ET, phone鈥� each other? If aliens really are conversing, we are not picking up what they are saying. Now one researcher claims to have a way of tuning in to alien cellphone chatter.
On Earth, the signal used to send information via cellphones has evolved from a single carrier wave to a 鈥渟pread spectrum鈥� method of transmission. It鈥檚 more efficient, because chunks of information are essentially carried on multiple low-powered carrier waves, and more secure because the waves continually change frequency so the signal is harder to intercept.
It follows that an advanced alien civilisation would have made this change too, but the search for extraterrestrial life (SETI) is not listening for such signals, says Claudio Maccone, co-chair of the SETI Permanent Study Group based in Paris, France.
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An algorithm known as the Fast Fourier Transform (FFT) is the method of choice for extracting an alien signal from cosmic background noise. However, the technique cannot extract a spread spectrum signal. Maccone argues that SETI should use an algorithm known as the Karhunen-Lo猫ve Transform (KLT), which could find a buried conversation with a signal-to-noise ratio 1000 times lower than the FFT.
A few people have been 鈥減reaching the KLT鈥� since the early 1980s but until now it has been impractical as it involves computing millions of simultaneous equations, something even today鈥檚 supercomputers would struggle with. At a recent meeting in Paris called Searching for Life Signatures, Maccone presented a mathematical method to get around this burden and suggested that the KLT should be programmed into computers at the new Low Frequency Array telescope in the Netherlands and the Square Kilometre Array telescope, due for completion in 2012.
Seth Shostak at the SETI Institute in California agrees that the KLT might be the way to go but thinks we shouldn鈥檛 abandon existing efforts yet. 鈥淚t is likely that for their own conversation they use a spread-spectrum method but it is not terribly crazy to assume that to get our attention they might use a 鈥榩ing鈥� signal that has a lot of energy in a narrow band 鈥� the kind of thing the FFT could find.鈥�
鈥淚t is likely that aliens use the same spread-spectrum method of transmission as us on their cellphones鈥�
