Satellite TV 'making humans invisible to aliens on other planets'
26 Jan 2010
Image above: The digital age is effectively gagging the Earth by cutting the transmission of TV and radio signals into space
That might be good news for anyone who fears an ''Independence Day'' – style invasion by little green men. But it is also likely to make the search for extraterrestrial intelligence by Earthly scientists harder, Dr Frank Drake believes.
Dr Drake, who founded the SETI (Search for Extraterrestrial Intelligence) organisation in the US 50 years ago, said the digital age was effectively gagging the Earth by cutting the transmission of TV and radio signals into space.
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At present, the Earth was surrounded by a 50 light year-wide ''shell'' of radiation from analogue TV, radio and radar transmissions, he said.
But although the signals had spread far enough to reach many nearby star systems, they were rapidly vanishing before the march of digital technology.
To a race of observing aliens, digital TV signals would look like noise, said Dr Drake.
Digital transmissions were also much weaker than their terrestrial equivalent.
While old-style TV transmitters might generate one million watts, the power of a satellite signal was around 20 watts. Satellites also aimed their transmissions at the Earth, with almost none being allowed to escape into space.
Use of cable prevented the leakage of signals even more effectively.
''Now the actual amount of radiation escaping into space is about two watts, not much more than you get from a cell phone,'' said Dr Drake.
''If this continues into the ...ure very soon our world will become undetectable. Using ourselves as an example, it means the difficulty of finding other civilisations will be much greater.
''We're going to have to search many more stars and many more frequencies.''
Any alien civilisations that existed were likely to be far more advanced than ours, he said. Their analogue TV age probably came and went long ago, before humans even thought about searching the sky for signs of intelligent life.
Dr Drake was speaking at a discussion meeting taking place at the Royal Society in London entitled ''The Detection of Extraterrestrial Life and the Consequences for Science and Society''.
He said he remained convinced that intelligent life existed beyond the Earth, despite the lack of success of SETI scientists who have spent half a century tuning into the stars.
The famous ''Drake Equation'' which he invented to estimate the chances of finding ET indicated there might be 10,000 detectable civilisations in our galaxy, the Milky Way.
However, even this large number equated to just one in 10 million stars.
''We have to search 10 million stars for signals and we have to do it over and over,'' said Dr Drake. ''We haven't remotely come close to that.''
Aliens could reveal themselves with technologies that are currently far beyond the scope of humans, he pointed out.
One possibility was using your own star as an incredibly powerful lens to amplify light and radio signals.
This could be done because of the way gravity bends light, as demonstrated by Albert Einstein.
The Sun bent light from distant stars to a focal point where one million-fold magnifications should be possible, dwarfing the abilities of the most powerful telescopes. Unfortunately, the focal point is far beyond the edge of the Solar System and too far to reach using current technology, said Dr Drake.
But it was likely advanced civilisations elsewhere had mastered the technique, he added.
A ''gravitational lens'' of this type could be powerful enough to map the continents and oceans of a planet in a distant star system.
Reversing the technology to use the lens as a transmitter instead of a receiver would enable aliens to beam massively powerful signals across the galaxy, said Dr Drake.
They could be using such a system to announce their presence to other planets, he said. But although the signal would be strong, it was likely to be transient as the beam was swept from place to place.
Another method of communication could be through the use of incredibly powerful pulsed lasers, such as those now being developed for nuclear fusion reactors.
Such a laser would produce a flash that for an instant could outshine a star. SETI had now started to look for signals of this type, so far with no success.
''In the universe elsewhere there is intelligent life. I'm confident about that, but how easy it is to find we don't know,'' said Dr Drake.
(Source: Telegraph.co.uk )
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