【英语时差8,16】为什么外星人不想吃我们

 Time for the mail bag. Let's see what we have.

Dear A Moment of Science. Are aliens going to eat us? Signed, Frightened.  Well, Frightened, that's more of a science fiction question. But science does have something to say here, and sometimes purely¹ imaginative questions are great tools for helping² us think about how the real world works.

First, it's not strictly³ impossible. Many scientists agree that the Milky⁴ Way galaxy⁵ 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 expend⁶ a lot of energy running down a zebra because, once it is caught, the calories contained in the meal far outweigh⁷ those expended⁸ 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 predators⁹ 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 munching¹⁰ 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 exhausted¹¹.   

1 purely   

adv.纯粹地，完全地

参考例句：

• I helped him purely and simply out of friendship.我帮他纯粹是出于友情。
• This disproves the theory that children are purely imitative.这证明认为儿童只会单纯地模仿的理论是站不住脚的。

2 helping   

n.食物的一份&adj.帮助人的，辅助的

参考例句：

• The poor children regularly pony up for a second helping of my hamburger. 那些可怜的孩子们总是要求我把我的汉堡包再给他们一份。
• By doing this, they may at times be helping to restore competition. 这样一来, 他在某些时候,有助于竞争的加强。

3 strictly   

adv.严厉地，严格地；严密地

参考例句：

• His doctor is dieting him strictly.他的医生严格规定他的饮食。
• The guests were seated strictly in order of precedence.客人严格按照地位高低就座。

4 milky   

adj.牛奶的，多奶的；乳白色的

参考例句：

• Alexander always has milky coffee at lunchtime.亚历山大总是在午餐时喝掺奶的咖啡。
• I like a hot milky drink at bedtime.我喜欢睡前喝杯热奶饮料。

5 galaxy   

n.星系；银河系；一群(杰出或著名的人物)

参考例句：

• The earth is one of the planets in the Galaxy.地球是银河系中的星球之一。
• The company has a galaxy of talent.该公司拥有一批优秀的人才。

6 expend   

vt.花费，消费，消耗

参考例句：

• Don't expend all your time on such a useless job.不要把时间消耗在这种无用的工作上。
• They expend all their strength in trying to climb out.他们费尽全力想爬出来。

7 outweigh   

vt.比...更重，...更重要

参考例句：

• The merits of your plan outweigh the defects.你制定的计划其优点胜过缺点。
• One's merits outweigh one's short-comings.功大于过。

8 expended   

v.花费( expend的过去式和过去分词 )；使用（钱等）做某事；用光；耗尽

参考例句：

• She expended all her efforts on the care of home and children. 她把所有精力都花在料理家务和照顾孩子上。
• The enemy had expended all their ammunition. 敌人已耗尽所有的弹药。 来自《简明英汉词典》

9 predators   

n.食肉动物( predator的名词复数 )；奴役他人者（尤指在财务或性关系方面）

参考例句：

• birds and their earthbound predators 鸟和地面上捕食它们的动物
• The eyes of predators are highly sensitive to the slightest movement. 捕食性动物的眼睛能感觉到最细小的动静。 来自《简明英汉词典》

10 munching   

v.用力咀嚼（某物），大嚼( munch的现在分词 )

参考例句：

• He was munching an apple. 他在津津有味地嚼着苹果。 来自《简明英汉词典》
• Munching the apple as he was, he had an eye for all her movements. 他虽然啃着苹果，但却很留神地监视着她的每一个动作。 来自辞典例句

11 exhausted   

adj.极其疲惫的，精疲力尽的

参考例句：

• It was a long haul home and we arrived exhausted.搬运回家的这段路程特别长，到家时我们已筋疲力尽。
• Jenny was exhausted by the hustle of city life.珍妮被城市生活的忙乱弄得筋疲力尽。