天文播客236：爱因斯坦是对的

本集《天文之声》由斯威本大学在线天文学项目赞助，这是全球历史最悠久的在线天文学学位课程。

This episode of Astronomy Cast is brought to you by Swinburne Astronomy Online, the world's longest running online astronomy degree program.

欲了解更多信息，请访问 astronomy.swin.edu.au。

Visit astronomy.swin.edu.au for more information.

《天文之声》第236集，2011年10月24日，星期一。

Astronomy Cast, episode two thirty six for Monday, 10/24/2011.

爱因斯坦是对的。

Einstein was right.

欢迎收听《天文之声》，这是我们每周基于事实的宇宙探索之旅，帮助您不仅了解我们知道了什么，还了解我们是如何知道的。

Welcome to Astronomy Cast, our weekly facts based journey through the cosmos, where we help you understand not only what we know, but how we know what we know.

我的名字是弗雷泽·凯恩。

My name is Fraser Cain.

我是《今日宇宙》的出版人，和我一起的是盖伊博士。

I'm the publisher of Universe Today, and with me is Doctor.

帕梅拉·盖伊，南伊利诺伊大学爱德华兹维尔分校的教授。

Pamela Gay, a professor at Southern Illinois University, Edwardsville.

帕梅拉，你最近怎么样？

Pamela, how are doing?

我很好。

I'm doing well.

弗雷泽，你怎么样？

How are you doing, Fraser?

我非常好。

Doing really well.

我们再次通过谷歌环聊与天体物理播客的八位亲密朋友连线。

Once again, we are having a Google plus Hangout with our eight close friends on Astronomy Cast.

大家挥挥手吧。

Everybody wave.

现场观众听不见。

The studio audience is unheard

我们已经把他们的麦克风全部静音了。

We've by the cast muted them all.

但不，这真的非常有趣，并且对我们所有的节目都非常有帮助。

But no, it's really fun and it's been really helpful for all of our episodes.

观众给我们提供点子，并在节目中纠正我们的错误，所以简直太棒了。

People giving us ideas and fixing our mistakes during the show, so it's super.

所以如果你想加入我们，你只需要在Google+上关注我或帕梅拉，当我们准备录制时，我们会发送邀请。

And so if you want to join us, all you have to do is circle me or Pamela in Google plus and then we send an invite when we're going to be doing the recording.

如果你恰好看到了，那就来加入我们，和我们一起聊天吧。

And if you happen to see it, then come join us and hang out with us.

所以这真的非常有趣。

So it's really fun.

好的，你刚从中国回来？

Okay, you're back from China?

中国、法国、华盛顿特区，以及沿途的所有地方。

China, France, DC, all points in between.

奥地利，没错。

Austria, yep.

你

You're

所以这里稍微

So here this for a little

这会是那种我的身体完全处于时差状态的节目。

is gonna be one of those episodes where my body is just like jet lag.

你为什么醒着？

Why are you awake?

你为什么醒着？

Why are you awake?

我脑子里有个声音在说：太阳不该升起，你也不该醒着。

There's this voice in the back of my brain saying, The sun should not be up nor should you.

所以，请原谅任何因疲惫导致的口误。

So yeah, please pardon any exhaustion induced word slippages.

好的。

All right.

好吧，每周我们至少会收到一封理论家的邮件，声称爱因斯坦是错的。

Okay, so at least once a week we get an email from a theorist claiming that Einstein was wrong.

那你知道吗？

Well, know what?

他并没有错。

He wasn't wrong.

事实上，爱因斯坦提出了许多具体的预测来验证他的理论。

In fact, Einstein made many specific predictions to help validate his theories.

每次实验都证明爱因斯坦是对的。

Each time experiments have shown that Einstein was right.

事实上，他一些更具争议的理论直到最近几年才被实验证实。

In fact, some of his more controversial theories were only tested experimentally in the last few years.

在我们深入讨论之前，有一个很棒的网站，你们可以去看看，这是来自Tree Lobsters的Steve做的。

And before we get into this, there is a great website that you might want to check out by Steve from Tree Lobsters.

他的网站是waseinsteinwrong.com。

His website is waseinsteinwrong.com.

如果你去那里，你就会知道爱因斯坦是否错了。

And if you go there, you'll find out whether Einstein was wrong.

所以这是一个不错的网站。

So it's a good site.

那么现在我们来谈谈爱因斯坦。

So now let's talk about Einstein.

上一期我们谈到了爱因斯坦，讲了他的生平、经历和理论，但没有过多讨论狭义相对论和广义相对论，因为以前已经讲过了。

So last show we talked about Einstein, talked about his history and his life and his theories, less about special relativity and general relativity because we've talked about that in the past.

但我们谈了很多关于他的感情生活，以及他是如何在各个大学之间辗转的。

But we talked about a lot of his love life and how he moved around from university to university.

但爱因斯坦最了不起的地方在于他的理论。

But the really great thing about Einstein is his theories.

爱因斯坦是一个绝佳的例子，让我们看到科学是如何运作的——科学家提出预测，说明他们的理论如何预测自然界的运行方式。

So Einstein is one of these great examples where you can see science at work, where a scientist makes these predictions about how his or her theories predict the way that nature seems to work.

