The basic question is, does life exist beyond Earth?
我们的根本问题是，地球之外还存在生命吗？
Scientists who are called astrobiologists are trying to find that out right now.
那些被称为天体生物学家的科学家们，正在尝试研究这个问题。
Most astrobiologists are trying to figure out if there's microbial life on Mars,
许多天体生物学家正在试图确定在火星上
or in the ocean under the frozen surface of Jupiter's moon Europa,
或者在木卫二的海洋冰面之下，
or in the liquid hydrocarbon lakes that we've found on Saturn's moon Titan.
又或者是在土卫六的液态烃湖中是否存在微生物。
But one group of astrobiologists works on SETI.
但一个天体生物学家小组正致力于SETI研究。
SETI is the Search for Extraterrestrial Intelligence, and SETI researchers are trying to detect some evidence
SETI是指对地外智能生物的探索，SETI研究者正尝试发掘一些证据，
that intelligent creatures elsewhere have used technology to build a transmitter of some sort.
来说明除了智能生物之外的其他生物已经使用科技建造了某种发射器。
But how likely is it that they will manage to find a signal?
但是他们想法设法发现信号的可能性有多大？
There are certainly no guarantees when it comes to SETI,
没有SETI能勘测到信号的绝对保证，
but something called the Drake equation, named after Frank Drake,
不过有个东西叫德雷克方程，由法兰克·德雷克命名，
can help us organize our thinking about what might be required for successful detection.
可以帮我们整理思路：成功的探测究竟需要什么。
If you've dealt with equations before, then you probably expect that there will be a solution to the equation, a right answer.
如果你之前已经处理过方程，那么你可能会期待这个方程会有一种解法可得出正确答案。
The Drake equation, however, is different, because there are so many unknowns. It has no right answer.
然而，德雷克方程是截然不同的，因为有许多未知数。它没有正确答案。
As we learn more about our universe and our place within it,
随着我们对宇宙以及我们所处在的土地了解越来越多，
some of the unknowns get better known, and we can estimate an answer a bit better.
一些未知数将会得到更好的理解，我们可以预估一个更好的答案。
But there won't be a definite answer to the Drake equation until SETI succeeds
但是德雷克方程将不会有明确的答案，直到SETI成功，
or something else proves that Earthlings are the only intelligent species in our portion of the cosmos.
或者其他事情能够证明地球人是宇宙中唯一的智能物种。
In the meantime, it is really useful to consider the unknowns.
同时，考虑未知数极为有用。
The Drake equation attempts to estimate the number of technological civilizations in the Milky Way Galaxy -- we call that N
德雷克方程试图预测银河系中的科技文明社会的数量--我们设其为N，
with whom we could make contact, and it's usually written as:
我们可以和之联系，这常常被写作：
N equals R-star multiplied by f-sub-p multiplied by n-sub-e multiplied by f-sub-l multiplied by f-sub-i multiplied by f-sub-c
N=R*×fp×ne×fl×fi×fc，
and lastly, multiplied by capital L.
最后，再乘以大写L.
All those factors multiplied together help to estimate the number of technological civilizations that we might be able to detect right now.
所有这些因素乘在一起，可以帮助预测科技文明的数量。这也许是我们目前能够做的。
R-star is the rate at which stars have been born in the Milky Way Galaxy over the last few billion years,
R*是一种比率，星星已经在银河系诞生了几十亿年，
so it's a number that is stars per year.
所以这是指星星每年诞生的数量。
Our galaxy is 10 billion years old, and early in its history stars formed at a different rate.
我们的银河系已有几百亿岁，在它的历史早期，星星就已经形成了不同的比率。
All of the f-factors are fractions. Each one must be less than or equal to one.
所有的f因素都是其中一部分。每个因素都必须小于或等于另一个。
F-sub-p is the fraction of stars that have planets.
fp是指具有行星的星星。
N-sub-e is the average number of habitable planets in any planetary system.
ne是指在任何一个行星系统中的可居住行星的平均数量。
F-sub-l is the fraction of planets on which life actually begins
fl是指开始有生命的行星，
and f-sub-i is the fraction of all those life forms that develop intelligence.
而fi是指那些所有能够发展智力的生命。
F-sub-c is the fraction of intelligent life that develops a civilization that decides to use some sort of transmitting technology.
fc是指能够发展文明的智能生命，它们能决定运用某种类型的传输技术。
And finally, L -- the longevity factor.
最后，L是指寿命因素。

On average, how many years do those transmitters continue to operate?
平均来说，那些传输器能够持续运作多少年？
Astronomers are now almost able to tell us what the product of the first three terms is.
