The time interval Ato measured by the observer(s) relative to whom the clock is at rest is called the proper time正确时间)”,and△t0<At That is the observer relative to whom the clock is in motion measures a greater interval between ticks. this effect is called time dilation all observer in motion relative to the clock measure onger intervals” Eg 20-3) is valid for any direction of the relative motion of s and sThe time interval measured by the observer (S’) relative to whom the clock is at rest is called the “proper time(正确时间) ”, and . That is, the observer relative to whom the clock is in motion measures a greater interval between ticks. This effect is called “time dilation”. All observer in motion relative to the clock measure “longer intervals”. 0 t t  t 0 Eq(20-3) is valid for any direction of the relative motion of S and S’