Drake's Equation

Old post.

==========

From: eric kline )
Subject: Drake's Equation
Newsgroups: sci.astro
Date: 1997/04/19

Christopher Michael Jones wrote:


*snip*


I disagree. Yes, it is true that we have only one data point that
corresponds to a planet with life (Earth, although the evidence for
Mars is looking better everyday), however this is not the only
data in the equation.

There is life on Earth. I think we can all agree on that. What other
data are you talking about? Drake's equation is based on a long string
of variables all of which are either unknown or extremely uncertain. It
would be irresponsible to try to draw a conclusion from Drake's equation
given the level of inherent uncertainty.

Just for reference, let's remember the Drake
equation.

N=R*fs*fp*ne*fl*fi*fc*L

R is the rate of formation of stars in stars per year.
fs is the fraction of stars that are suitable for supporting life.
fp is the fraction of stars that have planets.
ne is the average number of habitable planets in a solar system
fl is the fraction of habitable planets that develop life (or the
probablity that a habitable planet will develop life).
fi is the fraction of planets with life that will develop intelligent
life (or the probablility that inhabited planets will develop
intelligent life).
fc is the fraction of intelligent life forms that will develop radio
technology (or the probabilit...).
L is the average lifetime that the society of intelligent radio capable
life forms will use radio (on the average of course).

And, of course, N is the number of radio capable societies (in our galaxy
if you use numbers for our galaxy, in terms of star formation etc.). This
is important since we will probably not be able to reach other civilizations
by radio that our outside the Milky Way (or actually, they will reach us,
since we will be recieving). mOf course, small modifications to the
Drake equation can allow one to determine other kinds of information,
like the number of planets supporting life of any kind, or the number
of planets in the entire universe with life, etc.

To do so, you'd be making assumptions which are meaningless because
there is not enough data to justify any of them.


Now, certainly a great deal of these numbers can be estimated currently
from the one data point of life, Earth.

*snip*

And that's the fallacy of your argument. You haven't got enough data to
refine your estimates of the variables in Drake's equation. You can't
even do a statistical analysis: you have 1 datum out of 100 billion.
I'm willing to concede some knowledge of what the value of R might be,
but all the other variables in Drake's equation range from 0-1 (L has
lower bound but is otherwise completely unknown) and there simple isn't
enough data to refine what their values might be. If it turns out that
life did/does exist on Mars and/or Europa then you can start to reduce
the uncertainty in ne and fl, but those variables will still be unknown
(maybe you can reduce their range to 0.1-0.9). Most of the variables
are unknown and trying to draw a concrete conclusion from an equation
whose variables are either unknown or extremely uncertain is
meaningless.

Eric

--

http://www.isc.tamu.edu/~kline/

Old post.

==========

From: eric kline )
Subject: Drake's Equation
Newsgroups: sci.astro
Date: 1997/04/19

Christopher Michael Jones wrote:


*snip*


I disagree. Yes, it is true that we have only one data point that
corresponds to a planet with life (Earth, although the evidence for
Mars is looking better everyday), however this is not the only
data in the equation.

There is life on Earth. I think we can all agree on that. What other
data are you talking about? Drake's equation is based on a long string
of variables all of which are either unknown or extremely uncertain. It
would be irresponsible to try to draw a conclusion from Drake's equation
given the level of inherent uncertainty.

Just for reference, let's remember the Drake
equation.

N=R*fs*fp*ne*fl*fi*fc*L

R is the rate of formation of stars in stars per year.
fs is the fraction of stars that are suitable for supporting life.
fp is the fraction of stars that have planets.
ne is the average number of habitable planets in a solar system
fl is the fraction of habitable planets that develop life (or the
probablity that a habitable planet will develop life).
fi is the fraction of planets with life that will develop intelligent
life (or the probablility that inhabited planets will develop
intelligent life).
fc is the fraction of intelligent life forms that will develop radio
technology (or the probabilit...).
L is the average lifetime that the society of intelligent radio capable
life forms will use radio (on the average of course).

And, of course, N is the number of radio capable societies (in our galaxy
if you use numbers for our galaxy, in terms of star formation etc.). This
is important since we will probably not be able to reach other civilizations
by radio that our outside the Milky Way (or actually, they will reach us,
since we will be recieving). mOf course, small modifications to the
Drake equation can allow one to determine other kinds of information,
like the number of planets supporting life of any kind, or the number
of planets in the entire universe with life, etc.

To do so, you'd be making assumptions which are meaningless because
there is not enough data to justify any of them.


Now, certainly a great deal of these numbers can be estimated currently
from the one data point of life, Earth.

*snip*

And that's the fallacy of your argument. You haven't got enough data to
refine your estimates of the variables in Drake's equation. You can't
even do a statistical analysis: you have 1 datum out of 100 billion.
I'm willing to concede some knowledge of what the value of R might be,
but all the other variables in Drake's equation range from 0-1 (L has
lower bound but is otherwise completely unknown) and there simple isn't
enough data to refine what their values might be. If it turns out that
life did/does exist on Mars and/or Europa then you can start to reduce
the uncertainty in ne and fl, but those variables will still be unknown
(maybe you can reduce their range to 0.1-0.9). Most of the variables
are unknown and trying to draw a concrete conclusion from an equation
whose variables are either unknown or extremely uncertain is
meaningless.

Eric

--

http://www.isc.tamu.edu/~kline/