Yesterday was a great day for physics as the most powerful particle accelerator ever, the Large Hadron Collider (LHC) at CERN, (European Organization for Nuclear Research), was switched on for the first time, with the initial beams of protons making their way around the great circular tunnel lying under the French-Swiss border. This huge physics experiment, now charmingly named by the media “the Big Bang experiment”, has been some fifteen years in the making, and has involved more than 8,000 scientists from around 85 countries, at a cost of around $10 billion.
The LHC has been constructed in the existing 27 km ring-shaped Large Electron-Positron collider tunnel, has 8,000 superconducting magnets, and will achieve proton beam energies of 7 TeV (teraelectronvolts). In terms of particle physics, this is the highest energy ever achieved by a machine, and will recreate the conditions a few moments after the Big Bang, producing the smallest particles humans have ever come across.
Energy is really what it’s all about - physicists believe that significant new discoveries are to be made in the region of around 1 TeV, known as the terascale. The protons will be collided head-on at a rate of 30-million collisions per second, each of which will generate thousands of particles travelling at close to the speed of light. These experiments may well help to solve some of the major puzzles about the composition of matter and energy in the universe, by allowing physicists to probe the shortest distances and the highest energies ever looked at.
How does the LHC work?
The 8,000 magnets are chilled by liquid helium to less than two kelvin, which makes them superconducting, and these steer and focus the beams of protons, that will differ in speed from light speed by only a breathtaking millionth of a percent. At impressive speeds such as this, each proton will have 7 TeV of energy, which, bearing in mind E = mc2, is 7,000 times more energy than a proton would have at rest.
The protons will travel in bunches, each bunch the size of a needle and composed of some 100 billion protons. At four locations around the 27km ring, these bunches will pass through one another, producing collisions. These collisions, or “events”, will actually occur between the particles that make up the protons, known as quarks and gluons, and will release at most about a seventh of the energy available in the parent protons, or about 2 TeV.
Desperately seeking the Higgs boson
So what will the study of these collisions tell us? Well, one of the first things that physicists will be seeking will be confirmation of the currently accepted theory of particle physics, known as the Standard Model. But there is one missing piece of this jigsaw puzzle, and that is a particle known as the Higgs boson, which gives particles the property of mass. Being the last remaining undiscovered piece of the current theory of matter, the Higgs boson, also dubbed “the God particle”, has become the most highly sought after item of particle physics. Actually finding the Higgs boson would be a tremendous step forward in the search for the Grand Unified Theory, which would be a unification of three of the fundamental forces of nature: electromagnetism, the strong nuclear force and the weak nuclear force. Finding the Higgs boson and learning something about its properties could also explain why gravitation is so mysteriously weak compared to the other three forces.
Going beyond the Standard Model
The current Standard Model of particle physics does begin to fall apart when things are probed much beyond the range of the current particle accelerators, suggesting that we need a more sophisticated theory to take its place. So the high levels of energy achieved by the LHC will hopefully lead the way to a theory beyond the Standard Model.
New forces and symmetries
The LHC may actually help us to find new forces of nature which could also reveal new symmetries within nature. For example, the idea of supersymmetry is a symmetry that suggests that elementary particles have superpartners that differ by half a unit of spin, meaning that for every type of boson there is a corresponding type of fermion, and vice versa. If supersymmetry were found to exist close to the terascale, it would provide answers to a number of questions relating to Grand Unified Theory, supersymmetric quantum field theory, and string theory.
Unlocking the secrests of dark matter
Yet another exciting possibility is that work with the new LHC could lead to the discovery of the particle or particles that make up that mysterious stuff known as dark matter, that amazingly actually seems to make up most of the material in the universe, if its apparent gravitational effects on visible matter are anything to go by. It has been suggested that this dark matter could be made up of hypothetical things called strangelets which would be a bound state of equal numbers of up, down and strange quarks.
Another novelty that will be researched with the collider is the idea of a magnetic monopole, a magnet with only one pole, which, as yet, has never been found. Back in 1931 Paul Dirac got people thinking about magnetic monopoles by mentioning them in relation to the quantization of electric charge. Current ideas suggest that while they could exist, they would have to be so massive that they might never be observed in practice.
The creation of black holes?
The remote possibility that the LHC might create a minuscule black hole has even caused some to take out a lawsuit against CERN, and caused people to panic about yesterday being the end of the world. Thankfully not.
A micro black hole is a tiny black hole, and Stephen Hawking has theorised that these micro black holes, due to quantum effects, evaporate by the emission of particles, with smaller black holes evaporating faster, and finally exploding in a burst of particles. Some say that the Large Hadron Collider might produce one of these micro black holes, but it is thought that this is really unlikely because the LHC, despite its impressive size, is not actually big enough to do this. To create a micro black hole with currently-available materials would require a circular accelerator roughly one thousand light years in diameter.
There are other possibilities besides these, including the exciting possibility that the collider might reveal hidden spacetime dimensions.
The LHC will be shut down over the winter for further fine tuning, and serious new physics will most likely not emerge until 2009. Whatever happens the LHC is bound to turn up something new, so physicists can look forward to some really exciting advances next year.