as long as you use the common, accepted definition of the word "prove". Here's something I posted on the atheist forum a few months ago. I never flame-proofed it for this forum, but it certainly applies to this conversation:
Why do we keep saying "there's no evidence of God"...
...when, by any objective definition, there is strong evidence (one might even say "proof") that there is no god?
The universe behaves in certain ways, and science has verified this. For one thing, it is conservative. The physical laws that apply in one part of the universe apply in all other parts. There is no place, time or special state where physical laws of science break down or change in any fundamental way.
The universe is persistent. Things that are in a particular state tend to stay that way. It is a scientific fact that the sun is still shining, even though I cannot see it at the moment. The earth will not suddenly stop being round, and Nevada will certainly border California next year.
The universe is also observable. Every advance in science, whether large or small, has been driven by and based on observation. There has never, in the history of our existence, been any progress or discovery based on that which cannot be observed in some way.
Finally, the universe is regular. We can apply mathematical and logical rigor to our observations and make predictions. When our math or logic is correct, the predictions are correct. When our deductions are incorrect, the predictions are also incorrect. It is impossible to make incorrect predictions with correct math or logic, and any "correct" predictions based on incorrect math or logic have always been shown to be local anomalies that do not stand up to further investigations.
We know all these things. They have been proven to us over and over again. It is how we can deduce the workings of a doorknob or a light switch, as well as how we know that China exists even though we may not be there right now. None of these things are open to doubt or debate. This is simply how our world works.
And yet, we have a large part of our population that denies this reality on a daily basis. They posit the existence of one or more invisible beings who are exempt from the laws of physics, even the laws of math and logic. They recite as truth stories in which basic properties of matter and energy change in fundamental ways -- where established facts (yes, facts) of physics, chemistry and biology are starkly violated.
This is not simply belief in things for which there is no evidence. We ALL believe in such things. I believe that the Green Bay Packers will win another Superbowl. I believe my pets love me. And I believe that someday, someday, I will be able to wear that pair of jeans that has been in the back of my closet for five years. I cannot provide any evidence of these things, and you cannot prove me wrong (though you would have a fairly good case on the jeans thing). But at least we live in a world where football teams, dogs, parrots and people in better shape than I exist.
But GOD?? An all-powerful, all-knowing entity who created the entire universe through sheer force of will? Someone who can hear our thoughts, affect our reality and grant us eternal life after our material bodies have died? If we have even a basic understanding of the universe in which we live, it is simply not enough to say that we see no evidence of such a being. We see proof, every day, that our world does not behave in a way that would allow for God to exist. It is just not possible for a person or object to transcend universal physical laws. It is almost meaningless to suggest it.
So I propose that we atheists set aside our "no evidence" talking points. There IS evidence -- mountains of evidence -- and all of it proves that God cannot possibly exist. We can demonstrate this, undeniably, as easily as we can show that our sun does not have a chewy caramel center, or that electrons do not wear hats. Someone who believes otherwise is not just engaging in wishful thinking or indulging in fantasy. They are denying fundamental, observable facts that have been proven to be true over and over again.
So we can listen to their stories, and we can decide whether or not to challenge their beliefs. But we cannot say there is "no evidence either way" and continue to call ourselves "atheists". I'm not even sure we can say that and continue to call ourselves "rational".