starlitveins asked: So, first let me say, I LOVEE the fact that you have a Doctor Who quote atop this ask box (well pretty much anyway). :'D Anyway, what I was going to say was, why do you believe that intelligent life is "very, very rare"?
As much as I love Carl Sagan, I find it a bit naïve to think the universe is teeming with complex intelligent life. There’s not much evidence to have an opinion one way or the other, but much like with the question of a god or gods, the burden of proof lies with the party of less evidence. I can’t prove that god doesn’t exist, I can’t prove that there aren’t tons of aliens out there, just like I can’t prove that you can’t fly. Thus it’s rational to believe that the reason there is no evidence apparent is because there is little or no evidence to find.
In 1950, Enrico Fermi posited a well known question: if intelligent life is very common in the galaxy, then why hasn’t evidence (probe, spacecraft, radio signals) been found? It’s a profound question and it raises a lot of good points in the debate. For instance, perhaps life is very rare or we are the first or only intelligent civilisation to arise in the Milky Way. The “Rare Earth hypothesis” takes this route, stating that life arose through a series of infinitesimally improbable events. This has quite a bit of validity, given that the only way we know how to make intelligent life is the exact way it happened, from the beginning of the universe until life first arose ~3 billion years ago.
Though it has every reason to be true, I think the Rare Earth hypothesis is a bit absolutist. In the (somewhat controversial, in the opinions of some) Miller–Urey experiments done at University of Chicago in the 1950s, the theorised conditions of the early earth were reproduced and amino acids — the building blocks of life! — were shown to form. When you understand the mechanics, it’s not that unbelievable that organic compounds can arise from conditions such as those on the early earth and from there it’s reasonable to predict that something similar could happen on other planets.
There’s just no easy answer. When that’s the case I tend to be skeptical, because I think empirical evidence is important.
