What existed before the Big Bang ?

The only correct answer, so far is "We don't know".

"THE" Big Bang was not a single event: the Big Bang theory - the real one - does not include an explosion.

The theory simply describes the effect of the expansion of space on the energy content of the universe:

Same total amount of energy + more space to spread it out = The energy density goes down with time (the universe "cools down").

It is when we use the theory backwards that we hit a wall. Sure enough, as you go back, the energy density goes up. There are threshold values where "things happen". The same way that if you allow water to cool, there is a threshold value (temperature of 0 C = 32 F) where liquid becomes solid, and latent energy is released.

Working backwards, we are able to identify many of these threshold values (for example, the creation of quarks precipitating from the initial "pure" energy) and even test many of them in labs (for example, hydrogen becoming transparent when the temperature drops below 3000 K).

However, still going backwards (energy density going up) we reach a density value where we no longer understand how things work.

Worst: we don't understand how time itself flows at that level of energy density. That moment is called the Planck Time (Max Planck is a scientist who used to calculate such things). The word "before" does not make sense at that moment. From our frame of reference, that moment happened 13,800 million years ago.

THAT is the moment many people call "the Big Bang". What we do know (or, what we think we know), at the Planck Time:

-- the initial energy already existed (it comes from "before")

-- space was already expanding

-- the energy density was NOT infinite (it was not a "singularity")

-- matter did not yet exist (matter comes "after" and the theory does explain how)

and (this last one is conditional):

IF the universe is now infinite in spatial extent (goes on forever in all directions), THEN it was already infinite in size at that moment.

There are roughly a half-dozen serious ideas about what could have come "before", and they could be classified in three categories:

A. Something happened in the tiniest fraction of a second "before" the Planck Time. This includes Father Lemaitre's idea that this was the moment of creation by [his] God. It also includes Stephen Hawking's "instanton" (a particle of time, lasting one "instant", with the suffix "-on" normally associeted with particles): in spacetime (3-D space + time), there exists a special "instanton" from where all time directions are "future", the same way that there is a special point on Earth - the North Pole - from where all directions are "south".

B. Something happened in a higher-dimension space (up to 11 dimensions) that caused three dimensions to expand. Our universe is this expandingsubspace of 3-dimensions. There are many ideas such as M-theory, String theory and so on.

C. Nothing happened. The universe has been expanding forever and it is only 13,800 million years ago that its density became low enough for us to perceive it (and understand) how it works. Anything that was going on before that moment just happened at too high an energy density value for us to ever detect any of it.

Nothing.

Why must anything have existed before the Big Bang? Because you can't imagine it otherwise? That's your limitation, not the universe's.

Nothing, really.

It was just the beggining

nothing. The big bang was the beginning of space, of time, of everything.

Cher

Do you believe in life after love ??

One viable theory is a massive singularity. Another is a cyclic expansion,contraction to critical mass and repeats like a heartbeat.

There are some interesting theories out there, I like Stephen Hawkins the best:-

https://www.sciencealert.com/stephen-hawking-expla...

No one knows. There are several conjectures though. The one I find most plausible is that there is a meta-universe from which all global universes, like ours, spring. The meta-universe is infinite and eternal. (Which is hard to imagine, but that's the conjecture.) And it is filled with high-entropy chaotic scalar fields made up of quanta.

The quantum fields vacillate between plus and minus energy levels. But overall, on average, they add up to zero energy...most of the time. However, occasionally over infinity and eternity, there is a local quantum event wherein a field causes a bit of space.time to become low entropy space time. And that is what we call the big bang.

Note that our little quantum event, the big bang, is presumed to be just one of an uncountable number over infinity and eternity. So events are ongoing within the meta-universe. And ongoing events define time. Thus time existed before our global universe began.

Also note that the premise also means that there have been, are, and will be an uncountable number of global universes...one for each quantum event over infinity and eternity. That gives rise to the so-called multiverse (multiple universes) concept. Which means before the big bang, there were other global universes out there beyond our own.

In short, space.time filled with high entropy scalar quantum fields existed before the big bang. And other global universes existed before ours was realized. But that's just one conjecture. Read "The Elegant Universe" by Brian Greene for this one and others. ANS

We have no way of knowing. For us *in* this universe, the ‘Big Bang’ was the beginning of everything, including time; for all intents and purposes - we can’t perceive of a time *before* the Big Bang occurred.