According to the fact that electric quantity and elastic force are unrelated to velocity, as well as the properties of gravitational field, it is proved that the gravitational mass of an object is inevitably unrelated to the velocity, while the inertial mass of an object is undoubtedly related to the velocity, so it can be concluded that the gravitational mass is not possibly equal to the inertial mass, and the equivalence principle is not tenable. The equivalence principle is the theoretical basis of general relativity. Now that the basis is untenable, according to the principle of physics, the general relativity will naturally be untenable. By analyzing the conditions under which the general relativity is approximately tenable and the conditions under which it is untenable, and combining with the fact that Black Hole is the analysis result of general relativity under the condition that equivalence principle is not tenable, the Black Hole is not considered to be possibly existent. Besides, the spacecraft rotates around the Black Hole, which is the only way for humans to travel through time. Now that the Black Hole does not exist, time travel will be impossible.