Lasers Could Hide Earth from Prying Aliens
地球：激光隐身

We could use laser light to mask our transits across the sun and thus hide Earth from any intelligent aliens looking for planets to invade
我们能使用镭射来隐藏地球的凌日，由此来蒙骗寻找可入侵星球的外星佬。

播音/撰文 李·比林斯 (Lee Billings)
翻译 Meatle
审校 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.
“Let’s do it—let’s cloak the Earth.”
“让我们把地球藏起来。”

David Kipping, a professor of astronomy at Columbia University who came up with the idea along with a graduate student, Alex Teachey.
哥伦比亚大学 (Columbia University) 的天文学教授，大卫·基平 (David Kipping，下称DK) ，与他的研究生，阿历克斯·蒂彻 (Alex Teachey，下称AT)，一同想出了这个想法。

DK: “So why would a civilization want to hide?”
DK：“为什么一个文明想要藏起来呢？”

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：“很多科学家，包括斯蒂芬·霍金 (Stephen Hawking)，都说过外星文明获知我们的存在或许是一件危险的事。人类的历史就是这样的一个示例。当两个文明首次接触，而其中一个文明的技术稍微领先于另一个的时候，技术先进的文明最终会征服另一个文明。因此，你明白，这样的事也会在行星规模上发生。”

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.
在过去20年中，天文学家已经发现了成千上万的围绕行星公转的天体。这些星体的发现大部分是因为观测到这些天体遮挡恒星时所产生的短暂且少量的光线强度下降。这种小型的日蚀就是凌日。在其他智慧生物看来，地球稍微遮挡太阳的光线，就像对全世界说“我们就在这儿呢”。那么我们如何躲起来？补足地球遮挡太阳所减少的光线即可。

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：“我们能用激光，适当强度的激光，实现这种目的。这听起来可能有点反常识，因为激光刚发射出来的时候相当狭窄，然而这光线穿行了许多光年后，这道光线的直径会显著上升，其宽度会达到数千万千米以上。因此在这光线之中的星球会难以发现我们的凌日。

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.
那么如何在外星人的眼皮底下把地球藏起来？地球人只需在地球凌日的时候，向外星人所在的星系每年发射一次30兆瓦的单色激光——别担心，做起来比听上去的要简单。

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：“地球凌日持续时间约10小时，每365天发生一次。因此本质上我们仅需要设置数平方米的太阳能发电板去收集阳光、储存电力，在那十小时的时间内释放峰值达到数十兆瓦的激光。因此实际上的能耗在一年的跨度上会很少很少。作为代替方案，我们可以在卫星上实现这些，仅需要面积等于国际空间站 (the International Space Station, ISS) 的太阳能板。我们可以将一整年的能量储藏起来，并在每年的那10个小时中释放这非常高能量的激光。”

The concept is in the Monthly Notices of the Royal Astronomical Society. [David M. Kipping and Alex Teachey, A Cloaking Device for Transiting Planets]
这个概念刊登在《皇家天文学月刊》 (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.
当然，这种用激光瞒天过海的法子不能彻底隐藏地球或是其上的生物。外星人能够经由观测凌日以外的手段发现地球，比如，它们能像银河狗仔队那样使用超大型的望远镜在数千光年外来偷拍我们的行星。对于基平和蒂彻来说，这也并无大碍。他们的激光隐蔽系统能够通过改装实现更加酷炫夺目的功能——不单单是隐蔽，该系统能够生成一个星际信标，以此来吸引其他智慧生命。也许某天我们将要用这个系统去发射求救信号，寄望于一些好心的外星人会在邪恶外星人手中——或是在人类自己手中——拯救我们。

原文链接：
http://www.scientificamerican.com/podcast/episode/lasers-could-hide-earth-from-prying-aliens/

（题图来源：http://www.scientificamerican.com）