I’m a little behind on the layman explanations of the latest theories, but from what I understood, scientists have been able to look farther and farther out (so farther back in time)—and the farthest they can ever get in any direction is 13.8 billion years ago—hence that dating of the universe—and the universe looks quite different that far back in time… things are less differentiated, more compressed, hotter, etc… even if the big bang theory gets overturned, even if the “universe” itself has existed without a beginning, I would presume we’ve got some particular epoch or era (or whatever you call a time period of at least 13.8 by) that had a beginning or transition-into of some sort, and probably (when the stars all burn out, etc., etc.,) will have an end…
I’ve never been able to believe in eternality or infinity. Even in mathematics, infinity always seemed more like a concept than a thing to me—a way of saying “and it’s still going, past what we can see or measure or even comprehend”—but I’ve never been able to believe it literally means “forever.” I can conceptualize a big bang that started the universe as we know it (with our matter, our physics)—a universe that is expanding and will expire in one way or another (there are several theories on that end as well.) I can conceptualize a spatial arena of “nothingness” that lacks our (four) dimensions until something carves and stretches them into being. Alternatively, I can conceptualize “it’s still going”—a universe that just keeps going, with different “epochs,” and we’re just a part of the current one, and we can’t comprehend the beginning or the end… I can even conceptualize a universe that has no boundaries whatever, just keeps going forever, but I don’t really believe that last conceptualization. I still believe there’s a beginning and end, and I still believe our universe is spatially finite, (though expanding in size and age continuously). Maybe that’s a limitation of my psyche, but there it is. For whatever reason, I can believe in the eternity of nothingness. Just not the eternity of matter—and the universe to me is only the matter.