The discussion on four-degree velocity and acceleration has turned many times, and the final result is still the same, so its discussion is a good approximation. When interacting particles interact, the velocity of electromagnetic field can never be constant as discussed in special relativity. The discovery of superluminal neutrinos in the universe denies the theoretical basis of special relativity. It is impossible for interacting particles to change the electromagnetic field velocity of other particles without changing their own electromagnetic field velocity, so the actual interacting particles should establish a new theory and choose between the transformation of pure theory and the transformation of special relativity, which can be described by the coefficient of change of electromagnetic field velocity. In some specific interaction cases, the speed of light has obvious changes in the relativity principle of pure theory, such as the change of light propagation speed in the medium that we will discuss below. In order to describe the interacting particle field truly and accurately, the current theory is only quantum mechanics, which uses a unified field to describe the motion of particles. The core of Maxwell's equation is the law of conservation of charge, and the transformation of coordinate values has nothing to do with the change of light speed, so the law of conservation of charge will not change with the transformation of coordinate system. In the following, when we discuss the reference frame of light in the medium, we don't regard the reference frame of the medium as a special reference frame, but refer to the approximate inertial frame to simplify the discussion, that is, we only describe the motion of photons in the form of two relative reference frames, without considering other factors in the system, including the density and interaction of matter, and we can't just call the area where matter exists a singularity without further study. Experiments related to the change of light speed, only Fizeau experiment is discussed here. Firstly, the refractive index of photons in liquid is discussed. Here, water medium is used to explain that photons are electromagnetic waves. When photons pass through the observation space and penetrate into the relatively static water medium, the coordinates of photons in the observation space are linear functions of time. We also know that photons can also be treated as linear functions in water media. When the electromagnetic field of photons meets the field of water molecules, it will inevitably lead to the interaction of fields. Because the interaction between particles is related to their mass and energy, and the energy of water molecules is not an order of magnitude compared with photon energy, we ignore the change of water molecule field velocity and only consider the change of photon field velocity. For the convenience of discussion, it is assumed that the reference frame in which the water medium is located can be approximately discussed by the relative motion of the inertial system at least on the trajectory of photon motion, that is, the influence of water molecule field velocity on light is not considered, but only the influence of water molecule field velocity on light in the light direction is discussed. We assume that the spin velocity component of each water molecule field in the X-axis direction of photon travel path is V, which is actually an average value. By promoting h? Under the same assumption of Lorenz, the components of water molecule field velocity perpendicular to the Y axis and Z axis of light only deflect light, but have no effect on the movement of light on the X axis. Then, in the path of photon travel, there are: although there is no absolute inertial system to describe the movement of light in the medium, in the approximate inertial system, we find that formula (2) describes the fluctuation of matter particles, and formula (3) describes the existence of matter to light.