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In the early 1960s, the well-known physicist Richard Feynman said something cool in a lecture.
在20世纪60年代初期，著名物理学家理查德·费曼在一次演讲中说了一些有趣的事。
I mean, he said a lot of cool things in his lectures.
我的意思是他在演讲中说了很多有趣的事。
But what he said this time, according to a transcript published later,
根据随后发表的听力文稿，他这次提到的是
was that the center of the Earth should be a day or two younger than the surface.
地心应该比其表面年轻一两天。
As strange as that sounds, the basic idea behind it makes sense, if you know something about the theory of relativity.
这听起来可能很奇怪，但如果你了解一些相对论的话，就该知道它背后的基本思想是有道理的。
And it was Feynman saying this, so people kept quoting him in lectures and textbooks, and nobody really questioned it.
因为这是费曼的言论，所以人们一直在演讲和教科书里引用，却没有人怀疑它。
That is, until April 2016, when three Danish physicists actually did the math, and realized that Feynman was wrong.
也就是说，直到2016年4月，三位丹麦物理学家确实用数学算过之后，才意识到费曼错了。
The center of the Earth isn't a day or two younger than the surface. It's two and a half years younger.
地心比地表年轻的不是一两天，而是两年半。
And the center of the sun? It's 39,000 years younger than its surface.
那么太阳中心呢？它比其表面年轻三万九千岁。
All because of general relativity.
这都是因为广义相对论。
General relativity is basically the science of the very fast, and the very massive.
广义相对论是一门围绕速度快和大质量的科学。
It takes the big-picture universe, like planets, stars, and galaxies, and describes it using math.
它研究宏观宇宙，如行星、恒星和星系，并用数学来描述它。
That math is built around a few fundamental ideas.
这门数学围绕几个基本思想。
One of those ideas is that the speed of light in a vacuum is always the same,
其中一个就是真空中的光速总是一样的，
it's about 300,000 kilometers per second, no matter what perspective you're looking at it from.
不管你从哪个角度看，都是大约每秒30万千米。
And that rule, that the speed of light is set, can seriously mess with both time and space,
如果光速固定，可能会严重扰乱时间和空间，
if you start to consider situations that are way more extreme than your everyday life on Earth.
这要比你在地球上的日常生活更极端。
For example, when you're traveling close to the speed of light, say in some hypothetical, ridiculously fast train,
假设你在一个速度出奇快的火车里，比如它的速度接近光速，
time will pass more slowly for you than for someone standing on the ground watching you zoom past.
对你来说，时间过得要比站在地上看你疾速而过的人慢好多。
Relativity shows that space and time are so closely interconnected
相对论表明，空间和时间是如此紧密地相联，
that you can really think of them as parts of the same thing. That's spacetime.
以致于你真的认为它们属于同一种事物，那就是时空。
And another thing relativity shows is that something with a lot of mass, like Earth or the sun, will warp spacetime.
相对论表明的另一件事是，像地球或太阳这样大质量的物体会扭曲时空。
One of the effects of this warping is that the closer you get to the center of one of these massive objects,
这种扭曲的影响之一就是你越接近这些大质量物体的中心，
the slower time will pass.
时间过得越慢。
It's a brain-bendy idea, but we know it's true.
这想法可能有点儿颠覆，但却是真的。
We have to correct GPS systems because of it.
因为它，我们不得不修正GPS定位系统。
GPS satellites orbit Earth from about 20,000 kilometers up,
GPS卫星的轨道大约在地球上方2万公里处，
so they're much farther from Earth's center than we are on the ground.
所以它到地心的距离要比我们在地面上远得多。
That means that time passes a little more quickly for a GPS satellite than for us.
这就意味着GPS卫星的时间要比我们快一点儿。
It's a tiny difference, which adds up to only about 38 millionths of a second per day.
这个差别非常小，每天加起来只差三千八百万分之一秒。
But for the satellites to keep track of your position, their clocks need to be synced up pretty much exactly.
但卫星要跟踪你的位置，它们的时钟需要完全同步。
So GPS satellites are designed to take relativity into account and correct their clocks.
