Many people who are into science (as I certainly am) are atheistic or leaning toward the atheist side of agnostic. In general, this is reasonable - the default scientific positioin "X does not exist" is both testable and falsifiable, and thus it brings the exploration of X within the bounds of science. The converse proposition "X does exist - even though X has not been observed" is testable, but not really falsifiable. Think of X as one of {Loch Ness Monster, Channeling, Bigfoot, telekinesis, alien abduction, Atlantis...} - it is possible that all of these exist, but why presuppose their existence in absence of data? If you do - do you also presuppose the existence of that intelligent tribe of pink elephants that lives on the far side of the Moon? You know - the one the guvmint has been covering up for decades. If not, why not? It has as much supporting data as telekinesis.

Anyway...

There's certainly no direct evidence for the existence or non-existence of a God (which is why it's a fun topic to debate), but despite the above, I have 2 good (to me) reasons why I am a theist:

1) The fundamental constants that define our universe are exquisitely balanced: Change any of them by a tiny amount and we wouldn't be here (Stars wouldn't form, etc.). Now, I know we only *could* be here to wonder about it if they were balanced... but still, it is suspicious. Check the link - it's a very thoughtful discussion of this point. The primary other hypothesis is the Multiverse - many universes exist (with many different definitions of the fundamental constants), and we're just one of them. I've always disliked this explanation - rather than invoke a designer, we invoke a large number of other universes - none of which have any data to support their existance.

2) The number Pi. It is everywhere in Math and Physics. Yes, it is the ratio of circumference to diameter for a circle - but it crops up in so many other places where it has no right to - frequency of prime numbers, converging infinite series, integrals... there's entire webpages devoted to the topic. Check out my "Pi and the Mandelbrot Set" page in my math section of my
homepage for another strange one. I like to think of it as a signature - "Made By God".

I think when I'm studying mathematics or science, I'm studying the mind of God.