--- author: Veritasium date: '2026-10-23' guest: '' layout: post.njk source: https://www.youtube.com/watch?v=eyZEqSPeMwg speaker: Veritasium tags: - general-relativity - quantum-mechanics - atomic-clock - time-dilation - optical-frequency-comb title: 颠覆引力理论的高精度实验：光晶格钟与广义相对论的极限测试 summary: 科学家在科罗拉多州博尔德与4000米高山天文台之间部署超高精度镱光晶格钟，通过自由空间激光链路与光学频率梳测量重力引起的时间膨胀，试图在18位有效数字精度下寻找广义相对论与量子力学冲突的破缺信号。 insight: '' draft: true series: '' category: science area: knowledge-meta project: [] people: [] companies_orgs: - NIST products_models: [] media_books: [] status: evergreen --- ### 引力与时间膨胀的终极测试 这可能是我见过的最雄心勃勃、极具挑战的高精度实验。科学家们在科罗拉多州博尔德放置了一台原子钟，并在海拔4000米的一处天文台上放置了另一台，他们试图测量广义相对论所预言的时间膨胀差异。因为在山顶这里，相对于博尔德地面，时间本身的流逝应当更快。
Original English - This might be the most ambitious long shot precision experiment that I've ever seen. Scientists have put one atomic clock down in Boulder, Colorado, and one up in this observatory 4,000 meters above sea level, and they're going to try and measure the difference in time dilation according to general relativity. Because up here, time itself should be passing faster relative to down in Boulder.
如果你走进科技馆，他们通常会把引力解释为时空的弯曲，摆出一个小漏斗，粒子绕着漏斗打转，以此让你直观感受地球为什么绕着太阳转。但这并不是实际发生的情况。与其说是空间在弯曲，不如说是时间在拉伸。因此，我们体验到的引力主导效应，实际上是当我们靠近大质量物体时时间的减慢。
Original English - If you go into a science center, often they will explain gravity as the bending of space time, and what they will have is a little funnel where the particle goes around the funnel, and that's meant to give you an impression of why the earth goes around the sun. But that's not actually what happens. It's not as much that space is curving, it's that time is stretching. So the dominant effect of gravity that we experience is the slowing down of time as we get closer to a massive object.
这是爱因斯坦广义相对论的预言之一，它甚至准确预言了高山上的时钟应该走快多少。将一台时钟放在博尔德，另一台放在高出2.7公里的地方，山上的时钟每天应该会快大约250亿分之一秒。广义相对论和时间膨胀的这种效应在实验中已经被一次又一次地证实。那我们为什么还要继续测试它？因为我们知道，在某种量子尺度下，这种引力理论将不再适用。
Original English - This is one of the predictions of Einstein's general theory of relativity, and it actually predicts how much faster the mountain clock should be ticking. Put one clock in Boulder and another 2.7 kilometers higher, and the mountain clock should gain about 25 billionths of a second every day. This effect of general relativity and time dilation has been proven in experiments time and time again. So why are we still testing it? Because we know that at some quantum scale, this theory of gravity is going to stop working.
我们之所以知道存在某种矛盾，是因为我们知道粒子可以处于这里与那里的两处叠加态。这就是量子力学告诉我们的。而爱因斯坦的广义相对论告诉我们的是，如果粒子在这里，它会以某种方式弯曲时空；如果它在那里，它又会以另一种方式弯曲时空。
Original English - The way we know there is some contradiction is that we know that particles can be in the superposition of two places here and there. That's what quantum mechanics tells us. And what Einstein's theory of general relativity tells us is that if a particle is here, it bends space time in a certain way. And if it's there, it bends space time in a certain way.
那么，如果一个有质量的粒子同时处于两个位置，时空会发生什么？
Original English - So what happens to spacetime if a particle with mass is in two places at once?
我们对这个问题没有答案。对于粒子处于叠加态时时空会发生什么，爱因斯坦的广义相对论保持了沉默。
Original English - We don't have an answer to that question. Einstein's theory of general relativity is silent on the question of what happens to spacetime when a particle is in superposition.
这给我们留下了物理学中最大的未解之谜之一：引力本身是否遵循量子力学规律？因此，世界各地的团队都在试图精确找出引力可能在何处不再符合爱因斯坦的预言。他们想弄清楚方程中是否需要修正项，而这可能会彻底改变我们对宇宙的理解。这意味着三大艰巨挑战：第一，制造出一台精确到能追踪时间小数点后18位的时钟；第二，把这台时钟带出实验室，送上高空；第三，找到一种读取快到连电子设备都无法处理的信号的方法。
Original English - And that leaves us with one of the biggest unanswered questions in physics. Does gravity itself obey the rules of quantum mechanics? So teams around the world are trying to pin down exactly where gravity might stop following Einstein's prediction. And they want to find out if there's a correction term needed in the equations that might completely change our understanding of the universe. Which means three massive challenges. One, build a clock so accurate it can track time to 18 decimal places. Two, take that clock out of the lab and into the sky. And three, find a way to read a signal so fast that electronics can't even process it.
### 原子钟的工作机制与铯喷泉钟 这里是位于科罗拉多州博尔德的美国国家标准与技术研究院（NIST）。NIST拥有一台极为精准的原子钟，如果它从宇宙大爆炸之初就开始计时，直到现在也不会快或慢一秒。NIST几乎是所有制造过的原子钟的摇篮，从微型芯片级原子钟、地球上最精确的原子钟，一直到早在1949年的第一台实验钟。正是这种极高的精度，使原子钟成为检验基础物理学的强大工具。
Original English This is the National Institute of Standards and Technology in Boulder, Colorado. NIST has an atomic clock that is so accurate that if it started counting when the universe began, it would not have lost or gained a second up until now. NIST has been home to pretty much every kind of atomic clock ever made from tiny chip scale clocks and the most accurate clock on earth to the first experimental clock from way back in 1949. And it's that accuracy that makes atomic clocks powerful tools for testing fundamental physics.
在NIST每一个放置原子钟的房间里，实际上都有这样一个微小的测量标记，它官方标明了你所处的海拔高度，以便在对准原子钟时将其考虑在内。他们甚至通过这个小穹顶，与地球表面400公里外的国际空间站上的时钟相连。
Original English This little survey marker is actually in every room that has an atomic clock at NIST, and it's the official telling of which altitude you're at above sea level so that you can take it into account for when you're aligning the atomic clocks. They even connect to clocks that are 400 kilometers off the earth's surface on the International Space Station through this little dome here.
