I’ve been following the search for extra-solar planets, and intelligent life, and apparently:
Traub estimated the frequency of terrestrial, habitable-zone planets around Sun-like (Classes F, G and K) stars at (34 ± 14) %.
F, G, and K class stars make up 22.7% of all stars, so 4.54% of all stars at lowest, 10.896% at highest have at least one terrestrial, habitable zone planet, but that’s not anywhere near the end of this game, as I hope to demonstrate.
I think a basic requirement to even attempt interstellar travel is very advanced, widely accepted philosophy. One cannot travel among the stars if one does not understand how to live one’s own life. Just the expenditure of energy involved, the necessary reliability of the engineering involved is mind numbing! Just to be able to have radio to transmit or receive anything, so many hurtles, in planet formation, in direction of evolution, in philosophy, in economics, in discovery, is amazing. To say the least, there is a great deal of opportunities for intelligence (or civilization!) to never develop. Consider that even though earth is around a stable star, and in a decent orbit, with plenty of water, humanity has only been around for 0.00419% (190k/4.5 billion) of that time, and we have been transmitting radio (weakly for most of this) for 0.0000022% (100/ 4.5 billion years) of that time, let alone being able to receive an interstellar radio signal. It may very well be that even if life is around on any of these habitable planets, and even if conditions are ideal for life to evolve intelligence, we’ll have to wait far too long to co-exist with any alien civilizations to have a conversation, much less visit each other. Add to all this the fact that civilization is not irreversible once achieved and that space is just really, really, huge. Intelligent life may be out there, but the odds of superior intelligences existing, knowing about us, maintaining complete electromagnetic spectrum silence even before they discovered us, and observing us without being detected, and deciding to not contact us (Why not? What could we possibly do to hurt such masters of the universe? We can’t even leave our own planet for long!) is complete madness. You might as well believe in god.
I wouldn’t assume a more advanced civilization would destroy a lesser civilization upon discovering one. That only happened in the New World because the Indians never discovered reason and philosophy, and, hell, for that matter, their whole civilization was a house of cards built on ritual human sacrifice! (In one word, context!) Does anyone really think that after traveling for hundreds of years, manipulating vast amounts of energy just to goddamned get here, and raw material in the galaxy being virtually limitless (thus aliens wanting to mine the earth for resources complete nonsense, never mind the idea of transporting resources), that an advanced alien civilization would exterminate us? What in the hell would be the point? It would be like using a hydrogen bomb (and all the respect for reason to make one in the first place) to kill a mosquito!
(edit, spell check. should have done that before posting the first time…)