Help on my thought experiment. We know the further galaxy, the faster it runs apart from us. Let's say there is a galaxy (assuming the laws of physics are the same there) running away from us at 99% of the speed of light. Let's say at the SAME time, the people in that galaxy doing the same thing with us on earth. The same thing can be: "start running an atomic clock". The people in that galaxy, according to General relativity, will know the atom clock on earth must run slower than theirs because the earth within milky way galaxy is speeding away at 99% light speed. We on earth will conclude the same that the atomic clock must run slower in the other galaxy speeding away from us at 99% light speed. We can also imagine a judge in exact middle point from the two galaxies and tell each side to start and stop the atomic clock and measure the time at exact the same time, because the judge is at exact middle point, and each galaxy is speeding away from him at exact time maybe 49.5% of light speed. (Maybe there is no need for such judge. if there are ways to ensure people on both sides start and stop the same time atomic clocks.) So now my puzzles, are the atomic clocks will measure same time? According to the General Relativity, each clock shall run slower against the other clock. if the atomic clocks measure the same time, then the earth people passed the same time as the other galaxy people, although General Relativity tells the other galaxy people must pass time slower than us as they are moving at 99% of light speed.