Re: From AAT to Wittgenstein? Skip it!

Gerrit Hanenburg (
Tue, 31 Oct 1995 00:26:53 GMT (H. M. Hubey) wrote:

>Not really. See "We Are Not Alone". If there's a planet like
>ours, a sun like ours, and the distance is in the same range, and
>a few billion years elapses, the conditions are there. And one can
>calculate a probability for this happening and hence a probability
>for life like ours existing somewhere in the universe. It was done
>in the 1950's, I think.

You mean the Drake Equation?

[N = R* x fp x ne x fl x fi x fc x L]

Talking about uncertain variables!


[N =] The number of communicative civilizations
The number of civilizations in the Milky Way Galaxy whose radio emissions
are detectable.

[R* =] The rate of formation of suitable stars
The rate of formation of stars with a large enough "habitable zone" and
long enough lifetime to be suitable for the development of intelligent

[fp =] The fraction of those stars with planets
The fraction of Sun-like stars with planets is currently unknown, but
evidence indicates that planetary systems may be common for stars like the

[ne =] The number of "earths" per planetary system
All stars have a habitable zone where a planet would be able to maintain a
temperature that would allow liquid water. A planet in the habitable zone
could have the basic conditions for life as we know it.

[fl =] The fraction of those planets where life develops
Although a planet orbits in the habitable zone of a suitable star, other
factors are necessary for life to arise. Thus, only a fraction of suitable
planets will actually develop life.

[fi =] The fraction life sites where intelligence develops
Life on Earth began over 3.5 billion years ago. Intelligence took a long
time to develop. On other life-bearing planets it may happen faster, it may
take longer, or it may not develop at all.

[fc =] The fraction of planets where technology develops
The fraction of planets with intelligent life that develop technological
civilizations, i.e., technology that releases detectable signs of their
existence into space.

[L =] The "Lifetime" of communicating civilizations
The length of time such civilizations release detectable signals into

>Unidirection idea pops up all the time. Entropy is the "arrow of
>time". Some things are not (and do not seem to be) reversible.

But in evolution they are.A species can evolve a pair of wings only to lose
them later,it can evolve eyes and lose 'em when they are no longer
needed.It can evolve a big brain and.......;-)
More and more I begin to realize how bad a choice the term "evolution" is
and how well chosen Darwins original expression "descent with modification"
Simple,and yet it says it all.Modification,nothing more nothing less.
Too bad it will all end in maximum entropy :-)
But then again,who cares.