It is the most ambitious and expensive civilian science experiment in history,
based on the biggest machine that humanity has yet built. It has sparked
alarmist fears that it might create a black hole that will tear the Earth
apart, and it has triggered two last-minute legal attempts to stop it. And
next Wednesday, after almost two decades of planning and construction, the
project in question will finally get under way.
Beneath the foothills of the Jura mountains, in a network of tunnels that
bring to mind the lair of a crazed Bond villain, scientists will fire a
first beam of particles around a ring as long as the Circle Line on the
London Underground. This colossal circuit, 17 miles (27km) in circumference,
is the world’s most powerful atom-smasher, the £3.5 billion Large Hadron
Collider (LHC), created at CERN, the European particle physics laboratory
near Geneva. Some 10,000 scientists and engineers from 85 countries have
been involved. In the years ahead it will recreate the high-energy
conditions that existed one trillionth of a second after the big bang. In
doing so, it should solve many of the most enduring mysteries of the
Universe.
This extraordinary feat of engineering will accelerate two streams of protons
to within 99.9999991 per cent of the speed of light, so that they complete
11,245 17-mile laps in a single second. The two streams will collide, at
four points, with the energy of two aircraft carriers sailing into each
other at 11 knots, inside detectors so vast that one is housed in a cavern
that could enclose the nave of Westminster Abbey. The detectors will trace
the sub-atomic debris that is thrown off by the collisions, to reveal new
particles and effects that may never have existed on Earth before.
The mountains of data produced will shed light on some of the toughest
questions in physics. The origin of mass, the workings of gravity, the
existence of extra dimensions and the nature of the 95 per cent of the
Universe that cannot be seen will all be examined. Perhaps the biggest prize
of all is the “God particle” – the Higgs boson. This was first proposed in
1964 by Peter Higgs, of Edinburgh University, as an explanation for why
matter has mass, and can thus coalesce to form stars, planets and people.
Previous atom-smashers, however, have failed to find it, but because the LHC
is so much more powerful, scientists are confident that it will succeed.
Even a failure, however, would be exciting, because that would pose new
questions about the laws of nature.
“What we find honestly depends on what’s there,” said Brian Cox, of the
University of Manchester, an investigator on one of the four detectors,
named Atlas. “I don’t believe there’s ever been a machine like this, that’s
guaranteed to deliver. We know it will discover exciting things. We just
don’t know what they are yet.” The guarantee applies, however, only if the
hardware works as it should, and the LHC’s first big test comes on
Wednesday, when the first beam of particles is injected into the
accelerator. That is a huge technical challenge. “The beam is 2mm in
diameter and has to be threaded into a vacuum pipe the size of a 50p piece
around a 27km loop,” said Lyn Evans, the LHC’s project manager, who will
oversee the insertion. “It is not going to be trivial.”
Engineers will use magnets to bend the beam around the LHC’s eight sectors,
until it finally begins to circulate. “That’ll be the first sight of relief,
that there are no obstacles in the vacuum chamber,” Dr Evans said. “There
could be a Kleenex in the chamber – we’ve had that before. Only when we get
the beam around will we be able to tell it’s clear.”
Once the first beam is in – probably the one running clockwise, though that
has yet to be decided – the team will insert the second, anticlockwise
stream of particles. The first collisions, to test the detectors, should
follow by the end of next week.
The next step will be to “capture” the beams so they fire in short pulses,
2,800 times a second. These will then be accelerated to an energy of 5
tera-electronvolts (TeV), generating collisions of 10TeV.The detectors
should be calibrated by the end of the year and the collisions will then be
ramped up to their maximum energy of 14TeV, generating the conditions that
prevailed fractions of a second after the Big Bang.
One of the first scientific discoveries is likely to concern a theory called
supersymmetry. Tejinder Virdee, of Imperial College, London, who leads the
Compact Muon Solenoid (CMS) detector team, said: “What supersymmetry
predicts is that, for every particle you have a partner, so it doubles up
the spectrum. You have a whole new zoology of particles, if you like.”
