《那些古怪又讓人憂心的問題》第32期:小世界(3)

Tidal forces would act on you in several ways. If you stretched your arm down toward the planet, it would be pulled much harder than the rest of you. And when you reach down with one arm, the rest of you gets pushed upward, which means other parts of your body feel even less gravity. Effectively, every part of your body would be trying to go in a different orbit. A large orbiting object under these kinds of tidal forces-say, a moon-will generally break apart into rings. This wouldn't happen to you. However, your orbit would become chaotic and unstable. These types of orbits were investigated in a paper by Radu D. Rugescu and Daniele Mortari. Their simulations showed that large, elongated objects follow strange paths around their central bodies. Even their centers of mass don't move in the traditional ellipses; some adopt pentagonal orbits, while others tumble chaotically and crash into the planet.

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潮汐力會以不同的方式作用在你身上。如果你的雙手下垂，那麼手受到的引力就會比身體其他部分受到的引力大很多。如果你一隻手往下伸，那麼你身體的其他部分就會被向上推，也就是說，你身體的其他部分感受到的引力要更小一些。實際上你身體的不同部分都試圖待在不同的軌道上。如果一個很大的物體——比如說月亮——處於這種潮汐力作用下，那麼它一般會裂成碎片並形成一個光環。3但這事不會發生在你身上，只是你的軌道會變得很隨機，並且很不穩定。拉杜•D．魯傑斯庫和達尼埃爾•莫爾塔裡在一篇很有意思的論文裡研究了這些軌道。他們的模擬結果顯示，大型細長的物體會繞著中心星球以詭異的軌道運動，即使質心並不在傳統的橢圓軌道上。在一些情況下，質心甚至會以五角星軌道運動，而另一些則像無頭蒼蠅一樣亂轉，最後一頭栽倒在星球上。

This type of analysis could actually have practical applications. There have been various proposals over the years to use long, whirling tethers to move cargo in and out of gravity wells-a sort of free-floating space elevator. Such tethers could transport cargo to and from the surface of the Moon, or to pick up spacecraft from the edge of the Earth's atmosphere. The inherent instability of many tether orbits poses a challenge for such a project. As for the residents of our superdense asteroid, they'd have to be careful; if they ran too fast, they'd be in serious danger of entering orbit, going into a tumble and losing their lunch. Fortunately, vertical jumps would be fine. Cleveland-area fans of French children's literature were disappointed by the Prince's decision to sign with the Miami Heat.

這種分析並不是無聊為之，它其實可以用於實踐。這幾十年來一直有人提議使用極長的旋轉繩索來將貨物搬入或搬出重力阱——就像自由飄浮的太空電梯一樣。這種繩索能夠將貨物運到月球表面或從那裡運回，也可以在地球大氣層邊緣搭載太空梭。只是這種繩索軌道內在的不穩定性給這些設想帶來了巨大的挑戰。但對於在這顆超級密實的星球上居住的人來說，他們可要小心一些：如果他們跑得太快，就很有可能飛進軌道，翻轉成一團，並把午餐吐出來。不過你要是豎著跳就沒什麼問題。聽說小王子和邁阿密熱隊簽約了，克利夫蘭的《小王子》迷們很不高興。

1 Although not everyone sees it this way. Mallory Ortberg, writing on , characterized the story of The Little Prince as a wealthy child demanding that a plane crash survivor draw him pictures, then critiquing his drawing style.

1． 但並不是每個人都這麼想。馬洛裡•奧特伯格曾在上撰文稱《小王子》講的是一個富有的小孩兒強制要求一位墜機倖存者給他畫畫，還批評他的畫風。

2 . . . which is why it should really be called “escape speed” - the fact that it has no direction (which is the distinction between “speed” and “velocity”) is unexpectedly significant here.

2． ……這也是為什麼它實際應該被稱為“逃逸速率”——這裡速率的無方向性（速度有方向性）莫名其妙地變得重要起來。

3 This is presumably what happened to Sonic the Hedgehog.

3． 這大概是刺蝟索尼克的遭遇。