When 30 years ago the Large Hadron Collider was first proposed, its construction was far from certain. Robin McKie writes: 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 [Sir Christopher] Llewellyn Smith [Cern’s director general in the 1990s]. “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.