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Photo taken on December 24, 2015 shows scientists of the National Space Science Center under the Chinese Academy of Sciences (CAS), work with the Dark Matter Particle Explorer (DAMPE) Satellite, "Wukong", at the science mission hall of the center in Beijing. China's DAMPE has detected unexpected and mysterious signals in its measurement of high-energy cosmic rays, which might bring scientists a step closer to shedding light on invisible dark matter. (XINHUA)

2015年12月24日,中国科学院国家空间科学中心(CAS)的科学家们在北京中心的科学任务大厅与暗物质粒子探测卫星(DAMPE)“悟空”合作。中国的DAMPE在测量高能宇宙射线的过程中发现了意想不到的神秘信号,这可能会让科学家们更接近于揭开暗物质的光。(新华社)

It constitutes most of the mass in the universe, but we've never seen it. Now China's first dark-matter detection satellite, "Wukong", is helping scientists lift the "cloak of invisibility" from dark matter.

它构成了宇宙中的大部分物质,但我们从未见过它。现在中国的第一颗暗物质探测卫星“悟空”正在帮助科学家揭开暗物质的“神秘形象”。

The initial detection results of cosmic ray electrons and positrons based on observation by Wukong, or the Dark Matter Particle Explorer (DAMPE) launched in December 2015, were published in the latest issue of the academic journal, Nature.

宇宙射线电子和正电子在2015年12月发射的“暗物质粒子探索者”的初步检测结果,在最新一期《自然》杂志上发表。

Scientists still need time to discern whether the signals detected by DAMPE come from dark matter or other astrophysical phenomena.

科学家们还需要时间来判断DAMPE探测到的信号来自暗物质还是其他天体物理现象。

But what is dark matter?

但是什么是暗物质呢?

Comparing the universe to a cosmic pie made up of three parts, scientists calculate that normal matter, such as atoms, stars, galaxies, trees, rocks and dust, accounts for just under 5 percent. About 26.8 percent is dark matter and 68.3 percent dark energy, both of which are invisible. Everything we experience is really a tiny fraction of reality.

将宇宙比作由三部分组成的宇宙派,科学家们计算出,普通物质,如原子、恒星、星系、树木、岩石和尘埃,占了不到5%。大约26.8%是暗物质,68.3%是暗能量,两者都是看不见的。我们所经历的一切都只是现实的一小部分。

How was dark matter discovered?

暗物质是如何被发现的?

Dark matter cannot be seen or touched. The ghost-like material passes right through you as if you don't exist. But why are scientists so sure it does exist?

暗物质是看不见摸不着的。幽灵般的物质通过你就像你不存在一样。但为什么科学家们如此确信它确实存在呢?

In the early 1930s, Swiss astrophysicist Fritz Zwicky was studying the Coma galaxy cluster. His calculations implied the visible mass didn't generate enough gravity to hold the galaxies together. Without another kind of matter that humans can't see, galaxies would have flown away from each other. So he concluded there must be something nobody had detected before to hold them in place. He coined the term "dark matter" to describe it.

在20世纪30年代早期,瑞士天体物理学家弗里茨•兹威基正在研究彗发星系团。他的计算表明,可见的质量并没有产生足够的引力将这些星系聚集在一起。如果没有人类看不到的另一种物质,星系就会相互远离。所以他得出结论,一定是以前没有人检测到的东西把它们固定住。他创造了“暗物质”一词来描述它。

Zwicky was decades ahead of his time. His deduction didn't raise attention in academic circles until the 1970s, when U.S. astronomer Vera Rubin and her colleagues confirmed it by studying galaxy rotation. They also found single galaxies, not just clusters, have more mass than the observable light suggested. The work of Rubin and her team helped to firmly establish the notion of dark matter.

兹威基比他的时代早了几十年。他的推论直到20世纪70年代才引起学术界的关注,当时美国天文学家Vera Rubin和她的同事通过研究星系旋转证实了这一点。他们还发现单个星系,而不仅仅是星团,比可见的光有更多的质量。鲁宾和她的团队的工作帮助坚定了暗物质的概念。

Since then, astronomical discoveries such as rotation curves of disk galaxies, X-ray observations of clusters and the gravitational lensing effect have all suggested the existence of dark matter.

从那时起,天文发现,如圆盘星系的旋转曲线,星系团的x射线观测和引力透镜效应都暗示着暗物质的存在。

How do we search for the cosmic ghost?

我们如何寻找宇宙的灵魂?

Dark matter, which does not emit or reflect any electromagnetic radiation, cannot be seen directly by optical or electromagnetic observation equipment. Currently, scientists mainly use three methods to detect dark matter.

暗物质,它不发射或反射任何电磁辐射,不能直接通过光学或电磁观测设备看到。目前,科学家主要使用三种方法来检测暗物质。

The first method involves extremely sensitive apparatuses on Earth based on the idea that dark matter should travel through the material of a detector until it hits a nucleus. The interaction would then provide a small amount of recoil heat or energy that can in principle be measured. Since the signal would be very weak, such experiments are usually conducted deep underground sheltered from cosmic rays and other interfering signals.

第一种方法涉及到地球上非常敏感的仪器,因为暗物质应该穿过探测器的材料,直到它到达原子核为止。然后,相互作用会提供少量的反冲热能或能量,这在原则上是可以测量的。由于信号很弱,这样的实验通常是在地下深处进行的,远离宇宙射线和其他干扰信号。

China runs the world's deepest underground dark matter lab in the southwest province of Sichuan, some 2,400 meters below the surface.

