1. How many of you would believe in God if you saw compelling scientific evidence for His existence and saw that evidence increase as we learned more about the universe and the record of nature?
2. How many of you here would not believe in God until the scientific evidence eliminated all other alternate conceivable explanations for the universe and life?
Ross reported that one-third of the audience answered in the affirmative for question #1 while two-thirds answered in the affirmative for question #2.
Those two hundred or so who responded affirmatively to question #2 are implicitly acknowledging a couple of things: They're saying, firstly, that they want to set the bar for belief in God impossibly high so as to insure that it'll never be reached, and secondly, and following from the first, the fundamental reason they don't believe is that they just don't want theism to be true.
As long as there's any possibility, no matter how small, that there's an alternative explanation for the evidence that points to a cosmic creator, they'll refuse to believe that there is one. In other words, unless the theist can establish with absolute certainty that theism is true, these atheists will be able to justify to themselves their unbelief, but certainty is an unrealistic bar. Nothing is ever proven in either science or philosophy with absolute certainty.
What's aimed for is not certainty but plausibility and probability. If the arguments for theism are more plausible than opposing arguments, if the theistic hypothesis is more probably true than false, then anyone who is willing to believe is within his or her epistemic rights in doing so. In fact, we are intellectually obligated, when confronted with a forced choice (e.g. to believe or not), to believe whatever hypothesis best comports with the evidence and is most probably true.
This approach [i.e. the response to question #2] presents [theists] with an impossible challenge. A [theist] would need to acquire complete knowledge not only about the physical universe but also about everything that could conceivably exist beyond the universe. Neither goal is possible.To satisfy the evidential demands of these atheists the theist would have to prove beyond any possible doubt that both the universe and life did not arise through purely natural processes. The atheists in Ross' audience are saying they're justified in clinging to their atheism, even if the probability of a naturalistic origin of either the cosmos or of life were so low as to be beyond comprehension, unless that probability can be shown with certainty to be zero.
Since our powers of investigation are constrained by the universe’s space-time dimensions, it is impossible for humans to ever gain a complete database about the properties of the universe, let alone about what lies beyond. Our inability to ever gain absolute proof, however, does not mean that we cannot attain practical proof.
This, it would seem, is not only irrational, but it makes plain the fact that much unbelief (like much belief) is often more a matter of the will and of the heart than it is of the reason.