Where Does the Quantum World End and Ours Begin?

Quantum mechanics may be one of the most precisely tested paradigms in science, but there’s still no universally accepted interpretation of what it tells us about reality.

量子力学可能是科学中经过最精确测试的范式之一，但对于它告诉我们的现实仍然没有普遍接受的解释。

How do we get from the wave-like behavior of quantum systems to the solid, macroscopic world of objects and the universe at large?

我们如何从量子系统的波状行为转向固体、宏观的物体世界和整个宇宙？

Jonathan Halliwell , a professor of theoretical physics at Imperial College London, has spent his career probing the foundations of quantum theory.

乔纳森·哈利韦尔（Jonathan Halliwell）是伦敦帝国理工学院的理论物理学教授，他的职业生涯一直在探索量子理论的基础。

In this episode, he tells Steven Strogatz why decoherence — the process by which fragile quantum behavior becomes dispersed through interactions with the surrounding environment — is key to the transition from quantum to classical behavior, and he describes the “histories” approach that he uses to understand this.

在这一集中，他告诉史蒂文·斯特罗加茨为什么退相干——脆弱的量子行为通过与周围环境的相互作用而分散的过程——是从量子行为到经典行为转变的关键，他描述了他用来理解这一点的“历史”方法。

Along the way, Halliwell tackles some of the field’s deepest paradoxes.

一路走来，哈利韦尔解决了该领域一些最深刻的悖论。

He explains why the quantum-to-classical transition doesn’t require a conscious observer, and he explores Einstein’s famous question of whether the moon is really there when no one looks.

他解释了为什么量子到经典的转变不需要有意识的观察者，并探讨了爱因斯坦的著名问题：当无人看时月球是否真的存在。

The conversation ends with Halliwell explaining how yoga and meditation help him sit with the mystery of competing perspectives in science.

谈话最后哈利韦尔解释了瑜伽和冥想如何帮助他面对科学中相互竞争的观点之谜。

Listen on Apple Podcasts , Spotify , TuneIn or your favorite podcasting app, or you can stream it from Quanta .

在 Apple 播客、Spotify、TuneIn 或您最喜爱的播客应用程序上收听，或者您也可以从 Quanta 进行流式传输。

My question about that, first of all, what a mind-blowing idea.

我的问题是，首先，这是一个多么令人兴奋的想法。

But also, like, when I took quantum mechanics in college or even when I used to read popular accounts of it, frequently we would hear about an observer and an experiment, and the observer is sort of outside the experiment, causing wave functions to collapse by making measurements and that sort of thing.

而且，就像当我在大学学习量子力学时，甚至当我以前阅读有关它的流行报道时，我们经常会听到观察者和实验，而观察者在实验之外，通过进行测量等导致波函数崩溃。

But when it’s the universe as a whole that’s the quantum object, the observer can’t be outside the system.

但当整个宇宙就是量子物体时，观察者就不能处于系统之外。

And I just wonder if that’s the sort of thing that made thinking about foundations of quantum theory irresistible to you.

我只是想知道这是否会让你无法抗拒思考量子理论的基础。

The original impetus for quantum cosmology is to do with the fact that the Big Bang model is based on quantum matter, but classical gravity.

量子宇宙学的最初推动力与大爆炸模型基于量子物质而不是经典引力这一事实有关。

And quantum matter plus classical gravity, as you go backwards in time, as theorems due to Hawking, Penrose, and others showed, it must have a singularity initially, at least classically.

量子物质加上经典引力，当你时光倒流时，正如霍金、彭罗斯和其他人的定理所表明的那样，它最初必须有一个奇点，至少在经典上是这样。

So a region of infinite gravity, infinite curvature.

所以这是一个引力无限、曲率无限的区域。

So that suggests that if it is still within the laws of physics, we need a quantum theory of gravity.

因此，这表明，如果它仍在物理定律之内，我们就需要量子引力理论。

And so perhaps the beginning of the universe is described by some quantum theory, which includes not just the matter modes, but also some modes of the gravitational field.

因此，宇宙的起源也许是由某种量子理论描述的，其中不仅包括物质模式，还包括引力场的某些模式。

We don’t really know what a full quantum gravity theory is even yet, and this was 40 years ago when I was doing that work.

我们还不知道什么是完整的量子引力理论，那是 40 年前我做这项工作的时候了。

But in quantum cosmology, what you can do is say, well, let’s just take a few elements of the gravitational fields, like the overall size of the universe, the scale factor, and maybe a few distortion parameters.

但在量子宇宙学中，你可以说，好吧，我们只考虑引力场的一些元素，比如宇宙的整体大小、比例因子，也许还有一些畸变参数。

And then you can quantize these models of the beginning of the universe using relatively standard techniques.

然后你可以使用相对标准的技术来量化这些宇宙开始的模型。

It’s all kind of heuristic.

这都是启发式的。

I’m not sure how much faith I would put in it, but at least gives you a picture.

我不确定我会对它有多少信心，但至少给你一张图片。

And what comes out of that, which is very appealing, is there is a non-singular beginning of the universe which is quantum in nature.

由此产生的结果非常吸引人，那就是宇宙存在一个非奇点的开端，它本质上是量子的。

That’s the beauty that comes out, at least in simple models.

这就是所呈现出来的美丽，至少在简单的模型中是这样。

So in the sort of older classical model, thinking geometrically, the beginning of the universe has a singularity like a cone.

因此，在更古老的经典模型中，从几何角度思考，宇宙的起点有一个像锥体一样的奇点。

A cone has a sharp point at the end.

圆锥体的末端有一个尖点。

So that’s what a classical Big Bang model looks like.

这就是经典的 Big Bang 模型的样子。

But in the quantum picture, as you go to very small scales, the very smallest bit becomes quantum, and then instead of the sharp point, you can actually close off with a kind of smooth hemisphere.

但在量子图像中，当你达到非常小的尺度时，最小的比特就会变成量子，然后你实际上可以用一种光滑的半球来封闭而不是尖点。

So the geometry we have in mind is sometimes called a shuttlecock geometry.

因此，我们想到的几何形状有时称为羽毛球几何形状。

This idea was due to Stephen Hawking and James Hartle.

