The way to NOT think about the big bang is to imagine space existing and then at some instant a gigantic explosion.

Instead, the better way to imagine this is to understand that, at the instant of the big Bang (13,700,000,000 years ago...that is 13.7 billion years ago), space and time as we know it was created!!!

So, from the perspective of our universe (there may be others!!) space and time were created at that singular event. In other words, there was no time before"... at least from the perspective of the universe we find ourselves in today...

A book that you may enjoy reading is by Brian Greene called THE HIDDEN UNIVERSE. He discusses in more detail these ideas.

A better way to describe it is that there was no "before". The Big Bang represents the beginning of both space and time in our universe. What this means for matter and energy I'm not sure anybody is prepared to answer, but it doesn't make sense for matter and energy to exist if there is no space for them to exist in.

Exactly why the Big Bang happened doubtless has to do with the nature of gravity and the shape of the Universe, and that really is just plain unknown at this time.

No one knows what happened before the Big Bang.The other answer about time before the big bang is that there wasn't any time before the Big Bang, because time started at the Big Bang. But I think the better answer is: We don't know!

Keep asking questions!
Best wishes.

Um, I can try to clarify it. The fact is that even Einstein had a hard time describing this: the Big Bang is a mathematical description of the four-dimensional shape of space-time, with the space and time expanding out of a singularity at one end of the universe (we have no idea what the other end looks like). I guess the best way to think about it is that the origin of the universe itself wasn't really an event, but rather a boundary or "edge" of the universe. The extremely rapid expansion of the universe during the Big Bang was an event, but time was already rolling by that point.

If this doesn't make much sense to you, then the best way I can describe it is that your perception of time and your understanding of time are based off of the way you experience it. In the Big Bang, time wasn't behaving in any way that we humans have ever experienced.