I challenge any human to explain how anything can exist. You can trace our universe back to the big bang.....Ok, fine.....a "singularity" expanded rapidly. Ok, fine. Now what is a singularity and where did it come from? As I imagine the theoritical backtracking, looking for the original "beginning of anything", no matter how many "thoerical steps" you go through, you would eventually have to arrive at the original "matter or energy or potential or whatever" which was there forever. (FOR EVER !!!....without anything causing it to be). That is not conceivable to me.
The thought of infinite universes was Impossible before Galalie. I see billions of star systems and wonder: if we can only see as far as we can see, just think of what we cannot see. Our puny minds cannot conceive of the vastness of space, Though Star Trek paints a pretty picture. Impossible is in the minds eye, time will reveal what is truly impossible.
I also struggle with the concept, so as usual when I struggle with something, I gave up.
It doesn't matter. It will have no effect on my life if I don't understand it. But inventing a magic pixie that is eternal doesn't change the problem or solve anything.
So for now, I just ignore it (it doesn't go away, but it helps a bit).
I really doubt you'll find many theoretical physicists on this site. If you really want answers to questions like this, you should probably ask people who dedicate their lives to answering the big questions. Even then, there are still a lot of unanswered questions. None are answered by saying "god did it" though.