这个想法是由史蒂芬·霍金和詹姆斯·哈特尔提出的。

It’s called the no boundary proposal of the universe.

这被称为宇宙无边界提议。

This has caused a huge amount of interest then 40 years ago, and it’s still very much an explored idea.

这在 40 年前引起了极大的兴趣，而且在很大程度上仍然是一个正在探索的想法。

It’s one of the very few models of how the universe actually began.

这是宇宙真正开始的极少数模型之一。

So that’s why that’s interesting.

这就是为什么这很有趣。

Now, to your question, is this really quantum?

现在，回答你的问题，这真的是量子吗？

What about observers, collapse of the wave function, and so on?

那么观察者、波函数的塌缩等等呢？

There aren’t any observers there to do the measurement or to collapse the wave function.

那里没有任何观察者进行测量或使波函数崩溃。

So what is actually happening is that there are observers now.

所以实际发生的情况是现在有观察员。

What we make measurements on things we can look at now, like the microwave background or the expansion of the universe, or more precisely, the detectors and the photographic plates that actually measure those.

我们对现在可以看到的事物进行测量，例如微波背景或宇宙的膨胀，或者更准确地说，是实际测量这些的探测器和照相底片。

We look at those, we measure those, and in some sense, we collapse the wave function when we actually do those measurements.

我们观察它们，测量它们，从某种意义上说，当我们实际进行这些测量时，我们折叠了波函数。

But the question then is: how do you relate those measurements made today, which we would call records, basically, how do we relate those to the Big Bang in the past?

但问题是：如何将今天进行的这些测量（我们称之为记录）联系起来，基本上，我们如何将这些与过去的大爆炸联系起来？

And the answer to that is there was a new reformulation of quantum mechanics developed by James Hartle, Murray Gell-Mann, and others, called the histories approach to quantum mechanics, or more precisely, decoherent histories approach.

答案是詹姆斯·哈特尔（James Hartle）、默里·盖尔曼（Murray Gell-Mann）等人开发了一种新的量子力学重新表述，称为量子力学历史方法，或更准确地说，退相干历史方法。

It tries to get away from ideas of external observers and collapse of the wave function.

它试图摆脱外部观察者的想法和波函数的崩溃。

We’re actually looking at present records and looking for the correlation between them.

我们实际上正在查看当前的记录并寻找它们之间的相关性。

So decoherent histories approach is a way in quantum mechanics of actually linking records in the present in terms of what we think happened in the past.

因此，退相干历史方法是量子力学中的一种方法，它实际上将当前的记录与我们认为过去发生的事情联系起来。

It’s a bit roundabout, but it avoids having to actually say that the past actually happened in some sense, or the wave function collapsed in the past.

这有点迂回，但它避免了必须说过去在某种意义上确实发生过，或者波函数在过去崩溃了。

I’m slightly averse to talking about cats, actually.

事实上，我有点不愿意谈论猫。

One of them being Schrödinger’s unfortunate cat.

其中之一是薛定谔不幸的猫。

I wonder if you could start our discussion by reminding us about that feline.

我想知道你是否可以通过提醒我们那只猫来开始我们的讨论。

What was that thought experiment supposed to illustrate?

这个思想实验想要说明什么？

I’m slightly averse to talking about cats, actually.

事实上，我有点不愿意谈论猫。

It’s a sort of nomenclature that’s stuck, to the point that non-physics friends of mine go, “Ugh,” when this actually comes up, and I sort of understand that, actually.

这是一种被卡住的术语，以至于当这个问题真正出现时，我的非物理学朋友会说“呃”，实际上我有点理解这一点。

And what happens is that the wave goes through both of the holes, and then it sort of gives an interference pattern, a set of light and dark patches on the screen.

发生的情况是，波穿过两个孔，然后在屏幕上产生干涉图案，即一组明暗斑块。

And then you might say, well, actually it’s really an electron.

然后你可能会说，好吧，实际上它确实是一个电子。

It’s a particle.

它是一个粒子。

It’s a lump.

这是一个肿块。

It’s like a billiard ball.

它就像一个台球。

Surely it just went through one or the other.

当然，它只是经历了其中之一。

And if you actually block one of the slits or block the other slit, then the interference pattern goes away.

如果你真的挡住了其中一个狭缝或挡住了另一个狭缝，那么干涉图案就会消失。

So if you actually make the assumption that it’s a definite particle that goes through one or the other, you don’t get the interference pattern anymore.

因此，如果您实际上假设它是穿过其中一个或另一个的确定粒子，那么您将不再获得干涉图样。

So in a very real sense, you can have what you think is a solid particle that very genuinely actually goes through both sides and creates the interference on the other side.

因此，在非常真实的意义上，您可以拥有您认为是固体粒子，它实际上非常真实地穿过两侧并在另一侧产生干扰。

Let me give you a nice pictorial analogy.

让我给你一个很好的形象类比。

There’s a lovely book by, uh, Yakir Aharonov on quantum paradoxes, and on the cover it’s got a picture of a man skiing through a forest in the snow.

嗯，亚基尔·阿哈罗诺夫（Yakir Aharonov）有一本关于量子悖论的可爱的书，封面上有一张男人在雪地里滑雪穿过森林的照片。

And he’s got parallel tracks, and at one stage he looks back to see where his tracks have gone, and he observes that his tracks have gone both sides of a tree.

他有平行的足迹，在某个阶段，他回头看看他的足迹去了哪里，他发现他的足迹已经去了一棵树的两侧。

And, and that, that is obviously impossible for a skier, but that’s exactly what happens in quantum physics.

而且，这对于滑雪者来说显然是不可能的，但这正是量子物理学中发生的事情。

The electron looks back and notices the tracks in the interferometer where it really has gone through both sides.

电子回头一看，注意到干涉仪中的轨迹，它确实穿过了两侧。

We learn about interference.

我们了解干扰。

But what I remember reading about that seems so astonishing is that even if you turn down the intensity of light so much that there’s effectively only one photon in the chamber at a time, or in your case, single electron in some sense like this amazing skier can sort of interfere with itself.

