Thursday, July 23, 2009

Signals and SETI@home

SETI@home is a distributed computing project scanning the sky for radio transmissions that bear traces of extra terrestrial intelligence. They define a "signal" as:

  • Spikes in power spectra
  • Gaussian rises and falls in transmission power
  • Triplets (three power spikes in a row)
  • Pulsing signals
Some of these are domain specific (Gaussian rises and falls are due to the telescope passing over a signal source), while others can be generalized. For example, triplets represent a kind of repetition. When you have two of something, there is ambiguity about whether it is chance or not. You can always fit a line to two data points. When there are three events, you can measure the similarity of the two intervals, and make at least three comparisons. Pulsing signals represent another kind of macroscopic repetition. There are really just two types of features: general (repetition), and domain specific (power spikes, Gaussian rises and falls).

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