I was musing about how we might react if we received a sign that God exists. Imagine that I send a letter to my sister. It’s hand-written, and signed “Love, Johnny”. My sister receives the letter in the mail, opens it up, reads it, recognizes my handwriting, sees my signature, and instantly knows that the letter came from me. After all, she knows that I exist (we DID grow up together!) and she knows I can write. She’s 99.999,999,999% sure that Johnny wrote her a letter. She has good reasons to.
In contrast, suppose my sister receives a letter, and it’s signed “Love, God". If God is the “uncaused, changeless, timeless, and immaterial being of unimaginable power” that some theologians posit, then it would presumably be capable of writing and sending a letter to my sister. But how sure can she be that the supreme, no-lie, it's-really-her God actually did this?
If you’ve thought about this sort of thing before, then that last sentence is where it gets interesting. You see, Sis can know that Johnny sent her a letter signed “Love, Johnny” because she knows to a very high degree of certainty that I exist prior to any scenario involving a letter. She’s seen me. She’s yelled at me. She’s tried to hit me. She’s even kissed me. Unless her senses and intellect are unreliable, she knows I exist and that I am capable of writing letters. This should bolster her belief that she currently is in receipt of a letter from me. But she has no such experience with God. If God fell out of the sky and landed on her head, she wouldn’t know him/her/it from shinola. There’s nothing in her experience that demonstrates to her that an actual entity in this world is God. She has to rely on her ability to mentally picture what God might be, and to feel some certainty that he/she/it exists in the form she imagines, without having a concrete demonstration that it actually does. Is writing a letter that demonstration?
In fact, she can’t confidently associate this piece of evidence (no matter what it points to) with God unless God is either 1) a known entity with a propensity to write letters to pretty ladies, or 2) her conception of God is a better explanation for a letter that is signed “Love, God” than all competing explanations. The evidence points to a letter-writer. That’s all. And here is the crux of the problem for most arguments that God exists. That “uncaused, changeless, timeless, and immaterial being of unimaginable power” that theologians posit cannot be established as a sensible concept in isolation from other concepts. There are no observations, hypotheses or theories that point to such a being existing as part of physical reality. Here in the twenty-first century, ideas such as “there must be a cause of the universe, or a designer, or a fine-tuner, or a being of greatest perfection” do not lead us to find an uncaused, changeless, timeless, and immaterial being of unimaginable power. In fact, finding a place where this thing might be situated is not even sensible. As cold as it sounds to people hoping there is a personal god behind the scenes, it appears that physical features are all there is. Space-time, matter, energy, the laws governing them and the attributes, behaviors and relationships that allow what we observe to be observed. There may always be that nagging question: “but what caused THAT?” - but the god-thingy doesn’t help us answer that question. It doesn’t stand on its own. Mankind continues to look for answers, and continues to find hypotheses such as the god-thingy useless in the search.
So, a letter signed “Love, God” ends up being better explained by a human letter-writer than an uncaused, changeless, timeless, and immaterial being of unimaginable power that also writes letters. It turns out that Sis has no good reason to believe she got a letter from God, because there’s no good reason to think God exists, based solely on this letter. I'm not suggesting that she can't believe in God, or have some other reasons to believe that don't rely on (weak) evidence like this. But this letter from God isn't a good reason. When you apply this type of thinking to the bigger questions - the origin of the universe, the origin of life, the existence of moral values, you find that those are not good reasons to think that God exists, either.