Spontaneous symmetry breaking

physical phenomenon in which the vacuum expectation value of a field is not invariant under a symmetry of the action, so that a symmetry present at high temperatures is broken at low temperatures

Spontaneous symmetry breaking is a way symmetry breaks in a physical system. The underlying laws do not change, but the system as a whole changes. Symmetry breaking in physics occurs when a system is crossing a critical point. Small fluctuations decide the system's fate, by determining which branch is taken.


There are several examples of spontaneous symmetry in nature.

  • A needle on its point is unstable, and will therefore fall over. The direction it falls, however, is random.
  • When a magnet is heated, above a certain temperature, it loses its magnetic properties. This is because the atoms are moving too fast to be aligned a particular direction.

Uses for spontaneous symmetry breakingEdit

Spontaneous symmetry breaking can create a particle called a Higgs boson. This is a particle which is the force transferring particle (boson) of the Higgs field. The Higgs field gives mass to fundamental particles such as electrons. Also, many scientists believe in the Higgs effect (which is very similar to spontaneous symmetry breaking) to answer questions that are not answered in the standard model of physics. The standard model predicts that certain types of quarks should have a mass of zero, while in reality they have a non-zero mass value. Some scientists believe that spontaneous symmetry breaking is the answer.

Method of spontaneous symmetry breakingEdit

For spontaneous symmetry breaking to happen, you need an environment which is completely symmetrical, and has at least two outcomes that are equally likely. Spontaneous symmetry breaking starts with two particles that are completely equal; their spin is equal, too. Mathematically, spontaneous symmetry breaking can be extremely puzzling, since you start out with two identical things and end up with two non-identical things. However, in practice, it is not so puzzling. If you have two particles moving at each other with equal speed, it would seem impossible for either of them to do anything but be symmetrical. However, if each particle has an equal 50-50 chance to be spinning one way or another, it is possible–in theory and in practice–to have this symmetry broken. It begins with symmetry to start with because the particles have an equal and symmetrical 50-50 chance of spinning one way or another.