For the people who say that they don't believe in aliens, I'm genuinely curious as to why? It seems like every week now, astronomers are finding more and more potentially habitable planets, and that's just within a small portion of our galaxy, with the very first generation of space-based telescopes.
This wikipedia article says that in 2013, there were an estimated 40 billion Earth-sized potentially habitable worlds in our galaxy. That doesn't even include the other planets that are either too big or too small but still are within the habitable zones of their parent stars, plus, the articles referenced in that wiki are based on 5+ years old data. If there are that many potentially habitable planets in what's basically our cosmic front yard, can you even imagine how many there are in the estimated
2 trillion galaxies outside of our own? And keep in mind that that number is just an estimate based on what the Hubble has been able to see. For simplicity's sake, if we assume that all 2 trillion galaxies contain roughly the same number of Earth-sized worlds occupying the habitable zone of their stars, there's 8e+22 of them in the universe. That's 80 sextillion or 80,000,000,000,000,000,000,000! With that many potential "alternate Earths" out there, how can anyone think that this is the only planet in the entirety of existence that contains life?