In a comment on my last post, Drew noted that debates over the existence of God ultimately come down to a question of what qualifies as satisfying evidence. Here is a post I wrote on the subject for Signs of the Times in 2006:
Doctor(logic) has been arguing that statements must be empirically verifiable to be meaningful, and “total undetectability” is indistinguishable from non-existence (e.g. here and here). He thinks this logical positivism implies that metaphysics is an exercise in futility, and claims such as “God exists” are ultimately meaningless.
Doctor(logic) is a clear thinker who has earned my respect, but I see at least two good reasons to reject this claim and accept that some things that almost certainly exist could be, or indeed must be undetectable. Non-verifiability does not equal non-existence nor make a proposition meaningless.
First, he ignores the very real limitations imposed by our finite embodiment. There are things that are true about our physical universe that are simply not verifiable, even theoretically. For instance, due to the finite speed of light, we simply cannot know what is currently happening in distant parts of the universe. When we look at a galaxy that exists light years away, we are actually seeing what it was like long ago, which would be quite different from what it is like now. No matter how long we wait, we will always be seeing such a galaxy as it was in the past. Nor could we travel there without a great deal of time passing (even if it didn’t feel like it).
There is simply no way we can verify what is currently happening in the distant universe (by “we” I mean myself and any other embodied person with whom I could theoretically have contact). Yet surely this does not mean that the distant universe does not exist, or that statements of fact about it (for instance, how many planets and stars currently exist in galaxy X) are meaningless. Our finitude limits what we can verify; it does not limit what can exist.
Second, he ignores the limitations created by personal agents with (at least the appearance of) free will. If such beings exist (I’m not sure if he thinks we qualify or not), then their actions might be consistent and meaningful, while only inconsistently verifiable from a given frame of reference. What I mean is best illustrated with a thought experiment: Imagine some sort of accident secured you to one place so that moving from that spot became impossible. Such immobility would put your interaction with other people entirely in their hands. If they chose to come and visit you, take your calls, provide you a computer, etc –- you would have access to them. But if they instead chose not to visit, took your phone and computer away and boarded up your door –- you would no have access to them at all, no matter how hard you tried.
Due to the limitations of your vantage point, your ability to detect or verify the existence or activities of your fellow human beings would be inconsistent (and in some cases, impossible), even if those actions themselves were consistent (morally, or socially, for instance). One day, your friends might spend hours and hours with you, providing ample opportunity for you to interact with them. Another day they might not come by at all. One day they might take your calls immediately. Another day they might not answer you in any way (for whatever reason). Some things they might do right in front of you for you to see. Other things they might only do elsewhere, and you could only know about them second-hand. Yet surely the existence of your friends would not hinge upon your own ability to verify or detect their actions at will. Would not their occasional interaction be evidence enough, even if there was no possible experiment you could perform to confirm their existence when they chose not to be available?
Now if that is true of a person trapped in one place, is it not also true of the other limitations imposed by our embodiment? The speed of light is a barrier we humans (probably) cannot cross, but if beings existed that were not so constrained, they could interact with us at will, even while we could not do the same with them. Our ability to verify and detect their existence would be entirely dependent upon their choice. If at a particular time and place they were not disposed to submit to our tests, nothing we did could verify their existence, even though at other times they might make themselves as obvious to us as we could ever wish.
Of course, doctor(logic) is correct that it would be foolish to simply assume (without evidence) that such beings exist. But it seems far from clear that the meaning of such claims must depend on our ability to verify them at will. Such beings could be real and have a real impact on our world without our possessing the ability to test for their existence at all times or places. Thus, I have a question for doctor(logic): Given that a great many people throughout history have claimed that such beings have taken the initiative to contact us, how much evidence of occasional interaction would be necessary for a logical positivist to accept the existence of such beings?
Doctor(logic) responded in the comments and the exchange that followed is well worth reading.