A Nobel prizewinning physicist looks past the Higgs boson to dark matter, technicolour forces and WIMPsby Steven Weinberg / November 16, 2011 / Leave a comment
The moment of impact: protons collide within the Large Hadron Collider, creating over 100 charged particles
Physicists working at the Large Hadron Collider at Cern are now engaged in a strenuous search for a particle of a new type, known as a Higgs boson. Much more is at stake in this search than the effort to add one more item to the quarks, electrons, and so on that make up the menu of known elementary particle types.
This is because the discovery of the Higgs boson would confirm a theory of how the symmetry between two of the fundamental forces of nature became broken, and how elementary particles get their masses. Not discovering it would be even more exciting, putting us back to work to understand all this. To explain what is at stake here, I first have to say something about what physicists mean by symmetries, and by symmetry breaking.
A symmetry of the laws of nature is a statement that the laws remain the same when we change our point of view in certain definite ways. A large part of the physics of the 20th century was devoted to the discovery of such symmetries. It started in 1905, when Einstein in his Special Theory of Relativity declared that all physical laws, including those that dictate the speed of light, remain the same when we change our point of view by viewing nature from a moving laboratory.
But the symmetries of the laws of nature are not limited to changes in the way we view space and time, as in Special Relativity. The laws of nature may also be unchanged when we replace various types of particles in our equations with other types of particles. For instance, there are two kinds of particles that make up atomic nuclei: protons and neutrons. In the 1930s it was discovered that the laws that govern the strong forces that hold these particles together in nuclei do not change their form if we replace protons with neutrons, or even replace protons (and neutrons) with a mixture, that might for example be 30 per cent proton (or neutron) and 70 per cent neutron (or proton).
It’s not that physicists in the 1930s knew the laws governing the strong nuclear force. The importance…