如果M87的黑洞揭示了一个全新的物理过程，那将是令人惊讶的。作为物理实体，黑洞比地球更大更壮观，但也更加简单，对生命更不友好。而我们的宇宙竟然同时拥有两者，这实在是太美妙了！
作者 | Frank Wilczek(麻省理工学院教授、2004年诺贝尔奖得主）
翻译 | 梁丁当、胡风
请输入图片描述
几十年来，物理学家一直在理论上研究黑洞，而今我们终于成功看到了它。
Physicists have been theorizing about black holes for generations. Now science has made it possible to see one.
4月10日，天文学家利用事件视界望远镜拍摄到了一张黑洞的“照片”，这个巨大的黑洞位于M87星系的中心，距离地球5400万光年。仅仅当作一张照片来看的话，它既平淡无奇又不怎么清晰：照片中是一个毫无特色、模模糊糊、半圈发光的圆环——它展示的并不是黑洞本身，而是黑洞扭曲时空，在周围的发光背景中留下的“影子”。但是，喜欢思考的人知道，这张照片代表了人类智慧的非凡成就，而擅长想象的人则会意识到它打开了通向空间、时间及宇宙久远历史的全新窗口。
On April 10, astronomers working with the Event Horizon Telescope unveiled a “photograph” of the monstrous black hole that sits at the center of the M87 galaxy, 54 million light years away. Viewed simply as an image, it is neither impressive nor straightforward: It presents a sort of nondescript, blurry, half-glazed doughnut, showing not the black hole itself but the shadow-like distortion it carves in the surrounding illumination. Yet, to a thinking mind, the image re?ects the glory of understanding, and to an alert imagination it opens new portals into space, time and deep history.
这张照片可以说是当代科技的伟大结晶。照片中的黑洞非常巨大，半径约有150亿千米——相当于地球到太阳距离的100倍，质量是地球的2000万亿倍。但因为太遥远，它只占据了极小的一块天空，所以我们必须用一个很大的、不同寻常的望远镜来观察它。实际上，事件视界望远镜并非一台单独的仪器，而是由分别位于夏威夷、亚利桑那、西班牙、 墨西哥、智利和南极洲的8台射电望远镜共同构成。天文学家利用精度高达万亿分之一秒的原子钟同步来自不同望远镜的数据，再通过超级计算机把它们整合起来。
The making of the image was a tour de force of science and technology. The black hole is enormous, with a radius of roughly 9 billion miles (or one hundred times the distance from the Earth to the sun) and a mass equivalent to two quadrillion Earths. But because it is so far away, it occupies only a tiny portion of the sky, so we must use a very large, exotic telescope to see it. In fact, the Event Horizon Telescope isn’t a single instrument but a system of eight radio dishes at six far-flung locations in Hawaii, Arizona, Spain, Mexico, Chile and Antarctica. Astronomers used precise atomic clocks, accurate within a trillionth of a second, to synchronize data from all these places and then stitched it all together using supercomputers.
黑洞的概念可以追溯到18世纪，当时英国的天文学家兼牧师约翰·米歇尔（John Michell）通过计算发现：如果一颗恒星具有足够大的质量，它将不会发光，因为脱离恒星引力所需的逃逸速度超过了光速。然而，由于18世纪的物理学对光、引力或者恒星都缺乏足够的认知，米歇尔的猜想远远超越了他所在的时代。
The concept of a black hole goes back to the 18th century, when the English astronomerclergyman John Michell calculated that a sufficiently large star couldn't shine because light wouldn’t move fast enough to “lift off” and escape the star’s gravity. But Michell’s conjecture outran the physics of its time, which didn’t understand light, gravity or stars well enough to support it.
直到20世纪初期，詹姆斯·克拉克·麦克斯韦（James Clerk Maxwell）的电磁场理论和爱因斯坦的相对论才奠定了现代黑洞物理学的基础。1939年，J·罗伯特·奥本海默（J. Robert Oppenheimer）和哈特兰·斯奈德（Hartland Snyder）撰写了黑洞研究史上最重要的论文《关于持续的引力收缩》（On Continued Gravitational Contraction）。这篇论文探讨了一团任意大小、密度均匀的尘埃云在自身引力作用下发生塌缩的结果。作者发现，如果观察者处于尘埃云中，他将发现自己被物质包围着，而他眼中的宇宙与我们的宇宙大致相似，最终以大挤压（big crunch）的方式终结。但是，外面的观察者会看到尘埃云在某个时刻突然失去光芒变成一个黑洞。这是因为尘埃云边界的引力变得非常强大，以至于光——或者说任何物质——都无法逃逸。
he foundations for the modern understanding of black holes weren’t laid until the early 20th century, building on James Clerk Maxwell’s theory of electromagnetism and Albert Einstein’s theory of relativity. In 1939, J. Robert Oppenheimer and Hartland Snyder wrote “On Continued Gravitational Contraction,” the most important paper in the history of black holes. They considered what would happen to a dust cloud of any size and uniform density as it collapses through the force of gravity. Observers within the dust cloud would find themselves surrounded by matter, and they would experience a universe broadly resembling our own, which would eventually end in a “big crunch.” But observers outside the collapsing cloud would see it wink out into a black hole, as gravity at its boundary increases beyond the ability of light—or any form of matter—to escape.
奥本海默和斯奈德的研究清晰地表明：黑洞的形成是已知物理过程的合理结果。他们还大胆地提出，黑洞本身可能就是一个宇宙，宇宙也可能是一个黑洞，只是观察角度不同而已。时至今日，我认为物理学也还没能充分消化这个思想。
Oppenheimer and Snyder’s work made it clear that black holes were a plausible outcome of known physical processes. It also makes the astonishing suggestion that a black hole can be a universe and vice versa, differently viewed. I don’t think physics has fully digested this idea, even today.
如果M87的黑洞揭示了一个全新的物理过程，那将是令人惊讶的。这类超大黑洞虽然质量巨大，但体积更大，因此密度反而很低。它们对外部施加的作用力尽管影响范围很广，但非常微弱。但是，通过对比不同星系的中心黑洞，我们可以了解星系是如何形成和演化的。我们的银河系也有一个巨大的中心黑洞，它笼罩在尘埃中，难以直接观测。
It would be surprising if M87’s black hole revealed fundamentally new physical processes. Such gigantic black holes have low density and exert only weak forces on the outside, albeit on a grand scale. But by comparing and contrasting the central black holes in different galaxies, we will learn about how galaxies form and evolve. Our own Milky Way galaxy also harbors a central, giant black hole, hidden from direct observation by enshrouding dust.
看着黑洞的照片，我脑海里浮现出更早的一张标志性照片——阿波罗8号在月球轨道上拍到的“地球升起”。作为物理实体，黑洞比地球更大更壮观，但也更加简单，对生命更不友好。而我们的宇宙竟然同时拥有两者，这实在是太美妙了！
Seeing the black hole image, my mind flashed back to an earlier iconic image, the “Earthrise” captured by Apollo 8. The black hole is much bigger and more imposing, as a physical object, but also much less complex—not to mention less user-friendly—than our Earth. It’s a wonderful world that is home to both.
作者简介
Frank Wilczek：弗兰克·维尔切克是麻省理工学院物理学教授、量子色动力学的奠基人之一。因在夸克粒子理论（强作用）方面所取得的成就，他在2004年获得了诺贝尔物理学奖。
本文经授权转载自微信公众号「蔻享学术」。
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