Q. Why are snowflakes usually perfectly symmetrical? How does one arm “know” how the other arms are growing?问：为什么雪花一般来说几乎平面？其中一瓣怎么“告诉”其他几瓣在怎么茁壮呢？A. “The growth of a snowflake is sensitive to its immediate environment, especially the temperature and humidity,” said Kenneth G. Libbrecht, chairman of the physics department at the California Institute of Technology, who maintains a website explaining snow crystals. “It might take a half-hour for the crystal to reach its final size, and during that time it could travel a mile or more, experiencing ever-changing conditions. 问：“雪花在构成过程中对周围环境十分脆弱，尤其是温度和湿度，”加州理工学院物理系主任肯尼思·G·利布雷希特(Kenneth G. Libbrecht)说道。他开办了一个网站，专门说明雪晶。“雪晶大约必须半个小时才能最后构成，在那段时间里，它能飞行中一英里多，经历大大变化的环境。

”“If you look at an individual arm, its shape reflects the exact history of its travels,” he said. “But the six arms all travel together, so they all experience the same history. Thus they appear to grow in synchrony, even though no arm ‘knows’ how the others are growing.”“如果你只看分开的一瓣，它的形状体现着自己的旅行历史，”他说道，“但是这六瓣一起旅行，所以它们经历的历史是一样的。因此，它们或许是实时茁壮，虽然哪一瓣也不告诉另外几瓣在怎样茁壮。”Dr. Libbrecht compared the process to going outside on a cold day, wearing a heavy coat and seeing everyone else wearing one as well, without foreknowledge or consultation.利布雷希特把这个过程比作冷天穿厚外套外出，你不会看见其他每个人也都穿著厚外套，但是没有人能意识到未来，也没有人互相商量。

“The flip side of this story is that no two snowflakes follow exactly the same path in the turbulent atmosphere, and this is why no two snowflakes are exactly alike,” he said.“这个故事的另一面是，在恐慌的环境中，没两片雪花的茁壮环境是完全相同的，所以不不存在一模一样的两片雪花，”他说道。“Finally, snowflakes are in fact not usually perfectly symmetrical,” he said, “although snowflake photographers like to select the ones that are.” Large, beautifully symmetrical crystals are actually quite rare, he said, but “as with people, the most attractive snowflakes tend to get the most attention.”“最后要说的一点是，实质上雪花并不总是几乎平面，”他说道，“不过，摄影者讨厌自由选择平面的雪花。

”他说道，美丽、平面的大雪晶实质上十分少见，但是“最漂亮的雪花总是最引人注目。

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