2. Fundamental interactions

2.1 The four fundamental interactions

In nature, any interaction between two particles can be reduced to one of the following four forces.

• Gravitational interaction

  Known for a very long time, it is responsible for the movement of planets and, closer to home, gravity. It manifests itself whenever masses are involved.

• Weak interaction

  It manifests itself, for example, in the β decay of nuclei, in the decay of certain particles and in thermonuclear fusion reactions inside the sun.

• Electromagnetic interaction

  This is what ensures the existence of...