The Large Hadron Collider (LHC) experiment has been restarted after a hiatus of 14 months. Engineers have now made two stable proton beams circulate in opposite directions around the machine. If all continues to go well, the team might even try to increase the dollar 10 billion collider's energy to record-breaking levels this weekend. <br/>The LHC, the world's largest machine, is housed in a 27km-long circular tunnel beneath the French-Swiss border. The experiment is designed to smash together beams of protons in a bid to shed light on the nature of the Universe. <br/>Among other things, scientists will search for signs of the Higgs boson, a sub-atomic particle that is crucial to our current understanding of physics. Although it is predicted to exist, scientists have never found it. <br/>