For instance, how do the radio astronomers in Contact (the Jodie Foster movie based on Carl Sagan’s novel of the same name) infer the presence of extraterrestrial intelligence in the beeps and pauses they monitor from space? The researchers run signals through computers that are programmed to recognize many preset patterns. Signals that do not match any of the patterns pass through the “sieve” and are classified as random. After years of receiving apparently meaningless “random” signals, the researchers discover a pattern of beats and pauses that corresponds to the sequence of all the prime numbers between 2 and 101. (Prime numbers, of course, are those that are divisible only by themselves and by one.) When a sequence begins with 2 beats, then a pause, 3 beats, then a pause… and continues all the way to 101 beats, the researchers must infer the presence of an extraterrestrial intelligence.