Journal of Astrobiology & Outreach

Abstrait

We are not alone: Extraterrestrial Technological Life in our Galaxy

Strom RG

This paper is an evaluation of the number of technological civilizations presently in our Milky Way galaxy. The current estimate of the present number of Earth-like planets (± 25% of Earth’s radius) in the habitable region of Sunlike stars is about 6.6 billion. Using a modified Drake Equation, “optimistic”, “pessimistic” and “unlikely” estimates of six constraints indicate that about 40,000 technological civilizations are presently in our galaxy for a “pessimistic evaluation”. Even “unlikely” values that are half the “pessimistic” values give over 600 technological civilizations in the galaxy. It would take a completely unrealistic value of 2.5% for each constraint to get just 1 technology (us). “Therefore, we are almost surely not alone in our Milky Way galaxy”. Furthermore, almost all of the extra-solar system technologies are probably much further advanced than ours, i.e., they probably began thousands to millions of years before our Industrial Revolution. It is possible, but highly uncertain, that we have been visited by one or more of these civilizations.