The International Journal of Astrobiology (1/23/2009) recently featured a new theoretical study by a University of Edinburgh scientist — Duncan Forgan — suggesting there are at least 361 advanced civilizations in our Galaxy now. As expected, Forgan’s model is highly assumption-dependent but does use observed statistics from 242 known extrasolar planets.

Are Earth-like planets and advanced civilizations rare in our Galaxy? Click .

Although no reliable evidence for extraterrestrial signals has been identified in the nearly 50 year history of the search for extraterrestrial intelligence (SETI) — including the first observational study by Frank Drake in 1960 — Forgan’s paper provides theoretical targets for researchers.

Given the onset of the next Maslow Window near 2015, it is likely that increased interest in SETI will occur, as it did at the beginning of the Apollo Maslow Window in 1960. The two fundamental drivers of the human expansion into the cosmos — for both the public and NASA — are the discovery and exploration of Earth-like worlds and the search for extraterrestrial life.

Forgan uses a Monte Carlo technique to generate a mathematical galaxy with similarities to our real one. His goal is to expand on the average values previously used in the Drake Equation (to estimate N, the number of advanced civilizations in our Galaxy now) and in the Fermi Paradox (which tries to explain the apparent absence of ETs on Earth). Forgan notes that previous estimates of N range from <<1 to 1 million. His estimate of 361 is based on the Rare Earth scenario of Ward and Brownlee, although other more Sagan-like assumptions lead to estimates of nearly 38,000 cvilizations.

Forgan recognizes that biological parameters are “pure conjecture” and his model is only preliminary, “It’s a process of quantifying our ignorance.” Others agree. For example, Ward and Brownlee expand on the traditional Drake Equation by adding factors that include selection effects like planets with a large moon (for climate stability) and systems with outer Jupiter-like planets (for comet security). They note that “many of these terms are known in only the sketchiest detail,” and that “Earth indeed may be extraordinarily rare.”

Nuclear physicist and UFO researcher Stanton Friedman thinks N is large, “probably in the many billions in our galaxy alone.” Although he agrees that many Drake Equation parameters are poorly known, his traditional objection is that it doesn’t include interstellar travel, which would increase N by reducing cosmic threats to civilizations. And in Earth’s history, “migration and colonization have been the major means of establishing communities.”

One of the scientific architects of the concept of a galactic habitable zone, astronomer Guillermo Gonzales thinks Ward and Brownlee are on the right track, but don’t go far enough. He presents a restructured Drake Equation with a total of 21 factors designed to minimize overlap. His value for N is 0.01, which “is an interesting result, of course, since we exist.”

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