天文学家现在几乎能够告诉我们前三种术语分别是什么。
We're now finding exoplanets almost everywhere.
我们正在尽可能四处探索外星行星。
The fractions dealing with life and intelligence and technological civilizations are ones that many, many experts ponder,
有无数的专家正在研究那些孕育生命、智能与技术文明的行星，
but nobody knows for sure.
但是没有人能完全了解。
So far, we only know of one place in the universe where life exists, and that's right here on Earth.
到目前为止，我们仅知道宇宙中有一个地方有生命存在，那个地方就是地球。
In the next couple of decades, as we explore Mars and Europa and Titan,
在接下来的几十年，随着我们对火星、木卫二以及土卫六的探索，
the discovery of any kind of life there will mean that life will be abundant in the Milky Way.
任何物种的发现，都意味着银河系将会有丰富多样的生命。
Because if life originated twice within this one Solar System, it means it was easy,
因为如果生命在这个太阳系内起源了两次，那么这意味着生命起源很容易，
and given similar conditions elsewhere, life will happen.
并假设别的地方也有相似条件，生命就会产生。
So the number two is a very important number here.
所以二这个数字在这里尤其重要。
Scientists, including SETI researchers, often tend to make very crude estimates
科学家，包括SETI研究者，经常想要做一些大致预测，
and acknowledge that there are very large uncertainties in these estimates, in order to make progress.
并承认在这些预测中会有巨大的未知数以获取进展。
We think we know that R-star and n-sub-e are both numbers that are closer to 10 than, say, to one, and all the f-factors are less than one.
我们认为我们都知道R*和ne是比10更接近1的参数，并且这些f因素都小于1。
Some of them may be much less than one.
其中一些可能要远远小于1。
But of all these unknowns, the biggest unknown is L,
但在这些未知数中，最大的未知数是L，
so perhaps the most useful version of the Drake equation is simply to say that N is approximately equal to L.
因此，德雷克方程可能最有用的版本，可以简单地说是N近似于L。
The information in this equation is very clear. Unless L is large, N will be small.
这方程式的信息十分清晰。除非L是较大的参数，那么N就是较小的参数。
But, you know, you can also turn that around.
但是你也可以把推论倒过来。
If SETI succeeds in detecting a signal in the near future, after examining only a small portion of the stars in the Milky Way,
如果SETI在不远的将来探测信号成功，验证到银河系的行星中只有一个小样本，
then we learn that L, on average, must be large.
那么我们可以得出，L通常一定是较大的参数。
Otherwise, we couldn't have succeeded so easily.
不然，我们不可能如此轻易成功。
A physicist named Philip Morrison summarizes by saying that SETI is the archaeology of the future.
一位名叫菲利普·莫里森的物理学家总结称，SEIT是对未来的考古学。
By this, he meant that because the speed of light is finite,
通过这个观点，他想表达因为光速是有限的，
any signals detected from distant technologies will be telling us about their past by the time they reach us.
所以任何从远传技术探测到的信号，都将会在传输到我们这里的时候告诉我们它们的过去。
But because L must be large for a successful detection,
但是因为对于一个成功的探测而言，L一定是一个较大的参数，
we also learn about our future, particularly that we can have a long future.
所以我们还会了解到我们的未来，尤其是我们可能会拥有一个很长远的未来。
We've developed technologies that can send signals into space and humans to the moon,
我们已经开发出能将信号发送到太空、并且能将人类送上月球的科技，
but we've also developed technologies that can destroy the environment, that can wage war with weapons and biological terrorism.
但是我们也开发出了能够破坏环境的科技，利用武器以及生物恐怖主义发动战争。
In the future, will our technology help stabilize our planet and our population, leading to a very long lifetime for us?
在未来，我们的科技能帮助稳定住我们的星球以及人口，从而使我们生存更长一段时间吗？
Or will we destroy our world and its inhabitants after only a brief appearance on the cosmic stage?
又或者，我们将会在宇宙的舞台上短暂的出现，然后毁掉我们的世界及其居民？
I encourage you to consider the unknowns in this equation.
我鼓励你们去思考这个方程式里的未知数。
Why don't you make your own estimates for these unknowns, and see what you come up with for N?
为什么你们不为这些未知数做一些自己的预测，然后看看你将如何算出N呢？
Compare that with the estimates made by Frank Drake, Carl Sagan, other scientists or your neighbors.
将这些预测与弗兰克·德雷克、卡尔·萨根、其他科学家，或者你邻居的预测比较。
Remember, there's no right answer. Not yet.
记住，这没有标准答案。至少目前还没有。