Using this principle, astronomers in Australia have surveyed 176 stars and stellar clusters for signs of lifeforms with a penchant for transmitting radio signals on a not-too-cryptic frequency.
They have used the 210ft (64m) Parkes Radio Telescope in New South Wales to listen for signals transmitted on what they consider to be one of the most likely frequencies.
The scientists chose the frequency of 4.462336275 gigahertz because it is a multiple of the natural oscillation frequency of hydrogen - the most abundant element in the universe - and pi, the ratio of the circumference of a circle to its diameter.
Professor David Blair, of the University of Western Australia, said anyone transmitting signals on this frequency would display signs of intelligence and would want the signals to be detected.
Knowledge of pi would be a signature of a civilisation and multiplying it with the natural frequency of hydrogen would give a clearly distinguishable signal of intelligent life, the researchers argue in the Monthly Notices of the Royal Astronomical Society.
But why would aliens want to make contact? 'The goal is to spread and acquire knowledge and possibly even to assist emerging civilisations during dangerous phases of possible self-destruction,' the researchers say. So far, however, they have failed to detect any signs of life.