It may never have "come from" anywhere. There are thousands (if not millions) of books and articles by philosophers on that and scads of other deep topics.

Also: the idea of an intelligent designer or a creator is NOt necessarily synonymous with the Christian God or any other god or deity.

If there's a god, why did he create billions of galaxies? He'd only need one to carry out his master plan.

Where have you gone Francesco ?. Don't you like the replies to your question ?

If nothing existed would "Why isn't there anything?" be a good question? Of course, if nothing existed there would be no one to ask it, but my point is whether being or nonbeing is the "natural" or "default" state. If nonbeing is assumed to be the natural state, then "Why is there something rather than nothing?" is a good question; but if being is assumed to be the natural state then it is not. So, it seems to me the question you pose assumes nonbeing to be the natural state, and I wonder why we should make that assumption.

Here is one that I thought was fun (improbably to be accurate, but fun) from a friend. We have a godless universe that came from gods. There was a war of the gods and they annihilated each other. The energy that was released from killing the gods was enough to spark the cosmic expansion into what we now consider the known universe.
In reality, we don't know, but we are working to find out.

When you say god you should specify what god are you talking about, Yahwa, Zeus..etc
Where did that god come from?

Good question, of course. But, IF there is a god, where did IT come from?

I don't know.

A scientific answer to a nonscientific question. You know how the scientific method works. You observe a phenomenon, you formulate a hypothesis, you test your hypothesis and 1000s of other people repeat the test trying to bring you down. If they can't, that proves your hypothesis more. That's why evolution is agreed upon by Buddhist, hindu, Christian, Muslim evolutionary biologists and experts. Same for big bang...
on the other hand, where's the scientific evidence for religion (god is a product of this hypothesis) for one you have 1000sof religions with no cross examining strong proofs. Of course you have miracles which are scientific or psychological tricks and they work only incidentally and anecdotally ie you can't conduct a study on multiple faiths and find okay Zeus answers most consistently so Zeus is true god or jésus or Buddha, islam, yahweh...

3rd, what's god is exactly? Is it the explanation of our gaps in knowledge without proof aka without evidence. For example, when we didn't know earth is round, god was literally in the sky. We still say so from a remenant of that thinking. Is it beyond the sun, the Galaxy, beyond the big bang? Whenever we find more, we push god to unknown. And I say this bcz u ask give me a scientific explanation. But that's science, we say we don't know, we say we are going to know and then we try to explain with tools we have. If we don't know, we can't just invent BS and say aha eureka. If u think god is the answer, why not Buddha, Zeus, hindu god ? What if it was god but judiasm or Islam is right? You burn in hell? That's how much the question is rigged and useless.

As much as you take it as a matter of fact, as much as it isn't

Who cares?! Who knows?! Its all here, we're in it! Let's enjoy every minute of it!

This is my opinion, but it’s based on facts, I believe. We see creation all the time, and we ignore it. When volcanoes erupt, the magma/lava creates land masses, etc. Over time, Islands form off of it, etc.

I’m not an expert in the subject, so I might not break this down as accurately as I like. The point is, there is evidence of natural creation, but it’s ignored, somehow.

[oceanservice.noaa.gov]

Matter has always been in the Universe, matter can not be created or destroyed, it just changes form. Matter interacts at a constant rate, which we call time. Matter attracts other matter, when enough matter collects gravity is created, gravity only effects other matter.

Read the book you all..... its just physics.

Your false leading question proves you are an ignorant troll here in agnostic land...."comes from" and "belief in" are syntax errors of speech.....you might have beliefs about doors but all are un-necessary TO WALK IN doors because doors exist needing zero faiths to go in or come outdoors.....matter can neither be created or destroyed....matter has the indwelling property of energy thus can be heated exploded or chilled near absolute zero slowing sub atomic particles to slow motion like your believer brain synapses retarded by the Church of England cults

No one knows, including you. You have a belief. Belief is not knowledge. Believe what you will. As long as you don't interfere with my life, l could not care less about what you believe.

It may well be that you would not be able to understand the answer (if it were given in scinetific terms) due to the Dunning-Kruger Effect.