来自《耶鲁大学开放课程：基础物理 第1集 第1集》

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  because it tells you there's a second solution
  因为数学告诉我有两个根
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  and you cannot throw them out."
  你不能随便丢掉
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  And it turns out the second solution,
  结果 后来证明 第二个根
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  with negative energy, was when the theory is telling you,
  也就是能量为负的那个根 正是理论的关键
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  hey, there are particles and there are anti-particles,
  世界上既有粒子 也有反粒子
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  and the negative energy when properly interpreted will describe anti-particles.
  负能量就是用来解释反粒子的
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  So the equations are very smart.
  这些方程真的很神奇
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  The way the physics works is
  在物理问题中
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  you will find some laws of motion in mathematical form,
  你可以用数学方法得到运动定律
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  you put in the initial conditions of whatever,
  你代入初始条件
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  you solve the equations, and the answer that comes,
  然后解方程 获得答案
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  you have no choice.
  你别无选择