Cosmic timeline 05
The Large Hadron Collider (LHC) is the world’s largest and highest-energy particle accelerator, intended to collide opposing particle beams of either protons at an energy of 7 TeV per particle, or lead nuclei at an energy of 574 TeV per nucleus. It is expected that it will address the most fundamental questions of physics, hopefully allowing progress in understanding the deepest laws of nature. The LHC lies in a tunnel 27 kilometres (17 miles) in circumference, as much as 175 metres (570 ft) beneath the Franco-Swiss border near Geneva, Switzerland.
Physicists hope that the LHC will help answer the most fundamental questions in physics, questions concerning the basic laws governing the interactions and forces among the elementary objects, the deep structure of space and time, especially regarding the intersection of quantum mechanics and general relativity, where current theories and knowledge are unclear or break down altogether. These issues include:
Is the Higgs mechanism for generating elementary particle masses via electroweak symmetry breaking indeed realised in nature? It is anticipated that the collider will either demonstrate (or rule out) the existence of the elusive Higgs boson(s), completing (or refuting) the Standard Model.
Are there extra dimensions, as predicted by various models inspired by string theory, and can we detect them?
Are electromagnetism, the strong nuclear force and the weak nuclear force just different manifestations of a single unified force, as predicted by various Grand Unification Theories?
Why is gravity so many orders of magnitude weaker than the other three fundamental forces?
Why are there apparent violations of the symmetry between matter and antimatter?
What was the nature of the quark-gluon plasma in the early universe?
On 10 September 2008, the proton beams were successfully circulated in the main ring of the LHC for the first time. On 19 September 2008, the operations were halted due to a serious fault between two superconducting bending magnets. Repairing the resulting damage and installing additional safety features took over a year. On 20 November 2009 the proton beams were successfully circulated again, On 23 November 2009, the first proton–proton collisions were recorded, at the injection energy of 450 GeV per particle. On 18 December 2009 the LHC was shut down after its initial commissioning run, which achieved proton collision energies of 2.36 TeV, with multiple bunches of protons circulating for several hours and data from over one million proton-proton collisions. The LHC resumed operations in February 2010, but it will operate at only half power. In 2012 it will be shut down for the repairs necessary to bring it to its design energy, and then it will start up again in 2013.
A simulated event in the CMS detector, featuring the appearance of the Higgs boson.
The Higgs boson particle
The particle known as the Higgs boson is named after Peter Higgs of the University of Edinburgh, who predicted its existence in 1964. At the beginning of the Universe it was as if there was a sea full of Higgs boson particles causing the Universe to inflate. In the rapid cosmic expansion we call inflation, quantum fluctuations put the sea of Higgs particles in a state of constant flux.
Virtual Higgs particles were popping in and out of existence, but were created in pairs. These pairs would be made up of one particle and an anti-particle, which re-combine when it’s time for the pair to disappear. But what happened when the Universe grew by a factor of 10 to the power of 70, was that these pairs were dragged apart before they had time to re-combine. These quantum fluctuations formed the initial irregularities from which the galaxies grew.
The imprint of these fluctuations can still be detected today in the cosmic microwave background radiation that is a lasting electromagnetic echo left by the Big Bang.
Particle physicists, the scientists who observe and wonder at the sub-atomic scale of Universe, believe that everything in the Universe is given its mass by the action of a single type of subatomic particle that was created from the energy that drove the rapid expansion of the early universe we call ‘inflation’.
When the idea of inflation was proposed as part of the explanation of how the Universe began, some scientists thought that the rapid cosmic expansion would make it impossible for galaxies to form in the Universe. Galaxies are formed by the gravitational attraction of matter that develops from irregularities in the density of matter in space. These irregularities are the seeds from which galaxies grow. The problem as they saw it was that this inflation and expansion of the early universe would smooth out these irregularities.