你可能会认为原子钟是靠放射性运转的，毕竟我们利用放射性衰变和元素的半衰期来测定数十亿年前发生的事情，误差可以小于1%，但原子钟并不是这样运作的。为了计时，我们需要某种来回振荡的东西。对于落地大摆钟来说，它是钟摆；对于手表来说，它是在电流下振动的石英晶体。但原子钟的频率来自于原子本身的固有基本特性。
Original English Now, you might think that an atomic clock runs on radioactivity because after all, we use radioactive decay in the half-life of elements to date things that happened billions of years ago and we can do that with an error of less than 1%, but that is not how an atomic clock works. For keeping time, we need something that will oscillate back and forth. For a grandfather clock, it's a pendulum and for a wristwatch, it's a piece of quartz that is vibrating under an electric current. But an atomic clock gets its frequency from a fundamental property of the atom itself.
电子只能处于特定的能级，它们可以通过吸收一个光子从一个能级跃迁到另一个能级。但这只有在光子的能量与两个能级之间的能量差完全吻合时才会发生，而光子的能量取决于其频率。因此，你可以使用激光并调节其频率，从而改变其光子的能量。大多数频率都会被直接忽略，但当激光的频率恰到好处时，就会发生这种跃迁，电子完成跳跃。这便告诉了我们该原子的固有共振频率。现在我们可以调节激光以精确匹配该频率，正是这种激光的振荡起到了原子钟“钟摆”的作用。
Original English Electrons can only occupy specific energy levels and they can jump from one level to another by absorbing a photon of light. But this only happens when a photon's energy matches the energy difference between the two levels and the energy of a photon depends on its frequency. So you can use a laser, tune its frequency, and that will change the energy of its photons. Now, most frequencies are simply ignored, but when the frequency of such a laser is just right, you get this transition and the electron makes the jump. And that tells us the atom's natural resonant frequency. Now we can tune the laser to match that frequency exactly, and it's the oscillations of this laser light that act as the atomic clock's pendulum.
- 这是NIST F3。它是我们在国家标准与技术研究院运行的铯喷泉钟之一。我们使用这些机器来实验性地实现国际单位制（SI）秒的定义。 - 确切的频率是多少？ - 数到9,192,631,770。当你数到这么多次时，你就数了整整一秒。
Original English - So this is NIST F3. It's one of the Caesium fountains we operate here at the National Institute of Standards and Technology. We use these machines in order to experimentally realize the definition of the SI second. - What is the exact frequency? - Count to 9,192,631,770. And after you've counted that high, you've counted exactly one second.
这台时钟接入了一个网络，协助确定协调世界时（UTC）。正是这个标准让你的手机、电脑以及世界上大部分系统保持同步。自1967年以来，检测器检测到这个精确次数的铯133振荡所需的时间，就一直是官方定义的一秒钟。保持时钟彼此同步是一个延续数百年的难题，因为每个振荡器在制造工艺上都存在不一致性。但对于原子来说，你从哪里获取原子并不重要。全宇宙中同一元素的所有原子，其固有共振频率都是完全相同的。正是特定同位素中这些电子的排布，成就了极佳的原子钟。
Original English - This clock feeds into a network that helps determine coordinated universal time or UTC. It's the standard that keeps your phone, your computer, and much of the world synchronized. Now, since 1967, the time it takes for this exact number of Caesium 133 oscillations to get past your detector has been the official definition of one second. Keeping clocks synchronized with each other is a centuries old problem, and that's because every oscillator has inconsistencies in the way that they're made. But for atoms, it doesn't matter where you get the atom from. The natural resonant frequency is the same for all atoms of the same element across the universe. And it's the arrangement of these electrons in particular isotopes that make a very good atomic clock.
这些原子提供了无比一致的节拍。一个节拍与下一个节拍的匹配可靠程度被称为时钟的**稳定性**。某些元素比其他元素更稳定，这也是铯133非常受欢迎的原因。但还有另一个挑战：每一个节拍保持一致是一回事；而知道你测量的是否是原子真正的振荡速率又是另一回事。换句话说，我们的测量结果与真实的原子频率有多接近？这就是**准确度**。与原子本身不同，准确度取决于时钟的建造水平。
Original English So these atoms give us ticks that are incredibly consistent. How reliably one tick matches the next is the clock's stability. Some elements are more stable than others, which is why Caesium 133 is really popular. But there's another challenge. It's one thing for every tick to be consistent. It's another to know that you're measuring the atom's true ticking rate. In other words, how close is our measurement to the true atomic frequency? That is accuracy. And unlike the atom itself, accuracy comes down to how well the clock is built.
如今最好的铯原子钟比你手表里的石英晶体要准确500亿倍以上。一台时钟的整体性能可以通过它在给定时间内会快或慢多少秒来描述，通常用数量级表示。那么，我们现在用来统一时间标准的铯原子钟处于什么数量级呢？
Original English Now, the best caesium atomic clocks are over 50 billion times more accurate than the quartz crystal in your wristwatch. The overall performance of a clock can be described by how many seconds it will gain or lose in a given time expressed as an order of magnitude. So what order of magnitude is the caesium clock that we're now using to standardize time?
- 它们的相对准确度达到了大约10的16次方分之一。也就是说在几千万年或一亿年的时间里，它大约只会跑偏一秒。
Original English - Those realize fractionally about a part in 10 to the 16 of accuracy. So over the course of maybe tens of millions or a hundred million years, it would only lose of order a second.
### 光晶格钟与镱原子：突破18位精度 但要寻找引力可能偏离广义相对论预言的蛛丝马迹，这依然不够好。如果你想要更精准的时钟，可以先从寻找更高的共振频率开始。因为一秒钟内能容纳的振荡次数越多，你对时间的定义就能越精细。事实证明不同元素具有不同的固有频率，因此你只需找到合适的那一种。而这一任务的绝佳候选者就是镱（ytterbium）。
Original English - But this is still not good enough to find where gravity might stray from the predictions of general relativity. If you want a more accurate clock, you can start with finding a higher resonant frequency. Because the more oscillations you can pack into a second, the more finally you can define it. And it turns out that elements have different natural frequencies, so you just have to find one that fits. And the perfect candidate for the job is ytterbium.
- 我喜欢说它看起来有点像黄铁矿，就像愚人金。
Original English - I like to say it looks a little bit like, like iron pyrite, like fool's gold.
铯原子钟工作在电磁波谱的微波波段，而镱原子的共振则在光学波段，其频率高出56,000倍。这相当于每秒振荡518万亿次，从而使精度达到10的18次方分之一。也就是说，这台时钟在超过宇宙年龄的时间跨度里也不会走偏一秒。
Original English - While caesium clocks operate in the microwave part of the spectrum, ytterbium resonates in the optical band with a frequency 56,000 times higher. This equates to 518 trillion oscillations every second, and that allows for accuracies of one part in 10 to the power of 18. So this clock won't gain or lose a second in more than the age of the universe.
但是当镱处于固态时，原子靠得太近，相邻原子的电子会互相拉扯离开原位，导致电子跃迁的频率展宽和模糊，使得几乎不可能测准其固有共振频率。因此，镱必须首先转化为气体。
Original English But when the ytterbium is solid, the atoms are so close together that neighboring atoms pull each other's electrons out of place, and this broadens and blurs the frequency at which the electrons make the transition, and that makes the natural resonant frequency pretty much impossible to find. So ytterbium first has to be turned into a gas.
