I have said in earlier posts that one of the criteria that distinguishes science from religion and pseudoscience is falsifiability. Scientific hypotheses should be falsifiable. There should be some evidence that could theoretically disprove a given hypothesis if it were false (See Karl Popper's "Conjectures and Refutations").

The god hypothesis is unfalsifiable. There is no theoretical test that could show that the god hypothesis is false. One cannot prove the non-existence of God or the Flying Spaghetti Monster because one cannot check each and every corner of the universe at once.  And even if one could, the theist would undoubtedly claim that God is hiding just outside of our universe.

And as for the belief that a god created the universe, no matter how implausible it may be, the believer can always produce new ad hoc hypotheses to accommodate every inconvenient fact that comes along. Every statement of belief will be made consistent with every contradiction. "God did it" cannot be refuted because "god works in mysterious ways" or "he got things started and then let evolution take over after that" etc. One can neither prove nor disprove this kind of belief, and thus it is not falsifiable.

The religious devotee has faith that the bible is the word of god. The scientist requires objective, testable evidence before she can assign some level of confidence that a given proposition is true.

But Christians will object that while god is unfalsifiable, Christianity is falsifiable. Produce the body of Jesus, they say, and you have falsified the resurrection and Christianity along with it. Really?

How would you know if you had found Jesus' actual body? How could you be certain beyond reasonable doubt that you had dug up the bones of the person that inspired your religion? Are you going to check the DNA? See if it was stolen from a tomb after being crucified? Check for dog tags?

And if after thorough searching we cannot locate the body of our 2,000 year-old dead rabbi, does this confirm the Christian's claim that Jesus came back from the dead?

A rigorous application of Occam's Razor is in order. There are too many possible explanations for the Christian's claim that Jesus was seen walking around after being interred:

1) It is purely fiction

2) People lied

3) Human psychology. Some of his depressed followers thought they saw him because they wanted to (this is a well-documented psychological phenomenon: http://www.csicop.org/sb/show/visitations_after-death_contacts/)

4) Drug-induced hallucination

5) Jesus was not dead but in a coma. In the past, people would sometimes mistake someone for dead and then accidentally bury them alive. There is evidence of this through the 19th century as evidenced by claw marks in coffins. That was just over 100 years ago. Now imagine what medical technology would have been like 2,000 years ago.

How do you verify unequivocally that a dead man came back to life 2,000 years ago?

But there is another problem. The resurrection even if it were somehow medically verified would not prove that Jesus was god. It would only show that Jesus was perhaps a mutant or a powerful alien being. There are many more plausible (though still unlikely) hypotheses to work through before coming to the fantastically implausible notion that Jesus was the son of an omnipotent super being that sacrificed himself to himself to save us from himself.

So what evidence could possibly falsify Christianity? Nothing. It is a matter of faith, not evidence. If god is unfalsifiable, it follows that a 2,000 year-old rabbi as god is also unfalsifiable. You can argue that it is absurd, but there is no evidence that could disconfirm it.  But this is precisely why it is worthless as a hypothesis.  The failure to meet the criterion of falsifiability is sufficient grounds to dismiss it.  It can be discarded into the rubbish bin along with all the other untestable hypotheses of pseudoscience.  If the theist wishes to believe in it on faith, he may, but he cannot present it as legitimate science.