内容来源：https://www.quantamagazine.org/in-expanding-de-sitter-space-quantum-mechanics-gets-even-more-elusive-20260330/

内容总结：

宇宙加速膨胀，量子力学规律面临新挑战

在理论物理中，宇宙的演化模型可简化为三种基本形态：膨胀、坍缩或保持静态。其中，膨胀的宇宙与我们的现实世界最为相似，却也最令物理学家感到困惑。当科学家尝试在膨胀的宇宙框架下理解量子理论时，往往会遭遇一系列悖论——微观量子规律与宏观宇宙经验难以调和。

这一难题的核心，与宇宙的时空几何形态密切相关。根据爱因斯坦广义相对论，时空结构受宇宙物质与能量支配。若宇宙中暗能量占据主导（表现为正的宇宙学常数），时空将呈现正曲率，即“德西特空间”。在此空间中，时空会指数级膨胀，形成“视界”：超出此范围的区域将永远无法被观测到，如同信息被膨胀的洪流吞噬。

德西特空间并非纯粹的假想。宇宙在早期暴胀阶段曾近似于德西特态，而当前随着暗能量驱动加速膨胀、物质密度持续稀释，我们的宇宙正再次趋近于德西特形态。然而，正是这种膨胀特性，给量子力学的基础带来了根本性挑战。

在量子理论中，测量行为依赖于观测者与被测系统的明确分离。但在德西特空间，剧烈的时空膨胀导致量子涨落无处不在，无法通过距离“屏蔽”。观测者仿佛永远被困在实验内部，无法找到一个稳定的参考边界来进行清晰测量。这使得定义粒子位置、数量甚至能量都变得异常困难，传统量子理论的框架在此近乎失效。

更令人意外的是，最新研究揭示，在指数膨胀的时空中，光子等无质量粒子可能由有质量的粒子构成，并可能发生自发衰变。这完全违背了平坦时空中的物理直觉，凸显了德西特空间的奇异性质。

为破解困局，部分物理学家将目光转向了黑洞。黑洞的视界与德西特视界具有相似性，且全息原理已在黑洞研究中取得进展——该原理认为，黑洞内部的三维信息可编码在其二维表面上。科学家希望借助黑洞这一“练习场”，将全息原理推广至德西特空间，从而理解量子引力在真实宇宙膨胀背景下的行为。

然而，初步尝试并不顺利。德西特空间存在无数以不同观测者为中心的视界，缺乏单一明确边界，导致现有计算工具难以直接套用。有理论甚至暗示，纯粹的德西特时空可能无法容纳任何量子态——这与我们充满量子粒子的宇宙观测事实明显矛盾。

尽管前路困难重重，物理学家仍持乐观态度。他们认为，通过对德西特空间、反德西特空间及平坦空间的比较研究，正有助于打破固有思维定式，剥离出技术性难题与本质性悖论。正如研究者所言，探索德西特空间如同“采摘低垂的果实”，虽充满未知，却可能为最终统一量子力学与宇宙学引力开辟关键路径。

中文翻译：

在膨胀的德西特空间中，量子力学变得更加难以捉摸

引言

理论上，宇宙可以呈现任何形状或大小，但科学家倾向于思考三种基本宇宙类型：膨胀型、坍缩型与静止型。在这三种简化模型中，膨胀宇宙是物理学家最难理解的类型。然而，我们的现实世界恰恰与这种模型最为相似。

当物理学家计算坍缩或静态宇宙中最微观量子层面的粒子行为时，他们能得到合乎逻辑的结果。但遗憾的是，我们的真实宇宙既非坍缩也非静止，而是在暗能量推动下持续膨胀的。

当科学家试图在膨胀宇宙中理解量子理论时，总会遭遇一个接一个令人困惑的悖论。在膨胀空间里，物理学家无法将我们体验的宏观世界与微观层面的运行规律统一起来。

如今，那些试图理解量子世界如何在膨胀宇宙中运作的物理学家，正寄望于一个意想不到的研究对象：黑洞。

时空的形态

1915年，阿尔伯特·爱因斯坦提出的引力理论——广义相对论，首次揭示了时空不可分割的本质。

时空会对宇宙中的物质作出反应：如果宇宙充满物质，随着时间的推移，物质引力的吸引作用会导致空间收缩；如果宇宙充满足够的暗能量（爱因斯坦时代称为宇宙学常数），其排斥力将导致空间膨胀。

