An expansion of space
The Big Bang should not be pictured as a bomb exploding at one point in empty space: it is the model describing the evolution of an initially very hot, dense universe in which space itself expands. Observations indicate an age of about 13.8 billion years. The cosmic microwave background preserves a trace of the universe when it was about 380,000 years old.
The inflation hypothesis
According to the cosmic inflation model, the universe underwent an extremely rapid expansion during an early phase. The model helps explain observed large-scale properties, but scientists do not know with certainty what caused inflation or what, if anything, came before it.
The limits of our knowledge
The idea of multiple universes appears in some theoretical proposals; it is not a confirmed discovery. Even asking what happened “before” requires care, because our theories do not describe all initial conditions with certainty. The Webb telescope observes very distant galaxies; it does not directly photograph the Big Bang.