; change a mere handful of symbols in Peter Higgs’ equations, however, and they would not work.

The theory is exciting conceptually, constructed from beautiful mathematical structures. Had this been a symphony or a work of literature, its value would have been recognised several decades ago. However, the ultimate value of a physical theory should not be decided by public opinion, but by experimental testing.

Among the sextet of theorists—known by colleagues as the “Gang of Six”—Higgs alone identified a means of testing the theory by a direct experiment. He drew attention to an ephemeral particle, known as the Higgs boson, which the theory implies must exist.  Find it, and confirm that it behaves as the theory predicts, and you have made a major breakthrough in understanding.

No such entity was known in 1964. No one, least of all Higgs, anticipated that nearly half a century would pass before the issue would be settled.

The idea leading to the Higgs boson is similar to something quite familiar: the nature of light as an electromagnetic wave. A compass needle will point towards the north magnetic pole as it senses the presence of the Earth’s magnetic field. Add energy to a magnetic or electric field, in the form of heat say, and it will stimulate an electromagnetic wave—such as a radio wave, or a sunbeam. In quantum mechanics, such waves consist of staccato bundles of “photons”: massless particles of light. A similar idea applies to the Higgs field. Add energy, and Higgs bosons—the analogues of the photons—will emerge.

The Higgs field is ubiquitous. Unlike a light, you cannot switch it off. This is because the vacuum of space is never empty but, according to quantum theory, is filled with ephemeral particles of matter and antimatter flitting in and out of existence, including the Higgs field. As an analogy, imagine space as an infinitely deep placid lake, whose surface is so smooth that we are unaware of it in everyday affairs. Supply energy, however, and waves form. In the real universe, these ripples, which herald the Higgs boson, are the telltale signs of that profound all-pervading stuff: the Higgs field

A big difference between a photon and the Higgs boson is that it is easy to create a particle of light as it has no mass—a torch battery is sufficient. The Higgs boson, however, is  massive—weighing in at more than an atom of iron. To produce this beast out of the vacuum requires a huge concentration of energy, greater than has existed since the first moments of the Big Bang. This technological challenge was beyond reach for at least 20 years after the theory was formulated, but the ideas underlying the Higgs boson increasingly interested the physics community.

As the Gang of Six laid claims to the original insights, I asked Higgs how his name had come to such prominence. In his opinion, it was partly due to an accident. Three years after the appearance of the Gang of Six’s original papers, Higgs met the leading American theorist, Ben Lee, at a physics conference, in Rochester New York. Up to that time, their ideas had been largely ignored, but Lee had realised the significance. At the end of that conference, Lee met Higgs at a party, and their conversation had a far greater impact than either anticipated.

“I was standing with a plate in one hand and a glass of wine in the other, being interrogated by Ben about my papers. I didn’t realise that five years later Ben Lee would be the [keynote speaker] at the High Energy Physics conference in Chicago,” Higgs told me, with a gentle laugh. In 1972, Lee must have recalled that conversation and forgotten the wider provenance of some of the ideas as in his talk he referred prominently to the massive “Higgs” boson (which is justified as only Higgs drew attention to this special aspect of the theory) and also the Higgs field (which has a wider provenance, Tom Kibble in particular having made unique contributions). In modern vernacular one would say that at that moment “#Higgs” began to trend.

Peter Higgs had not been in Chicago. The first that he knew of this was when he met a colleague, Ken Peach, in the Edinburgh University staff club. Peach, just returned from the conference, announced: “Peter! You’re famous!”

Lee had made Higgs famous, but finding the boson was out of reach at that time. What was Higgs’ reaction back then? “At that time it looked as if the question would not be answered in my lifetime. In the 1980s, I began to realise that finding the boson might be possible, but the timescales were completely unclear.”