- 有一个炉子，我们把它加热—— - 是的。 - 加热到大约500摄氏度。我们把它蒸发成蒸汽，然后在炉子的末端实际上有一个小孔，一股由这些物质组成的气流就会喷射出来。
Original English - There's an oven where we heat this up - Yeah. To about 500 Celsius. We make a vapor of it, and then at the end of the oven, there's actually a hole where just a, a stream of this stuff comes shooting out.
但此时这些原子的飞行速度约为每秒300米，这引发了另一个问题。如果原子在被光子撞击时正朝着光子移动或背离光子移动，它就会以不同的频率吸收光线。这被称为**多普勒频移**，它会使测得的固有共振频率产生百万分之一的偏差。当你追求18位数字的精度时，第6位就出现误差将直接断送整个实验。因此，团队必须找到一种方法，在原子到达主真空腔后减慢其运动。
Original English - But now these atoms are traveling at around 300 meters per second, which causes a different problem. If an atom is moving towards or away from a photon as it's hit, it will absorb the light at a different frequency. This is called a Doppler shift, and it alters the reading of the natural resonant frequency by one part in a millionth. An error at the sixth digit when you're aiming for 18 digits of accuracy would end the experiment there. So the team has to find a way to slow down the atom's movement once they've reached the main vacuum chamber.
- 你必须在自由空间的三维维度上把它们冷却下来，因此这就需要激光束也在三维方向上传播。首先由蓝光激光器工作。它接收数百开尔文温度的高温原子束，将其一路降温到大约1毫开尔文，也就是绝对零度之上的千分之一度。然后切换到同样沿着相同轴传播的绿光激光器，它接收这些处于毫开尔文温度的原子，并将它们降到大约微开尔文左右。
Original English - You have to cool them down in three dimensions in free space, and so that requires having these laser beams in three-dimension as well. So the blue laser operates first. It takes the hot beam of atoms that are at hundreds of Kelvin temperature and brings them all the way down to about a millikelvin or a thousandth of a degree above absolute zero. And then it trades off with the green laser also propagating along the same axes, and that takes those millikelvin temperature atoms and brings them down to about a microkelvin or so.
用激光照射原子来进行冷却，这听起来可能违反直觉，但科学家们利用的是镱171内部不同的电子跃迁。他们现在反过来利用了多普勒频移。激光被调谐到略低于原子吸收频率的数值，因此原子只有在朝向光束运动时才会吸收光子。由于光携带动量，它吸收的每个光子都会给它一个微小的推力使其减速。随后原子会向随机方向发射一个光子，因此在经过许多次循环后，那些随机发射相互抵消，而吸收的光子持续让原子减速。总体而言，激光可以将原子冷却到绝对零度之上仅百万分之一度。
Original English - It might seem counterintuitive that you can cool atoms by firing lasers at them, but what the scientists are doing is using different electron transitions inside ytterbium 171. They're now taking advantage of that Doppler shift. The lasers are tuned just below the frequency the atoms absorb, so an atom only absorbs light from a beam it's moving towards. And because light carries momentum, each photon it absorbs gives it a tiny kick slowing it down. The atom then emits a photon in a random direction, so over many cycles, those random emissions average out while the absorbed photons keep slowing the atoms down. Overall, the lasers can cool the atoms down to just a millionth of a degree above absolute zero.
原子冷却之后，下一个挑战是将它们固定在一个地方，事实证明这也需要激光。
Original English Now, once the atoms are cooled, the next challenge is keeping them in one place, and it turns out you need a laser for this too.
- 我们把一束光聚焦到镱原子所在的真空系统中，然后放置一面反射镜将其原路反射回去。如果我们在微观上放大足够倍数，就会看到两个方向的光波发生干涉，形成具有激光强度波节和波腹的干涉图样。
Original English - We'll focus a beam into our vacuum system where the ytterbium atoms are located, and then we'll actually just put a mirror there to reflect it back onto itself. And if we could kind of zoom in enough, we'd see that there's this interference pattern between the two directions that leads to nodes and anti-nodes of laser intensity.
射出与反射的光波相互叠加，在某些地方相互抵消，在另一些地方相互加强。其结果是一种被称为**驻波**的重复图样。镱171原子本身是中性的，其质子和电子的电荷相互平衡，但光是一种电磁波。因此激光束携带电场，该电场会使这些正负电荷向相反方向发生极其微小的位移。这被称为**感应偶极**，它赋予了原子势能，使电磁力现在能够对其施加作用。
Original English - The outgoing and reflected light waves overlap, and in some places they cancel each other out and in others they reinforce each other. And the result is a repeating pattern called a standing wave. Now, the ytterbium 171 atom is neutral. The charges of its protons and electrons balance out, but light is an electromagnetic wave. So the laser beam carries an electric field, and that electric field pulls those charges very slightly in opposite directions. This is called an induced dipole, and it gives the atom a potential energy so that now the electromagnetic force can act on it.
电场的强度沿着驻波的图样变化。电场在波节处最弱，在波腹处最强。这赋予了偶极子势能，导致原子被一步步吸引向波腹，直到电场强度开始趋于平稳。你可以把它想象成把一颗弹珠放在碗边。在这里，弹珠拥有最大的重力势能，当你松开弹珠让它顺坡而下时，势能变得越来越小，直到在碗底达到最小值。弹珠无法自行爬出碗外，因此被困在了里面。现在以同样的方式，原子在电场力的作用下远离最大势能点，去往势能达到最小的地方。这种结构被称为**光晶格**。
Original English The strength of the field varies along that same pattern as the standing wave. The electric field is weakest at the nodes of the wave and strongest at the antinodes. This gives the dipole a potential energy, causing the atom to be drawn closer and closer to the antinode until the field strength starts to level out. You can think of this like holding a marble on the lip of a bowl. Here, the marble has maximum gravitational potential energy, and when you let the marble go and it moves down the slope, the potential gets smaller and smaller until at the bottom of the bowl it reaches a minimum. The marble can't climb back out of the bowl, so it's trapped. Now, in the same way, the atom is drawn by the electric force away from the point of maximum potential energy to where the potential reaches a minimum. This formation is called an optical lattice.
现在，原子被束缚在只有300纳米宽的区域内，它们的运动受到极大限制，不再影响测量。终于，时钟的频率可以被读取了。
Original English Now, the atoms are trapped in antinodes just 300 nanometers across, and their movement is so limited that it no longer impacts the measurement. And at last, the clock's frequency can be read out.
- 在这个软件上，我们正在观察时钟的实际运行情况。这里我们测量处于基态的原子数量，这里测量处于激发态的原子数量。
Original English - So at this software, we are looking at the actual clock operation. So here we measure the number of atoms in the ground state, and then here we measure the number of atoms in the excited state.
