23 Feb 1927. Werner Heisenberg writes Wolfgang Pauli to first describe the uncertainty principle in physics. The uncertainty principle says that we cannot measure the position (x) and the momentum (p) of a particle with absolute precision. The more accurately we know one of these values, the less accurately we know the other.
https://www.theguardian.com/science/2013/nov/10/what-is-heisenbergs-uncertainty-principle