This is Scientific American — 60-Second Science. I'm Christopher Intagliata.
The Earth is studded with telescopes, listening for electromagnetic radiation from the great beyond. And a decade ago, astronomers stumbled upon a mysterious signal: a powerful pulse of radio waves just a few thousandths of a second long. Mysterious because:
"What is the nature of the sources?" Avi Loeb, a theoretical astrophysicist at Harvard. Whatever the sources are, he says, "they seem to be brighter by 10 of billions of times more than the brightest radio sources we know about."
The radio pulses are known as "fast radio bursts"—and Loeb says you'd need something tens of billions of times brighter than a pulsar to produce them. So he and his colleague Manasvi Lingam investigated another possibility: "We know of one simple way to generate very powerful radio waves, and that's using a radio antenna."
A radio antenna built and controlled by extraterrestrials, to be more precise. Loeb and Lingam did the math on how big that stellar-powered radio antenna would have to be, to transmit signals like fast radio bursts. And whether it would even hold up from an engineering standpoint—like would it melt under its own heat?
Using those energy and engineering constraints, they found that the radio beam emitter would have to be twice the diameter of Earth. Pretty big—for us. But at least theoretically possible, he says, for more advanced civilizations. The study is in The Astrophysical Journal Letters.
To be clear: this is definitely not proof that intelligent aliens exist. It's just proof of concept, that someone, smarter than us, could in theory build such a thing. And why you might build it? "The idea is that an advanced technological civilization could produce a beam of radio waves focused on a sail that is pushing on the sail, such that eventually the sail will reach a fraction of the speed of light." We'll just have to see what arrives first: alien sailors, pushed by radio waves? Or the technological advances to allow us humans to build such a thing ourselves.
Thanks for listening for Scientific American — 60-Second Science Science. I'm Christopher Intagliata.
地球上的望远镜星罗棋布，接收来自远方的电磁辐射 。10年前，天文学家们偶然发现了一个神秘的信号：仅有千分之几秒长的强大无线电波脉冲 。其神秘的原因：
“这一信号来源的本质是什么？”艾维·勒布是哈佛大学的天体物理学家 。他表示，无论这些信号的来源是什么，“似乎都比我们知道的最亮的无线电来源还要亮百亿倍 。”
这些射电脉冲被称为“快速射电爆发”，勒布表示，比脉冲还要亮百亿倍的物体才能产生快速射电爆发 。所以，勒布和同事玛纳维斯·林加姆研究了另外一种可能性：“我们知道有种方法能产生非常强大的无线电电波，那就是利用无线电天线 。”
更准确的说，无线电天线由外星人建造并控制 。勒布和林加姆对发射快速射电爆发这样的信号需要恒星为无线电天线提供多大能量进行了计算 。他们还研究了从工程学角度而言这是否经得起检验，比如它是否会被自己的热量熔化 。
利用这些能源和工程约束，他们发现这种无线电光束发射体的直径为地球的两倍 。对我们来说，这个发射体非常大 。但是，勒布认为，至少在理论上来说更先进的文明是可能存在的 。这项研究结果发表在《天体物理学》期刊上 。
需要澄清的是：这绝对不能证明智慧外星人的存在 。这只是概念验证，比我们更聪明的生物，在理论上能建造这种发射体 。可是为什么要构建呢？“有一种想法是，先进的技术文明能产生一束集中于帆的无线电波，这种无线电波会推动帆的速度最终达到光速的一小部分 。”我们要看看哪个先到来：是被无线电波推来的外星水手？还是基于技术进步，我们人类自己建造出了这样的东西 。
谢谢大家收听科学美国人——60秒科学 。我是克里斯托弗·因塔利亚塔 。
1. stumble upon 意外发现；偶然看见；
例句：It had surprised him to stumble upon a dirty, forgotten place like that in a bank that was always so tidy.
2. be known as 称为；叫做；
例句：This process is known as adaptation.
3. hold up （论点、理论等）经受得住检验；
例句：I'm not sure if the argument holds up, but it's stimulating.
4. in theory 从理论上说；照理说；
例句：That may be reasonable in theory but it sounds fanciful in practice.