This questions has recently been dealt with by both PZ Myers and Jerry Coyne - who are both atheists and biologists, and usually agree on most things, as far as I can discern. This time they don't, however. PZ argues that nothing would persuade him, and Coyne explains how he could be persuaded (two other bloggers I follow, Massimo Pigliucci and John Wilkins - both philosophers with a heavy interest in biology, and both atheists, even though Wilkins doesn't know it, have indicated that they side with PZ on this one).
First off, the question as stated doesn't completely make sense. In order to refute a concept/hypothesis, it must be adequately defined. And quite frankly, those people who say they will not be persuaded by any evidence whatsoever, are exactly the ones who seem to me not to own up to this problem. If I just say 'God', then one can always refute positive evidence for the concept by saying that something else could explain it, by pushing further back what 'God' means. For example, if we define 'God' as that which caused a particular person with leprosy to be healed, then evidence that this particular person with leprosy was healed would be evidence of 'God'. Stupid definition, of course, but the problem is that all the definitions are stupid, in this sense. Events purported to be explained by some God-concept can all be explained in other ways, too. And this is exactly the problem, and the reason that tree quarters of people surveyed (see above) will say that no evidence is sufficient to persuade them.
Since we are people of science - people who believe that belief should be based solely on evidence - it seems a pretty big problem that there is something we just would not ever accept as true NO MATTER WHAT THE EVIDENCE. It is, quite frankly, a totally untenable position that we cannot afford to take, especially given that we are asking everyone else to accept the evidence we have for evolution.
Coyne gives an example that I think is pretty good. Take it away, Jerry:
Suppose that you, P.Z., were present at the following events, and they were also witnessed by lots of other skeptical eyewitnesses and, importantly, documented on film: A bright light appears in the heavens and, supported by wingéd angels, a being clad in white robe and sandals descends onto the UMM quad from the sky, accompanied by a pack of apostles with the same names given in the Bible. Loud heavenly music is heard everywhere, with the blaring of trumps. The being, who describes himself as Jesus, puts his hand atop your head, P.Z., and suddenly your arms are turned into tentacles. As you flail about with your new appendages, Jesus asks, “Now do you believe in me?” Another touch on the head and the tentacles disappear and your arms return. Jesus and his pack then repair to the Mayo clinic and, also on film, heal a bunch of amputees (who remain permanently arméd and leggéd after Jesus’s departure). After a while Jesus and his minions, supported by angels, ascend back into the sky with another chorus of music. The heavens swiftly darken, there is thunder, and a single lightning bolt strikes P.Z.’s front yard. Then, just as suddenly, the heavens clear.PZ responded in a post consisting of
2. There's a certain unfairness in the evidence postulated for god. I used the example of a 900 foot tall Jesus appearing on earth; there is no religion (other than the addled hallucinations of Oral Roberts) that ever proposes such a thing, so such a being would not prove the existence of any prior concept of god, and will even contradict many religions. It's rather like proposing a crocoduck as a test of evolution.Swoosh, swoosh. God should be able to make a 900 foot Jesus (and all sorts of other amazing things that aren't described in the Bible).
6. One other odd feature of the proposed evidence for god is that it is all so petty and superficial. Remember, this omnipotent god we're talking about has been called "the ground state of all being" and is supposed to be omnipresent and essential to the maintenance of the universe, so I expect the evidence for god to be rather more fundamental. No one seems to think to invent a property of nature that is supernatural; even the terms are self-contradictory. But shouldn't a god be as ubiquitous and consequential as bosons? Despite calling some particles "god particles", though, the fact of existence makes them natural and immediately disqualifies them from godhood.Fwoooshhhh.
We could then counter that those events could be explained by something else, of course. As people would. However, if we do that, then I would have to ask why? Why not at this point simply admit that, okay, there is indeed a god, and this god did this. We simply defined 'God' as the one who would cause these events to happen. Why not? Because God is more than that, you say? Well, then let's hear what that 'more', and I can come up with another (crazy) example of an event to add to Coyne's, and we could ask the same question. Suppose this 'God' said that he would now create a copy of Earth orbiting Earth One, and on it start creating life again, just like he tells us that he did some 6000 years ago. And he somehow let us all see it, and let all the scientists and atheists have front row seats of it all. Suppose this 'God' could tell each one of us what we were thinking, predict the future, explain away the fossil record, and make a stick that is longer than itself, etc. etc. At one point 'God' would have done everything we think that God is supposed to be capable of, and at that point we would have no other tactic than the claim that everything that is happening is some malfunction of our brains (all 6+ billion), and that it's all just an illusion. However, our daily (normal) lives might all be like that (The Matrix, yada-yada), and the way we think we are not living under a constant elaborate illusion is by verifying what we experience with other humans. "Did you see those planes fly into that building?" "Yes, dude, it was all over the news." "Did you see that ball of lightning?" "What?! You're crazy, balls of lightning don't exist!".
In the process of accepting that 'God' did the things that he says that he did (including creating us, say), we may learn something new about 'God', and this may be off-putting to a lot of people, who may not recognize their own idea of God (there are, after all, over 33,000 Christian denominations that disagree on some aspect of theology, amazingly). This may prompt some people to say that this 'God' is not God after all, but that is exactly the problem of definition that I referred to above. I personally don't think the concept of the 'supernatural' make any sense in the first place; if some 'supernatural' event occurred for us to see, then it happened in the natural world that we inhabit, and we would immediately set out to explain it in terms of natural laws (physics, biology, geology, chemistry, etc.). If we could not do this, then we would simply update our natural laws as we always do when some new phenomenon is observed. As Michael Shermer* puts it, "the job of science is to make the paranormal normal." Same goes for the supernatural.
If such a God really appeared and did all of the above, what would you say? How about, "Okay, God, you exist. You are truly a being of wonder, and all evidence points to you being the creator of ourselves, which we must thank you for. However, screw you for keeping us in the dark for so long. Why on Earth didn't you show yourself earlier? Can you really blame us for not believing in you? I mean, with all the fucked-up things going on here every day, couldn't you have come a little earlier to feed the starving children, and to punish all the sinners? Why the hell did you have to plant all that evidence to make it look like we evolved without any help from you? Do you really despise us so much that you had to deceive us? Did we really mean anything to you after all, or were those just lies in that super-self-contradictory book containing the only information hitherto about your doings in the past? Given the really, really apparent evidence for your existence and your powers, are you going to be much offended if I'm gonna have to pass on loving you "back", and devoting my life to your glory?"
Or something like that.
* Shermer sides with those who would not accept any evidence for a deity, even though I am unsure how he would feel about Coyne's example and my extension.