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Date: Tue, 15 Dec 1998 19:57:32 -0800
From: "Alfred A. Aburto Jr." <aburto@cts.com>
Reply-To: aburto@cts.com
Organization: Calco, Inc.
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To: seti@sni.net
CC: aburto@cts.com, jreese@aharinc.com
Subject: Probability of other ET Life is 1
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An interesting book to read is:
"Probability 1, Why There Must Be Intelligent Life in the
Universe", by Amir D. Aczel, Harcourt Brace & Company, 1998,
ISBN 0-15-100376-9.
In the book Aczel writes that the probability (P) that there
is life around at least one other star in the Galaxy or
Universe is given by:
P = 1 - (1-P0)^N, where P0 is the probability of life existing
around any given star, and N is the number
of stars (in our Galaxy N is approximately
3.0E+11, or in the observable Universe N
is approximately 3.0E+22)...
First of all, we know that P0 is not zero, because life
already exists on Earth.
Second we really have miniscule knowledge of the actual value
of P0. Aczel attempts to use the Drake Equation in determining
P0 but in the final analysis he winds up assuming P0 is
"extremely" small with a value of P0 = 5.0E-14. In this case,
with N = 3.0E+22 as the number of stars in the Universe, P is
so close to 1 that we might as well say P is 1! So, if this
value of P0 is accurate, then, yes (!), there must be other
life in the Universe! This is a pretty profound conclusion!
With P0 very small compared to one, we can write approximately
that P = N * P0 provided N*P0 <= 1. If N*P0 > 1 then we'll take
P = 1 (as a first order approximation).
The problem with Aczel's analysis is that we really don't know
the value of P0. It will take many, many years of research and
effort to determine P0 (the probability of life existing around
any given star).
We can determine limits on P0 though as shown in the table below.
The results show that, in our Galaxy alone, P > 0.9 if P0 > 3.0E-12.
If we consider the number of stars in the Universe then P > 0.9 if
P0 > 3.0E-23.
Or, put in other words, there can be little hope of finding life in
our Galaxy if P0 < 1.0E-13. And there can be little hope of finding
other life in the Universe if P0 < 1.0E-24.
Well, in any event, it seems important to attempt to determine what
exactly is the probability of finding life around any given star.
It can be done empirically of course, but it may well take many, many
years of time and effort to do it...
P0 P P
(Galaxy) (Universe)
N=3.0E+11 N=3.0E+22
1.0E-00 1 1
1.0E-09 1 1
1.0E-10 1 1
1.0E-11 1 1
3.3E-12 0.99 1
3.0E-12 0.9 1
2.0E-12 0.6 1
1.0E-12 0.3 1
1.0E-13 0.03 1
1.0E-14 0.00 1
1.0E-16 0.00 1
1.0E-18 0.00 1
1.0E-20 0.00 1
1.0E-21 0.00 1
1.0E-22 0.00 1
3.3E-23 0.00 0.99
3.0E-23 0.00 0.9
2.0E-23 0.00 0.6
1.0E-23 0.00 0.3
1.0E-24 0.00 0.03
------------------------------
Al Aburto Jr.
aburto@cts.com
15 Dec 1998
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