It has been hailed as a triumph for international science, the coalescing of four decades of intellectual and engineering effort to create a new understanding of the universe's structure. And certainly the discovery of the Higgs boson represents a significant milestone in the history of particle physics.
Consider the logistics. At Cern, in Geneva, around 10,000 scientists have collaborated for several years at the £5bn Large Hadron Collider (LHC) – an underground circular device built on the scale of London's Circle line but constructed to a billionth of a metre accuracy – to uncover a sub-atomic entity that gives stars, planets and living creatures their mass. By battering streams of protons together at colossal energies round this tunnel, they have transformed our understanding of the cosmos. We now know that an invisible energy field, the Higgs field, stretches across the universe, one that clings to fundamental particles like the proton to give them mass. The Higgs boson is the signature particle of that field.
And it is particularly sweet success for the UK. Not only was the boson's existence predicted by a Brit, Edinburgh University's Peter Higgs, but the machine that detected it, the LHC, was designed by Lyn Evans, another UK scientist. At the same time, one of our most distinguished physicists, Sir Christopher Llewellyn Smith, was Cern's director general in the 1990s and was responsible for negotiating the collider's construction. "It has performed far better than I envisaged," he says of the device he nurtured. "It is a wonderful machine."
But at the time of its proposal 30 years ago, the idea of the LHC certainly did not overwhelm scientists or politicians. And thereby hangs a tale.
The collider, today hailed as a triumph of science and engineering, was almost cancelled on several occasions, a point that should be noted by those physicists who are now dreaming of a successor. Indeed, there are many other scientists who now believe the LHC could be the last major particle accelerator ever built.
"People today think the LHC's construction was inevitable once we came up with the proposal but it didn't seem that way at the time," says Llewellyn Smith. In fact, the project was assailed with criticisms. The US was then planning the Superconducting Super Collider (SSC), an underground tunnel – 54 miles in circumference – round which protons would be hurled at energies three times those generated by those in the LHC. Why construct an inferior device, critics asked?
But the SSC proved to be a debacle. Individual congressmen initially backed it because they hoped it would be built in their state. But after Texas was selected, those outside the state lost interest. Costs soared and the SSC, now friendless, was cancelled. So the US put its money into the international space station, a project of no scientific value but which upset no vested interests.
After its rival disappeared, the case for the LHC looked stronger. Yet it still took a decade of negotiations to get Cern's member nations to agree to build it. Eventually a deal was signed – only for Britain, following its 1993 economic crisis, and Germany, reeling under the cost of reunification, to renege. In both cases, last-minute deals saved the project, although Llewellyn Smith says it had balanced, several times, on the edge of extinction. "It was touch and go on a number of occasions. It could so easily not have happened."
And that point has clear implications for the LHC. If its giant detectors produce evidence of Higgs bosons and little else in its lifetime, particle physicists will struggle to persuade the world they need a bigger machine to probe even further into the structure of matter, a point stressed by the Nobel prize-winning physicist Steven Weinberg.
"My nightmare is that the LHC's only important discovery will be the Higgs," says Weinberg. "Its discovery was important. It confirms existing theory but it does not give us any new ideas. We need to find new things that cry out for further investigation if we are to get money for a next generation collider."
Candidate discoveries would include particles that could explain the presence of dark matter in the universe. Astronomers know that the quarks, electrons and other forms of normal matter found on Earth can only explain about a sixth of the mass of the universe. There is something else out there. Scientists call it dark matter but cannot agree about its nature. A particle, as yet undetected, that permeates the cosmos, might be responsible.
As Weinberg says: "What could be more exciting than finding a particle that makes up most of the universe's mass?" Certainly, finding hints of dark matter would help scientists get the billions they will need for a next generation collider. But if they find no exotic fare like this, they will flounder.
This point is backed by Llewellyn Smith. "The only real case for a next generation device would be the discovery of a phenomenon that the LHC could only just detect but could not study properly. We will have to wait and see if something like that happens. Certainly, it will give scientists plenty to do at the LHC for the next few years."
As to the nature of that next generation device, by far the most likely candidate would be a linear – as opposed to a circular – accelerator which would fire electrons in straight lines for miles before smashing them together. A world consortium of experts, including Lyn Evans, has already been set up to create plans. But until the LHC produces results, its design will remain uncertain. "It is quite conceivable that we have reached the end of the line," adds Llewellyn Smith. "Certainly, unless someone comes up with an unexpected breakthrough, it is hard not to conclude we have come about as far as we can with accelerator technology." After 50 years of whizzing sub-atomic particles along tunnels before battering them together, we appear to be approaching the limits of this technology.
And even if the technical hurdles can be overcome, the political issues may be insurmountable. Battles over local interests will inevitably strike again. Scientists will then have to use other methods to study the fabric of the cosmos: powerful, space-based telescopes that could peer back into the early universe. On their own, these are unlikely to produce major breakthroughs. As a result, when LHC has completed its work next decade, we may face a long pause in our progress in unravelling the universe's structure.
"We had to wait more than 2,000 years to prove Democritus was right when he said matter was made of atoms," says Weinberg. "Then, in the 20th century, there were further pauses as we waited for the technical breakthroughs needed to probe the sub-atomic world at deeper and deeper levels.
"We have been here before. But unless the LHC comes up with something really striking, it is possible that the search to uncover the laws of nature will come to a halt and not be resumed in our lifetimes." In short, we should make the most of the glory of the Higgs boson's discovery, and the magnificent machine that found it – while we can.
