Tantum ergo:
I guess I would wonder how an atheist would explain existence.
This is a good question. I think there’s some level at which the “explanation” has to be: It just
is. We can push the “just is” around, we can dress it up with fancy words, but I don’t think we can do away with it. I say, “The universe just is;” you might say, “God just is.”
Is it all random, and if so, how did that start? How could 'Something" come into being from “nothing”…
Starting and coming into being assume there is time for things to start
in or in which to come into being. But time itself is something, not nothing, so where how did time come into being?
…and even assuming infinite possibilities manage to bring out not only sentiate beings but beings who, out of all evidence to the contrary, have not only a capacity for thought and action which is simply not empirically foreseeable, but not indeed related to SELF at all (personal altruism), and which even if randomly achieved, should have evolved or mutated out long ago.
I don’t think there’s really any evidence to the contrary that humans cannot or “should” not exist. Evolution is very complicated, and I don’t think there’s sufficient evidence to say that altruism is selectively unfavorable. I don’t think human beings are really all that altruistic, and genetic evolution has been working on people for only a relatively short time.
I find the idea that somehow the entire known earth/galaxy/comos/universe just “banged” into existence and randomly and chaotically combined far less believable, on rational grounds, than the idea that some creator was responsible.
I have the opposite intuition. I find the Big Bang theory rationally plausible, especially given the enormous amount of time that has passed since then.
Science really cannot “explain” itself, but a sentiate being CAN (and to people of faith, HAS) explain (ed).
I don’t find that the idea of a creator really “explains” anything. Why did the creator create this creation and not some other? Why did the creator create anything at all? An explanation, in my view, ought to show that what we see logically follows from the explanation, logically precludes what we don’t see.
Theistic or creationist explanations seem always to have to specify how the universe is as premises. Well, that’s all well and good; fundamentally, saying the universe just exists includes the same premises. Adding a god seems to do nothing but make the explanation more complicated, without actually explaining any more evidence.
You’ve touched on some complictated and deep philosophical topics. I apologize for not answering in greater depth. If you’d like to pick a single topic at a time and start a thread on it, I’d be happy to go into more detail and depth.