来自《耶鲁大学开放课程：基础物理 第13集 第13集》

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  That's the time for a round trip.
  也就是那道光完成一个来回的时间
• 
  
  You look at my clock and what do you think is happening?
  你看着这块手表 你觉得会看到什么
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  Remember, you are moving to the right, relative to me,
  记住 你正在相对于我向右移动
• 
  
  so according to you my clock is moving to the left,
  那么对你来说我的表是在向左移动
• 
  
  and it looks like this.
  它看上去就是这样的
• 
  
  Light beam is going on a zigzag path, according to you.
  对于你 光线是呈 Z 字形移动
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  You agree that's very clear.
  这些都很明显
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  For me, the pulse is going up and down,
  对于我来说 光线上下移动
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  for you it's going on the hypotenuse.
  对于你来说 它走斜边路线
• 
  
  You can imagine how with the hypotenuse u squared
  你可以画个三角形 想象一下
• 
  
  and c squared are going to come from drawing the sides of the triangle.
  u 平方和 c 平方形成的斜边是怎样
• 
  
  That's why the time would come out longer.
  这就是为什么时间会显得长一些