爱因斯坦正是这样一个绝佳的例子，他不断提出预测、进行实验、再提出预测、再进行实验。

And Einstein is one of these wonderful examples where you've got just prediction, experiment, prediction, experiment.

所以我们想谈谈他所做的各种实验。

And so what we wanted to do was talk about the different kinds of experiments that he did.

我们有针对狭义相对论和广义相对论的实验。

We've got the ones for special relativity and general relativity.

在每一个实验中，他说，如果你去检查一下，你应该会看到那样的结果。

And in each one of these experiments, you know, they he said, if you go and check out this, you should probably see that.

实验人员走出去做了实验，发现了他所预测的现象，一切都非常顺利。

And the experimenters went out and did and found what he predicted and everything worked out great.

让我们来谈谈，先从狭义相对论开始吧，因为那是他最初的起点。

So let's talk about, let's start with special relativity because that was sort of the first It's where he started.

但他立刻用一堆疯狂的想法颠覆了整个物理学，并做出了具体的预测。

And but he right away upset all of physics with a bunch of crazy ideas, but made some concrete predictions.

这正是关键的区别：当那些玄学怪人声称爱因斯坦错了时，他们并没有提供任何关于为什么他错了、或者我们应该看到什么替代现象的预测。

And this is the big difference that when the woo woo crackpots send in their theories, they're like Einstein was wrong, they don't actually include the predictions that they make about why he was wrong or what we should see instead.

你必须解释所有已经观测到的现象。

You have to you have to explain everything that's already been seen.

此外，你还需要做出一些新的预测，以展示不同之处或解释某些未知的现象。

Plus, you have to make some new predictions about to show what's different or explain something that is unknown.

我话说太多了，帕梅拉。

I'm talking too much, Pamela.

好的。

Okay.

所以最好的起点是光速，因为爱因斯坦所做的一切都基于光速在所有方向上对所有观察者都相同的这一基本观点。

So so the the best place to start is with the speed of light because everything that Einstein did sort of hung off of the basic idea that the speed of light is the same for all observers in all directions.

证明这一点最简单的方法是使用某种光源，这样你就能察觉到任何变化。

And the easiest way to prove that is to take some sort of a light source that you'll be able to tell if something changed.

所以一个好的相干光源，比如激光束，或者经过适当透镜组处理后变得相干的光，都算在内。

So a good coherent light source, something like a laser beam, something that's been made coherent by passing through, the right set of lenses, all of those things count.

取一个相干光源并将其分束。

So take a coherent light source and split it.

你可以用半镀银镜来实现，这样一半的光被反射，另一半光则穿透过去。

You can do this with a semi silvered mirror so that half the light gets reflected and half the light passes through.

这就是单面镜的工作原理。

This is how those one way mirrors work.

如果你恰当地将光束分开，可以让一部分光朝着地球运动的方向传播，另一部分光垂直于该方向传播，然后再将光重新合并。

Now if you split the light just right, you can have some of the light go off in the direction of say the Earth's motion, some of the light go off perpendicular to that, and then you recombine the light.

如果光在两个方向上本应传播的距离相同，而你测量发现，即使地球在运动，光在两个方向上的传播时间也相同。

And if the distances that the light should have traveled if we weren't moving are the same in both directions, And you measure that the light took the same type of travel in both directions even though the earth is moving.

这表明，光速是恒定的，无论进行测量的人或发射光的人是否在运动。

Well, starts to show that while the speed of light is constant irregardless of the motion of the person who's doing the measuring and doing the light sending off into space as well.

对。

Right.

你能给我举个例子吗？

So can you give me then an example?

所以他预测，无论光从哪里发出，它的速度都是一样的？

So he made the prediction that light should move at the same speed no matter where it's coming from?

对。

Right.

因此，这类首个实验是迈克尔逊-莫雷实验，它早于爱因斯坦的时代。

So the first experiment of its kind was the Michelson Morley experiment, which predates Einstein.

但随后爱因斯坦指出：看，这就是它发生的原因。

But then Einstein went on to to basically say, look, here's why it's going on.

实际上，并不存在以太。

Really, there's no ether.

自那以后的所有实验一再证明，光速对所有观察者而言都是相同的。

And every experiment that's been done since then shows over and over and over, speed of light is the same for all observers.

对。

Right.

于是他们做了这个实验。

And so they did this experiment.

他们让光通过一个镜子，光被分成了两束，即使一组随地球运动方向移动，另一组逆着地球运动方向移动，光速对两组人来说却是一样的。

They shone this light through a mirror, it split up, and the speed of light was the same for both people even though one group was moving one way around the Earth, I guess with the motion of the Earth and the other group was moving against the motion of the Earth.

对，通常你会发射两束光，一束沿着运动方向，一束垂直于运动方向，然后再将它们重新合并。

Right, so what you usually do is you shoot two beams, one in the direction of motion, one perpendicular to the direction of motion, recombine them.

如果光波叠加后以正确的方式产生漂亮的干涉条纹，你就知道一切正常。

If the light combines and you get pretty little interference fringes in the right way, you know everything is good.

狭义相对论的下一个推论是，既然光速对所有人来说都一样，那么时间就不是了。

Now the next thing that came out of special relativity is well since the speed of light is the same for everyone, time is not.

