'Atheism' says nothing about cosmology.
A big part of the problem here is that while atheism doesn't say anything about cosmology, atheists often do. They don't always qualify their assertions with "It seems to me..." or anything like that.
"There is not and cannot be a God" is a big, unsupported, assertion. Most non-theists don't say that, but some do. I find many hard atheists quite as irrational and limited as hard theists. There aren't many, but enough to be aggravating.
Tom
It's not a particularly big assertion, any more than "there is and cannot be a dragon in my garage" is a big assertion.
Those two assertions are hugely different.
Perhaps the difference is so big you don't see it.
"garage" and "dragon" are both small concepts. They're both reasonably well understood and clearly defined. It's not difficult to assess the plausibility of your assertion.
"God" and "universe" are totally different. Nobody can explain what god(s) mean, outside of "category of character commonly found in fiction".
We know lots more about the universe than ancient people did. But we're still limited humans doing the best we can to understand with what we've got to work with. Ancient people believed that the universe is a huge, solid, lumpy plain. It has a blue dome over it. The sun is a relatively small object that scoots along under the dome daily.
It's not that ancient people were stupid. They and their technology were primitive. They lived in an illusion created by their limited abilities.
We do too.
Primitive people didn't have the tools, methods, or skills to escape the illusion of a flat earth. We don't have the tools, methods, or skills to escape the illusion of a material universe. Doesn't mean we never will.
And it's not unsupported; For all but the most esoteric and unpopular ideas about what 'god' might be, the fact that they do not and cannot exist is supported by their being contradictory to quantum field theory.
For any of the mainstream gods to exist, QFT would need to be very badly wrong.
It's not.
We checked.
Maybe if you didn't limit yourself to the fictional characters humans have created in their own image.
I'm pretty sure you grew up in a world similar to the one I grew up in. Either you believed in the bumbling sky king with superpowers described by Abrahamic religionists or you're an atheist. It took me a long time to get past that limited world view. But eventually I realized that Moses, the Popes, and Muhammad don't know as much about God as I do, which is next to nothing. The only reason I know any more is because I have more sophisticated sources to draw upon.
Even the word "know" is messy, since it's mostly "I don't have any particularly strong evidence. I prefer to believe some things, but I don't expect anyone else to believe what I do just because I believe it."
Tom