What makes the big bang the biggest explosion in the universe?
Why even should such an explosion ever happens?
Through what process and how does this amount of energy get released as a big bang?
Are there there behind the darkness of universe more big bangs?
If there are how could we ever know (since the speed of light is constant)?
The big bang is not an explosion in the conventional sense of the word. The big bang corresponds to an exponential expansion of spacetime and it is this incredible rate of expansion that can be dubbed "explosive".
There are people suggesting that there might be "more universes" and that we can detect their effect in the CMB. I remember however that recent Planck data seemed to rule out the circles they found as statistical noise.