"Probability of Christianity" is way too vague, so I can't answer that. I'm 50% confident in my philosophical (meta-ethical, decision theoretic, cosmological) theism, 92.5% confident in my phenomenal-belief-in-decisions-relevant-transhumanly-intelligent-entities. My confidence in atheism is some weird mixture of the inverse of those two because those two variants of theism strike me as pretty disjunctive, and either would falsify atheism. These are impression-belief mixtures: not entirely Aumann-adjusted, but a little. My impressions are more confident of theism, but my betting odds are less confident.
Retracted the above because I don't really like Bayes for this sort of thing. If we had better decision theory and game theory then I would have the tools to answer.
A friend recently asked how strongly I believe that my deconversion from Christianity was not a mistake. Here's my response, and for those of you who are not Christians, I'm just wondering what numbers you would give:
"There is a part of me that wants to say the chance is far less than 1 percent. But when I consider what 1% must mean about my ability to follow complex arguments and base my judgement on the right premises, it seems absurd to say that.
Trying to honestly estimate the chance that I'm wrong about the Bible being generally reliable is a fascinating exercise... I know the number is low, but I'm not sure how low.
Today I would give myself a 1 in 20 chance of being wrong. If I were to consider the arguments of 20 other groups similar to Christian theologians, I would probably misunderstand them at least 1 time in 20. After talking with 20 groups that have a very different worldview, I might think they are all are mistaken, but once in a while, maybe 5% of the time, it would actually be me.
Wow, 5%!?! If I convert that into "There is a 5% probability that the God of the Bible exists and will send me to hell", I feel scared. But I know how to cheer myself up: I just say, "No way, the chance I'll end up in hell MUST be less than 5%. After all, the God of the Bible is CLEARLY just a big, mean alpha-monkey and... [rehearse all the atheistic arguments here]".
This back-and-forth from certainty to uncertainty makes me feel like I'm doing something seriously wrong.
So what about you? What chance do you place on some variant of Christianity turning up to be true, and what chance do you think a god of some sort exists?"
Numbers please.