dipper@utastro.UUCP (Debbie Byrd) (09/07/85)
How likely is it that life exists elsewhere in the galaxy? We talk
about it -- after this.
September 7: The Green Bank Equation
There has been no direct evidence for life anywhere in the galaxy
except on our planet Earth. But scientists, like everyone else, are
interested in the question of extraterrestrial life. They explore the
question scientifically. . .
In 1961, a group of eleven scientists met in Green Bank, West
Virginia. Their meeting resulted in the famous Green Bank equation,
which estimates the likely number of extraterrestrial civilizations
that could communicate with us, if they chose to.
The Green Bank equation gives an idea of the kind of things you need to
consider, when exploring the question of other life in the galaxy. It
consists of the following variables:
-- The average rate of star formation in
the galaxy.
-- The fraction of stars that have planets.
-- The average number of planets around one
star with an environment favorable for life.
-- The fraction of suitable planets on which
life actually develops.
-- The fraction of life-bearing planets that
spawn beings with both intelligence and the ability to manipulate
tools.
-- The fraction of these planets that evolve
an advanced technical civilization.
-- And the average lifetime of such a civilization.
If we could fill in the correct numbers, we could determine how many
alien civilizations have the capacity for communication between the
stars. The problem is that we don't know the correct numbers. For
example, we don't even know what fraction of stars form planets. So,
depending on the estimates used in the Green Bank Equation, we might
predict that the number of civilizations able to communicate with Earth
will turn out to be between two-tenths -- and 20 billion.
Script by Deborah Byrd.
(c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin