Rewind time, and you won't find our universe exploding into a dark, empty void. Instead, the entire observable cosmos was packed into a space smaller than a single subatomic particle.
To understand this initial singularity, it helps to look at what physical laws actually describe. The Big Bang theory traces the current expansion of the universe backward in time. As the clock runs in reverse, matter and energy become increasingly compressed and intensely hot. Eventually, the math reaches a point of infinite density and temperature. The singularity did not sit inside a larger emptiness, because it contained all of space within it.
Explaining exactly how this singularity formed remains one of the greatest unresolved challenges in physics. The difficulty lies in the fact that the two most successful frameworks in science—general relativity (which governs gravity and the macroscopic universe) and quantum mechanics (which governs the subatomic world)—are fundamentally incompatible under such extreme conditions. At the singularity, gravity becomes so intensely powerful at a microscopic scale that general relativity breaks down entirely. Without a unified theory of quantum gravity, physicists cannot mathematically describe the exact moment the singularity formed, or whether "formed" is even the correct word to use.
Furthermore, asking what existed before the singularity, or how it emerged from "nothing," may be a conceptually flawed question. Time itself is inextricably linked to space, forming the fabric of spacetime. If spacetime originated at the Big Bang, then the concept of "before" ceases to have any physical meaning. The physicist Stephen Hawking famously compared asking what happened before the Big Bang to asking what lies north of the North Pole. There is no direction further north, just as there may be no time before the singularity. Rather than forming from a state of nothingness, the singularity simply represents the absolute boundary of time and space.