但我记得读过的内容似乎非常令人惊讶的是，即使你将光的强度调低得如此之低，以至于腔室中一次实际上只有一个光子，或者在你的例子中，单个电子在某种意义上就像这个令人惊叹的滑雪者一样可以自我干扰。

And in fact, they now can do interference experiments with pretty big things, like containing thousands of atoms.

事实上，他们现在可以对相当大的物体进行干涉实验，比如包含数千个原子。

They’re borderline visible with the naked eye actually, some of the effects.

实际上，其中一些效果是肉眼可见的。

I mean, this links to sort of macroscopic quantum experiments, and, it does lead to this question of how big a system can you interfere with itself?

我的意思是，这与某种宏观量子实验有关，并且，它确实引出了这样一个问题：一个多大的系统可以干扰自身？

I spent a lot of time looking at different types of quantum effects and understanding which ones get killed quickly and which ones actually are quite robust.

我花了很多时间研究不同类型的量子效应，并了解哪些量子效应会很快消失，哪些实际上非常强大。

The fundamental issue really beneath all of this, it is actually about the worldview at the quantum level.

这一切背后的根本问题实际上是关于量子层面的世界观。

There are all these weird effects, but behind that, there is this worldview that the quantum world is actually about waves, and their intuitive properties are just not the same as those of particles.

有所有这些奇怪的效应，但在这背后，有一种世界观，即量子世界实际上是关于波的，它们的直观属性与粒子的直观属性不同。

Just to give another simple example, if a police car comes past w- with its siren blaring and if you’ve got the doors and the window open, then the sound comes in both the door and the window.

再举一个简单的例子，如果一辆警车鸣笛驶过，如果你把门和窗都打开了，那么声音就会从门和窗里传进来。

There’s nothing unusual about that.

这并没有什么不寻常的。

But if it’s a solid object that appears to come in through both the door and the window, that would be rather striking.

但如果它是一个看似从门和窗进来的固体物体，那就相当引人注目了。

But that is, in principle, true because wavelike is the fundamental nature of matter at the microscopic level.

但原则上这是正确的，因为波状是微观层面物质的基本性质。

So that’s one of the things is from a coarse grain scale, the wave-like pattern goes away.

所以，其中一件事就是粗粒度，波浪状的图案消失了。

But it’s more concrete than that.

但它比这更具体。

There are certain quantities which describe a physical system which are very slowly varying, and some which vary extremely rapidly.

描述物理系统的某些量变化非常缓慢，有些量变化非常快。

Suppose you have a big massive particle that’s being bombarded by molecules.

假设有一个巨大的粒子正在被分子轰击。

Like, there’s the famous Brownian motion example where you have, like, a pollen particle, which is kind of big compared to the atomic scale, being bombarded by molecules that makes it jiggle around a bit.

比如，有一个著名的布朗运动的例子，其中有一个花粉颗粒，与原子尺度相比有点大，受到分子的轰击，使它稍微摇晃。

The big particle will be effectively classical.

大粒子实际上是经典的。

What happens is the bombardment by other systems, which we o- often call an environment, it actually, it kills the interference, is the phrase we use.

所发生的是其他系统的轰炸，我们通常称之为环境，实际上，它消除了干扰，这是我们使用的短语。

It suppresses the interferences that create the wave-like properties by kind of smoothing things out and destroying the wave-like nature.

它通过平滑事物并破坏波状性质来抑制产生波状特性的干扰。

Is the moon really there when no one looks?

没人看的时候月亮真的存在吗？

But it was also important to do the return journey, which said, if everything’s quantum, my table isn’t, or what happened?

但回程也很重要，也就是说，如果一切都是量子的，我的桌子不是，或者发生了什么？

And when you come back to the coarse-grain world, why is that not in fact quantum even though it’s made of very quantum stuff?

当你回到粗粒世界时，为什么它实际上不是量子的，尽管它是由非常量子的物质组成的？

That is the process of decoherence.

这就是退相干的过程。

That the quantum effects are actually very fragile, as you say.

正如你所说，量子效应实际上非常脆弱。

You have to work hard to maintain them.

你必须努力工作来维护它们。

You need sort of isolated chambers and so on.

你需要一些隔离室等等。

And it is quite hard to find quantum effects which persist.

而且很难找到持续存在的量子效应。

I mean, there are some like properties of electrically conducting materials and so on have relatively robust properties.

我的意思是，有一些类似导电材料的特性，等等具有相对稳健的特性。

But in terms of the really kind of, let’s say, out there freaky stuff like superpositions, those are quite easily destroyed.

但就真正的，比方说，像叠加这样的怪异东西来说，它们很容易被破坏。

For all sorts of reasons, I spent a lot of time looking at different types of quantum effects and understanding which ones get killed quickly and which ones actually are quite robust.

由于各种原因，我花了很多时间研究不同类型的量子效应，并了解哪些量子效应会很快消失，哪些实际上非常强大。

Now in practice, in a realistic experiment, any large system would be very quickly decohered by its, uh, immediate environment, by surrounding photons.

现在在实践中，在现实的实验中，任何大型系统都会很快被它的，呃，直接环境，周围的光子消相干。

But the entanglement, the quantum stuff, is actually still there.

但纠缠，量子的东西，实际上仍然存在。

It’s just scattered far and wide.

它只是分散得很远。

So if you have a small particle, like the Brownian motion particle, that is in some sense still actually quantum even though it’s scattered, but there’s so much information.

因此，如果你有一个小粒子，比如布朗运动粒子，那么在某种意义上它实际上仍然是量子的，尽管它是分散的，但其中蕴藏着如此多的信息。

You know, all the bits of information are just out there beyond the horizon that you can probably even never get them.

你知道，所有的信息都在你的地平线之外，你甚至可能永远无法获取它们。

But it does still leave the question, could you have, let’s say, some sort of super-observer with actually unlimited information processing capacity that could actually measure everything that’s going on?

但它仍然留下了一个问题，比如说，你是否可以拥有某种具有无限信息处理能力的超级观察者，可以真正测量正在发生的一切？

And in principle, that’s true.

原则上来说，确实如此。

There is actually, let’s say, an information theoretic dimension to this.

