There are four fundamental forces in the universe, sometimes called fundamental interactions. They are called 'fundamental' because they cannot be reduced to anything simpler.
- Gravity and electromagnetism are experienced by people in their everyday life. A complete description of the forces requires advanced physics.
- The strong and weak interactions produce forces at minute, subatomic distances and govern nuclear interactions. These forces are the
It is thought by most physicists that three of these forces (electromagnetism, the weak force, and the strong force) become a single force under very high temperatures. This idea is known as the grand unification theory.
- Franklin, Allan; Fischbach, Ephraim 2016. The rise and fall of the fifth force: discovery, pursuit, and justification in modern physics. 2nd ed, Springer. ISBN 978-3319284125