当我们向外太空移动时，从这些遥远的星系发出的光都是如此的长，我们实质上正在飞离而回到过去。
As we move out, the light from these distant galaxies have taken so long, we're essentially backing up into the past.
“时光旅行是真的”，纸条上写道，“然而你只能单程回到过去”。
Time travel works!“ the note read. “However you can only travel to the past and one-way.
但是，让事物回到过去的轨道不仅是不现实的，在道德上也是站不住脚的。
But returning to the way things were is neither realistic nor morally tenable.
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