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Thinker
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« Reply #2 on: July 26, 2004, 01:31:48 AM » |
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My take would be that this guy is wildly optomistic on the number of ET civilizations out there.
A lot of it depends on what assumptions you plug into the Drake Equation - and it is worth keeping in mind that some aspects of the Drake Equation are a tad dated. I have seen Drake Equation results predicting something on the order of 1 civilization/race per galaxy, and others, like this one predicting as many as a million.
About six months ago, I made a sort of thumbnail calculation on this forum, based on the best astronomical data I could dig up, much of it from the leading researchers looking into extra-solar planets. I came up with something on the order of two million earthlike worlds in the `galactic habitable zone' a sort of `ring' superimposed on the galaxy. Stars closer in than this get way to much radiation; stars further out are likely to have severe metallicity problems, greatly reducing the likelyhood of them having planets. Now, granted, my calculation was a tad conservative - but even with the more optomistic version, I still came up with less than ten million `earths' out there.
As to sapient races on those worlds...I would say that at any given time, there is probably something on the order of a few dozen to a few hundred sapient races on them.
Just because a planet is `habitable' does not mean it has complex lifeforms. Earth has been `habitable' for around 900 million years, yet complex life didn't enter the picture until around 500 million years ago, give or take.
Nor does `sapient race' automatically translate into `technological civilization', or even the ability for a race to develop a technological civilization. H. Sapiens has been around for several tens of millenia, yet `civilization' is only a few thousand years old here.
Nor is it an automatic assumption that a technological civilization would have a communication technology we could intercept, or even a great interest in worlds beyond their own.
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