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Friday, September 5, 2008

From gluons to sparticles :large hadron collider

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
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 bosonA 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 modelThe 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 mechanicsThe 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
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

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