这种平衡就是NIST科学家确认激光仍然锁定在原子固有频率上的方式。因此，激光变成了原子的替身。计算它的振荡次数——大约518万亿次——那就是一秒钟。
Original English - That balance is how the NIST scientists know the laser is still locked onto the atom's natural frequency. So the laser becomes a stand-in for the atoms. Count its oscillations, about 518 trillion of them, and that's a second.
- 你可以看到这里有一个大型的中央腔体，上面布满了窗口。是的，那就是激光注入系统的地方。 - 我的意思是，你在解释这些的时候我脑子里冒出的一个问题是：如果这里的装置是这样的，而你用来操控它的激光就在那个光学平台上以及走廊对面的房间里，你怎么把这套东西搬到山上去？
Original English - You can see that there's this large central chamber which has all of the windows on it. Yeah. That's where the lasers are inserted into the system. - I mean, one question that is in my mind as you're explaining this is if this is the setup here and, you know, the lasers that you're using to treat it are on that bench and in the room across the hall, how do you bring this up a mountain?
### 登上蓝天山：高山野外环境中的微缩系统 为了测量引力对时间的影响，时钟需要在不同海拔高度运行，这意味着要攀登到海拔4326米、位于蓝天山（Mount Blue Sky）的山顶。 哦，那就是那处天文台吗？ - 就在上面，是的，那就是我们要去的地方。 - 哦，这是一条真正的山路。现在差不多进入最后的弯道了。 - 我们差不多到了。 - 我们刚到达天文台。我走了一小段路拍风景，从上面往坡下走走得我有点喘不上气。
Original English To measure the effect of gravity on time, the clock needs to run at different elevations, and that means climbing to 4,326 meters above sea level to the top of Mount Blue Sky. Oh, is that the observatory right there? - That is right up there. Yeah, that's where we're headed. - Oh, this is, this is a proper trail. Kind of on the final bends now. - We're, we're nearly there. - So we just got to the observatory. I went on this little walk to video the view and I'm kind of out of breath going downhill from up there.
- 看起来挺冷的，Gregor。不过这份工作确实会让你置身于各种极端环境中，无论是在14,000英尺的高空，还是困在沙漠里。问题是，在如此极端的环境下你该如何保护自己？ 计时器上有60秒，我们开始。 在烈日炙烤的沙漠中，涂抹充足的防晒霜，多喝水，尽量找遮阳处。 冒着一切危险去解决物理学争端？好吧，戴上安全头盔，相信工程技术。 调查公共卫生危机？好吧，也许是时候穿上全套防化服并戴上呼吸器了。 那网络诈骗呢？好吧，那很简单。使用NordVPN的防病毒功能。它就像互联网的防化服。NordVPN具有预防性，在诈骗和网络钓鱼发生之前就将其拦截。反恶意软件功能主动运行，扫描正在下载的文件并在危险时将其清除。大多数VPN无法保护你免受虚假在线商店的侵害，而NordVPN的新一代防病毒软件可以。所有功能都直接内置在NordVPN应用程序中，只需轻按一下即可为你提供一体化数字安全。因此，使用NordVPN的新一代防病毒软件加强你的在线防护。只需前往nordvpn.com/veritasium或点击说明中的链接，即可获得独家优惠并额外赠送4个月。通过其30天退款保证，完全无风险。感谢NordVPN赞助本视频，现在画面转回给你，Gregor。
Original English - That looks pretty cold, Gregor. But this job gets you into some wild situations, whether you're at 14,000 feet or stranded out here in the desert. The question is, how do you protect yourself in such extreme environments? Got 60 seconds on the clock. Let's go. Scorching in the desert heat, wear plenty of sunscreen, drink a lot of water and find whatever shade you can. Risking it all to settle a physics debate? Well, time to wear a crash helmet and trust in the engineering. Investigating a public health crisis? Well, it might be time for a full hazmat and a respirator. What about online scams? Well, that's easy. Use Nord VPN's antivirus. It's like a hazmat suit for the internet. NordVPN is preventative and it works to block scams and phishing attempts before they happen. The anti-malware functions proactively. It scans downloading files and removes them if they're dangerous. And while most VPNs don't protect you against fake web stores, NordVPN's next gen antivirus does. It's all built right into the NordVPN app, giving you all in one digital security in just one tap. So go big on your online protection with NordVPN's Next Gen Antivirus. Just head to nordvpn.com/veritasium or click the link in the description for an exclusive deal and four months extra. It's completely risk-free with their 30-day money back guarantee. I wanted to thank NordVPN for sponsoring this video, and now back to you, Gregor.
这是使用高精度时钟进行过的垂直落差最大的实验尝试。在高海拔地区进行实验意味着要对抗雷暴、冰雹、降雪，甚至当地野生动物。而短暂的夏季天气窗口意味着他们只有几周的时间来完成这项工作。
Original English - This is the biggest vertical separation ever attempted using high precision clocks. An experiment at altitude means contending with lightning storms, hail and snow, even the local wildlife. And this short summer weather window means they only have a few weeks to do it.
- 我们进到这个帐篷里。我们有几台加热器来保持温度更加稳定，它还可以防止这种入侵性蛾类进入。它们会飞进天文台，数量可能非常多。不管怎么说，帐篷在阻止它们接触激光器方面做得很好。 - 这就是全部设备了吗？ - 这实际上与我们之前看到的完全一样，只是规模稍微小了一点。我们在这一端有那个高温加热炉，里面的镱原子形成一束粒子，穿行进入主腔体，然后是一些引入不同颜色用于原子操控的激光器。 - 但在实验室里，你们有一张相当庞大的光学平台来搭建所有这些激光器。这些全都在这里了吗？ - 是的，全都在这里。其中一些塞在下面和相邻的机架上。全都在这里。 - 太不可思议了。
Original English - So we'll go into the tent here. So we've got a couple of heaters that keep the temperature a little bit more stable, and it also keeps out this kind of invasive moth. They get into the observatory. There can be tons of them. Anyways, the tent does a nice job of keeping them off of the, the lasers as well. - And is this, this is everything? - This is really the same as what we were looking at before, just on a little bit smaller scale. So we've got down on this end is that, that hot oven where we have the ytterbium atoms that form the beam that travels down to the main chamber, and then some of the lasers that introduce the, the different colors for atomic manipulation. - But at the lab, you had a pretty extensive optical bench building up all these lasers. Is that all here? - Yep. That's all here. Some of it is tucked away below and on this adjacent rack. It's all here. - That's incredible.