In 1983, the Americans started designing a machine known as the Superconducting Super Collider, or SSC, capable of finding the Higgs boson. The SSC was a pragmatic but ambitious approach, which involved building a gargantuan ring of magnets underground in a tunnel, 87 kilometres in length. Their strategy was to produce the boson by means of conventional technology and brute force. Higgs says that “for the first time it began to look as if I might see the answer after all.” But this burst of optimism was quickly dashed as in 1993 the Americans quit. The future of particle physics, including the quest for the Higgs boson, was now in jeopardy.

“The cancellation of the SSC was a disappointment because they should have been able to find [the boson] with their technology. Then the LHC [Large Hadron Collider] plans came through. Given some years of technological development, I began to hope again it might happen after all while I was around to see it.” This emotional rollercoaster continued, Higgs recalling: “Perhaps I was  more optimistic [than I should have been] as I was ignorant of some of the technological challenges facing the LHC.” Compared to the SSC, the LHC is relatively compact—a ring the size of the Circle Line on the London Underground. To produce the necessary conditions in this device would require novel techniques, however. There were any number of possible showstoppers: technological barriers that could ruin the project. It took 20 years to design, and build the LHC. In addition, scientists and engineers from around the world had to construct detectors the size of battleships, to record the results and tease out the Higgs boson, which would live for less than a billionth of a billionth of a second.

Peter Higgs, luckily, had not worried about this. Eventually, in 2008, the LHC was complete; beams of protons circulated, collided and experiments were eagerly anticipated. Then there was a component failure, so serious that the repairs took over a year to complete. “By then I was getting frustrated,” Higgs reflected, as he reviewed the tale of two steps forward and one step back. Finally all was well, and in 2010 the data began to pour in.

Looking for the Higgs boson is analogous to rolling a pair of dice inside a closed box. If sixes happen every time, you can be certain that the dice are special—the boson exists. However if sixes happen once every 36 throws, the results are no more than random chance and there is no Higgs boson. Opening the box is the analogue of smashing two protons head on at the LHC and detecting the debris. Recording the characteristics of the by-products—their varieties, energies and flight paths of the constituent particles—is analogous to determining the numbers on our metaphorical dice. Correlations among the particles may show them to be the debris from the decay of an ephemeral boson—the dice each being a six.

If only it were that simple. In practice what happens is that the sixes turn up slightly more often than mere chance and you have to decide whether this is significant—evidence for the boson—or mere vagaries of luck, in which case there is no boson. Perform a few throws and it is not possible to tell the answer; after millions of throws, clear excess will become more certain.

By the end of 2011 there was a hint the dice were coming up six more often than mere chance, but many more throws would be needed to establish this with confidence. If there were no breakdowns and the LHC continued to work well, then the autumn of 2012 seemed to be the earliest that a clear answer would emerge. Thus it was that I found myself in Melrose in June 2012, talking to Higgs during the interregnum, before an answer was known.

The total cost of the enterprise has been estimated in the order of €10bn. In the public’s perception this has all been done with the purpose of finding Higgs’ boson. So my first question at Melrose was this: “Peter, if tomorrow you found a mistake in your arithmetic, would you tell anybody?” It was a rhetorical question as there are no mistakes. The basic ideas of the theory have been used like pieces of Lego, building other theories, which have been tested experimentally. As the 21st century began, awareness that the boson could be found began to take hold. “Higgs boson” became a brand, the answer to cryptic crosswords, as an anagram within the clue: “Gosh! Big’s no way to describe it though it’s important in theory.” One reason why the public has been so enamoured could be the solid ordinariness of the name, one syllable long. Had it been Kibble or Englert for example, less attention might have ensued.

Two weeks after our event in Melrose, I met Higgs again, in the hilltop Sicilian town of Erice. We were at a summer school giving lectures to the new generation of young particle physicists. All of them knew of Peter Higgs; most had never met him or knew what he looked like. Unlike some, who hog the limelight and are highly visible at conferences, Higgs has for most of the last half century been primarily a name, the man himself having managed to maintain a life of “peace and quiet” and devoting much time to activism on behalf of the Campaign for Nuclear Disarmament (he stopped when they extended their campaign to opposing nuclear power). That was rapidly changing, and events were about to overtake him much earlier than he had expected.

