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READING PASSAGE 1
IS THERE ANYBODY OUT THERE'
The Search for Extra-terrestrial Intelligence
The question of whether we are alone in the Universe has haunted humanity for centuries, but we may now
stand poised on the brink of the answer to that question, as we search for radio signals from other intelligent
civilisations. This search, often known by the acronym SETI (search for extra-terrestrial intelligence], is
a difficult one. Although groups around the world have been searching intermittently for three decades, it is
only now that we have reached the level of technology where we can make a determined attempt to search all
nearby stars for any sign of life.
A
The primary reason for the search is basic curiosity - the same curiosity about the natural world that drives all
pure science. We want to know whether we are alone in the Universe. We want to know whether life evolves
naturally if given the right conditions, or whether there is something very special about the Earth to have
fostered the variety of life forms that we see around us on the planet. The simple detection of a radio signal
will be sufficient to answer this most basic of all questions. In this sense, SETI is another cog in the
machinery of pure science which is continually pushing out the horizon of our knowledge. However, there are
other reasons for being interested in whether life exists elsewhere. For example, we have had civilisation on
Earth for perhaps only a few thousand years, and the threats of nuclear war and pollution over the last few
decades have told us that our survival may be tenuous. Will we last another two thousand years or will we
wipe ourselves out? Since the lifetime of a planet like ours is several billion years, we can expect that, if other
civilisations do survive in our galaxy, their ages will range from zero to several billion years. Thus any other
civilisation that we hear from is likely to be far older, on average, than ourselves. The mere existence of such a
civilisation will tell us that long-term survival is possible, and gives us some cause for optimism. It is even
possible that the older civilisation may pass on the benefits of their experience in dealing with threats to
survival such as nuclear war and global pollution, and other threats that we haven’t yet discovered.
B
In discussing whether we are alone, most SETI scientists adopt two ground rules. First, UFQs (Unidentified
Flying Objects) are generally ignored since most scientists don’t consider the evidence for them to be strong
enough to bear serious consideration (although it is also important to keep an open mind in case any really
convincing evidence emerges in the future). Second, we make a very conservative assumption that we
are looking for a life form that is pretty well like us, since if it differs radically from us we may well not
recognise it as a life form, quite apart from whether we are able to communicate with it. In other words, the life
form we are looking for may well have two green heads and seven fingers, but it will nevertheless resemble us
in that it should communicate with its fellows, be interested in the Universe, live on a planet orbiting a star like
our Sun, and perhaps most restrictively, have a chemistry, like us, based on carbon and water.
C
Even when we make these assumptions, our understanding of other life forms is still severely limited. We do
not even know, for example, how many stars have planets, and we certainly do not know how likely it is that
life will arise naturally, given the right conditions. However, when we look at the 100 billion stars in our
galaxy (the Milky Way), and 100 billion galaxies in the observable Universe, it seems inconceivable that at
least one of these planets does not have a life form on it; in fact, the best educated guess we can make, using
the little that we do know about the conditions for carbon-based life, leads us to estimate that perhaps one in
100,000 stars might have a life-bearing planet orbiting it. That means that our nearest neighbours are perhaps
100 light years away, which is almost next door in astronomical terms.
D
An alien civilisation could choose many different ways of sending information across the galaxy, but many of
these either require too much energy, or else are severely attenuated while traversing the vast distances across
the galaxy. It turns out that, for a given amount of transmitted power, radio waves in the frequency range 1000
to 3000 MHz travel the greatest distance, and so all searches to date have concentrated on looking for radio
waves in this frequency range. So far there have been a number of searches by various groups around the
world, including Australian searches using the radio telescope at Parkes, New South Wales. Until now there
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have not been any detections from the few hundred stars which have been searched. The scale of the searches
has been increased dramatically since 1992, when the US Congress voted NASA $10 million per year for ten
years to conduct a thorough search for extra-terrestrial life. Much of the money in this project is being spent on
developing the special hardware needed to search many frequencies at once. The project has two parts. One
part is a targeted search using the world’s largest radio telescopes, the American-operated telescope in
Arecibo, Puerto Rico and the French telescope in Nancy in France. This part of the project is searching the
nearest 1000 likely stars with high sensitivity for signals in the frequency range 1000 to 3000 MHz. The other
part of the project is an undirected search which is monitoring all of space with a lower sensitivity, using the
smaller antennas of NASA’s Deep Space Network.
E
There is considerable debate over how we should react if we detect a signal from an alien civilisation.
Everybody agrees that we should not reply immediately. Quite apart from the impracticality of sending a reply
over such large distances at short notice, it raises a host of ethical questions that would have to be addressed by
the global community before any reply could be sent. Would the human race face the culture shock if faced
with a superior and much older civilisation? Luckily, there is no urgency about this. The stars being searched
are hundreds of light years away, so it takes hundreds of years for their signal to reach us, and a further few
hundred years for our reply to reach them. It’s not important, then, if there’s a delay of a few years, or decades,
while the human race debates the question of whether to reply, and perhaps carefully drafts a reply.
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