How Many Extra-Solar Civilizations?

star field

4 Civilizations: 2

The initial calculation can be understood better by adding an extra term that shows what happens over the course of time, and extending the average civilization lifetime to 10,000 years to allow the Existence of an Earth 2.0. Table 2 shows that the combination of factors in the equation before civilization lifetime is inserted can be associated with the period within which one civilization can be expected to appear.

Table 2: Explicit Drake Equation, Assumptions 2

Stars per Year        20
Planets per Star                         1
Planets per Year                                20
Fraction in Habitable Zone          0.2
Habitable Zone Planets per Year          4
Fraction with Life          0.5
Planets with Life per year          2
Fraction with civilization           0.0001
Planets with civilization per year  0.0002
Civilization Lifetime, years 10,000
Number of Civilizations           2

The assumptions have been modified by doubling the civilization lifetime to allow for the emergence of Earth 2.0.

In this second example, the civilization lifetime has been chosen deliberately to show the assumptions that lead to the conclusion that there are only two civilization present in the Galaxy at this time at this time. Given a population of 200 billion galaxies in the universe, this still implies many billions of active civilizations. However, as far as our own galaxy is concerned, the assumptions allow for many other civilizations in the past and in the future.

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