Cern had planned some months before to make a progress report on 4th July. As the date approached, it was like being at the eye of a hurricane. As rumours as to the likely birth announcement of the Higgs boson raged all around the globe, the man himself was in a haven of peace in Erice.

A Dutch film crew, who were making a documentary about Higgs and the boson, had come to Erice for three days. On 30th June they were with Higgs, in the Restaurant Venus, for lunch. Higgs’s colleague and aide, Alan Walker, had been trying to find out how significant the 4th July event might be, as Peter was due to return to Scotland, with no plans to go to Cern. He had contacted the Cern press office in the morning to ask: “What should we do?” Suddenly the lunch was interrupted when his phone rang. He recalled: “I saw the code +41, which is Switzerland, so I thought it was the Cern press office calling me back, but it was John Ellis [a senior theorist at Cern].” So as not to disrupt the lunch, Alan left the table and went over to the window to take the call. He turned round to see the film crew had set up their equipment and were filming “the moment.” The crew motioned to him “to continue acting naturally” so Alan “started a conversation with Peter saying—”Pssst, it’s John Ellis saying we should go to Cern.” Higgs replied: “If John Ellis says that, then we should go.”

If there was a moment when Higgs knew that, at last, theory was about to become lore, that was it. After 48 years of waiting, instead of a feeling of triumph, his immediate reaction was of panic. His life had become increasingly taken over in the previous couple of years with the media attention given to a “personality.” The discovery of the Higgs boson would have unexpected consequences. “I had in a way been dreading the occasion, and been preparing for how to cope with it, and suddenly realised that I was going to have to face up to this event in my life some months earlier than I had expected.”

Two experiments at Cern were chasing the Higgs boson, and both announced their results to a packed auditorium, and to several millions watching thanks to the world wide web—itself one of the unexpected creations that had arisen out of the international quest for knowledge at Cern. When the first experiment announced that they had strong evidence for the boson, the audience burst into prolonged applause. When the second speaker announced that they too had found the same phenomena, independently, and with the same conclusions, there was cheering. Former directors-general who had gathered for the occasion, including staid octogenarians, were slapping one another on the back, like excited children. We were witnessing a seminal moment in human culture. What had been conjecture for so long was now on the tablets for all time.

Peter recalled that, before the announcement, he was reasonably sure that his ideas were correct and that the boson was there to be found, but was not prepared for the overwhelming emotions that erupted. “It was very moving. I burst into tears. It was partly the result of the audience reaction, their euphoria. There was a huge buzz.”

I was in England, watching online then as well, with a crowd of physicists at the Rutherford Appleton Laboratory in Oxfordshire. Even as kibitzers, we felt the sense of living through a historic moment. Only three weeks had elapsed since I had talked with him in Melrose, but it seemed a lifetime. The questions from the audience on that occasion had included: Is this a seminal moment in culture or is it a media creation? If it is real, what do we know now that we didn’t before, and what happens next?

The answer to the first question was already obvious. Many of the scientists had devoted 20 years to the endeavour. Higgs had waited for more than half a lifetime. What had been conjecture was now confirmed as reality, knowledge about the fundamental nature of the universe that would be there for as long as humanity itself, passed down the generations, as we ourselves have been taught about the insights of Isaac Newton, Archimedes, Pythagaros. The mysterious power of mathematics had been confirmed once more; the ability of equations written on pieces of paper to know nature. If a thunderbolt had come through the roof of the auditorium at that moment, with the voice of Charlton Heston berating impertinent humans for entering where we had no right, I could hardly have been more overwhelmed than in those moments when I felt contact with the infinite.