爱因斯坦最初构建广义相对论时，坚信宇宙必须是永恒不变的。从几何角度而言，他认为宇宙应是无限平坦的，推动与拉扯时空的力会完全抵消。

但荷兰物理学家威廉·德西特持有更开放的观点。他意识到宇宙演化是相对论的必然结果。1916至1917年间，德西特发表了三篇探讨相对论可能性的论文（在此过程中，他向许多英语学者介绍了爱因斯坦的理论——这些原以德语撰写的成果因一战期间科学交流中断而被隔绝）。

德西特发现，一个空无一物（没有物质但存在宇宙学常数）的宇宙，根据宇宙学常数的符号，只能呈现三种形态之一：如爱因斯坦预言的平坦形态、正曲率形态或负曲率形态。

若宇宙学常数为正，时空将呈现正曲率，形成如今所称的德西特空间；若为负，则形成负曲率的反德西特空间；若为零，时空便是平坦的。

通过观察两个静止物体随时间推移的变化，可以判断所处宇宙的形状。想象在气球上标记两个点：当气球膨胀时，两点会彼此远离——这正是正曲率时空中的现象。在负曲率时空中，静止粒子会相互靠近，如同泄气的气球。

在正曲率的德西特空间里，空间以指数级速率膨胀。身处其中的观测者会因膨胀形成视界，界外信息永远无法传递进来。试图向视界外发送信息，就如同游泳者无法抗衡激流——膨胀空间会永远阻隔信息的传递。"膨胀如此迅猛，时空的某些区域即使等待永恒也无法观测到。"纽约大学理论物理学家莫妮卡·佩特解释道。

反德西特空间则如同一个盒子。这个盒子的边界无法触及（只有光能抵达），但它像画框般束缚着整个宇宙。万物都被拉回盒子中心。在此空间发送信息或投掷石块，最终都会像回旋镖般返回。"可以将其理解为无处不在的持续引力场。"佩特补充道。

我们并不完全生活在这些理想化宇宙中，而是处于物质与暗能量失衡的真实宇宙。不过，在远古的暴胀时期，我们的宇宙很可能与德西特空间极为相似。此后由于物质与光的存在，宇宙曾一度显得更平坦。但随着空间持续膨胀、物质日益稀薄，宇宙正重新变得越来越像德西特空间。

"人们认为最终我们将长期生活在纯粹或近似的德西特空间中。"加州大学圣地亚哥分校宇宙学家丹尼尔·格林表示。

量子难题

遗憾的是，德西特空间给试图理解微观宇宙的物理学家带来了巨大困扰。问题根源往往在于量子力学的奇异规则。

量子力学中不存在确定性。由于随机量子涨落，即使是"粒子位置"或"微小区域内粒子数量"这类简单问题，也无法获得明确答案。

然而，我们必须探究这些最微小的空间单元，才能理解量子世界与宏观经验的关联。探测精度越高，所需克服量子涨落背景的能量就越大。这正是物理学家使用数英里长的粒子对撞机、将粒子加速到极高能量的根本原因。

但单次测量所能使用的能量存在极限。在微小空间注入过多能量就会形成黑洞。为避免触及极限又能进行精确测量，物理学家需要找到降低量子涨落的新方法。

在平坦空间中，物理学家可以通过（等效于）无限远距离的测量来屏蔽涨落影响。反德西特空间中操作更简单：盒状宇宙边界处的量子涨落趋于零，在宇宙边缘开展实验就能获得完美的量子测量结果。

德西特空间则存在根本问题：离被测粒子越远，量子涨落并不会减小。"引力无处不在发生量子力学层面的涨落，没有任何地方可以屏蔽这种影响。"格林指出。由于缺乏可触及的测量边界，德西特空间中的实验者仿佛永远被困在自己的实验内部。

"量子力学的整个理论体系建立在'量子系统与被观测系统分离'的基础上。"格林解释道。但在德西特空间，量子系统与观测者之间没有界限，这套理论体系便土崩瓦解。

镜像迷思

德西特空间的问题远不止于此。在膨胀宇宙中，物理学家的许多直觉都失去了作用。例如能量不再守恒："膨胀本身就在持续注入能量，改变着宇宙。"瑞士洛桑联邦理工学院的若昂·佩内多内斯指出。

甚至连"粒子"的概念都变得不同。我们通常认为粒子是具有位置、能在空间中移动的物体。"在德西特空间中，这种概念不复存在。"佩内多内斯的前研究生、现任职于都灵大学的曼努埃尔·洛帕尔科表示。德西特空间中持续涌入的能量最终会导致粒子扩散或衰变。

