Strong CP Problem

The Strong CP Problem is a puzzle in physics related to why the fundamental theory of strong interactions (quantum chromodynamics) doesn't seem to violate a symmetry called CP (charge conjugation and parity). While the theory allows for a small violation, experiments show no evidence of it, implying an extremely fine-tuned or mysterious reason for this absence. This inconsistency suggests there might be new physics or underlying principles yet to be understood, making it one of the key unresolved questions in understanding the laws of nature.