Audio Edition: Old ‘Ghost’ Theory of Quantum Gravity Makes a Comeback

欢迎收听Quanta音频版。

Welcome to the Quanta audio edition.

在每两周一次的节目中，我们会为您带来来自Quanta网站关于基础科学和数学发展的故事。

In each of these biweekly episodes, we bring you a story direct from the Quanta website about developments in basic science and mathematics.

我是苏珊·瓦莱特。

I'm Susan Vallet.

理解引力的秘密是否近五十年来一直就在我们眼前？

Has the secret to understanding gravity been hiding in plain sight for almost fifty years?

越来越多的物理学家发现，量子场论在引力方面的表现远超预期。

A growing number of physicists are discovering that quantum field theory works far better for gravity than previously expected.

接下来请收听。

That's next.

如果你发现了一种天然的基因编辑机制，并由此引发了一场革命，那会怎样？

What if your discovery of a natural gene editing mechanism launched a revolution.

如果你的抽象数学证明与现实世界有着意想不到的联系，那会怎样？

What if your abstract math proofs had unexpected connections to the real world?

如果你的诺贝尔奖获奖成果——关于宇宙膨胀的研究——只是故事的开端呢？

What if your Nobel Prize winning work on the expanding universe was just the beginning of the story?

如果你加入我们，史蒂夫·斯特罗加茨和简·艾琳，在一个播客里了解所有这些以及更多内容呢？

And what if you joined us, Steve Strogatz and Jan eleven, to learn about all of this and much more on one podcast?

收听《Quanta》杂志《为什么的乐趣》第五季。

Listen to season five of Quanta Magazine's The Joy of Why.

新剧集从6月11日起每隔一个周四更新。

New episodes drop every other Thursday starting June 11.

我们最熟悉的那种力，仍然是最神秘的——重力。

The force we experience most intimately remains the most mysterious, gravity.

物理学家知道，被称为光子的粒子大规模迁移如何照亮我们的家，也知道胶子粒子群如何把原子核凝聚在一起。

Physicists understand how vast migrations of particles called photons light up our homes and how swarms of gluon particles hold together the cores of our atoms.

但他们无法解释，如果有重力粒子的话，它们是如何让我们小时候的勺子掉到地上的。

But they can't say what gravity particles, if any, delight us as babies by enabling our spoons to plummet to the floor.

重力这种力一直很难用粒子来解释，以至于许多物理学家干脆放弃了这种思路。

The force of gravity has proved so difficult to account for in terms of particles that many physicists have abandoned that approach altogether.

他们考虑的是，引力，以及整个现实，可能不是由粒子构成的，而是由微小的弦或者其他奇怪的东西构成的。

They consider the possibility that gravity, and with it, reality as a whole, might instead be made of tiny strings or other strange things.

但在理论物理学的某个角落，粒子方法正在卷土重来。

But in one corner of the theoretical physics world, the particle approach is staging a comeback.

越来越多的物理学家正在用粒子物理学的标准方法——量子场论——来研究引力。

A growing band of physicists has been using the typical approach to particle physics known as quantum field theory for gravity.

长期以来，人们一直认为这种理论的应用存在致命缺陷。

This use of the theory was long considered fatally flawed.

但这些物理学家现在发现，它的效果比前辈们预期的要好得多。

But these physicists are now finding that it works far better than their predecessors expected.

卢卡·博宁·范特是罗特博德大学的理论物理学家，他的计算帮助巩固了旧理论。

Luca Bonin Fante is a theoretical physicist at Rotbaud University in the whose calculations have helped shore up the old theory.

他说，到目前为止，没有任何迹象表明我们应该抛弃量子场论。

He says so far there's no hint telling us that we should throw quantum field theory away.

他说，实际上恰恰相反。

He says actually it's the opposite.

当你把标准的量子场论应用到引力上时，你得到的不仅仅是一个叫二次引力的独特理论。

When you apply the standard quantum field theory to gravity, you don't just get a unique theory called quadratic gravity.

他说，你还会得到新的预测。

He says you also get new predictions.

这些预测还没有经过测试。

Those predictions have not yet been tested.

而且从纯理论的角度来看，二次引力有一些诡异的特性，仍然让很多物理学家感到不安。

And on purely theoretical grounds, quadratic gravity has eerie features that still spook many physicists.

但是二次引力的爱好者们并没有被它的异常特性吓退。

But quadratic gravity enthusiasts aren't put off by its abnormalities.

相反，他们认为这些特性是之前未被重视的可能性，可能是量子场论所允许的。

On the contrary, they view these features as previously unappreciated possibilities that may be permitted by quantum field theory.

比如，也许在微观层面上，效应偶尔会跑到原因前面，也许二次引力中出现的负能量幽灵粒子可以在方程中安全存在，而不会在实验中制造悖论。

For instance, perhaps effects occasionally sneak ahead of their causes at the microscopic level, and perhaps negative energy ghost particles that arise in quadratic gravity can exist safely in the equations without creating paradoxes in experiments.

博宁·范特说，幽灵粒子可能是当我们试图在更深层次上理解引力和量子场论时出现的新物体。

Bonin Fante says ghosts may be new objects that appear when we try to understand gravity and quantum field theory at a deeper level.

你知道，场论是物理学家用来描述其他所有基本力的框架。

As you know, field theory is the framework physicists use to describe all of the other fundamental forces.

而且从他们一开始尝试把引力纳入量子场论起，就明显看出这两者的结合不会顺利。

And from the moment they tried to fit gravity into quantum field theory, it was obvious the union was going to be a rocky one.

量子场是不断波动的物质，逐渐在空间中扩散。

Quantum fields are rippling substances that gradually spread through space.

量子场中的波动就是粒子。

A ripple in a quantum field is a particle.

通过交换这些粒子波动的流，一个物体可以推或拉另一个物体，从而产生力。

By exchanging streams of these particle ripples, one object can push or pull on another, exerting a force.

比如，电磁力是通过电磁场中的扰动传递的，我们把这些扰动称为光子。

For instance, the electromagnetic force is conveyed through disturbances in the electromagnetic field that we call photons.

量子场论中一个非常令人头疼的事实是，场的行为取决于它可能支持的所有波动。

A deeply inconvenient truth of quantum field theory is that what a field does depends on each and every one of the ripples it can conceivably support.

而这些波动有无数种形状和大小。

And those ripples come in an unending number of shapes and sizes.

当物理学家最初发明量子场论时，他们试图用它来研究电子和光子的问题。

When physicists first invented quantum field theory, they tried to use it to ask questions about electrons and photons.

他们的计算变成了无穷大，因为求和中的每一项都要考虑无限连续、越来越小的波动。

And their calculations went infinite because each term in a sum tried to account for a never ending continuum of ever smaller ripples.

但无限项的和根本不是答案。

But a sum of infinite terms was no answer at all.

在20世纪40年代末，物理学家理查德·费曼、朱利安·施温格和朝永振一郎各自独立地找到了一个变通方法，把那些无穷无尽的波动变成了清晰的答案，并因此获得了诺贝尔奖。

In the late nineteen forties, physicists Richard Feynman, Julian Schwinger, and Shinichiro Tomanaga independently hit on a workaround that would turn those endless ripples into clear answers, earning themselves a Nobel Prize.

他们意识到，可以把计算中那些看似无穷大、无法直接处理的部分，重新表达为对两个已知常数的净效应，这两个常数已经在实验室里测量过，就是电子的质量和电荷。

They realized that they could reexpress the unknowable infinite seeming parts of their calculations in terms of their net effect on two known constants that had already been measured in the lab, the electron's mass and charge.

这样一来，各项的值就固定了，之后物理学家就可以预测关于电磁场的任何他们想知道的量。

Doing so fixed the values of the terms, after which physicists could predict anything they liked about the electromagnetic field.

这个技巧被称为重正化。

The trick is known as renormalization.

它看起来像是一个代数上的小把戏，但在接下来的几十年里，物理学家逐渐明白了它为什么有效。

It seemed like an algebraic hack, but over the following decades, physicists came to understand why it worked.

重整化是一种把场中最小的波动模糊掉、只保留它们整体效果的方法。

Renormalization was a way of blurring out the smallest ripples in a field and including only their net effects.

在电磁场的情况下，这个方法之所以有效，是因为那些小波动的影响是有限的。

In the case of the electromagnetic field, this works because the impact of the small ripples is limited.

波动越小，它们对大波动的影响就越小。

The smaller the ripples get, the less they influence the larger ripples.

