编者按：茫茫宇宙中我们有同伴吗？人类一直在寻求这个问题的答案。本文将向你解释为什么来自天空的奇怪信号可能是外星人发出的。你还将了解不靠燃料驱动的宇宙飞船的设计原理。无论目前是否真的找到外星人，相信有一天人类终将发明出载人飞船脱离银河系，探索无尽的未知世界。
本文译自《经济学人》3月18日刊。

太阳帆

Astronomy

Flashes of inspiration

灵光乍现

A batch of strange signals from the sky might, just possibly, be signs of aliens
来自天空的一批奇怪信号可能，只是可能，是外星人的标志

1. ON AUGUST 24th 2001 the Parkes Observatory, in Australia, picked up an unusual signal. It was a burst of radio waves coming more or less from the direction of the Small Magellanic Cloud, a miniature galaxy that orbits the Milky Way. This burst was as brief as it was potent. It lasted less than 5 milliseconds but, during that period, shone with the power of 100m suns. It was, though, noticed by astronomers only in 2007, when they were poking around in Parkes’s archived data. As far as they can tell, it has never been repeated.
   1）2001年 8月24日，澳大利亚的帕克斯天文台探测到一个不寻常的信号。这是一阵无线电波的爆发，或多或少来自小麦哲伦星云的方向，该星云是一个在银河系的轨道上运转的微型星系。这次爆发短促而强劲。它持续不到5毫秒，但在这短短一瞬，却闪耀着一亿个太阳放射的能量。然而，这一切天文学家2007年才注意到，当时他们在帕克斯的存档数据中四处检索。据他们所知，它再也未重复过。

2. Similar unrepeated signals have since been noted elsewhere in the heavens. So far, 17 such “fast radio bursts” (FRBs) have been recognised. They do not look like anything observed before, and there is much speculation about what causes them. One possibility is magnetars—highly magnetised, fast-rotating superdense stars. Another is a particularly exotic sort of black hole, formed when the centrifugal force of a rotating, superdense star proves no longer adequate to the task of stopping that star collapsing suddenly under its own gravity. But, as Manasvi Lingam of Harvard University and Abraham Loeb of the Harvard-Smithsonian Centre for Astrophysics observe, there is at least one further possibility: alien spaceships.
   2）从那时起类似的不重复的信号在天空中其它地方被注意到。迄今为止，17组这样的“快速无线电波爆发”（FRBs或称为“快速射电暴”）已被确认。它们看起来不像以前观察到的任何东西，（天文学界）存在很多关于其成因的猜测。一种可能性是磁星——高度磁化、快速旋转的超密星。另一种可能性是一种特别异乎寻常的黑洞，是一颗旋转的高密恒星的离心力不足以阻止其在自重力作用下突然坍塌时形成的。但是，正如美国哈佛大学的马纳斯韦·林加姆和哈佛-史密森天体物理学中心的阿维·勒布所观察到的，至少有一种另外的可能性：外星人的宇宙飞船。

3. Specifically, the two researchers suggest, in a paper to be published in Astrophysical Journal Letters, that FRBs might be generated by giant radio transmitters designed to push such spaceships around. With the rotation of the galaxies in which these transmitters are located, the transmitter-beams sweep across the heavens. Occasionally, one washes over Earth, producing an FRB.
   3）具体来说，这两位研究者认为，（这篇论文即将发表在《天体物理学期刊通讯》上），“ 快速射电暴”可能会由推动这些飞船的超级巨大的无线电发射器产生。随着这些发射器所在星系的旋转，发射波束扫过天空。 偶然间其中一束扫过地球，产生了一次快速射电暴。

4. This idea is not completely mad. Human rocket scientists have toyed with something similar, in order to overcome one of the biggest problems of spaceship design: that a craft propelled by a rocket motor must carry its fuel with it. Fuel has mass. That mass must be moved by more fuel—which adds more mass to the craft, which thus needs still more fuel. And so on. For this reason, 90% or more of a conventional rocket’s launch mass is its fuel.
   4）这种想法并非完全异想天开。人类的火箭科学家曾考虑过类似的情况，为了克服一个飞船设计最大的问题：火箭发动机推动的飞行器必须携带燃料。燃料有质量。有质量就必须由更多的燃料去推动——这使飞行器增加了更多的质量，因此需要更多的燃料。以此类推。 因此，90%或更多的常规火箭的发射质量是其燃料。

5. It is possible, though, to separate the fuel from the craft. That is the principle behind a solar sail, which employs the gentle pressure exerted by sunlight to propel a vehicle. A nippier alternative is to use focused light beams to provide the pressure. Yuri Milner, a Russian billionaire with a long-standing interest in science, is paying for research into such a machine. He proposes to drive a tiny probe to Alpha Centauri, one of Earth’s nearest stellar neighbours, using banks of powerful lasers.

