Humboldt-Universität zu Berlin - Faculty of Mathematics and Natural Sciences - Experimental Particle Physics

Symmetry

Symmetries are the key to understand our world.  Based on the so-called Noether-Theorem every symmetry is connected to a conserved variable leading to a force.  In our all-day experience the geometrical space owns a transversal symmetry, implying the conservation of momentum in conjunction with the Newton's laws.  The same concept is used to discribe the fundamental forces, as electroweak and strong interaction, in particle physics.  However, the symmetries are then of more complicated nature.

In the strong interaction forces are mediated by gluons carrying colour charge.  The invariance of the strong forces under exchange of the three colours (green, red, blue) is the symmetry here.  Even more involved is the symmetry in the case of the electroweak interaction.  The invariance of electromagnetic forces under charge transformation is still understandable in daily life.  But the symmetry discribing the weak interaction is based on a not-obvious quantity: weakly interacting particles can only couple if they are left-handed.  This is described in the so-called weak isospin, which is conserved in the weak interaction


Forces | Strong Force | Weak Force | Symmetry | Symmetry Breaking