I apologize for the horrible question title. I'll try to explain and someone can edit it. I am thinking of the explosion of the Big Bang in terms of the explosion of C-4. Once the C-4 is detonated, it rapidly sublimates (turns from the solid to a gas) into a rapidly expanding mass of gas. This causes the atmosphere to compress and expand outward, called the shockwave. Now, the shockwave doesn't start at max speed. It starts slow, then builds to its max, and then fades.
So, my question is, how do we determine if the accelerating of the expansion of the Universe is a result of us happening to find ourselves living in that early phase of the building shockwave?