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

Text

This text came with the file. It may have mistakes. When the text and the image disagree, the image is right.

0
l \ ' "-­ ~
UNCLASSIFIED/ /FOR OFFIEiIAk Wlii QPU,¥
Average DIST A CE of the nearest ET civilization vs. the ASSUMED NUMBffi of ET civilizations in the Gah
Cl)
0:::
<(
UJ
>­!­
:I:
:i
.!::
!'.l
g
~
!'l=
200
175
150
125
100
750
500
25 0
0
0
I 00000
200000
300000
400000
500000
600000
700000
800000
900000
I 000000
ASS MED NUMBER of civiliz ations in the Galaxy (that is, Nin the Drake equation)
Figure 1. DISTANCE LAW; i.e., the Average Distance (plot along the ver-1:ical axis in light years) Versus
the NUMBER of Communicating Civilizations ASSUMED to Exist in the Galaxy Right Now
3. Computing N By Virtue of the Drake Equation (1961)
In the previous section, the problem of finding how close the nearest ET civilization may
be was "solved" by reducing it to the computation of N, the total number of
extraterrestrial civilizations now existing in this galaxy. In this section the famous
Drake equation is described, that was proposed back in 1961 by Frank Donald Drake
(born 1930) to estimate the numerical value of N. We believe that no better
introductory description of the Drake equations exists other than the one given by Carl
Sagan in his 1983 book "Cosmos" (ref. [2]), in its turn based on the famous TV series
"Cosmos." So, in this paragraph we report Carl Sagan's description of the Drake
equation unabridged.
"But is there anyone out there to talk to? With a third or a half a trillion stars in our
Milky Way galaxy alone, could ours be the only one accompanied by an inhabited
planet? How much more likely it is that technical civilizations are a cosmic
commonplace, that the galaxy is pulsing and humming with advanced societies, and,
therefore, that the nearest such culture is not so very far away - perhaps transmitting
from antennas established on a planet of a naked-eye star just next door. Perhaps
when we look up at the sky at night, near one of those faint pinpoints of light is a world
on which someone quite different from us is then glancing id ly at a star we call the Sun
and entertaining, for just a moment, an outrageous speculation.
UNCLASSIFIED//FOR OFFIEiIAk Wlii QPllsV
7