怎樣在外星人面前把地球藏起來

播音/撰文 李·比林斯 (Lee Billings)

翻譯 Meatle

審校 Arc Ma

Lasers are the preferred weapons for interplanetary warfare in countless works of science fiction. But they might actually be better at keeping the peace. Because a new study finds that lasers offer an efficient, elegant wayto conceal our planet, hiding us from any prying malevolent aliens throughout the cosmos.

在眾多科幻作品當中，激光都是星際戰爭的首選武器。不過，激光更適合於維持和平。有新的研究發現，激光技術提供了一種高效且睿智的將地球隱匿在茫茫星海中的方法，讓圖謀不軌的外星人無從發現我們的老家。

David Kipping, a professor of astronomy at Columbia University who came up with the idea along with a graduate student, Alex Teachey.

哥倫比亞大學 (Columbia University) 的天文學教授，大衛·基平 (David Kipping，下稱DK) ，與他的研究生，阿歷克斯·蒂徹 (Alex Teachey，下稱AT)，一同構思了這個想法。

DK: 「So why would a civilization want to hide?」

DK：「為什麼一個文明想要藏起來呢？」

AT: 「So a lot of scientists, including Stephen Hawking, have said it actually might be dangerous for other civilizations out there to know that we exist. If you look at the history of humanity there have been cases where two civilizations have come in contact for the first time, one of these civilizations with a slightly more advanced technology, and that group has ended up subjugating the other group. And so, ya know, something like that could happen on a planetary scale.」

AT：「很多科學家，包括斯蒂芬·霍金 ，都說過外星文明獲知我們的存在搞不好是一件危險的事。人類的歷史就是這樣的一個示例。當兩個文明首次接觸，而其中一個文明的技術稍微領先於另一個的時候，技術先進的文明最終會征服另一個文明。所以說，這樣的事也會在行星規模上發生。」

Over the past two decades, astronomers have discovered thousands of planets orbiting other stars. Most of those were found by observing temporary small decreases in the light coming from those stars due to a planet passing. That mini-eclipse is called a transit. And it』s possible that from the point of view of some intelligent aliens the Earth causes small dips in our sun』s light—telling anyone watching that we』re here. So how can we hide? By making up for the sunlight we』re blocking.

在過去20年中，天文學家已經發現了成千上萬的圍繞行星公轉的天體。這些星體的發現大部分是因為觀測到這些天體遮擋恆星時所產生的短暫且少量的光線強度下降。這種小型的日蝕就是凌日。在其他智慧生物看來，地球稍微遮擋太陽的光線，就像對全世界說「我們就在這兒呢」。那麼我們如何躲起來？補足地球遮擋太陽所減少的光線即可。

AT: 「And you can do this with lasers—moderately powered lasers. That might sound a little counter-intuitive because lasers are very narrow when they are first emitted, but if that light travels across many light-years that beam widens significantly, and so the beam width can be on the order of tens of millions of kilometers across or more, and so any planet lying within that beam would be unable to see our transit.」

AT：「我們能用激光，適當強度的激光，實現這種目的。這聽起來可能有點反常識，因為激光剛發射出來的時候相當狹窄，然而這光線穿行了許多光年後，這道光線的直徑會顯著上升，其寬度會達到數千萬千米以上。因此在這光線之中的星球會難以發現我們的凌日。「

Cloaking the Earth from the view of aliens would require firing a 30-megawatt monochromatic laser once per year towards the targeted star system for the duration of our planet』s transit across the sun—something not nearly as difficult as it may sound.

那麼如何在外星人的眼皮底下把地球藏起來？地球人只需在地球凌日的時候，向外星人所在的星系每年發射一次30兆瓦的單色激光——別擔心，做起來比聽上去的要簡單。

DK: 「The earth』s transit takes about 10 hours, and it does that once every 365 days. So you could essentially have just a few meters squared of solar panels collecting sunlight, storing it up, and then being released at a peak intensity on the order of megawatts for these ten hour periods. So the actual energy requirements, when you think about it, over the entire year are very, very low…an alternative thing you could do is just build a satellite…you』d just have solar panels about the same sort of size that the ISS, the International Space Station, has. You would store up that energy over the course of a year and then you』d release it with a very high power laser over the course of ten hours once per year.」

DK：「地球凌日持續時間約10小時，每365天發生一次。因此本質上我們僅需要設置數平方米的太陽能發電板去收集陽光、儲存電力，在那十小時的時間內釋放峰值達到數十兆瓦的激光。因此實際上的能耗在一年的跨度上會很少很少。作為代替方案，我們可以在衛星上實現這些，僅需要面積等於國際空間站 (the International Space Station, ISS) 的太陽能板。我們可以將一整年的能量儲藏起來，並在每年的那10個小時中釋放這非常高能量的激光。」

The concept is in the Monthly Notices of the Royal Astronomical Society. [David M. Kipping and Alex Teachey, A Cloaking Device for Transiting Planets]

這個概念刊登在《皇家天文學月刊》 (the Monthly Notices of the Royal Astronomical Society)。

Of course, the laser cloak could not entirely conceal the Earth or its life from the rest of the universe. Aliens could always find us in other ways besides transits, for example, with telescopes so big they could snap pictures of our planet from light-years away like galactic paparazzi. Which is fine with Kipping and Teachey—their laser-cloaking system, they say, could also be repurposed for bolder, more flamboyant things: instead of hiding, we could create a cosmic beacon to attract the attention of intelligent aliens. Perhaps one day we』ll need to send out an SOS in the hopes that some good aliens will come to save us from evil ones—or, more likely, from ourselves.

當然，這種用激光瞞天過海的法子不能徹底隱藏地球或是其上的生物。外星人能夠經由觀測凌日以外的手段發現地球，比如，它們能像銀河狗仔隊那樣使用超大型的望遠鏡在數千光年外來偷拍我們的行星。對於基平和蒂徹來說，這也並無大礙。他們的激光隱蔽系統能夠通過改裝實現更加酷炫奪目的功能——不單單是隱蔽，該系統能夠生成一個星際信標，以此來吸引其他智慧生命。也許某天我們將要用這個系統去發射求救信號，寄望於一些好心的外星人會在邪惡外星人手中——或是在人類自己手中——拯救我們。

「科學60秒」（60-Second Science）是全球最著名的科學英文廣播，由《科學美國人》出品，網羅全球最新奇的科學發現，用過山車式的飛快語速，將其濃縮在60秒的播音之中。收聽「科學60秒」，既能知新，又可練耳。

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