In recent years, a curious hypothetical particle called the axion, invented to address challenging problems with the strong nuclear force, has emerged as a leading candidate to explain dark matter. Although the potential for axions to explain dark matter has been around for decades, cosmologists have only recently begun to seriously search for them. Not only might they be able to resolve some issues with older hypotheses about dark matter, but they also offer a dizzying array of promising avenues for finding them.
近年来，发明的一个奇怪的假设粒子称为轴心，以解决强大的核力量的挑战性问题，已成为解释暗物质的领先候选人。尽管斧头解释暗物质的潜力已经存在数十年了，但宇宙学家直到最近才开始认真寻找它们。他们不仅可以通过关于暗物质的旧假设来解决一些问题，而且还为寻找它们提供了令人眼花di乱的有前途的途径。
But before digging into what the axion could be and why it’s so useful, we have to explore why the vast majority of physicists, astronomers, and cosmologists accept the evidence that dark matter exists and that it’s some new kind of particle. While it’s easy to dismiss the dark matter hypothesis as some sort of modern-day epicycle, the reality is much more complex (to be fair to epicycles, it was an excellent idea that fit the data extremely well for many centuries).
但是，在挖掘斧头可能是什么以及为什么如此有用的原因之前，我们必须探讨为什么绝大多数物理学家，天文学家和宇宙学家都接受了存在暗物质存在的证据，并且它是一种新的粒子。尽管很容易将暗物质假设视为某种现代的日志车，但现实却更为复杂（公平到周年环保，这是一个绝妙的想法，在许多世纪中非常适合数据）。
The short version is that nothing in the Universe adds up.
简短的版本是，宇宙中没有任何内容加起来。
We have many methods available to measure the mass of large objects like galaxies and clusters. We also have various methods to assess the effects of matter in the Universe, like the details of the cosmic microwave background or the evolution of the cosmic web. There are two broad categories: methods that rely solely on estimating the amount of light-emitting matter and methods that estimate the total amount of matter, whether it’s visible or not.
我们有许多可用的方法来测量星系和簇等大物体的质量。我们也有各种方法来评估物质在宇宙中的影响，例如宇宙微波背景的细节或宇宙网络的演变。有两个广泛的类别：方法仅依赖于估计发光物质和估计物质总量（无论是否可见）的方法。
For example, if you take a picture of a generic galaxy, you’ll see that most of the light-emitting matter is concentrated in the core. But when you measure the rotation rate of the galaxy and use that to estimate the total amount of matter, you get a much larger number, plus some hints that it doesn’t perfectly overlap with the light-emitting stuff. The same thing happens for clusters of galaxies—the dynamics of galaxies within a cluster suggest the presence of much more matter than what we can see, and the two types of matter don’t always align. When we use gravitational lensing to measure a cluster’s contents, we again see evidence for much more matter than is plainly visible.
例如，如果您为通用星系拍照，您会发现大多数发光物质都集中在核心中。但是，当您测量银河系的旋转速率并使用它来估计物质总量时，您会得到更大的数量，并提示它与发光的东西并不完美地重叠。星系群也发生了同样的事情 - 集群中星系的动态表明存在比我们看到的要多得多，而两种类型的物质并不总是对齐。当我们使用重力镜头来测量簇的内容时，我们再次看到证据比清晰可见的要多得多。