因此，我们必须进行各种实验，比如发射原子钟、让钟表绕地球飞行，做各种疯狂的事情，来证明时间确实会发生变化。

So this is where we've had to do experiments along the lines of launching atomic clocks, of flying clocks around the planet, of all sorts of crazy things to show that, well, time does change.

对。

Right.

所以他预测，如果光速必须保持不变，那么必须让步的就是时间。

So he made the prediction then that if light has to stay the same speed, then the thing that has to give is gonna be time.

所以如果你移动得更快，你所经历的时间就会与一个相对于你移动较慢的人不同。

So if you're moving faster, then you're going to experience time differently than a person who is moving slower compared to to each other.

因此，他们进行的实验是将这些原子钟搭载在飞机上，后来又搭载在航天器上，对吧？

And so the experiment that they ran was they had to fly these atomic clocks in airplanes and later on spacecraft, right?

对。

Right.

果然，两个时钟之间的差异完全符合预测。

And sure enough, the differences between the two clocks was exactly what was predicted.

所以，是的，时间的流逝速度会发生变化，尽管光速保持不变。

So yeah, we have the speed of time changes even though the speed of light does not.

好的，这就是第二个预测。

Okay, so that's prediction number two.

还有其他的吗？

Were there any more?

那么，我们还面临着相对论中的质量和能量问题。

Well, so then we also have the whole relativistic mass and energy problem.

这就是 E=mc² 的概念。

So this is the idea that E equals MC squared.

虽然这并不是狭义相对论原始论文的一部分，但质量和能量统一的思想始于狭义相对论，并随着他不断完善理论而发展起来。

Now that wasn't part of the original special relativity paper, but the idea that mass and energy come together started with special relativity and evolved as he detailed out the theory.

因此，我们有了像回旋加速器这样的装置，它们将粒子加速到极高的速度，然后使它们相互碰撞。

And so here we have things like cyclotrons that accelerate particles to extremely high velocities and then collide them together.

当这些碰撞发生时，你会在很小的空间内看到能量爆发，这些能量会迅速凝结成粒子。

Now, when these collisions happen you end up with a burst of energy concentrated in a small place and that energy very quickly condenses into particles.

这种过程的巧妙之处在于，所有产生的粒子都具有特定的质量。

Now the neat thing about the way this happens is the particles all have a given amount of mass.

当你把所有粒子的质量加总起来时，这个总质量大于入射粒子的静止质量。

When you add up all of the mass particles, that mass is greater than the rest mass of the particles that went in.

因此，你可能将几个电子或质子以接近光速的速度在回旋加速器中不断加速、碰撞，而产生的粒子总质量会超过一个静止质子和一个静止电子的质量之和。

So you might fling a couple of electrons or a couple of protons at close to the speed of light in circles and circles and circles around the cyclotron, collide them together, and the array of particles that come out weigh more than a proton at rest and electron at rest.

当你试图弄清楚这些额外的质量是从哪里来的时。

And when you try and figure out, well, where did all of that mass come from?

你必须考虑粒子在接近光速运动过程中积累的动能。

And you take into account the kinetic energy that was built up during the motion at close to the speed of light.

这种动能并不像在非相对论情况下那样是二分之一mv平方的形式。

The kinetic energy isn't a function of one half m v squared like it would be if relativity didn't exist.

相反，存在相对论效应，会使粒子在速度越来越接近光速时质量增加。

But rather there's relativistic effects that increase the mass as the particle starts going closer and closer to the speed of light.

因此，我们看到了由于速度引起的相对论性质量增加。

So we see the relativistic increase in mass due to the speed.

我们在碰撞产生的这些粒子中看到了 E=mc²。

We see the e equals m c squared all in these particles that come out of the collision.

这太酷了。

That's really cool.

所以你是在回旋加速器中从外部注入能量，而这些能量在碰撞中转化为质量。

So you it's in the cyclotron that you are you're injecting energy from outside and that energy is turning into mass in the collision.

是的。

Yes.

太神奇了。

That's amazing.

嗯。

Yeah.

所以他做出了这个预测。

And so he had made this prediction.

我不知道，他预测过吗？

I don't know, did he predict?

比如，他只是说，当你建造粒子加速器时，如果让它们相撞

Like he just say like when you build particle accelerators, if you It's crash them always

那样的话。

that way.

对他来说，关键是如果你取任何质量，将其加速到越来越接近光速，你会看到物体的表观质量增加，即物体的相对论质量增加。

For him, was a matter of if you take a mass, any mass, and you accelerate it closer and closer to the speed of light, what you're going to see is the apparent mass of the object increases, the relativistic mass of the object increases.

所以当我们开始实际使用回旋加速器将物体加速到接近光速时，我们就看到了这一点。

So then we saw that when we started actually using cyclotrons to accelerate things to close to the speed of light.

这真的很酷。

That's really cool.

好的。

Okay.

所以为了澄清一下，我们有三个。

So just to clarify them, so we've got three.

还有其他的吗？

Were there any more?

抱歉，我之前问的是，还有其他的吗？

Sorry, before I Were there any more?

所以我们有时间收缩，还有质能等价。

So we had time contraction, we had mass energy equivalence.

