One of the major breakthroughs in particle physics in the 1970s was the
successful development of "electroweak" theory. This brings together electricity
and magnetism, light and radioactivity, in a unified description of the electromagnetic
and weak forces that underlie these very different phenomena. Now theorists are attempting
a broader "grand unification", which will also include the strong force that
holds the bulk of matter together at the nuclear level.
Experiments show that the strong force becomes weaker in its effects as energies increase.
This suggests that at very high energies, the strengths of the electromagnetic, weak and
strong force are the same, and the forces are basically indistinguishable. The energies
involved are thousand millions of times greater than particle accelerators can reach, but
they would have existed in the very early Universe, almost immediately after the Big Bang,
when the Universe was a mere 10-34 seconds old.
Fortunately for present-day experiments, grand unified theories do have consequences at
lower energies. In particular, for the theories to be sensible they generally require that
Natures has a deep symmetry, known as "supersymmetry", which so far has been
hidden from view.
Supersymmetry links the matter particles (the quarks and leptons) with the force-carrying
particles, and implies that there are additional "superparticles" necessary to
complete the symmetry. These superparticles must be much heavier than their ordinary
relations, and so have not been seen. But the lightest superparticles should be only
around ten times heavier than the heaviest particles studied so far. This puts them in
range of the LHC, CERN's machine for the 21st century.
© Copyright CERN - Last modified on 1998-02-18 - Tradotto da Sofia Sabatti