
The Drake
equation is used to estimate the number of
intelligent civilizations in our Milky Way. It
was developed by Frank Drake, a US
astrophysicist.
In November 1960, for the first time, scientists
from various disciplines met at Greenbank to
discuss the probability of extraterrestrial
intelligence and the search for it Frank Drake
was responsible for the scientific content and
conceivable topics.
For the conference Drake wrote some important
points of discussion and wondered in what
sequence the topics should be dealt with. All
agenda items had the same importance, but they
were not directly related. 
Drake assigned a
symbolic factor to every meeting point and drew the
individual factors into a simple multiplication formula
to determine the number of highly developed and
communicative civilizations, in the galaxy.
Frank Drake introduced this equation at the conference,
and it is also referred to as the Green Bank formula or
the SETI equation. (Frank Drake uses other indices
than defined in Definition 2.7.2)
9.1.1 Equation 
N = R · f_{p}
· n · f_{L}
· f_{i}
· f_{c}
· L 
R is the average star formation rate per
year in our galaxy. Depending on whether one is
looking at galaxies, star clusters or stellar nebulae,
the value for R varies between 4
and 19. The mean value is then 11.5.
f_{p} is the
probability for a star system with planets. Here the
value from the previous considerations is taken f_{p}
= F_{p} =
0.014,357 = 201:14,000.
n is the number of planets in the
habitable zone. Since probably only one planet in the
habitable zone produces a civilization, n
is set equal to one. The explanation is given below.
f_{L} is the
probability for planets to have lives. Again, the value
from the previous considerations is taken, thus f_{L}
= F_{L} = 0.111
= 1:9.
f_{i} is the
probability for planets with technological civilizations.
The Approach here is: f_{i}
= F_{i }· F_{z}
The value from the previous considerations (chapter 5.3)
for F_{i} is
taken, thus F_{i}
= 0.071,428 = 1:14
The value from the previous considerations (chapter 6.4)
for F_{z} is
also taken here, thus F_{z}
= 0.125,895 = 1:7943
The following applies:: f_{i}
= F_{i} · F_{z}
= 1:14 · 1:7943 = 1:111.203
f_{c} is the
probability of the desire for communication. This value
is set equal to 1. The explanation follows later.
L is the life span of a communicable
civilization. As defined in Axiom 7.2.1, the lifetime is
set to a minimum of 400,000 years.
N is the number of extraterrestrial
technological civilizations in the
galaxy.
The Drake equation can now be partly expressed as a
function of the parameters of the basic model:
9.1.2 Equation 
N = R · F_{p}·
n · F_{L}
· F_{iz}
· f_{c}
· L 
Applying the values, in the Drake equation 9.1.2,
provides:
N = (1,4519)_{ }· 201:14,000
· 1:· 1:9_{
}· 1:111.203_{
}· 1:· 400,000
N = 9  109 extraterrestrial technological
civilizations
Equivalent and thus comparable to the Drake equation, is
equation 8.4.5 from the General Basic Model, which
describes all technological civilizations in the galaxy,
on Earthlike planets. According to theorem 8.4.5, the
maximum number of star systems in the galaxy with
Earthlike planets in habitable zones that could support
technological civilizations is probably between 35 
1,034, and the Drake window is well located in the lower
part of the generalized basic model window.
This results in a correspondence of the Drake window with
the previous probability considerations from the basic
model (chapters 17) or the general basic model (chapter
8).
It can be concluded that the value in the basic model for
an Earthlike planet is closer to F_{e} = 0,01