但引力就不一样了。

But gravity works differently.

对。

Yes.

引力也有自己的场，那就是时空本身的结构。

Gravity too has a field, the fabric of space time itself.

在广义相对论中，爱因斯坦把引力描述为物体沿着时空结构的曲线下落的结果。

In his general theory of relativity, Einstein described gravity as a consequence of objects falling along curves in this space time fabric.

这个引力场并不是充满空间的某种波动的东西，而是空间本身就是波动的。

This gravitational field is not a rippling thing that fills space per se, but rather a rippling thing that is space.

物理学家已经探测到穿过这个场的引力波，而这个场中最微小的涟漪会带来无穷无尽的麻烦。

Physicists have detected gravitational waves traveling through this field, and the tiniest ripples in this field cause no end of trouble.

当费曼和一位名叫布莱斯·德维特的同事尝试对引力进行重整化时，他们发现时空涟漪越小，它们的影响反而越大。

When Feynman and a colleague by the name of Bryce DeWitt tried to renormalize gravity, they found that the tinier the space time ripples, the more they matter.

它们以无数微妙的方式影响更高层次的时空波动，这些影响无法仅用几个可测量的常数来概括。

They influence the rippling of space time at higher levels in innumerable subtle ways that can't be summed up only in terms of a few measurable constants.

这个方法失败了。

The trick failed.

微小的时空涟漪拒绝被模糊掉。

The tiny space time ripples refused to be blurred out.

马萨诸塞大学阿默斯特分校的量子场论专家约翰·多纳休说，大家都对此感到担忧。

John Donahue, an expert in quantum field theory at the University of Massachusetts Amherst, says everyone was concerned about this.

他说，这就是为什么量子广义相对论被视为一个难题。

He says it's the reason that quantum general relativity was considered a problem.

在二十世纪七十年代中期，已故的凯洛格·斯特尔，当时还是布兰迪斯大学的研究生，发现有一种方法，也是唯一的方法，可以阻止那些困扰早期量子广义相对论尝试的无穷大泛滥。

In the mid nineteen seventies, the late Kellogg Stell, then a graduate student at Brandeis University, saw that there was a way and only one way to stop the inundation of infinities that had plagued earlier attempts to quantize general relativity.

广义相对论可以写成一个方程，其中只有一个项代表时空的曲率。

General relativity can be written as an equation that has a single term representing space times curvature.

把费曼和德维特的重新规范化方法应用到这条方程上，你会得到一种粒子波动，也就是引力子，以无数种方式波动。

Apply Feynman and DeWitt's renormalization procedure to this equation and you get one type of particle ripple, the graviton, rippling in infinite ways.

但斯特尔发现，他可以修改爱因斯坦的方程，让时空更接近电磁场，波动越小，其影响就越小。

But Stel figured out that he could modify Einstein's equation so that space time more closely resembled the electromagnetic field with ripples that became less significant as they got smaller.

这样，它们的总体效应就可以用几个可测量的常数来概括，就像电磁学中的电子电荷和质量一样。

Their overall effects could then be captured in just a few measurable constants, analogous to the electron's charge and mass in electromagnetism.

这个引力理论后来被称为二次引力，因为它包含了两个与曲率平方相关的新项，而且它是可重新规范化的。

This theory of gravity came to be known as quadratic gravity because it contained two new terms related to the square of the curvature, and it was renormalizable.

它和电磁学一样合理。

It made just as much sense as electromagnetism.

斯特尔去年去世前一直是伦敦帝国理工学院的教授，他说，这给了你一个引力的量子理论。

Stell, who was a professor at Imperial College London until his death last year, said that gives you a quantum theory of gravity.

他说，那么当然，问题就是，你喜欢它吗？

He said, then, of course, the question is, do you like it?

大多数物理学家，包括其中一些人，并不这么认为。

Most physicists, among them, did not.

在2025年4月的一次采访中，斯特尔说他也意识到这不会一帆风顺。

In an April 2025 interview, Stell said he was also aware that not everything was going to be hunky dory about this.

问题在于，这种增强的时空结构现在可以承载三种类型的涟漪。

The problem was that this enhanced fabric of space time could now host three types of ripples.

第一项代表正常的引力子，但两个曲率平方项引入了两种新粒子。

The first term represents the normal gravitons but the two curvature squared terms spring two new particles into the picture.

