Everyone knows about the Big Bang theory, but where did the singularity exist before the Big Bang?

The origin of the singularity is now simply not known where it exists. Singularity characteristics can be sure that it is not human recognition of conventional matter, and can not be any conventional energy fields and waves. So it cannot exist in conventional space, so conventional space theory cannot explain its existence.

Based on the Big Bang theory, 13.8 billion years ago, at that time the universe had not yet exploded, and everything in the universe coalesced into a singularity of infinite density the size of an atom, and in this particle all the laws of math, physics, space, and time ceased to function, and everything seemed to have no meaning.

This means that there is no way to get out of this space with the "common sense" of up and down, back and forth, left and right, i.e., dimensions cannot be used to describe the "space" outside the singularity. The singularity is a point of infinite size and mass, where all matter is compressed, including the nucleus of an atom. There is no space, no dimension: whether space is three-dimensional or eleven-dimensional, there is no up, down, left, right, forward or back, not even a straight line. So if you're asking what it's really like, all I can say is that there's nothing in here. Or to explain it another way: the dimensions in here have been completely distorted into a point, like a circle that goes back to the origin by going around upwards, and the same goes for downwards. I.e.: all directions at the singularity point to the same point! Up is down, it's back and forth, it's left and right.

What we can surmise now is that 13.7 billion years ago, there was a Big Bang singularity, almost infinitely small, with almost infinite density & heat. One day, because of unknown quantum effects, it exploded! The force of its explosion made it as big as an orange in a few Planck times. A **** over 13.7 billion years later, it formed the universe as it is today. This is the theory of a hot big bang.