BBC Ideas｜六边形奇迹：雪花背后的科学

Six-Sided Wonders: The Science of Snowflakes

Snowflakes are intricate, beautiful, mysterious, and totally captivating. But for all their complexity – and endless variety – the structure of a snowflake can be explained by a few universal laws of nature – laws that explain everything from snowflakes to galaxies.
雪花是精致、美丽、神秘且极其迷人的。尽管它们结构复杂，形态各异，但雪花的结构可以通过一些自然界的普遍法则来解释——这些规律可以解释从雪花到星系的一切。

Let's start at the beginning. What is a snowflake, or, to use its more technical name, a snow crystal? A snow crystal forms up in the clouds when water vapour meets little specks of dust or pollen. This forms its tiny hexagonal heart. The tips stick out and are rough. This attracts water molecules, and then more water molecules, and then more. These form the branches of our snowflake.
让我们从头开始。雪花是什么，或者用它更专业的名字，雪晶是什么？
当水蒸气与微小的尘埃或花粉相遇时，就会在云层中形成雪晶。这就形成了雪花小小的六角形核心。尖端向外伸展且粗糙，这有助于吸引水分子，然后更多的水分子，接着更多。这些水分子形成了雪花的分支。

The size and shape of these branches depends on the exact temperature and humidity that the snowflake meets on its journey through the clouds, pulled down by the force of gravity. Each one takes a very slightly different route – meaning no two snowflakes are quite the same. When a snowflake lands on your sleeve, it has been on its own, totally unique, journey to reach you before melting away in a moment.
这些分支的大小和形状取决于雪花在重力作用下穿过云层时遇到的确切温度和湿度。每一片雪花的路线都略有不同，这意味着没有两片雪花是完全相同的。当一片雪花落在你的衣袖上时，它已经走过了自己完全独特的旅程，到达你的身边，然后瞬间融化。

Way back in 1611, on a bitterly cold January morning in Prague, a snowflake landed on the sleeve of mathematician Johannes Kepler, and it got him thinking, "Why do snowflakes have six sides?" Kepler's breakthrough was his theory that this hexagonal pattern is the most efficient use of space – whether it's a honeycomb within a beehive, or piles of stacked cannonballs, or a delicate, transient snowflake. It took 400 years – 400 years – for his theory to be proven.
早在1611年，在布拉格一个寒冷刺骨的一月早晨，一片雪花落在数学家约翰内斯·开普勒的袖子上，这让他陷入了思考：“为什么雪花有六个边？”开普勒的重大发现在于他的理论，即这种六边形图案是对空间最有效的利用——无论是蜂巢中的蜂窝结构，还是堆叠的炮弹，或是精致的、转瞬即逝的雪花。他的理论经过了400年——整整400年——才被证实。

What Kepler didn't know at the time is that each molecule of water, or H2O, is made up of two hydrogen atoms and one oxygen atom. As the water molecules cluster together when they freeze, the angle between the hydrogen atoms is always, approximately, 105 degrees. And that gives us the six sides.
开普勒当时不知道的是，每个水分子（或 H2O）都是由两个氢原子和一个氧原子组成的。当水分子凝固时聚集在一起，氢原子之间的夹角总是约为105度。这就得到了六个边。

At its heart, a snowflake is always a hexagon. But it can grow into all sorts of weird and wonderful shapes: long and thin, like a pencil; sharp like a needle; cylindrical like a bullet; or, just occasionally, triangular. The truth is though, most snowflakes are kind of...well, blob-like.
雪花的核心总是一个六边形。但它可以长成各种奇异美妙的形状：像铅笔一样长而细；像针一样尖锐；像子弹一样圆柱形；或者偶尔，呈现三角形。然而，事实上，大多数雪花都是……嗯，有点像……一团模糊的形状。

If you speak to a snowflake photographer – there are just a handful in the world – they'll tell you it takes days and days out in the cold to get that "money shot". And the conditions have to be just right – between minus 15 and minus 13 degrees. But ever since Wilson Bentley, a farmer from the US state of Vermont, painstakingly took the first photos of stunning snowflakes in 1885, we've been hooked.
如果你和在全世界屈指可数的雪花摄影师交谈，他们会告诉你，要想拍出这样的“完美瞬间”，你得在寒冷中待上好几天。而且条件必须在零下15度到零下13度之间。但自从1885年，美国佛蒙特州的农民威尔逊·本特利煞费苦心地首次拍摄了令人惊叹的雪花照片以来，我们就为之着迷了。

Scientists have shown that symmetry is incredibly pleasing to the human brain. Snowflakes are all radially symmetrical, which means you can cut them into identical slices, like a cake. Shells, flowers, starfish, even spiral galaxies, like the Milky Way, share this type of symmetry. And nature has one last trick up its sleeve.
科学家们已经表明，对称性对人类大脑来说是非常愉悦的。雪花都是辐射对称的，这意味着你可以像切蛋糕一样将它们切成相同的片。贝壳、花朵、海星，甚至是螺旋星系，比如我们的银河系，都具有这种对称性。大自然还有最后一招。

Snowflakes aren't actually white. They're clear, but they have lots of edges, and this scatters the light, making them appear white. Each snowflake is a microcosm of the laws of physics. Gravity makes it fall. Electromagnetism dictates its shape. And you've got symmetry. It's the same with the stars, and solar systems, and planets, and with us.
雪花其实上并不是白色的。它们是透明的，但有很多边缘，这会散射光线，使它们看起来是白色的。每一片雪花都是物理定律的缩影。重力使它下落。电磁学决定了它的形状。还有对称性。星星、太阳系、行星，以及我们自己，都是如此。

When you look at a snowflake, you can read its history – its own unique story. The experiences it encounters shape it into what it is, just like us, really.
当你看着一片雪花，你可以读到它的历史——它自己独特的故事。它遇到的经历塑造了它，真的就像我们一样。



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