My friend Caleb writes with a fun question:
I saw this article a few weeks ago where the Vatican said it was OK to believe in aliens and God. I know you have mentioned the book Rare Earth, which suggests that Earth may be the only planet capable of supporting life, but what do you think personally on this subject? Do you think that there is the possibility of life on other planets, or do you think Earth is the only planet with life? Or, is it impossible to know for sure? I look forward to hearing your thoughts on this.
Here's part of my reply to him with one or two thoughts tacked on:
I agree with the Vatican, Caleb, that it's perfectly okay to keep an open mind on the possibility of extra-terrestrial life (ETL). Such a phenomenon, if it existed, would have no bearing on the existence of God. Everything that exists in the cosmos is a product of God's creative effort and there's really no theological reason to think that we are the only life forms He has chosen to create.
Indeed, it seems to me that although most people might think that the discovery of ETL would be a blow to theism, I think it would be just the opposite. If there is no Creator then the origin of life is so astronomically improbable as to be quite miraculous. No one knows how it could have happened given that chance and physical law are the only factors operating in the universe. The sheer improbability of abiogenesis occurring through purely naturalistic means suggests to me, then, that if there's sentient life elsewhere it's more probable, not less, that there's an intelligence guiding its origin and development.
Having said that I think that there are scientific reasons to be skeptical of ETL. You mentioned the "Rare Earth" problem which for me is the biggest barrier to ETL.
For instance, only a fraction of the 300 billion galaxies in the universe are suitable for higher life, and of that fraction, only a portion of their stars are capable of sustaining life. Of those stars only a fraction would possess the appropriate satellites, and of those that do have planets, there are so many (hundreds) highly improbable physical conditions that the planet would have to meet in order to provide a haven for higher life forms that the odds are not in ETL's favor. See here for some of the qualifications any life sustaining planet would have to have.
To me, then, it seems most reasonable, scientifically speaking, to assume that intelligent life probably exists nowhere else but here.
RLC
