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Chances of aliens finding Earth disappearing
15:59 09 August 04
NewScientist.com news service
A pioneer of the search for extraterrestrial intelligence (SETI) has warned that for any intelligent aliens trying to search for us, "the Earth is going to disappear" very soon.
Frank Drake's point, made at a SETI workshop at Harvard University on Friday, is that television services are increasingly being delivered by technologies that do not leak radio frequencies into space.
But he added that in some ways the observation is good news for SETI, as it means that the failure of Earth-based observers to detect aliens so far may be less worrisome than it would otherwise seem.
Most SETI efforts have focused on detecting radio signals that might be emitted by intelligent beings on planets around nearby stars. For humans, such signals "are the strongest signs of our existence", Drake said, thanks to television.
Traditional television broadcast antennas put out one megawatt each, and this radio-wave bubble now extends about 50 light years out from the solar system.
Straight down
But that is changing fast, Drake says. More and more television is now delivered by cable, with no radio-frequency leakage to space, and by direct-broadcast satellites that put out just 20 watts per channel, all efficiently directed straight down the intended areas on the Earth's surface.
So from the point of view of being detected through such inadvertent broadcasts, the longevity of humanity's detectability may be just 100 years.
And longevity may be the most important figure in Drake's famous equation for estimating the number of detectable intelligent civilisations on other worlds. The best estimates show that all the other crucial factors nearly cancel out, so that the number of such civilisations in our Milky Way galaxy is roughly equal to their average longevity of detectability in years.
Laser beacon
Drake's insight has important implications for search strategies. It means that eavesdropping on unintended alien transmissions is unlikely to succeed and "argues for an emphasis on detecting beacons", i.e. signals intentionally sent our way.
Subscribe to New Scientist for more news and features
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Weblinks
SETI symposium, Planetary Society
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Drake Equation
SETI, Harvard University
Some SETI strategies have already begun shifting toward that approach, including efforts to find optical beacons based on high-powered lasers deliberately aimed at nearby stars.
While optical communications across interstellar distances was initially thought impractical, military research has led to lasers sufficiently powerful to make such signalling much more efficient than any radio beacon.
Nuclear-powered lasers on the drawing boards could produce pulses that would outshine the sun by a factor of 10,000, said Harvard University physicist Paul Horowitz, who has already been searching for such pulses. He has designed a new telescope that will soon be dedicated full-time to that search.
And other innovative ideas keep coming along. Planet hunter Geoffrey Marcy of the University of California, Berkeley, said someday we may learn to use the sun itself as a gravitational-lens telescope, with a detector parked at its focal length of 500 astronomical units.
David L Chandler\\\
contrasting at http://www.subversiveelement.com/DulceSchneider.html
from linkhttp://www.newscientist.com/news/news.jsp?id=ns99996255&lpos=home3
Chances of aliens finding Earth disappearing
15:59 09 August 04
NewScientist.com news service
A pioneer of the search for extraterrestrial intelligence (SETI) has warned that for any intelligent aliens trying to search for us, "the Earth is going to disappear" very soon.
Frank Drake's point, made at a SETI workshop at Harvard University on Friday, is that television services are increasingly being delivered by technologies that do not leak radio frequencies into space.
But he added that in some ways the observation is good news for SETI, as it means that the failure of Earth-based observers to detect aliens so far may be less worrisome than it would otherwise seem.
Most SETI efforts have focused on detecting radio signals that might be emitted by intelligent beings on planets around nearby stars. For humans, such signals "are the strongest signs of our existence", Drake said, thanks to television.
Traditional television broadcast antennas put out one megawatt each, and this radio-wave bubble now extends about 50 light years out from the solar system.
Straight down
But that is changing fast, Drake says. More and more television is now delivered by cable, with no radio-frequency leakage to space, and by direct-broadcast satellites that put out just 20 watts per channel, all efficiently directed straight down the intended areas on the Earth's surface.
So from the point of view of being detected through such inadvertent broadcasts, the longevity of humanity's detectability may be just 100 years.
And longevity may be the most important figure in Drake's famous equation for estimating the number of detectable intelligent civilisations on other worlds. The best estimates show that all the other crucial factors nearly cancel out, so that the number of such civilisations in our Milky Way galaxy is roughly equal to their average longevity of detectability in years.
Laser beacon
Drake's insight has important implications for search strategies. It means that eavesdropping on unintended alien transmissions is unlikely to succeed and "argues for an emphasis on detecting beacons", i.e. signals intentionally sent our way.
Subscribe to New Scientist for more news and features
Related Stories
ET first contact 'within 20 years'
23 July 2004
SETI to target most tantalising radio transmissions
11 March 2003
Alien hunters remove trick of the light
25 May 2001
For more related stories
search the print edition Archive
Weblinks
SETI symposium, Planetary Society
Search for Extraterrestrial Intelligence Institute
Drake Equation
SETI, Harvard University
Some SETI strategies have already begun shifting toward that approach, including efforts to find optical beacons based on high-powered lasers deliberately aimed at nearby stars.
While optical communications across interstellar distances was initially thought impractical, military research has led to lasers sufficiently powerful to make such signalling much more efficient than any radio beacon.
Nuclear-powered lasers on the drawing boards could produce pulses that would outshine the sun by a factor of 10,000, said Harvard University physicist Paul Horowitz, who has already been searching for such pulses. He has designed a new telescope that will soon be dedicated full-time to that search.
And other innovative ideas keep coming along. Planet hunter Geoffrey Marcy of the University of California, Berkeley, said someday we may learn to use the sun itself as a gravitational-lens telescope, with a detector parked at its focal length of 500 astronomical units.
David L Chandler\\\
contrasting at http://www.subversiveelement.com/DulceSchneider.html
from linkhttp://www.newscientist.com/news/news.jsp?id=ns99996255&lpos=home3