With the eponymous boson confirmed, speculation grew about the destination of the 2012 Nobel Prize. During the early autumn each year, as the second week of October approaches, a highly selective epidemic breaks out: Nobelitis, a psychological condition that takes over the minds of scientists who see the finishing line of the Nobel race coming into their view. Some will have been cured forever, perhaps to come down with another fear: do I deserve to be counted as one with Einstein? Others will have a temporary remission, before suffering a renewed outbreak next year.

Cautious, or wise, counsel said that the discovery of the boson was probably too late for it to affect the destination of any award that same year, but this did not prevent a media circus generating controversy by making speculations on how to select at most three out of a cast of worthy characters. The debate continued to rage all the way up until this year’s announcement. The question became not so much “will Peter Higgs win it” as “who will share it with him?” Three at most can share a Nobel, and as we have seen, at least six had ideas similar to Higgs in the halcyon days of 1964 when this story began. So, there was a degree of surprise when only two names were announced on 8^th October 2013. Both Englert and Higgs were much-predicted recipients, but for a deserving third place: Tom Kibble, Jeffrey Goldstone or even the CERN laboratory itself were among the numerous suggestions. However, I think that the Nobel committee has made a profound decision. Englert produced his prize-winning work with the US/Belgian theoretical physicist Robert Brout. Brout sadly passed away last year. Had he been alive, he would have completed the trio.

A year after our memorable first visit, on 30th June 2013, Higgs and I were once again in Erice, in the same restaurant where he had received the call to Cern. I asked him how the reality had compared with the anticipation. Although he had been thrust into the spotlight for some time before the announcement, he realised that “the experimental confirmation would make an order of magnitude difference.” And had it? “Yup... A few orders of magnitude judging by the numbers of incoming emails.”

Although his face is not recognised like that of a TV personality, in his home city of Edinburgh he is increasingly stopped on the street. I had noticed the change myself, between our performance at Melrose in June 2012, and when I interviewed him at the Edinburgh Festival in August that year, just four weeks after the confirmation. In Melrose everyone was thrilled that Higgs was there on stage; the applause was loud but standard length. In Edinburgh it was quite singular. When an audience applauds before an event, it’s as if there is a metronome in your head, which tells you when you expect the clapping to die down. But it didn’t. It went on. And on. I realised: “This is their boy.” I thought: “We don’t need to say anything. We can stand here for an hour, let them applaud and they will be happy.”

How does the discovery affect our view of the universe and the future of physics? In the public’s mind, the Large Hadron Collider was made in order to find the Higgs boson. Is this a great success for physics? Higgs was cautious: “The LHC was built to explore many things, not just the boson. There could be a reaction like ‘OK, you can close the machine down now. It’s expensive and it has done its job.’ That particular aspect [the boson] was possibly too successful at the expense of the other things.”

The LHC is currently being refurbished and will start up again in a little over a year from now with more power. Higgs is hoping that “when the LHC restarts it will find evidence for supersymmetry, and dark matter particles.” Therein is the sober message of what we know and, more relevant perhaps, what we do not yet know. The stuff that we are made of, and whose existence is now beginning to be understood thanks to the discovery of the boson, constitutes only about 5 per cent of the total. Most of the universe is made of “dark” matter, which tugs the galaxies by gravity, but which does not shine. The particles that make this, the dominant stuff, remain to be discovered.

After the ancient Greeks started musing about the nature of matter, at last, following the discovery of the Higgs boson, we are at the end of the beginning, not the beginning of the end. We are made of mere flotsam on a sea of dark matter. What this is made of, and whether there are further “dark Higgs bosons” to be found, is for the future. Theorists suspect that dark matter may consist of “supersymmetric” particles, whose existence will be within reach of the LHC in the next round of experiments. Whether the existence of supersymmetry will be revealed within a few years, or whether we are at the start of another long wait, comparable to that which Higgs endured, we cannot know.

Frank Close is a particle physicist and Professor of Physics at the University of Oxford. His latest book, The Infinity Puzzle, tells the full story of the search for the Higgs Boson