在2025年5月发表于科学预印本网站arxiv.org的论文中，佩内多内斯与洛帕尔科提出了一个简单问题：指数膨胀空间中的光子（光粒子）会呈现何种形态？严谨数学推导得出的答案令他们震惊：在德西特空间中，无质量的光子竟可能由有质量粒子构成。

这一发现带来诸多奇特推论。例如，若无质量的光子本应稳定（粒子只能衰变成更轻的物体），但德西特空间中的有质量光子却能自发衰变成物质，而后物质又可再次衰变成光。"我们仍在努力理解其中的物理意义。"佩内多内斯坦言。

这正是物理学家在德西特空间中努力解析的典型计算。他们的目标是区分技术性难题与概念性难题，厘清"哪些可计算，哪些不可计算"。格林表示，希望这项工作能让科学家"更从容地解决其他重大难题，避免将小问题与可处理的难题混淆"。

佩内多内斯认为，尝试理解德西特、反德西特及平坦空间等不同宇宙形态具有重要价值，至少能深化对量子理论的认识。"德西特空间告诉我们，在平坦空间形成的直觉并非普适真理。研究德西特空间的意义就在于打破认知偏见。"

边界突破

为理解德西特空间的量子力学，部分物理学家转向研究黑洞。黑洞是光都无法逃脱的超致密天体。虽然无法直接探测黑洞内部，但物理学家已从理论上开展研究，近年来更取得了重大进展。

对黑洞认知的进步建立在全息原理基础上——黑洞二维表面能以某种方式编码内部三维空间的所有信息。物理学家将黑洞体积视为全息图般的幻象。

黑洞一直是研究量子引力的理想场景，因为其极端引力即使在量子尺度也产生强烈作用。但近年来物理学家发现，黑洞与德西特空间竟有着惊人的相似性。

黑洞周围光线无法克服引力的区域形成事件视界。德西特空间中，由于空间膨胀过快，超出特定距离的光线无法抵达观测者，也会形成类似视界。如果宇宙如物理学家预测般永远膨胀，我们就像被困在黑洞中——德西特视界之外的一切将永远无法触及。

"我们将黑洞宇宙学视为理解量子效应与宇宙学的热身课题。"斯坦福大学物理学家汤姆·哈特曼说，"每当在黑洞研究取得进展，我们都会追问：能否将其应用于德西特空间？"

迄今为止，当哈特曼等人尝试将黑洞研究成果应用于德西特空间时，结果总是难以理解。黑洞只有一个视界，而德西特空间存在无数以不同观测者为中心的视界。缺乏单一计算锚点的德西特宇宙，似乎根本无法容纳任何量子存在。"它本质上是空洞的。"哈特曼指出，"就像试图构建德西特空间的量子理论时，会发现它本质上排斥任何量子态。"

这与我们观测到的世界形成鲜明对比——现实既充满量子粒子，又日益呈现德西特特征。"最可能的解释是我们尚未正确理解那些计算结果。"格林分析道。

尽管如此，物理学家仍期待全息原理终将更广泛地应用于德西特空间，解答量子引力领域的重大谜题。"这一直是学界信念，而近年来的进展让这个信念更具说服力。"哈特曼表示。

德西特空间还隐藏着多少惊喜尚未可知，但洛帕尔科认为这片研究沃土已孕育出丰硕成果："我们正在采摘的，确实是那些唾手可得的果实。"

