英語聽力文摘 外星人要吃人？

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Are aliens going to eat us?

That’s more of a science fiction question. But science does have something to say here, and sometimes purely imaginative questions are great tools for helping us think about how the real world works.

First, it’s not strictly impossible. Many scientists agree that the Milky Way galaxy is probably brimming with living things. That doesn’t mean any of them are smart enough to build interstellar spaceships, but let’s assume they are. Still, why are they unlikely to eat us? One reason lies in energy itself.

The point of eating is to take in usable energy. A lion will expend a lot of energy running down a zebra because, once it is caught, the calories contained in the meal far outweigh those expended in the chase. If this weren’t true–say, if the zebra’s body only had the caloric content of a grape–then the energy expended would outweigh the energy gained, and the lion would lose out.

Any alien predators would face the same problem. The amount of energy expended in building a space program, fueling rockets, to say nothing of getting from one star to another, would be huge. For any realistic technology it would far outweigh the benefit of just munching on people. It would be like climbing Mount Everest in order to pick a few berries.

Some day we ourselves may travel to other planets. But any species that goes to such lengths merely to find food will find itself quickly exhausted.

為什么外星人不吃我們呢?

外星人會來吃我們嗎?

這更像是科幻小說里的才會出現(xiàn)的問題。但是在這個(gè)問題上我們還是可以尋求科學(xué)的答案。很多時(shí)候像這種純粹異想天開的問題卻能夠幫助我們更好地思考，更好地認(rèn)識這個(gè)世界。

首先，嚴(yán)格地說，這也不無可能。許多科學(xué)家都認(rèn)為銀河系里可能到處都是生物，但這并不是說它們就有能力建造星際間飛船。退一萬步說，就算它們有這個(gè)能力來建造星際間飛船，可是，它們又為什么要吃我們呢?原因之一就在于能量本身。

吃東西最主要就是為了攝入可用的能量。一頭獅子可以耗掉大量的體力去追捕一匹斑馬，那是因?yàn)橐坏┳プ×四瞧グ唏R，它能攝入的斑馬肉里的能量大大超過了他在追捕過程中消耗的能量。如果以上都不成立，假如斑馬肉里所含能量很少——少到根本就無法補(bǔ)充獅子追捕所耗能量，那么這頭獅子也只能是白白耗掉體力了。

既然有這樣的說法，那么食肉的外星人也會面對同樣的問題。建造一個(gè)空間計(jì)劃，制造燃料火箭都需要消耗很多能量。更不用說從一個(gè)星球飛至另一個(gè)星球需要消耗更多的能量!與其獵食人類，還不如將那些能量用于更有實(shí)際意義的科技開發(fā)。其實(shí)獵食人類就像是辛辛苦苦攀上珠穆朗瑪卻只為摘些果子一樣大材小用，勞民傷財(cái)。

也許某一天人類能夠踏上其他星球的土地。但是，任何一個(gè)為尋覓食物而踏上其他星球的物種終將認(rèn)識到如此行徑只會消耗掉自己的能量——自取滅亡。

Note: science fiction n. 科幻小說