### 80公里自由空间激光链路 山上的时钟必须与实验室运行的时钟进行比对。问题是，如何让这两台时钟互相通信？ 你当然可以一路铺设一根光纤到博尔德，但事实证明该地区的动物可能会咬断它，而且当地根本没有相应的基础设施。因此，时钟信号被发射到丹佛郊外的一处屋顶上，但首先它必须通过光纤从帐篷里的时钟传输到这个盒子里。
Original English The mountain clock has to be compared against the one running down in the lab. The problem is, how do you get the clocks to communicate with each other? Well, you could run a fiber optic cable all the way down to Boulder, but it turns out the animals in the region would probably chew through it and the infrastructure just isn't there. So instead, the clock signal is beamed to a rooftop just outside of Denver, but first it has to travel from the clock in the tent through optical fiber to this box.
- 光从光纤中出来，变成一束较细的光束，然后进入扩束镜，变成一束粗光束。从门口出去时光束直径大约是10厘米。但是光束会发散，大气湍流会让它变得更宽。所以当它到达丹佛时，光斑大约有一米宽。 - 实际的视线距离是多少？ - 大约80公里。 - 所以你们瞄准的是80公里外的一米光斑。 - 是的。它的纤芯是8微米。这是一个非常小的目标。所以—— - 等等，你们试图瞄准的光线要射入一根纤芯只有8微米开孔的光纤电缆中？ - 是的。 - 这太疯狂了。
Original English - Comes out of the fiber, it gets into a small beam, and then it gets into a beam expander, gets to a big beam. It's about 10 centimeters going out the door. But beams diverge and turbulence makes it wider. So it's about a meter by the time it gets to Denver. - What, what is actually the line of sight distance? - It is about 80 kilometers. - So you're aiming at one meter spotlight, 80 kilometers. - Yeah. So it's an eight micron core. It's a very small target. So - - Wait, the light that you're trying to aim down is going into an eight micron opening fiber optic cable? - Yeah. - That's insane.
旅程的最后一部分是通过光纤完成的，实验室时钟的信号反向沿着相同的路径到达山上的终端。这样两台时钟就可以直接进行比对了。
Original English - The final part of the journey is made through optical fiber, and the same path is taken in reverse by the signal from the lab clock arriving to the terminal on the mountain. So the two clocks can be compared directly.
- 我们启动了所有信号，然后现在来到电脑前，我们在链路上没有看到任何光线。我们基本上只是在测量探测器的噪声。我们的探测阈值是这里的这条虚线。因此当我们锁定它时，我们真正希望的是看到这个数值升到上面这里。如果我们按下这个“寻找接收”按钮，然后你就会看到这个弹出来。 - 好的。 - 这就是链路上的光信号。 - 所以我们锁定了，我们找到了…… - 我们锁定了。我们找到了它。
Original English - So we get all the signals going and then we come over to our computer right now, and we're seeing no light over the link. We're measuring essentially the detector noise. Our detection threshold is, is this dash line here. And so what we really want when we lock this up is we want to see this guy hanging out up here. If we hit this find receive button, and then you just see this pop up. - Yeah. - So that is light over the link. - So we locked in, we found... - We're locked in. We found it.
### 通向太空的前哨：直升机动态跟踪挑战 随着这条链路建立并运行，实验终于开始了。但实际上有另一个团队已经在放眼高山之外，因为为了在更精细的尺度上测试引力，这样的一台时钟最终需要进入太空，而这又带来了一个全新的问题：因为你不再是击中一个静止的目标，而是必须瞄准一个移动的目标。
Original English - With this link up and running, the experiment is finally underway, but there's actually another team who is already looking beyond the mountains because to test gravity to even finer scales, eventually a clock like this needs to get into space, which creates a whole new problem because now instead of hitting a stationary target, you have to hit one that is moving.
在西澳大学（University of Western Australia），一个团队正在努力解决这个难题。他们设计了一个系统，希望在短短几年内将光学时钟信号从一颗移动的卫星发射回地面。在皮卡车和船只上测试了链路之后，现在他们正尝试将它安装在直升机上。那么为什么要从直升机开始呢？
Original English - At the University of Western Australia, one team is trying to solve exactly that. They've designed a system they hope will send optical clock signals from a moving satellite down to the ground in just a few years time. And after trialing the link on pickup trucks and boats, now they're trying putting it on a helicopter. So why start with a helicopter?
- 当然以前从来没有人把时钟装在直升机上，对于我们进入太空的这些场景，人们希望看到一些阶梯式的步骤，比如把时钟放在以前从未有人放置过光学时钟的地方。
Original English - Certainly no one's put a clock on a helicopter before, and for these sort of, I think, scenarios where we're going to space, you know, people want to see that those stepping stones where it's like a clock in a place that no one's ever put an optical clock before.
几十年来，卫星上一直搭载着原子钟，但它们是微波钟，在频率和精度上都更低，并且它们的信号也是使用微波发射回地面的。微波的波长比可见光更长，因此在多云天气可能会吸收或散射光学信号的地方，微波通常仍能穿透。因此，听起来前进的道路似乎只需使用微波来传输任何信号即可，但正是这种更长的波长，使得它无法用于光学时钟。
Original English - Atomic clocks have been on board satellites for decades, but they're microwave clocks lower in both frequency and accuracy, and their signals are beamed down using microwaves too. Microwaves have a longer wavelength than visible light, so where a cloudy sky might absorb or scatter an optical signal, microwaves can often still make it through. So it might sound like the way forward is just to use microwave to transfer any signal, but that longer wavelength is actually why it doesn't work for optical clocks.
因为要通过链路比对两台时钟，你必须确切知道信号何时到达，而你可以通过测量每个电磁波传入时在其周期中的相位来计算出这一点。但是大气的波动会使信号失真，此外还有所有其他类型的噪声，甚至来自于探测信号的设备。信号相对于噪声的强弱被称为**信噪比**。噪声越多，就越难确定每个波在其周期中所处的确切位置。你只能把它精确到波长的一小部分之内。对于波长长得多的微波，那一小部分波长所持续的时间要长数万倍。因此你的测量误差可能会高出数万倍。所以为了跟上光学时钟的精度，信号必须保持在光学频率上。而这意味着必须用激光束击中一个移动的目标。
Original English See, to compare two clocks over a link, you need to know exactly when the signal arrives, and you work that out by measuring where each wave is in its cycle as it comes in. But fluctuations in the atmosphere distort the signal, plus there are all other kinds of noise, even from the equipment that detects it. How strong the signal is compared with that noise is called the signal to noise ratio. The more noise there is, the harder it is to work out exactly where each wave is in its cycle. You can only pin it down to within a small fraction of a wave. For a microwave with its much longer waves, that small fraction of a wave lasts tens of thousands of times longer. So your measurement could be out by tens of thousands of times more. So to keep up with the precision of optical clocks, the signal has to stay at an optical frequency. And that means hitting a moving target with a laser beam.