英文来源：

In Expanding de Sitter Space, Quantum Mechanics Gets Even More Elusive
Introduction
In theory, a universe can come in any shape or size, but scientists prefer to think about three basic kinds of universes: one that’s expanding, one that’s collapsing, and one that stays the same. Out of these three simplified models, an expanding universe is the hardest for physicists to understand. Yet it’s exactly the one our real world most resembles.
When physicists calculate what’s going on with particles at the smallest, quantum levels in a universe that is collapsing or static, they can get their results to make sense. Unfortunately for physicists, our real universe is not collapsing or static but expanding — being pushed apart by dark energy.
When scientists try to make sense of quantum theory in an expanding universe, they are met with one confusing paradox after another. In expanding space, physicists cannot square the world we experience with the way things work at the smallest levels.
Now physicists trying to make sense of how the quantum world works within our expanding universe are hoping to learn from an unexpected source: black holes.
The Shapes of Space-Time
In 1915, Albert Einstein’s theory of gravity, called general relativity, introduced the idea that space and time are inextricably linked.
Space and time react to the contents of the universe: If the universe is filled with matter, then over time, the attractive pull of that matter’s gravity should cause space to contract. If the universe is filled with enough dark energy — or what in Einstein’s day was called a cosmological constant — then over time, its push should cause space to expand.
When Einstein first wrote his general theory of relativity, he believed that our universe must be eternal and unchanging. In geometric terms, he believed that the universe should be infinite and flat, and that the forces that push and pull on space-time should exactly cancel out.
But a Dutch physicist named Willem de Sitter was more open-minded. He realized that it was a natural consequence of relativity for the universe to evolve. In 1916-17, de Sitter published three papers exploring relativity’s possibilities. (In the process, he introduced many English speakers to Einstein’s theories, which, originally written in German, had been siloed off because of severed scientific communications during World War I.)
De Sitter found that an empty universe — one devoid of matter, but which still has a cosmological constant — could take on one of just three shapes, depending on the sign of the cosmological constant: It could be flat, as Einstein predicted, positively curved, or negatively curved.
If the cosmological constant is positive, then space-time is positively curved into what is now called de Sitter space. If the cosmological constant is negative, then space-time is negatively curved into anti-de Sitter space. And if the cosmological constant is zero, then space-time is flat.
You can tell the shape of the universe you’re in by observing how two otherwise stationary objects evolve as time ticks forward. Imagine marking two dots on a balloon; if you blow up the balloon, the two dots will move away from each other as the balloon expands. This is what happens in positively curved space-time. In negatively curved space-time, stationary particles move toward each other, as if the balloon were deflating.
In positively curved de Sitter space, space expands at an exponential rate. If you are an observer living within de Sitter space, this expansion creates a horizon beyond which it’s impossible to communicate. If you try to send a message to someone beyond your horizon, the expanding space will ensure that it never makes it, almost like a current too powerful for a swimmer to overcome. “It’s expanding so fast that there are parts of space-time which, if you wait forever, you will never be able to see,” said Monica Pate, a theoretical physicist at New York University.
Anti-de Sitter space, on the other hand, acts like a box. The edge of this box isn’t something you can touch — only light can reach it — but it bounds an anti-de Sitter universe like a picture frame. Everything is drawn back to the box’s center. If you broadcast a message in anti-de Sitter space, or throw a rock, it will eventually boomerang back to you. “You can think of it as a constant” — not uniform, but persistent — “gravity everywhere,” Pate said.
We don’t live in exactly any of these idealized universes; we live in a universe with an unbalanced amount of both matter and dark energy. However, our universe likely looked a lot like de Sitter space in the far past, during a period of rapid expansion called inflation. After that, it looked flatter for a while, thanks to the presence of matter and light. But as space continues to expand today, and matter becomes sparser, the universe is looking increasingly like de Sitter space again.
“People think eventually we will live in pure de Sitter space, or something like it, for a very long time,” said Daniel Green, a cosmologist from the University of California, San Diego.
Quantum Questions
Unfortunately, de Sitter space causes huge problems for physicists trying to understand the universe at the smallest scales. The issue, as is so often the case, lies with the strange rules of quantum mechanics.
In quantum mechanics, there’s no such thing as certainty. Because of random quantum fluctuations, even simple questions about where a particle is or how many particles there are in a small area don’t have well-defined answers.
And yet, we need to probe those smallest bits of space to make sense of how the quantum world relates to our macroscopic experience. The more precisely you want to probe, the more energy you need to use to overcome a background of quantum fluctuations. Essentially, this is why physicists use miles-long particle colliders that accelerate particles to enormous energies.
But there’s a limit to how much energy you can use for a single measurement. Put too much energy in a small space, and you’ll create a black hole. To make precise measurements without hitting this limit, physicists need to find another way to reduce the quantum fluctuations.
