Ok, so you're somewhere talking to people about the Gospel and you've encountered an atheist. Or, perhaps you're noticing an atheist in a blog thread or on a forum of some kind.
And they are "struttin' their stuff", acting all intellectual about how God doesn't exist. They give out challenge after challenge and never seem happy with what you, or anyone else, may have to offer as "evidence" or "proof" to the contrary. What 'cha gonna do?
Well, you don't panic, that's for sure. There is no need to. First, remember that some people, regardless of how they challenge you, won't accept anything as a valid answer. It's a control issue.
However, it's not even about providing proof! Yes, you heard me right. I'm saying you don't have to prove anything! (Well, save that they don't know it all...)
Let's step away from this big ornery atheist bit for a second and rethink the issue. And maybe this will help you if and (more likely) when you find yourself with someone who proudly says "there is no God".
What would you think if I told you "there is no gold on Mars"? What if I told you "there is no gold in China" for that matter? Or how about if I told you "I want to move to Australia because I know there are absolutely no rats in Australia"?
Well, if you think this through much at all, you should notice a flag going up that says "Hey, you can't say that! How do you know that!". Why? Because claims like I have mentioned assume knowledge. And the bigger the claim, the more knowledge is presumed by the one who makes the claim.
So, I say "There is no gold on Mars! I know that. There is no proof that there is no gold on Mars." "Yes, there is", "No, there isn't", "Yes, there is!", "No, there isn't".
When you get in a position like this, just remember your pie!
Let me illustrate:
Let's say the pie below represents the sum total of all knowledge. Everything. How many molecules and atoms there are in the whole universe. How many hairs are on every head in the world, including the astronauts in space. Everything. No exceptions! That even includes knowing how many dust molecules are on the smallest particle that landed three years ago on a planet in the furthest galaxy from Earth! Wow. That's a whole lot of knowledge, isn't it? Sure!
And guess what? No one has it! So let's say that the pie represents the sum total of all knowledge and the blue slice represents what the atheist knows. Let's give him, what is it, a 16th of the whole knowledge pie? Wow, that is a lot! But that leaves a whole lot of stuff that is outside one's knowledge, doesn't it? Sure it does!
So, ask them "Do you possess the sum total of all knowledge?" If they are being honest at all, they will have to admit they don't know everything. The point is "Let's assume you only know 1/16th of everything there is to know. Do you think it is possible that in the remaining 15/16ths that there is the evidence you are looking for?" You are forcing them to admit that they, after all, do not know for sure that there is no God.
Now, does this always work? Of course not. Some are so set in their unbelief that nothing will move them save a sovereign act of God. But that is not your problem. All you are doing is planting a seed to help them understand that they cannot honestly say "there is no God" with certainty, any more than I can say that "there is no gold on Mars", although there probably is (we sent electronic gear there...and if it wasn't there before, there is now because gold is often used in electronics).
So, next time, don't fear those who put on the appearance of intellectualism by expressing their strident atheism. "Remember your pie" and watch them backslide to "agnosticism", which is a more accurate term, which means "I don't know".
From there, you can give them evidences and by God's grace, they will listen.