This is a common error that non-scientists make. They assume that to "prove" anything, a smoking gun is needed. So let's discuss smoking guns. There's a dead body in the living room, with an apparent gunshot wound. Is that evidence that a murderer exists? Not everybody would agree that it is, says Jan Ardena. Witnesses say they saw a murderer shoot the victim with a gun. Not everybody would agree that this proves there was a murderer, says Jan Ardena. A suspect is interviewed and confesses to the crime. Not everybody would agree that this proves the suspect was the murderer, says Jan Ardena. At the end of the day, if we think like Jan Ardena, no amount of evidence is sufficient to establish the existence of a murderer. Therefore, it is impossible for any detective who starts his investigation with an open mind to ever conclude that a murderer exists. No, what is needed is that we must assume there is a murderer, have faith there is a murderer. Without faith, there's no way to conclude there is a murderer. Real science doesn't often deal in smoking guns. The most important conclusions of science are based not on a single, conclusive piece of evidence, but on an accumulation of many pieces of evidence that all support the same conclusion. Jan wonders what an atheist would need to be convinced that God exists? Would toppling a mountain do the trick? Well, the least that can be said is that see a mountain topple due to no apparent physical cause would be remarkable. If the Atlantic Ocean (or the Red Sea) were to part like magic, that too would be an eye-opener for an atheist. People also levitating into heaven. An interesting additional datum. Sure, it's possible that a particularly pedantic and immovable individual might insist, like Jan, that none of these apparently miraculous events would be conclusive evidence of the supernatural, but any reasonable individual would have to conclude that something fishy was going on. After a while, the accumulation of things that look like ducks would suggest to a rational thinker that it's time to start taking the possibility of a flock of ducks seriously. There might be ways to arrange for mountains to topple through mundane means. What we know is that, as things stand, achieving that result is beyond the current capability of human beings. Therefore, if such an event were to be observed, even on its own, it would attract a lot of interest from atheists. Now, maybe it's God doing his magic, or maybe it's advanced aliens visiting Earth. Telling the difference might mean collecting more evidence, but even in the absence of such evidence an atheist scientist could draw up a short list of possible explanations, which would likely include the machinations of a capricious deity. As I've said before, though, evidence for God need not necessarily be anything as dramatic a toppling mountains. For example, if somebody could demonstrate the efficacy of prayer under scientifically controlled conditions, that would every likely point the atheists in the direction that theists desire them to go. One can think of many other examples of evidence that would add into the mix.