Space Archaeology

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Review: ‘Searching for interstellar communications’, by Giuseppe Cocconi and Philip Morrison

[This post is the first in a series exploring major works in the field of space archaeology. The next will be more artefact-based, but it was important to begin with the origin of SETI itself.]

On 19 September 1959, the modern search for extraterrestrial intelligence was born with the publication in the prestigious journal Nature of an article by Giuseppe Cocconi and Philip Morrison of Cornell University. The piece, ‘Searching for interstellar communications,’ proposed a search of nearby sun-like stars for microwave radio signals on the 21-centimeter hydrogen line.

You can read the article online at the (paywalled) Nature archive, or for free here and here. It’s quite short, go read!

Welcome back! For such a brief article, there’s a lot to think about.

First of all, it’s remarkable to see the seeds of the Drake equation in the first paragraph. The factors of planet formation, origin of life, and the evolution and lifespan of technological civilisations are all mentioned, and it will only take a little unpacking by Frank Drake in 1961 to produce his famous formalism.

The second paragraph is interesting too – assuming that advanced technological civilisations will actively signal to stellar systems where they expect intelligence to emerge. It’s never said explicitly, but the surely the implication is that we ourselves should take on the role not just of responder but of signaller to potentially inhabited worlds?

Leaving aside that implication, we can see that Cocconi and Morrison envision a benign ‘community of intelligence,’ looking forward patiently to our call. Ronald Bracewell will, in 1975, dub this vision the ‘Galactic Club.’ Picture civilisations of geological age sharing scientific knowledge among themselves and waiting to greet new species as they emerge.

There seems to be no consideration by the authors of space travel. The only practical method of communicating over interstellar distances, they say, is electromagnetic.

The authors explain their reasoning that the 21-cm hydrogen line is the optimum place to conduct a search, make some speculations about the nature of the signal, and suggest some targets in the Solar neighbourhood. SETI in the electromagnetic spectrum has remained the mainstream of the program to this day.

They close with the immortal line: ‘The probability of success is difficult to estimate; but if we never search the chance of success is zero.’

The following year, in 1960, Frank Drake followed Cocconi and Morrison’s proposal in conducting the first search for extraterrestrial signals – Project Ozma – from the National Radio Astronomy Observatory at Green Bank, West Virginia.

1960 also saw the publication of two works inspired by Cocconi and Morrison’s seminal article. These would themselves spawn new fields of inquiry, or subfields: Ronald Bracewell’s May 1960 paper on probes and Freeman Dyson’s June 1960 paper on what would become known as Dyson spheres.

The early emergence of the search for circumsolar and interstellar extraterrestrial artefacts – so soon after the birth of SETI itself – is satisfying for those who defend what has been a fringe of the mainstream search program.

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