Theory suggests that if supersymmetry is real, evidence to confirm it should
emerge quickly from the LHC, possibly as soon as next year. “If it pops up
it’ll be quite easy to see,” Professor Cox said.
Such a discovery might also help to explain dark matter, which is thought to
account for much of the missing mass of the Universe. Only about 4 per cent
of matter – galaxies and the like – is visible to our telescopes. “In this
new zoology, the lightest super-symmetric particle is a prime candidate for
explaining dark matter,” Professor Virdee said.
The search for the Higgs could take longer, though it depends on the
particle’s mass and thus the energy of the collisions in which it might be
found. If it is at the heavier end of the possible range, the discovery
could take as little as 12 months. A lighter Higgs would take longer to
find, as the particles into which it would decay would also be lighter and
harder to track.
Other potential discoveries include evidence for the existence of extra
dimensions beyond the familiar three of space and one of time, and the
creation of miniature (and harmless) black holes, though these are less
probable. “Most of us think we’d be very lucky to find these things,”
Professor Cox said.
There are two more detectors. The LHCb will investigate why there is any
matter in the Universe at all, while Alice aims to study a mixture known as
quark-gluon plasma, which last existed in the first millionth of a second
after the big bang.
From gluons to sparticles
Particle
In physics, this term refers to sub-atomic particles – entities that are
smaller than atoms. Some, such as protons and electrons, are the
constituents of atoms. Others, such as quarks, are the constituents of other
particles. Still others, such as photons and neutrinos, are generated by the
Sun. And yet more, such as the Higgs boson, are theoretical: predicted but
still undiscovered
Hadron
This is more than an excuse for a geeky physics joke – “Is that your hadron,
or are you just pleased to see me?” Hadrons are particles with mass, made up
of quarks that have been bound together
Protons, neutrons, quarks and gluons
Protons and neutrons are the best-known types of hadron. Each is composed of
three smaller units, called quarks, and gluons that stick the quarks
together. Protons have a positive charge, while neutrons have a neutral
charge
Higgs boson
A theoretical particle, which is thought to give matter its mass. First
proposed by Peter Higgs, of the University of Edinburgh, in 1964, it is
sometimes nicknamed the “God particle”. The Large Hadron Collider (LHC)
should confirm whether it exists. The theory suggests that other particles
travel through and interact with a field of Higgs bosons, which slows the
particles down and gives rise to their mass. The process is often likened to
moving through treacle. In the early 1990s Lord Waldegrave of North Hill,
then the Science Minister, staged a competition for the best explanation.
The winning analogy was of Margaret Thatcher – a massive particle –
wandering through a Tory cocktail party and gathering hangers-on as she went
Standard model
The orthodox theory of modern physics. It is based on two other theories –
general relativity and quantum mechanics – and its main weakness is that it
cannot yet fully describe gravity or mass
Quantum mechanics
The main principle of the standard model, which describes how particles and
forces behave at atomic and sub-atomic scales
General relativity
Einstein’s theory describing gravity. It is exceptionally well attested, but
not fully compatible with quantum mechanics
Supersymmetry
The hypothesis that all particles have an accompanying partner known as a
“superparticle” or “sparticle”. There is good theoretical evidence for it,
but it has not yet been confirmed by experiment
Dark matter
Only about 4 per cent of the Universe is made up of visible matter. Another
25 per cent is “dark matter” – which can be inferred from its gravity, but
cannot be seen. The remaining 71 per cent is still more mysterious “dark
energy”. The LHC could shed light on what dark matter is, possibly through
discoveries about supersymmetry
Extra dimensions
We are all familiar with four dimensions – three of space and one of time.
But some theoretical physicists suggest that there could be as many as 26.
Most physicists find these every bit as hard to visualise as normal people,
but they make mathematical sense