中国是世界上最深的地下暗物质实验室,位于中国西南部的四川省,大约有2400米深。

In the second method, scientists collide high-energy particles with the aim of creating dark matter. Although the dark matter particle cannot be observed directly, it will take away energy. By analyzing the missing energy, scientists can infer the properties of the dark matter particle.

在第二种方法中,科学家们将高能粒子与制造暗物质的目标相碰撞。虽然暗物质粒子不能直接观测,但它会带走能量。通过分析缺失的能量,科学家可以推断出暗物质粒子的性质。

The Large Hadron Collider (LHC), at the CERN (the European Organization for Nuclear Research) near Geneva, is believed to have the potential to create dark matter.

位于日内瓦附近的欧洲核子研究中心(CERN)的大型强子对撞机(LHC)被认为具有制造暗物质的潜力。

Another promising strategy is to look for signals from dark matter annihilation. Such searches look for particles such as electrons and their anti-particles - positrons - or pairs of photons, which are created after the annihilating dark matter particles disappear.

另一个有希望的策略是寻找暗物质湮灭的信号。这样的搜索寻找粒子,如电子和它们的反粒子——正电子或成对的光子,它们是在湮灭暗物质粒子消失后产生的。

The Alpha Magnetic Spectrometer (AMS02), developed by scientists led by Nobel Laureate Samuel Chao Chung Ting and installed on the International Space Station (ISS) in 2011, the CALorimetric Electron Telescope (CALET), developed by the Japan Aerospace Exploration Agency for the ISS in 2015, and China's DAMPE all use the third method.

阿尔法磁谱仪(AMS02),由诺贝尔奖得主塞缪尔曹国伟为首的一群科学家开发中鼎和安装在国际空间站(ISS)2011年,量热电子望远镜(CALET),由国际空间站的日本宇宙航空研究开发机构2015年,和中国DAMPE都使用第三种方法。

"This is like tracking the 'son' of dark matter - if you cannot find the father, you go to the son and you can understand at least some properties of his father," said Chang Jin, chief scientist of DAMPE.

这就像跟踪‘儿子’的暗物质——如果你找不到父亲,你就去找他的儿子,你至少可以了解他父亲的一些特性,”DAMPE首席科学家常进说。

The invisible world 

看不见的世界

Although scientists don't yet know what dark matter actually is, they learned something by observing how it affects ordinary matter through gravity.

虽然科学家们还不知道暗物质到底是什么,但他们通过观察重力对普通物质的影响而学到了一些东西。

Dark matter is electrically neutral. Its density is small. Dark matter should have been created out of the Big Bang. It's been working since the dawn of time. It triggers the birth of galaxies and keeps them from falling apart. In a halo form around galaxies, dark matter doesn't just hold them together; it might have sparked them into life.

暗物质是电中性的。它的密度很小。暗物质应该是由大爆炸产生的。它从一开始就一直在工作。它触发了星系的诞生,防止它们分崩离析。在星系周围的晕圈里,暗物质不只是把它们放在一起;这可能会激发他们的生活。

Scientists know more about what dark matter is not than what it is. They know dark matter is not just clouds of normal matter without stars, because it would emit particles that can be detected. Dark matter is not anti-matter, because anti-matter produces unique gamma rays when it reacts with normal matter. Dark matter is not made up of black holes, which are very compact objects, while dark matter seems to be scattered everywhere.

科学家们对暗物质的了解更多,而不是它是什么。他们知道暗物质不仅仅是没有恒星的正常物质云,因为它会释放出能被探测到的粒子。暗物质不是反物质,因为反物质在与正常物质发生反应时产生独特的伽马射线。暗物质不是由黑洞组成的,它们是非常紧凑的物体,而暗物质似乎到处都是。

Dark matter is probably made up of a complicated exotic particle. Many physicists have their favorite dark matter candidates, among which WIMP, the acronym for "weakly interacting massive particle", is promising.

暗物质可能是由一个复杂的奇异粒子组成的。许多物理学家都有他们最喜欢的暗物质候选者,其中WIMP是“弱相互作用的大颗粒”的缩写,它很有前途。

Even if dark matter consists of an elementary particle, scientists don't know its mass, if it has any non-gravitational interactions, or how it was created in the early universe.

即使暗物质由一个基本粒子组成,科学家也不知道它的质量,如果它有任何非引力的相互作用,或者它是如何在早期宇宙中形成的。

That's what makes dark matter one of the great mysteries of science.

这就是为什么暗物质是科学的一大奥秘。

Discovering its true nature has become the most pressing question in cosmology, perhaps in all physics. Any discovery in this area could be as significant as heliocentric theory, the law of gravity, the theory of relativity and quantum mechanics.

发现它的真实性质已经成为宇宙学中最紧迫的问题,也许在所有物理中。这一领域的任何发现都可能与日心说、万有引力定律、相对论和量子力学一样重要。

Exploration of dark matter could give us a clearer idea about the past and future of galaxies and the universe, and will be revolutionary for the world of physics and space science, said Chang.

张说,对暗物质的探索可以让我们对星系和宇宙的过去和未来有更清晰的认识,对物理学和空间科学的世界来说将是革命性的。

When scientists discovered quantum mechanics in the early 1900s, many at first thought it had no use. Now quantum mechanics is a pillar of modern physics and everything is related to it.

当科学家们在20世纪初发现量子力学时,许多人起初认为它毫无用处。量子力学是现代物理学的支柱,一切都与量子力学有关。

"Only when we understand the nature of dark matter, can we find how it will change the future. But the development of fundamental physics will definitely boost science and technology," said Chang.

“只有当我们理解了暗物质的本质,我们才能发现它将如何改变未来。”但基础物理学的发展肯定会促进科学技术的发展。