NOTHING to do with a Hollywood film-making process, technicolour takes us back to the beginning of the universe, when two of the fundamental forces of nature, electromagnetism and the weak force (which governs particle decay within the atomic nucleus), were united in a single force 鈥� the electroweak force. When the universe cooled, the forces split apart. The two seem very different today: photons, carriers of electromagnetism, are massless, while W and Z particles, carriers of the weak force, have mass. But why?
To explain how the Ws and Zs got mass, physicists proposed something called the Higgs 鈥� a quantum field that permeates all space. The particle associated with the Higgs field, the Higgs boson, is so revered it is dubbed 鈥渢he God particle鈥�. But some physicists are putting their faith in another theory: technicolour.
First, a bit on Higgs. Many physicists believe the Higgs field formed as the universe cooled, giving empty space an ordered structure, like an ice crystal freezing out of water. The W and Z particles, which started off massless like the photon, suddenly found it difficult to move through the Higgs field: they became sluggish, as if they鈥檇 put on mass.
Advertisement
But the Higgs theory offers no explanation as to why space should have this ordered structure. Enter technicolour. Technicolour is a fifth force, an addition to the known four, which acts on particles named techniquarks. The force is so strong that a techniquark pair cannot be separated except at very high energies, as at the big bang. As the universe cooled after the big bang, the techniquarks paired off and have remained glued together ever since. This sea of techniquark pairs explains the ordered structure of empty space.
鈥淭echnicolour could explain the structure of empty space鈥�
But how does technicolour give Ws and Zs mass? Like ordinary particles, techniquarks have a property called spin, which can be left or right-handed. At high energies, when techniquarks are unpaired, the laws of physics dictate that a left-handed techniquark cannot transform into a right-handed one, and vice versa. These rules would be broken even if a techniquark was observed as having the opposite spin. However, something moving faster than a left-handed techniquark would see it spinning the other way (the way a car in the next lane appears to move backward as you pass it). To prevent that from happening, techniquarks have to move at the speed of light so nothing can outrun them 鈥� and the only particles that can do that are massless ones. Therefore, in the searing energies of the early universe, photons, and the constituents of Ws and Zs, were all massless.
But as the universe cooled, left and right-handed techniquarks paired up. Techniquarks now appear only as combinations of each other. Right-handed can look like left-handed, and vice versa, which means that techniquarks must be moving slower than the speed of light and have therefore acquired mass. The massive techniquark pairs form massive W and Z particles.
So which theory is correct? Only experiment can decide. The Large Hadron Collider at CERN in Switzerland, due to begin particle-smashing in 2007, should find the Higgs boson if it exists. If it doesn鈥檛, the hunt for techniquarks is on.