光速不变。

Speed of light being the same.

还有光速。

And the speed of light.

所以这些是狭义相对论的关键点。

So those are really the key things for special relativity.

这些是我们需要应对的主要因素。

Those are the big factors that we needed to deal with.

好的，这总结了他对狭义相对论所做的预测。

Okay, so that wraps up the predictions that he made for special relativity.

但真正让他震惊全世界的，是他最伟大的理论——广义相对论。

But then really, his greatest theory, the one that blew everyone's minds was general relativity.

这正是我在节目开头提到的，他通过广义相对论做出了一些预测，而天文学家直到最近五年才具备能力去验证这些预测。

And this is what I said at the beginning of the show that he made some predictions with general relativity that astronomers haven't had the capability to test until just within the last five years.

这太疯狂了。

It's crazy.

我们还在努力，让所有人都真正接受并认同这些理论，就像说：‘是的，是的，是的。’

We're still working at getting things totally at the level where everyone's like, Yeah, yeah, yeah.

好吧，你证明了。

Okay, you proved it.

我认为它仍然是正确的。

I'd say it was still right.

好的，让我们来梳理一下他做出的一些预测，并按实验验证它们为真的时间顺序排列。

Okay, so let's run through some of the predictions that he made and try to put them in order of when they were able to do experiments to prove that they were true with general relativity.

在某种程度上，最简单的一个是水星近日点的进动。

The easiest one in some ways was the perihelion precession of Mercury.

什么？

What?

那么什么是

So what was

发生了什么？

going on?

那里有很多花哨的术语。

Lots of fancy words there.

花哨的天文学术语。

Fancy astronomy words.

水星发生了什么？

What was going on with Mercury?

对于任何绕行物体，根据开普勒和后来的牛顿理论，轨道是椭圆，也就是被压扁的圆，其中包含两个完美的圆，椭圆的焦点就在那里，搜索一下‘椭圆’，你就明白我的意思了。

So with any orbiting object, according to Kepler and later Newton, orbits are ellipses, flattened circles, two perfect circles somewhere in there, that have at the foci of the ellipse, Google ellipse, you'll see what I mean.

你有恒星、行星，或者任何被绕行的天体，而近日点就是最接近太阳的点。

You have the star, the planet, whatever is being orbited, and the perihelion is the point of closest approach to the Sun.

当水星围绕太阳沿椭圆轨道运行时，它有一个最近点，也有一个最远点。

So as Mercury goes around on its elliptical orbit around the Sun, It has a closest approach, it has a furthest approach.

如果你把太阳系中其他所有东西都抹去，只剩下太阳，且太阳是一个完美的圆形，那么水星的轨道将永远保持完全相同的取向。

Now, if you were to erase everything else from the solar system, so you have no other planets, if you were to make the sun a perfect circle, then Mercury's orbit would just happily be exactly the same orientation for all of time.

但实际上，太阳并不是完美的圆形，它在赤道处略微扁平，专业术语叫‘扁球体’。

Now the truth is sun's not a perfect circle, it's a bit squished around the middle, it's oblate is the fancy word.

这种扁球体形状会对轨道产生一些影响，使轨道随时间缓慢变化。

And so that oblateness causes some effects on the orbit, makes the orbit slowly change over time.

事实上，我们还有另外七颗行星，以及其他众多岩石和冰质天体。

Fact is we do have seven other planets that are a bunch of other rocks and icy bodies.

随着时间推移，这些岩石、冰质天体以及其他行星主要会对水星产生影响。

And over time, those rocks and icy bodies and other planets for the most part have effects on Mercury.

但当你把所有这些其他影响加总起来，再观察水星的轨道时，会发现水星距离太阳最近的点仍在以一种无法被其他效应完全解释的方式缓慢移动。

But when you add up all these other effects, and you look at Mercury's orbit, Mercury's point of closest approach to the Sun is slowly moving over time in a way that all those other effects can't take account of.

它的进动速度就像一个旋转的陀螺，比预期的还要快。

It's precessing like the top of a spinning top at a rate that's faster than would be expected.

当爱因斯坦将引力纳入他的相对论理论时，他发现这种进动是被预测到的。

And when Einstein integrated gravity into his theory of relativity, he found that precession was predicted.

关键是，他实际上能够预测出进动的具体数值，其精确度甚至超过了当时人们的测量水平。

And the thing was, is he could actually predict how much the precession would be at a level that was greater accuracy than they had really done in their measurements at that point.

果然，随着我们获得越来越精确的测量数据，我们发现：哇，他完全猜对了。

Sure enough, as we've gotten more and more accurate measurements, we're able to find, wow, he nailed it.

他准确无误地告诉我们，在任何时刻，水星围绕太阳运行时其位置究竟在哪里。

He was exactly right in being able to tell us where we can find Mercury at any given moment as it process around the Sun.

这正是一个完美的理论：你拿出了天文学家几十年来苦苦思索的问题，通过数学和理论推导，然后说：‘如果你运行我的计算，就能解释你们所观察到的现象。’

And that is really just the perfect theory that you take something that astronomers have been puzzling about for decades and come up with the math and the theory and go, Oh, if you run my math, this will explain what you're looking for.

而这还只是刚刚起步。

And that's just getting out of the gate.