- 这里是时钟，然后在上面，这是我们的频率传输系统和我们的信标激光器。 - 光源。 该信标激光将与时钟信号并行发射，作为地面站跟踪的一个更大目标。 - 我们在直升机上拥有的一切与我们在地面上拥有的完全是对等的。因此他们也有自己的信标激光器，当我们用终端四处扫描时也会寻找它。
Original English - So this is the clock here, and then we've got on top, this is our frequency transfer system and our beacon laser - Source. That beacon laser will run alongside the clock signal as a bigger target for the ground station to track. - Everything that we have on the helicopter is completely reciprocal to what we have on the ground. So they also have their own beacon laser that we look for when we're scanning around with our terminal as well.
但还记得大气中的那些扰动吗？那些也必须考虑在内。
Original English - But remember those fluctuations in the atmosphere? Well, those have to be accounted for too.
- 如果从道路或城市上空升起大量热气团，那会使我们试图发射的激光束晃动偏移并引入大量误差。所以我们做的是配备一面非常特殊的反射镜，我们称之为**快速倾斜镜（tip-tilt mirror）**，它的移动速度足够快，可以补偿我们观察到的所有这些偏差角。 - 它的移动速度有多快？ - 它的移动速度大约在600赫兹，也就是每秒能移动600次。好了，打开时钟。
Original English - And if you have lots of pockets of hot air rising from the road or over the city as well, that will take our laser beam that we're trying to send and move it around and introduce a lot of errors. So what we do is we have a very special mirror, we call it a tip tilt mirror, and what it does is it moves fast enough that it can account for all of those deviation angles that we're seeing. - How fast does it move? - So it's moving at about 600 hertz, so 600 times a second is the rate that it can move. But yeah, so switching on the clock.
当技术检查完成后，实验便准备起飞。 - 时钟启动并运行。我们出发吧。 - 我们刚刚告别了Leilani。她现在要上直升机了，他们很快就要起飞。所以我们正在赶回西澳大学。如果成功，两个信标将相互锁定，直升机上时钟的信号就可以发送下来并与地面上的时钟进行比对。
Original English - When the technical checks are done, the experiment is ready for takeoff. - Clock's up and running. Let's go. - So we've just left Leilani. She's going to get into the helicopter now and they're going to take off really soon. So we're rushing back to UWA. If it works, the two beacons will lock onto each other and the signal from the clock on the helicopter can be sent down and compared with a clock on the ground.
- 这是西澳大学物理楼的楼顶，那边的Sabrina正在查看我们本地的光学终端。就在这里。你可以认出这与之前直升机上的终端非常相似。 哦看，就在那里。我们已经能看到了。小心碰头。 - 略微…… - 吓人。 - 应该差不多了。你看到什么了吗？你偏上挺多的，往右多移一点。好的，应该差不多了。对，抓到了。你可以看到这扇门正对着有一小道闪光。那应该就是射进来的信标激光。 - 进到这里了。哦，好的，太神奇了。
Original English - So this is the roof of the physics building here at the University of Western Australia, and then Sabrina over here is looking at our local optical terminal. So that's just in here. You've been able to recognize a very similar one that was on the helicopter before. Oh yeah, look, that's it there. We can see it already. Now watch your head. - Slightly - Terrifying. - Should be about it. Can you see anything yet? So you're going up a fair bit. Go more to the right. Okay, that should be about it. Yeah, got it. You can see that little flash of light that's in for the door here. That'd be the beacon laser coming - In here. Oh, okay. So that's amazing.
- 但是，是的，我想它还没有对准到足以完全锁定链路的程度。我认为问题在于今天风有点大，而且直升机在尝试悬停。这实际上是直升机最不稳定、颠簸最大的飞行状态。所以也许我们运气好偶尔能看到一道闪光，能获取一点点数据，但这并不是我们想要达到的最终状态。情况怎么样了？我们看到有些东西在晃动。
Original English - But yeah, I guess it's not yet well aligned enough to get the link fully locked. I think the problem is with that, it's a bit windy today and trying to have it like hovering. It's actually like the least smoothest kind of flight configuration of the helicopter. So maybe we kind of get lucky and we get like a flash occasionally and we might get a little bit of data, but that's not really the ultimate configuration we want to get. How's it looking? We're seeing some sort of stuff moving around.
- 问题在于，当我们在空间上找到彼此后，我们还需要在光谱上找到彼此。 - 哦是的。 - 频率会改变。激光器的频率很容易就会偏离几个吉赫兹甚至几十个吉赫兹。 - 为什么会这样？ - 在光学波段，可用的额外带宽非常非常多，但我们彼此之间仍需要保持在五兆赫兹以内。
Original English - The issue is when we find ourselves spatially, we still need to find ourselves spectrally. Oh yeah. The - Frequency - Changes. The lasers can be gigahertz or tens of gigahertz off pretty easily. - How come? - At optical, there's so much extra, extra bandwidth that's available, but we still need to be within, I don't know, five megahertz of each other.
因此，仅仅把光束相互对准是不够的。两台激光器的频率也必须几乎完全相同。举个例子，汽车收音机只需调谐到电台频率的百分之几以内就能收到信号，但这些激光器必须匹配到亿分之几以内。因此终端来回扫描，寻找一个比其搜索范围窄数千倍的微小窗口。
Original English - So pointing the beams at each other isn't enough. The two lasers also have to be at almost exactly the same frequency. To put that in perspective, a car radio only has to tune to within a fraction of a percent of a station to pick it up, but these lasers have to match within a few parts in a hundred million. So the terminal scans back and forth, hunting for a window thousands of times narrower than the range it's searching.
- 是的，我们还剩20分钟的燃油。 - 这包括回程时间吗？我不知道。 - 他们证明了地面系统可以找到空中的搭档，即使他们只获得了几次短暂的锁定。这些数据目前还不足以对两台时钟进行完整的比对，但这是迈向未来地面与卫星传输的重要一步。
Original English - Yeah, we've got 20 more minutes of fuel left. - Does that include going home time? I don't know. - And they proved the system on the ground could find its partner in the sky, even if they only got a few brief locks. It's not enough data yet to properly compare the two clocks, but it's a big step towards future ground satellite transfers.
- 说到底，听起来很简单，我们所要做的就是让云台跟踪得更好一点、更快一点等等。只要有更多的时间和工程投入，这是我们很容易做到的事情。 - 从那以后，他们登上了富士山，在两次接踵而至的台风中测试了他们的传输系统。 - 我想我们的目标就在下面。这是我们当天的终端装置。四周风景优美，绝对令人叹为观止。 - 他们的链路将帮助理化学研究所（RIKEN）和东京大学的香取秀俊（Hidetoshi Katori）团队在春季进行他们自己的广义相对论检验。
Original English - In the end, it sounds easy, but all we have to do is make the mounts just track a bit better and just a bit faster and stuff. And that's one thing that we can easily do, you know, with a bit more time and a bit more engineering. - Since then, they've been up Mount Fuji, testing their transfer system through two back-to-back typhoons. - I think our target is just down here. Here's our terminal set up for the day. Beautiful views all around. Absolutely amazing. - Their link will help Hidatoshi Katori's group at Recon and the University of Tokyo do their own test of general relativity in the spring.
