IS THERE ANYBODY OUT THERE?
The Search for Extra-terrestrial Intelligence
A
For centuries people have wondered whether life exists beyond our own world, and today, by listening for radio transmissions sent out by other intelligent beings, we may finally be close to settling the matter. Known widely by its acronym SETI - short for the search for extra-terrestrial intelligence - this undertaking is far from straightforward. Teams in various countries have hunted on and off for close to forty years, yet only recently has our technology advanced far enough to let us mount a serious, systematic sweep of every nearby star in the hope of finding some trace of life.
B
Curiosity lies at the heart of the search - the very same curiosity about the natural world that motivates every branch of pure science. Are we alone? Does life spring up of its own accord wherever conditions allow, or is there something exceptional about the Earth that has given rise to the abundance of living things around us? To resolve this most fundamental of questions, merely picking up a single radio signal would be enough. Viewed this way, SETI is simply one more part of the pure-science enterprise that keeps extending the boundaries of what we know. There are, however, further motives for wanting to know whether life exists elsewhere. Human civilisation, after all, has lasted perhaps no more than a couple of thousand years, and the dangers of nuclear war and pollution that have loomed over recent decades remind us how fragile our continued existence might be. Are we destined to survive a further three thousand years, or to destroy ourselves? Because a world such as ours can persist for roughly ten billion years, any civilisations that endure elsewhere in our galaxy could be anything from newly formed to billions of years old. It follows that whichever civilisation we do pick up will, on average, almost certainly be much older than we are. Simply knowing that such a civilisation exists would prove that long-term survival is achievable, which gives grounds for optimism; and it is even conceivable that a more ancient people might share what they have learned about surviving hazards like nuclear war, global pollution and dangers we have yet to imagine.
1
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Drop or Select
Two working rules guide most researchers as they weigh up the question of our solitude. The first is that unidentified flying objects are set aside, because the evidence for them strikes most scientists as too flimsy to warrant serious attention - though a genuinely persuasive case, should one ever surface, would of course deserve an open mind. The second is a deliberately cautious premise: the beings sought are assumed to be broadly similar to ourselves, for anything wildly unlike us might not register as life at all, quite aside from the problem of communicating with it. Such a creature might, admittedly, sport two green heads and seven fingers, and yet in the essentials it would still echo us - talking to its own kind, curious about the cosmos, dwelling on a planet that circles a Sun-like star, and, most constraining of all, built on a chemistry of carbon and water just as we are - the only chemical basis we currently know of that is capable of sustaining living systems.
2
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Drop or Select
Even granting these premises, how much we can say about other living things remains very slight. We have no firm idea, for instance, of how many stars possess planets at all, still less of the odds that life will emerge naturally once the right conditions are in place. And yet, faced with the several hundred billion stars of our own galaxy, the Milky Way, and the hundreds of billions of galaxies that fill the observable Universe, the notion that not one of these worlds bears life seems scarcely credible; indeed, the best estimate we can venture - drawing on the little we understand about what carbon-based life requires - puts the figure at something like one star in every 80,000 hosting a life-bearing planet. If so, our closest neighbours may lie about 120 light years off, which, on the scale of the cosmos, is practically next door.
3
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Drop or Select
To scatter information across the galaxy an alien society might use any number of methods, but most either demand enormous power or fade badly over the immense stretches between the stars. As it happens, radio waves in the band from 1200 to 3400 MHz carry furthest for a given transmitting power, which is why every search so far has focused on that part of the spectrum. A range of programmes worldwide has already made the attempt, among them a New Zealand effort using the dish at Rangimoana, on the country's South Island. From the couple of hundred stars examined to date, nothing has yet been picked up. Since 1995, however, the effort has been scaled up sharply: that year the Canadian federal legislature approved an eight-year grant of $12 million a year to fund a thorough hunt for life beyond the Earth. A large share of that money is going into the specialised equipment required to monitor many frequencies simultaneously. The work is split in two. One half is a targeted survey carried out on some of the largest dishes in existence - the Canadian-run instrument at Fenwick Bay in Newfoundland and the German telescope at Osterholt - which sweeps the nearest 1,500 promising stars at high sensitivity across the 1200-to-3400 MHz band. The other half, a broader and less sensitive watch over the whole sky, relies on the smaller antennas of the Orbital Tracking Network.
4
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Drop or Select
How we ought to respond, should a signal from another civilisation actually be detected, is a matter of real dispute. On one point there is unanimity: an immediate reply is out of the question. Setting aside the sheer impracticality of despatching an answer across such distances on short notice, the act would throw up a whole range of ethical problems that the world as a whole would need to work through before any message went out. Could humanity withstand the shock of confronting a civilisation far older and more advanced than itself? Fortunately, none of this is pressing. Because the stars under examination sit hundreds of light years away, their signals take centuries to reach us, and our reply would take centuries more to arrive; a pause of a few years, or even decades, while humanity argues over whether to answer and painstakingly composes a response, would therefore make little practical difference to how events eventually unfold.
Kéo chỉnh
Question 1 - 4
From the list of headings below choose the most suitable heading for each paragraph.
List of heading
Deciding how to answer a message
What we currently understand about alien biology
Estimating the chances of life elsewhere
The great gulf separating us from our nearest neighbours
Listening for broadcasts from the stars
The starting premises behind the hunt