这不过是热身而已，接下来我要解释一大堆摆在你们面前的未解之谜。

That's to warm up the engines, I'm going to explain a bunch of the unsolved mysteries that you've got in front of you.

现在，我要提出一些你们根本没想到的、关于宇宙的疯狂预测。

And now, here's a bunch of crazy predictions that didn't even occur to you that I'm about to make about the Universe.

欢迎去验证这些预测是否也成立。

Feel free to go out and prove that those are true too.

这太棒了。

That's fantastic.

所以水星的进动，完美吻合。

So that precession of Mercury, perfect.

那么，什么是

So what was Well,

与水星进动相关的物理原理，同样适用于水星绕太阳运行，也适用于双星系统和双脉冲星系统。

the thing that went in with the precession of Mercury is the exact same physics that applies to Mercury going around the sun, applies to binary stars, applies to binary pulsar systems.

随着我们长期观测更高质量的致密天体，这种现象以惊人的形式显现出来。

And we're seeing this in dramatic ways as we look at higher mass compact objects over time.

我们观测到一颗脉冲星，它的进动速度达到每年4.2度。

So there's a a pulsar that we see actually its precession is 4.2 degrees per year.

这就像高密度天体的高速进动。

So this is like high speed precession with high mass objects.

接下来，他提出的另一个重要证据是引力质量物体对光线的偏折。

Now, the the next big thing of evidence that he came up with was the defect deflection of light by gravitationally massive objects.

所以恒星光在太阳周围发生弯曲。

So starlight getting bent around the sun.

我必须承认，我和许多其他人曾错误地认为，爱丁顿在1919年日食期间观测并证实了这一点。

And, I have to admit, I and many other people are guilty of saying, and Eddington went out and showed this when he looked at the nineteen nineteen solar eclipse.

是的，爱丁顿确实观测到了光线的弯曲。

And yeah, Eddington did see light bending.

但问题是，自那以后，人们一直争论这是否足以构成确凿证据，因为甚至牛顿也预测光会发生弯曲。

But the the thing is people have argued over whether or not that's sufficient evidence ever since because, well, even even Newton predicted that light would bend.

关键在于弯曲的幅度。

It's the amount that it would bend.

当你审视爱丁顿测量数据的误差时，结果并不完全具有决定性。

And when you look at the errors in Eddington's measurements, it's just not quite entirely conclusive.

因此，人们至今仍在质疑：这一证据是否完全确凿？

And so people are still This is the one piece of evidence that people are still going, okay, is it fully conclusive?

我们观察像爱因斯坦环这样的现象，但并不精确知道其质量。

And we look at things like Einstein rings where we don't know the masses precisely.

但我们正开始达到前所未有的精度，不是通过观测恒星的光学光线，而是通过射电天文学观测背景类星体，从而获得高度精确的测量数据。

But we're starting to get as precise as you could hope for, not by looking at the optical light of starlight, but rather by looking at background quasars using radio astronomy to get highly precise measurements.

借助我们最精密的射电望远镜，我们终于能够说，误差范围已经小到足以确认：大质量物体对光线的偏折确实 conclusively 证明了爱因斯坦是正确的。

And with our most sophisticated radio telescopes, we're just starting to be able to say the error bars are small enough that yes, the amount of deflection of light by massive objects does conclusively say Einstein was right.

没错，这个理论认为，我们不应该把引力看作是具有质量的物体之间的某种吸引力，而应该将其视为宇宙本身结构的弯曲，实际上，这是时空中的一个凹陷，因此，无论是大质量物体还是能量，都会沿着这些大质量物体造成的时空弯曲路径运动。

Right, and so this was this theory, right, that he said that we should look at gravity not as some kind of attractive force between objects with mass, that we should see it as a bending of the very fabric of the universe that in fact it's this depression in the space time, and so both massive objects and energy will follow the the bended curves in the space time caused by these massive objects.

我们观测到的光线弯曲与这一预测完全吻合。

This bending of the light that we see matches this prediction exactly.

正如你所说，人们仍在以越来越高的精度对其进行检验。

And as you said, they're still testing it out to higher and higher degrees of accuracy.

为什么要用一颗围绕太阳运行的恒星呢？

Why use a star going around the Sun?

让我们使用一个已经旅行了120亿年的遥远类星体。

Let's use a distant quasar that's been traveling for twelve billion years.

通过无线电波，我们也可以获得更精确的测量结果。

Well, can also just get more precise measurements that way because of the radio light.

使用雷达更容易。

It's just easier to use radar.

用无线电波更好。

Radio rather.

类星体是不动的。

And quasars aren't moving.

恒星的问题在于，它们和我们一样围绕同一星系运行。

The problem with stars is they're orbiting the same galaxy we're orbiting.

因此，背景中的类星体是天空中运动最少的天体。

And so it's the quasars in the background, they're the most non moving things in the sky.

对。

Right.

好的。

Okay.

酷。

Cool.

酷。

Cool.

那么下一个。

So next.

引力红移。

Gravitational redshift.

引力红移。

Gravitational redshift.

那这是什么？

So what is that?

这个概念是，光在逃离引力阱时。

This is the idea that light as it climbs out of a gravity well.