其中一种无害，斯特尔称之为可爱的小标量粒子，但另一种则是个幽灵。

One is inoffensive, what Stel called a sweet little scalar particle, but the other is a ghoul.

第三项带来的一个不受欢迎的负号引发了混乱。

An unwelcome minus sign stemming from the third term unleashes chaos.

相关的粒子具有负能量，因此时空结构通过产生它而实际上获得了能量。

The associated particle has negative energy so the space time fabric actually gains energy by creating it.

这意味着越来越多的这种粒子会自发出现，将空间本身搅动成一场越来越剧烈的能量风暴。

This means that more and more of such a particle will spontaneously appear whipping space itself into an increasingly energetic inferno.

更糟糕的是，涉及这第三种粒子的过程可能具有负概率，这简直毫无意义。

Worse, events involving this third particle may have a negative probability of taking place, a meaningless proposition.

物理学家把这种粒子称为幽灵粒子，并说被幽灵纠缠的理论是有问题的。

Physicists call such particles ghosts and say that theories haunted by ghosts are sick.

它们在数学上是不自洽的。

They're mathematically inconsistent.

1977年，斯特尔发表他的研究后不久，物理学家们偶然发现了一种更健康的量子引力理论，叫做超引力。

Shortly after Stel published his research in 1977, physicists stumbled across a healthier quantum gravity theory called supergravity.

它通过假设每种已知的基本粒子都有一个尚未发现的超对称伙伴粒子，解决了一系列问题。

It solved a handful of problems by positing that each known elementary particle teams up with an as yet undiscovered superpartner particle.

超引力立刻引起了理论物理学家的关注，斯特尔也不例外。

Supergravity immediately captured the attention of theoretical physicists, including Stel.

这个理论最终与弦理论融合，主导了该领域数十年。

The theory would eventually merge with string theory and dominate the field for decades.

而带有幽灵粒子和不自洽性的二次引力，根本无法与之竞争。

Quadratic gravity, with its ghosts and inconsistencies, couldn't compete.

物理学家们对它关注不多，每年引用斯特尔的论文只有10到20次。

Physicists paid it little attention, citing Stel's paper just 10 to 20 times per year.

但这个理论从未完全消失。

But the theory never completely faded away.

理论物理学家们时不时地会重新研究它。

Theorists returned to it here and there.

到了20年代，由于弦理论未能实现早期研究者承诺的惊人突破，超对称粒子也在大型强子对撞机的实验中未能现身，人们对二次引力的兴趣又回升了。

Interest rose in the 20 as string theory failed to deliver the spectacular breakthroughs its early practitioners had promised, and superpartners failed to materialize in experiments at the Large Hadron Collider.

2014年，意大利物理学家阿尔贝托·萨尔维奥和亚历山德罗·斯特鲁米亚想知道二次引力能否解决一个许多人曾期望超对称粒子来解决的难题。

In 2014, Italian physicists, Alberto Salviou and Alessandro Strumia wondered whether quadratic gravity could solve a puzzle that many had expected the super partners to address.

这个难题被称为层级问题。

The puzzle is known as the hierarchy problem.

它问的是，为什么引力与其他三种基本力相比显得极其微弱。

It asks why gravity seems impossibly weak compared to the other three fundamental forces.

为什么其他力有一个尺度，而引力却有一个截然不同的特殊尺度？

Why is there one scale for those forces and a special dramatically different one for gravity?

萨尔维乌和斯特鲁米亚发现，斯特尔理论中的两个额外粒子可能有助于将这两个尺度分开。

Salviou and Strumia found that the two extra particles from Stel's theory could help push the two scales apart.

这让他们开始思考，那个鬼粒子是否真的是个致命问题。

That got them wondering whether the ghost was truly a deal breaker.

几年后，比萨大学的达米亚诺·安塞尔米发现，研究人员可以通过使用费曼为描述量子事件所制定的规则的其他版本，来避免带有鬼粒子的理论所遇到的陷阱。

A few years later, Damiano Anselmi of the University of Pisa found that researchers can avoid the pitfalls encountered by theories with ghosts by using alternative versions of the rules Feynman laid out for describing quantum events.

安塞尔米说，人们曾有一种印象，认为这个问题已经有了定论，但实际上并非如此。

Anselmi says there was an impression that the last word had been said, but that wasn't true.

