It didn't happen "Where" as there was no space.
Time and space are dimensions and there are further dimensions beyond the ones we perceive, so "it didn't happen where or when" as there were no dimensions.
So the term "happen" is meaningless.
It was not the "cause" and the afterward the "effect" as, being dimensionless, causality did not exist.
The human mind has evolved to perceive causality but without the use of the mind, causality does not exist.
Following causality back then to an inferred start point is false method and will only, at best, satisfy the mind and not provide a true answer which must in fact be absent of causality as it is absent of dimensions.
Many of us are happy with the idea of the universe being infinite. If not happy with infinite then we must be left wondering what the finite universe is within, and so we must also deduce from there infinity.
To visualise the Big Bang many minds will picture empty space and a zero point exploding. This is what nearly all animations show also but is absolutely false.
The universe as is, by our best current measurements, "expanding and accelerating in its expansion" so all lumps of stuff, galaxies and so on, are becoming more widely spaced. The galaxies are not expanding though. We visualise this by placing coins on a rubber sheet to represent galaxies as we stretch the sheet to show space expanding. Oddly though we have witnessed galaxies in space colliding and we predict our nearest neighbouring galaxy will collide with us. When galaxies collide though it is rarely catastrophic as most stuff is so far apart that very little hits anything else. We result in either one larger galaxy or the two carry on with just a change in shape.
So we see some galaxies collide but the large majority spacing apart. Not just moving apart but accelerating apart. We naturally infer with our minds that what is now big and expanding must have once been small. Yet we say the universe is "infinite" and not "finitely big and getting bigger".
We model the expansion as something growing out into an infinite space but this is not the case. As with the Big Bang which did not happen in space but gave birth to space, so the idea of 'stuff' now expanding into nothingness, is a false view.
What we are shown by cosmological observation is that space is coming into being. What we are shown from quantum theory is that empty space is not empty and it teems with virtual particles coming into and out of existence. A very curious thing which has come about from these two curious things is that: When two virtual particles come into being they then rush to annihilate but if space is accelerating in its expansion they can often be left in existence and so space coming into being then brings about "something from nothing" and it leaves behind particles, stuff and energy.
Perhaps then The Big Bang was not such a "bang" in a "place" (as we have seen, no place or time for that bang could exist previous to it) but instead the first calculated occurrence of expansion, where nothing came to be something.
Our minds work very well with dualism. As we saw earlier they love the dualism of cause and effect. We can then easily see how "nothing" naturally leads to "something". This model then is perhaps acceptable as it fits our predisposed framework, it is also though, measurably, true.
Tao Wow | Daily Cup of Tao