光在垂直于地球、黑洞、白矮星或任何有引力的天体表面传播时，会因爬升而损失能量。

Light as it shines perpendicular to the surface of the earth, of a black hole, of a white dwarf, of anything with gravity will lose energy as it climbs.

所以它以光速上升。

So it climbs at the speed of light.

光对所有观察者来说都以光速传播，但没人说过它在过程中不会改变颜色。

Light travels at the speed of light for all observers, but no one ever said it wasn't gonna change colors in the process.

因此，阳光照射到地球时会发生蓝移，而阳光从太阳的引力井中上升时则会发生红移。

So sunlight as it falls to Earth gets blue shifted, and sunlight as it climbs out of the Sun's gravity well gets red shifted.

这听起来不错，但实际测量起来相当困难。

And that's all well and good, but it's kinda hard to measure.

所以关键的实验实际上是在哈佛大学进行的，实验地点至今仍然存在。

So the key experiment was actually done at Harvard, and the place where it was done still exists.

如果你带着合适的人在哈佛物理系里逛，他们会指给你看。

And if you go wandering the Harvard Physics Department with the right person in hand, they'll point it out to you.

那里有一座塔，他们在那里向上发射了伽马射线能量。

There there's a tower there where they shined or more or less emitted gamma ray energy up the tower.

他们测量了这种光因克服地球引力井而产生的微小颜色变化。

And they measured the slight change in color of that light that was a result of climbing up the Earth's gravity well.

这很有趣的一点是，光从黑洞逃逸时遇到的问题不仅是速度不够，而且实际上会被红移到彻底消失。

And this is something that, What's neat about it is one of the problems with light getting off of a black hole is it not only can't go fast enough, but it actually gets red shifted into oblivion.

对。

Right.

所以你可以想象，天文学家已经以各种方式验证了这一点。

And so you can imagine now astronomers have demonstrated this in all kinds of different ways.

他们通过来自不同类星体、行星、恒星、中子星以及各种辐射的光来验证这一点。

Mean, they demonstrate it from light coming from different quasars, light coming from planets, from stars, from neutron stars, and all the different kinds of radiation.

他们一次又一次地做出了这些预测。

They're able to make these predictions again and again and again.

太棒了。

It's awesome.

所以这是一个很好的例子。

So that's a good one.

是的。

Yeah.

所以我们观察到的高质量天体越多，就越能确认这种现象确实在宇宙中发生。

So the more high mass objects we look at, the more we're able to see that this is really going on out there.

太酷了。

Really cool.

好的，到目前为止是三个吗？

Okay, so that's three so far?

还有人吗？

Anyone?

说吧。

Hit me.

接下来是参考系拖曳，这是我最喜欢的一个。

Then we have frame dragging, which is one of my favorite ones.

这个观点认为，一个旋转的天体会带动周围的时空一起旋转，而你围绕天体运动时，时间的流逝和能量的变化会因方向不同而产生可测量的差异。

So this is the idea that a rotating body actually rotates the space time continuum around it, and that the way time passes, the way your energy changes depending on which direction you're going around an object is measurable in terms of there's differences depending on the direction you go in.

所以引力探测器B号最终证实了参考系拖曳确实存在。

So the gravity probe b is is actually the way we finally said, yes, there is frame dragging.

之前已经有过一些实验。

There there had been earlier experiments.

我们发射了LEGOS卫星，试图用它来测量这一现象，但结果并不完全确定。

We launched the LEGOs satellite looking to try and measure it using that wasn't entirely conclusive.

我们从火星全球探勘者号环绕火星时的数据中也看到过一些证据。

We'd we'd seen some evidence from the Mars Global Surveyor as it orbited Mars.

但直到我们发射了引力探测器B，它配备了极其精密的陀螺仪球体，我们才最终通过观察这些旋转的陀螺球随时间发生的变化，确认了这些变化正是框架拖拽所预测的那样。

But it was finally when we launched Gravity Probe B with its extremely precisely made balls in its gyroscope that we were able to by looking at how over time those spinning gyroscopic balls changed, we're able to see yes, the changes are what was predicted by frame dragging.

这只是我们在测量事物时必须考虑的众多奇妙现象之一。

This is just one of those awesome things that we have to take into account when we measure things.

他们实际上是相对于飞马座的α星进行测量的。

They actually did it relative to the star I am Pegasus.

他们测量了陀螺仪相对于一颗恒星的对齐情况，而这种效应会随着时间累积。

They measured the alignment of the gyroscopes relative to a star, and, it builds up over time.

因此，他们观察到的变化在实验期间累计达到了37毫角秒。

So what they were able to see was a change that added up to thirty seven milliarcseconds over the period of the experiment.

所以为了正确理解这一点，你们把卫星发射到太空中，让这些陀螺仪旋转起来，使其与这颗恒星完美对齐，然后航天器围绕地球运行，如果不存在帧拖曳效应，那么即使经过一百万年，这些陀螺仪仍然会与这颗恒星保持完美对齐。

So just to understand this correctly, you've got the satellite, you launch it into space, you spin up these gyroscopes so that they are perfectly aligned with this star, and then you have the spacecraft going around the Earth in such a way that if there was no such thing as frame dragging, then you could go a million years, and these these gyros would still be perfectly lined up with this star.

