I recently saw somebody respond to the challenge of how an Atheist can know there is no God.
And his response was "That's is a very good question. Why don't you explain to me the formula by which you know there is no Zeus, no Odin, no Ra, and I will use that to determine the nonexistence of the Christian God as well."
Atheists don't have the burden of proof, we just have a reasonable expectation that somebody trying to prove something extraordinary would have extraordinary evidence to support it.
