One of the enduring puzzles in high energy particle physics is why quarks do not exist independently despite their existence inside the hadron as quarks have never been found in isolation.

Charge conservation in the theory of elementary particle physics is one of the best-established principles in physics. As such, if there are magnetic monopoles in the universe,

Energy conservation is one of the most fundamental and well-established principles of physics. E. Noether extended the energy conservation principle to the quantum field theoretical domain in empty.