Long long ago, there was a story that four spaceships were sent out from the earth to fly in different directions. Their relative speed to the earth was 0.9c. According to the calculation of "special relativity", their time became slower. It's only 0.435 * the time of the earth. t' = t*sqrt*(1-v^2/C^2) But one day the earth exploded, there was no residue left, so the four spacecraft lost their original reference. They could only make reference to each other, and found that there was a relative speed between them, so they were surprised to find that the time between them was different. God, without the earth, the time on the spaceship will be different. With the earth, it will be the same again. Who can explain it? Thanks very much.