最近因对量子场论的贡献而获得著名的J·J·樱井奖的约翰·多纳休，也开始研究这个被认为有问题的理论。

John Donahue, who recently won the prestigious JJ Sakurai Prize for his contributions to quantum field theory, also started studying the allegedly sick theory.

多纳休与现在巴西圣保罗大学的加布里埃尔·梅内塞斯合作，发现在简单场景中，鬼粒子实际上并不会造成物理学家所担心的那种破坏。

Working with Gabriel Menezes, now of the University of Sao Paulo in Brazil, Donohue found that in simple scenarios, the ghost particles don't actually wreak the havoc physicists feared.

它们非常不稳定，往往在有机会激发真空或表现出负概率之前就消失了。

They're so unstable, they tend to vanish before they have time to fire up the vacuum or manifest negative probabilities.

真空保持稳定，概率总和仍然为100%，这是被称为幺正性的基本性质。

The vacuum stayed calm and probabilities continued to add up to 100%, an essential property known as unitarity.

多纳休说他们有几个例子，正是这些例子让他相信了这一点。

Donahue says they have a few examples, which are what made him believe it.

他说，那些别人认为会违反幺正性的情况，实际上似乎并没有违反。

He says things that everyone else would have said violated unitarity don't seem to.

那么，为什么幽灵粒子在斯特尔的理论中似乎只是悄悄潜伏，而不是积极作祟呢？

So why does the ghost seem to silently lurk rather than actively haunting Stell's theory?

二次引力理论的爱好者们提出了几个相互关联的想法。

Quadratic gravity enthusiasts have hit on a couple of overlapping ideas.

萨尔维奥和多伦多大学的名誉物理学家鲍勃·霍尔德姆分别注意到，在计算概率的最后一步，也就是最可疑的那一步，可以通过调整来保证概率始终为正。

Salvio and Bob Holdem, a physicist emeritus at the University of Toronto, have independently noticed that it's possible to tweak the final and rather suspect step in the calculation of probabilities in a way that guarantees they'll always stay positive.

多纳休还指出，即使你不按照安塞尔米提出的方式修改费曼规则，幽灵粒子也几乎不存在。

And Donahue points out that even if you don't change Feynman's rules in the manner proposed by Ansami, ghosts barely exist.

它们只在短距离内短暂出现。

They show up only fleetingly over short distances.

在这些情况下，需要付出沉重的代价，要么是稳定性，要么是幺正性。

In those instances, there's a heavy price to be paid, stability or unitarity.

相反，问题在于通常严格的因果顺序。

Rather, it's the normally rigid ordering of cause and effect.

那个负号让幽灵粒子能短暂地回到过去，从而影响它们原本无法影响的粒子。

That minus sign allows ghost particles to briefly skip backward in time where they can influence particles that they otherwise couldn't.

在这种图景下，我们所体验到的不可阻挡的时间向前流动，其实是许多时间上模糊的微观瞬间的平均结果。

In this picture, the relentless forward flow of time that we experience would emerge as a delicate average over lots of temporally squishy micro moments.

理解其他基本力都需要物理学家掌握像重整化这样的新奇概念。

Understanding each of the other fundamental forces required physicists to master strange new concepts like renormalization.

所以研究人员认为，也许幽灵粒子以及为处理它们而修改的量子场论规则，正是解开引力的关键。

So the researchers argue, perhaps ghosts and the modified rules of quantum field theory that are needed to deal with them are the key that will unlock gravity.

即使引力并非如此运作，物理学家也认为，严格探索带有幽灵负号的量子场论行为是有价值的。

And even if gravity doesn't work this way, physicists see value in rigorously exploring the behavior of quantum field theories with ghostly minus signs.

海德堡大学研究其他引力理论的研究员本杰明·诺尔表示，这里面确实有值得理解的东西。

Benjamin Knorr, a researcher at Heidelberg University who works on other gravity theories, says there's something to understand there.

要确定这些对标准量子场论的扩展彼此之间有多兼容，以及它们是否会在更严苛的情况下失效，还有很多工作要做。

Much work remains to determine how compatible these proposed extensions of standard quantum field theory are with each other and whether they'll fail in more demanding situation.

