Question: What is the large Hadron collider and what is its purpouse

Susan Cartwright answered on 15 Jun 2015:

The Large Hadron Collider is a particle accelerator which accelerates protons to within a very small fraction of the speed of light, and then collides them with another beam of protons coming in the opposite direction. The hope is that the collision will create, by way of E = mc^2, unstable particles that have not existed in nature since the first few moments after the Big Bang, and therefore help us to better understand the structure of matter. So far, the LHC has allowed us to discover the Higgs boson, which has been expected as part of the Standard Model for the last 40 years, but had not been seen until the LHC began operation. This discovery has not changed anything – since this was a particle whose existence had been predicted – but it has further enhanced our confidence in the Standard Model of particle physics, in which it was an essential ingredient. It’s a bit like the neutrino, which was only discovered 25 years after its existence was first suggested – although by 1955 everyone “knew” that the neutrino existed, because Fermi’s theory of the weak interaction, which WORKED, required the neutrino to exist, it was still a great relief when Reines and Cowan finally managed to demonstrate that neutrinos were real particles and not just something you had to put in to make the maths come out right.

We hope that the LHC will do more than discover the Higgs. The Standard Model is an incomplete theory – for a start, there is nothing in the Standard Model that can explain dark matter – and there are theoretical reasons to expect that this incompleteness will begin to make itself apparent at an energy of 1 TeV – that’s the energy equivalent of 1000 times the mass of the proton. The LHC was designed to probe this energy range, and in many theories attempting to extend the Standard Model we expect it to discover a whole zoo of new particles. It hasn’t, so far, but it has only just started operating at the energy it was designed for (up to now it’s only been working at just over half its design energy) so there is still a good chance that this might happen.