# 6: The Four Fundamental Forces


The fundamental forces are normally divided in four groups, of the four so-called “fundamental” forces.

• 6.1: Prelude to the Fundamental Forces
The fundamental forces are normally divided in four groups, of the four so-called “fundamental” forces.
• 6.2: Gravity
The theory of gravity can be looked at in three ways: (1) The old fashioned Newtonian gravity,  (2) Einstein’s theory of gravity and (3)quantum theory. Latter is still under development.
• 6.3: Electromagnetism
• 6.4: Weak Nuclear Force
The weak nuclear force is manifests itself through nuclear β decay.
• 6.5: Strong Nuclear Force
The strong force is what keeps nuclei together. It is described by a theory called quantum chromodynamics (QCD), which described the forces between fermions called quarks that make up the hadrons. These forces are mediated by spin-1 bosons called gluons.

Thumbnail: The Feynman diagram for the weak decay of a neutron.

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