jb, this was originally written for someone else on the same general topic. It seems a good fit for you as well; the question I address is - if everything has a beginning and an end (a contention I don't agree with, BTW), then how could the Universe be an exception? What follows is my explanation of the origins of the universe with no god involved. (This is not original to me, my son planted the seed of it over lunch one day)
Ok, key points:
1. Time is a concept, an idea, an abstract. It doesn’t exist in the way people often speak of it; for instance, no one ever “ran out of time”. At worst, one could run out of life, but time continues to pass, regardless of any individual’s participation, or lack thereof. It’s not an actual thing; it’s a way of explaining other things.
2. Earth is a planet in the Milky Way galaxy, which is one galaxy of many (no, seriously, MANY) in the universe. For this conversation, we’re not going to include such theories as the multiverse – this one is enough for now.
If we can agree for the purposes of this conversation that black holes exist, and function as described by science (very generally: given enough time they absorb whatever is in their path), then follow that as far as it can take you.
Given enough time (and yes, I do take for granted that the universe is at least billions of years old), even black holes will be sucked in to other black holes. Eventually, all matter that exists in the entirety of the universe gets sucked into a single immeasurably dense/intensely pressurized/mind-bendingly squished teenytinydot.
Can you guess what would happen next?
A big frickin’ bang, that’s what.
The universe is not an exception, you’re trying to force the whole existence of it into a concept, time, that only exists to allow us to communicate about things related to it, like “yesterday”, or “next month” or “in ten years”. Or “many millions of years ago”. Or “one hundred twenty seven light years away”.
It’s a measure of distance more than anything else, just not necessarily physical distance.
So, the central point is that the universe could quite easily have always existed, based on what we know about black holes. What we think of as "eternity" is just the most recent expansion of matter since the last big bang from the single black hole that contained everything for a time. Essentially, this has been happening forever and will continue to do so. We humans are just a single example of what matter can gather into, given enough time, along with everything else in the whole universe. Next time, things will probably shake out differently and the alignment of newly created stars and planets will form different galaxies and solar systems than the ones in this ... incarnation.
Let's set aside the "does god exist" question for a moment - does what I said above make sense to you as a possibility?