AAWSAP DIRD, An Introduction to the Statistical Drake Equation, March 2010

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N = Number of ET Civilizations in Galaxy
Figure 4. Comparing the two probability density functions of the random variable N found:
1) At the end of Section 3.3. in a purely numeric way and without resorting to the CLT at all (thick curve) and
2) AnalyticaJly by using the CLT and the relevant lognormal approximation (thin curve).
PROBABILITY DENSITY FUNCTION OF Y=ln(N)
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0.1
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Independent variable Y = ln(N )
Figure 5. Comparing the two probability density functions of the random variable Y=ln(N) found:
I)
At the end of Section 3.3. in a purely numeric way and without resorting to the CL Tat all (thick curve) and
2)
Analytically by using the CL T and the relevant normal (Gaussian) approximation (thin Gaussian curve).
8. DISTANCE OF THE NEAREST
and in several web sites, the solution to this
EXTRA TERRESTRIAL CIVILIZATION
problem is reported with only slight differences in
AS A PROBABILITY DISTRIBUTION
the mathematical proofs among the various authors.
In the first of the coming two sections (section 7 .1 )
As an application of the Statistical Drake
we derive the expression for this "ET_Distance"
Equation developed in the previous sections of this
(as we like to denote it) in the classical, non­
paper, we now want to consider the problem of
probabilistic way: in other words, this is the
estimating the distance of the ExtraTerrestrial
classical, deterministic derivation. In the second
Civilization nearest to us in the Galaxy. In all
section
(7.2)
we
provide
the
probabilistic
Astrobiology textbooks (see, for instance, ref. [10))
derivation, arising from our Statistical Drake
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