entropy and its implications on "design"

Agreed -- he is prone to a great deal of speculation on the nature of "consciousness" etc. but I suppose I can allow him that luxury in his later years, given that he has been one of the most influential relativists of all time. In any case, the cosmological arguments he presents are certainly very relevant and depend only upon the most general principles -- any thoughtful person can follow the logic and see the heart of the problem without much trouble.

[benkahuna]

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How likely it is that life has arisen somewhere else seems impossible to answer to me.

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You don't need to answer it because Drake already did.


Description

The Drake Equation was developed by Frank Drake in 1961 as a way to focus on the factors which determine how many intelligent, communicating civilizations there are in our galaxy. The Drake Equation is:
N = N* fp ne fl fi fc fL

The equation can really be looked at as a number of questions:

N* represents the number of stars in the Milky Way Galaxy

Question: How many stars are in the Milky Way Galaxy?
Answer: Current estimates are 100 billion.

fp is the fraction of stars that have planets around them

Question: What percentage of stars have planetary systems?
Answer: Current estimates range from 20% to 50%.

ne is the number of planets per star that are capable of sustaining life

Question: For each star that does have a planetary system, how many planets are capable of sustaining life?
Answer: Current estimates range from 1 to 5.

fl is the fraction of planets in ne where life evolves

Question: On what percentage of the planets that are capable of sustaining life does life actually evolve?
Answer: Current estimates range from 100% (where life can evolve it will) down to close to 0%.

fi is the fraction of fl where intelligent life evolves

Question: On the planets where life does evolve, what percentage evolves intelligent life?
Answer: Estimates range from 100% (intelligence is such a survival advantage that it will certainly evolve) down to near 0%.

fc is the fraction of fi that communicate

Question: What percentage of intelligent races have the means and the desire to communicate?
Answer: 10% to 20%

fL is fraction of the planet's life during which the communicating civilizations live

Question: For each civilization that does communicate, for what fraction of the planet's life does the civilization survive?
Answer: This is the toughest of the questions. If we take Earth as an example, the expected lifetime of our Sun and the Earth is roughly 10 billion years. So far we've been communicating with radio waves for less than 100 years. How long will our civilization survive? Will we destroy ourselves in a few years like some predict or will we overcome our problems and survive for millennia? If we were destroyed tomorrow the answer to this question would be 1/100,000,000th. If we survive for 10,000 years the answer will be 1/1,000,000th.

When all of these variables are multiplied together when come up with:

N, the number of communicating civilizations in the galaxy.

The real value of the Drake Equation is not in the answer itself, but the questions that are prompted when attempting to come up with an answer. Obviously there is a tremendous amount of guess work involved when filling in the variables. As we learn more from astronomy, biology, and other sciences, we'll be able to better estimate the answers to the above questions.

I guess this is what I meant by impossible to answer, at least for the forseeable future. Questions like "What is the probability that intelligence develops on a planet where life evolves?" require such an enormous amount of observation to answer that the whole thing rapidly degenerates into pseudoscience.

Another interesting argument is the Fermi paradox. It turns out that the time scale for colonization of the galaxy (given any reasonable assumptions) is tiny compared to the time scale for evolution of intelligent life. Thus, if even one intelligent species was interested in colonizing the galaxy, it would almost certainly have been done by the time we evolved. Yet the galaxy (and in particular, our solar system) seems completely un-colonized. The conclusion is that intelligent life is much more rare (improbable) than popular opinion would suggest.