Reddit reviews The Inflationary Universe

>Time surely existed before the big bang

Though I tend to agree that time did not 'begin' with the big bang, we definitely cannot say that it surely existed before the big bang. We cannot even say with certainty that time surely exists at all. It is feasible that the so-called dimension of time is nothing more than a byproduct of our perception of motion, and some physicists (Julian Barbour comes to mind most readily) have proposed models in favor of this view.

As for what came before the big bang, the only legitimate scientific theory to turn to would be the inflationary model. It says that our universe decayed from a false vacuum state that expands at an exponential rate. The false vacuum is unstable and decays at an exponential rate as well, but in most formulations of the theory its rate of expansion is greater than its rate of decay. This implies that the false vacuum state will never decay entirely.

Our universe, in the modern inflationary theory, is a single expanding bubble of true vacuum within a much larger false vacuum state. The transition from a false vacuum to a true vacuum state is the event we term the 'big bang.' Pockets of true vacuum such as our universe are continually forming within it, sometimes collapsing again and sometimes expanding eternally at the own much more mundane rates, but overall the expanding false vacuum should approach a steady-state condition in a manner similar to the steady-state model of our own expanding universe that Fred Hoyle favored over the big bang hypothesis.

(This is paraphrased from a passage in Alan Guth's book on the subject that really stuck with me. I hope I did it justice.)

EDIT: Though that inflationary model opens the door for what Guth called an "eternally inflating" false vacuum with neither beginning nor end, and definitely implies that the false vacuum should continue to expand infinitely, there are still mathematical arguments that have been made suggesting it still must have had a definite 'beginning' at some point.

I had the exact same thought. The Inflationary Universe by Alan Guth was a fairly decent intro to the concept.

Thanks for your response. My understanding and phrasing came from these sources:

1. Parallel Worlds: A Journey Through Creation, Higher Dimensions, and the Future of the Cosmos
   
2. Many Worlds in One: The Search for Other Universes
   
3. The Inflationary Universe
   
4. The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos
   
5. Our Mathematical Universe: My Quest for the Ultimate Nature of Reality
   
6. A Universe from Nothing: Why There Is Something Rather than Nothing
   
   Yes, I read all of those. Several of them more than once. I've been reading about inflationary cosmology for a little less than a decade. Wikipedia's page on eternal inflation is also an interesting read, though brief. Regarding ontology, I'd welcome any argument you'd like to make. I'm not an expert in the scholastics, but I've been reading apologetics on and off for a couple of decades. I was treating ontology as being "the study of what there is," to quote the Stanford Encyclopedia of Philosophy. If that's too broad for you, please make an argument, or clarify what you're claiming.
   

>Single point... a very hot and dense... already existing... single point... which rapidly expanded (the expansion being the Big Bang).

Ahh gotcha, so this is what you're talking about asking for proof the universe began.

Then I'd recommend the following further reading:

A Universe from Nothing: Why There Is Something Rather than Nothing by Lawrence M. Krauss
The Grand Design by Stephen Hawking
The Inflationary Universe by Alan Guth

>Universe was not created per evidence.

There's a high level primer here.