比如说，这实际上有一个信息论维度。

But, part of it is that, as you probably know, quantum systems have vastly greater information storage capacities than classical ones.

但是，正如您可能知道的，部分原因是量子系统的信息存储容量比经典系统大得多。

That’s one of the ways of characterizing quantum physics.

这是表征量子物理学的方法之一。

Two distant particles in an entangled state, you arrange it so they can’t possibly signal.

两个相距较远的粒子处于纠缠状态，你可以对其进行排列，这样它们就不可能发出信号。

It still looks like they’re talking to each other.

看起来他们仍然在互相交谈。

I mean, that’s really the true mystery.

我的意思是，这才是真正的谜团。

Maybe the way to say it is things were in superposition until the observer rendered the quantum object in a definite state.

也许可以这么说，在观察者将量子物体呈现为确定状态之前，事物一直处于叠加状态。

And that’s just a total red herring in many ways, and I believe Jonathan probably went to great pains to explain how you don’t need a human consciousness.

从很多方面来说，这完全是在转移注意力，我相信乔纳森可能煞费苦心地解释了为什么不需要人类意识。

But it led to so much stuff out there, just ephemera out there about consciousness.

但它导致了太多的东西，只是关于意识的短暂的东西。

And quantum mechanics that has been very hard to whack back actually.

而量子力学实际上很难反击。

So even now, people will still say, “Ah, but, you know, quantum and consciousness.” Those are not connected ideas.

所以即使是现在，人们仍然会说，“啊，但是，你知道，量子和意识。”这些不是相互关联的想法。

And I believe Jonathan’s done really important work to separate that out, to say the observer could be just the environment, a thoughtless environment, an unthinking collection of molecules.

我相信乔纳森做了非常重要的工作来区分这一点，他说观察者可能只是环境，一个不加思考的环境，一个不加思考的分子集合。

Now, in the many worlds, that’s not what happens.

现在，在许多世界中，情况并非如此。

What happens is you, the observer, or the hot room or the cat, whichever it is, becomes superposed and branches off, and the two possibilities coexist in some meta world, some many worlds interpretation and, and all possibilities continue to be realized branching over and over again.

发生的事情是你，观察者，或者热房间或猫，无论它是什么，都会叠加并分支，两种可能性共存于某个元世界，一些多世界的解释，并且所有可能性继续一遍又一遍地分支实现。

That is surprisingly popular in quantum mechanics and completely confounded.

这在量子力学中出人意料地流行，而且完全令人困惑。

The quantum-ness doesn’t go away.

量子性并没有消失。

It just becomes, in some sense, less distinct on these macroscopic scales where there’s so many histories, which is like saying so many particles macroscopic.

从某种意义上说，它只是在这些有如此多历史的宏观尺度上变得不那么明显，这就像说有如此多的宏观粒子一样。

And I think that’s where he’s going.

我认为这就是他要去的地方。

I don’t know if you took a sampling of quantum physicists where they’d land on all of these.

我不知道你是否对量子物理学家进行了抽样调查，他们对所有这些问题的看法如何。

The whole area is just riddled with loopholes.

整个区域都充满了漏洞。

So, at this point, I’d like to get into this notion of macroscopic realism that I know has been of interest to you, you’ve worked on extensively.

所以，在这一点上，我想谈谈宏观现实主义的概念，我知道你对此很感兴趣，你已经进行了广泛的研究。

Let me start by bringing up a quote of Einstein that is close to what I think we wanna talk about.

让我首先引用爱因斯坦的一句话，这句话与我认为我们想讨论的内容很接近。

But one of Einstein’s famous quotes in thinking about paradoxes of quantum theory in the old days was, “I like to think that the moon is there even if I’m not looking at it.” Back in the days when Niels Bohr was drilling in the idea that you had to think about the observer, and does it make sense to say that an object has properties like a certain velocity or a position, or its spin state even before you measure it.

但爱因斯坦在过去思考量子理论悖论时的著名名言之一是：“我喜欢认为月亮就在那里，即使我没有看它。”早在尼尔斯·玻尔（Niels Bohr）钻研这样的想法时，你必须考虑观察者，甚至在测量之前就说一个物体具有特定速度或位置或其自旋状态等属性是否有意义。

And Einstein thought, “Of course, I wanna believe that the moon is there even when I’m not looking at it.” Tell us what we mean by macroscopic realism, and what’s missing in this little analogy of Einstein and the moon?

爱因斯坦想：“当然，我想相信月亮就在那里，即使我不看它。”告诉我们宏观现实主义是什么意思，爱因斯坦和月球的这个小比喻中缺少了什么？

So, there’s a whole set of things here which I can try and sketch.

所以，这里有一整套我可以尝试和绘制草图的东西。

So though on the one hand, these tests of macroscopic realism, it’s a version of what is classicality, and it’s designed for single systems that you measure sequentially in time.

因此，虽然一方面，这些宏观现实主义的测试是经典的一个版本，并且它是为您按时间顺序测量的单个系统而设计的。

So when you measure something and the outcome you get is not the real outcome of what it actually is, but it might depend on what’s going on somewhere else.

因此，当你测量某些东西时，你得到的结果并不是它实际的真实结果，但它可能取决于其他地方发生的事情。

This is what is called contextuality.

这就是所谓的情境性。

Now, this is what happens in Leggett-Garg tests of macroscopic realism.

现在，这就是宏观现实主义 Leggett-Garg 测试中发生的情况。

What Leggett-Garg tests are doing is trying to eliminate classical explanations of quantum results, when you do a two-time measurement.

当进行两次测量时，Leggett-Garg 测试正在尝试消除量子结果的经典解释。

When you’ve got a very quantum situation, you get something that would classically be quite paradoxical.

当你遇到一个非常量子的情况时，你会得到一些传统上相当矛盾的东西。

To go on to what macrorealism is, what we do is have a simple system with, say, it could be a spin, which just has two values, or it could be something more complicated by, you know, approximate position measurements of a particle like the moon, and then you just measure it a bunch of times and you compute average positions or average spins.

为了继续讨论宏观现实主义是什么，我们所做的是建立一个简单的系统，比如说，它可能是一个自旋，只有两个值，或者它可能是更复杂的东西，比如月球等粒子的近似位置测量，然后你只需对其进行多次测量，然后计算平均位置或平均自旋。

The important thing is you also have to compute correlations between different spins, like are two spins the same?

