Off into the wild, blue yonder

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Sep 11th 2008 | GENEVA
From The Economist print edition

The world’s biggest particle accelerator starts up, more or less
AFP
THE Large Hadron Collider (LHC) is a machine which will measure events that happen within a millionth of a billionth of a billionth of a second. What no one seems to be able to measure, though, even to an accuracy of several weeks, is when it really opens for business. Is it the moment when the first protons are injected into its 27km ring? When they first travel all the way around? When they are first made to collide with each other, thus generating the exciting new subatomic particles that are the whole point of the exercise? Or is it the moment at which those collisions become stable enough for real scientific data to be collected?

Well, popular opinion—or, rather, a tacit agreement between the authorities at CERN, the European particle-physics laboratory whose baby the LHC is, and the journalists who report on these matters—decided on the second. Though individual bits of the machine have been under test for several weeks, a complete circuit gives everyone the excuse to declare victory and splash the LHC as the “machine that will unlock the mysteries of the Big Bang”, in the hope that politicians and the public will take notice.

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The protons were duly unleashed at 9.30am local time on September 10th as the world’s press assembled at CERN’s headquarters in Geneva to witness the event. Someone at the BBC suggested that a Big Red Button should be used to speed the protons on their way, but that was deemed too flashy. Instead Lyn Evans, the physicist in charge of the collider, cautiously nursed the first proton beam around the circuit an eighth of the way at a time. Then, to prove the point, he sent one in the opposite direction.

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Like a circle in a spiral
Razzmatazz aside, the LHC is an awesome machine. When it is working at full throttle, the protons going around the LHC will travel very close to the speed of light. That speed, beyond which it is impossible to accelerate, is 299,792km a second.

The power of accelerators has risen more than a thousandfold since the 1960s, and a hundred millionfold since the first cyclotron, a mere 30cm in circumference, was tested by Ernest Lawrence at the University of California, Berkeley in 1931. But the basic idea behind both that cyclotron and the LHC is the same. A combination of electricity and magnetism accelerates the protons and thus endows them with energy. Then they are brought to a sudden halt by a collision with something else, at which point the energy is converted into mass, creating new particles, according to Einstein’s well known equation, E=mc2. The main difference, apart from the scale of the machines, is that the cyclotron fired particles into a static target, whereas the LHC uses contra-rotating beams to achieve head-on collisions.

The real news, of course, will come when CERN actually finds something. But then, too, the question of “when” will be moot. Scientific discoveries are only occasionally eureka moments. More often, the data have to be collected, reviewed, analysed statistically, found wanting, collected again and analysed again. Eventually, if all has gone well, a clear result will emerge. It then has to be written up, reviewed by critical peers and, if it passes review, published in a scientific journal.

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That process is likely to be shorter for the LHC than it is for most scientific papers because the convention in physics is, increasingly, to do without peer review and post papers online, where all and sundry can tear them to shreds if they do not measure up. Moreover, promising but unconfirmed results are likely to leak—particularly if they concern the Higgs boson, the LHC’s famous first target. Scientists can be as garrulous in bars as politicians are.

The Higgs—which is required by theory to explain the existence of mass—has become such a cliché that it will be a relief when it does turn up and effort can be directed towards other things, such as probing the mysteries of gravity, doubling the number of known particles through a mechanism called supersymmetry and even generating minuscule black holes. Indeed, if the boson’s properties obey the strictures laid down for it by Peter Higgs and the other physicists who predicted it way back in the 1960s, the moment of discovery may turn out to be something of an anticlimax. Assuming that moment can be defined, of course.