A Dark Dimension Could Link Two of the Universe’s Great Unknowns

Ada Zejun Shen/ Quanta Magazine

沉泽君/广达杂志

For those who see the world as a dark place, the universe seems to offer little solace.

对于那些将世界视为黑暗之地的人来说，宇宙似乎无法提供多少安慰。

According to current estimates, approximately 70% of the stuff that makes up the cosmos consists of dark energy, an unknown force that pushes space to expand.

根据目前的估计，构成宇宙的物质大约有 70% 由暗能量组成，暗能量是一种推动空间膨胀的未知力量。

And another 25% consists of dark matter, a mysterious material that holds galaxies together.

另外 25% 由暗物质组成，暗物质是一种将星系维系在一起的神秘物质。

But semantically speaking, dark energy and dark matter are not so much “dark” as they are invisible.

但从语义上来说，暗能量和暗物质与其说是“暗”，不如说是看不见的。

They do not emit, reflect, nor absorb light, and they have so far proven impossible to observe directly.

它们不发射、反射或吸收光，迄今为止已证明无法直接观察它们。

Generally, dark energy and dark matter are regarded as separate entities, their elusiveness their primary link.

一般来说，暗能量和暗物质被视为独立的实体，它们的难以捉摸是它们的主要联系。

But recent astronomical observations have spurred scientists to look further into a less popular idea — that the two are in fact physically intertwined.

但最近的天文观测促使科学家进一步研究一个不太受欢迎的想法——两者实际上在物理上是交织在一起的。

Generally, dark energy and dark matter are regarded as separate entities.

一般来说，暗能量和暗物质被视为独立的实体。

But what if the two are in fact physically intertwined?

但如果两者实际上在物理上交织在一起呢？

In 2024, the research team known as DESI, for Dark Energy Spectroscopic Instrument, found evidence that the strength of dark energy, sometimes referred to as the “cosmological constant,” had lost its presumed constancy .

2024 年，名为 DESI（暗能量光谱仪器）的研究小组发现了证据，表明暗能量的强度（有时称为“宇宙常数”）已经失去了其假定的恒定性。

A 2025 study based on more than twice as much data also concluded that dark energy was changing over time .

2025 年的一项基于两倍以上数据的研究也得出结论，暗能量正在随着时间的推移而变化。

These results indicate that after attaining a maximum value about 2 billion years ago, dark energy may have begun to weaken.

这些结果表明，暗能量在大约 20 亿年前达到最大值后可能已经开始减弱。

But the results also suggested that in an earlier era, dark energy could have grown stronger, in seeming defiance of the law of energy conservation.

但结果还表明，在更早的时代，暗能量可能会变得更强，这似乎违反了能量守恒定律。

Researchers describe this as dark energy entering the “phantom regime.” They liken the situation to a ball rolling uphill.

研究人员将其描述为暗能量进入“幻影状态”。他们把这种情况比作一个球滚上坡。

It’s certainly possible, but only if the ball is under the influence of something other than gravity.

这当然是可能的，但前提是球受到重力以外的其他因素的影响。

A slice of a 3D map produced by the Dark Energy Spectroscopic Instrument team shows connected strands of galaxies forming the structure of our universe.

暗能量光谱仪器团队制作的 3D 地图切片显示了形成宇宙结构的相互连接的星系链。

Claire Lamman/DESI collaboration; custom colormap package by cmastro

Claire Lamman/DESI 合作； cmastro 的自定义颜色图包

A growing number of theorists are looking into the possibility that what’s influencing dark energy are its ties to dark matter.

越来越多的理论家正在研究影响暗能量的因素是它与暗物质的联系的可能性。

Even though scientists have assumed that dark energy and dark matter “don’t have anything to do with each other,” said Tim Tait , a particle physicist at the University of California, Irvine, “you can imagine a case where one influences the other.

加州大学欧文分校的粒子物理学家蒂姆·泰特（Tim Tait）表示，尽管科学家们假设暗能量和暗物质“彼此没有任何关系”，但“你可以想象其中一个影响另一个的情况。

And it would not be surprising if [they] were manifestations of a kind of unified theory of the dark universe.”

如果[它们]是一种黑暗宇宙统一理论的表现，也就不足为奇了。”

The idea that dark energy and dark matter interact is not new.

暗能量和暗物质相互作用的想法并不新鲜。

For example, Justin Khoury , a physicist at the University of Pennsylvania, investigated the prospect in 2005 .

例如，宾夕法尼亚大学物理学家贾斯汀·库里 (Justin Khoury) 于 2005 年对这一前景进行了调查。

Khoury explained that in that study, he and two coauthors posed a hypothetical question: Could there be a form of dark energy whose energy density increased over time?