In flat space, physicists can do this by taking measurements from (effectively) infinitely far away — far enough away to shield their measuring devices from the fluctuations. In anti-de Sitter space, it’s even easier: Quantum fluctuations go to zero on the boundary of a boxlike universe, so you can make perfect sense of quantum measurements by setting up your experiment on the universe’s edge.
In de Sitter space, there’s a problem. As you go farther away from the particles you’re measuring, quantum fluctuations don’t get any smaller. “Gravity is fluctuating, quantum mechanically, everywhere,” Green said. “And there’s no place to shield yourself from that.” Without an accessible boundary to take a measurement from, it’s as if an experimenter in de Sitter space is always stuck inside their own experiment.
“The whole machinery of quantum mechanics is built on the idea that there’s a quantum system, and then some big, giant experimentalist comes along and measures that system,” Green said. In de Sitter space, where there’s no line between the quantum system and the observer, this machinery falls apart.
Through the Looking Glass
The problems with de Sitter space get worse. Much of physicists’ intuition stops being helpful in an expanding universe. Energy, for instance, is not conserved. “The expansion is literally pumping energy, changing the universe,” said João Penedones of the Swiss Federal Institute of Technology Lausanne.
Even the concept of a particle is different. We typically think of a particle as an object that has some location and moves through space. “In de Sitter, there is no such thing,” said Manuel Loparco, a former graduate student of Penedones who is now at the University of Turin. The constant influx of energy in de Sitter space will eventually cause a particle to spread out or decay.
In a paper first posted to the scientific preprint site arxiv.org in May 2025, Penedones and Loparco tried asking a simple question: What does a photon, or a particle of light, look like in exponentially expanding space? The answer, which arose from careful mathematics, shocked them. Photons, which are massless, could be made out of massive particles in de Sitter space.
The finding has strange implications. For example, if photons don’t have any mass, they should be stable, because particles can only decay into lighter things. But massive photons in de Sitter space could spontaneously decay into matter — which could then decay back into light again. “We’re still trying to understand the physical implications of that,” Penedones said.
These are the types of calculations that physicists are working to make sense of in de Sitter space. Their goal is to sort the hard technical problems from the hard conceptual problems, asking “What can we calculate; what can’t we calculate?” Green said. The hope, he said, is that this work will leave scientists “in a much better position to solve some of these other bigger problems, because we won’t be confusing them with the smaller, more tractable problems.”
Penedones still finds value in the challenge of trying to understand different versions of the universe — de Sitter, anti-de Sitter, flat — if only to better understand quantum theory. “De Sitter tells you that your intuition that you develop in flat space is not true in all spaces,” he said. “That’s why it’s useful to do some things in de Sitter: to lose your prejudice.”
Pushing Boundaries
To try to make sense of the quantum mechanics of de Sitter space, some physicists have turned to black holes. Black holes are ultra-dense objects from which light cannot escape. While you cannot physically probe a black hole, physicists have studied their insides theoretically. And over the last few years, they’ve made a lot of progress.
Advancements in understanding black holes build on holography, the idea that the two-dimensional surface of the black hole somehow captures everything about the three-dimensional space inside it. Physicists treat the volume of the black hole as illusory, like a hologram.
Black holes have been useful settings for studying quantum gravity, since the extreme gravity of a black hole acts strongly even on the quantum scale. But in recent years, physicists have noted that black holes are also surprisingly similar to de Sitter space.
Around a black hole, the region where light can no longer overcome the black hole’s gravitational pull forms what’s called a horizon. In de Sitter space, a kind of horizon forms around an observer because space is expanding too quickly for light to reach them from beyond a certain distance. If our universe continues to expand forever as physicists predict, then it will be as if we are trapped in a black hole; everything beyond our de Sitter horizon will always remain out of reach.
“We think of black hole cosmology as being sort of a warm-up problem for understanding quantum effects and cosmology,” said Tom Hartman, a physicist at Stanford University. “So anytime we make progress on black holes, we go back and ask: Can we apply this to de Sitter?”
So far, when Hartman and others have tried to apply their advancements in understanding black holes to de Sitter space, they can’t seem to make sense of the results. A black hole has a single horizon, whereas de Sitter space has many, centered on different observers. Without a single boundary to anchor physicists’ calculations, a de Sitter universe seems incapable of holding anything quantum at all. “There’s something empty about it,” Hartman said. “Like if you try to formulate a quantum theory of de Sitter space, there’s some sense in which it wants to not have any states in it.”
This is a clear contrast to the world we observe, which is both full of quantum particles and increasingly de Sitter–looking. “The most likely answer is that we’re not interpreting that calculation correctly,” Green said.
Still, physicists are hopeful that holography will one day apply more generally to de Sitter space, and that it will answer some of our biggest questions about quantum gravity. “That’s always been kind of believed, but I think in the last few years, it’s become more convincing,” Hartman said.
What other surprises de Sitter holds are yet to be seen, but the landscape seems to be ripe for insights, Loparco said. “It’s really low-hanging fruit that we’re picking.”