因此，设计GPS卫星时要将相对论考虑进去，并修正它们的时钟。
And this is the same basic idea Feynman pointed out in his lecture:
这和费曼在演讲中提到的基本观点相同：
If something with lots of mass warps spacetime,
如果大质量物体扭曲时空，
and if time passes more slowly the closer you are to Earth's center,
如果你越接近地心，时间过得越慢，
that means the center of the Earth must be younger than the surface. And that part was right.
这就是说地心要比其表面年轻。这部分是对的。
The thing is, he said that in the 4.5 billion years or so that Earth's been around,
问题是，他说地球在大约45亿年前就存在了，
the center would be younger than the surface by a day or two.
所以地心要比表面年轻一两天。
And no one checked his math for more than 50 years, until that group of Danish physicists decided to look into it.
过去50多年都没人验证他的数学，直到那组丹麦物理学家决定研究它。
In a paper published in the European Journal of Physics,
在《欧洲物理杂志》上发表的一篇论文中，
first, they did a simpler version of the calculation, using equations that treated Earth like a uniformly dense sphere,
首先，他们做了一个简单点儿的计算，用方程式把地球当作一个密度均匀的球体来计算，
which it's not, by the way, because of all those different layers of rock.
这不是事实，因为地球有各种不同的岩层。
But it's still a pretty good way to get a sense of the physics,
但这仍然是一种了解物理学的好方法，
and that's probably how Feynman would've done the calculations..
也可能是费曼做计算的方法。
They found that the center of the Earth would be about a year and a half younger than the surface,
他们发现地心要比其表面小一年半左右，
which was their first sign that Feynman's famous fact was wrong.
他们的第一个结果就表明费曼的著名事实是错的。
Next, the team did a more detailed calculation, using a model that takes into account the variations in Earth's density.
接下来，这个团队又利用把地球密度变化考虑在内的模型，做了一次更复杂的计算，
That gave them a more exact answer: Earth's center is about 2.5 years younger than its surface.
得出了一个更加准确的结果：地心比其表面小两年半。
It's hard to know whether Feynman himself was wrong,
我们很难知道是费曼自己错了，
or whether the people transcribing his lectures just wrote down "day" instead of "year".
还是人们在记录他的演讲时把“year”写作了“day”。
But, either way, the fact that people kept repeating in all those lectures and textbooks was wrong.
但不管怎么说，人们在各个演讲和课本中重复的事实都是错的。
While they were at it, the Danish researchers did the same detailed calculation for the sun,
与此同时，这些丹麦研究人员又对太阳做了同样复杂的计算，
since there's a similar model of the sun's density that they could use.
因为他们可以使用一个类似的太阳密度模型。
And they found that the sun's center is about 39,000 years younger than its surface,
他们发现太阳中心比其表面小三万九千岁，
which is a much bigger age difference than for Earth.
这要比地球的年龄差大很多。
A lot of that is because much more of the sun's mass is concentrated close to its center, and warps spacetime so much more.
这很大程度是因为太阳的质量更多地集中在它的中心，时空扭曲更严重。
Practically speaking, the fact that time passes more slowly at the center of the Earth and the sun doesn't really matter that much.
事实上，地心和太阳中心的时间过得更慢，对我们真得没多大影响。
But relativity is one of our most useful tools for learning about the universe,
但相对论是我们学习宇宙最有用的工具之一，
so it's important to understand the way it affects everything around us.
所以理解它对我们周围事物的影响是很重要的。
And for scientists, the fact that Feynman's numbers were wrong
而对于科学家来说，费曼数据是错误的，
is a reminder of one of the most fundamental aspects of scientific thinking: question everything.
这一事实提醒我们科学思维有一个最基本的方面：质疑一切。
Thanks for watching this episode of SciShow Space,
感谢您收看本期的太空科学秀，
and thanks especially to our patrons on Patreon who help make this show possible.
特别感谢“Patreon”对本节目的大力支持。
If you want to help us keep making episodes just like this, you can go to patreon.com/scishow to learn more.
如果你想帮助我们继续做这类节目，请登录patreon.com/scishow了解更多信息。
And don't forget to go to youtube.com/scishowspace and subscribe!
也不要忘了登录youtube.com/scishowspace点击订阅哦！