库里解释说，在这项研究中，他和两位合著者提出了一个假设性问题：是否存在一种能量密度随着时间而增加的暗能量形式？

He and his collaborators found that if dark energy and dark matter could affect one another, they could produce what looked like (but was not) phantom behavior.

他和他的合作者发现，如果暗能量和暗物质可以相互影响，它们就可以产生看起来像（但不是）幻象的行为。

“It is the most natural, simplest way of achieving this,” Khoury said.

“这是实现这一目标的最自然、最简单的方法，”库里说。

Two decades later came the DESI finding that dark energy might actually be changing over time.

二十年后，DESI 发现暗能量实际上可能会随着时间的推移而发生变化。

The result spurred Khoury and two Pennsylvania colleagues, Meng-Xiang Lin and Mark Trodden, to construct a model of dark interactions based on a dark-sector analogue of quantum chromodynamics, a cornerstone theory of particle physics.

这一结果促使库里和两位宾夕法尼亚州的同事林梦翔和马克·特罗登基于量子色动力学的暗区模拟（粒子物理学的基石理论）构建了暗相互作用模型。

In the new model, both the energy density of dark energy and the mass of dark matter change in concert.

在新模型中，暗能量的能量密度和暗物质的质量同时变化。

Another recent study imagines something similar.

最近的另一项研究设想了类似的情况。

According to this model, which was published in January in the journal Physical Review D , dark matter could have transferred a small fraction of its energy to dark energy during a previous era of cosmic history.

根据一月份发表在《物理评论 D》杂志上的这个模型，暗物质可能在宇宙历史的前一个时代将其一小部分能量转移为暗能量。

“Dark matter is the main brake on [the universe’s] expansion,” said one of the authors, Elsa Teixeira, a cosmologist at the University of Montpellier in France, so easing up on that brake would have caused the expansion of the universe to accelerate.

“暗物质是[宇宙]膨胀的主要制动器，”该研究的作者之一、法国蒙彼利埃大学的宇宙学家埃尔莎·特谢拉（Elsa Teixeira）说，因此放松这种制动器将导致宇宙加速膨胀。

Elsa Teixeira, a cosmologist at the University of Montpellier in France, investigated a cosmological model in which dark energy and dark matter interact.

法国蒙彼利埃大学的宇宙学家艾尔莎·特谢拉（Elsa Teixeira）研究了暗能量和暗物质相互作用的宇宙学模型。

The appearance of phantom behavior is basically the result of bookkeeping, said David Andriot, a physicist at CNRS, the French National Center for Scientific Research.

法国国家科学研究中心 (CNRS) 的物理学家大卫·安德里奥 (David Andriot) 表示，幽灵行为的出现基本上是簿记的结果。

“Any change or evolution of the mass of dark matter has been put into the box of dark energy,” said Andriot, who presented his own coupled dark energy-dark matter model in May 2025 .

安德里奥特表示：“暗物质质量的任何变化或演化都被放入暗能量的盒子中。”他于 2025 年 5 月提出了自己的暗能量-暗物质耦合模型。

Cumrun Vafa , a physicist at Harvard University, agreed.

哈佛大学物理学家卡姆伦·瓦法 (Cumrun Vafa) 对此表示同意。

“The notion that you can compute dark energy independently of dark matter is wrong,” he said.

“可以独立于暗物质计算暗能量的想法是错误的，”他说。

“That assumption, often made by cosmologists and also followed by the DESI team, led to the physically unacceptable phantom behavior.”

“这种假设通常由宇宙学家做出，DESI 团队也遵循，导致了物理上不可接受的幻象行为。”

The DESI findings are not the only reason to consider an association between dark energy and dark matter.

DESI 的发现并不是考虑暗能量和暗物质之间关联的唯一原因。

Teixeira and colleagues’ recent study shows how allowing the two to interact can, at least in some scenarios, ameliorate one of the most persistent problems in cosmology: the Hubble tension.

特谢拉和同事最近的研究表明，至少在某些情况下，允许两者相互作用可以改善宇宙学中最持久的问题之一：哈勃张力。

At issue is the current expansion rate of the universe, known as the Hubble constant.

问题在于宇宙当前的膨胀率，即哈勃常数。

Its value can be measured by using light from the early universe, which provides a view of how the cosmos was growing in its earliest days.

它的价值可以通过使用早期宇宙的光来测量，这提供了宇宙早期如何生长的视图。

It can also be measured by drawing upon more recent phenomena, such as exploding stars called supernovas, which reveal how the universe is growing now.

它还可以通过利用最近的现象来测量，例如被称为超新星的爆炸恒星，它揭示了宇宙现在如何生长。

Studying the light from supernovas like this one — the flash of light in the bottom right of an image from the Hubble Space Telescope — can tell us about the expansion rate of the universe.

