The Big Bang itself cannot be directly witnessed as an event from any point in space because it wasn’t an explosion in space; rather, it was an event that happened everywhere in the universe simultaneously, as space itself expanded. Instead, what can be ‘witnessed’ is the Cosmic Microwave Background (CMB) radiation, which is the residual thermal radiation from the hot, dense state of the early universe, approximately 380,000 years after the Big Bang, when the universe cooled enough for atoms to form and for photons to travel freely.
Every observer, regardless of their position in the universe, sees the CMB as it fills the entire sky, coming from all directions. It serves as a sort of ‘cosmic wallpaper’ that marks a boundary in time—the limit of the observable universe—rather than a spatial edge. Beyond this, we cannot see anything directly because the universe was opaque before this epoch.
Regarding the concept of existence being defined by what we can observe, the CMB represents the “edge” of our observable universe but not an edge of space itself. The universe could be infinite and unbounded; the light from the Big Bang simply marks how far we can look back in time. Thus, it is not physically the edge of space but is the furthest back we can observe, giving us a practical boundary to our observable universe, which is constantly expanding as the universe ages.