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I don't think they're going to visit.
我觉得他们不会访问地球。
However, very reasonable that we will in Carl Sagan fashion detect a signal from some other star system.
但是，如果我们用卡尔·萨根的方法探测到来自其他星系的信号是非常合理的。
That's very reasonable. I make no guarantees.
这是非常合理的。我不能保证。
It's the Christmas light problem, the holiday light problem where the lights are blinking.
这个问题就像圣诞节的彩灯一样，所有小灯此起彼伏地闪烁。
Our light of being able to receive electromagnetic wave from another civilization has to be on when another blinking civilization light is on so that we can cross paths not only in space but in time.
只有在另一个文明的光亮着的时候，我们才能够接收到来自它的电磁波，这样我们不仅能在空间上而且也能在时间上偶遇。
We have to have both civilizations existing at the same time.
两种文明必须同时存在。
And with a universe that's at least 13.6 billion years old it's not necessarily a given thing that everybody their lights will be on at the same time.
对于一个至少有136亿年历史的宇宙来说，并不是每颗星球的光都会同时亮起来。
What would life be like on other planets if it is evolved?
如果其他行星也进化了，那上面的生命会是什么样子?
Would it be like the world today here on Earth or would it be completely different?
它会和今天的地球一样，还是会完全不同?
This question has taken on some increased urgency or at least interest in recent years because we now realize that there are many planets out there that are like Earth.
近年来，这个问题变得越来越紧迫，或者说至少越来越引起人们的兴趣，因为我们现在意识到有许多像地球一样的行星。
We used to think that Earth was perhaps unique and so perhaps life as we know it is unique because we're the only place that it could evolve.
我们曾经认为地球是独一无二的，所以我们以为生命也是独一无二的，因为地球是生命唯一可以进化的地方。
But quite the contrary. We've now discovered there are lots of what are called habitable exoplanets.
但事实恰恰相反。现在我们发现了很多所谓的宜居系外行星。
Some people estimate millions, even billions just in our own Milky Way Galaxy.
有些人估计，单在银河系就有数百万，甚至数十亿颗那样的行星。
If there are really that many Earth-like planets many people think that it's very likely that life has evolved on them.
如果真的有那么多类地行星的话，很多人认为生命很有可能已经在这些行星上进化。
And so the question is what will that life look like?
所以问题是，那里的生命会是什么样子?
It's very reasonable, absolutely not proven.
这是非常合理的，还没有得到证实。
We may have the means to prove it, very reasonable that you and I are descendent of extraterrestrials.
我们可能有办法证明它，说你和我是外星人的后裔也是讲得通的。
We just found liquid water on Mars.
我们刚刚在火星上发现了液态水。
Super salty water on Mars that apparently flows every Martian year, every time Mars goes around the sun and gets warm enough in this one area liquid water flows for a while.
火星上的超咸水显然每年都在流动，每次火星绕太阳运转的时候，温度会高到让该区域的液态水流动一段时间。
Briny water evaporates.
咸水会蒸发。
It's very reasonable that there's something alive on Mars or certainly that there was something alive on Mars.
火星上有生命存活是很合理的，或者说火星上确实有生命。
Then it's very reasonable that Mars was hit with an impact.
那么说火星曾经被撞击过也就很合理了。
You can show that Mars was hit with an impactor, a comet or asteroid, about three billion years ago.
你可以证明火星在大约30亿年前被一个撞击物——彗星或小行星撞击过。
And some of the material of Mars was thrown off into space and some of it landed here.
火星上的一些物质散向太空，其中一些降落在地球上。
We find rocks on Earth that are clearly of Martian origin.
我们在地球上发现了明显源于火星的岩石。
I bought one online for kicks and suppose some especially robust Martian microbe, a Mars-crobe, was in this piece of material, landed on Earth at an especially fertile time here on Earth three billion years ago.
为了好玩，我在网上买了一个，假设有一些特别强壮的火星微生物，火星生物，就包含在这块物质中，在30亿年前地球特别肥沃的时候降落在这里。
And you and I are descendants of Martians. Do-do-do-do, do-do-do-do.
那么我们都是火星人的后裔哦。
