If it existed, it occupied space , so therefore space existed . For it to have exploded , implies that time already existed . Wouldn't that make sense ?
From what you've written there it seems to view the big bang under a common misconception - that it was an incredibly vast explosion of matter, light and energy that occurred in an already present three dimensional space (well at least three dimensions.)
No, that's not what the big bang was all about. Space-time itself came into existence (mathematically) at the moment of the big bang and it is that that is really expanding.
The easiest analogy is that of a rubber balloon. Take a balloon and draw spots on it with ink. In this analogy the rubber of the balloon is 'Space-time' and the ink is matter. Blow it up and the surface area of rubber gets bigger and the spots of ink get further and further apart. In a similar way the universe is expanding and drags the matter away from each other at a particular rate. Now you could view Time as some sort of 'property' of the expansion and internal interactions of a three spatial dimension Space-time universe...*
...so under some explanations of the start of the universe, the big bang singularity just popped into existence from a piece of 'false vacuum' (whatever that is!) and then started to expand**. Therefore if you believe Time is some sort of state wrapped up with Space-time, matter and energy, then it becomes totally meaningless to apply any concept of time to the state of the false vacuum (which apparently does not have matter or space-time)
However, that does not mean that like you say there have been other things 'before' the big bang. The issue here though is (and I apologise for banging on about this!) evidence, hypotheses and testing - back to science. It may be that we are stuck in infinite loops of: big bang, expansion, contraction, compression into some incredibly dense singularity, then big bang, expansion and it goes all again etc.... But if there can be no evidence of anything before the big bang, i.e. information from one expansion is wiped out in the eventual contraction of itself then we have no way of knowing if that actually happened. The fact of the matter is then really
anything could have existed or happened 'before'. Thus is becomes physically meaningless yet again.
That is not to say that we might find echoes or clues of what happened before - never say never - but at the moment it's difficult to see where or what they might be.
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* Of course this just raises all sorts of question like, will there be the same sense of time if the universe
contracts instead of expanding, or will be 'go backwards'. Would the entropic arrow of time go backwards? It rapidly gets quite complex
**This must have the ancient Greek philosophers spinning in their graves - who basically believed that you can't create something out of nothing. They did have starting points, big bangs if you will, but forms were made out of formless matter. In their minds there was always something there.