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The setup for the twins paradox is as follows – suppose I sit on earth
双生子悖论的设定如下——假设我在地球上静止
while you head off on a rocketship at a constant speed for a while, then turn around and come back.
而你在火箭上以恒定的速度前进一段时间，然后转身返回。
We know that moving things experience time more slowly, so I'll think that when you get back, you should be younger than me.
我们知道移动的物体经历时间更慢，所以我会认为当你回来的时候，你应该比我年轻。
But from your perspective, the earth (with me on it) is doing the moving, receding and then returning,
但从你的角度来看，我所在的地球正在移动移动、后退，然后返回，
so you think that I should be younger than you. Who's right? We'll use the fact that time rotates to sort this all out.
所以你认为我应该比你年轻。谁对谁错？我们将利用时间旋转的事实来解决这个问题。
Ok, so from my perspective, every second that passes I stay in the same place,
所以从我的角度来看，时间流逝的每一秒，我都是待在同一个地方的，
while every second that passes, you get farther away, and then closer. Simple enough.
而时间流逝的每一秒，你越走越远，然后越来越近。很简单。
From my perspective, you'll take ten seconds to get back.
从我的角度来看，你得花十秒钟才能回来。
And since you're moving, I'll think that time is passing more slowly for you,
由于你正在移动，我会认为你的时间过得比较慢，
so I'll calculate that your journey, for you, takes eight seconds.
所以我计算得出你的旅程花了8秒。
Now – and this is the important bit – since you're moving,
现在——这是重要的一点——由于你正在移动，
what you think of as the forward direction of time will be rotated relative to my perception of time.
你认为的时间的前进方向会随着我对时间的感知而旋转。
So on your outward journey, the seconds will tick away like this. And on your return journey, the seconds will look like this.
所以在你的外出旅行中，时间就像这样一秒一秒地流逝。在你回来的路上，时间是这样流逝。
From your perspective, your journey does indeed take eight seconds!
从你的角度来看，你的旅程确实花了8秒！
But almost immediately, we also see the solution to the twins paradox: right here.
但几乎同时，我们也看到了双生子悖论的解决方案：就在这里。
This bit of my time is unaccounted for by you.
因为你，我的这段时间是无法解释的。
During your entire journey, you'll think that time is passing more slowly for me than for you
在你的整段旅途中，你会认为我的时间过得比你慢
(and indeed it is – here, and here, add up to only 6.4 seconds),
（确实如此——这里和这里，加起来只有6.4秒），
but because of your change in velocity when you turn around to come home,
但是由于你转身返回时的速度发生了改变，
your notion of time rotates and skips right over a large swath of my time.
在我的大部分时间里，你对时间的观念是旋转、跳跃的。
Which amounts to precisely – you guessed it – the missing 3.6 seconds.
准确来讲，总共少了3.6秒。
And this is the resolution to the twins paradox: because you changed velocity, your notion of simultaneous times rotates,
这是双生子悖论的解决方法：因为你的速度变了，你对同步时间的概念是旋转的，
so your accounting of how time passes in parts of the universe far away from you will have gaps in it.
所以你对宇宙中远离你的部分时间如何流逝的计算将会有空隙。
Well, in reality it wouldn't have gaps, because you couldn't instantaneously change direction
实际上，这段时间是不会出现空隙的，因为你不可能瞬间改变方向
– you'd have to fire your rockets to start heading home,
你得给火箭助燃才能开始回程，
and during that acceleration your notion of time would have very very quickly rotated through the missing gap in my journey,
并且在加速的这段时间，你对时间的概念将以很快的速度在我旅途中消失的间隙中旋转，
allowing you to properly account for the missing time.
这就给出了消失时间的恰当解释。
In summary: during your outward and return journeys, ten seconds would pass for me,
总结：在你外出和返程的旅途中，对我来说是过去了10秒，
and I'd calculate eight seconds as passing for you.
而对你来说，过去了8秒。
Eight seconds would pass for you, and you'd calculate 6.4 seconds as passing for me during your outward and return journeys,
对你来说过去了8秒，在你外出返程途中，你计算出我的时间过去了6.4秒，
and 3.6 seconds as passing for me during your acceleration (even if it was basically instantaneous).
并且在你加速的时候（即使是瞬间加速），我也只过去了3.6秒。
So we both agree that when you come home, you'll be younger!
所以我们都认为当你返程时，你会更年轻！
And indeed, this is what happens when you send an atomic clock flying around in in an airplane:
确实，这就是当你把一个原子钟送上飞机时所发生的事情：
it records less time as having passed than a twin atomic clock that stays on the ground.
它记录的时间比停留在地面上的两个原子钟还少。
PS the time rotations I've been talking about are actually called Lorentz Transformations,
我所说的时间旋转实际上叫做洛伦兹变换，
and they're the way that most working physicists think about special relativity
它们是大多数物理学家思考狭义相对论和时间膨胀、
and things like time dilation, relativistic doppler shifts, and so on.
相对论多普勒频移等问题的方式。
Trying to understand relativity just by using basic equations for time dilation and length contraction
试图用时间膨胀和长度收缩的基本方程来理解相对论
(like is often done in beginning physics classes) will often lead to confusing apparent contradictions,
（就像在开始上物理课时经常做的那样）往往会导致明显的矛盾，
because they don't take into account the full changing of simultaneity of events, and so on.
因为它们没有考虑到事件同时性的全部变化，等等。
