According to Adam Frank and Woodruff Sullivan, both astronomy professors, there’s no way that Earth is the only planet to have developed intelligent life. Based on new research by NASA, which has certified the existence of thousands of other planets in other solar systems, there are simply too many planets out there for other intelligent species to not have evolved. All those stars you see, and the billions and billions more out there that are too far away to see past all the light pollution, have planets, and many have planets that could hose life as we know it.
Put simply, even if only 1 in 100 billion habitable planets hosted such life there would still have been over a trillion civilizations out there. The universe is 13 billion years old after all, and our solar system is much younger than that.
But those numbers are impotent because, of all the civilizations that must exist out there, most of them would be gone by now. In order for civilizations in older star systems to still exist, they would have to be far older than humanity, on the order of billions of years in some cases. Considering how unlikely it is, currently, for us to survive that long, if they’re anything like humans they aren’t still around. Of course, they don’t have to be just like us, do they? Why would then even be like us?
While it may take a while for us to find life on other planets, considering how big the haystack is, regardless of how many needles there are, it’s safe to say that intelligent life is out there, even if most of it has gone extinct. But just because humans are likely to kill ourselves with pollution or war, doesn’t mean that we’ll eradicate life on this planet. It will find a way, and maybe new intelligent species will evolve, and that is just as likely on other worlds as well.