来自《耶鲁大学开放课程：基础物理 第7集 第7集》

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  So far that seems to be true,
  至今看来这都是正确的
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  and that's a big break for us.
  对于我们而言是巨大的成功
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  But for that you really couldn't do anything,
  但如果你今天发现的定律明天就失效了
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  if the laws you discovered today are not valid tomorrow,
  不能用预言任何东西
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  you cannot make any predictions.
  对你就毫无意义
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  So, it's another unwritten benefit we got unspoken
  所以这就是发现一条普适定律
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  it's a great benefit that the laws you find are universal.
  不言而喻的好处
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  Somebody had to stick his neck out and say,
  但必须有人愿意冒险提出定律
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  this is one of the first occasions.
  这就是其中的第一个
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  So now, you are going to apply this law to understand
  现在 你要通过应用这一定律来理解
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  what Kepler did.
  开普勒当时的想法
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  Okay, so what do you have to do to do what Kepler did?
  如何再现开普勒的推导过程呢