To contribute my 2c worth
Interestingly, I was just thinking about atheism and came up with this interesting idea, which I've posted on my blog, and thought for the atheists on this forum I would repost it here.
My proof for atheism (that is, demonstration of the non-existence of God) is by argument from agnosticism as follows:
We cannot know if the universe is the product of an intelligent mind or not (the agnostic hypothesis). This is because our minds, contained within our physical forms, cannot perceive beyond the limits of the universe in order to establish the existence of such an entity. The universe could, for example, be a virtual reality (a la the Matrix) or a lab experiment, or simply some super-being passing the time. Alternatively, it could simply be the result of a random combination of physical events that gave rise to what we now perceive as the universe.
So we could assume that for the existence of *any* form of creator-intelligence there is a probability of x, and for the non-existence of same there is a probability of y, where x and y are finite values between zero and one, and where x + y = 1 (there is/is not a creator-intelligence being all possible states).
So, there exists a finite and potentially measurable probability that the universe was created by *some* form of intelligence. But the moment you start *defining* the nature of said putative intelligence the odds become infinitely stacked against you. So if you say that the creator of the universe is called Yahweh and he sent his son in the form of Jesus to die for our sins, you've just defined one member of an infinite set of possible creator-intelligences that *could* exist. What if you're off by one letter and god's real name is Yalweh? Or Yarweh? Or... you get the idea.
Thus, regardless of the *actual* probability of *any* kind of creator-intelligence existing (be it 0.5 or 0.1 or any other finite and measurable probability), the moment you put limits on any putative creator-intelligence by defining it in any way, because there exist an infinite number of *possible* creator-intelligences, as well as an infinite number of ways the universe could have come into existence without any creator-intelligence being involved, you are by definition instantiating one of an infinite possible number of creator-intelligences (this is why so many different religions exist, and in fact there are an infinite number of possible religions, one for each possible defined creator-intelligence.) Note that Protestant, Catholic, Baptist etc churches are classed as different religions in this context, because although the gods they worship are all called Yahweh and Jesus, their *definitions* of those putative intelligences differ by biblical interpretation and denomination.
Unless you can perceive outside the universe (which we by nature cannot do) you cannot collapse this set to a defined quantum state by physical observation of the existence or non-existence of any said creator-intelligence - to "see the true face of god", as it were. The set of all possible creator-intelligences remains infinite unless we can thus perceive beyond the limits of the universe.
Consequently, the probability of existence of any *defined* creator-intelligence, being a finite member of an infinite set, must mathematically be zero, since any finite number divided by infinity is zero.
Therefore, the gods defined in the Bible, the Koran, the Vedas, the Talmud, or any other holy text that ever has been or ever will be written, do not exist. QED.