Vast cosmic voids are far from empty  — they're hiding something dark

浩瀚宇宙虚空并非空无一物 —— 它们隐藏着黑暗之物

At the very largest scales, galaxies are not scattered around randomly. Instead, they form a pattern called the cosmic web. In fact, this is the largest pattern found in nature, with galaxies clumping together to form clusters, stringing themselves along filaments that stretch tens of millions of light-years on a side, and extending along broad walls that separate vast regions of the universe from each other.

在最宏大的宇宙尺度上，星系并非随机散布。相反，它们构成了一种被称为 “宇宙网络” 的结构。事实上，这是自然界中发现的最大型结构：星系聚集形成星团，沿着长达数千万光年的纤维状结构排列，并延伸至广阔的 “宇宙墙”，这些 “墙” 将宇宙中的广袤区域彼此分隔开来。

These are the cosmic voids. The smallest voids are about 20 million light-years across on a side, and the largest ones go for hundreds of millions of light-years. They are the true cosmic deserts. But just like deserts on Earth, they're not entirely empty. So what's in these cosmic voids?

这些区域便是宇宙虚空。最小的虚空直径约 2000 万光年，而最大的虚空直径可达数亿光年。它们堪称真正的 “宇宙沙漠”。但就像地球上的沙漠一样，它们并非完全空无一物。那么，这些宇宙虚空里究竟有什么？

Within the voids, sophisticated observations can detect faint hints of structures, like small, dim dwarf galaxies dotting the vast expanses. Computer simulations reveal that there is even more to the story.

在虚空中，通过精密观测可以探测到微弱的结构迹象，例如点缀在广袤空间中的小型昏暗矮星系。计算机模拟则揭示了更多奥秘。

In addition to normal matter, there's dark matter. We can only see high-density clumps of dark matter because those have enough gravity to pull in normal matter that turns into stars and galaxies to illuminate our observations. And in the voids, there simply isn't enough density of dark matter, so nothing really lights up.

除了普通物质，这里还存在暗物质。我们只能观测到高密度的暗物质团块，因为它们拥有足够的引力吸引普通物质，后者会坍缩形成恒星和星系，从而照亮我们的观测视野。而在虚空中，暗物质的密度根本不足，因此没有任何物质能够发光。

But computer simulations show that there are filaments and tendrils of dark matter crisscrossing the voids like a faint echo of the grand cosmic web, repeating itself in miniature.

但计算机模拟显示，暗物质构成的纤维和卷须如同宇宙网络的微弱回声，以微型的形式在虚空中纵横交错。

Yet there are regions deep within the cosmic voids where not even dark matter penetrates. These are the lowest-density regions of the entire universe.

然而，在宇宙虚空的深处，仍有一些连暗物质都无法渗透的区域。这些地方是整个宇宙中密度最低的区域。

Still, if you work hard enough and are patient enough, you will detect an occasional bit of matter. The overall average density of the universe is roughly one hydrogen atom per cubic meter, and in the deepest corners of the voids, the average density is over 100 times less than that. So you could swim through the deepest voids and encounter a single hydrogen atom in, say, an entire football field's worth of space.

尽管如此，只要足够努力和耐心，仍能探测到偶尔出现的微量物质。宇宙的整体平均密度约为每立方米一个氢原子，而在虚空的最深处，平均密度比这还要低 100 倍以上。因此，即便在最深处的虚空中 “遨游”，可能在一整个足球场大小的空间里，也只能遇到一个氢原子。

There is something else that fills up the voids: radiation. The cosmic microwave background — the leftover light from when the universe was only 380,000 years old — soaks the entire cosmos, filling every cubic centimeter. It makes up the vast majority of the radiation in the universe. No matter where you go, you can't escape the cosmic microwave background.

虚空中还充满了另一种物质：辐射。宇宙微波背景 —— 这种来自宇宙诞生仅 38 万年时的残余光线 —— 浸透了整个宇宙，填满了每一个立方厘米的空间。它构成了宇宙中绝大部分的辐射。无论身处何处，都无法逃脱宇宙微波背景的 “笼罩”。

But that radiation is very old and very deeply redshifted into the microwave bands. It carries essentially no energy, so it barely counts.

但这种辐射非常古老，且因严重红移而处于微波波段。它几乎不携带能量，因此几乎可以忽略不计。

That leaves one other component of the deepest parts of the voids. It's a very weak component, but it is a critical one for the universe: dark energy. Dark energy accounts for roughly 70% of the total energy density of the cosmos, but in most of the dense structures, like galaxies and clusters, you never know it's there.

这就引出了虚空最深处的另一个组成部分。它虽然极其微弱，但对宇宙而言却至关重要：暗能量。暗能量约占宇宙总能量密度的 70%，但在星系和星团等大多数高密度结构中，它的存在几乎无从察觉。

Deep in the voids, however, dark energy takes over. It's the only thing left. This means that although the voids lack matter, they are filled to the brim with dark energy. And it's in the voids that dark energy is doing its work of tearing the universe apart.

然而，在虚空深处，暗能量占据了主导地位。它是唯一的 “幸存者”。这意味着，尽管虚空缺乏物质，却被暗能量填满。正是在这些虚空中，暗能量正推动着撕裂宇宙的进程。