ALIEN ASTRONOMERS
外星天文学家
Q. Let's assume there's life on the nearest habitable exoplanet and that they have technology comparable to ours. If they looked at our star right now, what would they see?
Q．不妨假设在离我们最近的一颗适于居住的地外星球上有生命存在，而且他们拥有和我们人类相近的科技。如果他们现在朝我们这边看过来，会看到什么？
Let's try a more complete answer. We'll start with . . .
让我回答得稍微详细一点。首先我们来谈谈……
Radio transmissions
无线电通信
Contact popularized the idea of aliens listening in on our broadcast media. Sadly, the odds are against it.
《超时空接触》让许多人以为外星人在监听着我们的无线电通信。很遗憾，这事儿希望不大。
Here's the problem: Space is really big.
问题在于：宇宙太大了，相当大。
You can work through the physics of interstellar radio attenuation, but the problem is captured pretty well by considering the economics of the situation: If your TV signals are getting to another star, you're wasting money. Powering a transmitter is expensive, and creatures on other stars aren't buying the products in the TV commercials that pay your power bill.
你当然可以计算星际无线电衰减的物理学，但光考虑这个场景的经济学就足够概括问题所在了——如果你的电视信号传到了另一颗星球上，这必定是赔本买卖。驱动一个发射机要花很多钱，而其他星球上的生物又不会买电视广告里的产品，要知道你是靠这些收入来支付电费的。
The full picture is more complicated, but the bottom line is that as our technology has gotten better, less of our radio traffic has been leaking out into space. We're closing down the giant transmitting antennas and switching to cable, fiber, and tightly focused cell-tower networks.
整个问题当然更加复杂，但底线是：随着科学技术的进步，越来越少的无线电信号会泄露到外太空中去。我们逐渐弃置了巨型传输天线，转而使用有线电缆、光缆和紧密排列的蜂窝网络。
While our TV signals may have been detectable-with great effort-for a while, that window is closing. Even in the late 20th century, when we were using TV and radio to scream into the void at the top of our lungs, the signal probably faded to undetectability after a few light-years. The potentially habitable exoplanets we've spotted so far are dozens of light-years away, so the odds are they aren't currently repeating our catchphrases.
就算外星人现在还能探测到我们的电视信号——虽然得花不少力气——但很快这个窗口期也要被关上了。就算在20世纪晚期，当我们在电视和广播里放声高歌时，这些声音信号在传播了几光年之后就基本探测不到了。我们现在观测的可能的宜居星球离我们有好几十光年，所以他们不太可能听得到我们的老故事。
But TV and radio transmissions still weren't Earth's most powerful radio signal. They were outshone by the beams from early-warning radar.
但电视和广播信号并非地球上最强大的无线电信号，早期预警雷达可以完爆它们。