What would the universe be like if the big bang had not occurred? What would be the nature of that unexploded object? What difference would it have, that would prevent it from exploding? Would it occupy time and space? Would it ever change? Would it emit anything in some non-exploding manner? Could any kind of recognizable universe ever evolve from it?
And, if you accept the possibility of parallel universes . . . could there indeed be such universes, or does “parallel” refer only to post-big-bang universes?
Without the Big Bang is there is no time or space, so the rest of the questions are meaningless.
There are some theories that the Big Bang was the outcome of a collision between two “branes” in higher-dimensional space. If that’s true, then parallel universes could exist even if the Big Bang never happened.
The Big Bang Theory was a derogatory term for the expanding universe idea used by its opponents and unfortunately the name stuck. The name implies some kind of explosion happening somewhere, and all the matter of the universe spewed out from this explosion, and thus here we are today. This is a misconception and not really what the theory is all about.
The theory is an extrapolation backward through time given the current trends of the universe. Right now, we observe the universe expanding. Every point in space is moving away from every other point. Space itself is inflating, getting bigger, and therefore the stuff within space is being pushed apart. If we extrapolate backward, this means that in the past, there was less space between everything, and everything was closer together. Go far enough in the past, and every atom in the universe is squished up against every other atom. Farther back still, and atoms are so close together that they get crushed down, and the particles themselves get crushed as well, so now there’s just a soup of plasma. This is the beginning of the universe as we know it.
Because of the name “Big Bang Theory”, the beginning of the universe is often compared to an explosion, but it’s a bad analogy, because it leads to a bunch of incorrect assumptions. An explosion implies bits and pieces flying apart from some original point, but in the BBT the “explosion” happened everywhere, and every piece flew apart from every other piece. There wasn’t some primeval atom sitting around in space that suddenly exploded one day, the entire universe was at an ultra dense, hot state, and it expanded into what we see today.
The Big Bang didn’t originate from an “object” in any normal sense. If you extrapolate the Big Bang backwards, the result is a singularity, where all known laws of physics break down. So we really don’t know what happened at the very beginning.
As has already been mentioned, the Big Bang was an expansion, not an explosion. It generated space and time itself, so there is no meaning to asking what the universe would be like if it hadn’t occurred. The Big Bang created the universe (at least the one we live in).
You’re asking essentially What happened before the big bang?. Not only is there not a known, factual answer to that, but the question itself is meaningless since “before” doesn’t really apply (at least not in the normal sense.)