The frequency change caused by Doppler effect is called Doppler frequency shift, which is directly proportional to the relative velocity V and the frequency of vibration. In essence, the reason for the Doppler effect is that the relative velocity V is superimposed on the speed of light. If there is no relative velocity V superposition, there will be no Doppler effect. Therefore, it can be proved that Einstein's second hypothesis is wrong: the speed of light is the same in all inertial systems. If the speed of light is the same, it is impossible to observe the Doppler effect at all. The modified ether theory can replace the theory of relativity. On the earth's surface, the ether moves with the earth's traction, and the earth cannot drag the ether of the whole universe. The optical aberration phenomenon also shows that the earth does not drag the ether of the whole universe. The optical aberration phenomenon occurs at the junction of the earth's ether traction area and non traction area, not in the telescope lens. That is, the earth only pulls the ether around it. The planet moves with the ether around it. The ether has mass, and the ether may be dark matter. The density of ether is distributed according to the size of gravity. The closer to a planet, the greater the density of ether.