### 光学频率梳：连接微波与光学的终极标尺 但是还有一个最后的问题，那就是即使链路成功建立，每秒钟仍有518万亿次振荡穿过那些电子设备。事实证明，世界上没有任何电子设备能够读取如此之快的信号。即使是一些最快的晶体管，每秒也只能开关大约100亿次。这仍然慢了50,000倍。因此几十年来，科学家们面临着一个奇特的问题：他们可以制造出光学原子钟，却根本没有办法准确测量其信号。
Original English - But there's one final problem, and that's because even if the link is established successfully, there are still 518 trillion oscillations coming through those electronics every second. And it turns out that there is no electronic device in the world that can read out signals this fast. Even some of the fastest transistors can only switch on and off about 10 billion times a second. And that's still 50,000 times too slow. So for decades, scientists had a strange problem because they could build an optical atomic clock, they just had no way to accurately measure its signal.
你需要的是某种参考基准，将其绑定到某个你已经确切知道的频率上。例如，你可以从微波波段中易于且熟悉制造的信号开始，然后分阶段将其频率向上倍频，直到达到光学波段，然后你可以通过将光学原子钟测得的光信号与你生成的参考信号进行比对，从而找出其确切频率。
Original English What you'd need is some sort of reference to tie it to at a frequency that you already know exactly. For example, you could start with a signal in the microwave spectrum that was easy and familiar to create and then multiply its frequency up in stages until it reached the optical range, and then you could find the exact frequency of the light that you want to measure from the optical atomic clock by comparing it against the signal that you generated.
好的，我这里有两个音叉，它们都是440赫兹。当我敲击它们时，你可以听到它们的频率完全相同。现在我在其中一个音叉上放了一个小配重，这会稍微改变其频率，听听现在会发生什么。你听到那声音了吗？你听到的是一种新的波形，它以这两个音叉之间的频率差进行脉动。这被称为**拍频（beat note）**，光也可以实现同样的效果。将两束不同频率的激光重叠，你也会得到拍频。
Original English Okay, so I have two tuning forks here and they're both at 440 hertz. And when I hit them, you can hear that they're both at the same frequency. Now I've put a small weight on one of the forks and that is going to change the frequency slightly, so listen to what happens now. You hear that? Sound. So what you're hearing is a new waveform that is pulsing at the frequency difference between these two forks. It's called a beat node, and the same thing can be done with light. You overlap two lasers of different frequencies and you get a beat node too.
关键在于，由于频率差远小于我们要寻找的信号本身，我们实际上可以使用晶体管读取它，并进行一个简单的计算：你所知道的参考频率加上拍频，就等于未知信号的确切频率。但这存在一个问题：仅可见光谱就跨越了大约400,000吉赫兹。它的范围极其宽广，而只有当两个信号彼此相差在几十吉赫兹之内时，才能测量到拍频。因此，你的参考信号与你要找的未知信号足够接近的概率非常小。
Original English And the thing is, since the frequency difference is so much smaller than the signal that we're trying to find, we can actually read it out using transistors and we can do a simple calculation. The reference frequency that you know plus the beat note would equal the exact frequency of the unknown signal. But there's a problem. The visible spectrum alone spans around 400,000 gigahertz. It's extremely broad, and a beat node can only be measured if the two signals are within a few tens of gigahertz of each other. So the chances of your reference signal being close enough to the unknown signal that you're trying to find are really small.
科学家需要的不是单一的频率，而是许多分散开来的频率，使得未知信号总能紧挨着其中至少一个。参考信号位于波谱底部的微波部分，我们称之为 $F_r$；而我们的未知信号位于上面光学波段的某处，即 $F_{optical}$。所以我需要的是某种标尺，能够量化参考信号与我们要寻找的时钟未知信号之间的频率差。理论上，你可以设置多台激光器作为标尺的刻度，但微波频率与光学频率相差太远。如果想弥合这个差距，就需要非常多的激光器。
Original English What scientists needed wasn't one frequency, but many spread out so that the unknown signal would always sit close to at least one of them. So a reference signal is down here in the microwave part of the spectrum, so let's call that F of R, and then our unknown signal is somewhere up here in the optical, so F of optical. So what I need is some sort of ruler that is going to be able to quantify this difference in frequency between my reference signal and my unknown signal of the clock that I'm trying to find. In theory, you could set up a number of lasers to act as the notches of the ruler, but this frequency in microwave and this frequency in optical are very far apart. So if I want to bridge this gap, I would need, well, a lot of lasers.
因此，更有用的方法是操纵单一激光器的光，使其同时产生所有这些不同的频率，能够一路从电子设备可以计数的微波跨越到科学家想要测量的光。1994年，一位名叫特奥多尔·亨施（Theodor Hänsch）的德国物理学家在一次展会上观看一种新型激光器演示时，脑海中萌生了一个想法。几十年来，他一直在想方设法测量光学信号，而这种特殊的钛蓝宝石激光器能够产生令人难以置信的超短光脉冲，每个脉冲都蕴含着宽广的频率范围。
Original English So instead what would be useful is if I could manipulate the light of just a single laser to produce all of these different frequencies at the same time, something that would span all the way from the microwaves that electronics could count up to the light scientists wanted to measure. In 1994, a German physicist called Theodor Hänsch was, had a trade show when a demonstration of a new type of laser struck him with an idea. See, for decades, he'd been coming up with different ways to try and measure optical signals, but this particular titanium sapphire laser could generate incredibly short pulses of light, each packed with a vast range of frequencies.
在频谱图上，那种光看起来就像梳子的梳齿。这终于可能成为每个人都在寻找的标尺。但是为了使宽范围的频率成为有效的标尺，每个频率都需要与其他频率相关联，否则你无法真正预测其图样。毕竟，一把尺子只有在刻度间距完全相等时才有用。于是亨施和他的同事们对激光器进行了测试。他们测量了它的光，发现里面包含的频率间隔完全均匀。这就是**光学频率梳**。
Original English Now on a frequency graph, that light looked like the teeth of a comb. This could finally be the ruler that everyone was searching for. But to make the wide range of frequencies an effective ruler, each frequency needs to be related to the other frequencies, otherwise you can't really predict the pattern. I mean, a ruler is only useful if these notches are equally spaced. So Hench and his colleagues put the laser to the test. They measured its light and found that the frequencies contained inside were perfectly evenly spaced. This is an optical frequency comb.