但事实上，由于引力探测器B号航天器在地球引力场中运动，而地球本身也在自转，因此你会因为地球引力对时空的扭曲而产生这种方向上的变化。

But instead, because the Gravity Pro b spacecraft is moving through the Earth's, gravity field and the Earth is turning, you get this this change in the orientation that comes purely from the way the Earth's gravity is warping space time.

我理解得对吗？

Did I get that right?

对。

Yeah.

但这并不是说旋转轴的极点与恒星对齐。

Now, it's not that you have the pole of the rotation lined up with the star.

你们是在观察物体相对于恒星的运动变化。

You're looking at how the motion of the objects change relative to the star.

对，没错。

Right, right.

但确实，我们随着时间的推移观察到了这些差异，这真的很酷。

But yeah, we actually see these differences over time and it's really kind of cool.

这真的挺酷的。

That is really kind of cool.

所以那是四个吗？

So was that four?

我觉得还有更多。

I think there's more.

还有引力波。

Well, also have gravitational waves.

引力波，对。

Gravitational waves, right.

我们已经做过关于这个的完整节目了。

We've done whole shows on this.

引力波就是指，大质量物体在太空中运动时，会向外辐射出使时空本身拉伸和收缩的波。

Gravitational waves, this is the idea that massive objects as they move through space should actually send out waves that stretch and contract space time itself as they emanate out from the object.

物体质量越大，事件越剧烈，我们应能探测到的引力波就越强。

And the more massive the object, the more violent the events, the bigger the gravitational waves that we should detect.

所以他做出了这个预测，但我们仍然不能完全确定

So he made this prediction and we still aren't entirely sure

它们真的存在，对吧？

that they're there, right?

所以这正是那种我们已经为此颁发了诺贝尔奖的发现。

So this is one of those things where we've actually given a Nobel Prize out for this one.

所以这

So It's

总归是算数的。

gotta count for something.

我们所观察到的是，回到牛顿物理的观点：两个物体相互绕行，如果没有摩擦力、外力或质量转移，它们将永远以相同的距离持续绕行。

What what we've seen is, again, you go back to the idea that given Newtonian physics, you have two objects orbiting each other, they will continue to orbit each other forever at the same distance, assuming there's frictional effects, no external forces, no mass transfer.

所以，两个没有相互作用、不受外力影响的物体彼此绕行，会一直这样持续下去。

So you have two non interacting objects with no external forces orbiting one another and they will happily just keep doing that.

但现实是，当我们观察高质量物体相互绕行时，比如双脉冲星、白矮星-黑洞系统，任何白矮星、中子星、黑洞的组合，我们都会发现它们的轨道正在发生变化。

Now the reality is that when we look at high mass objects orbiting each other, when we look at pairs of pulsars, when we look at white dwarf black hole systems, any combination of white dwarf neutron star black hole, we start to see their orbits are changing.

它们的轨道正在逐渐靠近。

Their orbits are getting closer.

它们随着时间推移在衰减。

They're decaying over time.

这并不是由于外力、摩擦或质量转移造成的。

And it's not due to an external force, it's not due to friction, it's not due to mass transfer.

这是由于引力波辐射带走能量所致。

It's due to energy being radiated away from gravitational waves.

然而，我们尚未探测到这些波在空间中传播。

Now, what we haven't detected yet is those waves propagating through space.

我们已经观测到它们释放的能量，但更令人期待的现实是，当引力波在空间中传播时，它们应该会沿着传播方向，使物体暂时地相互靠近又远离。

We've seen the energy they give off, but the much sought reality is as those gravitational waves propagate through space, they should actually, in the direction they are propagating, cause objects to temporarily get closer and further apart.

而正是在这里，人们建造了相应的设备。

And this is where devices have been built.

地球上有多个激光干涉仪，被设置成巨大的三角形结构，我们预期在这些干涉仪中会观测到距离先缩短再拉长的现象。

There's several laser interferometers on the planet Earth that, have been set up in giant triangles where we'd expect that you'd see at one set of these interferometers, the distance getting closer and then further.

然后，在光速传播这段距离所需的时间后，我们会在另一个探测器上看到同样的现象。

And then at a speed of light traveling that distance time later, we'd see the same thing at one of the other detectors.

但我们至今尚未观测到。

And we just haven't seen it yet.

部分原因在于，像UPS卡车这样的东西也会被探测到。

And partially this is because, well, things like the UPS truck can get detected as well.

因此存在大量的背景噪声。

So there's a lot of background noise.

对。

Right.

对。

Right.

但我认为，地面方法，我的意思是，人们早就知道用地面方法探测这种现象并不理想。

But I think the that the ground I mean, I think people have known that a ground based method of detecting this is is not great.

正确的方法是发射航天器，让它们持续追踪彼此之间的距离，这样我们就能以更高的精度进行测量。

The way to do it is to launch spacecraft and have them keep track of their distance to each other, then we'll know with a higher degree of accuracy.

你得等待附近发生巨大而剧烈的事件，但这样的事件可能不够多，因此你仍然没有机会进行探测。

And you're kind of waiting for great big violent events to happen nearby, and so you might not get enough of them, and so again, you just don't get a chance at detection.

