《那些古怪又讓人憂心的問題》第45期:外星天文學家(1)
AlieN ASTRONOMERS
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．不妨假設在離我們最近的一顆適於居住的地外星球上有生命存在，而且他們擁有和我們人類相近的科技。如果他們現在朝我們這邊看過來，會看到什麼？Let's try a more complete answer. We'll start with . . .
讓我回答得稍微詳細一點。首先我們來談談……
Radio transmissions
無線電通信Contact popularized the idea of aliens listening in on our broadcast media. Sadly, the odds are against it.
《超時空接觸》讓許多人以爲外星人在監聽着我們的無線電通信。很遺憾，這事兒希望不大。Here's the problem: Space is really big.
問題在於：宇宙太大了，相當大。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.
你當然可以計算星際無線電衰減的物理學，但光考慮這個場景的經濟學就足夠概括問題所在了——如果你的電視信號傳到了另一顆星球上，這必定是賠本買賣。驅動一個發射機要花很多錢，而其他星球上的生物又不會買電視廣告裏的產品，要知道你是靠這些收入來支付電費的。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.
整個問題當然更加複雜，但底線是：隨着科學技術的進步，越來越少的無線電信號會泄露到外太空中去。我們逐漸棄置了巨型傳輸天線，轉而使用有線電纜、光纜和緊密排列的蜂窩網絡。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.
就算外星人現在還能探測到我們的電視信號——雖然得花不少力氣——但很快這個窗口期也要被關上了。就算在20世紀晚期，當我們在電視和廣播裏放聲高歌時，這些聲音信號在傳播了幾光年之後就基本探測不到了。我們現在觀測的可能的宜居星球離我們有好幾十光年，所以他們不太可能聽得到我們的老故事。But TV and radio transmissions still weren't Earth's most powerful radio signal. They were outshone by the beams from early-warning radar.
但電視和廣播信號並非地球上最強大的無線電信號，早期預警雷達可以完爆它們。
