今日单词

agreeable
adj.惬意的，宜人的；可接受的，适合的；欣然同意的

gleam
v.发微光；闪烁；隐约闪光；（在眼中）闪现；表露

hypothesis
n.[复数hypotheses] 假设, 假说; (凭空的)猜测

chip
n.集成电路片，芯片；炸薯条，炸薯片；碎屑，碎片；缺口

plastic
adj.塑料的；可塑的；不自然的，做作的

intrepid
adj.勇敢的，无畏的

convection
n.对流；传送

decree
n.法令，政令；（法院的）裁定，判决

focus
n.焦点，焦距；（活动、兴趣等的）中心

sardonic
adj.嘲笑的，讥讽的

dictate
v.口授, 口述; 使听写; 命令, 发号施令; 支配

transform
v.转换，变形；改善，使改头换面

parliament
n.议会, 国会, 英国议会（包括下议院和上议院）

contribute
v.捐助；投稿；贡献；促使

zinc
n.锌

enthusiastic
adj.热情的，热心的

troposphere
n.对流层

contest
n.比赛，竞赛；竞争

command
n.命令，指挥；司令部

meteorite
n.陨石

今日短文

Why Scientists Can’t Give up the Hunt for Alien Life
为什么科学家执着于寻找外星生命？
Within our observable Universe, since the dawn of the hot Big Bang, sextillions of stars have formed.Of those, the majority of them are found in large, massive, rich galaxies: galaxies comparable in size and mass to the Milky Way or greater.

By the time billions of years have gone by, most of the new stars will have sufficiently large fractions of heavy elements to lead to the formation of rocky planets and molecules that are known as precursors to life.

These precursor molecules have been found everywhere, from comets and asteroids to the interstellar medium to stellar outflows to planet-forming disks.

And, at this critical step, we find ourselves face-to-face with the end of our scientific certainty.

Where, and under what conditions, does life come into existence?

On those worlds where life arises, how frequently does it survive and thrive, persisting for billions of years?

How often does that life saturate its habitable regions, transforming and feeding back on its biosphere?

Where this occurs, how often does life diversify, becoming complex and differentiated?
And where that occurs, how frequently does life become intelligent enough to become technologically advanced, capable of communicating across or even traversing the vast interstellar distances?

These questions aren’t merely there for us to philosophically ponder; they’re there for us to gather information about, and eventually, to draw scientifically valid conclusions about such probabilities.

Of course, there are plenty of valid explanations for why we haven’t succeeded in our searches for life just yet.

The most sobering — and the most pessimistic — is that it’s possible that one or more of the steps required to give rise to the type of life we’d be sensitive to are particularly difficult, and only rarely can the Universe achieve them.

In other words, it’s possible that any one of life, sustained life, complex and differentiated life, or intelligent and technologically advanced life are rare, and none of the worlds we’ve surveyed possess them.That’s a possibility we have to keep in mind so long as we’re committed to remaining intellectually honest.

But there’s no reason, at least so far, to suspect that’s the primary reason we haven’t discovered life beyond Earth just yet.

The old saying, “If at first you don’t succeed, try, try again,” applies wherever the odds of success are unknown, but we have every indication that success is possible under the right circumstances.

Here on Earth, the evidence strongly indicates that our home planet is an example of such circumstances, and hence it’s likely that there are places all throughout space and time where life sustains itself, evolves to become complex and differentiated, and achieves a level of technological advancement sufficient for interstellar communication.

The big unknowns are in the probabilities of the various types of alien life that are actually out there, not in the question of whether such achievements are possible within our Universe.

That doesn’t mean that we should take seriously every claim that’s been made — even by scientists — that alien life has been found.

The “Wow!” signal, for example, was a high-powered radio signal received over the span of 72 seconds back in 1977; although its nature is unknown, it has never been replicated, either back at the original source or anywhere else.

Without confirmation or repeatability, we can draw no affirmative, definitive conclusions.
NASA’s Mars Viking lander conducted numerous tests for life on the Martian surface, with one experiment (the Labeled Release experiment) giving a positive signature.

However, the possibility of contamination, the lack of reproducibility, and the lack of a verified follow-up experiment has cast tremendous doubt on the “biological positive” interpretation of the experiment.

And despite the possibility of encountering interstellar space probes, direct alien contact, or even the ubiquity of alien abduction stories, no robust verification of any of these claims has ever come forth.

We have to keep our minds open while at the same time remaining skeptical of any grand claims.The conclusions we draw can only be as strong as the supporting evidence for them.

It’s primarily for these reasons — we have every indication that the Universe has all the necessary ingredients for life, but no indication that we’ve found it just yet — that it’s so vital to keep looking in a scientifically scrupulous way.