At the end of the 19th century, at the celebration of the Royal Society of Great Britain to welcome the coming of the new century, Lord Kelvin proudly declared: "The theoretical building of physics has been built, and future physicists only need to do some patchwork." However, in the atmosphere of joy, there are still "two disturbing dark clouds", one is the zero result of the Michelson Morey experiment on the measurement of the speed of the ether, and the other is the ultraviolet disaster problem related to black body radiation. The first dark cloud gave birth to Relativity, and the second dark cloud gave birth to Quantum mechanics. Relativity and Quantum mechanics are called the two pillars of modern physics. However, more than 100 years later, Relativity and Quantum mechanics have not been integrated. Not only that, there are many irreconcilable contradictions between the two. In the past century, theoretical physics has not made any breakthrough, even at a standstill. We have never heard of a theory that can drive the new physics revolution. There may be three reasons why Relativity and Quantum mechanics cannot be unified: 1. One of the two theories is incorrect, 2. Neither of the two theories is correct, 3. Both of the two theories are correct, but no method has been found to unify them. In this paper, we will carry out mathematical derivation and analysis from the core formula of Relativity and Quantum mechanics, and then give the answer. In the end, we will find that the modern physics theory system has chosen two dark clouds, however, gave up the whole sky.