I've gone back and forth in my mind (fueled by a layperson's love for astrophysics) on the matter of the possibly "infinite" state of the universe, on the possibility of there being myriad "bubbles" in a multiverse format, and other permutations thereof. I've never come to any kind of satisfactory conclusion (see" that "layperson" part!).

I'm prepared to believe that a single "meta-universe" exists, but I don't conceive of it as some sort of single, vast "box" in which a bunch of universes exist "side-by-side" as it were. That is, not as one all-containing space in which at least some of the known laws of physics prevail throughout the volume and the differentiation between "universes" is made via different criteria. For one universe to be differentiated from another would, as I see it, require different fundamental properties. Otherwise, wouldn't they simply be separate parts of the same universe? You know...universal?

It may well be that our universe (regardless of whether others exist) is indeed only a little over 14 billion years old. Because time itself would seem to be something that emerges from the fundamental nature of matter and energy and the clearly demonstrable fact that matter and energy change state. State change implies, by logical necessity, a "before" and an "after," and those terms are meaningless without time. "Time" is how we experience (and measure one aspect of) change-of-state. If time indeed emerges from phenomena, and a "zero point" marking the instantiation of phenomena can be established (more on that below), then asking "what existed before?" might not be a valid query. They may have been no "before" because there were no phenomena to give rise to time.

But here's the problem with establishing that instantiation: when looking back in time, we can never be 100% certain about any physical state any further back towards the instantiation moment than a certain length of time (the Planck Time). It is literally physically impossible to achieve certainty about physical states during that inconceivably short time.

Other uncertainties are present in our physical observations, of course...the well-known problem with observing both the position and velocity of any object simultaneously with certain accuracy being the best example. As you say, "no way of proving it." And we are indeed just getting started.

Great thread!