研究像这样的超新星发出的光——哈勃太空望远镜图像右下角的闪光——可以告诉我们宇宙的膨胀率。

NASA, ESA, A.

美国宇航局、欧洲航天局、A.

Goobar (Stockholm University), and the Hubble Heritage Team (STScI_AURA)

Goobar（斯德哥尔摩大学）和哈勃遗产团队 (STScI_AURA)

According to the standard model of cosmology, that expansion rate should be the same no matter how you measure it.

根据宇宙学的标准模型，无论你如何测量，膨胀率都应该是相同的。

But in recent years, scientists have found that the expansion rate of the early universe and that of the more recent universe vary by approximately 9%.

但近年来，科学家发现早期宇宙和较近代宇宙的膨胀率相差约9%。

That discrepancy, or tension, “has provoked heated debates in the cosmology community about whether this difference could be due to systematic errors or whether it is a signal of new physics,” Teixeira and her co-authors wrote.

特谢拉和她的合著者写道，这种差异或紧张“在宇宙学界引发了激烈的争论，争论这种差异是否是由于系统错误造成的，或者是否是新物理学的信号。”

Their model posits that in a world where dark energy and dark matter interact, what seemed to be a crisis caused by disparate expansion rates instead becomes something to be expected.

他们的模型假设，在暗能量和暗物质相互作用的世界中，由不同的膨胀率引起的看似危机反而变成了可以预料的事情。

If dark energy and dark matter do interact, it could mean that they have a common origin, Khoury said.

库里说，如果暗能量和暗物质确实相互作用，这可能意味着它们有共同的起源。

Ongoing work in string theory — the idea that our universe, at its smallest, most fundamental level, is made up of vibrating strings — suggests a way these concepts might be connected.

弦理论中正在进行的工作——我们的宇宙在最小、最基本的层面上是由振动的弦组成的——提出了一种可能将这些概念联系起来的方式。

In 2019, building on the idea in string theory that dark energy is naturally varying , Vafa and two collaborators concluded that the mass of dark matter particles may also vary over time.

2019 年，基于弦理论中暗能量自然变化的观点，Vafa 和两位合作者得出结论，暗物质粒子的质量也可能随时间而变化。

This led them to propose in 2022 that dark matter and dark energy could share a link with a so-called dark dimension.

这导致他们在 2022 年提出暗物质和暗能量可以与所谓的暗维度共享联系。

Cumrun Vafa, a physicist at Harvard University, thinks the mass of dark matter may vary over time.

哈佛大学物理学家卡姆伦·瓦法认为，暗物质的质量可能会随着时间的推移而变化。

String theory posits the existence of six or seven extra dimensions in addition to our familiar three dimensions of space and one of time.

弦理论假设除了我们熟悉的空间的三个维度和时间的一个维度之外，还存在六到七个额外的维度。

All of these dimensions are thought to be as small as physically possible — close to the Planck scale (10 -35 meters) — but the researchers proposed that the dark dimension could be significantly bigger than the others — on the order of a micron (10 -6 meters).

所有这些维度都被认为是物理上尽可能小的——接近普朗克尺度（10 -35 米）——但研究人员提出，暗维度可能比其他维度大得多——大约为微米（10 -6 米）。

Gravitons, theoretical particles that impart the force of gravity, could leak into this enlarged dark dimension.

引力子，一种赋予重力的理论粒子，可能会泄漏到这个扩大的黑暗维度中。

If they did, they would pick up mass and become what are called dark gravitons.

如果它们这样做了，它们就会获得质量并成为所谓的暗引力子。

These massive gravitons would reside in the dark dimension, but their gravitational effects could be felt in other dimensions, allowing them to fulfill the role that is normally ascribed to dark matter.

这些巨大的引力子将驻留在黑暗维度中，但它们的引力效应可以在其他维度中感受到，从而使它们能够发挥通常归因于暗物质的作用。

In this scenario, “there is a very natural coupling between dark energy and dark matter,” said Georges Obied , a physicist at the University of Chicago.

在这种情况下，“暗能量和暗物质之间存在非常自然的耦合，”芝加哥大学物理学家乔治·奥比德说。

Changes in the size of the dark dimension would affect both dark energy and dark matter.

暗维度大小的变化会影响暗能量和暗物质。

In a July 2025 paper , Obied and Vafa, along with Alek Bedroya of Princeton and David Wu of Harvard, found that the scenario proposed in 2019 was consistent with the DESI data.

