Why I think there are ET's (1)
While on the one hand the thickly populated galaxies of Star Trek and Star Wars force us all to suspend our disbelief, part of me cannot help but feel that our own galaxy could be any other way. I'm not talking about fleets of starships or grand duels. I'm simply referring to the vast number of ET's spread throughout the stars. Consider this. Of all the galaxies catalogued, and all the billions of stars in each, and all the millions of planets orbiting these stars, it seems reasonable to suppose that a percentage of these planets are hospitable to extra-terrestrial life. Even if only 1% of all such planets supported ET life, we are still talking about a very large number.
What I am talking about is known as the Drake equation. Proposed by astronomer Francis Drake, N = R x f p x n e x f l x f i x f c x L , is a measure of the possibility of us Earthlings locating another communicating civilization, an ET civilization. N represents the number of civilizations in the galaxy based on a set of variables multiplied accordingly: the rate of galactic star formation (R); the number of these stars with solar systems (f p ); the number of 'earth-like' planets in these solar systems (n e ) ('class M' planets for those who watch too much Star Trek); the number of these 'earth-like' planets where life establishes itself (f l ); the number of these life-bearing planets where evolution produces intelligence (f i ); the number of these intelligent species which became civilizations capable of interstellar communication (f c ); and the average survival time of these civilizations (L).
Of course many of these variables are unknown, and even our civilization is just becoming capable of interstellar communication, however to frame the question of whether or not ET's exist in terms of the Drake equation makes it feel as though ET's must exist. The challenge is, of course, to find them (assuming some already haven't found us!).