重要的是您还必须计算不同自旋之间的相关性，例如两个自旋是否相同？

And then from those you can actually try and assess are these correlations, are these measurements consistent with a classical model?

然后，您可以实际尝试评估这些相关性，这些测量结果是否与经典模型一致？

And by a classical model, what you really mean is an underlying system in which the thing you measure has a definite value, so the spin is either plus or minus, or the position is definitely this or definitely not that.

通过经典模型，您真正的意思是一个底层系统，在该系统中您测量的东西具有确定的值，因此旋转要么是正值，要么是负值，或者位置肯定是这个或绝对不是那个。

I know experts in quantum foundations who even said to me, “Why do you work on Leggett-Garg inequalities which confirm quantum behavior when we know quantum physics is true anyway?”

我认识量子基础领域的专家，他们甚至对我说：“当我们知道量子物理学是正确的时候，你为什么还要研究证实量子行为的 Leggett-Garg 不等式呢？”

And it seems like such a simple thing, but this is the idea of definiteness of value that actually is probably not true in quantum theory, and you prove that it’s not true by assuming that it is, and then deriving some contradictory consequences.

这看起来是一件很简单的事情，但这就是价值确定性的想法，实际上在量子理论中可能不是真的，你可以通过假设它是真的来证明它不是真的，然后推导出一些矛盾的结果。

But quantum physics, you can do a measurement that shows it definitely is in two places at the same time, and then you can measure it in each place and find it’s definitely there and definitely there.

但是量子物理学，你可以做一个测量，表明它肯定同时在两个地方，然后你可以在每个地方测量它，发现它肯定在那里，肯定在那里。

So sometimes people say like misty states or indefinite states.

所以有时人们会说像迷雾状态或不确定状态。

The only thing you can say is that if you assume it’s indefinite states and you assume also various measurements can’t influence each other, then you find a contradiction.

你唯一能说的是，如果你假设它是不确定的状态，并且你假设各种测量不能相互影响，那么你就会发现矛盾。

Therefore, the assumption that it was in a definite state is false.

因此，它处于确定状态的假设是错误的。

So it’s indirect actually.

所以实际上是间接的。

You can only refute the worldview of definite states.

你只能反驳一定状态的世界观。

It’s very elusive concept.

这是一个非常难以捉摸的概念。

And it’s the most important one in quantum physics, actually, I would say, conceptually.

实际上，我想说，从概念上讲，它是量子物理学中最重要的一个。

Except that in quantum physics, we do these experiments in such a way that there isn’t a dependent on context.

除了在量子物理学中，我们以不依赖于上下文的方式进行这些实验。

So two distant particles in an entangled state, you arrange it so they can’t possibly signal.

因此，两个遥远的粒子处于纠缠状态，你可以对其进行排列，这样它们就不可能发出信号。

It still looks like they’re talking to each other.

看起来他们仍然在互相交谈。

I mean, that’s really the true mystery.

我的意思是，这才是真正的谜团。

There is a quantum mechanical explanation.

有一个量子力学的解释。

The quantum mechanical explanation is it’s described by a wave, and the wave is a non-local thing that spreads out over space.

量子力学的解释是它是用波来描述的，而波是一种在空间中传播的非局域事物。

And it’s only when you try to think of it as two separate particles that it looks like two particles with different states.

只有当你试图将其视为两个独立的粒子时，它看起来才像两个具有不同状态的粒子。

The wave is like a hologram, and every little bit of the hologram contains a whole.

波就像全息图，全息图的每一点都包含一个整体。

That’s the best analogy, actually.

实际上，这是最好的比喻。

So, you’ve got simple histories at two times, and then you do a bunch of measurements of correlations and averages, and well, what you find is that if you assign definite values to these, then you end up with a contradiction, or more specifically, you end up with a probability which is negative.

所以，你有两次简单的历史，然后你对相关性和平均值进行了一系列测量，你发现，如果你为这些分配明确的值，那么你最终会得到一个矛盾，或者更具体地说，你最终会得到一个负的概率。

That essentially, a Leggett-Garg inequality or a Bell inequality, they are essentially probabilities for something.

本质上，Leggett-Garg 不等式或 Bell 不等式，它们本质上是某件事的概率。

But they actually turn out to be negative, which means that actually there isn’t an underlying probability, which means you were wrong to assume that they have definite values.

但它们实际上是负数，这意味着实际上不存在潜在的概率，这意味着你错误地假设它们具有确定的值。

In Leggett-Garg, we’re trying to actually explain that sequential measurements obey very non-classical ideas as long as we can justify this idea about invasiveness.

在 Leggett-Garg 中，我们试图实际解释，只要我们能够证明这种关于侵入性的想法是合理的，顺序测量就遵循非常非经典的想法。

I’ve spent quite a lot of time in my book on this to try understand it, but it’s very, very hard.

我在书中花了很多时间试图理解它，但这非常非常困难。

The whole area is just riddled with loopholes.

整个区域都充满了漏洞。

I don’t believe in truth.

我不相信真理。

I believe in multiple perspectives.

我相信多种观点。

It became a kind of credo of old-fashioned Copenhagen interpretation of quantum theory.

它成为老式哥本哈根量子理论解释的一种信条。

And it seems like the Leggett-Garg tests, if I’m understanding you, are maybe saying something deeper, that even if we take a lot of care to measure a system without disturbing it, that we do a non-invasive measurement, the classical picture could still fail.

如果我理解你的意思的话，Leggett-Garg 测试似乎可能在说一些更深层次的东西，即即使我们非常小心地测量一个系统而不干扰它，我们进行非侵入性测量，经典的图像仍然可能会失败。

Am, am I getting that right?

嗯，我说得对吗？

Now, in Leggett-Garg tests, you could do two sequential measurements, and if you get the expected quantum result, you could always say, “Well, the first measurement you actually, you were clumsy.” That’s the word we use.

