Are We Alone?

3. HOW TO SEARCH FOR INTELLIGENT LIFE

The reader may seek to consign these speculations wholly to the domain of science-fiction. We submit rather, that the foregoing line of argument demonstrates that the presence of interstellar signals are entirely consistent with all we now know. . . . We therefore feel that a discriminating search for signals deserves a considerable effort. The probability of success is difficult to estimate; but if we never search the chance of success is zero.

— Giuseppe Cocconi and Philip Morrison, “Searching for Interstellar Communications,” the first formally argued rationale for SETI published in a scientific journal, Nature, vol. 184, no. 4690, pages 844-846, 19 September 1959

In 1959, Guiseppe Cocconi and Philip Morrison of Cornell University published a landmark article in the journal Nature entitled “Searching for Interstellar Communications”, which offered a realistic strategy for a search for extraterrestrial intelligence. Cocconi and Morrison’s paper, now considered a classic, contained the following lines:

“…near some star rather like the Sun there are civilizations with scientific interests and with technical possibilities much greater than those now available to us…”

“We shall assume that long ago they established a channel of communication that would one day become known to us, and that they look forward patiently to the answering signals from the Sun which would make known to them that a now society has entered the community of intelligence. What sort of a channel would it be?”

Cocconi and Morrison figured there would be one radio channel at a frequency of about 1420 MHz, the frequency of the hydrogen atom, the most abundant element in the Universe. This universal frequency should be known to all civilizations capable of communication across space, so Cocconi and Morrison suggested that the frequency band close to 1420 MHz should be searched.

cocconi-morrison-nature
Figure 3-1: Cocconi and Morrison’s classic paper published in Nature.

Cocconi and Morrison’s argument is still valid today. Additionally, they assumed:

  • Majority of other lifeforms would be based on the same chemistry as in the Earth where life is based on the chemistry of Carbon.
  • Water is a necessity ingredient for life.

Cocconi and Morrison’s work transformed a speculative curiosity into a scientific discipline. Scientists could now conduct a search for an alien civilization by making use of the strategy so brilliantly propounded by them. And indeed, the first radio search was conducted one year later in 1960 by the radio astronomer Frank D. Drake of the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia, using a single channel around that frequency.

Project Ozma, as it was called, focused on two stars about the same age as our Sun and about eleven light years (66 trillion miles) away from us: Tau Ceti in the constellation Cetus (the Whale) and Epsilon Eridani in the constellation Eridanus (the River).

Project Ozma’s 85-foot NRAO radio telescope was tuned to the 21-centimeter emission (1420 MHz) coming from cold hydrogen gas in interstellar space. A single 100 Hz channel receiver scanned 400 kHz of bandwidth for six hours a day, between April to July 1960. Drake’s team of astronomers looked for a repetitive series of uniformly patterned pulses that would indicate a message sent by intelligent beings or a series of prime numbers such as 1, 2, 3, 5 or 7. But none was detected (with the exception of an early false alarm which the team was able to eliminate as caused by a secret military experiment). The only sound that came from their equipment was random static.

Although Project Ozma did not find any alien civilizations, the pioneering steps it took almost fifty years ago, enabled SETI to become a feasible scientific objective. For years various radio telescopes around the world were commissioned to survey the sky, searching for something that might arrive from an alien civilization. For years they heard nothing except white noise…

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