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The Manga Guide to the Universe by Verte Corp., Kiyoshi Kawabata, Kenji Ishikawa

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Do Aliens Exist? 181
Here is the equation:
To use this equation, we must decide the values of its various parameters (variables).
However, this is very difficult to do, since many of these factors are not known. Therefore,
if we enter the numbers that Drake used in 1961, N is considerably greater than 1. In other
words, he concluded that there were many highly advanced (at least having communication
technology) extraterrestrial civilizations in the galaxy.
Although this equation may seem like a parlor trick, many scholars, including Carl
Sagan (1934–1996), have generally approved of Drake’s idea and assume there is an
intriguing probability that extraterrestrials can communicate with us. (However, the various
values of N obtained by the calculation range from 10 to 1,000,000.) Despite these flaws
and the variations that can be generated by using differing starting parameters, aliens may
be closer than we think.
Extraterrestrial Life and a World-Renowned Physicist
Since there are somewhere between 200 billion and 400 billion planetary systems like our
solar system in the galaxy, it would not seem unusual for there to be planets that have envi-
ronments similar to Earths, where life has developed. However, the Italian physicist Enrico
Fermi (1901–1954) directly challenged this optimistic prediction. Fermi was a Nobel Prize
winner in physics who worked on developing the first atomic reactor in the world.
One day in 1950, while eating lunch with his fellow scientists, Fermi got into a discus-
sion concerning the existence of aliens. The Drake equation was still 11 years from being
published, yet astronomers in those days were already confident that the existence of extra-
terrestrial civilizations was highly probable, and scholars in other fields, like Fermi, were also
interested in this topic.
Perhaps they had considered the possibility of extraterrestrial life from various param-
eters, as Drake did, but Fermi wanted to look into the idea further—and specifically, to think
about where aliens might exist.
Although it’s a simple question, it points directly to the heart of the matter.
N = R* × f
p
× n
e
× f
l
× f
i
× f
c
× L
N:
Number of extraterrestrial civilizations in our galaxy with which
communication might be possible
R*:
Average rate at which stars are formed in our galaxy per year
f
p
:
Fraction of those stars that have planets
n
e
:
Average number of planets on which life can potentially exist in
each star system with planets
f
l
:
Fraction of the above star systems where life actually occurs
f
i
:
Fraction of the above star systems where the life that occurs has
evolved to intelligent life
f
c
:
Fraction of those intelligent civilizations that develop interstellar
communication
L: Average length of time those civilizations perform interstellar
communication

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