solar sail: 太阳帆（也称为光帆，特别是它使用来自于太阳以外的光源时）是使用巨大的薄膜镜片，以太阳的辐射压做为太空船推进力的一种计划。辐射压不仅非常小，而且与太阳距离的平方成反比，但不同于火箭的是，太阳帆不需要燃料。推进力虽然很小，但是只要太阳继续照耀着，太阳帆就能继续运作。——维基百科

5）然而，从飞行器分离燃料是可能的。这就是光帆背后的原理，它利用阳光施加的柔和压力推动交通工具前进。一个更快的替代方案是使用聚焦光束提供压力。尤里·米尔纳是一位长期以来对科学感兴趣的俄罗斯亿万富翁，他正投资研究这种机器。 他提出利用强大的激光堆去驱动一个微型探测器飞往半人马座阿尔法星，地球最近的恒星邻居之一。

6. Dr Lingam and Dr Loeb suggest FRBs might be the result of vastly bigger takes on the same principle, except that they employ the radio portions of the electromagnetic spectrum rather than visible light. The two researchers have worked out what would be needed if the transmitter behind such a burst were solar-powered. They calculate that the amount of sunlight falling onto a planet about twice the size of Earth, and at the right distance from its star to have liquid water on its surface, would yield enough energy to accelerate a spaceship weighing a million tonnes or so to a speed close to that of light before the propulsion beam became too attenuated to propel it any faster. This would be perfect for ferrying large numbers of beings from one star system to another, as long as there was an equivalent device at the other end to slow the craft down again.
   6）林加姆博士和勒布博士认为“快速射电暴”可能是采用同样的原理形成的大得多得多的结果，但其使用了电磁波频谱的无线电部分而非可见光。这两位研究人员已经计算出，假设在这样一阵爆发之后的发射器是太阳能驱动的，哪些东西是必要的。他们计算出落在一颗体积约为地球两倍的行星上的太阳光总量，并且其恒星距其距离合适以使其表面上有液态水，将产生足够的能量来加速一艘重达一百万吨左右的飞船，在推进光束变得太弱而不能推动其速度更快之前使其接近于光速。这对于从一个星系到另一个星系运送大量生物会是完美的（方式），只要在另一端有一个使飞船减速的等效装置。

7. To check whether such a machine is technologically plausible, the two researchers calculated that the necessary planet-sized array of radio transmitters could be kept cool by nothing more exotic than ordinary water. So, as far as they can see, while building such a machine would be a heroic feat of engineering, nothing in the laws of physics actually forbids it.
   7）为了检验这种机器在技术上是否合理，两位研究员计算出必要的无线电发射器的行星大小的阵列可以用普通水保持低温而不需要其他外来的物质。 所以，就他们所知，虽然建造这样一台机器将是工程上的英雄壮举，实际在物理学规律上是完全可行的。

8. Saying that the features of FRBs are consistent with their being signs of an alien space-propulsion system is not, of course, the same as saying that this is what they actually are. One early explanation of pulsars—regular cosmic radio signals first observed in 1967 was that they were alien radio beacons. They later turned out to be caused by fast-spinning neutron stars. For physicists, though, that explanation was almost as interesting. A neutron star is one whose protons and electrons have merged with each other to create neutrons. These, together with the star’s pre-existing neutrons, result in an object that has no atoms in it. Since atoms are composed mostly of empty space a neutron star, instead of being star size, is just a few kilometres across. If FRBs turn out to be even a fraction as curious as that, most astronomers would forgive them for not being artificial.
   8）当然，说“快速射电暴”的特征与外星人空间推进系统的标志是一致的，不等于说它们实际上是相同的。脉冲星——在1967年首次观测到的常规宇宙射电信号的一个早期解释是，它们是外星人无线电发送器。它们后来证明是由快速旋转的中子星造成的。然而，对于物理学家来说，这种解释几乎同样有趣。中子星是一种由质子和电子相互结合产生中子的星球。(中子星里，压力是如此之大，电子被压缩到原子核中，同质子中和为中子，使原子变得仅由中子组成。——译者按)这些，连同恒星中预先存在的中子，导致了一个没有原子的物体。由于原子主要由空间隙组成，中子星（密度极大）只有几公里的直径，而非恒星那么大。如果“快速射电暴”最后被证实只是一个同那一样令人好奇的小片段，大多数天文学家都会原谅它们不是（外星）人造的。（意思是就算FRBs不是外星人造成的，对天体物理学家来说同样有价值，正如中子星曾被认为是外星人无线电发射器一样——编者按）

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1、来自天空的一批奇怪信号可能，只是可能，是外星人的标志。

2、这对于从一个星系到另一个星系运送大量生物会是完美的（方式），只要在另一端有一个使飞船减速的等效装置。

3、所以，就他们所知，虽然建造这样一台机器将是工程上的英雄壮举，实际在物理学规律上是完全可行的。

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原文出处：经济学人杂志

翻译：追梦心；校对：七呵夫；编辑：七呵夫

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