在 2025 年 7 月的一篇论文中，Oied 和 Vafa 以及普林斯顿大学的 Alek Bedroya 和哈佛大学的 David Wu 发现，2019 年提出的情景与 DESI 数据一致。

Their model predicts that the strength of dark energy and the mass of dark matter will decrease over time and that the rate at which dark energy changes will be proportional to its energy density.

他们的模型预测，暗能量的强度和暗物质的质量将随着时间的推移而减少，并且暗能量变化的速度将与其能量密度成正比。

Because astrophysical measurements tell us that the energy density of dark energy is extraordinarily small, “it won’t change fast,” Vafa said.

因为天体物理测量告诉我们暗能量的能量密度非常小，“它不会很快改变，”瓦法说。

“It’s not surprising that we didn’t see it until now,” he said, because the rate of change is so tiny.

“我们直到现在才看到这一点并不奇怪，”他说，因为变化的速度是如此之小。

“We had to wait the entire age of the universe to detect something that small.”

“我们必须等待整个宇宙的年龄才能探测到这么小的东西。”

If dark matter is coupled to dark energy, dark matter particles could interact with one another through a new, long-range force that is separate from gravity.

如果暗物质与暗能量耦合，暗物质粒子可以通过一种与重力无关的新的远程力相互作用。

The good news, Obied said, is that “there could be astrophysical ways of testing this.”

奥比德说，好消息是“可能有天体物理学的方法来测试这一点。”

Coincidentally, two physicists — Marc Kamionkowski , now at Johns Hopkins University, and Michael Kesden, now at the University of Texas at Dallas — have already looked into one such test.

巧合的是，两位物理学家——约翰·霍普金斯大学的马克·卡米恩科夫斯基和德克萨斯大学达拉斯分校的迈克尔·凯斯登——已经研究了一项这样的测试。

In a paper published in 2006, they imagined a sequence of events in which two galaxies come close to each other and the gravity of one galaxy tugs at the other.

在 2006 年发表的一篇论文中，他们想象了一系列事件，其中两个星系彼此靠近，一个星系的引力拉扯另一个星系。

If dark matter has a stronger gravitational attraction to other dark matter than it does to ordinary matter, a special kind of “tidal tail” — an extended stream of stars, gas, and dust — would form behind one of the galaxies.

如果暗物质对其他暗物质的引力比对普通物质的引力更强，那么一种特殊的“潮汐尾”——由恒星、气体和尘埃组成的延伸流——就会在其中一个星系后面形成。

Kesden and Kamionkowski looked for this effect and didn’t find it, which enabled them to set an upper bound on the possible strength of the extra attractive force.

凯斯登和卡米翁科斯基寻找这种效应，但没有找到，这使他们能够为额外吸引力的可能强度设定上限。

The upper bound was about 20 times bigger than the number Vafa’s team proposed, so the predicted value fell well within the observational bound.

上限大约比 Vafa 团队提出的数字大 20 倍，因此预测值完全在观测范围内。

“It is interesting that we are now finding connections between that fairly abstract work and observational and experimental work,” Kamionkowski said.

卡米翁科夫斯基说：“有趣的是，我们现在正在寻找相当抽象的工作与观察和实验工作之间的联系。”

The fact that a prediction based on calculations from string theory roughly agreed with the astrophysical evidence does not confirm the validity of these “stringy” models.

基于弦理论计算的预测与天体物理学证据大致一致这一事实并不能证实这些“弦”模型的有效性。

But any correspondence between string theory and experiment is gratifying to Vafa, who has spent the past four decades trying to wrest the theory from the purely conceptual realm to the point of generating testable predictions.

但弦理论和实验之间的任何对应关系都令瓦法感到满意，他在过去的四十年里一直试图将弦理论从纯粹的概念领域提升到产生可检验的预测的地步。

Obied, one of Vafa’s former Ph.D. students, is driven by the same goal.

奥比德是瓦法的前博士生之一。同学们，都在同一个目标的推动下。

Understanding dark energy and dark matter and the relationship they may share is a daunting problem, he said.

他说，了解暗能量和暗物质以及它们可能共享的关系是一个艰巨的问题。

“And I think it’s very beneficial to come at this in different ways” — be it from observational cosmology, from particle physics, or from string theory.

“我认为以不同的方式来解决这个问题是非常有益的”——无论是从观测宇宙学、粒子物理学还是弦理论。

“This is how people should do science,” Obied said.

“这就是人们从事科学研究的方式，”奥比德说。

“I mean, it’s the job of theoretical physicists to explore everything that’s possible, to get all the possibilities on the table.

“我的意思是，理论物理学家的工作就是探索一切可能的事物，将所有的可能性摆上桌面。

And eventually, the data will help us decide.”

最终，数据将帮助我们做出决定。”

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《Quanta》杂志对评论进行审核，以促进知情、实质性、文明的对话。

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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。

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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。