The most complex device ever built by man
A simulated event in the CMS detector, featuring the appearance of the Higgs boson
Physicists hope that the LHC will help answer many of 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, at least:
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.
Is supersymmetry, an extension of the Standard Model and Poincaré symmetry, realised in nature, implying that all known particles have supersymmetric partners?
Are there extra dimensions, as predicted by various models inspired by string theory, and can we detect them?
What is the nature of the Dark Matter which appears to account for 23% of the energy density of the Universe?
Other questions are:
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? See also Hierarchy problem.
Are there additional sources of quark flavour mixing, beyond those already predicted within the Standard Model?
Why are there apparent violations of the symmetry between matter and antimatter? See also CP violation.
What was the nature of the quark-gluon plasma in the early universe? This will be investigated by heavy ion collisions in ALICE.