Take the rocket as an example. Put two calibrated clocks into AB respectively. The rocket moves from point A to point B at a speed V, and the distance between two points AB is S. Let Δ t1be the time difference recorded by the observer at AB when the rocket passes through AB. Observers who set Δ T2 as point A record the time difference of the rocket passing through AB ... When an object arrives at point B, the time required for light to return to point A is the distance S between AB divided by the speed of light C. According to the above conditions, we can get: Δ T2-δ T 1 = s/c (1) s = v× δ T1(. Δ t1= Δ t2÷ (1+v/c) (3) From the analysis of formula (3), we can see that when the rocket speed is V=C, Δ t2 = 2× Δ t1; When the rocket speed is v < < c, δt 1≈δT2, because 1+v/c ≥ 1, δT2≥δt 1. We come to the conclusion that time on the rocket has slowed down, that is, time has expanded. Of course, this is the conclusion observed at point A. What is the conclusion from point B? Let Δ t1be the time difference recorded by the observer in AB when the rocket passes through AB, Δ t2 be the time difference recorded by the observer in B, and the time required for light to travel from A to B is S/C ... Similar to the above, we can get: Δ t1-Δ t2 = s/c (4) s = v× Δ t/kloc-. When the rocket speed is v < < c, δt 1≈δT2, because the equation 1-v/c ≤ 1, δT2≤δt 1. So we come to the opposite conclusion that the time of the rocket has become faster, that is, the time has shrunk.