到了1999年，博尔德由约翰·霍尔（John Hall）领导的一个团队将这把梳子设计成了一把足够宽的标尺，几乎可以测量任何颜色的光。现在我有了一把拥有数十万根梳齿的梳子，其中一些齿肯定会非常接近我要寻找的未知信号。频率梳会发射自身的频率，因此在这个梳齿和未知信号之间会产生拍频。通过用光电二极管观测该拍频，我们就有了一个公式来计算未知光学信号的频率：梳齿位置序号乘以重复率，再加上拍频的频率。而且由于重复率锁定在我们的参考信号上，该公式中的每个数值都是电子设备可以测量的。一年之内，频率梳就读取了第一台光学原子钟的数据。亨施和霍尔与罗伊·格劳伯（Roy Glauber）一道因这项工作荣获2005年诺贝尔物理学奖。
Original English By 1999, a team in Boulder led by John Hall had engineered this comb into a ruler so wide that it could measure almost any color of light. So now I have a comb with, well, hundreds of thousands of teeth, and some of them are going to be close enough to that unknown signal that I'm trying to find. The comb is emitting its own frequency. So there's going to be a beat note that rings between this comb tooth and the unknown signal. So by observing that beat note with a photo diode, we have a formula to calculate the frequency of our unknown optical signal. That's the tooth position number multiplied by the repetition rate plus the frequency of the beat note. And because the repetition rate is locked to our reference signal, every number in that formula is one that electronics can measure. Within a year, frequency combs were reading the first optical atomic clocks. Hänsch and Hall alongside Roy Glauber were awarded the 2005 Nobel Prize for this work.
### 数据揭晓：爱因斯坦依然正确吗？ 在山上，每个时钟信号都使用频率梳的脉冲通过空气传输。广义相对论预言，当把这些脉冲汇合在一起时，实验室里的时钟走时应该比山上的时钟稍微慢一点点。这是理论预言，但山上的计数器到底显示了什么？
Original English On the mountain, each clock signal is being sent over the air using pulses of a frequency cone. General relativity predicts that when you bring those pulses together, the clock in the lab should take ever so slightly slower compared to the clock on the mountain. That is the theory. But what does the counter on the mountain actually say?
- 这就是链路上的光。 - 所以我们锁定了，我们找到了…… - 我们锁定了。我们找到了它。这个数据正在缓慢爬升这一事实—— - 是的。 - 这就是时间输出的变化，因为时钟以不同的速率运行。所以时间偏差正在慢慢爬升，我们或多或少可以在实时中看到它。开始了。
Original English - So that is light over the link. - So we locked in we found... - We locked in. We found it. So the fact that this is moving slowly ramping - Yeah. That's the time output changing because the clocks are running at different rates. So the time offset is slowly ramping and we can see it more or less in real time. Here it goes.
如果爱因斯坦是对的，这两台时钟每过一秒应该相差 $2.885 \times 10^{-13}$ 秒。这个数字是由另一个研究小组根据实验室和高山的重力场测量结果计算出来的。尽管两个团队都在计算比这多得多的有效小数位，但在准备好比对研究结果之前，他们实际上对彼此保密了最后几位数字。如果时钟测得的斜率角度不同，那么这就证明广义相对论在这一层面上可能失效了。
Original English - If Einstein is right, these two clocks should differ by 2.885 times 10 to the power of negative 13 seconds every second. This number has been calculated by another group based on measurements of the gravitational field in the lab and on the mountain. And while both teams are working to many more decimal places than this, they're actually keeping those final digits secret from each other until they're ready to compare findings. If the clocks measure a different angle on the slope, well, that's evidence that general relativity might stop working at this level.
几周后，我们与团队通了电话，看看数据说明了什么。 爱因斯坦依然正确吗？ - 我要用两种方式回答这个问题。第一种是非常简单的回答，那就是：是的。 - 好的。 - 我们没有证据表明不是。第二个回答是，我们仍在分析数据。你已经深入到了大约第13位数字，而当你在寻找新物理学时，你要找的是斜率大约百万分之一的变化。所以这是一个非常微小的变化。
Original English So a few weeks later, we hopped on a call with the team to check out what the data is saying. Is Einstein still right? I'm going to answer that two ways. The first is a very simple answer, which is yes. - Okay. - We have no evidence that says no. The second answer is that we're still analyzing the data. So you're down at sort of the 13th digit and a little change at sort of the, a millionth of that slope is what you're looking for when you're looking for new physics. So it's a very small change.
- 我的意思是，你们具备这种灵敏度，能去观察原本就只有万亿分之一秒的斜率中百万分之一的变化，这太不可思议了。这太疯狂了。你们兴奋吗？知道数据就在那里、只需要处理这些数字，你们紧张吗？睡得好吗？ - 无论结果是什么，你都必须把那个数字公布出来。不管它与经典预言一致与否，那都是一个让人有点紧张的时刻。 - 是的，确实意义重大。
Original English - I mean, it's incredible that you have the sensitivity to look at a millionth of, of this slope that is already a trillionth of a second. So wow. I mean that, that's crazy. And are you guys excited? Are you nervous to, to know that the data is there, you just have to crunch the numbers? Are you sleeping well? - You got to kind of, whatever it is, put that number out there. And whether it agrees with the classical prediction or not, that's a little bit of a nerve-wracking moment. - Yeah, I mean it's huge.
- 目前在地球上完成的最佳地面测试大约在百万分之一百（100 ppm）的水平。我们的希望是能够接近百万分之十（10 ppm）的水平，以一种全新的、更深刻的方式检验广义相对论。 - 你们还计划进行更多的测试吗？ - 我认为下一个重大步骤将是尝试建立通向太空的链路。
Original English - The best terrestrial test that's been done here on Earth is about at the 100 part per million level. Our hope is that we'll be able to do approaching the 10 part per million level with testing general relativity in a, in a new and deeper way. - Have you got any more of these tests planned in? - I think the big next step would be to try for a link to space.
在Laura和Andrew的团队准备好分享他们的最终结果之前还需要几个月的时间。所以如果你想关注他们的进展，我们在描述中附上了他们团队主页的链接。非常感谢他们以及NIST团队的其他成员，也感谢Sasha、Leilani和珀斯团队在本期视频中给予的所有帮助。最后还有一件事，你可能已经注意到我们推出了第二个名为InGenius的频道。他们最近的一期节目是关于预测市场以及究竟是谁在其中获利。令人震惊的是，事实证明获利的仅仅是位于顶部的0.1%。团队梳理了Polymarket上三年来的历史交易，以找出该平台上到底发生了什么，非常值得一看。如果你感兴趣，我非常建议你去看看。感谢大家的支持，当然，一如既往，感谢大家的观看。
Original English - It'll be a few months before Laura and Andrew's team are ready to share their final results. So we've linked their group's page in the description if you want to follow their progress. I wanted to say a huge thank you to them and the rest of the NIST team and to Sasha Leilani and the team in Perth for all their help in this video. And one final thing, you might have noticed that we launched a second channel called InGenius. Their recent episode was about prediction markets and who actually wins on them. Shockingly, it turns out it's just the 0.1% at the top. The team scoured three years worth of past trades on Polymarket to find out what really happens on the platform and it's a really fascinating watch. So if you're interested, I really recommend you check it out. I want to thank you for your support and of course, as ever, thank you for watching.