现在，在 Leggett-Garg 测试中，你可以进行两次连续测量，如果你得到预期的量子结果，你总是可以说，“好吧，实际上，你的第一次测量很笨拙。”这就是我们使用的词。

So it’s not particularly a quantum issue here.

所以这里这并不是一个特别的量子问题。

It’s really, can you eliminate a classical model which has some invasive measurement?

真的，你能消除具有一些侵入性测量的经典模型吗？

But there is a quantum measurement aspect also to do with the wave function that’s affected, but you can actually factor that out.

但量子测量方面也与受影响的波函数有关，但你实际上可以将其分解出来。

So I mean classically supposing, uh, you’re speeding down the highway and a policeman has a radar gun, and they bounce the radar off your car and that’s how they work out the speed.

所以我的意思是，传统上假设，呃，你在高速公路上超速行驶，警察有一把雷达枪，他们将雷达从你的车上反射回来，这就是他们计算速度的方法。

The bounce actually slows the car down a tiny, tiny little bit.

弹跳实际上使汽车减慢了一点点。

There’s a change of momentum but it’s absolutely minuscule.

势头发生了变化，但绝对微乎其微。

But when you do that for a quantum particle, then the bouncing off of a photon can actually be quite significant.

但当你对量子粒子这样做时，光子的反弹实际上可能非常重要。

There is a way that Leggett and Garg first suggested for creating this non-invasiveness, and they called it an ideal negative measurement, where supposing this particle has two options at the first time, then you attach a detector on option A but not to option B.

Leggett 和 Garg 首先建议采用一种方法来创建这种非侵入性，他们称之为理想的负测量，假设该粒子第一次有两个选项，然后在选项 A 上安装一个探测器，而不是在选项 B 上安装探测器。

And if the detector doesn’t click, you say, “Well, option B happened,” but the detector wasn’t attached to B, so we didn’t actually disturb anything.

如果探测器没有发出咔哒声，你会说，“好吧，选项 B 发生了”，但探测器并未连接到 B，所以我们实际上并没有干扰任何东西。

Classically, that would actually be non-invasive.

传统上，这实际上是非侵入性的。

But there’s a tricky debate there saying, “Well, it’s really quantum, and it’s actually a wave function, and the wave function goes through both slits at the same time,” so it was still invasive at a quantum level.

但那里有一个棘手的争论，“嗯，它真的是量子的，它实际上是一个波函数，波函数同时穿过两个狭缝”，所以它在量子水平上仍然是侵入性的。

So a certain number of pirouettes have to be performed in order to actually get past that.

因此，必须进行一定次数的旋转才能真正克服这一点。

Those experiments simply confirm there’s an interference pattern, when you do a double slit experiment.

这些实验只是确认当你进行双缝实验时存在干涉图案。

Leggett-Garg tests they do more than that.

Leggett-Garg 测试他们做的还不止这些。

They not only confirm quantum, but they rule out alternative classical explanations, which is a stronger thing to do.

他们不仅证实了量子，而且排除了其他经典解释，这是更强有力的事情。

This is sort of interesting.

这有点有趣。

You can still get an interference pattern, but there’s a classical model for it actually, if the interference isn’t too big.

你仍然可以获得干涉图案，但如果干涉不太大，实际上有一个经典模型。

The thing is, interference is created by the fact that the wave goes through two holes, and what come out is two waves.

事实是，干涉是由于波穿过两个孔而产生的，结果是两个波。

They’re not probabilities, they’re waves that can be all positive and negative, and they can constructively interfere, so they get bigger.

它们不是概率，它们是波，可以是积极的，也可以是消极的，它们可以建设性地干扰，所以它们会变得更大。

And that’s like a classical effect actually, ’cause if you add two probabilities, they get bigger.

这实际上就像一个经典效应，因为如果你将两个概率相加，它们就会变得更大。

But they can destructively interfere, so they cancel each other out.

但它们可以破坏性地干扰，因此它们会相互抵消。

So you can get two waves coming in and you get nothing, which can’t happen with probabilities.

所以你可能会收到两波进来，但你什么也得不到，这在概率上是不可能发生的。

Now, if the destructive interference isn’t too big, you can still model them as like classical probabilistic flows, and that would satisfy the Leggett-Garg inequalities, which actually means that there is a classical model of interference patterns in a certain limited regime.

现在，如果破坏性干扰不是太大，您仍然可以将它们建模为经典概率流，这将满足 Leggett-Garg 不等式，这实际上意味着在某个有限范围内存在干扰模式的经典模型。

So for one of these big interferometers experiments with big particles, to really say this is definitely quantum and not pseudo-classical, you’d need to violate a Leggett-Garg inequality, basically.

因此，对于这些大粒子的大型干涉仪实验之一，要真正说这绝对是量子的而不是伪经典的，基本上你需要违反 Leggett-Garg 不等式。

That can all be done in principle.

原则上都是可以做到的。

I mean, even just with the data from existing experiments, basically.

我的意思是，即使只是利用现有实验的数据，基本上也是如此。

There’s always new perspectives coming along.

总是有新的观点出现。

The next generation of scientists will have new ways of thinking about these things.

下一代科学家将有新的方式来思考这些事情。

Um, I have a problem with that.

嗯，我有一个问题。

I mean, it’s this bordering on a kind of fundamentalism about accepting something as truth, that could be a wider discussion.

我的意思是，这接近于一种接受某事为真理的原教旨主义，这可能是一个更广泛的讨论。

But whatever theories are, they must be exposed to experimental tests and confirmation.

但无论理论是什么，它们都必须经过实验测试和证实。

I mean, really, absolutely.

我的意思是，真的，绝对。

I mean, it would be a wonderful thing if we started seeing differences.

我的意思是，如果我们开始看到差异，那将是一件很棒的事情。

But it is still a really striking thing that there have been no differences with theory ever observed.

但与观察到的理论没有任何差异仍然是一件非常惊人的事情。

I think behind this it is about what is the true interpretation of quantum physics, behind all these investigations, Bell inequalities, Leggett-Garg inequalities.

我认为这背后是关于所有这些研究背后的量子物理学的真正解释是什么，贝尔不等式，莱格特-加格不等式。

What these things do, they eliminate certain very natural worldviews.