但大多数情况下，研究二次引力的科学家们已经不再害怕鬼粒子了。

But for the most part, quadratic gravity researchers have stopped fearing ghosts.

布埃南凡特说，它们在数学上现在讲得通了。

Buonenfante says they mathematically make sense now.

不过，其他理论家仍然担心这些修正是否真的能解决所有潜在问题。

However, other theorists still harbor qualms as to whether these fixes really address all the potential problems.

你不能随便改动物理学中像因果性和幺正性这样关键的原则。

You don't simply tinker with critical tenets of physics like causality and unitarity.

哥本哈根大学的量子引力研究员阿莱西娅·普拉塔尼亚说，他们正在努力，但这个问题仍然悬而未决。

Alessia Platania, a quantum gravity researcher at the University of Copenhagen, says they're working hard, but it's still open as a question.

对于二次引力的研究者来说，这种不确定的“捉鬼”工作还是值得的。

For quadratic gravity researchers, the uncertain work of ghostbusting is worthwhile.

除了理论上的数学优势，斯特尔的那个可爱的小标量粒子，正是那种可能在大爆炸期间推动宇宙急剧膨胀的粒子和相关量子场，许多宇宙学家认为这造就了我们今天看到的宇宙。

On top of the theory's mathematical advantages, Stell's sweet little scalar is exactly the sort of particle and associated quantum field that could have driven an explosive expansion of the cosmos during the Big Bang, which many cosmologists believe set up the universe we see today.

事实上，苏联物理学家阿列克谢·斯塔罗宾斯基在1980年就用二次引力提出了第一个关于这种初始增长的理论，即宇宙暴胀。

In fact, Soviet physicist Alexei Starobinsky used quadratic gravity to formulate the first theory of that initial growth spurt termed cosmic inflation in 1980.

宇宙暴胀应该在时空中激起涟漪，在天空中留下微妙的印记。

Cosmic inflation should have set off ripples in space time that left subtle imprints on the sky.

尽管进行了大量搜索，这些印记仍未被发现，这排除了几种暴胀模型。

These haven't been seen despite intense searching, ruling out several models of inflation.

但也许我们目前还看不到它们。

But maybe we can't see them yet.

安塞尔米等人的最新研究表明，在二次引力理论下，宇宙产生的涟漪太小，目前的望远镜无法探测到。

Recent work from Anselmi and others suggests that a universe with quadratic gravity should produce ripples too small for current telescopes to detect.

下一代天文台或许能够捕捉到这些微弱的波动。

Next generation observatories may be able to pick up these weak waves.

多纳休表示，在他看来，从量子场论的角度来看，斯塔罗宾斯基暴胀是唯一仍然合理的模型。

Donahue says in his opinion, Starobinsky inflation is the only remaining one that makes sense from a quantum field theory point of view.

由于意外友好的幽灵、斯塔罗宾斯基暴胀的日益流行，以及其他量子引力理论陷入困境，二次引力理论越来越受欢迎。

Through a combination of unexpectedly friendly ghosts, the growing popularity of Starobinsky inflation, and other quantum gravity theories languishing in the doldrums, quadratic gravity has grown in popularity.

斯托尔的原始论文最近每年被引用超过150次。

Stall's original paper has recently been accruing more than 150 citations each year.

如果这些幽灵能被彻底消除，而且有一天我们探测到了斯塔罗宾斯基暴胀产生的时空涟漪，那么二次引力对现实意味着什么呢？

If the ghosts can be fully vanquished and the space time ripples from Starobinsky inflation are detected someday, what would quadratic gravity imply about reality?

看法不一。

Opinions vary.

来自弦理论、黑洞物理学以及其他领域的线索，让很多人普遍认为，在某个微观尺度上，时空应该会分解成更奇特的东西。

Clues from string theory, black hole physics, and other places have led to a widespread belief that space time should unravel into stranger stuff at some microscopic scale.

但如果二次引力最终被证明是引力的终极理论，那么无论你放大多少倍，那颤抖的时空结构都可能一直存在。

But if quadratic gravity turns out to be the ultimate theory of gravity, then the quivering space time fabric could persist no matter how far you zoom in.

荣休物理学家鲍勃·霍尔登说，我们谈论的是一种真正的连续描述，一直到任意小的尺度。

Physicist emeritus Bob Holdem says we're talking about a true continuum description all the way to arbitrarily small scales.

