A friend asked me what I would view as evidence for God and it's a question I have to take seriously. I view the God hypothesis as falling within the realm of science. I don't view much of anything as falling outside the realm of science; she brought up the example of love as an unprovable, which I contend it isn't. Just because something cannot be perceived directly doesn't mean it doesn't leave evidence behind. I can't see UV light, but I can still get a sunburn. I can't see my friend's love, but I can see him doing lots of really stupid things and generally acting like a soppy asshole saying things like, "Don't you just love love, man?"
So, what would I view as evidence for the existence of a deity or other supernatural element? At this point: Nothing. There is no evidence for anything supernatural, that hypothesis has been rigorously tested for the last 200 thousand years by every human agent produced on this planet and the result has always been an astounding null. Every single supposedly supernatural phenomenon has been proven to have a natural causative agent, to in fact not have occurred, or to be a fraud practiced upon a credulous public.
First, why do I dismiss all the supposed evidence? As I understand, most supernatural claims come in three forms: anecdotes and miracles, revelation, and scripture.
I separate out anecdotes because I'm referring to things akin to cryptozoology. That is to say, big foot and the creature of Loch Ness. I lump these in with the supernatural because they have all the same foundations in personal experience and credulity and because skepticism deals with them in the same way. Amazing creatures still wait to be found and studied; living fossils are encountered all the time and extreme and distant environments are full of wonderful and surprising things that we don't know about because they're really damn hard to get to. Loch Ness and the mountains of the Pacific Northwest are neither distant nor extreme. To give one example: the Loch Ness monster and similar aquatic sightings is best attributed not to an illusive large animal, but to common smaller animals. Otters and other aquatic mammals behave in fashions that cause an optical illusion of a single large creature. The effect is said to be arresting and almost impossible to dismiss from a distance (basically, they like to play follow the leader). These and other types of things (when not fraudulent) are best ascribed to honest but mistaken reports of less fantastical phenomena. In other words, there is no yeti, no alien abductions, and no Nessie.
Miracles are of a category with the anecdotes of cryptozoology. When they're not outright frauds for deliberate profit, or a portion of the brain going hyperactive and seeing things that aren't there, like the face on Mars, they're either easily proven to be accidents and natural phenomena or completely impossible to track down. For example, the healing power of Lourdes is 67 (according to the Catholic Church) out of more than 200 million, and none of those are self-evidently miraculous, like the regrowth of a severed limb. As with most miracles, it's always in the realm of the nebulous, the distant, and the (at best) unimpeachable. In the face of better explanations (many diseases go into remission), frauds, and simple absence, why believe any miracle has occurred?
Perhaps you feel yourself to have been witness to or beneficiary of a miracle. Perhaps something astonishingly unlikely happened that you witnessed. This is not a miracle. Everything is coincidental. Any two things that happen at the same time, any two incidents, are co-incident. Some may appear to have connection, as when you are thinking of your grandmother as she calls; but you forget the thousands of people you think of who don't call. Everything is unlikely. A pin falling on any particular spot in a square meter of space is unlikely, it is one in five hundred thousand. And yet, it will land somewhere. No matter how unlikely, unlikely things happen. They are not miracles. Only if something is genuinely impossible could you call it miraculous. Even then... it probably isn't. What is not yet explained need not be called inexplicable. Not yet having an explanation doesn't mean it won't be explained in the future.
As an aside, part of what spurred this is a rash of other blogs considering this question. What it boils down to is this: if you witnessed a miracle, who's to say it's your god doing it? Even if A two hundred foot tall statue of Yeshua Bin Yusef appeared, floating two feet off the ground, what makes you think it's Yahweh rather than space aliens? Or Loki tricking everyone because that's what he does? Or Coyote just having fun with the pale-faced devils? In other words, it's bad enough that miracles either simply can't be tracked down or have better explanations such as fraud, but they aren't even proof of anything. A miracle doesn't explain anything. "Miracle" is as much a non-explanation as the god hypothesis. It enshrines ignorance in protective "DO NOT TOUCH" bubble. An explanation fits all the available data and makes predictions for the future. Miracle just says "Something happened and I don't know why." So does the god hypothesis. And what predictions can these non-explanations make? That tomorrow something else might happen that you will also fail to understand? That may be true, but it certainly doesn't enlighten.
Revelation might appear to be harder to dismiss. After all, can one prove that a supernatural entity didn't put voices in someone's head (a non-psychotic someone)? I think the argument can be made. Pop someone in a machine and scan his brain while asking him about morality. Ask him about the morality of others and a part of his brain lights up. Ask him about his own morality and a different part of his brain lights up. Ask him about the morality of his god and the same part of his brain lights up. A cynic is unsurprised to learn that a person claims his god's morality matches his own. The cynic is less surprised to learn that it's neurological in nature. It's not just god's morality, either, everything about god may be egocentric. And it's not just the penitent's relationship with his deity, but the very basis for believing an experience is numinous, since science has identified "the god spot", AKA the part of the brain that lights up during revelation. It's located in the temporal lobe, which is responsible for, among other things, processing speech and vision. In other words, you think you're hearing and seeing things that aren't there. Why ascribe this to a deity who happens to match your own opinions point for point when you can instead ascribe it to a misfiring of a portion of your brain and then an attribution of your own feelings to a wholly internal experience?
Scripture is perhaps the most pathetic of all possible evidence because it's the only so-called evidence that's actually evident. They contain factual errors and contradictions and the most horrific barbarity. If they were actually inspired by something more than human, you wouldn't expect errors or contradictions. If they were actually morally superior, you wouldn't expect barbarity. You would expect a morally superior being to say that rape is bad. The Christian bible, for example, never condemns rape. It condemns vandalism in the form of sex with someone else's property (daughter, wife), but not rape, because the Chrsitian bible never considers her consent an issue. After all, property can't consent, nor can it withhold consent; consent belongs to her owner, whether that be father or husband or eldest living male relative. That's why spousal rape wasn't legally a thing until the last decade or so. Now it is, because we're morally superior to the Christian bible. Rape, slavery, genocide, these are all things not merely condoned by the Christian bible, but all three were encouraged by the Christian bible against conquered peoples. Well, not "people". As far as the Christian bible and other holy texts are concerned, foreigners, heathens, and apostates are like women: not human, but property (at best) or dead (at worst).
The argument that a supposed miracle could be, rather than a sign from your deity, a trick from someone else could equally apply to these texts. While this diminishes some of the strength of the argument that the texts are wholly human creations, it also weakens the argument that any is divinely inspired or created. However, if you're arguing not for generic multiple supernatural entities with superior knowledge (from which true morality rises) but rather for a single entity, the multiplicity of holy texts is particularly damning. If there were one entity capable of inspiring a holy document, there would be only one document. When it comes to a cosmic dictatorship, there can be no more effective censor. One god, one book. No god, many books.
In the end, the holy texts are at best not evidence at all or evidence of maltheism (being the work of a trickster). Miracles are either nothing at all (being the unfortunate result of human predilection for seeing patterns), another bit of maltheism, or evidence of nothing in particular because, being a non-explanation, it cannot be connected to anything in particular. And again revelation is again no evidence at all or et cetera.
So there is at best absolutely no evidence for the god hypothesis. Next up, Absence of Evidence is Evidence of Absence.