i pose it as this. the chance for life as we know it to exist can be broken down like this (note these are estimates off the top of my head that I'm using to prove a point). the chances of a planet being in the right proximity and stable orbit of a star, made of a solid composition, able to support a stable atmosphere, and posses the necessary resources to sustain any life is like 1 to 1,000,000,000 (probably much more) and that does not even guaranty the existence of life. as i understand what the current popular theory it was a set of pure accidents in chemical composition of materials on earth as well as atmospheric shifts. also taking into account that any number of things (meteors, collapsing stars, change in orbit, reactions in the atmosphere, if ANYTHING and i mean ANYTHING becomes unstable) can end all life that cannot immediately adapt to it. and yet despite all these odds i pose to you that the universe as i come to understand it is infinite (or at least REALLY (i feel that it truly deserves a capitol really) big and im talking of space not matter and we also assume theres only one big bang) and so there are probably an uncountable number of worlds with life. and that is just our definition of what life is. do i think life exist? undoubtedly. do i ever think we will find it? almost certainly not. even if we could travel the distances of space instantly we might never come across life or find it and not recognize it for what it is. ooh deep stuff.
