Fermi Paradox/Drake Equation

Circa 1991


Question:  I am not sure whether this is physics or not but,
what is the Fermi Paradox? and what is the Drake
Equation.  I would be happy if anyone could give some
insight to this.
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I have not heard of, and cannot find any reference to, Fermi's paradox.
Can you give any more information (like where you heard or read of it)?
Drake's equation is named for the astronomer Frank Drake, who came up
with it in 1961.  It attempts to estimate the number N of currently extant
civilizations in our galaxy that would be able to contact each other.  I
will quote from p.  684 of the astronomy text "Exploration of the Universe"
by Abell, Morrison and Wolff.  They write the equation as
 N = (R_s)(f_p)(n_p)(f_b)(f_i)(f_c)(L_c)
"where R_s is the rate of star formation in the Galaxy, f_p is the fraction
of those stars with planetary systems, n_p is the mean number of planets
suitable for life per planetary system, f_b is the fraction of those plan-
ets suitable for life on which life actually developed, f_i is the fraction
of those planets with life on which intelligent organisms have evolved, f_c
is the fraction of those intelligent species that have developed communica-
tative civilizations, and L_c is the mean lifetime of those civilizations.
The first three factors are essentially astronomical in nature, the next
two are biological, and the last two are sociological.  We are able to make
some educated estimates regarding the astronomical factors, we may be on
shaky ground with the biological ones, and we are almost playing numbers
games in trying to estimate values for the last two." All 3 of the texts I
use for reference discuss this topic, so more info should be easy to find.

rcwinther 
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A fellow Newtonian, rgstrickert, was kind enough to fill me in on the
Fermi's Paradox question via Newton mail.  I will quote from his note:
I think Fermi's Paradox refers to a quote attributed to Enrico Fermi
concerning the question of extraterrestrials.  I have seen the quote in
more than one source, but I have found it on page 578 of *The Anthropic
Cosmological Principle* by John D.  Barrow & Frank J.  Tipler -
 " If they existed, they would be here."
I never met Enrico Fermi, but from what others have told me about him
when I was a student at the University of Chicago, it sounds as if the
quote is just how Fermi would sum up the whole ET issue.

rcwinther  
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