他称之为“永恒的时空”。

He calls it space time forever.

这种可能性最近得到了推动。

That possibility recently received a boost.

2024年，多纳休和合作者发现了关于二次引力中引力子碰撞的一个重要数学事实。

In 2024, Donahue and collaborators discovered an important mathematical fact about how gravitons collide in quadratic gravity.

随着碰撞越来越激烈，引力反而变弱，这让计算变得更容易。

As collisions get more intense, gravity gets weaker, making calculations easier.

这种现象被称为渐近自由。

It's a phenomenon known as asymptomatic freedom.

这个结果表明，二次引力永远不会失效，可以带你一直深入到现实的最深层。

The result suggests that quadratic gravity never breaks down and could take you all the way to the deepest levels of reality.

多纳休说，这可能让它成为终极理论，但他并不确信这就是终极理论。

Donahue says this could allow it to be the final theory, but he is not convinced that this is the final theory.

另一种可能是，二次引力虽然可重整化且渐近自由，但仍然不是对引力的完整描述。

The alternative is that quadratic gravity, despite being renormalizable and asymptomatically free, still isn't a complete account of gravity.

记住，重整化就像是对世界进行过滤，把最细微的波动模糊掉。

Remember that renormalization amounts to a filter over the world that blurs out its tiniest ripples.

可重整化的理论就是那些即使忽略这些细节，整体图景也不会改变太多的理论。

Renormalizable theories are those in which glossing over those features doesn't change the overall picture much.

模糊的图景依然很有效。

The blurry picture works well.

不可重整化的理论，就是那种模糊图像和清晰图像差别很大的理论。

Non renormalizable theories are those where the blurry picture looks quite different from the sharp picture.

这种理论的效果不如你期望的那么好，因为每一个微小的细节都很重要。

It doesn't work as well as you'd like because every tiny detail matters.

所以，像量子化广义相对论这样的不可重整化理论，迫使物理学家同时去理解现实的所有层次。

So non renormalizable theories like quantized general relativity challenge physicists to understand all of reality's layers at once.

二次引力理论出人意料的成功，暗示着引力或许最终也能有一个足够好用的模糊图像。

The surprising successes of quadratic gravity hint that gravity may yet turn out to have a blurry picture that works well enough after all.

在某个空间尺度以下，也许任何复杂的细节，无论是弦、圈还是什么都没有，都可以被忽略，而你仍然能得到一个完全自洽的理论。

Below a certain spatial scale, it may be that any complicated details, whether those are strings, loops or nothing at all, can be ignored and you'll still get a fully consistent theory.

如果是这样的话，物理学家就能准确预测引力子的碰撞以及宇宙的膨胀，而不用去担心最小尺度上到底发生了什么。

If that's the case, physicists can accurately predict how gravitons collide and how the universe inflated without worrying about what's truly going on at the smallest scales.

多纳休说，这可能是终极理论，也可能不是，但也许它会成为一个封闭的、自洽的现实层次。

Donahue says it may or may not be the ultimate theory, but maybe it becomes a closed self consistent layer of reality.

斯特尔也持同样的看法。

Stell shared that view.

他自己再也没有回到这个理论，只是远远地关注着它最近的复兴。

He never returned to his theory himself, keeping tabs on its recent revival from afar.

但他后来开始怀疑，这个理论可能确实有些价值。

But he came to suspect that it had some value after all.

斯特尔说，他自己的反应是，它可能是一个中间状态的联系。

Stell said his own reaction to it is its possible link, a kind of intermediate regime.

迈克尔·肯永戈洛协助制作了本期节目。

Michael Kenyongolo helped with this episode.

我是苏珊·瓦布莱特。

I'm Susan Vablet.

想了解更多这个故事，请阅读查理·伍德的完整文章《量子引力的旧幽灵理论卷土重来》，在我们的网站quantamagazine.org上。

For more on this story, read Charlie Wood's full article, Old Ghost Theory of Quantum Gravity Makes a Comeback, on our website, quantamagazine.org.

《量子杂志》是一份编辑独立的在线出版物，由西蒙斯基金会支持，旨在增进公众对科学的理解。

Quantum Magazine is an editorially independent online publication supported by the Simons Foundation to enhance public understanding of science.

来自PRX。

From PRX.