这归根结底取决于实验的质量。

So this comes down to really the quality of the experiment.

我们仍在等待资金和批准，以便发射真正能实现这一探测的航天器。

And we're still waiting for the funding and for approval for people to launch the spacecraft that will actually make this detection.

那这就是全部了吗？

And will that be it?

这会是爱因斯坦提出的最后一个需要实验验证的预言吗？

Will that be the final prediction made by Einstein to be experimentally tested?

人们真正期待的最后一个就是引力波。

That's really the last one that people are really waiting for is gravitational waves.

LISA任务目前在NASA那里处于一种‘半死不活’的状态，既没有被完全取消，也没有获得实际建造的资金。

And Lisa is the mission that is currently somewhat undead with NASA, neither completely canceled nor actually funded to be built.

它由三艘航天器组成，彼此之间发射激光以测量间距，从而探测经过时由引力波引起的距离变化。

It's a set of three spacecraft that, shoot lasers between one another to measure their separation and look for that change in distance that comes from a gravitational wave passing over them.

所以希望我们能实现。

So hopefully we'll get there.

不过有个问题，你说能量会丢失。

So one question though, you said that the energy gets lost.

它丢失到哪里去了？

Where does it get lost to?

嗯，实际上是系统失去了能量。

Well, gets ready it gets gets lost from the system.

可以这样理解：蜡烛燃烧时，会将其化学势能以红外辐射的形式传递给周围的空气分子。

So the way to think of it is as a candle burns, it gives up its, chemical potential energy to the room around it in the form of transfer of infrared radiation to the air molecules around it.

所以蜡烛正在将能量释放到房间中。

So the candle's losing the energy to the room.

在双星系统中，它们释放引力能，并通过空间辐射出去，这种能量在传播过程中会改变物体之间的距离。

In the case of binary star systems, they're giving up their gravitational energy and radiating it through space, and that energy is radiating away and nominally changing the distance between things as it goes.

对。

Right.

在整个宇宙中。

Across the whole universe.

所以宇宙是守恒能量的，但恒星系统不是。

So the universe is conserving energy, but the star system isn't.

这太酷了。

That's really cool.

好的。

Alright.

所以下次如果有人告诉你他们认为爱因斯坦错了，你就伸出八根手指，让他们逐一解释爱因斯坦提出的三个狭义相对论预测和五个广义相对论预测，并让他们说明他们的替代理论如何也能解释爱因斯坦的所有这些预测，还能做出进一步的预测。

So so next time someone tells you that they believe that Einstein was wrong, hold up eight fingers and have them run through the three special relativity and the five general relativity predictions that Einstein made and have them explain how their alternative theory gives also explains all those predictions that Einstein made and then makes further predictions.

并且拿走他们的GPS设备，因为如果他们不相信相对论，他们就不相信GPS。

And take away their GPS unit because if they don't believe in relativity, they don't believe in GPS.

对。

Right.

但这就是他们必须证明的证据水平。

So but that is the level of of proof that they have to demonstrate.

太棒了，帕梅拉。

So that was great, Pamela.

非常感谢，我们下周再聊。

Thank you very much, and we'll talk to you next week.

听起来很棒，弗雷泽。

Sounds great, Fraser.

回头见。

Talk to you

再见。

later.

再见。

Bye.

这是《天文小知识》，一档每周带你探索宇宙的基于事实的节目。

This has been Astronomy Cast, a weekly facts based journey through the cosmos.

每期节目的节目单和文字稿均可在我们的网站上获取。

Show notes and transcripts for every episode are available on our website.

请访问 astronomycast.com 查看。

Check it out at astronomycast.com.

您可以将任何评论、问题或反馈发送至 info@astronomycast.com。

You can send us any comments, questions, or feedback to info@astronomycast.com.

我们会阅读每一封邮件。

We read every email.

本节目是由弗雷泽·凯恩和帕梅拉·盖伊博士提供的非营利性教育资源。

The show is a nonprofit educational resource provided by Fraser Cain and doctor Pamela Gay.

我们依靠像您这样的听众的慷慨捐赠来维持运营。

We're supported through the kind donations of listeners like you.

如果您喜欢《天文广播》，为什么不给我们捐一点呢？

If you enjoy astronomy cast, why not give us a donation?

这有助于我们支付带宽、字幕和节目笔记的费用。

It helps us pay for bandwidth, transcripts, and show notes.

只需点击网站上的捐赠链接即可。

Just click the donate link on the website.

所有捐赠对美国纳税人来说都是免税的。

All donations are tax deductible for US taxpayers.

你也可以免费支持本节目。

You can support the show for free too.

写一篇评论或向你的朋友推荐。

Write a review or recommend it to your friends.

每一份帮助都很重要。

Every little bit helps.

点击我们网站上的“支持本节目”以查看一些建议。

Click support the show on our website to see some suggestions.

要订阅本节目，请将你的播客软件指向 astronomycast.com/podcast.xml，或直接从 iTunes 订阅。

To subscribe to the show, point your pod catching software at astronomycast.com/podcast.xml or subscribe directly from iTunes.

音乐由特拉维斯·西尔提供。

Music is provided by Travis Searle.

本节目由普雷斯顿·吉布森剪辑。

The show was edited by Preston Gibson.