《那些古怪又讓人憂心的問題》第113期:地球擴張(6)
t = 300 years
It's a shame humans wouldn't live this long, because at this point, something really neat would happen.
我們人類活不到這一天真是遺憾，因爲此時會發生一件非常讚的事情。As the Earth grows, the Moon would, like all our satellites, gradually spiral inward. After several centuries, it would be close enough to the swollen Earth that the tidal forces between Earth and the Moon would be stronger than the gravitational forces holding the Moon together.
隨着地球不斷變大，月亮會像那些衛星一樣軌道高度越轉越低。幾個世紀後，終有一天地球與月球之間的引潮力會超過月球聚攏自身的引力。
When the Moon passed this boundary-called the Roche limit-it would gradually break apart,9 and Earth would, for a short time, have rings.
當那個界限——叫作洛希極限——被跨越後，月亮會被撕裂9，而在短時間內地球會擁有一個美麗的光環。If you liked it, then you should have moved a mass inside its Roche limit.
如果你喜歡它，就應該把一個物體移動到它的洛希半徑內。101 The smoking gun that confirmed the theory of plate tectonics was the discovery of sea-floor spreading. The way sea-floor spreading and magnetic pole reversal neatly confirmed each other is one of my favorite examples of scientific discovery at work.
1． 板塊構造學說的確鑿證據是海牀在不斷延展。海牀延展和地磁極倒轉兩者能夠很好地互相印證，這是我最喜歡的科學發現管用的例子之一。2 It turns out it's kind of dumb.
2． 事實證明這理論挺蠢的。3 As it turns out, the ocean is expanding, since it's getting warmer. This is (currently) the main way global warming is raising the sea level.
3． 實際上海洋確實在擴張，因爲海水在變暖，而這也是（目前）全球變暖導致海平面上升的主要原因。4 Mass is proportional to radius cubed, and gravity is proportional to mass times inverse square of radius, so radius3 / radius2 = radius.
4． 質量正比於半徑的三次方，而重力正比於質量乘以半徑平方的倒數，所以半徑的三次方除以半徑的平方等於半徑。5 Just what you want in a skyscraper.
5． 造摩天大樓要的不就是這個嘛。6 Although I wouldn't trust the elevators.
6． 雖然我可不敢再去乘電梯了。7 Over decades, the force of gravity would grow slightly faster than you'd expect, since the material in the Earth would compress under its own weight. The pressure inside planets is roughly proportional to the square of their surface area, so the Earth's core would be squeezed tightly.
7． 幾十年後地球重力增加的速度會比你所期望的略快一些。因爲不斷增加的重量會壓迫地球自身，地球內部的壓強粗略正比於表面積的平方，因而地核會被壓得十分緊密。8 Although some radioactive elements, like uranium, are heavy, they get squeezed out of the lower layers because their atoms don't mesh well with the rock lattices at those depths.
8． 雖然一些放射性物質（比如鈾）很重，但它們會被從地球內部擠出來，因爲在那種深度下它們沒法和岩石晶格很好地混合9 Sorry, Moon!
9． 對不起啦，月亮！
