史黛拉在前往恒星的旅程中将再发出四次光脉冲，一次比一次离地球远。
Stella will send four more light bursts during her outbound journey, each one from farther away.
等特拉观察到史黛拉返程中发出的第一个光脉冲时，时间已过了21年多。
By the time Terra observes the first pulse from Stella's inbound journey, over 21 years will have passed for her.
对于史黛拉返回地球的剩余旅程，特拉每年都会收到多个光脉冲。
For the rest of Stella's return home, Terra receives multiple light bursts each year.
因此，在分开的23年里，特拉观察到：在90%的时间里，史黛拉减缓衰老，而在最后的10％时间，她则加速衰老。
Thus, Terra observes Stella aging slowly for about 90% of their 23 years apart, and aging rapidly during the last 10%.
这种不对称解释了为何该悖论并非真正的悖论。
This asymmetry accounts for why the paradox isn’t really a paradox.
尽管双胞胎二人都见证了彼此的时间加速和减速，但史黛拉看到的是时间均等的加速和减速，而特拉在大部分时间里看到的是史黛拉减缓衰老。
Although each twin witnesses time both speeding up and slowing down for the other, Stella sees an even split, while Terra sees Stella aging slowly for most of the time they’re apart.
这与每个双胞胎所测量的对太空航行的结果是一致的，该过程需要23个地球年，但飞船上只有11.5年。
This is consistent with each twin’s measurement of the space voyage, which takes 23 Earth years, but only 11.5 as experienced aboard the ship.
当双胞胎团聚时，特拉43岁，而史黛拉将会是31岁。
When the twins are reunited, Terra will be 43 years old, while Stella will be 31.
史黛拉出错是因为她的假设错了，即假设她和特拉都是惯性观测者。
Where Stella went wrong was her assumption that she and Terra had equal claim to being inertial observers.
作为惯性观测者，必须相对于宇宙的其余部分保持恒定的速度和方向。
To be an inertial observer, one has to maintain a constant speed and direction relative to the rest of the universe.
特拉一直处于静止状态，因此她的速度恒定为零。
Terra was at rest the entire time, so her velocity was a constant zero.
但当史黛拉改变方向返程时，她输入的参考系与开始时的参考系不同。
But when Stella changed her direction for the return journey, she entered a different reference frame from the one she’d started in.
我拍了这张相片上星期贴上我的Facebook页面有人留言说“哼，他为何让他像这样立正？”
Now I had this picture taken, and it was put up on my Facebook page last week, and somebody wrote in, "Huh, why does he have him standing at attention like that?"
接着写道，“但他看起来不错”（笑声）
And then they said, "But he looks good." (Laughter)
“啊！”（笑声）
"Huh!" (Laughter)
“是，将军。是，将军”
"Yes, General.
Yes, General."
“你没刮胡子”“但长官－”
"You didn't shave.""But sir —"
“没有理由，长官”“好小子，算你识相”
"No excuse, sir.""Attaboy, you're learning fast."
“你是…嗯…你是鲍威尔将军”
You're, well, you're General Powell."
“是、是”“喔…”
"Yes, yes.""Oh ... "
我把钱递给他
I hand him the money.
我接受他的好意，继续沿着街道前进脑海里浮现一个念头，天哪这就是九十年前以同样方式欢迎我父母的国家
I accept the generosity, continue up the street, and it washes over me, my God, it's the same country that greeted my parents this way 90 years ago.
因此，这依然是当年那个泱泱大国但来自世界各地的年轻人为这个国家贡献心力我们的义务是成为对这个美好国家有所贡献的公民确保没有任何孩子会被遗忘
So we are still that magnificent country, but we are fueled by young people coming up from every land in the world, and it is our obligation as contributing citizens to this wonderful country of ours to make sure that no child gets left behind.
十分感谢
Thank you very much.