这些东西的作用是消除某些非常自然的世界观。

So Bell inequalities shows that quantum physics and experiment are consistent with the worldview of local realism.

因此贝尔不等式表明量子物理和实验与局域实在论的世界观是一致的。

So the idea is that a particle has definite properties independent of what distant particles are doing.

因此，我们的想法是，粒子具有确定的属性，与远处粒子的行为无关。

Similarly, Leggett-Garg is testing macroscopic realism.

同样，Leggett-Garg 正在测试宏观现实主义。

A particle has definite properties irrespective of measurements in the past or measurements in the future, for that matter.

就此而言，无论过去或未来的测量结果如何，粒子都具有确定的属性。

So we know what reality is not.

所以我们知道现实不是什么。

But there are other worldviews, if you like, other interpretations.

但如果你愿意的话，还有其他的世界观，还有其他的解释。

One of the most famous, complements to these ideas is Bohmian mechanics, if you’re familiar with that one, or de Broglie–Bohm theory, which basically does take standard quantum mechanics, which is based on a wave function, but says the particle has a wave function, and it also has a position trajectory.

最著名的、对这些想法的补充之一是波姆力学（如果你熟悉这个理论）或德布罗意-玻姆理论，它基本上采用标准量子力学，它基于波函数，但说粒子具有波函数，并且它也有位置轨迹。

Then you don’t need to worry about is the particle here or there?

那么你就不用担心粒子是在这里还是那里？

The particle definitely has a trajectory.

粒子肯定有轨迹。

It’s definitely somewhere.

它肯定在某个地方。

The wave function has a back seat as a kind of, they call it a guidance field, like a fluid that sort of flows along and tells the particle what to do, but the particle always has a definite position.

波函数有一个后座，他们称之为引导场，就像流体一样流动并告诉粒子要做什么，但粒子总是有一个确定的位置。

And that’s very appealing, and it was invented actually shortly after quantum physics was invented.

这非常吸引人，而且它实际上是在量子物理学发明后不久就发明的。

And a lot of people like it because you know where you are, basically.

很多人喜欢它，因为基本上你知道自己在哪里。

You’ve got a definite path through.

你有一条明确的路径。

But it has a feature, which is that it’s non-local.

但它有一个特点，那就是它是非本地的。

Because there’s a wave function and a particle, that where the particle goes, the wave function can be spread out all over the place.

因为有波函数和粒子，粒子走到哪里，波函数就可以扩散到哪里。

So the guidance field for the particle can depend on very distant observers.

因此粒子的引导场可能取决于非常远的观察者。

It basically says that in an entanglement situation with distant particles, that one particle really can depend on what the other one is doing or what you measure on the other particle.

它基本上说，在与遥远粒子纠缠的情况下，一个粒子实际上可以依赖于另一个粒子正在做什么或你在另一个粒子上测量的东西。

But that might be it.

但也许就是这样。

I mean, you can have a world in which everything is definite, but it’s non-local.

我的意思是，你可以拥有一个一切都是确定的世界，但它是非局部的。

And that might also be true, actually.

事实上，这也可能是真的。

So that’s why I don’t believe in truth.

所以这就是我不相信真理的原因。

I believe in multiple perspectives.

我相信多种观点。

When I’ve given popular talks, I have the sense that the general public interested in physics, feel discomfort at the lack of understanding.

当我做大众演讲时，我有一种感觉，对物理学感兴趣的公众对缺乏理解感到不安。

That they want the physicist to deliver something mythologically meaningful to them in terms of the Big Bang, and they’re dissatisfied.

他们希望物理学家能够向他们传达一些关于大爆炸的具有神话意义的东西，但他们并不满意。

For me, I found a sort of other perspective in a more, let’s say, spiritual side, where I’m just happier to sit with the mystery of multiple perspectives.

对我来说，我在精神方面找到了一种其他视角，我更乐意坐在一起面对多重视角的神秘。

There was an American cosmologist who’s now more of a sort of mythologist and writer called Brian Swimme, S-W-I-M-M-E, who you may have come across.

有一位美国宇宙学家，现在更像是神话学家和作家，名叫布莱恩·斯维姆（Brian Swimme），S-W-I-M-M-E，你可能见过他。

And he’s basically…

而他基本上是……

starts with the idea that all societies have creation myths of one form or another, and modern society doesn’t necessarily have that.

首先是这样一种想法：所有社会都有一种或另一种形式的创世神话，而现代社会不一定有这种形式。

But he said, “Well, look, let’s take the Big Bang cosmology as a modern myth for our time.

但他说：“好吧，听着，让我们把大爆炸宇宙学当作我们这个时代的现代神话。

We don’t have to take it as true, but we can take it as a meaningful mythological tale from which we can draw a sense of guidance or purpose or perspective and so on.”

我们不必将其视为真实，但我们可以将其视为一个有意义的神话故事，从中我们可以汲取指导感、目的感或视角等等。”

And I felt in popular talks I’ve given, I felt that actually filled a gap in things where people have the Big Bang, but it’s presented to them as, almost as truth, but it doesn’t really fulfill people to a degree that they actually want.

我觉得在我做过的流行演讲中，我觉得这实际上填补了人们拥有大爆炸的事物的空白，但它呈现给他们的几乎是真理，但它并没有真正满足人们真正想要的程度。

Instead of worrying about “What it is”, you can ask, “Well, who am I in relation to that?”

你不必担心“它是什么”，而是可以问：“那么，与此相关的我是谁？”

Well, here’s the thing.

嗯，事情是这样的。

You see in physics, of course, we had two major revolutions at the beginning of the 20th century, one in relativity, one in quantum theory.

当然，在物理学中，我们在 20 世纪初发生了两次重大革命，一次是相对论，一次是量子理论。

In relativity, suddenly space and time are not even anything like what you think it is.

在相对论中，空间和时间突然变得完全不像你想象的那样。

In quantum theory, matter is not what you think it is.

在量子理论中，物质并不像你想象的那样。

So physicists had to get used to adjusting enormously their worldviews.

因此物理学家必须习惯于大幅调整他们的世界观。

There’s always new perspectives coming along.

总是有新的观点出现。

For sure the next generation of scientists will have new ways of thinking about these things.

