and this is the outgoing momentum, call it the P outgoing.

这是总的出四动量叫做 P出
If P incoming is equal to P outgoing for me,

如果对我来说 P入等于 P出
so two vectors that equal in space-time,

这两个矢量在时空里就是相等的
for the rotated observer they will be equal.

对旋转了的观察者也是一样
Do you understand why?

能理解吗
Because my total incoming vector will undergo Lorentz transformation

因为我的总入矢量经过洛伦兹变换后
to become your incoming vector.

会变成你的总入矢量
My outgoing vector will undergo lorentz transformation

而我的出矢量经过洛伦兹变换后
to find your outgoing.

也会变成你的出矢量
But if the input of the Lorentz transformation is the same,

如果洛伦兹变换的输入量一样
the output will also be the same,

那么输出也会是一样的
because you will be putting the very same numbers

因为输入量相同