Using the idea of lookback time, they could predict how far away it would be from us, and therefore calculate its redshift.

利用回溯时间的概念，他们可以预测它离我们有多远，从而计算它的红移。

This is called the “lookback time”, and it's a cru cial tool for cosmology: by observing very distant objects, we can see the Universe when it was young!

这叫做“回溯时间”，是宇宙学的一个重要工具：通过观察非常遥远的物体，我们可以看到宇宙年轻时的样子！