可以肯定的是，下一代科学家将会有新的方式来思考这些事情。

Quantum information is a very current vogue, and a lot of people turn the question of interpretation into quantum informational notions.

量子信息是当前的时尚，很多人将解释问题转化为量子信息概念。

So I, I think what we will see is kind of multiple ways of actually saying the same thing about the sort of bizarreness and mystery of quantum mechanics.

所以我，我认为我们将看到的是多种方式实际上对量子力学的奇异性和神秘性说同样的事情。

So I think at the end of the day, I believe in mystery.

所以我想归根结底，我相信神秘。

Sitting with the mystery and the uncertainty, and that, that is the most comfortable position.

带着神秘和不确定性坐着，这是最舒服的姿势。

In fact, one of my meditation teachers said, I think, quoting from thousands of years, that a lot of these things are about the infinite one way or another, the beginning of the universe.

事实上，我的一位冥想老师说，我认为，引用数千年的经验，其中很多事情都与无限有关，宇宙的起源。

And instead of worrying about “What it is”, you can ask, “Well, who am I in relation to that?” That’s the simple question, I think, which is there in a lot of spiritual traditions.

你不必担心“这是什么”，而是可以问：“那么，与此相关的我是谁？”我认为这是一个简单的问题，很多精神传统中都存在这个问题。

So that’s where I am with physics.

这就是我对物理学的看法。

You know, how do I feel in relation to all this uncertainty and immensity?

你知道，面对所有这些不确定性和巨大性，我有何感受？

This dual modes that we were living.

我们生活在这种双重模式中。

One is theorizing about the world precisely in an attempt to understand it.

人们对世界进行理论化正是为了试图理解它。

And one is this other mode of meditating on thoughts and not trying to understand it.

一种是冥想思想而不是试图理解它的另一种模式。

And it seems to me that that’s kind of what he’s describing, this duality that he’s comfortable entertaining or or, you know, just experiencing.

在我看来，这就是他所描述的，他乐于娱乐或者，或者，你知道，只是体验这种二元性。

I mean, it was interesting to hear him talk about that.

我的意思是，听他谈论这个很有趣。

I’m uncertain, even in that conversation, if he’s suggesting that this is part of what people are looking for when they’re looking to understand the Big Bang, is they’re looking for a replacement or the myth itself.

即使在那次谈话中，我也不确定他是否暗示这是人们在寻求理解大爆炸时所寻找的一部分，他们是在寻找替代品还是神话本身。

And whether or not people are searching for it, that’s certainly not what we’re doing when we’re practicing scientists trying to understand the origin of the universe.

无论人们是否在寻找它，当我们科学家试图了解宇宙的起源时，这肯定不是我们正在做的事情。

You know, if you destroy all myths today and all memory of them and rebuild civilization, there’s gonna be different myths.

你知道，如果你摧毁今天所有的神话和它们的所有记忆并重建文明，就会有不同的神话。

But quantum mechanics is still gonna be there you know?

但量子力学仍然会存在，你知道吗？

Whether it’s described by matrices or anything else, quantum mechanics is still discoverable in a way that myth is not.

无论是用矩阵还是其他任何东西来描述，量子力学仍然是可以通过神话所无法发现的方式被发现的。

I don’t know that…

我不知道……

what do you think, Steve?

你觉得怎么样，史蒂夫？

And so when Jonathan talks about the multiple perspectives, there’s really the one universe, okay, leaving aside the multiverse, the universe we seem to be in, our observable part of the whatever multiverse, there’s one thing.

因此，当乔纳森谈到多重视角时，确实存在一个宇宙，好吧，撇开多元宇宙，我们似乎所处的宇宙，无论多元宇宙中我们可观察到的部分，只有一件事。

And if we have multiple perspectives, don’t they have to agree?

如果我们有多种观点，他们不是必须同意吗？

The Joy of Why is produced by PRX Productions.

《为什么的喜悦》由 PRX Productions 制作。

The production team is Caitlin Faulds, Jade Abdul-Malik, Genevieve Sponsler, and Merritt Jacob.

制作团队包括 Caitlin Faulds、Jade Abdul-Malik、Genevieve Sponsler 和 Merritt Jacob。

The executive producer of PRX Productions is Jocelyn Gonzales.

PRX Productions 的执行制片人是乔斯林·冈萨雷斯 (Jocelyn Gonzales)。

Edwin Ochoa is our project manager.

埃德温·奥乔亚是我们的项目经理。

From Quanta Magazine , Simon Frantz and Samir Patel provided editorial guidance with support from Samuel Velasco, Kit Sudol, Simone Barr, and Michael Kanyongolo.

Quanta 杂志的 Simon Frantz 和 Samir Patel 在 Samuel Velasco、Kit Sudol、Simone Barr 和 Michael Kanyongolo 的支持下提供了编辑指导。

Samir Patel is Quanta’s editor-in-chief.

萨米尔·帕特尔 (Samir Patel) 是广达的主编。

The episode art is by Chanelle Nibbelink, and our logo is by Jaki King and Kristina Armitage.

剧集艺术由 Chanelle Nibbelink 创作，我们的徽标由 Jaki King 和 Kristina Armitage 创作。

Special thanks to Garth Avery at the Cornell Broadcast Studio.

特别感谢康奈尔广播工作室的 Garth Avery。

I’m your host, Steve Strogatz.

我是你们的主持人，史蒂夫·斯特罗加茨。

If you have any questions or comments, please email us at [email protected] .

如果您有任何问题或意见，请发送电子邮件至 [email protected]。

Thanks for listening.

感谢您的聆听。

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获取发送到您的电子邮件收件箱的最重要新闻的摘要

Quanta Magazine moderates comments to facilitate an informed, substantive, civil conversation.

《Quanta》杂志对评论进行审核，以促进知情、实质性、文明的对话。

Abusive, profane, self-promotional, misleading, incoherent or off-topic comments will be rejected.

辱骂、亵渎、自我推销、误导、语无伦次或偏离主题的评论将被拒绝。

Moderators are staffed during regular business hours (New York time) and can only accept comments written in English.

版主在正常工作时间（纽约时间）有工作人员，并且只能接受英文评论。