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Back in 1950, the Nobel prize-winning physicist Enrico Fermi washaving lunch with friends.
早在1950年，諾貝爾獎獲得者恩里克費爾米正與他的朋友吃午餐。
Conversation turned to the possibilityof extraterrestrial life.
他們的話題轉到是否可能存在外太空生命上。
According to the popular story, Fermi fell silent for a moment and thenasked the simple but profound question: Where Is Everybody?
按照那個受歡迎故事的說法，當時費米爾沉默了一會，然后問到了這個簡單而又深刻的問題：他們都去哪了？
That question is now known as the Fermi Paradox.
現在，那個問題被稱為是費米爾悖論。
A version goes like this.
有個版本是這樣的：
There are a fewhundred billion stars in the Milky Way Galaxy.
在銀河系里，有幾千億顆恒星。
Suppose even half those stars have planets.
假設說那些恒星半數周圍有行星。
Then suppose only one or two of, say, ten planets per star is conducive to the formation of life, asis the case with our own solar system.
然后假設和我們的太陽系一樣，每顆恒星周圍每十顆行星有一顆或兩顆有利于形成生命。
Suppose life takes a billion years to get started, ashappened on earth.
假設那的生命和地球上的一樣，要花費十億年才開始形成。
Suppose the evolution of higher life forms takes another couple billion years,as it did here.
再假設更高級形式的生命要再花幾十億年才能進化，就如地球上所經歷的那樣。
None of that would matter.
沒有一項有問題。
The Milky Way galaxy is around ten billion years old.
銀河系已經近一百億光年了。
Even with veryconservative estimates, it should still be swarming with life-even intelligent life.
即使很保守的估計，它應該還是擠滿了生命—甚至是智能生命。
The late Carl Sagancalculated that there should be something like a million advanced civilizations out there right now.
后來的卡爾薩根計算了一下，目前應該大約有100萬先進文明在那了。
So where are they?
那么他們在哪呢？
Tabloid stories aside, there's no scientific evidence from any corner to suggestwe aren't alone in the Milky Way.
把小報故事放一邊看，現在還沒有任何角度的科學證據表明我們不是銀河系中唯一存在的人類。
But why not? The evidence should be everywhere.
但是為什么不是呢？證據應該到處都是。
That's Fermi's paradox.
那就是費米爾悖論。
It has nothing to do with whether you believe in flying saucers or not.
你是否相信有飛碟都不重要。
It'sa simple estimation: given what we know about our star, our planet, and how life evolved here, wecan extrapolate to what probably happens elsewhere.
這只是一個簡單的估計：假如讓我們知道有關我們所在的恒星，行星的知識，還有生命如何進化的，那就可以推斷別處可能發生什么。
And yet: there's no sign of alien civilizations.
可是，還沒有外星文明的跡象呢。
Something must have gone wrong in our thinking.
我們的思想一定是哪出了問題。
But what? More next time.
但是是什么問題呢？下次再說吧。
