第一章 当我们抬头看天，到底看到了啥？ / Chapter 1 When We Look Up at the Sky, What Do We Actually See?

三月的晚风还带着料峭的春寒，你裹着羽绒服蹲在老家院子的台阶上，手里攥着半块没吃完的烤红薯，抬头看向头顶那片墨蓝色的天——那是你第一次注意到，原来城里的路灯灭了之后，天上的星星比路灯还密。奶奶搬个小凳子坐在你旁边，指着天上连成勺子的七颗星说那是“北斗”，指着南边像镰刀一样的星群说那是“狮子座”，你那时候以为，天上所有的星星就是宇宙的全部了，直到后来你学了天文课，才知道：你奶奶说的没错，但你看到的那些亮晶晶的星星，加起来还不到宇宙所有物质的5%。The late March breeze still carries the chill of early spring. Wrapped in your down jacket, you squat on the steps of your grandma’s courtyard, holding half an uneaten roasted sweet potato, and look up at the dark blue sky overhead—it’s the first time you notice that once the city streetlights go out, the stars in the sky are denser than the streetlights. Grandma sits on a small stool next to you, pointing to the seven stars connected into a ladle and saying that’s the “Big Dipper”, pointing to the sickle-shaped star cluster in the south and saying that’s “Leo”. At that time you thought that all the stars in the sky were the entire universe, until later when you took an astronomy class, you realized: Grandma was right, but those shiny stars you see add up to less than 5% of all the matter in the universe.

这个结论听起来像科幻小说里的情节，但它是过去一百年里天文学家通过无数观测和计算得出的共识：我们能用任何手段探测到的、发光的普通物质，只占宇宙总质量能量密度的4.9%，剩下的26.8%是看不见摸不着的暗物质，68.3%是让宇宙加速膨胀的暗能量。换句话说，你从小到大所有天文课本里画的恒星、行星、星云、星系，所有你能“看到”的宇宙，都只是宇宙的“冰山一角”，而真正占主体的“暗影”，我们至今还没摸清楚它们的真面目。This conclusion sounds like something out of a sci-fi novel, but it is a consensus reached by astronomers over the past century through countless observations and calculations: the luminous ordinary matter that we can detect by any means accounts for only 4.9% of the total mass-energy density of the universe, the remaining 26.8% is invisible and intangible dark matter, and 68.3% is dark energy that makes the universe expand faster and faster. In other words, all the stars, planets, nebulae, and galaxies drawn in all the astronomy textbooks you have read since childhood, everything you can "see" in the universe, is just the "tip of the iceberg" of the universe, and the real "shadows" that make up the majority, we have not yet figured out their true faces.

如果你觉得这个结论太颠覆，那接下来的内容会让你更惊讶：人类对宇宙的认知，本身就是一部不断推翻“常识”的追光史，而暗物质和暗能量的发现，就是这部追光史里最精彩的“反转剧情”。If you think this conclusion is too subversive, then the following content will surprise you even more: human cognition of the universe is itself a history of constantly overturning "common sense", and the discovery of dark matter and dark energy is the most exciting "plot twist" in this history of chasing light.

一、从“天圆地方”到“日心说”：人类宇宙观的第一次大翻转 / From "Round Sky and Flat Earth" to "Heliocentrism": The First Great Flip of Human Cosmic View

咱们先回到几千年前，看看老祖宗是怎么看星空的。Before we go back thousands of years, let's see how our ancestors looked at the stars.

咱们中国的上古先民早就把星空当成了“天然日历”：《尚书》里记载“乃命羲和，钦若昊天，历象日月星辰，敬授民时”，就是说让羲和观测天象，推算历法，告诉老百姓什么时候种庄稼什么时候收获，比欧洲的古代天文学早了上千年。Our ancient Chinese ancestors long regarded the starry sky as a "natural calendar": the *Shangshu* (Book of Documents) records "Then we commanded Xihe, to respectfully observe the heavens, to calculate the sun, moon and stars, and respectfully impart the seasons to the people", which means letting Xihe observe astronomical phenomena, calculate the calendar,

咱们中国的上古先民早就把星空当成了“天然日历”：《尚书》里记载“乃命羲和，钦若昊天，历象日月星辰，敬授民时”，就是说让羲和观测天象，推算历法，告诉老百姓什么时候种庄稼什么时候收获，比欧洲的古代天文学早了上千年。Our ancient Chinese ancestors long regarded the starry sky as a "natural calendar": the *Shangshu* (Book of Documents) records "Then we commanded Xihe, to respectfully observe the heavens, to calculate the sun, moon and stars, and respectfully impart the seasons to the people", which means letting Xihe observe astronomical phenomena, calculate the calendar, and tell the people when to plant and when to harvest, a thousand years earlier than ancient astronomy in Europe.

羲和观测天象用的工具叫“圭表”，就是一根竖在地上的竿子（表），和一把水平放置的尺子（圭），通过测量表在圭上的影子长度，就能确定冬至、夏至、春分、秋分这四个关键节气，误差不到一天。为了更精准地记录星星的位置，古人又把星空分成“二十八宿”，就是把天球赤道附近的星空分成28个区域，每个区域对应一颗“主星”，比如东方苍龙七宿的角宿，对应的主星就是角宿一（室女座α星），是春季星空最亮的星之一，春天傍晚的时候，苍龙七宿会从东方升起，正好对应春耕的时节，你奶奶当年给你指的大熊座北斗，就是用来定方向和定季节的：斗柄朝东，天下皆春；斗柄朝南，天下皆夏，比现在的天气预报准多了，一准就是几千年。Xihe used a tool called “guibiao” to observe astronomical phenomena: a vertical pole (biao) planted in the ground and a horizontal ruler (gui) placed at the bottom. By measuring the length of the shadow cast by the pole on the ruler, one could determine the four key solar terms of winter solstice, summer solstice, spring equinox, and autumn equinox, with an error of less than one day. To record the positions of the stars more accurately, the ancients divided the starry sky into the “Twenty-Eight Mansions”, splitting the area near the celestial equator into 28 regions, each corresponding to a “main star”. For example, the Horn Mansion of the Azure Dragon of the East corresponds to Alpha Virginis (Spica), one of the brightest stars in the spring sky. In the early evening of spring